Pharmacokinetic Interactions
These interactions affect the absorption, distribution, metabolism, or excretion (ADME) of drugs.
- Warfarin + Rifampicin: Rifampicin induces CYP450 enzymes, accelerating warfarin metabolism and reducing its anticoagulant effect. Warfarin dosage may need to be increased.
- Digoxin + Amiodarone: Amiodarone inhibits P-glycoprotein, increasing digoxin absorption and reducing its renal clearance. This can lead to digoxin toxicity.
- Ketoconazole + Proton Pump Inhibitors (PPIs): PPIs reduce stomach acid, decreasing ketoconazole absorption. This may result in reduced antifungal efficacy.
- Cyclosporine + St. John's Wort: St. John's Wort induces CYP3A4, increasing cyclosporine metabolism. This can lead to subtherapeutic cyclosporine levels and potential transplant rejection.
- Clarithromycin + Statins: Clarithromycin inhibits CYP3A4, leading to increased statin levels and a higher risk of myopathy.
- Grapefruit juice + Carbamazepine: Grapefruit juice inhibits CYP3A4, increasing carbamazepine levels, which may lead to toxicity.
- Antacids + Tetracycline: Antacids containing aluminum or magnesium can bind tetracycline, reducing its absorption and effectiveness.
- Metformin + Cimetidine: Cimetidine can increase metformin plasma levels, raising the risk of lactic acidosis.
- Oral Contraceptives + Rifampicin: Rifampicin can reduce the efficacy of oral contraceptives by increasing their metabolism.
- Levothyroxine + Calcium supplements: Calcium can inhibit the absorption of levothyroxine, reducing its effectiveness.
- Phenobarbital + Warfarin: Phenobarbital can induce CYP450 enzymes, increasing warfarin metabolism and reducing its anticoagulant effect.
- Valproate + Lamotrigine: Valproate increases lamotrigine levels, heightening the risk of lamotrigine toxicity.
- Ritonavir + Atorvastatin: Ritonavir can increase atorvastatin levels, leading to a higher risk of adverse effects.
- Isosorbide dinitrate + Sildenafil: Both can cause additive hypotension; their combined use is contraindicated.
- Quetiapine + Ketoconazole: Ketoconazole can increase quetiapine levels, increasing the risk of side effects.
- Fluconazole + Warfarin: Fluconazole can increase warfarin levels, necessitating careful monitoring of INR.
- Rifampicin + Protease Inhibitors: Rifampicin can reduce the effectiveness of protease inhibitors by increasing their metabolism.
- Phenytoin + Oral Contraceptives: Phenytoin can reduce the effectiveness of oral contraceptives through increased metabolism.
- Aspirin + Methotrexate: Aspirin can inhibit renal excretion of methotrexate, increasing its toxicity.
- Barbiturates + Digoxin: Barbiturates can lower digoxin levels, leading to subtherapeutic effects.
Pharmacodynamic Interactions
These interactions occur when drugs have additive, synergistic, or antagonistic effects on the same target or physiological system.
- Alcohol + Benzodiazepines: Both substances enhance GABA activity, leading to additive central nervous system depression. This increases the risk of respiratory depression and accidents.
- ACE inhibitors + Potassium supplements: Both can increase serum potassium levels, potentially leading to hyperkalemia. This is particularly risky in patients with renal impairment.
- Sildenafil + Nitrates: Both drugs increase nitric oxide levels, causing additive vasodilation. This can result in severe hypotension and cardiovascular collapse.
- Warfarin + NSAIDs: NSAIDs can cause gastric erosions while warfarin inhibits clotting, synergistically increasing the risk of gastrointestinal bleeding.
- SSRIs + MAO Inhibitors: Combined use can lead to serotonin syndrome, a potentially life-threatening condition.
- Beta-blockers + Calcium Channel Blockers: Both can lower heart rate; their combination may lead to bradycardia.
- Opioids + Benzodiazepines: Increased risk of respiratory depression and overdose due to additive sedative effects.
- Warfarin + Vitamin E: Vitamin E can enhance the anticoagulant effect of warfarin, increasing the risk of bleeding.
- Digoxin + Verapamil: Verapamil can increase digoxin levels, leading to toxicity due to decreased clearance.
- Antipsychotics + Antidepressants: Combination can lead to increased risk of QT interval prolongation and arrhythmias.
- Metformin + Sulfonylureas: Both can lower blood sugar levels, increasing the risk of hypoglycemia.
- NSAIDs + Antihypertensives: NSAIDs can reduce the effectiveness of antihypertensive medications, potentially leading to elevated blood pressure.
- MAOIs + Tyramine: High tyramine intake can lead to hypertensive crisis in patients taking MAOIs.
- ACE inhibitors + Diuretics: Combined use can lead to additive hypotension, particularly in volume-depleted patients.
- Statins + Fibrates: Increased risk of myopathy and rhabdomyolysis when used together.
- Clonidine + Beta-blockers: Sudden withdrawal of either can lead to rebound hypertension.
- Oral Anticoagulants + Herbal Supplements: Some herbs can enhance the effects of anticoagulants, increasing bleeding risk.
- Calcium Channel Blockers + Grapefruit Juice: Grapefruit juice can increase the levels of calcium channel blockers, leading to hypotension.
- Antidepressants + Antiepileptics: Certain combinations can lead to increased seizure risk or altered drug metabolism.
