Original Article
Hematologic Responses of Patients with Sickle Cell Disease to Treatment with Hydroxyurea
N Engl J Med 1990; 322:1037-1045April 12, 1990
- Abstract
- Abstract
Because fetal hemoglobin contains gamma-globin chains instead of beta chains, it is not affected by the genetic defect that causes sickle cell disease. Increased levels of fetal hemoglobin decrease the tendency toward intracellular polymerization of sickle hemoglobin that characterizes this disease. Hydroxyurea is one of several cytostatic agents that have been shown to increase the production of fetal hemoglobin in some patients with sickle cell disease.
We studied the effects of hydroxyurea administration in 10 hospitalized patients with sickle cell disease, each of whom was treated for three months. Seven patients responded with a 2– to 10-fold increase in fetal hemoglobin, from a mean (±SD) of 1.6±1.6 percent of total hemoglobin to 6.8±4.7 percent; three patients had fetal-hemoglobin levels of 10 to 15 percent of total hemoglobin. Three did not respond to treatment. Four of the patients who responded were retreated with hydroxyurea after one to four months without treatment and were found to have larger increases in fetal-hemoglobin levels. In most patients, levels were still rising at the end of the study, even after 90 days of therapy. Fetal-hemoglobin levels tended to peak at dosages of hydroxyurea that were myelosuppressive. In the patients who responded to treatment, there were significant increases In the percentage of reticulocytes and erythrocytes containing fetal hemoglobin and in the amount of fetal hemoglobin within these cells. The percentage of dense red cells decreased in the patients who responded to treatment. The tendency toward intracellular polymerization at physiologic oxygen saturation was reduced by about 33 percent in the cells containing fetal hemoglobin, whereas there was no change in the other cells.
We conclude that hydroxyurea is effective in Increasing the production of fetal hemoglobin, which in this study was found to be associated with a small decrease in hemolysis and an increase in hemoglobin levels despite myelosuppression. Controlled, prospective trials are necessary to establish whether these effects will lead to clinical benefit. (N Engl J Med 1990; 322:1037–45.)
Media in This Article
Figure 1
The Fetal-Hemoglobin (×) and F-Reticulocyte (●) Response in Six Patients Who Had Increased Fetal-Hemoglobin Production in Response to Treatment with Escalating Doses of Hydroxyurea over a Period of Three Months.Figure 2
The Fetal-Hemoglobin Response in Four Patients to the Treatment with Escalating Doses (First Course []) and Fixed, "Optimal" Doses (Second Course [
]) of Hydroxyurea.
Article Activity
- Article
THE finding that 5-azacytidine selectively increases the production of fetal hemoglobin in primates1 led to clinical trials in which increases in fetal-hemoglobin levels were demonstrated in patients with beta-thalassemia2 and with sickle cell disease.3 , 4 Increases in fetal hemoglobin, resulting from increased gamma-chain synthesis, should be useful in the treatment of the beta-thalassemia syndromes by decreasing globin-chain imbalance5 and in the treatment of the sickle cell syndromes because of the sparing effect of fetal hemoglobin on the polymerization of sickle hemoglobin.6 Recently, other cytostatic agents, particularly hydroxyurea, have been shown to increase fetal-hemoglobin production in patients with sickle cell anemia.7 8 9 10 11 Treatment of two severely affected patients with hydroxyurea, along with careful observations of several other patients treated for shorter periods, revealed a dramatic increase in the absolute fetal-hemoglobin level after several months of therapy. The total hemoglobin level also increased, reflecting a decrease in the rate of hemolysis.10
These studies have led to the consideration of prospective, clinical trials to establish the benefits of hydroxyurea in the treatment of sickle cell disease. For such trials to be feasible, more information is needed about the clinical pharmacologic features of hydroxyurea, including the optimal dosage regimens, and about predictive factors associated with maximal increases in the production of fetal hemoglobin. Recently, biophysical data on the inhibition of sickle hemoglobin polymer formation by fetal hemoglobin and epidemiologic data on the relation between fetal-hemoglobin levels and the clinical status of various patient groups have made possible estimates of the increases in fetal-hemoglobin levels that might be necessary for clinical benefit.12 In this report we present data on 10 patients with sickle cell disease who were treated as inpatients for periods of three months (4 of the 10 patients were treated for an additional three-month period) in an attempt to clarify the pharmacodynamics of hydroxyurea, the increases in fetal hemoglobin and other hematologic responses to its administration, and the effects of such responses on the intracellular polymerization of sickle hemoglobin.
Methods
Patients with severe, long-standing complications of homozygous sickle cell disease, such as recurrent crises of severe pain, chronic bone pain, or severe symptomatic aseptic necrosis or intractable leg ulcerations, who had relatively well preserved renal and hepatic function were considered eligible for this study. The patients, eight men and two women, ranged in age from 22 to 42 years (average age, 37). The patients were hospitalized for approximately three months at the Clinical Center of the National Institutes of Health and were monitored carefully during the hydroxyurea trial. An exemption for treatment with an investigational new drug was obtained from the Food and Drug Administration. The treatment protocol was approved by the clinical research subpanel of the National Heart, Lung, and Blood Institute. After informed consent was obtained from the patients, we performed base-line and serial hematologic tests and measurements, including a complete blood count, reticulocyte count, hemoglobin electrophoresis, measurement of the fetal-hemoglobin level (as a percentage of total hemoglobin) by alkaline denaturation, profile of red-cell density,13 and determination of the percentages of F reticulocytes and F cells.14 , 15 Blood tests indicating the level of hepatic and renal function were performed three times a week; serum hydroxyurea levels one and four hours after the ingestion of the drug were measured once a week. Base-line serum erythropoietin levels were determined by radioimmunoassay (Smith-Kline BioScience Laboratories, Philadelphia). Restriction-endonuclease analysis of genomic leukocyte DNA was performed to assess the alpha-globin genotype16 and the haplotype of the beta-globin gene cluster.17
Because previous studies indicated that diminished renal elimination of hydroxyurea could result in hematopoietic toxicity, the initial dose of hydroxyurea was based on duplicate determinations of hydroxyurea clearance.9 The starting dose ranged from 10 to 20 mg per kilogram of body weight, taken orally in a single dose (Hydrea, Squibb, Princeton, N.J.) on four consecutive days each week. The dose was adjusted upward by increments of 5 mg per kilogram at four-week intervals until the patient reached an optimal dose or had had two dose adjustments. The dose was adjusted downward or maintained at a constant level if bone marrow suppression (defined as an absolute reticulocyte count <40,000 per cubic millimeter, a white-cell count <5000 per cubic millimeter, or a platelet count <150,000 per cubic millimeter) was observed. Patients were considered to be responding to treatment if they had more than a twofold increase in the percentage of F reticulocytes in total reticulocytes and the percentage of fetal hemoglobin in total hemoglobin. Four patients were retreated with what appeared to be the optimal dose of hydroxyurea for them after a period of one to four months without treatment. The retreatment dose was that at which increases in the fetal-hemoglobin level and the percentage of F reticulocytes occurred in the absence of a decline of more than 20 percent from the average of three base-line values in one or more peripheral-blood counts.
