The pharmacokinetics of medroxyprogesterone acetate following two different loading dose schedules in advanced carcinoma of the breast.

A loading dose of MPA employing a regimen of 1,000 mg six hourly for 8 doses can achieve plateau levels above 100 ng ml-1 within the first 36 h of treatment, without any untoward toxicity. This raises the possibility of shortening the time to response for this agent. The additional factor of the time required to achieve adequate serum levels may explain the apparent contradictions between reports correlating response rates and dose and those correlating serum level and response.