Modelling the PKPD of oxycodone in experimental pain - Impact of opioid receptor polymorphisms

Polymorphisms in the opioid receptor genes may affect the pharmacodynamics (PD) of oxycodone and be part of the reason behind the diversity in clinical response. The aim of the analysis was to model the exposure-response profile of oxycodone for three different pain variables and search for genetic covariates. Model simulations were used to predict how population and effect-size impact the power to detect clinical significant SNPs.

The population pharmacokinetic-pharmacodynamic (PKPD) model of oral single-dosed oxycodone was based on pooled data from three published studies in healthy volunteers. Pain tolerance data from muscle pressure (n=36), visceral pressure (n=54) and skin pinch (n=34) were included. Genetic associations with 18 opioid-receptor SNPs were explored using a stepwise covariate approach. Model simulations were performed using the estimated model parameters.

None of the selected SNPs were associated with analgesic response of oxycodone at P<0.001. Baseline response in muscle cuff pressure was associated with OPRK1 rs7016778 and rs7824175 (P<0.001). Simulations indicated that large differences in drug response between genotypes (>50% for similar population sizes) or large populations (n>200 for a 20% response difference) are necessary to identify clinical significant SNP effects due to high population variability.

A population PKPD model has been developed for oral oxycodone using three different pain variables to explore impact of genetic covariates and study design. None of the selected polymorphisms were significantly associated with analgesic response of oxycodone, but an association of baseline response in muscle cuff pressure with two OPRK1 SNPs was identified.