Short answer: Drowsiness is a known side effect of Seroquel which is actually started for his delirium and not UTI. Detailed answer: Seroquel is always started at lower doses and then dose is increased gradually in the increments of 25mg to 50 mg till desired effects are achieved. The drug is not as much effective at lower doses and that is why the dose is increased gradually. So it is not recommended to lower the dose for side effects alone. But if the drwosiness is totally incapacitating him then you should talk to his doctor regarding change of medicine or if he/she thinks it is possible to reduce the dose. Hope this clears your doubt. Thank you.