Clinical Pharmacology of Systemic Chemotherapeutic Agents in Skin Neoplasms

: Considerable progress recently has been made in the systemic chemotherapy of disseminated skin neoplasms. Several agents are particularly useful in this regard: the nitrosoureas, methotrexate, actinomycin D, and dacarbazine. This paper reviews their pharmacologic disposition in man. The nitrosoureas have short plasma half-lives; however, they are extensively degraded to metabolites that persist in the body, and are only slowly excreted. Highly soluble in lipids, the nitrosoureas penetrate significantly into the central nervous system. Actinomycin D is only minimally metabolized in vivo; its elimination from the plasma shows a prolonged slow phase with a half-life of 36 hours; but its excretion is even slower than expected about 30% in a week. A potent inhibitor of dihydrofolate reductase, methotrexate exhibits a multiphasic plasma disappearance, and accumulates in tissues with high dihydrofolate reductase activities. At the normal therapeutic dosages, methotrexate is eliminated by the kidneys as the unchanged drug; appropriate dosage modifications are mandatory if renal function is compromised. Dacarbazine has a relatively short plasma half-life, and is rapidly excreted partly as the unchanged drug; it undergoes extensive biotransformation in the body. Like other antitumor agents, these drugs may cause gastrointestinal toxicities and myelosuppression; in addition each drug can have its own individual organ toxicity.