Effect of Fiduxosin, an Antagonist Selective for α1A- and α1D-Adrenoceptors, on Intraurethral and Arterial Pressure Responses in Conscious Dogs

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Abstract
Fiduxosin is an alpha(1)-adrenoceptor antagonist with higher affinity for alpha(1A)-adrenoceptors and for alpha(1D)-adrenoceptors than for alpha(1B)-adrenoceptors. Our hypothesis is that such a compound with higher affinity for subtypes implicated in the control of lower urinary tract function and lower affinity for a subtype implicated in the control of arterial pressure could result in a superior clinical profile for the treatment of lower urinary tract symptoms suggestive of benign prostatic obstruction. The purpose of this study was to evaluate the potency and selectivity of fiduxosin for effects on prostatic intraurethral pressure (IUP) versus mean arterial pressure (MAP) relative to current clinical standards, terazosin and tamsulosin, in conscious dogs. Phenylephrine (PE)-induced increases in IUP and MAP were determined before and at various time points after an oral dose of each antagonist. Hypotensive potency was also determined. All three antagonists caused dose- and time-dependent blockade of the IUP and MAP pressor effects of PE. The IUP ED(50) values of fiduxosin, tamsulosin, and terazosin were 0.24, 0.004, and 0.23 mg/kg p.o., respectively. The corresponding MAP ED(50) values were 1.79, 0.006, and 0.09 mg/kg p.o. The rank order of IUP selectivity (ratio) was fiduxosin (7.5-fold), tamsulosin (1.5-fold), and terazosin (0.4 = 2.5-fold MAP-selective). Tamsulosin and terazosin caused dose-dependent hypotension, whereas no change in arterial pressure was seen after fiduxosin. These data, illustrating a superior selectivity profile of fiduxosin, are consistent with our hypothesis.