Explore real-world scenarios where pharmacogenomics transforms treatment outcomes.
Codeine
Clinical Risk
Poor Metabolizers: No pain relief (codeine inactive); Ultra-Rapid Metabolizers: Overdose risk (morphine toxicity)
Recommendation
Test CYP2D6 before prescribing. Poor metabolizers: avoid. Ultra-rapid metabolizers: avoid or max 30mg dose.
The Science
Codeine is a prodrug converted to morphine by CYP2D6. Your metabolizer status determines efficacy and safety.
Clopidogrel
Clinical Risk
Poor Metabolizers: Reduced platelet inhibition; stent thrombosis; heart attack
Recommendation
Poor metabolizers: avoid clopidogrel. Use prasugrel or ticagrelor instead (active drugs, not prodrugs).
The Science
Clopidogrel is a prodrug requiring CYP2C19 activation. Poor metabolizers receive minimal benefit and face higher cardiovascular risk.
Warfarin
Clinical Risk
Patients with variants in CYP2C9 (*2, *3) or VKORC1 (-1639G>A): Excessive INR elevation, bleeding
Recommendation
FDA recommends PGx-guided dosing. Variants = lower starting dose, frequent INR monitoring.
The Science
Warfarin response is highly polygenic. Testing CYP2C9 and VKORC1 improves dosing accuracy and reduces bleeding events.
Simvastatin
Clinical Risk
Variants (521T>C, 388A>G): Increased statin levels, muscle pain, rhabdomyolysis
Recommendation
Carriers: avoid simvastatin >20mg. Use pravastatin or rosuvastatin instead (no SLCO1B1 transport).
The Science
SLCO1B1 transports simvastatin into liver cells. Variants reduce clearance, increasing myopathy risk.
Paroxetine, Fluoxetine, Escitalopram
Clinical Risk
Poor Metabolizers: Excessive plasma levels, serotonin syndrome, QT prolongation, seizures
Recommendation
Poor metabolizers: lower starting dose; frequent symptom monitoring; consider alternative SSRI or tricyclic.
The Science
SSRIs are metabolized by CYP2D6 or CYP2C19. Poor metabolizers experience side effects at standard doses.
Azathioprine
Clinical Risk
Poor Metabolizers: Severe bone marrow suppression, infections, aplastic anemia; Heterozygotes: moderate toxicity
Recommendation
MANDATORY testing before use. Poor metabolizers: avoid or use 10% of standard dose.
The Science
Azathioprine is converted to thioguanine nucleotides. TPMT poor metabolizers cannot clear these toxic metabolites.
Carbamazepine
Clinical Risk
Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN); mortality up to 30%
Recommendation
Screen before use, especially in East/Southeast Asian populations. HLA-B*15:02 carriers: avoid carbamazepine; use alternative anticonvulsant.
The Science
HLA-B*15:02 is a strong predictor of severe cutaneous reactions to carbamazepine. FDA recommends screening.
Abacavir
Clinical Risk
HLA-B*5701 carriers: Hypersensitivity reaction (fever, rash, GI, respiratory symptoms) within 1-3 weeks
Recommendation
Mandatory screening before initiation. HLA-B*5701 positive: contraindicated; use alternative antiretroviral.
The Science
Abacavir triggers immune hypersensitivity in 5-8% of patients. Genetic screening prevents life-threatening reactions.
For Healthcare Professionals: These scenarios are educational summaries. Always consult full CPIC guidelines, FDA labels, and clinical evidence when making treatment decisions. Each patient's care must be individualized.