Pharmacology and pharmaceutics

Clinical pharmacology Erythropoietin is instrumental in the production of red cells from the erythroid tissues in the bone marrow. The majority of this hormone is produced in the kidney in response to hypoxia, with an additional 10% to 15% of synthesis occurring in the liver. Erythro-poietin functions as a growth factor, stimulating the mitotic activity of the erythroid progenitor cells and early precursor cells. Chronic renal failure patients often manifest the sequelae of renal dysfunction, including anemia. Anemia in cancer patients may be related to the disease itself or the effect of concomitantly administered chemotherapeutic agents.

Pharmacokinetics The bioavailability of a subcutaneous dose of epoetin alfa, relative to an intravenous bolus, has been estimated at 22% to 31%. The elimination half-life of epoetin alfa after an intravenous dose is 6 to 13 hours in patients with chronic renal failure. Mean clearance ranges from 0.032 to 0.055 ml/min per kg. The apparent half-life after a subcutaneous dose is 27 hours. Volume of distribution estimates range from 0.021 to 0.063 l/kg.

Disposition According to Micromed-ex, some metabolic degradation of epoetin alfa occurs, with small amounts recovered in the urine.

Drug interactions No evidence of interaction of epoetin alfa with other drugs was observed in the course of clinical trials.

E. Therapeutic response Epoetin alfa has been shown to stimulate erythropoiesis in anemic patients with chronic renal failure, including both patients on dialysis and those who do not require regular dialysis. The first evidence of a response to the administration of epoetin alfa is an increase in the reticulocyte count within 10 days, followed by increases in the red cell count, hemoglobin, and hematocrit, usually within 2 to 6 weeks. Once the hematocrit reaches the suggested target range (3036%), that level can be sustained by epoetin alfa therapy.

F. Role in therapy Epoetin alfa represents a major advance in the treatment of anemia associated with chronic renal failure. The hormone is an alternative to androgen and red blood cell transfusion therapy, which had been the mainstay of treatment. It may also provide an alternative for those patients who previously could not be treated with blood transfusions because of religious reasons.

G. Other applications Epoetin alfa may find a place in the therapy of anemia of other diseases such as those associated with sickle cell disease, rheumatoid arthritis, and prematurity. In addition the potential for use in autologous blood transfusion programs merits study.

H. Other considerations Epoetin alfa has been designated an orphan product for use in the treatment of anemia of end-stage renal disease, HIV infection, or prematurity in preterm infants, or treatment of myelodysplastic syndrome.



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