LC-MS/MS determination of avanafil and its metabolites in rat plasma and brain: pharmacokinetic study after oral administration and transdermal film application

Avanafil (AVA) has been FDA approved in 2012 as a phosphodiesterase-type five inhibitor drug (PDE-5), for the treatment of erectile dysfunction (ED). It was necessary to study the pharmacokinetics and bioavailability parameters of AVA since it exhibits side effects, a long time from drug administration. As a result of this, we described a sensitive high-performance-liquid chromatography-triple quad-mass spectrometric method (LC-QqQ-MS) for the analysis of AVA in rat plasma and brain. Furthermore, the concentrations of AVA and its primary metabolites were determined in rat brain since it is known that PDE-5 inhibitor drugs are capable of crossing the blood-brain barrier (BBB). The liquid-liquid extraction method was developed, optimized, and applied for maximum recovery of AVA from plasma and brain homogenates. The percentage of recovery was 96.60 ± 2.44% and 94.50 ± 1.86%, in rat plasma and brain homogenate, respectively. The separation was performed on a Nucleodur C18 column, with mobile phase composed of 0.1% formic acid and acetonitrile (29 : 71, v/v), at flow rate 0.5 mL min^-1, and monitored with QqQ-MS applying positive multiple reaction monitoring (MRM) mode. The calculated pharmacokinetic parameters, noncompartmental model, were: C _max 1503.82 ± 354.11 ng mL^-1 with a t _1/2 value of 4.87 ± 0.42 h and C _max 141.94 ± 22.57 ng mL^-1 with a t _1/2 value of 7.05 ± 1.59 h, for oral AVA suspension and transdermal film, respectively. The average percentage of total metabolites in plasma and brain was 27.1 ± 2.2% and 7.0 ± 1.0%, respectively.