FLOMAX
Clinical safety rating
cautionComprehensive clinical and safety monograph for FLOMAX (FLOMAX).
Selective antagonist of alpha-1A and alpha-1D adrenergic receptors in the prostate, bladder base, and bladder neck, leading to relaxation of smooth muscle and improved urinary flow.
| Metabolism | Extensively metabolized in the liver via CYP3A4 and CYP2D6 enzymes. |
| Excretion | Primarily hepatic metabolism (CYP3A4, CYP2D6) with <10% excreted unchanged in urine; fecal excretion accounts for ~76% of metabolites. |
| Half-life | Terminal elimination half-life is approximately 14-15 hours (range 6-20 hours) in healthy adults, allowing once-daily dosing. |
| Protein binding | 94-99% bound primarily to alpha-1 acid glycoprotein, with high affinity. |
| Volume of Distribution | Approximately 16 L/kg (or 16 L for an average 70 kg patient), indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability is approximately 90% (capsule) due to extensive absorption, with minimal first-pass metabolism. |
| Onset of Action | Oral: Onset of symptomatic improvement in benign prostatic hyperplasia occurs within 2-6 hours after first dose, with maximal effect on urinary flow in 2-4 weeks. |
| Duration of Action | Duration of clinical effect is approximately 24 hours after oral administration, supporting once-daily dosing; sustained effect with chronic therapy. |
| Molecular Weight | 408.5 |
| Action Class | Quinolones/ Fluroquinolones |
| Brand Substitutes | Tariflox 200mg Tablet, Oflotas 200mg Tablet, Olox 200mg Tablet, Zenflox 200 Tablet, Onoff 200mg Tablet |
0.4 mg orally once daily, approximately 30 minutes after the same meal each day. If no response after 2-4 weeks, may increase to 0.8 mg once daily.
| Dosage form | CAPSULE |
| Renal impairment | No adjustment required for GFR ≥10 mL/min; insufficient data for GFR <10 mL/min, use with caution. |
| Liver impairment | Child-Pugh Class A: No adjustment. Child-Pugh Class B: Use with caution; consider starting at 0.4 mg once daily. Child-Pugh Class C: Contraindicated. |
| Pediatric use | Not approved for pediatric use; safety and efficacy not established. |
| Geriatric use | Same dosing as adults; monitor for orthostatic hypotension and dizziness. Consider starting at 0.4 mg once daily. |
| 1st trimester | Tamsulosin is not recommended during the first trimester due to potential risks, though human data are limited. Animal studies have shown some fetal toxicity at high doses. |
| 2nd trimester | Use only if clearly needed; no well-controlled studies in pregnant women. Risk cannot be ruled out. |
| 3rd trimester | Avoid in third trimester as alpha-blockers may cause hypotension and reduce uterine blood flow. Use only if potential benefit justifies risk. |
Clinical note
Comprehensive clinical and safety monograph for FLOMAX (FLOMAX).
| Placental transfer | Tamsulosin crosses the placenta in animal studies; human data are not available. |
| Breastfeeding | Tamsulosin is excreted into breast milk in small amounts. The risk to the nursing infant is likely low, but caution is advised. Monitor infant for hypotension, drowsiness, or feeding difficulties. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Tamsulosin is FDA Pregnancy Category B. Animal studies revealed no evidence of teratogenicity at doses up to 50 mg/kg/day in rats and 5 mg/kg/day in rabbits (approximately 50 and 30 times the human exposure). There are no adequate and well-controlled studies in pregnant women; use only if clearly needed. First trimester: no known increased risk of major malformations. Second/third trimester: no known specific fetal risks; however, alpha-blockers may cause hypotension in the mother, potentially affecting placental perfusion. No reports of teratogenic effects in humans. |
| Fetal Monitoring | Monitor maternal blood pressure and heart rate, especially during initiation or dose titration. Assess for orthostatic hypotension. In third trimester, monitor fetal heart rate and uterine contractions if used for tocolysis (though tamsulosin is not indicated for tocolysis). No specific fetal monitoring required beyond routine prenatal care. |
| Fertility Effects | Tamsulosin is associated with decreased ejaculate volume due to relaxation of seminal vesicle smooth muscle, but does not affect sperm production or male fertility per se. In women, no data on fertility impact. No known effects on female fertility; animal studies showed no impairment of fertility in male or female rats at doses up to 100 mg/kg/day. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to tamsulosin or any component of the formulationHistory of orthostatic hypotensionSevere hepatic impairment
| Precautions | Orthostatic hypotension and syncope, especially upon initiation or dose increase, Intraoperative floppy iris syndrome (IFIS) during cataract surgery, Priapism (rare), Hepatic impairment, Consideration of prostate cancer before initiating therapy |
| Food/Dietary | Grapefruit juice may increase tamsulosin levels; avoid concurrent intake. High-fat meals can decrease absorption; administer 30 minutes after the same meal daily. |
| Clinical Pearls | First-dose orthostatic hypotension is common; administer at bedtime. Avoid use in patients with history of cataract surgery due to intraoperative floppy iris syndrome (IFIS). Tamsulosin is not recommended for hypertension. Renal impairment does not require dose adjustment. Use caution with strong CYP3A4 inhibitors (e.g., ketoconazole) and PDE5 inhibitors (e.g., sildenafil) due to enhanced hypotensive effects. |
| Patient Advice | Take this medication approximately 30 minutes after the same meal each day to maintain consistent absorption. · Avoid getting up too quickly from a sitting or lying position to minimize dizziness. · Inform your ophthalmologist about tamsulosin use before any cataract surgery due to risk of floppy iris syndrome. · Do not drive or operate heavy machinery until you know how this medication affects you. · If you miss a dose, skip it and take the next dose at the usual time; do not double the dose. |
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