ACEPHEN
Clinical safety rating
cautionComprehensive clinical and safety monograph for ACEPHEN (ACEPHEN).
ACEPHEN (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism involves inhibition of cyclooxygenase (COX) enzymes in the central nervous system, particularly COX-2, reducing prostaglandin synthesis. It has weak peripheral COX inhibition and minimal anti-inflammatory effect.
| Metabolism | Acetaminophen is primarily metabolized in the liver via glucuronidation (UGT1A1, UGT1A6, UGT1A9) and sulfation (SULT1A1, SULT1A3). A minor fraction is oxidized by cytochrome P450 enzymes (CYP2E1, CYP1A2, CYP3A4) to a reactive toxic metabolite (NAPQI), which is normally detoxified by conjugation with glutathione. |
| Excretion | Renal: 90-95% as unchanged drug; tubular secretion and glomerular filtration. Biliary/fecal: <5%. |
| Half-life | Terminal elimination half-life: 1.0-1.5 hours in adults with normal renal function. Prolonged to 2-5 hours in hepatic impairment or elderly; requires dose adjustment in severe hepatic disease. |
| Protein binding | Approximately 10-20% bound to serum albumin; extensive tissue binding. |
| Volume of Distribution | Apparent Vd: 0.5-0.7 L/kg (30-40 L in a 70 kg adult). Distributions into CSF and breast milk. |
| Bioavailability | Oral: 85-90% (first-pass metabolism minimal). Rectal: approximately 70-80% of oral bioavailability. |
| Onset of Action | Oral: 30-60 minutes (peak plasma concentration at 1-2 hours). Rectal: 1-2 hours. No parenteral formulation available. |
| Duration of Action | Duration of analgesia: 4-6 hours following oral administration. Duration may be extended in hepatic dysfunction due to reduced clearance. |
| Molecular Weight | 233.2 |
| Brand Substitutes | Xtra P 100 mg/500 mg Tablet, Jetace 100 mg/500 mg Tablet, Acebloc P 100 mg/500 mg Tablet, Icobit P 100 mg/500 mg Tablet, Aclomp P 100 mg/500 mg Tablet |
325-650 mg orally every 4-6 hours as needed; maximum 4 g/day.
| Dosage form | SUPPOSITORY |
| Renal impairment | GFR 10-50 mL/min: 650 mg every 6 hours; GFR <10 mL/min: 650 mg every 8 hours. |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B: maximum 2 g/day; Child-Pugh Class C: maximum 1 g/day. |
| Pediatric use | 10-15 mg/kg/dose orally every 4-6 hours; maximum 75 mg/kg/day or 4 g/day, whichever is less. |
| Geriatric use | Start at lowest effective dose (325 mg every 6 hours); avoid exceeding 3 g/day unless closely monitored. |
| 1st trimester | Avoid; associated with neural tube defects if folate deficient. |
| 2nd trimester | Use only if clearly needed; no known teratogenicity. |
| 3rd trimester | Avoid near term; may cause premature closure of ductus arteriosus. |
Clinical note
Comprehensive clinical and safety monograph for ACEPHEN (ACEPHEN).
| Placental transfer | Crosses placenta readily; fetal levels approach maternal levels. |
| Breastfeeding | Excreted in breast milk in low amounts; considered compatible with breastfeeding due to lack of adverse effects in infants. |
| Lactation Rating | L1 |
| Teratogenic Risk | Pregnancy Category C. First trimester: potential risk of neural tube defects and orofacial clefts (limited human data, animal studies show embryotoxicity). Second and third trimesters: NSAID exposure associated with oligohydramnios, premature ductus arteriosus constriction, and fetal renal impairment. Avoid in third trimester. |
| Fetal Monitoring | Monitor maternal renal function, liver enzymes, and complete blood count. In third trimester, ultrasound to assess amniotic fluid volume and ductal patency. Fetal monitoring for oligohydramnios. |
| Fertility Effects | May impair female fertility via inhibition of prostaglandin synthesis; reversible upon discontinuation. Not associated with male infertility. |
■ 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 at doses that exceed 4,000 milligrams per day, and often involve more than one acetaminophen-containing product.
| Serious Effects |
Hypersensitivity to acephenSevere hepatic impairment
| Precautions | Risk of severe liver injury with doses >4000 mg/day; use caution with hepatic impairment, chronic alcoholism, malnutrition, or concomitant hepatotoxic drugs; avoid exceeding recommended dose; limit use to 10 days for pain or 3 days for fever unless directed by physician; serious skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis) have occurred. |
| Food/Dietary | Alcohol: increased risk of hepatotoxicity. Avoid concurrent use. Food: no significant interaction, but taking with food may reduce minor gastrointestinal irritation. |
| Clinical Pearls | ACEPHEN (acetaminophen) is commonly used for mild to moderate pain and fever. Avoid exceeding 4 g/day in adults to prevent hepatotoxicity. In patients with hepatic impairment, reduce maximum daily dose to 2 g. Consider acetylcysteine for overdose. Onset of action is 15-30 minutes orally. |
| Patient Advice | Do not exceed 4000 mg (4 grams) in 24 hours. · Avoid drinking alcohol while taking this medication. · Do not combine with other products containing acetaminophen. · Take with food if stomach upset occurs. · Seek immediate medical help if you experience symptoms of liver damage: yellowing of skin/eyes, dark urine, severe abdominal pain. |
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