What are the side effects of Bentyl (dicyclomine)?

Side Effects of Bentyl (Dicyclomine)

Bentyl (dicyclomine) commonly causes anticholinergic side effects, with dry mouth, dizziness, blurred vision, and nausea being the most frequent adverse reactions. 1

Common Side Effects

• Anticholinergic effects - These represent the most common adverse reactions and occur in approximately 61% of patients taking dicyclomine at therapeutic doses (40 mg four times daily) 1:

  • Dry mouth (33% vs 5% with placebo) 1
  • Dizziness (40% vs 5% with placebo) 1
  • Blurred vision (27% vs 2% with placebo) 1
  • Nausea (14% vs 6% with placebo) 1
  • Somnolence/drowsiness (9% vs 1% with placebo) 1
  • Asthenia/weakness (7% vs 1% with placebo) 1
  • Nervousness (6% vs 2% with placebo) 1

• Gastrointestinal effects - Beyond dry mouth and nausea, other GI effects include 1:

  • Abdominal distension 1
  • Abdominal pain 1
  • Constipation 1
  • Dyspepsia 1
  • Vomiting 1

Serious Side Effects

• Cardiovascular effects - Though less common, these can include 1:

  • Palpitations 1
  • Tachyarrhythmias 1
  • Hypertension 1

• Central nervous system effects - More serious neurological reactions may include 1:

  • Syncope (fainting) 1
  • Headache 1
  • Psychiatric effects including delirium, amnesia, agitation, confusion, hallucinations 1
  • Speech disturbance 1
  • Insomnia 1

• Muscle effects - With high doses or overdosage 1, 2:

  • Muscle cramps 2
  • Neuromuscular blockade leading to muscle weakness 1
  • Possible paralysis (in overdose situations) 1

Rare but Significant Side Effects

• Allergic reactions - Can range from mild to severe 1:

  • Dermatitis allergic 1
  • Erythema 1
  • Rash 1
  • Face edema 1
  • Angioedema 1
  • Anaphylactic shock (rare but life-threatening) 1

• Other reported effects include 1:

  • Suppressed lactation 1
  • Dyspnea 1
  • Nasal congestion 1
  • Decreased sweating (which can lead to hyperthermia) 1
  • Urinary hesitancy and retention, especially in patients with prostatic hypertrophy 1

Discontinuation Rates and Dose Adjustments

• Approximately 9% of patients discontinue dicyclomine due to side effects (compared to 2% with placebo) 1
• In 41% of patients experiencing side effects, the adverse reactions either disappeared or became tolerable at the standard 160 mg daily dose 1
• 46% of patients with side effects required dose reduction (from 160 mg daily to an average of 90 mg daily) to continue treatment while maintaining clinical benefit 1

Special Considerations

• Elderly patients are more susceptible to anticholinergic side effects 2
• Overdose symptoms include headache, nausea, vomiting, blurred vision, dilated pupils, hot/dry skin, difficulty swallowing, and potential CNS stimulation including convulsions 1
• Thrombosis risk - Intravenous administration should be avoided due to potential thrombotic complications 3
• Drug interactions - May occur with other medications that have anticholinergic properties, potentially increasing side effects 1

Management of Side Effects

• For mild anticholinergic side effects, dose reduction may be sufficient while maintaining therapeutic benefit 1
• Maintaining adequate hydration may help minimize some side effects like muscle cramping 2
• For persistent side effects, alternative antispasmodics with fewer anticholinergic properties (like mebeverine or alverine citrate) may be considered 4
• Regular monitoring for side effects is recommended when initiating therapy 2

Recognizing and managing these side effects appropriately can help improve medication adherence and treatment outcomes for patients taking dicyclomine.