NEI Podcast E46 - Drug Interactions and Pharmacokinetics with Dr. Patrick Finley
Oct 16, 2019
In this engaging discussion, Dr. Patrick Finley, a Professor of Clinical Pharmacy at UCSF and a board-certified psychiatric pharmacist, dives into the intricate world of drug interactions and pharmacokinetics. He highlights that 20% of hospitalizations are linked to drug interactions, emphasizing their often underestimated risk, particularly for the elderly. Dr. Finley explains key concepts like cytochrome P450 enzymes, discusses the impact of grapefruit juice on drug metabolism, and addresses the importance of pharmacogenetic testing for personalized medicine.
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CYP450 Isoenzymes Drive Metabolism
- Cytochrome P450 enzymes (phase I) drive major drug metabolism like demethylation and hydroxylation.
- CYP3A4 metabolizes >50% of drugs while CYP2D6 handles ~25% and is highly relevant in psychiatry.
Watch CYP2D6 Inhibitor + Beta Blocker Combos
- Avoid combining potent CYP2D6-inhibiting antidepressants with metoprolol or propranolol due to large plasma increases.
- Monitor for bradycardia, falls, and hospitalization when such combinations exist.
Beware CYP2D6 Effects On Prodrug Opioids
- Do not expect analgesia from codeine if CYP2D6 is inhibited or the patient is a poor metabolizer.
- Consider alternatives when co-prescribing CYP2D6 inhibitors with prodrug opioids like tramadol.