Oral dosage of melphalan and response to treatment in multiple myeloma.

Forty-nine consecutive patients with multiple myeloma were analysed for treatment response in relation to dose of orally administered melphalan (induction therapy). All patients were given at least six courses of melphalan-prednisone. Treatment response, defined as a reduction of the myeloma protein of greater than 50%, was seen in 26 patients while 23 were non-responders. When treatment response was related to the dosage of melphalan given by mg/kg of body weight, the numbers of responding and non-responding patients were similar in the group of patients without dose reduction as well as in that with dose reduction. Drug-induced suppression of white blood cell and platelet count was similar in the responding as well as in the non-responding group indicating that the reason for non-response is not simply explained by deficient drug absorption. When the cumulative dose of melphalan given during the induction therapy was analysed, however, a positive correlation (r = 0.47, P less than 0.001) was seen between the cumulative dose and the degree of response. Thus, the cumulative dose of melphalan given during induction therapy seems to be of importance for the response, but other factors as intrinsic differences in cell sensitivity may also explain the individual responsiveness.