Statistical methods used to determine the significance of the differences in the paired sets of data included the paired Student's t-test for data with a gaussian distribution and the Mann—Whitney U test for data with a nongaussian distribution.18 Univariate and multivariate analyses were used to determine the strength of relations between variables.18 The period before a significant increase in the fetal-hemoglobin level and the F-reticulocyte level was termed the lag period. Lag periods were calculated from the intercept generated by fitting the initial and final data to two "best-fit" linear regression lines. The linear least-squares method19 was used to determine the "best-fit" linear regression lines, and the final two lines were optimized for their respective correlation coefficients and residual errors.
The number of dense cells was defined as the percentage of cells with an intracellular hemoglobin concentration of more than 23.0 mmol per liter (37 g per deciliter), as measured by phthalate-ester gradient centrifugation.13 The median corpuscular hemoglobin concentration (MCHC; the average hemoglobin concentration in erythrocytes),10 which in normal persons is comparable to the mean corpuscular hemoglobin concentration, was determined from these gradients and used to calculate the tendency toward the intracellular polymerization of hemoglobin S for the bulk of the cells (i.e., the non-dense cells). Measurements of the mean corpuscular volume (MCV; the average volume of an erythrocyte) and the mean corpuscular hemoglobin (MCH; the average hemoglobin content of an erythrocyte) were obtained with use of a Coulter electronic cell analyzer. Calculation of intracellular polymerization was performed as previously described12 , 20 on the basis of measurements of total intracellular hemoglobin concentration and the percentages of sickle hemoglobin and fetal hemoglobin. Although calculated for the full range of oxygen-saturation values, these measurements are presented here only for values at 70 percent oxygen saturation, the physiologically important range, for convenience of comparison. The polymerization tendency was calculated separately for the F cells and the non-F cells of the bulk of the cell population, as well as for the dense cells.
Results
Fetal-Hemoglobin Responses
Of the 10 patients treated for three months with increasing doses of hydroxyurea, 7 were considered to have responded to treatment because they had at least a twofold increase in the levels of F reticulocytes and fetal hemoglobin. Among those who responded, fetal-hemoglobin levels increased 2– to 10-fold, with three patients reaching maximal fetal-hemoglobin levels between 10 and 15 percent of total hemoglobin. Initial values for hemoglobin, reticulocytes, or fetal hemoglobin did not predict the response to treatment, since patients with a wide range of values for these indexes were included among both the patients who responded and those who did not (Table 1Table 1
Levels of Hemoglobin, Reticulocytes, and Fetal Hemoglobin before and after Treatment with Hydroxyurea and Presence or Absence of the Xmnl Restriction Site in 10 Patients with Sickle Cell Disease.). Base-line values on tests of hepatic or renal chemistry, hydroxyurea clearance rates, and serum erythropoietin levels did not predict the ultimate response to treatment among the 10 patients (data not shown). We found no absolute correlation between either the alpha-globin genotype16 or the specific beta-globin gene-cluster haplotype17 , 21 , 22 and the production of fetal hemoglobin. In particular, the presence of the XmnI restriction site22 did not necessarily predict a favorable response to hydroxyurea treatment (Table 1). In the responding patients, there was a slight increase in total hemoglobin, despite the myelosuppressive nature of the doses of hydroxyurea. Although the moderate decline in the percentage of reticulocytes can-not be unequivocally interpreted, our finding of a decrease in the indirect bilirubin level (mean ±SD, 35.6±30.8 μmol per liter [2.1±1.8 mg per deciliter] before treatment and 18.8±15.4 μmol per liter [1.1 ±0.9 mg per deciliter] after treatment; P<0.03) in the patients who responded to treatment is consistent with a mild improvement in the hemolytic rate.Three factors determine the level of fetal hemoglobin in patients with sickle cell anemia: F-cell production, as measured by the percentage of F reticulocytes in total reticulocytes, the quantity of fetal hemoglobin per F cell, and the preferential survival of F cells (the ratio of the percentage of F cells to the percentage of F reticulocytes) as compared with red cells that lack fetal hemoglobin (non-F cells).14 , 23 We measured these three variables in order to determine the basis for the increased fetal-hemoglobin level in the patients treated with hydroxyurea. As shown in Table 2Table 2
F-Reticulocyte Levels, F-Cell Levels, and Amount of Fetal Hemoglobin per F Cell (Hb F/F cell) before and after Treatment with Hydroxyurea in 10 Patients with Sickle Cell Disease., the increase in fetal hemoglobin observed in the patients who responded (Group 1) resulted primarily from an augmentation of F-cell production; F reticulocytes increased an average of six-fold, which accounted for about 70 percent of the increase in fetal hemoglobin. The quantity of fetal hemoglobin per F cell also increased in the responding patients during treatment, albeit more modestly, as did the percentage of F cells among total red cells. No effects of hydroxyurea administration on these three variables were observed in the patients who did not respond to treatment (Group 2). The initial values for the percentage of F reticulocytes, the percentage of F cells, the preferential survival of F cells, and the quantity of fetal hemoglobin per F cell did not predict the response to treatment, as patients who responded had values at both extremes for these indexes.Figure 1Figure 1
The Fetal-Hemoglobin (×) and F-Reticulocyte (●) Response in Six Patients Who Had Increased Fetal-Hemoglobin Production in Response to Treatment with Escalating Doses of Hydroxyurea over a Period of Three Months. shows the pattern of fetal-hemoglobin and F-reticulocyte response in six responding patients during their initial course of therapy. Patient I (not shown) had values similar to those of Patient J, with respect to both base-line hematologic measures and the magnitude of the fetal-hemoglobin response to hydroxyurea. Among the responding patients, there was a spectrum of responses, evident in both the rapidity and the absolute magnitude of the change in the levels of fetal hemoglobin and F reticulocytes. Some patients (A, B, G, and I) had increased production of fetal hemoglobin after a prolonged lag period (average, 40 days), perhaps because the initial dose of hydroxyurea was suboptimal. Other patients (C and H) had increases in fetal hemoglobin within the first 20 days of treatment with hydroxyurea. In both groups of responders, the increase in fetal-hemoglobin levels was preceded and paralleled by an increase in the F-reticulocyte count. Patient J had a prompt increase in the F-reticulocyte count within two weeks of the beginning of treatment with hydroxyurea, yet it took an additional five to six weeks before increases in fetal hemoglobin were observed.Retreatment
