Generic drug: silodosin

Brand name: Rapaflo

What is Rapaflo (silodosin), and how does it work?

Rapaflo (silodosin) is an alpha-adrenergic blocker used to improve urination in men with benign prostatic hyperplasia (enlarged prostate).

What are the side effects of Rapaflo?

Side effects of Rapaflo include:

Tell your doctor if you have serious side effects of Rapaflo including:

  • feeling like you might pass out, or
  • an erection that is painful or lasts 4 hours or longer.

What is the dosage for Rapaflo?

  • The recommended dose is 8 mg orally once daily with a meal.
  • Patients who have difficulty swallowing pills and capsules may carefully open the Rapaflo capsule and sprinkle the powder inside on a tablespoonful of applesauce.
  • The applesauce should be swallowed immediately (within 5 minutes) without chewing and followed with an 8 oz glass of cool water to ensure complete swallowing of the powder.
  • The applesauce used should not be hot, and it should be soft enough to be swallowed without chewing.
  • Any powder/applesauce mixture should be used immediately (within 5 minutes) and not stored for future use.
  • Subdividing the contents of a Rapaflo capsule is not recommended.

Dosage Adjustment In Special Populations

Renal Impairment
  • Rapaflo is contraindicated in patients with severe renal impairment (CCr < 30 mL/min).
  • In patients with moderate renal impairment (CCr 30-50 mL/min), the dose should be reduced to 4 mg once daily taken with a meal.
  • No dosage adjustment is needed in patients with mild renal impairment (CCr 50-80 mL/min).
  • Hepatic impairment: Rapaflo has not been studied in patients with severe hepatic impairment (Child-Pugh score = 10) and is therefore contraindicated in these patients. No dosage adjustment is needed in patients with mild or moderate hepatic impairment.


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What drugs interact with Rapaflo?

Moderate And Strong CYP3A4 Inhibitors

  • In a clinical metabolic inhibition study, a 3.8-fold increase in silodosin maximum plasma concentrations and 3.2-fold increase in silodosin exposure were observed with concurrent administration of a strong CYP3A4 inhibitor, 400 mg ketoconazole. Use of strong CYP3A4 inhibitors such as itraconazole or ritonavir may cause plasma concentrations of silodosin to increase. Concomitant administration of strong CYP3A4 inhibitors and Rapaflo is contraindicated.
  • The effect of moderate CYP3A4 inhibitors on the pharmacokinetics of silodosin has not been evaluated. Concomitant administration with moderate CYP3A4 inhibitors (e.g., diltiazem, erythromycin, verapamil) may increase concentration of Rapaflo. Exercise caution and monitor patients for adverse events when co-administering Rapaflo with moderate CYP3A4 inhibitors.

Strong P-glycoprotein (P-gp) Inhibitors

  • In vitro studies indicated that silodosin is a P-gp substrate. Ketoconazole, a CYP3A4 inhibitor that also inhibits P-gp, caused significant increase in exposure to silodosin. Inhibition of P-gp may lead to increased silodosin concentration.
  • Rapaflo is therefore not recommended in patients taking strong Pgp inhibitors such as cyclosporine.


  • The pharmacodynamic interactions between silodosin and other alpha-blockers have not been determined. However, interactions may be expected, and Rapaflo should not be used in combination with other alpha-blockers.


  • The effect of co-administration of Rapaflo and digoxin 0.25 mg/day for 7 days was evaluated in a clinical trial in 16 healthy males, aged 18 to 45 years.
  • Concomitant administration of Rapaflo and digoxin did not significantly alter the steady state pharmacokinetics of digoxin. No dose adjustment is required.

PDE5 Inhibitors

  • Co-administration of Rapaflo with a single dose of 100 mg sildenafil or 20 mg tadalafil was evaluated in a placebo-controlled clinical study that included 24 healthy male subjects, 45 to 78 years of age. Orthostatic vital signs were monitored in the 12-hour period following concomitant dosing.
  • During this period, the total number of positive orthostatic test results was greater in the group receiving Rapaflo plus a PDE5 inhibitor compared with Rapaflo alone. No events of symptomatic orthostasis or dizziness were reported in subjects receiving Rapaflo with a PDE5 inhibitor.

Other Concomitant Drug Therapy

  • The pharmacodynamic interactions between silodosin and antihypertensives have not been rigorously investigated in a clinical study. However, approximately one-third of the patients in clinical studies used concomitant antihypertensive medications with Rapaflo.
  • The incidence of dizziness and orthostatic hypotension in these patients was higher than in the general silodosin population (4.6% versus 3.8% and 3.4% versus 3.2%, respectively).
  • Exercise caution during concomitant use with antihypertensives and monitor patients for possible adverse events.
Metabolic Interactions
  • In vitro data indicate that silodosin does not have the potential to inhibit or induce cytochrome P450 enzyme systems.

Food Interactions

  • The effect of a moderate fat, moderate calorie meal on silodosin pharmacokinetics was variable and decreased silodosin maximum plasma concentration (Cmax) by approximately 18 to 43% and exposure (AUC) by 4 to 49% across three different studies.
  • Safety and efficacy clinical trials for Rapaflo were always conducted in the presence of food intake.
  • Patients should be instructed to take silodosin with a meal to reduce risk of adverse events.

Is Rapaflo safe to use while pregnant or breastfeeding?

Rapaflo is not indicated for use in females, and therefore has not been tested in pregnant or lactating women.


Rapaflo (silodosin) is an alpha-adrenergic blocker used to improve urination in men with benign prostatic hyperplasia (enlarged prostate). Side effects of Rapaflo include dizziness, weakness, headache, sleep problems (insomnia), diarrhea, stomach pain, decreased amount of semen released during sex, abnormal ejaculation, runny or stuffy nose, or sore throat.

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Medically Reviewed on 3/11/2021
All sections courtesy of the U.S. Food and Drug Administration