MEDIGESIC PLUS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MEDIGESIC PLUS (MEDIGESIC PLUS).
Acetaminophen inhibits cyclooxygenase (COX) enzymes centrally, reducing prostaglandin synthesis; chlorzoxazone acts centrally as a muscle relaxant via inhibition of polysynaptic reflexes at spinal and subcortical levels.
| Metabolism | Acetaminophen: primarily hepatic via conjugation (glucuronidation and sulfation) and CYP2E1-mediated oxidation to N-acetyl-p-benzoquinone imine (NAPQI). Chlorzoxazone: extensively hepatic via CYP2E1 and CYP1A2. |
| Excretion | Renal elimination of unchanged drug and metabolites: paracetamol ~90-100% (primarily as glucuronide and sulfate conjugates, ~5% unchanged), pseudoephedrine ~70-90% (mostly unchanged, dependent on urine pH), chlorpheniramine ~30-50% as metabolites. Biliary/fecal: minimal (<5%). |
| Half-life | Paracetamol: 2-3 hours. Pseudoephedrine: 5-8 hours (alkaline urine increases half-life). Chlorpheniramine: 12-15 hours in adults. Context: paracetamol half-life prolonged in hepatic impairment; pseudoephedrine/chlorpheniramine half-lives may be prolonged in renal impairment. |
| Protein binding | Paracetamol: 10-25% (albumin). Pseudoephedrine: negligible (<10%). Chlorpheniramine: 69-72% (albumin, lipoproteins). |
| Volume of Distribution | Paracetamol: 0.9-1.0 L/kg (distributes into most body fluids). Pseudoephedrine: 2.5-3.0 L/kg (extensive tissue distribution). Chlorpheniramine: 3.2-4.2 L/kg (high tissue binding). |
| Bioavailability | Oral: paracetamol 85-98%; pseudoephedrine ~100% (well absorbed); chlorpheniramine 25-50% (extensive first-pass metabolism). |
| Onset of Action | Oral: paracetamol analgesic effect 30-60 minutes; pseudoephedrine decongestant effect 30-60 minutes; chlorpheniramine antihistamine effect 1-2 hours. |
| Duration of Action | Paracetamol: analgesic effect 4-6 hours; pseudoephedrine: decongestant effect 4-6 hours; chlorpheniramine: antihistamine effect 4-6 hours (up to 24 hours for some clinical endpoints). Duration may be extended in overdose or with hepatic/renal impairment. |
| Brand Substitutes | Ipecee 400 mg/500 mg/65 mg Tablet, Eliflam Plus Tablet |
1-2 tablets orally every 4-6 hours as needed; maximum 8 tablets per day.
| Dosage form | CAPSULE |
| Renal impairment | GFR 30-50 mL/min: avoid use; GFR <30 mL/min: contraindicated due to ibuprofen content. |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B: use with caution, avoid if severe; Child-Pugh Class C: contraindicated. |
| Pediatric use | Not recommended for children under 12 years due to aspirin content and risk of Reye's syndrome. For children 12 years and older, same as adult dosing. |
| Geriatric use | Initiate at lower end of dosing range (1 tablet every 6 hours). Monitor renal function and GI bleeding risk. Avoid in patients with creatinine clearance <50 mL/min. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MEDIGESIC PLUS (MEDIGESIC PLUS).
| Breastfeeding | Paracetamol is excreted into breast milk in small amounts (M/P ratio ~0.91-1.42, with infant dose <2% of maternal weight-adjusted dose). Considered compatible with breastfeeding. Dicyclomine is excreted into breast milk; M/P ratio unknown. Case reports of infant anticholinergic effects (e.g., apnea, drowsiness) with maternal use. Avoid in breastfeeding unless benefit outweighs risk. American Academy of Pediatrics recommends use with caution. |
| Teratogenic Risk | MEDIGESIC PLUS contains paracetamol and dicyclomine. Paracetamol is generally considered low risk in pregnancy; however, high doses may be associated with neonatal hepatic toxicity. First trimester: case-control studies show no consistent increased risk of major malformations. Second/third trimester: no known fetal toxicity at therapeutic doses; overdose may cause maternal hepatic necrosis with secondary fetal effects. Dicyclomine: FDA Pregnancy Category B. Animal studies indicate no fetal harm, but adequate human studies are lacking. Avoid in first trimester due to theoretical anticholinergic effects. Overall, use only if clearly needed, at lowest effective dose. |
■ FDA Black Box Warning
Acetaminophen has been associated with cases of acute liver failure, sometimes resulting in liver transplant and death. Hepatotoxicity is often associated with doses exceeding 4000 mg per day.
| Serious Effects |
Hypersensitivity to acetaminophen, chlorzoxazone, or any component; severe hepatic impairment; concurrent use of alcohol or other hepatotoxic drugs; history of chlorzoxazone-induced hepatic injury.
| Precautions | Severe liver injury (dose-dependent), hypersensitivity reactions (including anaphylaxis), use caution in hepatic impairment, avoid exceeding recommended dose, monitor for signs of hepatotoxicity. |
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| Fetal Monitoring | For paracetamol: monitor maternal liver function tests (ALT, AST, bilirubin) if used long-term or high doses; fetal ultrasound if overdose suspected (hepatic necrosis). For dicyclomine: monitor maternal heart rate and blood pressure (anticholinergic effects); fetal heart rate monitoring for signs of tachycardia. In late pregnancy, monitor for reduced uterine contractions if used near term. No specific routine monitoring required for short-term use. |
| Fertility Effects | Paracetamol: animal studies suggest high doses may impair female fertility (reduced implantation sites); human data limited. Dicyclomine: anticholinergic properties may affect cervical mucus consistency theoretically, but no significant human fertility effects reported. No conclusive evidence of male fertility impairment. |