Of the seven patients who responded to the initial course of therapy, four were retreated with a second course of hydroxyurea at a fixed dose. This was the dose at which the levels of F reticulocytes and fetal hemoglobin rose, in the absence of hematologic toxicity (see Methods). Patients A and H received 20 mg per kilogram, Patient G received 25 mg per kilogram, and Patient C 30 mg per kilogram each day for four consecutive days per week. These patients were hospitalized for the second three-month course of treatment after an average of 100 days without treatment (range, 32 to 125 days). As Figure 2Figure 2
The Fetal-Hemoglobin Response in Four Patients to the Treatment with Escalating Doses (First Course [Marrow Suppression
During the first course, when dosages were increased, only mild marrow toxicity was observed (10 to 15 percent reductions in one or more counts) in the patients who did not respond to hydroxyurea (Group 2). On the other hand, among the patients who did respond (Group 1), there was a statistically significant decline in the reticulocyte count in four of seven patients (Table 1), in the white-cell count in five of seven patients, and in the platelet count in two of seven patients. However, the absolute nadir of these counts in all instances remained within the normal range for these hematologic values and therefore did not necessitate adjustments in the dosage. Despite the decrease in the reticulocyte count, most of the responding patients had some increase in total hemoglobin (Table 1), presumably because of the preferential survival of F cells and because of reduced hemolysis.
Although the four patients who underwent retreatment with hydroxyurea received a calculated "optimal" dose, each had evidence of hematopoietic suppression. The average magnitude of bone marrow depression observed was 28.3 percent for white cells (P<0.04) and 18.6 percent for platelets (P<0.02). Although the average decline in the reticulocyte count was 49 percent, because of the wide variations in the values among the four patients, this decline was not statistically significant, and dose reduction was not required. Thus, it may be concluded that doses of hydroxyurea that achieve fetal-hemoglobin responses are at or near the threshold of marrow suppression.
In most patients who responded during the first course of therapy and in the four who were retreated, levels of fetal hemoglobin were still increasing at the end of the three months. These data are consistent with the findings of Charache et al.10 At the end of three months, three of the four patients on fixed doses of hydroxyurea reached a plateau in F-reticulocyte levels, suggesting the contribution of the preferential survival of F cells,14 an increase in the amount of fetal hemoglobin per F cell, or both to the elevation in fetal-hemoglobin levels.
hematologic Responses
The responding patients had striking changes in the MCV and MCH (Table 3Table 3
Values for Red-Cell Indexes before and after Treatment with Hydroxyurea in 10 Patients with Sickle Cell Disease.*). Among the seven responders, the MCV increased from 90.0±16.3 fl before treatment to 104.4±19.8 fl after three months of treatment with hydroxyurea (P<0.006). Similarly, there was an increase in the MCH from 30.0±5.8 to 34.7±7.2 pg per red cell (P<0.02). There was no net change in the MCHC in the responders. Using phthalate-ester gradients to monitor distributions of red-cell density,13 we found that the patients who responded had a significant decrease in the percentage of dense cells (from 5.5±5.7 to 1.5±2.3 percent; P<0.01) and a slight decrease in the extent of cellular heterogeneity in corpuscular hemoglobin concentrations (R60 values [middle 60 percent density range]; from 0.014±0.004 to 0.010±0.004; P<0.01). There was no net change in the MCHC as measured by phthalate-ester gradients, a more sensitive indicator of the MCHC in patients with sickle cell disease.13 In contrast, among the three patients who did not respond to treatment, only Patient E had changes in the red-cell indexes similar to those observed in the responders (Table 3).Intracellular Polymerization
We examined the effects of hydroxyurea therapy on the tendency toward intracellular polymerization of sickle hemoglobin12 , 20 in the responders. Since the beneficial hematologic effect of hydroxyurea in patients with sickle cell disease would be expected to be restricted to the F cells, the relative changes in the expected polymer fraction in F cells and non-F cells was considered. We calculated that there was a 33 percent reduction in the expected polymer fraction within F cells (from 0.09 to 0.06) at, for example, 70 percent oxygen saturation, as a result of the increased amount of fetal hemoglobin per F cell. The tendency to polymerization, as expected, remained unchanged (at 0.12) after hydroxyurea treatment in the bulk (non-F cell) population. Taking into account the change in the number of F cells after hydroxyurea therapy, as well as that in the number of dense cells, there was an average overall decline of approximately 25 percent (from 0.12 to 0.09) in the expected polymer fraction weighted for changes in the numbers of dense cells and F cells. This effect was seen in both the initial and the second course of treatment.
Discussion
Hydroxyurea has previously been shown to induce the synthesis of fetal hemoglobin in anemic primates24 , 25 used as models of hematopoietic-response patterns and in patients with sickle cell disease,7 8 9 10 11 by an unknown mechanism. One of the aims of this study was to identify predictive factors in patients with sickle cell disease that might be associated with maximal fetal-hemoglobin production. Previous trials of hydroxyurea in sickle cell disease have employed a starting dosage of 50 mg per kilogram,7 8 9 a dose that leads uniformly to substantial hematopoietic suppression.9 , 10 Accordingly, in this investigation, we used lower initial doses of hydroxyurea (usually 10 to 15 mg per kilogram), then gradually increased them by 5 mg per kilogram per month, in order to estimate a retreatment dose for maximal increases in fetal hemoglobin with minimal toxicity.
