Abstract
Tasosartan is a long-acting angiotensin II (AngII) receptor blocker. Its long duration of action has been attributed to its active metabolite enoltasosartan. In this study we evaluated the relative contribution of tasosartan and enoltasosartan to the overall pharmacological effect of tasosartan. AngII receptor blockade effect of single doses of tasosartan (100 mg p.o. and 50 mg i.v) and enoltasosartan (2.5 mg i.v.) were compared in 12 healthy subjects in a randomized, double blind, three-period crossover study using two approaches: the in vivo blood pressure response to exogenous AngII and an ex vivo AngII radioreceptor assay. Tasosartan induced a rapid and sustained blockade of AngII subtype-1 (AT1) receptors. In vivo, tasosartan (p.o. or i.v.) blocked by 80% AT1 receptors 1 to 2 h after drug administration and still had a 40% effect at 32 h. In vitro, the blockade was estimated to be 90% at 2 h and 20% at 32 h. In contrast, the blockade induced by enoltasosartan was markedly delayed and hardly reached 60 to 70% despite the i.v. administration and high plasma levels.In vitro, the AT1 antagonistic effect of enoltasosartan was markedly influenced by the presence of plasma proteins, leading to a decrease in its affinity for the receptor and a slower receptor association rate. The early effect of tasosartan is due mainly to tasosartan itself with little if any contribution of enoltasosartan. The antagonistic effect of enoltasosartan appears later. The delayed in vivo blockade effect observed for enoltasosartan appears to be due to a high and tight protein binding and a slow dissociation process from the carrier.
Footnotes
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Send reprint requests to: Dr. Marc Maillard, Division of Hypertension, Lausanne University Hospital, Hôpital Nestlé, Av. Pierre Decker, CH-1011 Lausanne-CHUV, Switzerland. E-mail:Marc.Maillard{at}chuv.hospvd.ch
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↵1 This study was supported by a research grant from Wyeth-Ayerst Research, Radnor, PA.
- Abbreviations:
- AngII
- angiotensin II
- AT1
- angiotensin II subtype-1
- BP
- blood pressure
- PD
- pharmacodynamic
- SBP
- sytolic blood pressure
- Cmax
- peak plasma drug concentration
- Tmax
- time toCmax
- DBP
- diastolic blood pressure
- Emax
- theoretical maximal inhibitory effect of an antagonist
- PK
- pharmacokinetic
- Received March 22, 2000.
- Accepted July 7, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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