When the bladder is functioning normally, the muscles in the bladder wall remain relaxed, allowing the bladder to expand and store urine. During urination (micturition), the muscles contract, the bladder sphincters open, and urine is voluntarily released.

People who have overactive bladder syndrome (OAB) experience "urgency", which is the sudden, strong urge to urinate. If the urge cannot be suppressed, the involuntary leakage of urine, or urge incontinence, results. Other symptoms of OAB include the need to urinate many times during the day (urinary frequency) and at night (nocturia).

A common cause of OAB is the overactivity of the detrusor muscle, found in the bladder wall. Treatment includes the use of anticholinergic drugs that by blocking the receptors that mediate bladder contraction, reduce the number of micturitions. However, treatment side effects, such as dry mouth, are common, and these agents are used only after, or in conjunction with, other methods, such as behavioral changes.

The "Drug Class Review on Agents for Overactive Bladder" compares the safety and effectiveness of nine drugs. A summary of the findings is below.

How do anticholinergics compare in treating overactive bladder syndrome?

Oxybutynin, tolterodine, and trospium are available in immediate release (IR) and extended release (ER) forms. The IR forms of these drugs are similar to each other in efficacy. Less evidence exists for the ER forms, but they also appear to be similar to each other - the better of two studies found that oxybutynin ER and tolterodine ER share a similar efficacy. [full review]

How do short-acting and long-acting forms of the same drug compare?

When the IR and ER forms of the same anticholinergic drug were compared, they were found to share similar efficacy. For example, no differences were found between oxybutynin IR vs. ER, and tolterodine IR vs. ER. [full review]

How do short-acting and long-acting forms of different anticholinergics compare?

In general, comparisons have found that the ER drug is superior to the IR drug. For example, single studies have found oxybutynin ER is superior to tolterodine IR, and tolterodine ER is superior to oxybutynin IR. However, there is no difference between darifenacin ER and oxybutynin IR. [full review]

Solifenacin (a long-acting drug) is superior to tolterodine (both IR and ER) for some outcomes (e.g. reducing urgency), but not for others (e.g. nocturia). [full review]

Data for comparing flavoxate, scopolamine, or hyoscyamine to other anticholinergic drugs are lacking. [full review]

How do anticholinergics compare in safety?

Overall, the most common side effect for all the anticholinergic drugs is dry mouth, and oxybutynin appears to cause more dry mouth and other adverse events overall.

Comparing the IR and ER forms of oxybutynin and tolterodine, there tended to be higher rates of dry mouth with the IR forms of both drugs (although this was not reflected in withdrawal rates).

The rate of severe dry mouth is less with trospium IR than with oxybutynin IR, but both drugs share a similar incidence of dry mouth and other adverse events overall. And a single trial found that the rate of dry mouth is lower for tolterodine ER than for solifenacin, but both drugs appear to share a similar rate of adverse events overall. [full review]

Does age, gender, or race influence the safety or effectiveness of anticholinergic drugs?

Fair quality evidence suggests that in older patients, response and adverse event rates found with the following drugs were similar to overall study populations: tolterodine ER, oxybutynin, darifenacin, and solifenacin. Evidence for other drugs was not found. Limited evidence exists for gender, but it appears that men and women respond similarly to tolterodine.

Compared to mainly white populations, Chinese women had a similar response and rate of adverse events to oxybutynin IR and tolterodine IR. In Japanese and Korean women, both IR and ER forms of tolterodine were found to be similarly effective, with fewer adverse events linked with the ER form. Finally, one study found that Hispanics enrolled in a trial of solifenacin had a similar rate of response and adverse events compared with the overall trial population. [full review]

Drugs included in this review

Further information

This PubMed Clinical Q&A was reviewed by Marian McDonagh, PharmD.

For the full report and evidence tables, please see:
McDonagh MS, Selover D, Santa J, et al. Drug Class Review: Agents for Overactive Bladder: Final Report Update 4 [Internet]. Portland (OR): Oregon Health & Science University; 2009 Mar. Available at: http://www.ncbi.nlm.nih.gov/books/NBK47183/.