The three patients who did not respond to hydroxyurea had only minor signs of hematopoietic toxicity, both after the initial dose and after two increases in the dose. In contrast, of the seven patients who responded, two had a statistically significant decline in the white-cell count during the first month of treatment. Moreover, after the dose was increased, all the responders had some degree of peripheral myelosuppression. Thus, in our patients, therapeutic benefit was observed in most patients at a dosage of hydroxyurea that was myelosuppressive. This observation is consistent with the hypothesis that hydroxyurea may stimulate the production of fetal hemoglobin by secondarily inducing erythroid regeneration.8 On the other hand, recent in vitro studies of erythroid progenitors from patients with sickle cell disease who had been treated with hydroxyurea suggest that other mechanisms may also be at work.26 In our study, no patient required either adjustments in the dosage or discontinuation of treatment because of clinical complications. This suggests that the patients who did not respond might tolerate higher doses of hydroxyurea than were given during the 90-day trial period; if the doses were increased to levels equal to or near those causing marrow suppression, fetal-hemoglobin production might increase in these patients, as was observed in the seven patients who responded to treatment.
There were no correlations between the initial hemoglobin level, reticulocyte count, fetal-hemoglobin level, F-reticulocyte level, amount of fetal hemoglobin per F cell, serum erythropoietin and serum hydroxyurea levels, or the results of blood tests for renal or hepatic function and the patient's subsequent response to hydroxyurea. Moreover, we were unable to detect a relation between the alpha-globin genotype16 or the DNA polymorphisms, such as the XmnI restriction site within the beta-globin gene cluster,17 , 21 , 22 and the F-cell response.
Three of the responders and one of the nonresponders had been treated previously with 5-azacytidine and had had similar responses27; this fact raises the possibility that there exists an as yet unrecognized genetic determinant in patients for F-cell responsiveness, which is activated by both drugs. The constant presence of macrocytosis in our patients (Table 3) and in those in other studies10 , 28 , 29 who responded to hydroxyurea by increasing fetal-hemoglobin synthesis may indicate that factors controlling F-cell production may interact directly or indirectly with the determinants of erythroid-volume regulation.
The patients who responded to hydroxyurea were notably heterogeneous with respect to the pattern and rapidity of their response. The range of the increase in fetal hemoglobin was 2– to 10-fold; three patients had levels between 10 and 15 percent of total hemoglobin during the three-month trial. Using multivariate analysis to dissociate the contributions of the three factors that determine levels of fetal hemoglobin in patients with sickle cell disease,14 we found that F-cell production, as estimated by F-reticulocyte levels, accounted for about 70 percent of the increase in fetal hemoglobin in these patients, with a smaller contribution resulting from an increase in the quantity of fetal hemoglobin per F cell. The preferential survival of F cells,14 , 23 presumably the result of decreased intracellular polymerization of hemoglobin S, became a more prominent factor in the patients retreated after an interval during which hydroxyurea was withheld. With long-term hydroxyurea therapy, fetal-hemoglobin levels may contribute a larger proportion to the final steady-state hemoglobin value. Alternatively, as evidenced by the continued increase in the level of fetal hemoglobin in Patient G between the first and the second course of treatment (Fig. 2), intermittent-treatment strategies may be developed to exploit the preferential survival of F cells in these patients.
There was a lag period between the initiation of treatment with hydroxyurea and the subsequent increases in fetal hemoglobin (or F reticulocytes) in two of the four patients who underwent retreatment. These results, which were obtained when the patients were hospitalized and closely monitored, indicate that hydroxyurea should be given for a trial period of at least 60 days before a patient is determined not to be responding to the drug.
The calculated steady-state polymer fraction at 70 percent oxygen saturation at the median cell density, which may be considered a rough guide to the efficacy of treatment, was unchanged in the non-F cells but declined by about 33 percent, to an average polymer fraction of 0.06, in the F cells. This is still a substantial polymerization potential,12 slightly higher than in cells from a patient with the mild sickle cell syndrome sickle hemoglobin-GγAγ-β°-HPFH (0.05 at 70 percent oxygen saturation), for example.12 , 30 There remain many non—F-containing cells in treated patients, which would retain their intrinsic tendency to form intracellular polymers under physiologic conditions and thus would be expected to continue to manifest their hemolytic and vaso-occlusive propensities. However, a second mechanism of possible benefit is the decrease in the number of dense cells. Although this effect was noted in an initial study of patients with sickle cell disease who were treated with 5-azacytidine,3 it has been an inconsistent finding in other studies.10 The overall decrease in dense cells, from 5.5 to 1.5 percent in our study, would also contribute to lowering the overall tendency toward the intracellular polymerization of hemoglobin S.16 , 20 A "weighted" polymer fraction was calculated on the basis of this decrease as well as the increase in the F-cell fraction and the amount of fetal hemoglobin per F cell. The analysis showed a decline of about 25 percent in the overall polymer fraction after treatment, from 0.12 to 0.09.
It is possible that further reductions in the polymer fraction might be achieved through other hydroxyurea regimens. In many of the patients who responded, fetal-hemoglobin levels were still rising at the end of the 90-day protocol. Longer periods of therapy might achieve higher steady-state levels of fetal hemoglobin. Daily hydroxyurea treatment might also result in higher fetal-hemoglobin levels28 , 31 than intermittent therapy. The increase in F cells in baboons treated with recombinant human erythropoietin is also of great interest in this regard.32 The study by Al-Khatti et al.32 and that by McDonagh et al.33 suggest that erythropoietin may act synergistically with hydroxyurea to increase both the number of F cells and the level of fetal hemoglobin. Therefore, treating patients with hydroxyurea for longer periods of time, with alternative dosage schedules, or with hydroxyurea in conjunction with agents such as erythropoietin may lead to higher levels of fetal hemoglobin and greater inhibition of the polymerization of sickle hemoglobin.
Supported in part by a grant (HL-28028) to Dr. Dover from the National Institutes of Health.
We are indebted to Dr. Geraldine P. Schechter for her critical review of the manuscript and to Mr. Marvin J. Podgor for his advice on the statistical methods employed.
