Abstract
Platelet function testing is an important laboratory measure in clopidogrel treatment. We sought to investigate the stability of the reactivity of clopidogrel after 1 month of treatment. A prospective analysis was carried out using a matched study design to compare platelet reactivity units (PRUs) and platelet inhibition in clopidogrel-treated patients. Patients with various cardiac diseases were divided into 2 matched groups. The first group was treated on an inpatient acute basis, and the other group was treated on an outpatient chronic basis. PRU was measured 5 days after clopidogrel administration in the acute group and 1 month after chronic use for several cardiac indications in the second group. VerifyNow (Accumetrics) was used to detect platelet reactivity and calculate inhibition rates in response to clopidogrel. A total of 260 Saudi patients were enrolled, including 90 inpatients and 170 outpatients. A significant difference was observed in PRU (173.69 vs. 195) and percent inhibition (24.05% vs. 16.13%) between the outpatient and inpatient groups. Platelet function evolves over time and initial readings may not be constant.