TYLENOL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TYLENOL (TYLENOL).
Acetaminophen is a centrally acting analgesic and antipyretic. Its mechanism is not fully understood but involves inhibition of cyclooxygenase (COX) enzymes in the central nervous system, preferentially COX-2, and modulation of descending serotonergic pathways.
| Metabolism | Primarily hepatic via conjugation with glucuronide (UGT1A1, UGT1A6, UGT1A9) and sulfate (SULT1A1, SULT1A3); minor oxidation by CYP2E1, CYP1A2, and CYP3A4 to N-acetyl-p-benzoquinone imine (NAPQI), which is detoxified by glutathione. |
| Excretion | Renal excretion of conjugated metabolites (glucuronide and sulfate conjugates) accounts for >90% of elimination; less than 5% excreted unchanged; minor biliary/fecal elimination (<5%) |
| Half-life | Terminal elimination half-life is 2-3 hours in adults; prolonged to 4-6 hours in neonates and patients with hepatic impairment |
| Protein binding | 10-25% bound to plasma proteins (primarily albumin); binding is minimal and not clinically significant |
| Volume of Distribution | 0.8-1.0 L/kg; low Vd indicates limited extravascular distribution, consistent with limited CNS penetration |
| Bioavailability | Oral: 60-90% (first-pass hepatic metabolism reduces bioavailability); Rectal: 70-90%; Intravenous: 100% |
| Onset of Action | Oral: 30-60 minutes; Rectal: 60-120 minutes; Intravenous: 5-10 minutes |
| Duration of Action | Analgesic/antipyretic effect: 4-6 hours; extended-release formulations may last up to 8 hours |
| Molecular Weight | 151.16 |
650 mg orally every 4-6 hours or 1000 mg orally every 6 hours; maximum 4000 mg per day.
| Dosage form | SUPPOSITORY |
| Renal impairment | GFR 10-50 mL/min: Administer every 6 hours. GFR <10 mL/min: Administer every 8 hours. |
| Liver impairment | Child-Pugh A: No adjustment. Child-Pugh B: Reduce dose by 50%; maximum 2000 mg/day. Child-Pugh C: Reduce dose by 75%; maximum 1000 mg/day. |
| Pediatric use | 10-15 mg/kg orally every 4-6 hours; maximum 75 mg/kg/day or 5 doses per day. |
| Geriatric use | Reduce dose by 25-50% in frail elderly; maximum 3000 mg/day due to increased hepatotoxicity risk. |
| 1st trimester | Acetaminophen is generally considered the analgesic/antipyretic of choice during pregnancy. Epidemiologic studies have not demonstrated an increased risk of major congenital malformations when used as directed. However, use the lowest effective dose for the shortest duration. |
| 2nd trimester | Considered safe when used as directed. No consistent evidence of fetal harm. Avoid prolonged use or high doses. |
| 3rd trimester | Generally safe at recommended doses. No significant risk of premature closure of ductus arteriosus or other fetal complications. Overdose may cause maternal hepatotoxicity and potential fetal distress. |
Clinical note
Comprehensive clinical and safety monograph for TYLENOL (TYLENOL).
| Placental transfer | Acetaminophen readily crosses the placenta via passive diffusion. Fetal serum concentrations approximate maternal levels within 30 minutes to 2 hours after maternal ingestion. The drug has been detected in cord blood and amniotic fluid. |
| Breastfeeding |
■ FDA Black Box Warning
Acetaminophen has been associated with cases of acute liver failure, at times resulting in liver transplant and death. Most of the cases of liver injury are associated with the use of acetaminophen in doses exceeding 4000 mg per day. The risk of acute liver failure may be higher in individuals with underlying liver disease and in those who consume alcohol chronically.
| Serious Effects |
Hypersensitivity to acetaminophen or any component of the formulationSevere hepatic impairment or active liver disease
| Precautions | Hepatotoxicity: Risk increases with doses > 4000 mg/day, chronic alcohol use, or preexisting liver disease., Severe skin reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, acute generalized exanthematous pustulosis., Hypersensitivity: Rare anaphylaxis. |
| Food/Dietary | No significant food interactions. Alcohol consumption increases risk of hepatotoxicity; avoid concurrent use. High-carbohydrate meals may slightly delay absorption. |
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| Acetaminophen is excreted into breast milk in low concentrations (less than 2% of maternal dose). It is considered compatible with breastfeeding. Peak milk levels occur 1-2 hours after maternal ingestion. No adverse effects in nursing infants have been reported with standard maternal doses. |
| Lactation Rating | L1 |
| Teratogenic Risk | Acetaminophen crosses the placenta. First trimester: no increased risk of major malformations in prospective studies; retrospective studies show possible association with gastroschisis and neural tube defects but confounding by indication is likely. Second and third trimesters: no consistent evidence of adverse fetal effects; chronic high doses may cause maternal hepatotoxicity with secondary fetal effects. Avoid prolonged high-dose therapy. |
| Fetal Monitoring | No specific fetal monitoring required for standard use. Monitor maternal liver function tests if high doses (>4g/day) or prolonged therapy. In overdose, monitor maternal acetaminophen levels, INR, liver enzymes, and fetal heart rate if viable. |
| Fertility Effects | No adverse effects on fertility based on available data. Acetaminophen does not affect ovulation, spermatogenesis, or conception rates at therapeutic doses. |
| Clinical Pearls | Acetaminophen has minimal anti-inflammatory effect; prefer NSAIDs for inflammation. Max daily dose 3 g (or 2 g in at-risk patients). N-acetylcysteine is antidote for overdose; administer if serum level above nomogram line. Avoid in severe hepatic impairment. Intravenous formulation available for acute pain. Onset of action 30-60 min, duration 4-6 h. No effect on platelets or GI mucosa. |
| Patient Advice | Do not exceed 3 g (3000 mg) per day from all products. · Check all over-the-counter medications for acetaminophen content. · Do not take with alcohol or if you have liver disease. · Seek immediate medical attention if overdose is suspected. · May be taken with food if GI upset occurs (though rare). |