Source Information
From the Laboratory of Chemical Biology, National Institute of Diabetes and Digestive and Kidney Diseases (G.P.R., C.T.N., A.N.S.), and the Clinical Hematology Branch. National Heart, Lung, and Blood Institute (A.W.N.), National Institutes of Health, Bethesda, Md., and the Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore (G.J.D.). Address reprint requests to Dr. Rodgers at the Laboratory of Chemical Biology, NIDDK, Bldg. 10, Rm. 9N-318, National Institutes of Health, Bethesda, MD 20892.
- References
References
1
DeSimone
CrossRef | Web of Science | Medline2
Ley
Full Text | Web of Science | Medline3
Ley
Web of Science | Medline4
Charache
CrossRef | Web of Science | Medline5
Shinar
Web of Science | Medline6
Schechter AN. Noguchi CT, Rodgers GP. Sickle cell anemia. In: Stamatoyannopoulos G, Nienhuis AW, Leder P, Majerus PW. eds. The molecular basis of blood diseases. Philadelphia: W.B. Saunders, 1987:179–218.
7
Platt
CrossRef | Web of Science | Medline8
Veith
Full Text | Web of Science | Medline9
Dover
Web of Science | Medline10
Charache
Web of Science | Medline11
Rodgers GP, Dover GJ, Noguchi CT, Schechter AN, Nienhuis AW. Induction of fetal hemoglobin in sickle cell patients by hydroxyurea: the N.I.H. experience. In: Stamatoyannopoulos G, Nienhuis AW, eds. Hemoglobin switching, part B: cellular and molecular mechanisms. Vol. 316B of Progress in clinical and biological research. New York: Alan R. Liss, 1989:281–93.
12
Noguchi
Full Text | Web of Science | Medline13
Rodgers
Medline14
Dover
Full Text | Web of Science | Medline15
Dover
Web of Science | Medline16
Noguchi
CrossRef | Web of Science | Medline17
Antonarakis
CrossRef | Web of Science | Medline18
Remington RD, Schork MA. Statistics with applications to the biological and health sciences. Englewood Cliffs, N.J.: Prentice-Hall, 1970.
19
Forsythe GE, Malcolm MA, Moler CB. Computer methods for mathematical computations. Englewood Cliffs, N.J.: Prentice-Hall, 1977.
20
Noguchi
CrossRef | Web of Science | Medline21
Nagel
Full Text | Web of Science | Medline22
Miller
Full Text | Web of Science | Medline23
Bertles
CrossRef | Web of Science | Medline24
Letvin
Full Text | Web of Science | Medline25
Lavelle
Web of Science | Medline26
Dover
Web of Science | Medline27
Humphries
CrossRef | Web of Science | Medline28
Alter
Web of Science | Medline29
Burns
Web of Science | Medline30
Brittenham
Web of Science | Medline31
Dover GJ, Charache S. Stimulation of fetal hemoglobin production by hydroxyurea in sickle cell anemia. In: Stamatoyannopoulos G, Nienhuis AW, eds. Hemoglobin switching, part B: cellular and molecular mechanisms. Vol. 316B of Progress in clinical and biological research. New York: Alan R. Liss, 1989:295–306.
32
AI-Khatti
Full Text | Web of Science | Medline33
McDonagh KT, Dover GJ, Donahue R, Nathan DG, Nienhuis AW. Manipulation of HbF production with hematopoietic growth factors. In: Stamatoyannopoulos G, Nienhuis AW, eds. Hemoglobin switching, part B: cellular and molecular mechanisms. Vol. 316B of Progress in clinical and biological research. New York: Alan R. Liss, 1989:307–15.
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Carolyn C. Hoppe. (2011) Novel Therapies Targeting the Endothelium in Sickle Cell Disease. Hemoglobin 35:5-6, 530-546
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M. M. Hsieh, C. D. Fitzhugh, J. F. Tisdale. (2011) Allogeneic hematopoietic stem cell transplantation for sickle cell disease: the time is now. Blood 118:5, 1197-1207
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Tae-gyu Nam, Jongkook Lee, John R. Walker, Achim Brinker, Charles Y. Cho, Peter G. Schultz. (2011) Identification and Characterization of Small-Molecule Inducers of Fetal Hemoglobin. ChemMedChem 6:5, 777-780
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J. Zhu, K. Chin, W. Aerbajinai, C. Trainor, P. Gao, G. P. Rodgers. (2011) Recombinant erythroid Kruppel-like factor fused to GATA1 up-regulates delta- and gamma-globin expression in erythroid cells. Blood 117:11, 3045-3052
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Ines Paule, Hind Sassi, Anoosha Habibi, Kim PD Pham, Dora Bachir, Frédéric Galactéros, Pascal Girard, Anne Hulin, Michel Tod. (2011) Population pharmacokinetics and pharmacodynamics of hydroxyurea in sickle cell anemia patients, a basis for optimizing the dosing regimen. Orphanet Journal of Rare Diseases 6:1, 30
CrossRef7
George Atweh, Hassana Fathallah. (2010) Pharmacologic Induction of Fetal Hemoglobin Production. Hematology/Oncology Clinics of North America 24:6, 1131-1144
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Hind Sassi, Dora Bachir, Anoosha Habibi, Alain Astier, Frédéric Galactéros, Anne Hulin. (2010) No effect of CYP450 and P-glycoprotein on hydroxyurea in vitro metabolism. Fundamental & Clinical Pharmacology 24:1, 83-90
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Fernanda Kelle de Souza Santos, Caroline Nogueira Maia. (2010) Patients with sickle cell disease taking hydroxyurea in the Hemocentro Regional de Montes Claros. Revista Brasileira de Hematologia e Hemoterapia 33:2, 105-109
