Alcohol | CNS depressants | Additive CNS depression, sedation, ataxia, increased risk of accidents |
Acetaminophen | Increased formation of hepatotoxic metabolites of acetaminophen |
Antacids | Digoxin, iron supplements, fluoroquinolones, ketoconazole, tetracyclines, thyroxine | Decreased gut absorption due either to reaction with the affected drug or due to reduced acidity |
Antihistamines (H1 blockers) | Antimuscarinics, sedatives | Additive effects with the drugs affected |
Antimuscarinic drugs | Drugs absorbed from the small intestine | Slowed onset of effect because stomach emptying is delayed |
Barbiturates, especially phenobarbital | Azoles, calcium channel blockers, cyclosporine, propranolol, protease inhibitors, quinidine, steroids, warfarin, and many other drugs metabolized in the liver | Increased clearance of the affected drugs due to enzyme induction, possibly leading to decreases in drug effectiveness |
Beta blockers | Insulin | Masking of symptoms of hypoglycemia |
Prazosin | Increased first-dose syncope |
Bile acid-binding resins | Acetaminophen, digitalis, thiazides, thyroxine | Reduced absorption of the affected drug |
Carbamazepine | Cyclosporine, doxycycline, estrogen, haloperidol, theophylline, warfarin | Reduced effect of other drugs because of induction of metabolism |
Cimetidine | Benzodiazepines, lidocaine, phenytoin, propranolol, quinidine, theophylline, warfarin, dofetilide | Risk of toxicity due to inhibition of metabolism or reduced renal excretion |
Disulfiram, metronidazole, certain cephalosporins | Ethanol | Increased hangover effect due to inhibition of aldehyde dehydrogenase |
Erythromycin | Carbamazepine, cisapride, quinidine, sildenafil, SSRIs | Risk of toxicity due to inhibition of metabolism |
Furanocoumarins (grapefruit juice) | Alprazolam, atorvastatin, cyclosporine, midazolam, nifedipine | Risk of toxicity due to inhibition of metabolism |
Ketoconazole and other azoles | Benzodiazepines, cisapride, cyclosporine, fluoxetine, lovastatin, omeprazole, quinidine, tolbutamide, oral anticoagulants (warfarin, apixaban, rivaroxaban) | Risk of toxicity due to inhibition of metabolism, eg, increased bleeding with oral anticoagulants, myopathy with statins |
MAO inhibitors | Catecholamine releasers (amphetamine, ephedrine) | Increased norepinephrine in sympathetic nerve endings released by the interacting drugs |
Tyramine-containing foods and beverages | Hypertensive crisis |
NSAIDs | Anticoagulants (warfarin, apixaban, dabigatran, rivaroxaban) | Increased bleeding tendency because of reduced platelet aggregation (additive anticoagulant effect) |
Angiotensin-converting enzyme (ACE) inhibitors | Decreased antihypertensive efficacy of ACE inhibitor |
Loop diuretics, thiazides | Reduced diuretic efficacy |
Phenytoin | Doxycycline, methadone, quinidine, steroids, verapamil, anticoagulants (warfarin, apixaban, rivaroxaban) | Reduced effect of other drugs because of induction of metabolism |
Rifampin | Azole antifungal drugs, corticosteroids, methadone, sulfonylureas, oral anticoagulants (warfarin, apixaban, dabigatran, rivaroxaban) | Reduced effect of other drugs because of induction of metabolism |
Ritonavir | Benzodiazepines, cyclosporine, diltiazem, HMG-CoA reductase inhibitors, lidocaine, metoprolol, other HIV protease inhibitors, SSRIs | Risk of toxicity due to inhibition of metabolism |
Salicylates | Corticosteroids | Additive toxicity to gastric mucosa |
Heparin, oral anticoagulants (warfarin, apixaban, dabigatran, rivaroxaban) | Increased bleeding tendency |
Methotrexate | Decreased clearance, causing greater methotrexate toxicity |
Sulfinpyrazone, probenecid | Decreased uricosuric effect |
Selective serotonin reuptake inhibitors (SSRIs) | Monoamine oxidase (MAO) inhibitors, meperidine, tricyclic antidepressants, St. John’s wort | Serotonin syndrome (hypertension, tachycardia, muscle rigidity, hyperthermia, seizures) |
Thiazides | Digitalis | Increased risk of digitalis toxicity because thiazides diminish potassium stores |
Lithium | Increased plasma levels of lithium due to decreased total body water |