Laboratory scienceComparative effect of alfuzosin and tamsulosin on the contractile response of isolated rabbit prostatic and iris dilator smooth muscles Possible model for intraoperative floppy-iris syndromePalea, Stefano PhD; Chang, David F. MD∗; Rekik, Moez PhD; Regnier, Alain VD; Lluel, Philippe PhD Author Information From UROsphere (Palea, Rekik, Lluel), Faculté des Sciences Pharmaceutiques, and the Department of Clinical Sciences (Regnier), Ecole Nationale Vétérinaire de Toulouse, Toulouse, France; and a private practice (Chang), Los Altos, California, USA ∗Corresponding author: David F. Chang, MD, 762 Altos Oaks Drive, Suite 1, Los Altos, California 94024, USA. E-mail: [email protected] Accepted for publication October 31, 2007. No author has a financial or proprietary interest in any material or method mentioned. Supported by Sanofi-Aventis, Paris, France. The staff of the National Veterinary School of Toulouse provided technical assistance in dissecting rabbit iris dilator muscles. SymbolFirst author:Symbol: No Caption available.Stefano Palea, PhD From UROsphere, Faculté des Sciences Pharmaceutiques, Toulouse, France Journal of Cataract & Refractive Surgery 34(3):p 489-496, March 2008. | DOI: 10.1016/j.jcrs.2007.10.045 Buy Metrics Abstract PURPOSE: To compare the pharmacologic properties of tamsulosin and alfuzosin in isolated prostatic and iris dilator smooth muscle from pigmented rabbits. SETTING: UROsphere Laboratories, Université Paul Sabatier, Toulouse, France. METHODS: Prostatic and iris dilator smooth muscle strips were placed in organ baths. A concentration-response curve to phenylephrine was compared before and after incubation with tamsulosin or alfuzosin. RESULTS: Both drugs were approximately 30 times less potent in iris dilator than prostatic smooth muscle. In the iris, tamsulosin acted as a competitive antagonist starting at the 0.03 μM concentration (pA2 = 7.96). This is in the same range as the maximum plasma concentration after a 0.4 mg dose of tamsulosin in humans (0.025 μM). The antagonistic effect of alfuzosin in the iris was weaker (calculated mean pA2 value of 5.63 ± 0.19). Concentrations with an equipotent antagonistic effect on rabbit iris dilator muscle (3.0 and 10.0 μM) were approximately 100 to 300 times higher than the maximum plasma concentrations after a 10.0 mg dose of alfuzosin in humans (0.032 μM). CONCLUSIONS: Tamsulosin was more effective than alfuzosin at blocking adrenergic contraction of the iris dilator muscle in pigmented rabbits. Both drugs were less potent in the iris than in the prostate, which suggests that an additional iris receptor could be involved. If valid in humans, our results suggest that attainable plasma concentrations of tamsulosin are able to antagonize iris dilator smooth muscle contraction, whereas those of alfuzosin are not. This could explain the higher frequency of intraoperative floppy-iris syndrome in patients treated with tamsulosin than with alfuzosin. © 2008 by Lippincott Williams & Wilkins, Inc.