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Matthew Olnes, Amy Chi, Carissa Haney, Rose May, Caterina Minniti, James Taylor, Gregory J. Kato. (2009) Improvement in hemolysis and pulmonary arterial systolic pressure in adult patients with sickle cell disease during treatment with hydroxyurea. American Journal of Hematology 84:8, 529-531
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Wen-Chen Liang, Chung-Yee Yuo, Jan-Gowth Chang, Yi-Ching Chen, Yung-Fu Chang, Hui-Yi Wang, Yun-Huei Ju, Shyh-Shin Chiou, Yuh-Jyh Jong. (2008) The effect of hydroxyurea in spinal muscular atrophy cells and patients. Journal of the Neurological Sciences 268:1-2, 87-94
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Chutima Kumkhaek, James G. Taylor, Jianqiong Zhu, Carolyn Hoppe, Gregory J. Kato, Griffin P. Rodgers. (2008) Fetal haemoglobin response to hydroxycarbamide treatment and sar1a promoter polymorphisms in sickle cell anaemia. British Journal of Haematology 141:2, 254-259
CrossRef13
Marina Kleanthous, Marios Phylactides. (2008) Thalassemia and its relevance to personalized medicine. Personalized Medicine 5:2, 141-153
CrossRef14
C. R. Morris. (2008) Mechanisms of Vasculopathy in Sickle Cell Disease and Thalassemia. Hematology 2008:1, 177-185
CrossRef15
Saqib H. Ansari, Tahir S. Shamsi, Fahad J. Siddiqui, Muhammad Irfan, Kausar Perveen, Tasneem Farzana, Vinodh K. Panjwani, Ayesha Yousuf, Tabassum Mehboob. (2007) Efficacy of Hydroxyurea (HU) in Reduction of Pack Red Cell (PRC) Transfusion Requirement Among Children Having Beta-thalassemia Major: Karachi HU Trial (KHUT). Journal of Pediatric Hematology/Oncology 29:11, 743-746
CrossRef16
Paul S. Frenette, George F. Atweh. (2007) Sickle cell disease: old discoveries, new concepts, and future promise. Journal of Clinical Investigation 117:4, 850-858
CrossRef17
J. Makani, T. N. Williams, K. Marsh. (2007) Sickle cell disease in Africa: burden and research priorities. Annals of Tropical Medicine and Parasitology 101:1, 3-14
CrossRef18
Eitan Fibach, Nicoletta Bianchi, Monica Borgatti, Cristina Zuccato, Alessia Finotti, Ilaria Lampronti, Eugenia Prus, Carlo Mischiati, Roberto Gambari. (2006) Effects of rapamycin on accumulation of ?-, ?- and ?-globin mRNAs in erythroid precursor cells from ?-thalassaemia patients. European Journal of Haematology 77:5, 437-441
CrossRef19
Hassana Fathallah, George F. Atweh. (2006) DNA hypomethylation therapy for hemoglobin disorders: Molecular mechanisms and clinical applications. Blood Reviews 20:4, 227-234
CrossRef20
Hutchinson James, Masoud Nahavandi, Melville Q. Wyche, Robert E. Taylor. (2006) Quantitative analysis of trimethylsilyl derivative of hydroxyurea in plasma by gas chromatography–mass spectrometry. Journal of Chromatography B 831:1-2, 42-47
CrossRef21
HASSANA FATHALLAH, MILLICENT SUTTON, GEORGE F. ATWEH. (2005) Pharmacological Induction of Fetal Hemoglobin: Why Haven't We Been More Successful in Thalassemia?. Annals of the New York Academy of Sciences 1054:1, 228-237
CrossRef22
Ilaria Lampronti, Nicoletta Bianchi, Monica Borgatti, Eitan Fibach, Eugenia Prus, Roberto Gambari. (2003) Accumulation of gamma-globin mRNA in human erythroid cells treated with angelicin. European Journal of Haematology 71:3, 189-198
CrossRef23
Claudia R. Morris, Elliott P. Vichinsky, Jane van Warmerdam, Lorenzo Machado, Diane Kepka-Lenhart, Sidney M. Morris,, Frans A. Kuypers. (2003) Hydroxyurea and Arginine Therapy: Impact on Nitric Oxide Production in Sickle Cell Disease. Journal of Pediatric Hematology/Oncology 25:8, 629-634
CrossRef24
Efemwonkiekie W Iyamu, Samuel E Adunyah, Hugo Fasold, Kazumi Horiuchi, Surendra Baliga, Kwaku Ohene-Frempong, Ernest A Turner, Toshio Asakura. (2003) Combined use of nonmyelosuppressive nitrosourea analogues with hydroxyurea in the induction of F-cell production in a human erythroleukemic cell line. Experimental Hematology 31:7, 592-600
CrossRef25
Min Wang, Delia C. Tang, Wenli Liu, Kyung Chin, Jianqion G. Zhu, Eitan Fibach, Griffin P. Rodgers. (2002) Hydroxyurea exerts bi-modal dose-dependent effects on erythropoiesis in human cultured erythroid cells via distinct pathways. British Journal of Haematology 119:4, 1098-1105
CrossRef26
Omar Y. Gonzalez, John F. Jovanovich, Douglas L. Mayers, Daniel M. Musher. (2002) The Lack of Therapeutic Benefit of Adding Hydroxyurea to Highly Active Antiretroviral Therapy (HAART). JAIDS Journal of Acquired Immune Deficiency Syndromes 30:3, 363-364
CrossRef27
Shu Bing ZHANG, Qi Ye HE, Hui ZHAO, Chang Yun GUI, Chu JIANG, Ruo Lan QIAN. (2001) Function of GATA transcription factors in hydroxyurea-induced HEL cells. Cell Research 11:4, 301-310
CrossRef28
George F Atweh, Dimitris Loukopoulos. (2001) Pharmacological induction of fetal hemoglobin in sickle cell disease and β-thalassemia. Seminars in Hematology 38:4, 367-373
CrossRef29
MARTIN H. STEINBERG, GRIFFIN P. RODGERS. (2001) Pharmacologic Modulation of Fetal Hemoglobin. Medicine 80:5, 328-344
CrossRef30
Nicoletta Bianchi, Cristiano Chiarabelli, Monica Borgatti, Carlo Mischiati, Eitan Fibach, Roberto Gambari. (2001) Accumulation of gamma-globin mRNA and induction of erythroid differentiation after treatment of human leukaemic K562 cells with tallimustine. British Journal of Haematology 113:4, 951-961
CrossRef31
Ashley P Jones, Sally C Davies, Adebayo Olujohungbe, Ashley P Jones. 2001. Hydroxyurea for sickle cell disease. .
