CYP2C19 | Clopidogrel | Reduced metabolism of clopidogrel, lower exposure to active metabolite and, thus, higher cardiovascular risk | Warning of potential effect; consider alternative treatment |
| Voriconazole | Reduced metabolism of voriconazole, thus increased drug exposure | Warning of potential effect |
CYP2C9 | Warfarin | Reduced metabolism resulting in higher bleeding risk | Warning of potential effect; reduced dose may be required |
CYP2D6 | Codeine | Leads to ultra-rapid metabolism to active metabolite | Warning of potential effect; use lowest effective dose |
| Tamoxifen | Poor metabolisers have higher plasma concentrations | Warning of potential effect |
EGFR | Gefitinib | Effectiveness depends on EGFR status of tumour in nonsmall cell lung cancer | Tumour profiling to guide therapy |
| Erlotinib | | |
ELM4-ALK | Crizotinib | Effectiveness depends on ELM4-ALK status of tumour in nonsmall cell lung cancer | Tumour profiling to guide therapy |
G6PD | Rasburicase | G6PD deficiency leads to severe haemolysis with several drugs | Screen patients in high-risk ethnic groups to exclude risk genotype before commencement |
HER 2 | Trastuzimab | Effect depends on HER2 expression levels in breast cancer | Screen for HER2 expression before treatment |
HLA-B*1502 | Carbamazepine | Greatly increased risk of severe dermatological hypersensitivity reaction | Screen patients in high-risk ethnic groups to exclude genotype before commencement |
| Abacavir | Greatly increased risk of generalised hypersensitivity reaction | Screen all patients prior to drug commencement |
LDLR | Atorvastatin | LDL receptor deficiency or absence leads to familial hypercholesterolaemia | Dose adjustments in genetic risk groups |
NAT | Rifampicin | Slow metabolism and greater drug exposure | Warning of potential effect |
TPMT | Azathioprine | Slower metabolism and greater resultant risk of myelotoxicity | Screen all patients prior to drug commencement |
UGT1A1 | Irinotecan | Reduced metabolism and increased neutropenia risk | Reduce initial dose in those known to be homozygous for UGT1A*28 |
| Nilotinib | Exacerbation of jaundice caused by drug | Warning of potential effects |
Urea cycle disorders | Valproate | Six potential culprit genes | Evaluate for UCD before commencement |
VKORC1 | Warfarin | SNPs associated with lower dose requirements | Warning of potential effects |