Side Effects of Bentyl (dicyclomine)

Bentyl (dicyclomine) is an anticholinergic used to treat irritable bowel syndrome (IBS). Anticholinergic drugs block the effects of acetylcholine, the chemical transmitter that nerves release in order to cause muscles to contract.

They prevent contraction of muscles by blocking the acetylcholine receptors on the muscle cells. Anticholinergic drugs also have a direct relaxing effect on muscle. Bentyl is used to reduce contraction of the muscles in the intestines. 

Common side effects of Bentyl include

• dry mouth,
• blurred vision,
• confusion,
• agitation,
• increased heart rate,
• heart palpitations,
• constipation,
• difficulty urinating,
• changes in taste perception,
• difficulty swallowing,
• headache,
• nervousness,
• drowsiness,
• weakness,
• dizziness,
• impotence,
• flushing,
• difficulty falling asleep,
• nausea,
• vomiting,
• rash,
• skin redness,
• fainting, and
• bloating.

Serious side effects of Bentyl include

• seizures,
• delirium, and
• difficulty breathing.

Drug interactions of Bentyl include amantadine, antiarrhythmics, antihistamines, antipsychotics, benzodiazepines, MAO inhibitors, narcotics, nitrates and nitrites, sympathomimetic agents, tricyclic antidepressants, and other drugs having anticholinergic activity may increase certain actions or side effects of anticholinergic drugs including Bentyl.

• Anticholinergics antagonize the effects of antiglaucoma agents and may increase intraocular pressure.
• Anticholinergic drugs in the presence of increased intraocular pressure may be hazardous when taken concurrently with agents such as corticosteroids.
• Use of Bentyl in patients with glaucoma is not recommended.
• Interaction with other gastrointestinal motility drugs may antagonize the effects of drugs that alter gastrointestinal motility, such as metoclopramide.
• Because antacids may interfere with the absorption of anticholinergic agents including Bentyl, simultaneous use of these drugs should be avoided.
• Anticholinergic agents may affect gastrointestinal absorption of various drugs by affecting gastrointestinal motility, such as slowly dissolving dosage forms of digoxin; increased serum digoxin concentration may result.
• The inhibiting effects of anticholinergic drugs on gastric hydrochloric acid secretion are antagonized by agents used to treat achlorhydria and those used to test gastric secretion.

There are no adequate studies of the effect of Bentyl in pregnant women at recommended doses.

Bentyl is excreted into breast milk. Since there have been reports of apnea (cessation of breathing) when Bentyl has been given to children, it should not be used by breastfeeding mothers.

Common side effects include:

• dry mouth (xerostomia),
• blurred vision,
• confusion,
• agitation,
• increased heart rate,
• heart palpitations,
• constipation,
• difficulty urinating, and
• seizures.

Other important side effects include:

• changes in taste perception,
• difficulty swallowing,
• headache, nervousness,
• drowsiness,
• weakness,
• dizziness,
• impotence,
• flushing,
• delirium,
• difficulty falling asleep,
• nausea,
• vomiting,
• rash,
• erythema,
• fainting,
• bloating, and
• difficulty breathing.

The pattern of adverse effects seen with dicyclomine is mostly related to its pharmacological actions at muscarinic receptors. They are a consequence of the inhibitory effect on muscarinic receptors within the autonomic nervous system. These effects are dose-related and are usually reversible when treatment is discontinued.

The most serious adverse reactions reported with dicyclomine hydrochloride include cardiovascular and central nervous system symptoms.

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The data described below reflect exposure in controlled clinical trials involving over 100 patients treated for functional bowel/irritable bowel syndrome with dicyclomine hydrochloride at initial doses of 160 mg daily (40 mg four times a day)

In these trials most of the side effects were typically anticholinergic in nature and were reported by 61% of the patients. Table 1 presents adverse reactions (MedDRA 13.0 preferred terms) by decreasing order of frequency in a side-by-side comparison with placebo.

