Factors affecting antibiotic concentrations in bladder urine.

High, but transient, antibiotic levels are achieved in bladder urine if a rapidly excreted agent is given to a patient with frequency of micturition and a normal residual bladder volume. Lower, but more prolonged levels are achieved if the drug is slowly excreted, if micturition is infrequent, or if the residual volume is increased. The magnitude of these effects has been calculated mathematically for various combinations of circumstances. Such considerations have implications for treatment, particularly with drugs, such as the beta-lactam group, that are rapidly excreted into urine.