General characteristics
Absorption
After intake of solifenacin tablets, maximum solifenacin plasma concentrations (Cmax) are reached after 3 to 8 hours. The tmax is independent of the dose. The Cmax and area under the curve (AUC) increase in proportion to the dose between 5 to 40 mg. Absolute bioavailability is approximately 90%. Food intake does not affect the Cmax and AUC of solifenacin.
Distribution
The apparent volume of distribution of solifenacin following intravenous administration is about 600 L. Solifenacin is to a great extent (approximately 98%) bound to plasma proteins, primarily α 1-acid glycoprotein.
Biotransformation
Solifenacin is extensively metabolised by the liver, primarily by cytochrome P450 3A4 (CYP3A4). However, alternative metabolic pathways exist, that can contribute to the metabolism of solifenacin. The systemic clearance of solifenacin is about 9.5 L/h and the terminal half-life of solifenacin is 45 - 68 hours. After oral dosing, one pharmacologically active (4R-hydroxy solifenacin) and three inactive metabolites (N-glucuronide, N-oxide and 4R-hydroxy-N-oxide of solifenacin) have been identified in plasma in addition to solifenacin.
Elimination
After a single administration of 10 mg [14C-labelled]-solifenacin, about 70% of the radioactivity was detected in urine and 23% in faeces over 26 days. In urine, approximately 11% of the radioactivity is recovered as unchanged active substance; about 18% as the N-oxide metabolite, 9% as the 4R-hydroxy- N-oxide metabolite and 8% as the 4R-hydroxy metabolite (active metabolite).
Linearity/non-linearity
Pharmacokinetics are linear in the therapeutic dose range.
Special populations
Elderly
No dosage adjustment based on patient age is required. Studies in the elderly have shown that the exposure to solifenacin, expressed as the AUC, after administration of solifenacin succinate (5 mg and 10 mg once daily) was similar in healthy elderly subjects (aged 65 – 80 years) and healthy young subjects (aged less than 55 years). The mean rate of absorption expressed as tmax was slightly slower in the elderly and the terminal half-life was approximately 20% longer in elderly subjects. These modest differences were considered not clinically significant.
The pharmacokinetics of solifenacin have not been established in children and adolescents.
Gender
The pharmacokinetics of solifenacin are not influenced by gender.
Race
The pharmacokinetics of solifenacin are not influenced by race.
Renal impairment
The AUC and Cmax of solifenacin in mild and moderate renally impaired patients was not significantly different from that found in healthy volunteers. In patients with severe renal impairment (creatinine clearance ≤ 30 ml/min), exposure to solifenacin was significantly greater than in the controls, with increases in Cmax of about 30%, AUC of more than 100% and t½ of more than 60%. A statistically significant relationship was observed between creatinine clearance and solifenacin clearance.
Pharmacokinetics in patients undergoing haemodialysis has not been studied.
Hepatic impairment
In patients with moderate hepatic impairment (Child-Pugh score of 7 to 9) the Cmax is not affected, AUC increased by 60% and t½ doubled. Pharmacokinetics of solifenacin in patients with severe hepatic impairment has not been studied.