Pharmacogenetic relevance of the CYP2C93 allele in a tenoxicam bioequivalence study performed on Spaniards

We performed a study to quantify CYP2C9 and CYP2C8 alleles influence on the variability observed in tenoxicam pharmacokinetic (PK) and implication in a bioequivalence study design performed on Spaniards. Eighteen healthy volunteers were included in an open, randomized, crossover, phase I bioequivalence study. Significant increases were found in CYP2C9*3 alleles vs. *1 and *2 in AUC 0–∞ (median (min–max)): 256 (230–516) vs. 150 (100–268) and 169 (124–197) μg h/mL ( p < 0.01) and half-life time ( t1/2) 102 (79–36) vs. 56 (45–94) and 64 (60–80) h ( p < 0.01). Non-significant differences were observed in C max 1.9 (1.8–2.9) vs. 2.4 (1.7–3.4), 2.5 (1.6–2.9) μg/mL or in according to CYP2C8 alleles presence. CYP2C9*3 allele is associated to a longer elimination time of tenoxicam. PK parameters calculated in bioequivalence studies (AUC 0–∞, t1/2) may be influenced by the presence of CYP2C9*3 allele resulting in a high variability. Thus, bioequivalence studies of tenoxicam formulations should be designed considering genotype profile.