• Patrick Gladding, Mark Webster, Irene Zeng, Helen Farrell, Jim Stewart, Peter Ruygrok, John Ormiston, Seif El-Jack, Guy Armstrong, Patrick Kay, Douglas Scott, Arzu Gunes, and Marja-Liisa Dahl.
• Green Lane Cardiovascular Service, Auckland City Hospital, Auckland, New Zealand. patrickg@adhb.govt.nz
• JACC Cardiovasc Interv. 2008 Dec 1; 1 (6): 612-9.

ObjectivesThis study evaluated the antiplatelet effect of a higher loading and maintenance dose regimen of clopidogrel and a possible drug interaction with verapamil.BackgroundClopidogrel loading doses above 600 mg have not resulted in more rapid or complete platelet inhibition. Higher maintenance dosages may be more effective than 75 mg/day.MethodsA double-blind, randomized, placebo-controlled trial was undertaken in 60 patients undergoing percutaneous coronary intervention. All patients received clopidogrel 600 mg at the start of the procedure. Using a 2 x 2 design, patients were allocated to clopidogrel 600 mg given 2 h later or matching placebo, and to verapamil 5 mg intra-arterial or placebo. Platelet function was measured using the VerifyNow P2Y12 analyzer (Accumetrics Ltd., San Diego, California) at 2, 4, and 7 h. Patients were further randomized to receive a clopidogrel 75 or 150 mg once daily, with platelet function assessed after 1 week.ResultsTwo hours after the second dose of clopidogrel or placebo, platelet inhibition was 42 +/- 27% with clopidogrel, compared with 24 +/- 22% with placebo (p = 0.0006). By 5 h after the second dose, platelet inhibition was 49 +/- 30% with clopidogrel, compared with 29 +/- 22% with placebo (p = 0.01). No drug interaction was seen with verapamil. A clopidogrel maintenance dosage of 150 mg daily for 1 week resulted in greater platelet inhibition than 75 mg daily (50 +/- 28% vs. 29 +/- 19%, p = 0.01).ConclusionsIn an unselected population undergoing percutaneous coronary intervention a clopidogrel 1,200-mg loading dose, given as two 600-mg doses 2 h apart, results in more rapid and complete platelet inhibition than a single 600-mg dose. A maintenance dosage of 150 mg daily produces greater platelet inhibition than 75 mg daily. (The PRINC trial; ACTRN12606000129583).

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