An overview of pharmacogenomics, including the definition, scope, and importance in personalized medicine. Discuss how genetic variations can influence drug response and metabolism.
Introduction to Pharmacogenomics
The study of how an individual’s genetic makeup influences their response to drugs.
1. What Is Pharmacogenomics?
| Term |
Definition |
| Pharmacogenomics |
Integration of pharmacology (the study of drug action) and genomics (the study of the genome) to predict drug efficacy and safety based on genetic variation. |
| Pharmacogenetics |
Often used interchangeably, but technically refers to the effect of a single gene on drug response, whereas pharmacogenomics looks at the whole genome. |
| Precision Medicine |
Clinical approach that uses pharmacogenomic data (among other biomarkers) to tailor therapy to each patient. |
2. Why It Matters
- Improved Efficacy – Matching drugs to patients who are most likely to benefit.
- Reduced Adverse Drug Reactions (ADRs) – Identifying carriers of risk alleles that predispose to toxicity.
- Optimized Dosing – Adjusting dose based on metabolic capacity (e.g., poor vs. ultra‑rapid metabolizers).
- Cost‑Effectiveness – Preventing trial‑and‑error prescribing and costly hospitalizations.
3. Core Concepts
| Concept |
Explanation |
Example |
| Genetic Polymorphism |
Variation in DNA sequence among individuals (e.g., SNPs, insertions, deletions). |
CYP2C19 *2 allele → reduced activation of clopidogrel. |
| Drug‑Metabolizing Enzymes |
Proteins that biotransform drugs (Phase I – oxidation/reduction; Phase II – conjugation). |
CYP450 family, UGT1A1. |
| Drug Targets |
Genes encoding receptors, enzymes, transporters that drugs bind to. |
VKORC1 variants → warfarin sensitivity. |
| Transporters |
Proteins that move drugs across membranes, influencing absorption and elimination. |
SLCO1B1 variants → statin‑induced myopathy. |
| Gene‑Drug Interaction |
The functional consequence of a genotype on a drug’s pharmacokinetics (PK) or pharmacodynamics (PD). |
TPMT deficiency → thiopurine toxicity. |
4. Major Gene Families Involved
| Gene Family |
Primary Role |
Clinically Relevant Drugs |
| CYP450 (e.g., CYP2D6, CYP2C9, CYP2C19) |
Phase I metabolism (oxidation) |
Codeine, warfarin, clopidogrel, antidepressants |
| UGT (UDP‑glucuronosyltransferases) |
Phase II metabolism (glucuronidation) |
Irinotecan, lamotrigine |
| DPD (DPYD) |
Catabolism of fluoropyrimidines |
5‑Fluorouracil, capecitabine |
| TPMT, NUDT15 |
Inactivation of thiopurines |
Azathioprine, 6‑mercaptopurine |
| SLCO1B1 |
Hepatic uptake transporter |
Simvastatin, rosuvastatin |
| VKORC1 |
Vitamin K epoxide reductase (warfarin target) |
Warfarin |
| HLA (e.g., HLA‑B *57:01) |
Immune presentation, drug hypersensitivity |
Abac |