Assessment of steady-state clopidogrel reactivity by using platelet reactivity units

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.