CrossRef32
George F. Atweh, Alan N. Schechter. (2001) Pharmacologic induction of fetal hemoglobin: raising the therapeutic bar in sickle cell disease. Current Opinion in Hematology 8:2, 123-130
CrossRef33
V. Sontini, A. Gozzini, B. Scappini, A. Grossi, P. Rossi Ferrini. (2001) Searching for the Magic Bullet Against Cancer: The Butyrate Saga. Leukemia & Lymphoma 42:3, 275-289
CrossRef34
Dimitris Loukopoulos, Ersi Voskaridou, Vassiliki Kalotychou, Maria Schina, Aphrodite Loutradi, Ilias Theodoropoulos. (2000) Reduction of the Clinical Severity of Sickle Cell/β-Thalassemia with Hydroxyurea: The Experience of a Single Center in Greece. Blood Cells, Molecules, and Diseases 26:5, 453-466
CrossRef35
Borys W. Hrinczenko, Abdu I. Alayash, David A. Wink, Mark T. Gladwin, Griffin P. Rodgers, Alan N. Schechter. (2000) Effect of nitric oxide and nitric oxide donors on red blood cell oxygen transport. British Journal of Haematology 110:2, 412-419
CrossRef36
Rathi Iyer, Radhakrishna Baliga, Ronald L. Nagel, Carlo Brugnara, Kent Kirchner, Shirley Hogan, Martin H. Steinberg. (2000) Maximum urine concentrating ability in children with Hb SC disease: Effects of hydroxyurea. American Journal of Hematology 64:1, 47-52
CrossRef37
Cheryl A. Hillery, Ming C. Du, Winfred C. Wang, J. Paul Scott. (2000) Hydroxyurea therapy decreases the in vitro adhesion of sickle erythrocytes to thrombospondin and laminin. British Journal of Haematology 109:2, 322-327
CrossRef38
Arlene M Buller, Howard L Elford, Charles C DuBois, Joanne Meyer, Joyce A Lloyd. (1999) A Combination of Hydroxyurea and Isobutyramide to Induce Fetal Hemoglobin in Transgenic Mice Is More Hematotoxic Than the Individual Agents. Blood Cells, Molecules, and Diseases 25:4, 255-269
CrossRef39
Wood, Alastair J.J., , Steinberg, Martin H., . (1999) Management of Sickle Cell Disease. New England Journal of Medicine 340:13, 1021-1030
Full Text40
John C. Schultz. (1999) Comparison of radial immunodiffusion and alkaline cellulose acetate electrophoresis for quantitating elevated levels of fetal hemoglobin (HbF): Application to evaluating patients with sickle cell disease treated with hydroxyurea. Journal of Clinical Laboratory Analysis 13:2, 82-89
CrossRef41
Philippe R. Pouillart. (1998) Role of butyric acid and its derivatives in the treatment of colorectal cancer and hemoglobinopathies. Life Sciences 63:20, 1739-1760
CrossRef42
PANAGOULA KOLLIA, EITAN FIBACH, MARIANNA POLITOU, CONSTANCE T. NOGUCHI, ALAN N. SCHECHTER, DIMITRIS LOUKOPOULOS. (1998) Hydroxyurea and Hemin Affect Both the Transcriptional and Post-Transcriptional Mechanisms of Some Globin Genes in Human Adult Erythroid Cellsa. Annals of the New York Academy of Sciences 850:1 COOLEY'S ANEM, 449-451
CrossRef43
Griffin P. Rodgers. (1998) 9 Pharmacological therapy. Baillière's Clinical Haematology 11:1, 239-255
CrossRef44
Yih-Ming Yang, Betty Pace, David Kitchens, Samir K. Ballas, Arvind Shah, B. Surendra Baliga. (1997) BFU-E colony growth in response to hydroxyurea: Correlation between in vitro and in vivo fetal hemoglobin induction. American Journal of Hematology 56:4, 252-258
CrossRef45
Epstein, Franklin H., , Bunn, H. Franklin, . (1997) Pathogenesis and Treatment of Sickle Cell Disease. New England Journal of Medicine 337:11, 762-769
Full Text46
M. de Montalembert, M. Belloy, F. Bernaudin, F. Gouraud, R. Capdeville, R. Mardini, N. Philippe, J. P. Jais, J. Bardakdjian, R. Ducrocq, M. Maier-Redelsperger, J. Elion, D. Labie, R. Girot. (1997) Three-Year Follow-Up of Hydroxyurea Treatment in Severely Ill Children with Sickle Cell Disease. Journal of Pediatric Hematology/Oncology 19:4, 313-318
CrossRef47
Ved P Choudhry, Amita Lal, H. P. Pati, L. S. Arya. (1997) Hematological responses to hydroxyurea therapy in multitransfused thalassemic children. The Indian Journal of Pediatrics 64:3, 395-398
CrossRef48
P. Rigano, L. Manfré, R. La Galla, D. Renda, M. C. Renda, A. Calabrese, R. Calzolari, A. Maggio. (1997) Clinical and Hematological Response to Hydroxyurea in a Patient with Hb Leporbp-Thalassemia. Hemoglobin 21:3, 219-226
CrossRef49
Samuel Charache. (1996) EXPERIMENTAL THERAPY. Hematology/Oncology Clinics of North America 10:6, 1373-1382
CrossRef50
Samuel Charache, Franca B. Barton, Richard D. Moore, Michael L. Terrin, Martin H. Steinberg, George J. Dover, Samir K. Ballas, Robert P. McMahon, Oswaldo Castro, Eugene P. Orringer. (1996) Hydroxyurea and Sickle Cell Anemia. Medicine 75:6, 300-326
CrossRef51
W Hudgins. (1996) Transcriptional upregulation of γ-globin by phenylbutyrate and analogous aromatic fatty acids. Biochemical Pharmacology 52:8, 1227-1233
CrossRef52
R. Pacelli, J. Taira, J.A. Cook, D.A. Wink, M.C. Krishna. (1996) Hydroxyurea reacts with heme proteins to generate nitric oxide. The Lancet 347:9005, 900
CrossRef53
(1996) Hydroxyurea in Sickle Cell Disease. New England Journal of Medicine 334:5, 333-334
Full Text54
Deborah Rund, Eliezer Rachmilewitz. (1995) Advances in the pathophysiology and treatment of thalassemia. Critical Reviews in Oncology/Hematology 20:3, 237-254
CrossRef55
