The purpose of this study was to investigate the absorption enhancement of acyclovir, an antiviral agent, by means of bile salt-acylcarnitine mixed micelles. The specificity, site dependence, palmitoyl-DL-carnitine chloride (PCC) concentration dependence, and effects of absorption promoters on acyclovir absorption via the nasal cavity (N) and four different intestinal segments of the rat, i.e., duodenum (D), upper jejunum (UJ), combined lower jejunum and ileum (LJ), and colon (C) were evaluated. The present study employed the rat in situ nasal and intestinal perfusion techniques and utilized sodium glycocholate (NaGC), three acylcarnitines, and their mixed micelles as potential nasal and intestinal absorption promoters. Acylcarnitines used were DL-octanoylcarnitine chloride (OCC), palmitoyl-DL-carnitine chloride (PCC), and DL-stearoylcarnitine chloride (SCC). All acylcarnitines and NaGC by themselves produced negligible enhancement of acyclovir absorption in the rat intestine, while OCC and SCC were totally ineffective in the nasal cavity. However, the mixed micellar solutions of NaGC with PCC or SCC could significantly increase the mucosal membrane permeability of acyclovir in the colon and nasal cavity. On the other hand, NaGC-OCC mixed micelles slightly increased the absorption of acyclovir by both routes. When a mixed micellar solution of NaGC with PCC was used, the rank order of apparent acyclovir permeability (Papp; cm/sec), corrected for surface area of absorption, was N (10.54 +/- 0.62 x 10(-5)) > D (6.82 +/- 0.30 x 10(-5)) > LJ (2.90 +/- 0.08 x 10(-5)) > C (2.54 +/- 0.14 x 10(-5)) > UJ (2.30 +/- 0.22 x 10(-5)).(ABSTRACT TRUNCATED AT 250 WORDS)