Bentyl - Drug Monograph

Introduction

Bentyl (dicyclomine hydrochloride) is an anticholinergic/antispasmodic medication primarily used to treat symptoms associated with irritable bowel syndrome (IBS). It belongs to the class of muscarinic antagonists that work by relaxing smooth muscles in the gastrointestinal tract. First approved by the FDA in 1950, Bentyl has been a mainstay in the management of functional bowel disorders for decades.

Mechanism of Action

Bentyl exerts its therapeutic effects through competitive inhibition of muscarinic acetylcholine receptors in the gastrointestinal tract. By blocking parasympathetic nervous system stimulation, it reduces:

• Smooth muscle contractions in the GI tract
• Gastric secretion
• Intestinal motility

The drug has approximately 1/8 the anticholinergic potency of atropine but demonstrates relatively selective action on gastrointestinal smooth muscle compared to other anticholinergic agents.

Indications

FDA-approved indications:

• Treatment of irritable bowel syndrome (IBS)
• Symptomatic relief of functional bowel disorders characterized by spasm

Off-label uses (not FDA-approved):

• Renal colic
• Biliary dyskinesia
• Urinary bladder spasms

Dosage and Administration

• Oral tablets: 20 mg four times daily
• Maximum recommended dose: 160 mg/day
• May initiate therapy with 10 mg four times daily and titrate upward

• Geriatric patients: Use with caution; consider lower initial doses
• Renal impairment: Use caution; dosage adjustment may be necessary
• Hepatic impairment: Contraindicated in severe hepatic impairment
• Pediatrics: Safety and effectiveness not established in children

• Take 30-60 minutes before meals
• May administer with food if gastrointestinal upset occurs

Pharmacokinetics

• Crosses blood-brain barrier (minimal amounts)
• Crosses placenta
• Appears in breast milk

• Half-life: Approximately 1.8 hours
• Excretion: Primarily renal (80%), with some fecal elimination
• Onset of action: 1-2 hours
• Duration of action: 4-6 hours

Contraindications

• Hypersensitivity to dicyclomine or any component of the formulation
• Obstructive uropathy
• Obstructive disease of the gastrointestinal tract
• Severe ulcerative colitis
• Toxic megacolon complicating ulcerative colitis
• Myasthenia gravis
• Unstable cardiovascular status in acute hemorrhage
• Glaucoma
• Hiatal hernia associated with reflux esophagitis

Warnings and Precautions

• May cause drowsiness or blurred vision; caution patients about driving or operating machinery
• Use with extreme caution in patients with:

- Autonomic neuropathy - Hepatic or renal disease - Hyperthyroidism - Coronary heart disease - Congestive heart failure - Cardiac arrhythmias - Hypertension - Hiatal hernia

• May produce anhidrosis, potentially leading to heat prostration
• Use caution in hot environments
• May aggravate symptoms of ulcerative colitis

Drug Interactions

• Other anticholinergic agents: Additive effects
• Amantadine: Increased anticholinergic effects
• Antipsychotics: Increased anticholinergic effects
• MAO inhibitors: May intensify anticholinergic effects
• Metoclopramide: Antagonistic effects
• Potassium chloride: Increased risk of GI lesions
• Digoxin: May increase serum digoxin concentrations
• Alcohol: Enhanced CNS depression

Adverse Effects

• Dry mouth (33%)
• Dizziness (2%)
• Blurred vision (2%)
• Nausea (2%)
• Drowsiness (1%)
• Weakness (1%)
• Nervousness (1%)

• Tachycardia
• Palpitations
• Urinary retention
• Constipation
• Anaphylaxis
• Heat stroke
• Confusion (especially in elderly)
• Hallucinations
• Seizures

Monitoring Parameters

• Therapeutic response: Reduction in abdominal pain and cramping
• Adverse effects: Monitor for anticholinergic effects
• Mental status: Especially in elderly patients
• Heart rate: Monitor for tachycardia
• Urinary output: Assess for retention
• Bowel function: Monitor for constipation or ileus
• Intraocular pressure: In patients with glaucoma risk factors
• Temperature regulation: In hot environments

Patient Education

• Take medication as directed; do not exceed prescribed dose
• May cause drowsiness or blurred vision; avoid driving or hazardous activities
• Maintain adequate hydration, especially in hot weather
• Report immediately: Rapid heartbeat, difficulty urinating, eye pain, or confusion
• Avoid alcohol while taking this medication
• Inform all healthcare providers about Bentyl use
• Chew sugarless gum or suck on ice chips for dry mouth relief
• Use caution with other medications that may cause drowsiness
• Store at room temperature away from moisture and heat

References

1. American Gastroenterological Association. (2021). AGA Clinical Practice Guidelines on the Pharmacological Management of Irritable Bowel Syndrome. Gastroenterology, 161(5), 1656-1668. 2. Lexicomp Online. (2023). Dicyclomine: Drug Information. Wolters Kluwer. 3. Micromedex Solutions. (2023). Dicyclomine Hydrochloride. IBM Watson Health. 4. FDA Prescribing Information for Bentyl. (2022). AbbVie Inc. 5. Saha L. (2014). Irritable bowel syndrome: pathogenesis, diagnosis, treatment, and evidence-based medicine. World Journal of Gastroenterology, 20(22), 6759-6773. 6. Brandt LJ, et al. (2009). Systematic review on the management of irritable bowel syndrome in North America. American Journal of Gastroenterology, 104(S1), S1-S35.