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. |
| Molecular Weight | 452.5 |
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 | Avoid; difenoxin crosses placenta and has anticholinergic effects; risk of fetal malformations not well studied. |
| 2nd trimester | Avoid; limited data; potential for anticholinergic effects on fetus. |
| 3rd trimester | Avoid; neonatal withdrawal syndrome reported with opioids; anticholinergic effects may cause respiratory depression. |
Clinical note
Comprehensive clinical and safety monograph for MOTOFEN HALF-STRENGTH (MOTOFEN HALF-STRENGTH).
| Placental transfer | Difenoxin crosses the placenta; extent unknown but expected due to molecular weight and lipophilicity. |
| Breastfeeding | Difenoxin is excreted into breast milk in small amounts; however, anticholinergic effects and potential for infant sedation or respiratory depression warrant caution. Use only if benefit outweighs risk. |
■ 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 atropineObstructive jaundiceSevere hepatic impairmentSevere diarrhea with bacterial enterocolitis or pseudomembranous colitisGlaucomaMyasthenia gravisSevere ulcerative colitis
| 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. |
| Food/Dietary | Avoid alcohol, as it may potentiate CNS depression. No specific food interactions; however, maintaining a bland diet (e.g., BRAT: bananas, rice, applesauce, toast) may help manage diarrhea. Avoid high-fat or greasy foods that can worsen diarrhea. Ensure adequate fluid intake to prevent dehydration. |
Loading safety data…
| Lactation Rating |
| L3 (Moderately Safe) |
| 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 | 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. |
| Clinical Pearls | Motofen Half-Strength contains diphenoxylate (2.5 mg) and atropine (0.025 mg) per tablet, half the strength of standard Lomotil. It is classified as a schedule V controlled substance due to diphenoxylate's opioid activity. Monitor for anticholinergic effects (dry mouth, blurred vision, urinary retention) mediated by atropine. Contraindicated in children under 6 years due to risk of respiratory depression. Use with caution in patients with hepatic impairment, inflammatory bowel disease, or pseudomembranous colitis. Avoid in patients with glaucoma or myasthenia gravis. Discontinue if abdominal distension or ileus develops. |
| Patient Advice | Take exactly as prescribed; do not exceed recommended dose or duration. · This medication may cause drowsiness or dizziness; avoid driving or operating machinery until you know how it affects you. · Avoid alcohol and other CNS depressants. · Report immediately if you experience severe constipation, abdominal pain, nausea, vomiting, or signs of allergic reaction (rash, difficulty breathing). · Keep out of reach of children; accidental overdose can cause severe respiratory depression. · Do not use for more than 48 hours without consulting your doctor. · May cause dry mouth; use sugarless candy or ice chips for relief. · If you miss a dose, skip it and continue with your next scheduled dose; do not double dose. |