Table 1: Adverse reactions experienced in controlled clinical trials with decreasing order of frequency

Nine percent (9%) of patients were discontinued from Bentyl because of one or more of these side effects (compared with 2% in the placebo group). In 41% of the patients with side effects, side effects disappeared or were tolerated at the 160 mg daily dose without reduction. A dose reduction from 160 mg daily to an average daily dose of 90 mg was required in 46% of the patients with side effects who then continued to experience a favorable clinical response; their side effects either disappeared or were tolerated.

Postmarketing Experience

The following adverse reactions, presented by system organ class in alphabetical order, have been identified during post approval use of Bentyl. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

• Cardiac disorders: palpitations, tachyarrhythmias
• Eye disorders: cycloplegia, mydriasis, vision blurred
• Gastrointestinal disorders: abdominal distension, abdominal pain, constipation, dry mouth, dyspepsia, nausea, vomiting
• General disorders and administration site conditions: fatigue, malaise
• Immune System Disorders: drug hypersensitivity including face edema, angioedema, anaphylactic shock
• Nervous system disorders: dizziness, headache, somnolence, syncope
• Psychiatric disorders: As with the other anti-cholinergic drugs, cases of delirium or symptoms of delirium such as amnesia (or transient global amnesia), agitation, confusional state, delusion, disorientation, hallucination (including visual hallucination) as well as mania, mood altered and pseudodementia, have been reported with the use of Dicyclomine. Nervousness and insomnia have also been reported.
• Reproductive system and breast disorders: suppressed lactation
• Respiratory, thoracic and mediastinal disorders: dyspnoea, nasal congestion
• Skin and subcutaneous tissue disorder: dermatitis allergic, erythema, rash

Cases of thrombosis, thrombophlebitis and injection site reactions such as local pain, edema, skin color change and even reflex sympathetic dystrophy syndrome have been reported following inadverent IV injection of Bentyl.

Adverse Reactions Reported With Similar Drugs With Anticholinergic/Antispasmodic Action

• Gastrointestinal: anorexia,
• Central Nervous System: tingling, numbness, dyskinesia, speech disturbance, insomnia
• Peripheral Nervous System: With overdosage, a curare-like action may occur (i.e., neuromuscular blockade leading to muscular weakness and possible paralysis).
• Ophthalmologic: diplopia, increased ocular tension
• Dermatologic/Allergic: urticaria, itching, and other dermal manifestations;
• Genitourinary: urinary hesitancy, urinary retention in patients with prostatic hypertrophy
• Cardiovascular: hypertension
• Respiratory: apnea
• Other: decreased sweating, sneezing, throat congestion, impotence. With the injectable form, there may be temporary sensation of light-headedness. Some local irritation and focal coagulation necrosis may occur following the intramuscular injection of Bentyl.

Antiglaucoma Agents

• Anticholinergics antagonize the effects of antiglaucoma agents. Anticholinergic drugs in the presence of increased intraocular pressure may be hazardous when taken concurrently with agents such as corticosteroids.
• Use of Bentyl in patients with glaucoma is not recommended.

Other Drugs With Anticholinergic Activity

• The following agents may increase certain actions or side effects of anticholinergic drugs including Bentyl:
  • amantadine,
  • antiarrhythmic agents of Class I (e.g., quinidine),
  • antihistamines,
  • antipsychotic agents (e.g., phenothiazines),
  • benzodiazepines,
  • MAO inhibitors,
  • narcotic analgesics (e.g., meperidine),
  • nitrates and nitrites,
  • sympathomimetic agents,
  • tricyclic antidepressants, and
  • other drugs having anticholinergic activity.

Other Gastrointestinal Motility Drugs

• Interaction with other gastrointestinal motility drugs may antagonize the effects of drugs that alter gastrointestinal motility, such as metoclopramide.

Effect Of Antacids

• Because antacids may interfere with the absorption of anticholinergic agents including Bentyl, simultaneous use of these drugs should be avoided.

Effect On Absorption Of Other Drugs

• Anticholinergic agents may affect gastrointestinal absorption of various drugs by affecting gastrointestinal motility, such as slowly dissolving dosage forms of digoxin; increased serum digoxin concentration may result.

Effect On Gastric Acid Secretion

• The inhibiting effects of anticholinergic drugs on gastric hydrochloric acid secretion are antagonized by agents used to treat achlorhydria and those used to test gastric secretion.