Side Effects of Dicyclomine (Bentyl)
Dicyclomine causes anticholinergic side effects in approximately 61% of patients, with dry mouth (33%), dizziness (40%), and blurred vision (27%) being the most common, and these effects are dose-related and typically reversible upon discontinuation. 1
Most Common Anticholinergic Side Effects
The FDA-approved labeling identifies the following side effects by frequency in clinical trials at standard dosing (40 mg four times daily):
- Dry mouth: 33% of patients (versus 5% placebo) 1
- Dizziness: 40% of patients (versus 5% placebo) 1
- Blurred vision: 27% of patients (versus 2% placebo) 1
- Nausea: 14% of patients (versus 6% placebo) 1
- Somnolence (drowsiness): 9% of patients (versus 1% placebo) 1
- Asthenia (weakness): 7% of patients (versus 1% placebo) 1
- Nervousness: 6% of patients (versus 2% placebo) 1
Serious Cardiovascular and Central Nervous System Effects
The most concerning adverse reactions involve cardiovascular and CNS symptoms:
- Cardiovascular: Palpitations, tachyarrhythmias, and hypertension 1
- Syncope (fainting) has been reported in postmarketing surveillance 2, 1
- CNS effects: Delirium, amnesia (including transient global amnesia), agitation, confusional state, delusion, disorientation, hallucinations (including visual), mania, mood alterations, and pseudodementia 1
Gastrointestinal Side Effects
Beyond the therapeutic target, dicyclomine can cause:
Ophthalmologic Effects
- Cycloplegia (paralysis of accommodation) 1
- Mydriasis (pupil dilation) 1
- Diplopia (double vision) 1
- Increased ocular tension 1
Other Significant Side Effects
- Urinary hesitancy and retention, particularly in patients with prostatic hypertrophy 1
- Suppressed lactation 1
- Decreased sweating, which can impair heat regulation 1
- Respiratory: Dyspnea and nasal congestion 1
- Allergic reactions: Drug hypersensitivity including face edema, angioedema, anaphylactic shock, urticaria, and rash 1
Discontinuation Rates and Dose Management
Nine percent (9%) of patients discontinued dicyclomine due to side effects (compared to 2% on placebo) 1. However, the side effects are manageable in many patients:
- In 41% of patients with side effects, symptoms disappeared or were tolerated at the full 160 mg daily dose 1
- In 46% of patients with side effects, dose reduction to an average of 90 mg daily allowed continuation with favorable clinical response 1
Special Population Considerations
Elderly patients are more susceptible to anticholinergic side effects 2. The Gut journal recommends maintaining adequate hydration to help minimize some side effects like muscle cramping 2.
Clinical Management Pitfalls
- Avoid intravenous administration due to risk of thrombosis mediated by M3-receptor-related nitric oxide inhibition 3
- For patients with persistent anticholinergic side effects, the Gut journal recommends considering alternative antispasmodics with fewer anticholinergic properties, such as mebeverine or alverine citrate 2
- Regular monitoring for side effects is recommended when initiating therapy 2
- The majority of adverse effects are related to the anticholinergic activity of the drug and are typically dose-dependent 4
Rare but Serious Effects
With overdosage, a curare-like action may occur (neuromuscular blockade leading to muscular weakness and possible paralysis) 1.