Griffin P. Rodgers, Eliezer A. Rachmilewitz. (1995) NOVEL TREATMENT OPTIONS IN THE SEVERE β-GLOBIN DISORDERS. British Journal of Haematology 91:2, 263-268
CrossRef56
A. W. Saleh, A. Van Goethem, R. Jansen, H. J. R. Velvis, L.-H. Gu, T. H. J. Huisman. (1995) Isobutyramide therapy in patients with sickle cell anemia. American Journal of Hematology 49:3, 244-246
CrossRef57
YI-TAO ZENG, SHU-ZHEN HUANG, ZHAO-RUI REN, ZHI-HONG LU, FAN-YI ZENG, ALAN N. SCHECHTER, GRIFFIN P. RODGERS. (1995) Hydroxyurea therapy in β-thalassaemia intermedia: improvement in haematological parameters due to enhanced β-globin synthesis. British Journal of Haematology 90:3, 557-563
CrossRef58
Sher, Graham D., Ginder, Gordon D., Little, Jane, Yang, Suya, Dover, George J., Olivieri, Nancy F., . (1995) Extended Therapy with Intravenous Arginine Butyrate in Patients with β-Hemoglobinopathies. New England Journal of Medicine 332:24, 1606-1610
Full Text59
M. H. Steinberg, H. Hsu, R. L. Nagel, P. F. Milner, J. G. Adams, L. Benjamin, S. Fryd, P. Gillette, J. Gilman, O. Josifovska, S. Hellman-Erlingsson, S. Safaya, L. Huey, R. F. Rieder. (1995) Gender and haplotype effects upon hematological manifestations of adult sickle cell anemia. American Journal of Hematology 48:3, 175-181
CrossRef60
Ersi Voskaridou, Vassiliki Kalotychou, Dimitris Loukopoulos. (1995) Clinical and laboratory effects of long-term administration of hydroxyurea to patients with sickle-cell/β-thalassaemia. British Journal of Haematology 89:3, 479-484
CrossRef61
Susan P. Perrine, George H. Dover, Pratibha Daftari, Carol T. Walsh, YuXin Jin, Abbie Mays, Douglas V. Faller. (1994) Isobutyramide, an orally bioavailable butyrate analogue, stimulates fetal globin gene expression in vitro and in vivo. British Journal of Haematology 88:3, 555-561
CrossRef62
Eitan Fibach, Alan N. Schechter, Constance T. Noguchi, Griffen P. Rodgers. (1994) Reducing erythropoietin in cultures of human erythroid precursors elevates the proportion of fetal haemoglobin. British Journal of Haematology 88:1, 39-45
CrossRef63
Vipul N. Mankad, Surendra Baliga, Karen Phillips, Arvind K. Shah, Yih-Ming Yang. (1994) Relationship of burst-forming-unit-erythroid progenitors and their DNA-synthesis stage to fetal hemoglobin levels in hydroxyurea-treated patients with sickle cell anemia. American Journal of Hematology 46:4, 259-263
CrossRef64
Griffin, Timothy C.McIntire, DonaldBuchanan, George R.. (1994) High-Dose Intravenous Methylprednisolone Therapy for Pain in Children and Adolescents with Sickle Cell Disease. New England Journal of Medicine 330:11, 733-737
Full Text65
J. D. Cavenagh, A. E. A. Joseph, S. Dilly, D. H. Bevan. (1994) Splenic sepsis in sickle cell disease. British Journal of Haematology 86:1, 187-189
CrossRef66
Weatherall, D.J., . (1993) The Treatment of Thalassemia -- Slow Progress and New Dilemmas. New England Journal of Medicine 329:12, 877-879
Full Text67
Blau, C. Anthony, . (1993) Therapy for Globin-Chain Disorders. New England Journal of Medicine 329:5, 364-364
Full Text68
S.C. Davies. (1993) Bone marrow transplant for sickle cell disease—the dilemma. Blood Reviews 7:1, 4-9
CrossRef69
C. Vermylen, G. Cornu. (1993) Bone marrow transplantation in sickle cell anaemia. Blood Reviews 7:1, 1-3
CrossRef70
S. P. Perrine, D. V. Faller. (1993) Butyrate-induced reactivation of the fetal globin genes: A molecular treatment for theβ-hemoglobinophaties. Experientia 49:2, 133-137
CrossRef71
Perrine, Susan P.Ginder, Gordon D.Faller, Douglas V.Dover, George H.Ikuta, TohruWitkowska, H. EwaCai, Shi-pingVichinsky, Elliott P.Olivieri, Nancy F.. (1993) A Short-Term Trial of Butyrate to Stimulate Fetal-Globin-Gene Expression in the β-Globin Disorders. New England Journal of Medicine 328:2, 81-86
Full Text72
Rodgers, Griffin P.Dover, George J.Uyesaka, NobuhiroNoguchi, Constance T.Schechter, Alan N.Nienhuis, Arthur W.. (1993) Augmentation by Erythropoietin of the Fetal-Hemoglobin Response to Hydroxyurea in Sickle Cell Disease. New England Journal of Medicine 328:2, 73-80
Full Text73
Donald Lavelle, Joseph Desimone, Paul Heller. (1993) Fetal hemoglobin reactivation in baboon and man: A short perspective. American Journal of Hematology 42:1, 91-95
CrossRef74
Armando R. Orlina, Steven D. Sosler, Mabel Koshy. (1991) Problems of chronic transfusion in sickle cell disease. Journal of Clinical Apheresis 6:4, 234-240
CrossRef75
Martin H. Steinberg. (1991) Sickle cell anemia: Pathophysiology, management, and prospects for the future. Journal of Clinical Apheresis 6:4, 221-223
CrossRef76
DAVID G. NATHAN. (1990) Pharmacologic Manipulation of Fetal Hemoglobin in the Hemoglobinopathies. Annals of the New York Academy of Sciences 612:1 Sixth Cooley', 179-182
CrossRef77
GEORGE J. DOVER. (1990) Pharmacologic Manipulation of Fetal Hemoglobin.. Annals of the New York Academy of Sciences 612:1 Sixth Cooley', 184-190
CrossRef78
Goldberg, Mark A., Brugnara, Carlo, Dover, George J., Schapira, Lidia, Charache, Samuel, Bunn, H. Franklin, . (1990) Treatment of Sickle Cell Anemia with Hydroxyurea and Erythropoietin. New England Journal of Medicine 323:6, 366-372
Full Text
