URISPAS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for URISPAS (URISPAS).
Urispas (flavoxate) is a smooth muscle relaxant that exerts a direct spasmolytic effect on the detrusor muscle of the urinary bladder. It has anticholinergic, local anesthetic, and analgesic properties, but its exact mechanism is not fully understood.
| Metabolism | Flavoxate is extensively metabolized in the liver, primarily via oxidation and conjugation pathways. The exact enzymes involved have not been fully elucidated, but hepatic metabolism is significant. |
| Excretion | Primarily renal (approximately 50-70% as unchanged drug and metabolites); minor biliary/fecal elimination (<10%). |
| Half-life | Terminal elimination half-life is approximately 2-3 hours in healthy adults; may be prolonged in renal impairment (creatinine clearance <30 mL/min extends half-life to 5-7 hours). |
| Protein binding | Approximately 50-70% bound to plasma proteins (albumin). |
| Volume of Distribution | Approximately 1.5-2.0 L/kg; indicates extensive tissue distribution (concentrations in bladder tissue exceed plasma by 2-3 fold). |
| Bioavailability | Oral: 60-80% (first-pass hepatic metabolism; food may reduce rate but not extent of absorption). |
| Onset of Action | Oral: 30-60 minutes (antispasmodic effect on urinary smooth muscle). |
| Duration of Action | Oral: 4-6 hours (symptom relief from urinary frequency/urgency); clinical effect correlates with plasma levels above 100 ng/mL. |
| Action Class | Direct antispasmodic (Bladder) |
| Brand Substitutes | Urinet 200mg Tablet, Relaxuro Tablet, Voxadol 200mg Tablet, Urikind Tablet, UT Friend 200mg Tablet |
20 mg orally three times daily.
| Dosage form | TABLET |
| Renal impairment | For GFR 10-50 mL/min: 20 mg orally twice daily. For GFR <10 mL/min: 20 mg orally once daily. |
| Liver impairment | Child-Pugh Class B: 20 mg orally twice daily. Child-Pugh Class C: avoid use. |
| Pediatric use | Not recommended for pediatric patients under 12 years. For children ≥12 years: 20 mg orally three times daily. |
| Geriatric use | Consider reduced initial dose of 10 mg orally twice daily due to increased anticholinergic sensitivity and risk of confusion. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for URISPAS (URISPAS).
| Breastfeeding | Flavoxate is excreted into human breast milk in unknown amounts. The milk-to-plasma (M/P) ratio has not been established. Due to the potential for anticholinergic effects in the nursing infant (e.g., gastrointestinal disturbances, dry mouth, or decreased feeding), caution is advised. The manufacturer recommends considering the developmental and health benefits of breastfeeding along with the mother's clinical need for the drug and any potential adverse effects on the breastfed child. |
| Teratogenic Risk | Urispas (flavoxate hydrochloride) is classified as FDA Pregnancy Category B. Animal studies have not demonstrated teratogenic effects, but there are no adequate and well-controlled studies in pregnant women. The drug should be used during pregnancy only if clearly needed. In the first trimester, theoretical risks of anticholinergic effects on fetal development exist; however, no specific malformations have been consistently reported. In the second and third trimesters, use may be associated with a risk of temporary neonatal anticholinergic effects such as tachycardia, constipation, or urinary retention if administered near term, but data are limited. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to flavoxate or any component of the formulation","Patients with pyloric or duodenal obstruction, obstructive intestinal lesions, ileus, achalasia, or gastrointestinal hemorrhage","Obstructive uropathy (e.g., bladder neck obstruction due to prostatic hypertrophy)","Glaucoma (narrow-angle)"]
| Precautions | ["May cause drowsiness, blurred vision, and dizziness; patients should exercise caution when driving or operating machinery","Use with caution in patients with glaucoma, gastrointestinal obstruction, or urinary retention (due to anticholinergic effects)","May potentiate the effects of other anticholinergic drugs"] |
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| Fetal Monitoring | Monitor for anticholinergic effects in the mother (e.g., blurred vision, dry mouth, urinary retention, constipation) and signs of fetal distress if used during pregnancy. No specific fetal monitoring is required beyond standard prenatal care. In the neonate, observe for temporary anticholinergic effects such as tachycardia, feeding difficulties, or urinary retention if the drug was used near term. |
| Fertility Effects | There are no adequate studies on the effect of flavoxate on fertility in humans. Animal studies have not shown impaired fertility at clinically relevant doses. However, anticholinergic drugs may theoretically affect reproductive function by altering autonomic innervation of the reproductive tract; no specific fertility impairment has been reported. |