Transdermal delivery of metoprolol. II: In-vitro skin permeation and bioavailability in hairless rats.

The absolute bioavailability of metoprolol (MP) was evaluated following oral and transdermal administration in hairless rats. The absolute bioavailability of MP following oral administration was 3.48 +/- 1.73%, indicating that MP is subject to extensive hepatic first-pass metabolism. Transdermal delivery of MP, via an adhesive delivery device, resulted in a bioavailability of 30.07 +/- 4.84%, indicating that the transdermal delivery of MP can significantly increase systemic bioavailability compared with oral administration. Preliminary skin irritation studies indicated that neither MP nor the adhesive used in the device caused any appreciable skin irritation in the hairless rats.