Oral bioavailability improvement of felodipine using tailored microemulsion: Surface science, ex vivo and in vivo studies.

Felodipine is a calcium channel blocker, which shows low oral bioavailability (<15%) owing to poor water solubility and high first pass metabolism. The aim of the present investigation was to study the surface science (dynamic surface tension) and characteristics of microemulsion (Capmul MCM, Tween 20 and polyethylene glycol) to enhance the oral bioavailability of felodipine by improving permeability of the drug in the intestine. The paper is the first attempt to study the stability of oil-water interface of microemulsion using bubble tensiometer. The Smix at 2:1 ratio showed the maximum microemulsion area which did not alter in the presence of drug. The microemulsion batch coded Fe-O5-Smix45 (5% Capmul MCM and 45% Smix) was selected based on transmittance (>99%), dilution (stable after 100 times dilution with water), size (15.1 nm), dispersibility (grade A) and thermodynamic stability studies. The dynamic surface tension at newly created surface indicate the stability of surfactant film at the oil/water interface. The microemulsion was also stable in the presence of drug and in different buffer phases. The ex vivo intestinal permeability studies showed significant increase in the microemulsion permeation (74.1% after 1 h) in comparison to the felodipine suspension (16.9% after 1 h). The in vivo pharmacokinetic parameters in the rat model confirmed the improvement in oral bioavailability with microemulsion (relative bioavailability = 21.9) in comparison to the felodipine suspension, due to high surface area of oil droplets and its lymphatic uptake via transcellular route. In conclusion, the stable microemulsion offers a promising approach to improve the oral bioavailability of felodipine which can help to reduce the dose and its associated side effects.