Effects of therapeutic drugs on lymphocyte transformation.

1 Over 40 non-steroidal drugs, routinely given on a long term therapeutic basis, were tested in lymphocyte transformation cultures at high therapeutic concentrations, or in serum cultures after short term oral drug administration. Lymphocyte transformation was assessed by measuring thymidine and 2-deoxyuridine incorporation into DNA. 2 When added in vitro, salicylate significantly inhibited thymidine (48%, n = 35) and deoxyuridine incorporation (20%, n = 12). Thymidine incorporation was specifically inhibited by phenylbutazone (39%, n = 6) and chlorpropamide (48%, n = 5). Specific inhibition of deoxyuridine incorporation, indicative of impaired lymphocyte folate metabolism, was obtained following the addition of pyrimethamine (51%, n = 3) and to some extent by carbimazole (30%, n = 2). In serum cultures, pyrimethamine inhibited deoxyuridine incorporation (30%, n = 3) and chloroquine inhibited the incorporation of both thymidine (37%, n = 3) and deoxyuridine (46%, n = 3). 3 Most classes of drugs used long term are unlikely to cause any significant clinical effect, by impairing lymphocyte function. Caution may be warranted when high doses of salicylate, phenylbutazone, chloroquine, pyrimethamine, chloropropamide or combinations of these drugs are prescribed.