Dicyclomine - Drug Monograph

Introduction

Dicyclomine hydrochloride is an anticholinergic/antispasmodic medication primarily used to treat symptoms associated with irritable bowel syndrome (IBS). First approved by the FDA in 1950, it remains a commonly prescribed agent for managing abdominal cramping and discomfort related to gastrointestinal smooth muscle spasm.

Mechanism of Action

Dicyclomine exerts its therapeutic effects through competitive inhibition of muscarinic acetylcholine receptors, particularly the M3 subtype found in gastrointestinal smooth muscle. By blocking parasympathetic nervous system transmission, it reduces smooth muscle contractions and motility in the gastrointestinal tract. The drug also possesses some local anesthetic properties that may contribute to its spasmolytic effects.

Indications

• FDA-approved: Treatment of irritable bowel syndrome (IBS)
• Off-label uses: Other functional gastrointestinal disorders with spasm
• Management of neurogenic bowel and bladder spasticity

Dosage and Administration

• Initial: 20 mg orally four times daily
• Maintenance: May reduce to 10 mg four times daily based on response
• Maximum: 160 mg daily (in divided doses)

• Geriatric: Use lower doses due to increased sensitivity
• Hepatic impairment: Dose reduction recommended
• Renal impairment: Use with caution; consider dose reduction
• Pediatrics: Not recommended for children under 6 months; use with extreme caution in older children

• Administer 30-60 minutes before meals
• Available as tablets, capsules, and oral solution
• Do not crush or chew extended-release formulations

Pharmacokinetics

Contraindications

• Obstructive uropathy (bladder neck obstruction)
• Gastrointestinal obstruction
• Severe ulcerative colitis
• Toxic megacolon complicating ulcerative colitis
• Myasthenia gravis
• Glaucoma (narrow-angle)
• Hypersensitivity to dicyclomine or related compounds
• Infants less than 6 months of age

Warnings and Precautions

• Heat prostration: May occur in hot weather due to decreased sweating
• Cognitive effects: May impair mental and/or physical abilities
• Cardiovascular effects: Use with caution in patients with cardiac disease, tachycardia, or hypertension
• Gastrointestinal conditions: May precipitate or aggravate toxic megacolon
• Prostatic hypertrophy: May cause urinary retention
• Geriatric patients: Increased risk of adverse reactions
• Pregnancy: Category B - use only if clearly needed
• Lactation: Excreted in breast milk; not recommended

Drug Interactions

• Other anticholinergic agents: Additive effects
• MAO inhibitors: May enhance anticholinergic effects
• Potassium chloride: Increased risk of mucosal lesions
• Metoclopramide: Antagonistic effects

• Opioid analgesics: Enhanced constipation
• Antihistamines: Additive CNS depression
• Tricyclic antidepressants: Enhanced anticholinergic effects
• Antipsychotics: Increased risk of heat stroke

Adverse Effects

• Dry mouth (33%)
• Dizziness (10%)
• Blurred vision (8%)
• Nausea (6%)
• Drowsiness (5%)
• Constipation (5%)

• Tachycardia
• Urinary retention
• Anaphylaxis
• Angioedema
• Hyperthermia
• Paralytic ileus
• CNS effects (confusion, hallucinations)

Monitoring Parameters

• Therapeutic response: Reduction in abdominal cramping and discomfort
• Adverse effects: Regular assessment of anticholinergic side effects
• Vital signs: Heart rate, blood pressure, temperature
• Renal and hepatic function: Baseline and periodic assessment
• Mental status: Especially in elderly patients
• Bowel function: Monitor for constipation or obstruction

Patient Education

• Take medication as directed, typically before meals
• Avoid alcohol and other CNS depressants
• Use caution when driving or operating machinery
• Maintain adequate hydration, especially in hot weather
• Report immediately: Rapid heartbeat, difficulty urinating, severe constipation, or confusion
• Chew sugarless gum or candy to relieve dry mouth
• Use artificial tears for dry eyes
• Do not stop medication abruptly without consulting healthcare provider
• Inform all healthcare providers about dicyclomine use

References

1. American Gastroenterological Association. (2021). Guidelines on the Management of Irritable Bowel Syndrome. Gastroenterology, 160(1), 263-286. 2. Lexicomp Online. (2023). Dicyclomine: Drug Information. Wolters Kluwer Clinical Drug Information. 3. Micromedex Solutions. (2023). Dicyclomine Hydrochloride. IBM Watson Health. 4. FDA Prescribing Information. (2022). Bentyl (dicyclomine hydrochloride). 5. Brunton, L. L., Hilal-Dandan, R., & Knollmann, B. C. (2023). Goodman & Gilman's: The Pharmacological Basis of Therapeutics (14th ed.). McGraw-Hill Education. 6. Clinical Pharmacology [database online]. (2023). Dicyclomine. Elsevier. 7. UpToDate. (2023). Anticholinergic medications for the treatment of irritable bowel syndrome. Wolters Kluwer.