ACETAMINOPHEN AND IBUPROFEN
Clinical safety rating: avoid
ACE inhibitors and ARBs may have diminished antihypertensive effect Increases risk of serious cardiovascular thrombotic events and GI bleeding.
Acetaminophen is a centrally acting analgesic and antipyretic whose exact mechanism is not fully understood, but is thought to involve inhibition of cyclooxygenase (COX) in the brain and modulation of cannabinoid receptors. Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that non-selectively inhibits COX-1 and COX-2, reducing prostaglandin synthesis.
| Metabolism | Acetaminophen is primarily metabolized via glucuronidation and sulfation; a minor pathway via CYP2E1 produces a toxic metabolite, NAPQI. Ibuprofen is metabolized primarily by CYP2C9 and to a lesser extent by CYP2C8. |
| Excretion | Acetaminophen: renal excretion of metabolites (glucuronide 55%, sulfate 30%, cysteine/mercapturate <10%); <5% unchanged. Ibuprofen: renal excretion of metabolites (conjugates) 90%; <10% unchanged; minor biliary/fecal. |
| Half-life | Acetaminophen: 2-3 hours (normal hepatic function). Ibuprofen: 2-4 hours (immediate-release); prolonged in overdose or hepatic impairment. |
| Protein binding | Acetaminophen: 10-25% (albumin). Ibuprofen: >99% (albumin). |
| Volume of Distribution | Acetaminophen: 0.9 L/kg; Ibuprofen: 0.15 L/kg (highly protein-bound, low Vd). |
| Bioavailability | Acetaminophen: 75-85% oral. Ibuprofen: 80-100% oral. |
| Onset of Action | Oral (immediate-release): 15-30 minutes for analgesic effect; 1 hour for antipyresis. |
| Duration of Action | Acetaminophen: 4-6 hours; Ibuprofen: 4-6 hours (immediate-release), 6-8 hours (extended-release). |
Oral: Acetaminophen 325 mg and ibuprofen 200 mg, 1-2 tablets every 6 hours as needed, not exceeding 6 tablets/24 hours.
| Dosage form | TABLET |
| Renal impairment | GFR 30-59: Caution, use lowest effective dose; GFR <30: Contraindicated due to ibuprofen component. |
| Liver impairment | Child-Pugh A: No adjustment; Child-Pugh B: Caution, reduce acetaminophen dose; Child-Pugh C: Contraindicated. |
| Pediatric use | Weight-based: 10-15 mg/kg acetaminophen + 5-10 mg/kg ibuprofen per dose, every 6-8 hours, max 4 doses/day. |
| Geriatric use | Use lowest effective dose; monitor renal function due to ibuprofen; avoid durations >10 days. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
ACE inhibitors and ARBs may have diminished antihypertensive effect Increases risk of serious cardiovascular thrombotic events and GI bleeding.
| FDA category | Positive |
| Breastfeeding | Acetaminophen: low levels in breast milk, M/P ratio ~0.9; considered compatible with breastfeeding. Ibuprofen: minimal excretion, M/P ratio ~0.01; considered compatible. Combination: low risk with recommended doses. |
| Teratogenic Risk | First trimester: Acetaminophen is considered low risk; ibuprofen is associated with increased risk of miscarriage and cardiac defects. Second trimester: Acetaminophen is safe; ibuprofen is relatively safe but may cause oligohydramnios. Third trimester: Acetaminophen is safe; ibuprofen is contraindicated due to risk of premature closure of ductus arteriosus, oligohydramnios, and neonatal renal impairment. |
■ FDA Black Box Warning
Acetaminophen may cause severe liver injury, including acute liver failure, at doses exceeding 4,000 mg/day. Ibuprofen: NSAIDs increase risk of serious cardiovascular thrombotic events, myocardial infarction, and stroke, which can be fatal. Risk increases with duration of use and in patients with cardiovascular risk factors. NSAIDs also increase risk of serious gastrointestinal adverse events including bleeding, ulceration, and perforation of stomach or intestines.
| Common Effects | fever |
| Serious Effects |
Acetaminophen: Severe hepatic impairment, allergy to acetaminophen. Ibuprofen: Hypersensitivity to ibuprofen or other NSAIDs, history of asthma/urticaria after NSAIDs, perioperative pain in CABG surgery, severe heart failure, active GI bleeding, late pregnancy.
| Precautions | Acetaminophen: Hepatotoxicity risk with excessive doses, use with caution in hepatic impairment, avoid with alcohol use >3 drinks/day. Ibuprofen: Cardiovascular risk, gastrointestinal bleeding, renal toxicity, hypertension, fluid retention, avoid late pregnancy. |
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| Fetal Monitoring | Monitor liver function tests with prolonged acetaminophen use; fetal ultrasound for oligohydramnios or ductus arteriosus constriction with ibuprofen beyond 20 weeks; neonatal renal function if ibuprofen used near term. |
| Fertility Effects | Ibuprofen may reversibly impair ovulation by inhibiting prostaglandin synthesis; acetaminophen has no known significant effect on fertility. |
| Food/Dietary | Avoid alcohol; take with food or milk to minimize GI irritation. No specific food restrictions. |
| Clinical Pearls | Combination product for acute pain; fixed-dose may exceed recommended daily acetaminophen limit if other acetaminophen-containing products are used. Onset of ibuprofen is 30-60 min, acetaminophen 15-30 min; duration 4-6 hours. Caution in renal impairment (ibuprofen) and hepatic impairment (acetaminophen). Avoid in third trimester of pregnancy. |
| Patient Advice | Do not exceed 10 tablets (500 mg acetaminophen/200 mg ibuprofen) per day. · Do not take with other products containing acetaminophen or NSAIDs. · Take with food or milk to reduce stomach upset. · Avoid alcohol while taking this medication. · Seek medical help if pain persists >10 days or fever >3 days. · Store at room temperature, away from moisture. |