Intramuscular administration of hydroxyprogesterone caproate in patients with endometrial carcinoma. Pharmacokinetics and effects on adrenal function.

A radio-immunoassay for the determination of the serum concentration of hydroxyprogesterone caproate (HPC) was established. After a single intramuscular injection of 1000 mg, the mean serum level reached its maximum (44-81 nmol/l) after 2-7 days. Patients on long-term adjuvant HPC treatment (consisting of 1000 mg daily for 5 days followed by 1000 mg every 2 weeks) presented peak hormone levels 2 weeks after commencing treatment. After a drop at 5 weeks, the mean serum level slowly increased again to 130 nmol/l after 25 weeks of treatment. Patients being treated with weekly injections had significantly higher serum levels than those treated every 2 weeks. Considerable inter-individual differences were observed. The serum concentrations of HPC measured in this study compare favorably with those previously found in patients treated with medroxyprogesterone acetate. The patients on adjuvant HPC showed no significant change in the levels of cortisol, dehydroepiandrosterone sulphate, androstenedione, or estrone during the first 25 weeks of treatment.