What are the side effects of oxybutynin (antimuscarinic medication)?

Side Effects of Oxybutynin

Oxybutynin causes significant anticholinergic side effects including dry mouth (71.4%), constipation (15.1%), blurred vision (9.6%), cognitive impairment, and urinary retention, which can negatively impact quality of life and lead to treatment discontinuation in up to 25% of patients. 1

Common Side Effects

Oxybutynin, an antimuscarinic medication used for overactive bladder (OAB), has a well-documented side effect profile. According to FDA data, the most common adverse events include:

• Anticholinergic effects 2, 1:

  • Dry mouth (71.4% of patients)
  • Constipation (15.1%)
  • Blurred vision (9.6%)
  • Dizziness (16.6%)
  • Somnolence/drowsiness (14%)
  • Headache (7.5%)

• Urinary effects 1:

  • Urinary hesitation (8.5%)
  • Urinary retention (6%)
  • Urinary tract infection (6.5%)

• Neuropsychiatric effects 1:

  • Insomnia (5.5%)
  • Nervousness (6.5%)

Cognitive Impairment

Oxybutynin has significant effects on cognitive function, particularly in older adults:

• Research demonstrates that oxybutynin can cause significant cognitive decrements on multiple cognitive measures, including memory and reaction time 3
• The drug crosses the blood-brain barrier and occupies central muscarinic receptors, with a strong correlation between receptor occupancy and cognitive impairment, particularly in the cortices and brainstem 4
• Cognitive effects are dose-dependent, with higher doses causing greater impairment 4

Serious Side Effects

Though less common, more serious adverse effects can occur 1:

• QT interval prolongation
• Tachycardia
• Decreased gastrointestinal motility
• Angioedema with airway obstruction
• Urticaria
• Anaphylactic reactions (rare)
• Suppression of lactation
• Convulsions (rare)
• Hallucinations

Special Considerations

Elderly Patients

Elderly patients are particularly susceptible to oxybutynin's side effects:

• Higher risk of cognitive impairment and confusion 3
• Appears ineffective in elderly institutionalized patients despite side effects 5

Contraindications and Cautions

Oxybutynin should not be used in patients with:

• Narrow-angle glaucoma (unless approved by ophthalmologist) 2
• Impaired gastric emptying 2
• History of urinary retention 2
• Patients using solid oral forms of potassium chloride 2

Alternative Formulations

For patients experiencing significant dry mouth with oral oxybutynin:

• Transdermal delivery systems (patches, gels) may be considered 2, 6
• Transdermal administration bypasses first-pass hepatic metabolism, resulting in:
  • Higher bioavailability of the parent drug (>80% vs <10% with oral)
  • Improved side effect profile while maintaining efficacy 6
  • However, application site reactions can occur 6

Comparison to Other Antimuscarinic Medications

When compared to other antimuscarinic medications:

• Tolterodine has a better side effect profile than oxybutynin 7
• Discontinuation rates due to adverse effects are higher with oxybutynin than with tolterodine 2, 7
• Solifenacin has the lowest risk for discontinuation due to adverse effects among antimuscarinic medications 2

Management of Side Effects

To minimize the impact of side effects:

• Consider starting with lower doses and titrating up as tolerated
• For dry mouth: adequate hydration, sugar-free gum/candy, or saliva substitutes 7
• Monitor for signs of urinary retention, especially in patients with bladder outlet obstruction 7
• Consider transdermal formulations if oral side effects are intolerable 2, 6
• Discontinue medication if serious adverse effects occur 7

Side effects are a major reason for treatment discontinuation, with up to 25% of patients stopping oxybutynin due to intolerable anticholinergic effects 5.