FLAVOXATE HYDROCHLORIDE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for FLAVOXATE HYDROCHLORIDE (FLAVOXATE HYDROCHLORIDE).
Flavoxate hydrochloride is a smooth muscle relaxant with anticholinergic and local anesthetic properties. Its mechanism of action involves direct inhibition of smooth muscle contraction in the urinary tract, reducing detrusor muscle spasm, and decreasing urinary frequency and urgency.
| Metabolism | Metabolized primarily in the liver via hydrolysis to flavoxate acid and other metabolites. CYP450 enzymes not significantly involved. |
| Excretion | Renal: approximately 30-60% of an oral dose is excreted unchanged in urine; the remainder is metabolized and eliminated via bile and feces. |
| Half-life | Approximately 3-4 hours; clinical context: short half-life supports multiple daily dosing in overactive bladder therapy. |
| Protein binding | Approximately 60-70% bound to serum proteins, primarily albumin. |
| Volume of Distribution | Approximately 3-4 L/kg; indicates extensive tissue distribution beyond plasma volume. |
| Bioavailability | Oral: approximately 90% (extensive absorption with first-pass metabolism minimal). |
| Onset of Action | Oral: within 30-60 minutes; peak plasma concentrations at 1-2 hours. |
| Duration of Action | Oral: 3-4 hours; clinical note: duration correlates with half-life, requiring dosing 3-4 times daily. |
100-200 mg orally 3-4 times daily; maximum 800 mg/day.
| Dosage form | TABLET |
| Renal impairment | CrCl <50 mL/min: reduce dose to 100 mg 2-3 times daily; CrCl <10 mL/min: avoid use. |
| Liver impairment | Child-Pugh class B or C: contraindicated or use only if benefit outweighs risk; no specific dose recommendations. |
| Pediatric use | Not recommended for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | Initiate at low end of dosing range (100 mg 3 times daily) due to increased sensitivity and risk of anticholinergic effects; titrate cautiously. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for FLAVOXATE HYDROCHLORIDE (FLAVOXATE HYDROCHLORIDE).
| Breastfeeding | It is unknown whether flavoxate is excreted in human breast milk. The M/P ratio has not been established. Due to the potential for anticholinergic effects in the nursing infant, discontinue breastfeeding or the drug, taking into account the importance of the drug to the mother. |
| Teratogenic Risk | Flavoxate hydrochloride is classified as FDA Pregnancy Category B. Animal studies have not demonstrated fetal harm, but no adequate and well-controlled studies exist in pregnant women. Risk cannot be ruled out; use only if clearly needed during the first trimester. For second and third trimesters, potential risks remain unclear; avoid unless benefit outweighs unknown fetal risks. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to flavoxate or any component of the formulation","Pyloric or duodenal obstruction","Intestinal atony","Obstructive uropathy (e.g., bladder neck obstruction due to prostatic hypertrophy)","Gastrointestinal hemorrhage","Myasthenia gravis","Angle-closure glaucoma (untreated)"]
| Precautions | ["Caution in patients with glaucoma, especially angle-closure glaucoma, due to anticholinergic effects","Caution in patients with pyloric or duodenal obstruction, intestinal atony, obstructive uropathy, or cardiovascular disease (e.g., tachycardia, arrhythmias)","May cause drowsiness, blurred vision, or dizziness; advise patients not to drive or operate machinery","Use with caution in patients with hepatic or renal impairment","May exacerbate symptoms of myasthenia gravis","Consider risk of urinary retention in patients with prostatic hypertrophy"] |
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| Fetal Monitoring | Monitor for anticholinergic adverse effects (e.g., dry mouth, blurred vision, constipation, urinary retention) in the mother. Fetal monitoring is not specifically required but standard obstetric care should be maintained. Assess for signs of fetal distress if used near term due to potential anticholinergic effects. |
| Fertility Effects | Flavoxate has not been studied for effects on human fertility. Animal studies have not reported impaired fertility. Anticholinergic effects may theoretically affect reproductive function, but no clinical data are available. |