liminfoDrug Interaction Checker
Free reference guide: Drug Interaction Checker
About Drug Interaction Checker
The Drug Interaction Reference is a clinical pharmacology guide covering 26 major drug-drug interaction categories organized by therapeutic class. It details anticoagulant interactions (Warfarin + NSAIDs, Warfarin + antibiotics, DOAC + P-gp inhibitors), cardiovascular interactions (ACEi/ARB + K+-sparing diuretics, statin + CYP3A4 inhibitors, digoxin, QT prolongation drugs, PPI + clopidogrel), and neuropsychiatric interactions (SSRI + MAOI, serotonin syndrome, lithium, phenytoin, opioid + benzodiazepine).
Each interaction entry includes severity rating (Lexicomp X/D/C/B/A scale), mechanism of action, clinical consequences, specific drug examples, monitoring parameters, and safer therapeutic alternatives. Antibiotic interactions (macrolides, fluoroquinolone + cations, aminoglycosides), anticancer/immunosuppressant combinations (methotrexate, cyclosporine), and metabolic drug interactions (metformin + contrast, grapefruit juice CYP3A4 inhibition, CYP inducers + OCP, tyramine + MAOI) are thoroughly covered.
The reference includes links to major drug interaction databases (Lexicomp, Micromedex, Drugs.com, Epocrates, UpToDate, CredibleMeds) and explains the Lexicomp and Micromedex severity classification systems used in clinical practice for risk assessment.
Key Features
- Warfarin interactions with NSAIDs, antibiotics (Fluconazole, TMP-SMX, Rifampin) and INR management
- DOAC P-glycoprotein interactions and CYP3A4-dependent statin rhabdomyolysis risk
- SSRI-MAOI serotonin syndrome with washout periods (2 weeks standard, 5 weeks for Fluoxetine)
- QT prolongation drug list including antiarrhythmics, antibiotics, antipsychotics, and risk factors
- Opioid + benzodiazepine FDA Black Box Warning with respiratory depression guidance
- Methotrexate toxicity combinations (NSAIDs, TMP-SMX, PPIs) and leucovorin rescue
- Grapefruit juice CYP3A4 inhibition, tyramine-MAOI crisis, and CYP inducer effects on oral contraceptives
- Lexicomp (X/D/C/B/A) and Micromedex severity classification systems for clinical decision-making
Frequently Asked Questions
What warfarin interactions does this reference cover?
It covers Warfarin + NSAIDs (bleeding risk via platelet inhibition and CYP2C9 effects), Warfarin + antibiotics (Fluconazole, Metronidazole, TMP-SMX increase INR; Rifampin decreases it), and general INR monitoring guidance. Safer alternatives like acetaminophen and PPI co-administration are noted.
How is serotonin syndrome explained?
The reference details the SSRI + MAOI contraindication (severity X) with full symptom list (clonus, tremor, hyperreflexia, fever, confusion), lists all serotonergic drugs (SSRIs, SNRIs, TCAs, tramadol, linezolid, triptans, St. John's Wort, dextromethorphan), and specifies washout periods: 2 weeks for most SSRIs, 5 weeks for fluoxetine. Treatment with cyproheptadine is noted.
Which drugs cause QT prolongation?
The reference lists QT-prolonging drugs by class: antiarrhythmics (Amiodarone, Sotalol, Dofetilide), antibiotics (Azithromycin, Fluoroquinolones), antifungals (Fluconazole, Ketoconazole), antipsychotics (Haloperidol, Ziprasidone), antiemetics (Ondansetron), and antidepressants (Citalopram). Risk factors include hypokalemia, hypomagnesemia, female sex, and bradycardia.
What statin interactions increase rhabdomyolysis risk?
CYP3A4-metabolized statins (Simvastatin, Lovastatin, Atorvastatin) interact with CYP3A4 inhibitors (Clarithromycin, Ketoconazole, HIV protease inhibitors, Cyclosporine, grapefruit juice >1L/day), elevating statin levels and causing myopathy. Rosuvastatin and Pravastatin are safer alternatives as they are not CYP3A4-dependent.
How are opioid-benzodiazepine interactions addressed?
This is an FDA Black Box Warning interaction. Both drug classes cause CNS depression with synergistic respiratory center depression. Specific dangerous combinations (Oxycodone + Alprazolam, Fentanyl + Midazolam) are listed. FDA recommends minimizing concomitant use, using the lowest effective dose for the shortest duration, and respiratory monitoring.
What methotrexate drug interactions are dangerous?
Five major interactions increase MTX toxicity: NSAIDs (decreased renal excretion), TMP-SMX (folate antagonism + excretion competition), Penicillins (tubular secretion competition), Probenecid (decreased excretion), and PPIs (decreased excretion with high-dose MTX). Toxicities include myelosuppression, mucositis, hepatotoxicity, and nephrotoxicity. Leucovorin rescue is essential for high-dose protocols.
How does grapefruit juice affect medications?
Grapefruit juice irreversibly inhibits intestinal CYP3A4, increasing oral bioavailability for 24-72 hours. Simvastatin shows up to 15x AUC increase. Other affected drugs include Lovastatin, Felodipine, Nifedipine, Cyclosporine, Tacrolimus, and Buspirone. Pravastatin, Rosuvastatin, and Fluvastatin are unaffected.
What severity classification systems are used?
Lexicomp uses a 5-level scale: X (avoid combination), D (consider modification), C (monitor therapy), B (no action needed), A (no interaction). Micromedex classifies as Contraindicated, Major, Moderate, or Minor. Assessment considers evidence level, onset time, and clinical severity.