Development of microemulsion for solubility enhancement of clopidogrel

Clopidogrel, an inhibitor of platelet aggregation, selectively inhibits the binding of adenosine diphosphate (ADP) to its platelet receptor and the subsequent ADP-mediated activation of the glycoprotein GPIIb/IIIa complex, thereby inhibiting platelet aggregation. Oral bioavailability of clopidogrel is very low (less than 50%), due to its poor water solubility. The aim of this investigation was to design and develop a microemulsion formulation of clopidogrel for enhancing its solubility, and hence its oral bioavailability. For this purpose, initially, solubility of clopidogrel was determined in various vehicles. Next, pseudo-ternary phase diagrams were constructed to identify the microemulsion existing zone. Solubility study was also performed for optimization of formulation. The optimized microemulsion formulation was characterized for its transparency, droplet size, zeta potential, viscosity, conductivity, % assay, and phase separation study. Particle size and zeta potential of the optimized microemulsion formulation were found to be 12.3 nm, and -6.34 mV, respectively. The viscosity and conductivity data indicated that the microemulsion was of the o/w type. Solubility of clopidogrel was successfully enhanced by 80.66 times, via capmul microemulsion, compared with distilled water (pH = 7.4). 75.53% and 71.2 % of the drug content were found to be released within 9 h in the in-vitro and ex-vivo studies, respectively. Hence, by formulating into microemulsion, the solubility of clopidogrel was found to be significantly enhanced.