Merbentyl

Action

Thought to exert direct effect on GI smooth muscle by inhibiting acetylcholine at receptor sites, thereby reducing GI tract motility and tone

Availability

Capsules: 10 mg

Solution for injection: 10 mg/ml

Syrup: 10 mg/5 ml

Tablets: 20 mg

Indications and dosages

➣ Irritable bowel syndrome in patients unresponsive to usual interventions

Adults: 20 mg P.O. or I.M. q.i.d.; may increase up to 160 mg/day

Contraindications

• Hypersensitivity to drug

• GI or genitourinary tract obstruction

• Severe ulcerative colitis

• Reflux esophagitis

• Unstable cardiovascular status

• Glaucoma

• Myasthenia gravis

• Breastfeeding

• Infants younger than 6 months

Precautions

Use cautiously in:

• hepatic or renal impairment, autonomic neuropathy, cardiovascular disease, prostatic hypertrophy

• elderly patients

• pregnant patients (safety not established).

Administration

• Give 30 to 60 minutes before meals; give bedtime dose at least 2 hours after evening meal.

See Don't administer by I.V. route.

• Don't give by I.M. route for more than 2 days.

Adverse reactions

CNS: confusion, drowsiness, light-headedness (with I.M. use), psychosis

CV: palpitations, tachycardia

EENT: blurred vision, increased intraocular pressure

GI: nausea, vomiting, constipation, heartburn, decreased salivation, dry mouth, paralytic ileus

GU: urinary hesitancy or retention, erectile dysfunction, decreased lactation

Skin: decreased sweating, rash, itching, urticaria

Other: pain and redness at I.M. site, allergic reactions including anaphylaxis

Interactions

Drug-drug. Adsorbent antidiarrheals, antacids: decreased dicyclomine absorption

Cyclopropane anesthetics: increased risk of cardiovascular adverse reactions

Oral drugs: altered absorption of these drugs

Potassium (oral): increased GI mucosal lesions

Other anticholinergics (including antihistamines, disopyramide, quinidine): additive anticholinergic effects

Drug-diagnostic tests. Gastric acid secretion test: antagonism of pentagastrin and histamine (testing agents)

Patient monitoring

See Stay alert for anaphylaxis.

• Monitor vital signs and fluid intake and output. Ask patient about palpitations.

See Assess for light-headedness, confusion, and rash after I.M. injection.

• Evaluate patient's vision, particularly for blurring and other signs and symptoms of increasing intraocular pressure.

• Assess bowel pattern, particularly for signs and symptoms of paralytic ileus.

Patient teaching

• Instruct patient to take drug 30 to 60 minutes before meals and to take bedtime dose at least 2 hours after evening meal.

• Advise patient not to take antacids or adsorbent antidiarrheals within 2 hours of dicyclomine.

See Urge patient to promptly report rash, abdominal pain, decreased urinary output, or absence of bowel movements.

• Caution patient to avoid driving or other hazardous activities until he knows how drug affects concentration, vision, and alertness.

See Instruct patient to avoid exposure to high temperatures and to immediately notify prescriber if fever and decreased sweating occur in high environmental temperature.

• Advise patient to minimize GI upset by eating small, frequent servings of healthy food and drinking plenty of fluids.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.