Clinical pharmacokinetics and pharmacodynamics of a new squalene synthase inhibitor, BMS-188494, in healthy volunteers

A double-blind, placebo-controlled, parallel-group, ascending, multiple- dose study was completed in 45 healthy male volunteers to assess the maximum tolerated dose, pharmacokinetics, and pharmacodynamics of BMS-187745, a squalene synthase inhibitor, administered as multiple oral doses of its prodrug BMS-188494. Participants received a daily oral dose of 10 mg for 2 weeks, or a daily oral dose of 25, 50, 100, or 200 mg for 4 weeks. The absorption rate constant (k(a)) and bioavailability (F) values were estimated by fitting the plasma BMS-187745 concentration-time data to a biexponential function with a first-order k(a). Values for F were similar for all five dose levels, and thus were independent of dose. The k(a) values also were similar for all dose groups except the 50-mg group, for which k(a) values were somewhat higher. The change in urinary excretion rate of farnesyl pyrophosphate metabolite (dioic acid) was determined to be a pharmacodynamic measure. There was no significant change in dioic acid excretion at doses of less than 100 mg given for 4 weeks. An indirect pharmacodynamic response model with threshold concentration (C(T)) and based on inhibition of squalene synthase was proposed to describe the effect versus time data. The pharmacodynamic data from all dose levels were fitted simultaneously to the proposed model and the fitted parameters estimated as C(T) = 3.9 μg/mL, k(out) = 0.47 hr^-1, IC₅₀ = 4.1 μg/mL, and I(max) = 1.0. The proposed indirect response model requiring a threshold concentration provides a useful means of quantitating responses for a new type of therapeutic agent.