The pharmacokinetics of melphalan during intermittent therapy of multiple myeloma.

During intermittent melphalan-prednisone therapy the area under the plasma concentration-time curve of melphalan increased by an average of 45% after oral or intravenous administration of the drug in myeloma patients during the initial three courses at six-week intervals. The rise in melphalan plasma concentrations could not be referred to an alteration in melphalan elimination, metabolism, erythrocyte/plasma partition ratio, or protein binding. A possible explanation could be that covalent binding sites of melphalan were successively saturated during intermittent treatment, resulting in higher drug concentrations during successive courses of therapy.