Can you take Solifenacin with Oxybutynin (antimuscarinic medication)?

From the Guidelines

No, you should not take Solifenacin with Oxybutynin together as they are both antimuscarinic medications that work in similar ways to treat overactive bladder. Taking these medications simultaneously significantly increases the risk of side effects such as severe dry mouth, constipation, blurred vision, confusion, urinary retention, and increased heart rate. These side effects occur because both medications block the same acetylcholine receptors in the body, creating an additive effect that can be potentially dangerous, especially in older adults. According to the American College of Physicians guideline 1, pharmacologic therapies, including oxybutynin and solifenacin, are effective in managing urgency UI, but they are associated with adverse effects, and evidence shows that some patients are likely to discontinue pharmacologic treatment because of these effects.

If your current medication isn't providing adequate symptom relief, consult your healthcare provider about switching from one medication to the other rather than combining them. Your doctor might also consider alternative medication classes or adjust your dosage to better manage your bladder symptoms while minimizing side effects. The choice of pharmacologic agents should be based on tolerability, adverse effect profile, ease of use, and cost of medication, as recommended by the American College of Physicians 1. Always inform your healthcare provider about all medications you're taking to avoid potentially harmful drug interactions.

Some key points to consider when taking antimuscarinic medications like oxybutynin and solifenacin include:

• Adverse effects are a major reason for treatment discontinuation
• Patient characteristics, such as age, race, comorbid conditions, or baseline UI, do not affect the outcomes of the various pharmacologic medications
• Adherence to pharmacologic treatments for UI is poor, and clinicians and their patients should compare the risk for pharmacologic adverse effects with the severity and bothersomeness of the patient’s symptoms, as stated in the guideline 1.

From the Research

Interaction between Solifenacin and Oxybutynin

• There is no direct evidence of a study that examines the interaction between Solifenacin and Oxybutynin 2, 3, 4, 5, 6.
• However, it is known that both Solifenacin and Oxybutynin are antimuscarinic medications used to treat overactive bladder syndrome (OAB) 2, 6.
• Solifenacin has a higher absolute bioavailability and is more bladder-specific, which may result in fewer anticholinergic side effects compared to Oxybutynin 2, 6.
• The use of anticholinergic drugs, including Solifenacin and Oxybutynin, has been associated with an increased risk of dementia in older adults 5.
• A study comparing the exocrine muscarinic receptor binding characteristics and inhibition of salivation of Solifenacin and Oxybutynin in mice found that Solifenacin had a weaker inhibitory effect on pilocarpine-induced salivary secretion and dissociated more readily from muscarinic receptors compared to Oxybutynin 6.

Safety and Tolerability

• The safety and tolerability of Solifenacin in children and adolescents with OAB have been evaluated, and the results show that the most common side effects are constipation and dry mouth 3.
• The use of Solifenacin in combination with other medications, such as mirabegron, has been shown to be safe and effective in treating OAB, without exacerbating anticholinergic side effects 4.
• However, the long-term risks and consequences of using anticholinergic drugs, including Solifenacin and Oxybutynin, should be considered, particularly in older adults 5.

Pharmacokinetics and Pharmacodynamics

• Solifenacin has a high absolute bioavailability, is extensively bound to plasma proteins, and is eliminated mainly through hepatic metabolism via cytochrome P450 (CYP) 3A4 2.
• The pharmacokinetics of Solifenacin are not significantly affected by food intake, and the drug has a terminal elimination half-life of 33-85 hours, allowing for once-daily administration 2.
• The pharmacodynamics of Solifenacin are characterized by its high affinity for muscarinic receptors, which results in a decrease in bladder contractions and an increase in bladder capacity 2.