Adults

The recommended starting dose is 5 mg once daily. The dose may be increased to 10 mg once daily based on patient response and tolerability.

Elderly

No dosage adjustment is generally required for elderly patients. However, caution should be exercised.

Renal_impairment

For patients with severe renal impairment (creatinine clearance <30 mL/min) or moderate hepatic impairment (Child-Pugh B), the maximum dose should not exceed 5 mg once daily. Avoid use in patients undergoing hemodialysis or with severe hepatic impairment (Child-Pugh C).

Onset

Clinical effects may be observed within a few days, but full therapeutic effect may take several weeks (e.g., 2-4 weeks).

Excretion

Approximately 70% of the dose is excreted in the urine and 13% in the feces after 26 days. Elimination is primarily via renal excretion.

Half life

Approximately 45-68 hours.

Absorption

Well absorbed from the gastrointestinal tract. Absolute bioavailability is approximately 90%. Peak plasma concentrations are reached 3 to 8 hours after administration.

Metabolism

Extensively metabolized by the liver, primarily by the cytochrome P450 3A4 (CYP3A4) enzyme system. Active metabolites exist but are less potent than the parent drug.

Potent CYP3A4 Inhibitors

Concomitant use with potent CYP3A4 inhibitors (e.g., ketoconazole, ritonavir) may significantly increase solifenacin exposure, requiring a maximum dose of 5 mg once daily. Concomitant use with CYP3A4 inducers (e.g., rifampicin) may decrease solifenacin efficacy.

Other Anticholinergic Drugs

Concomitant administration with other anticholinergic drugs may potentiate both therapeutic effects and side effects. This increases the risk of severe anticholinergic adverse effects such as dry mouth, constipation, and blurred vision.