Pharmacokinetic-pharmacodynamic model for fantofarone cardiac and brachial haemodynamic effects in healthy volunteers

Aims To investigate the pharmacokinetics of SR 33671, the main active metabolite of the calcium antagonist fantofarone, and the relationships between its concentrations and pharmacodynamic effects after a single oral administration of two doses (100 and 300 mg) of fantofarone. Methods A placebo-controlled, randomized, double-blind and crossover study was performed in six healthy volunteers. SR 33671 plasma concentrations (C, ng ml(-1) ) and effects (E) on heart rate (HR, beats min(-1) ), PR interval duration (ms), brachial artery flow (BAF, ml min(-1) ) and brachial vascular resistance (BVR, mmHg s ml(-1) ) were determined repeatedly after drug intake. Haemodynamic effects were expressed as percent changes from initial values. Bi-exponential (pharmacokinetics), and linear [E = S.C + E-0, for cardiac effects] or sigmoid [E = Emax .Cgamma/(CE50gamma + C-gamma ), for haemodynamic effects] models were fitted to individual data. Results Peak plasma concentrations and areas under the curve up to 24 h were (mean +/- s.d.) 16 +/- 10 ng ml(-1) and 157.50 +/- 89.13 ng ml(-1) h, and 63 +/- 11 ng ml(-1) and 535.50 +/- 135.11 ng ml(-1) h, after 100 and 300 mg, respectively. Terminal half-life was approximately 4 h. For pharmacodynamics, we obtained: S = -0.201 +/- 0.057 beats min(-1)/ng ml(-1) for HR, S = 0.526 +/- 0.114 ms/ng ml(-1) for PR interval duration, E-max = 42 +/- 6%, CE50 = 8.8 +/- 7.2 ng ml(-1) and gamma = 2.2 +/- 1.5 for BAF, and E-max = -28 +/- 4%, CE50 = 5.8 +/- 5.1 ng ml(-1) and gamma = 3.4 +/- 1.8 for BVR. At a SR 33671 concentration of 15 ng ml(-1), BVR is decreased by 27% whereas HR is reduced by less than 3 beats min(-1) and PR interval duration is increased by less than 8 ms. Conclusions Fantofarone is able to induce submaximal peripheral vasodilating effects at doses that are devoid of any clinically significant cardiac effect.