Generic Name

Dicyclomine

Brand Names

Bentyl®, other generic formulations) is a long‑acting antimuscarinic antispasmodic used primarily for irritable bowel syndrome (IBS) and other functional abdominal disorders. It reduces smooth‑muscle spasm by antagonizing muscarinic receptors in the gastrointestinal tract.

Mechanism

• Selective muscarinic antagonist: Binds competitively to M1, M2, and M3 muscarinic receptors in the gut, inhibiting acetylcholine‑induced contraction.
• Smooth‑muscle relaxation: Decreases tone of intestinal and urethral sphincters, reducing cramping and abdominal pain.
• Minimal central effects: Its relatively low lipophilicity limits blood‑brain‑barrier penetration, causing fewer CNS adverse reactions compared with other anticholinergics.

Pharmacokinetics

• Absorption: Rapid oral uptake; peak plasma concentrations within 1–2 h.
• Distribution: Low penetration into CNS; mainly systemic antimuscarinic activity.
• Metabolism: Hepatic hydroxylation → active metabolite (desmethyldicyclomine); glucuronide conjugation.
• Elimination: Renal excretion of unchanged drug + conjugates; half‑life ≈ 10–12 h (single‑dose) but extends up to 21 h with multiple dosing.
• Drug interactions: Minimal CYP interactions; may increase systemic exposure when renal function is impaired.

Indications

• Irritable bowel syndrome (IBS): Relieves abdominal cramping, pain, and bloating.
• Other functional GI disorders: Such as functional abdominal pain or dyspepsia when antispasmodic effect is desired.
• Adjunctive therapy: In patients refractory to lifestyle modifications or low‑dose antispasmodics.

Contraindications

• Absolute contraindications

* Acute colonic obstruction or bowel perforation

* Suspected bowel obstruction or diverticulitis

* Glaucoma due to risk of increased intraocular pressure

* Urinary retention or obstruction; myasthenia gravis

* Severe hepatic or renal impairment (renal dosing adjustments required)
• Pregnancy & Lactation

* Category C: Limited data; use only if benefits outweigh risks.
• Warnings

* Anticholinergic toxicity (dry mouth, blurred vision, tachycardia, urinary retention)

* Caution in elderly with cognitive or cardiovascular disease

* Monitor for signs of constipation or a paralytic ileus

Dosing

• First‑dose adjustments: Use minimal effective dose; titrate based on symptom relief and tolerability.
• Long‑term use: Recommended for patients with chronic symptoms; reassess yearly for efficacy and adverse events.

Adverse Effects

Common (≥5 %)
• Dry mouth, blurred vision, constipation
• Urinary retention, tachycardia, dizziness
• Heat intolerance, sexual dysfunction (erectile dysfunction; decreased libido)

Serious (≤1 %)
• Severe anticholinergic syndrome (hyperthermia, seizures, hallucinations)
• Acute urinary retention or bladder distension
• Glaucoma attacks (intraocular pressure ↑)
• Cardiac arrhythmias (QT prolongation).

Monitoring

• Baseline: Blood pressure, heart rate, baseline hepatic and renal function; visual acuity if glaucoma history.
• During therapy: Monitor for anticholinergic symptoms, urinary retention, constipation.
• Laboratory: Renal function at baseline and every 3–6 months in chronic therapy.

Clinical Pearls

• “Double‑dose, double‑tired”: Dosing 25 mg q4–6 h ensures a therapeutic drug level while minimizing adverse events; avoid >150 mg/day.
• Avoid in “Frog‑legs”: Patients with chronic constipation or a history of urinary retention should receive careful titration or consider alternative antispasmodics (e.g., hyoscine).
• Switch back with caution: Gradual tapering prevents rebound cramping; abruptly stopping can worsen IBS symptoms.
• Drug‑drug synergy: Concomitant use with other anticholinergics (e.g., antihistamines, antipsychotics) increases risk—dose reduction or discontinuation may be warranted.
• Age‑adjustment: In elderly patients, start at the lowest possible dose (e.g., 2.5 mg BID) to evaluate tolerability before escalating.

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• *This drug card is intended for medical educational purposes and should not replace the evaluation of complete prescribing information.*