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alpha1-adrenoceptor selectivity: the North American experience
1Urodoc, Herne Bay, Kent, UK. urodoc@dial.pipex.com
European Urology
|July 7, 1999
Summary
The 0.4 mg dose of tamsulosin is suboptimal for blocking alpha-adrenergic receptors, offering less efficacy than 0.8 mg. This dose is equivalent to 1 mg of doxazosin, with no evidence of prostate selectivity observed for tamsulosin.
Area of Science:
- Pharmacology
- Urology
Background:
- Recent studies suggest tamsulosin's response may be dose-dependent and suboptimal at 0.4 mg.
- Investigating the dose-response relationship of alpha-blockers is crucial for optimizing treatment.
Purpose of the Study:
- To determine pharmacologically equivalent alpha-blocking doses of doxazosin and tamsulosin.
- To further evaluate the concepts of 'uroselectivity' and 'prostate selectivity' in a clinical context.
Main Methods:
- Controlled, crossover studies in healthy male volunteers.
- Measurement of phenylephrine (PE)-induced urethral and vascular responses.
- Correlation of drug effects with plasma concentrations and in vitro receptor binding data.
Main Results:
- Doxazosin demonstrated effective blockade of PE-induced responses from 1-16 mg without organ selectivity.
- Tamsulosin's blockade efficacy was time-dependent.
- 0.4 mg tamsulosin showed significantly less blockade than 0.8 mg tamsulosin or 1 mg doxazosin.
Conclusions:
- No evidence of prostate selectivity for tamsulosin was found.
- 0.4 mg tamsulosin is an under-dosed regimen, equivalent to 1 mg of doxazosin.
- Future studies should assess a range of doses including the ED50 for benefit-risk analysis.