Intra- and interindividual variabilities of valacyclovir oral bioavailability and effect of coadministration of an hPEPT1 inhibitor.

Variability in valacyclovir bioavailability and the potential for cephalexin-valacyclovir interaction were evaluated. The intraindividual acyclovir area under the concentration-time curve (AUC) varied minimally, whereas interindividual differences were substantial. Coadministration of the human peptide transporter 1 (hPEPT1) substrates valacyclovir and cephalexin minimally reduced the acyclovir AUC. These results suggest a stable valacyclovir absorption phenotype, significant interindividual variability, and minimal interaction between these hPEPT1 substrates.