SOLIFENACIN SUCCINATE

Clinical safety rating: safe

Animal studies have demonstrated safety

How it works

Solifenacin is a competitive muscarinic receptor antagonist. It binds selectively to M3 muscarinic receptors, inhibiting acetylcholine action on smooth muscle of the urinary bladder, reducing detrusor overactivity and increasing bladder capacity.

What the body does with it

Metabolism	Primarily metabolized by CYP3A4 to active metabolites including 4R-hydroxy solifenacin and N-glucuronide conjugates. Minor contribution from CYP2C9 and CYP2C19.
Excretion	Primarily renal: ~69% as metabolites (including active metabolite 4R-hydroxy solifenacin) and ~7% as unchanged drug. Fecal excretion accounts for ~23% (mainly as metabolites).
Half-life	Terminal elimination half-life is approximately 45-68 hours (mean ~55 hours) in healthy adults, allowing once-daily dosing.
Protein binding	Approximately 98% bound to plasma proteins (primarily alpha-1-acid glycoprotein).
Volume of Distribution	Vd/F is approximately 600 L (~8.6 L/kg for a 70 kg person), indicating extensive tissue distribution.
Bioavailability	Absolute oral bioavailability is approximately 88% (range 80-95%), not significantly affected by food.
Onset of Action	Oral: Onset of anticholinergic effect (e.g., reduction in urinary frequency) occurs within 3-8 hours after first dose, with peak effect at steady state (by day 10-14).
Duration of Action	Duration of antimuscarinic effect supports once-daily dosing; effect persists for up to 24 hours. Clinical benefit (e.g., decreased incontinence episodes) continues with regular dosing.

Classification & Brands

Dosing & administration

5 mg orally once daily, may increase to 10 mg once daily if tolerated.

Dosage form	TABLET
Renal impairment	eGFR 30-89 mL/min/1.73 m²: No adjustment. eGFR <30 mL/min/1.73 m²: Not recommended (insufficient data).
Liver impairment	Child-Pugh A: No adjustment. Child-Pugh B: 5 mg once daily; no data for Child-Pugh C.
Pediatric use	Safety and efficacy not established in pediatric patients.
Geriatric use	Start at 5 mg once daily; monitor for anticholinergic effects; no specific dose adjustment required based on age alone.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Strong CYP3A4 inhibitors may increase levels Can cause blurred vision and urinary retention.

Breastfeeding

No data on solifenacin in human milk; the M/P ratio is unknown. Solifenacin is excreted in milk of lactating rats. Due to potential for anticholinergic effects in the infant (e.g., constipation, urinary retention), breastfeeding is not recommended during therapy. If treatment is necessary, consider pumping and discarding milk during treatment.

Teratogenic Risk

FDA Pregnancy Category C. No adequate studies in pregnant women. In animal studies, solifenacin caused fetal malformations (cleft palate, skeletal abnormalities) at doses equivalent to human exposures. Risk cannot be ruled out. First trimester: potential teratogenic risk based on animal data; use only if benefit outweighs risk. Second/third trimester: limited data; may cause anticholinergic effects in fetus (e.g., tachycardia, meconium ileus). Avoid use during pregnancy unless essential.

Warnings & precautions

■ FDA Black Box Warning

None

Side Effect Profile

Common Effects	Dry mouth
Serious Effects

Absolute Contraindications

["Urinary retention","Gastric retention","Uncontrolled narrow-angle glaucoma","Hypersensitivity to solifenacin or any excipient"]

Clinical Precautions

Precautions

["Angioedema of the face, lips, tongue, and/or larynx has been reported, requiring immediate treatment discontinuation.","Urinary retention: Use with caution in patients with clinically significant bladder outflow obstruction.","Gastric retention: Use with caution in patients with decreased gastrointestinal motility.","Prolonged QT interval: Use with caution in patients with known QT prolongation or those taking drugs known to prolong QT interval.","Central nervous system effects: Somnolence, dizziness, and blurred vision have been reported; advise caution when driving or operating machinery.","Hepatic impairment: Not recommended in severe hepatic impairment (Child-Pugh Class C)."]

Clinical Tips & Counseling

Drug interactions

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