Potentiation of chlorambucil activity by phenylbutazone.

Phenylbutazone increased the cytotoxicity of chlorambucil to L1210 and P388 leukemia cells in vitro by displacing alkylating agent bound to serum of the tissue culture medium. Administration of phenylbutazone with chlorambucil to mice bearing the P388 tumor lowers the dose of chlorambucil required to achieve maximum increase in life span, but also lowers the dose required for host toxicity. No therapeutic advantage is obtained by the combination.