Effects of tolterodine, trospium chloride, and oxybutynin on the central nervous system

Antimuscarinic compounds are increasingly used to treat the symptoms of overactive bladder; however, their use is often restricted by peripheral adverse effects (AEs). On the other hand, data regarding their influence on the central nervous system (CNS) are limited. This randomized, single-blind, parallel-group quantitative-topographical EEG (qEEG) study of clinical phase I investigates the potential CNS adverse effects of the three antimuscarinic drugs--tolterodine, oxybutynin, and trospium chloride--in comparison to placebo. Overall, 4 x 16 (total 64) young, healthy male volunteers were included in the study. The subjects were given either placebo or the clinically recommended daily doses of the drugs dispensed in three doses on a single day (tolterodine 2 mg bid and once placebo, total 4 mg/d; oxybutynin 5 mg tid, total 15 mg/d; and trospium chloride 15 mg tid, total 45 mg/d). The qEEG was recorded prior to and up to 4 hours after each intake of the trial medication (a total of 10 qEEG sessions) under three different conditions: at rest with eyes open, eyes closed, and under mental demand. The drug tolerability was subjectively evaluated by the volunteer and the investigator. In comparison to placebo (10% confidence interval), tolterodine and trospium chloride did not induce changes of the qEEG power in five of the six frequency bands (i.e., delta, alpha 1, alpha 2, beta 1, and beta 2). Isolated power decreases were only observed in the theta frequency band. In contrast, oxybutynin caused significant power reductions in four frequency bands (theta, alpha 1, alpha 2, and beta 1; p < 0.01). The subjectively evaluated drug tolerability was comparable between all treatment groups, although differences in the AE occurrence existed, with the AE frequency being higher in the oxybutynin group. The results of this study support the findings that oxybutynin as a tertiary amine crosses the blood-brain barrier, causing significant qEEG activity changes and more pronounced central adverse effects. Although tolterodine is also a tertiary amine, it shows limited effects on qEEG activity (i.e., slight theta power reductions), comparable to the effects of trospium chloride, a quarternary amine, which barely crosses the blood-brain barrier. The minimal qEEG changes observed with tolterodine and trospium chloride reflect most probably a rebound message from the peripheral target organs. Prescription of oxybutynin thus implicates a higher risk of CNS side effects.