- Thiazides + Lithium: Thiazides can decrease lithium clearance, leading to toxicity.
- Beta-agonists + Corticosteroids: Combined use may increase the risk of hyperglycemia.
Drug-Food Interactions
These interactions occur when food affects the absorption, metabolism, or effectiveness of a drug, or when a drug affects nutrient absorption or metabolism.
- Grapefruit juice + Statins: Grapefruit juice inhibits CYP3A4 enzymes, increasing statin bioavailability. This can lead to increased risk of myopathy and rhabdomyolysis.
- Dairy products + Tetracyclines: Calcium in dairy forms insoluble complexes with tetracyclines, reducing antibiotic absorption and efficacy.
- Vitamin K-rich foods + Warfarin: High intake of vitamin K (found in green leafy vegetables) can antagonize warfarin's anticoagulant effect, requiring dosage adjustments.
- Tyramine-rich foods + MAO Inhibitors: MAOIs inhibit tyramine metabolism. Consuming tyramine-rich foods (aged cheeses, cured meats) can lead to dangerous hypertensive crisis.
- Alcohol + Metronidazole: Alcohol can lead to a disulfiram-like reaction when taken with metronidazole, causing nausea and vomiting.
- High-fiber foods + Digoxin: Excessive fiber can decrease digoxin absorption, reducing its effectiveness.
- Calcium + Fluoroquinolones: Calcium can bind to fluoroquinolones, significantly reducing their absorption and effectiveness.
- High-fat meals + Raltegravir: High-fat meals can increase the absorption of raltegravir, affecting its pharmacokinetics.
- Warfarin + Cranberry juice: Cranberry juice can enhance the anticoagulant effect of warfarin, increasing bleeding risk.
- Iron supplements + Antacids: Antacids can decrease the absorption of iron supplements, reducing their efficacy.
- Antibiotics + Probiotics: Some antibiotics can reduce the effectiveness of probiotics; timing of administration is important.
- Grapefruit juice + Buspirone: Grapefruit juice can increase buspirone levels, leading to increased sedation and dizziness.
- Fiber-rich foods + Acetaminophen: High fiber can reduce the absorption of acetaminophen, potentially decreasing its effectiveness.
- Caffeine + Certain Antidepressants: Caffeine can increase the effects of some antidepressants, leading to increased anxiety or insomnia.
- High-sodium foods + Lithium: High sodium intake can affect lithium levels, leading to toxicity.
- Potassium-rich foods + ACE inhibitors: High potassium intake can lead to hyperkalemia in patients on ACE inhibitors.
- Fiber + Carbamazepine: High fiber diets can decrease carbamazepine absorption, leading to subtherapeutic levels.
- Antacids + Levothyroxine: Antacids can inhibit the absorption of levothyroxine, reducing its effectiveness.
- Cranberry juice + Atorvastatin: Cranberry juice may increase atorvastatin levels, raising the risk of side effects.
- High-fat meals + Saquinavir: High-fat meals can enhance the absorption of saquinavir, altering its pharmacokinetics.
- Spinach + Warfarin: Spinach can increase vitamin K intake, impacting warfarin's effectiveness.
Toxicity Interactions
These interactions lead to increased toxicity or adverse effects when drugs are combined, often due to overlapping side effect profiles or altered drug clearance.
- Acetaminophen + Alcohol: Both can cause hepatotoxicity, particularly in chronic alcohol users.
- Digoxin + Amiodarone: Amiodarone can increase digoxin levels, leading to a higher risk of toxicity.
- Warfarin + NSAIDs: Increased risk of gastrointestinal bleeding due to additive effects on coagulation.
- Statins + Fibrates: The combination increases the risk of myopathy and rhabdomyolysis.
- SSRIs + Triptans: Increased risk of serotonin syndrome when used together.
- Quinidine + Digoxin: Quinidine can increase digoxin levels, heightening the risk of toxicity.
- Propranolol + Verapamil: Combined use can lead to significant bradycardia and heart block.
- MAO Inhibitors + Tyramine: Risk of hypertensive crisis due to elevated tyramine levels.
- Glyburide + Metformin: Increased risk of hypoglycemia when used together.
- Antidepressants + St. John's Wort: The combination can lead to increased side effects or serotonin syndrome.
- Amiodarone + Warfarin: Amiodarone can increase warfarin levels, leading to bleeding complications.
- Clarithromycin + Statins: Increased risk of statin-related side effects due to elevated statin levels.
- Calcium Channel Blockers + Beta-Blockers: Risk of bradycardia and hypotension when combined.
- Antipsychotics + Benzodiazepines: Increased sedation and respiratory depression risk.
- Diuretics + Lithium: Risk of lithium toxicity due to altered renal clearance.
- Rifampicin + Oral Contraceptives: Reduced efficacy of oral contraceptives due to increased metabolism.
- Azole antifungals + Statins: Increased risk of statin-related muscle toxicity.
- Opioids + Benzodiazepines: Increased risk of overdose and respiratory depression due to additive effects.
- Valproate + Lamotrigine: Valproate can increase lamotrigine levels, raising toxicity risk.
- Clonidine + Beta-Blockers: Risk of rebound hypertension upon withdrawal of either agent.
- Cholestyramine + Digoxin: Cholestyramine can bind digoxin, reducing its absorption and effectiveness.