The efficacy and potency of antiplatelet activity of ticlopidine is increased by aspirin.

Concomitant therapy with ticlopidine (T) and aspirin (ASA) profoundly increases spectrum of antiplatelet activities of both drugs. It was hypothesized that in addition to increased spectrum of activity (efficacy) each drug may potentiate the specific antiplatelet activity (potency) of the other. In 32 volunteers whole blood platelet aggregation (PA) in response to ADP, collagen, and arachidonic acid was evaluated ex vivo following 10-day treatments with normal or subthreshold doses of T or ASA with addition of second drug on the 5th day of administration of the first. PA was measured before, on day 5 and 10 of treatment. The results indicate that ASA increased spectrum of activity of T, i.e. T and ASA in combination, were significantly more effective against collagen-induced PA than either drug alone. This increased efficacy was retained when subthreshold dose of T (100 mg, qd) was used. T was without effect on AA-induced and ASA on ADP-induced PA. However, ASA potentiated effect of T on ADP-induced PA; the subthreshold dose of T (100 mg, qd) in presence of ASA (100 mg, qd) exerted powerful inhibition. Thus, combination therapy increases both efficacy and potency of T allowing for reduction of the dose.