Prevalence Estimates of Cytochrome P450 Phenoconversion in Youth Receiving Pharmacotherapy for Mental Health Conditions.

Pharmacogenetics-predicted drug metabolism may not match clinically observed metabolism due to a phenomenon known as phenoconversion. Phenoconversion can occur when an inhibitor or inducer of a drug-metabolizing enzyme is present. Although estimates of phenoconversion in adult populations are available, prevalence estimates in youth populations are limited. To address this gap, we estimated the prevalence of phenoconversion in 1281 youth (6-24 years) receiving pharmacotherapy for mental health conditions and who had pharmacogenetics testing completed for four genes (CYP2B6, CYP2C19, CYP2D6, CYP3A4). Self-reported medication and cannabidiol/cannabis use were collected at the time of pharmacogenetics testing. Nearly, half (46%) of the cohort was estimated to be phenoconverted for one of the four genes examined. Comparison of metabolizer phenotype frequencies before and after adjustment for phenoconversion showed significantly more youth had actionable phenotypes for CYP2C19 (60.3% vs. 69.1%; P =< 0.001), CYP2D6 (49.3% vs. 63.0%; P =< 0.001), and CYP3A4 (8.5% vs.12.2%; P = 0.003) after phenoconversion adjustment. Of youth who were phenoconverted, 24% had a change in their metabolizer phenotype that would lead to current pharmacogenetics-based prescribing guidelines recommending a change to standard prescribing (dose adjustment, alternative medication). Our findings indicate a high prevalence of cytochrome P450 phenoconversion among youth receiving pharmacotherapy for mental health conditions. Adjustment for phenoconversion should be considered when implementing pharmacogenetics testing in youth populations to improve the clinical utility of this testing in practice.