What is the equivalent dosing of Flomax (tamsulosin) when converting from Rapaflow (silodosin)?

From the Guidelines

To convert from Rapaflow (silodosin) to Flomax (tamsulosin), the equivalent dosing is not directly established in the provided evidence, but based on the information given, a reasonable approach would be to start with 0.4 mg of Flomax, as this is a common and effective dose for treating LUTS secondary to BPH, as noted in the 2003 AUA guideline 1. When considering the conversion, it's essential to understand that both silodosin and tamsulosin are alpha-1 blockers, but they have different pharmacological profiles. The provided evidence does not offer a direct comparison or conversion guideline between silodosin and tamsulosin. However, it does suggest that tamsulosin, at a dose of 0.4 mg to 0.8 mg, is effective in relieving symptoms of BPH, with the higher dose potentially offering greater improvement, as indicated by the dose-dependent efficacy of alpha blockers like doxazosin and terazosin 1. Key points to consider when switching from Rapaflow to Flomax include:

• The mechanism of action is similar, as both drugs relax smooth muscles in the prostate and bladder neck to improve urinary flow.
• The recommended starting dose of Flomax is 0.4 mg once daily, which should be taken approximately 30 minutes after the same meal each day to minimize gastrointestinal side effects.
• Patients should be advised to swallow the capsule whole with water and not to crush or chew it.
• Common side effects include dizziness, headache, and orthostatic hypotension, particularly with the first dose, so patients should be cautious when starting the medication.
• If a dose is missed, patients should take it as soon as remembered on the same day but should not double the dose the next day. Given the lack of direct conversion data and considering the goal of minimizing morbidity, mortality, and improving quality of life, starting with a standard and effective dose of Flomax (0.4 mg) and adjusting as necessary based on patient response and tolerance is a prudent approach.

From the Research

Equivalent Dosing of Flomax (Tamsulosin) when Converting from Rapaflow (Silodosin)

• The equivalent dosing of Flomax (tamsulosin) when converting from Rapaflow (silodosin) can be determined by comparing the efficacy of the two drugs in treating lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH) 2.
• A study comparing the efficacy of silodosin 4 mg twice daily to tamsulosin 0.2 mg once daily found that silodosin was non-inferior to tamsulosin in treating patients with LUTS associated with BPH 2.
• Another study found that silodosin 8 mg once daily was more efficacious than tamsulosin 0.4 mg once daily in improving IPSS, QOL, and Qmax in patients with LUTS due to BPH 3.
• Based on these studies, the equivalent dosing of Flomax (tamsulosin) when converting from Rapaflow (silodosin) can be estimated as follows:
  • Silodosin 4 mg twice daily is equivalent to tamsulosin 0.2 mg once daily 2.
  • Silodosin 8 mg once daily is equivalent to tamsulosin 0.4 mg once daily 3.
• It is worth noting that the dosing of silodosin may need to be adjusted based on renal function, with a reduced dose of 4 mg once daily recommended for patients with moderate renal dysfunction 4.