Common drug interactions

Cytochrome P-450 interactions

Inducers (+)

Modafinil, Chronic alcohol use, St. John’s wart, Phenytoin, Phenobarbital, Nevirapine, Rifampin, Griseofulvin, Carbamazepine

“Most chronic alcoholics Steal Phen-Phen and Never Refuse Greasy Carbs”

Substrates

Anti-epileptics, Theophylline, Warfarin, OCPs

“TWO epilepsies”

Inhibitors (-)

Sodium valproate, Isoniazid, Cimetidine, Ketoconazole, Fluconazole, Acute alcohol abuse, Chloramphenicol, Erythromycin/clarithromycin, Sulfonamides, Ciprofloxacin, Omeprazole, Metronidazole, Amiodarone, Grapefruit juice

“SICKFACES.COM (when I Am drinking Grapefruit juice)”

Acute alcohol abues, Antibiotics, Azoles, Amiodarone, Cimetidine/Omeprazole, Grapefruit juice.

Medications

Warfarin

Dietary changes

  • Foods containing high levels of vitamin K
    • Leafy green vegetables (eg, spinach, Brussels sprouts)
    • ? therapeutic effect of warfarin
  • Medications that prolongs INR in those on warfarin
    • Acetaminophen – d/t interruption of vitamin K recycling in the liver
  • Medications that inhibit cytochrome P450 activity
    • Amiodarone
    • Antibiotics/antifungal
      • Most of the quinolones and macrolides.
      • Trimethoprim/sulfamethoxazole, metronidazole, fluconazole
  • Medications that enhance cytochrome P450 activity
    • Rifampin

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