MOTOFEN HALF-STRENGTH
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MOTOFEN HALF-STRENGTH (MOTOFEN HALF-STRENGTH).
Motofen Half-Strength contains difenoxin (an opioid agonist) and atropine (an anticholinergic). Difenoxin inhibits gastrointestinal motility by acting on mu-opioid receptors in the gut, reducing peristalsis. Atropine discourages abuse by producing unpleasant anticholinergic effects at supratherapeutic doses.
| Metabolism | Difenoxin is metabolized primarily via CYP3A4 and also undergoes conjugation. Atropine is metabolized by hydrolysis and N-demethylation. |
| Excretion | Renal (50% as unchanged drug and conjugates), biliary/fecal (30% as metabolites), 20% unknown. |
| Half-life | Terminal elimination half-life is 2-3 hours for diphenoxylate, 12-14 hours for atropine. Clinical context: Steady-state achieved within 1 day for diphenoxylate, 3 days for atropine. |
| Protein binding | Diphenoxylate: 90-95% bound to plasma proteins; atropine: 40-50% bound to albumin. |
| Volume of Distribution | Diphenoxylate: 4-5 L/kg, indicating extensive tissue distribution; atropine: 2-4 L/kg. |
| Bioavailability | Oral: 90% for diphenoxylate (extensive first-pass metabolism reduces systemic exposure); 100% for atropine. |
| Onset of Action | Oral: 45-60 minutes; peak effect at 2 hours. |
| Duration of Action | Oral: 3-4 hours for antidiarrheal effect; 6-8 hours for anticholinergic effects of atropine. |
Adults: 1 tablet (diphenoxylate 1 mg + atropine 0.0125 mg) orally 4 times daily as needed for diarrhea, up to 8 tablets per day.
| Dosage form | TABLET |
| Renal impairment | eGFR < 30 mL/min: Not recommended due to risk of CNS toxicity and fluid imbalance. |
| Liver impairment | Child-Pugh class B or C: Avoid use; risk of hepatic coma. |
| Pediatric use | Not recommended in children under 6 years. For ages 6-12: 1 tablet (half-strength) orally 2-4 times daily; maximum 4 tablets per day. |
| Geriatric use | Use with caution due to anticholinergic effects and risk of CNS depression; initiate at lowest effective dose. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MOTOFEN HALF-STRENGTH (MOTOFEN HALF-STRENGTH).
| Breastfeeding | Contraindicated. Excreted in human milk; M/P ratio unknown. Potential for serious adverse effects in nursing infant (respiratory depression, sedation). |
| Teratogenic Risk | High risk. First trimester: congenital malformations (neural tube defects, cleft palate) based on animal studies and limited human data. Second and third trimesters: fetal growth restriction, oligohydramnios, neonatal respiratory depression, and withdrawal syndrome. Avoid in pregnancy. |
| Fetal Monitoring |
■ FDA Black Box Warning
Risk of respiratory depression, especially in children; contraindicated in children <2 years old. Risk of anticholinergic toxicity with overdose.
| Serious Effects |
["Hypersensitivity to difenoxin or atropine","Children <2 years of age","Obstructive jaundice","Diarrhea associated with pseudomembranous colitis or enterotoxin-producing bacteria","Angle-closure glaucoma","Myasthenia gravis","Severe hepatic impairment"]
| Precautions | Risk of severe anticholinergic effects (e.g., hyperthermia, tachycardia, urinary retention). Discontinue if diarrhea persists >48 hours or if fever, blood/mucus in stool occur. Use caution in patients with hepatic or renal impairment, ulcerative colitis, or history of drug abuse. |
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| Monitor maternal vital signs, respiratory rate, and sedation level. Fetal surveillance: ultrasound for growth, amniotic fluid index, and non-stress test. Assess for neonatal abstinence syndrome postpartum. |
| Fertility Effects | May impair female fertility (animals: disrupted estrous cycle; human: limited data). Males: no significant reported effects. Discontinuation recommended when attempting conception. |