Low Fixed Dose Hydroxyurea for the Treatment of Adults with Sickle Cell Disease in Nigeria

Background: The vast majority of births with sickle cell anemia occur in Africa ¹ and early-life mortality, generally before age five years, is as high as 90% ^2,3. Hydroxyurea was approved for sickle cell anemia by the US FDA in 1998 but is not commonly used in Africa due to fear of toxicity, lack of awareness and limited availability. Hemoglobin F is a protective factor that decreases severity of sickle cell anemia, and hydroxyurea treatment leads to an increase in hemoglobin F. In the US, hydroxyurea is typically initiated at a dose of 15 mg/kg followed by dose escalations of up to 35 mg/kg if tolerated with a goal of maximal tolerated dose and maximal response in hemoglobin F. Neutropenia and thrombocytopenia are the usual limitations to achieving maximal dose. In the landmark Multicenter Study of Hydroxyurea, the clinical response to hydroxyurea correlated strongly with a reduction in the neutrophil count as well as an increase in the fetal hemoglobin concentration as reflected in percentage of F cells. A striking decrease in pain crises was observed in the first three months of therapy, before dose escalation and before maximal increase in hemoglobin F levels ⁴. Furthermore, hydroxyurea in the range of 10-15.9 mg/kg/day was reportedly effective in decreasing the frequency of pain episodes in children and adolescents in Oman ⁵, and hydroxyurea 10 mg/kg/day decreased pain episodes in children and adults with sickle cell anemia in India ⁶. From these perspectives, we reasoned that a fixed dose of hydroxyurea 10 mg/kg/day is reasonable to investigate in the African setting where the safety in relationship to the resources and infectious exposures is not known.

Methods: We assigned 48 sickle cell anemia patients to hydroxyurea 500 mg/day for 24 weeks to determine safety and efficacy; 28 had high-risk disease based on hemoglobin F<8.6% and absence of alpha-thalassemia. We defined a clinically meaningful adverse outcome category as ≥10% of patients developing platelets <50,000/uL, granulocytes <500/uL, clinical malaria and/or active tuberculosis. Picking up refills every four weeks was the adherence metric. We analyzed the results on an intent-to-treat basis.

Results: The median (interquartile range) age was 25 (22-27) years and the median hydroxyurea dose 9.8 (9.1-10.4) mg/kg per day. The patients complied with treatment for a median of 20 (16-24) weeks. Four (8.3%) developed a pre-specified adverse outcome: clinical malaria (N=2), thrombocytopenia in combination with malaria (N=1), pulmonary tuberculosis (N=1). During therapy the median hemoglobin increased by 9.0 g/L, mean corpuscular volume by 11.2 fL and body weight by 3.0 kg while median white blood cells declined by 2600 per uL and platelets by 127,000 per uL (P<0.001). The median hemoglobin F increased from 4.1% (2.3-6.3%) at baseline (N=27) to 8.5% (6.3-12.9%) during therapy (N=24) (P<0.001).

Conclusion: Our results suggest that low, fixed-dose dose hydroxyurea for sickle cell anemia in Nigeria is associated with a low adverse outcome rate and with improvements in blood counts, hemoglobin F and body weight. The effects on vaso-occlusive episodes and on the risks of recrudescent tuberculosis and malaria-associated thrombocytopenia should be assessed in further studies.

Acknowledgment: Supported by a grant from the Doris Duke Foundation.

References

1. Williams TN, Obaro SK. Sickle cell disease and malaria morbidity: a tale with two tails. Trends Parasitol 2011;27:315-20.

2. Grosse SD, Odame I, Atrash HK, Amendah DD, Piel FB, Williams TN. Sickle cell disease in Africa: a neglected cause of early childhood mortality. Am J Prev Med 2011;41:S398-405.

3. Makani J, Cox SE, Soka D, et al. Mortality in sickle cell anemia in Africa: a prospective cohort study in Tanzania. PLoS One 2011;6:e14699.

4. Charache S, Barton FB, Moore RD, et al. Hydroxyurea and sickle cell anemia. Clinical utility of a myelosuppressive "switching" agent. The Multicenter Study of Hydroxyurea in Sickle Cell Anemia. Medicine (Baltimore) 1996;75:300-26.

5. Sharef SW, Al-Hajri M, Beshlawi I, et al. Optimizing Hydroxyurea use in children with sickle cell disease: low dose regimen is effective. Eur J Haematol 2013.

6. Patel DK, Mashon RS, Patel S, Das BS, Purohit P, Bishwal SC. Low dose hydroxyurea is effective in reducing the incidence of painful crisis and frequency of blood transfusion in sickle cell anemia patients from eastern India. Hemoglobin 2012;36:409-20.