Bentyl
Bentyl
Generic Name
Bentyl
Mechanism
Bentyl competitively inhibits muscarinic acetylcholine receptors (particularly M₃) in the gastrointestinal smooth muscle. This blockade
• ↓ reduces intracellular Ca²⁺ release,
• ↓ dampens peristaltic tone, and
• ↓ alleviates cramp‑like abdominal pain.
It has modest antimuscarinic activity at the bladder but minimal central nervous system penetration due to limited lipophilicity.
Pharmacokinetics
| Parameter | Typical Value | Notes |
| Absorption | 40‑70 % oral | Peak plasma conc. within 30–60 min |
| Distribution | C₁₀H₁₇NO₂; Vₐ ≈ 3 L/kg | Moderate protein binding; crosses placenta |
| Metabolism | Hepatic via CYP3A4 → N‑oxide & glucuronides | Metabolism largely non‑enzymatic; minimal drug‑drug interactions |
| Elimination | Renal (≈80 %) & biliary | Terminal t₁⁄₂ ≈ 12 h; shorter in children |
| Dose‑adjustment | No specific adjustments for mild hepatic/renal impairment | Monitor in severe CKD (CrCl <30 mL/min) |
Indications
- Irritable bowel syndrome (IBS) – predominantly motility‑related subtype
- Non‑specific dyspepsia or abdominal cramping
- Acute antispasmodic relief during IBS flares
*Off‑label*: short‑course use for functional constipation when anticholinergics are indicated.
Contraindications
- Absolute contraindications:
- Mechanical bowel obstruction
- Neuromuscular disease (e.g., myasthenia gravis)
- Acute urinary retention or bladder outlet obstruction
- Severe hepatic disease
- Relative contraindications:
- Narrow‑angle glaucoma
- Prostate hypertrophy (risk of urinary retention)
- Pregnancy: category C – use only if benefits outweigh risks
- Warnings:
- Anticholinergic toxicity (dry mouth, blurred vision, tachycardia)
- Avoid in patients on serotonergic agents (QT prolongation)
- Potential for drug interactions with CYP3A4 inhibitors/inducers
Dosing
| Population | Dose | Schedule | Max Daily Dose |
| Adults | 1 mg PO | Every 4–6 h as needed | 20 mg/day |
| Pediatrics (≥12 y) | 0.6 mg/kg PO | Every 4–6 h as needed | 10 mg/kg/day |
| Infants/Children <12 y | <0.6 mg/kg PO | Not approved – use with caution if deemed necessary |
• *Route*: Oral (tablet or liquid).
• *Formulation*: Standard tablets; liquid suspension (0.2 mg/mL) for young patients.
Adverse Effects
Common (≥5 %)
• Dry mouth, blurred vision, constipation
• Dizziness, headache, fatigue
Serious (≤1 %)
• Urinary retention or obstruction
• Severe constipation with fecal impaction
• Neuropsychiatric events (amnesia, agitation) in predisposed individuals
• Severe cardiac arrhythmias (rare with high doses/CR patients)
Monitoring
- Renal function (CrCl) every 3–6 months in patients on long‑term therapy.
- Urinary retention: Counsel patients on voiding intervals; use bladder diary if complaints arise.
- Drug interactions: Review CYP3A4 inhibitors/inducers; adjust dose accordingly.
- Adverse effect screening: Monitor for dry mouth, constipation, and visual changes at each visit.
Clinical Pearls
- Start low, go slow: Children often need 0.3–0.4 mg/kg to minimize anticholinergic burden.
- Avoid concomitant anticholinergics (e.g., diphenhydramine) to reduce cumulative dry‑mouth and blurred‑vision risk.
- Use the liquid formulation in patients with dysphagia or children who cannot swallow tablets.
- Consider a split‑dose in advanced IBS‑C (constipation‑predominant) to mitigate constipation.
- Anticholinergic effect can mask tachycardia—watch for hidden heart rate changes in older adults on beta‑blockers.
- Pregnancy & breastfeeding: Limited data; if essential, use the lowest effective dose and monitor infant for excessive sedation.
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• *Prepared by a precision‑pharmacology assistant. For detailed pharmacologic data, refer to the latest peer‑reviewed literature and prescribing information.*