Pharmacists will be familiar with the impact of cytochrome P450 (CYP) enzymes, the main metabolisers of drugs cleared through the liver. However, the alleles expressing CYP enzymes can vary widely, so there can be considerable differences in drug activity between populations.¹¹

The bulk of CYP enzymes fall into one of three groups: CYP1, CYP2, and CYP3. Among the significant CYP allele variants and the drugs they affect are:^{11,12,13,14,15}

• CYP2C9 (phenytoin, tolbutamide, ibuprofen and S-warfarin)
• CYP2C19 (omeprazole, clopidogrel, proguanil, diazepam, citalopram, amitriptyline, possibly tamoxifen) – variants in this gene are more common with East Asian ancestry
• CYP2D6 (including antidepressants, antipsychotics, analgesics and antitussives, beta blockers, antiarrhythmics and antiemetics)
• CYP3A5 (testosterone, progesterone).

Pharmacokinetic changes have also been associated with CYP1A2, CYP2A6, CYP2B6, CYP2C8, and CYP3A4 variability.