Irbesartan (Avapro) for Hypertension
Irbesartan (Avapro / Sanofi Pharmaceuticals), an angiotensin receptor antagonist, approved for marketing in the USA. Along with losartan and valsartan, irbesartan offers yet another alternative in treating hypertension. Irbesartan is available as a 75 mg, 150 mg, and 300 mg tablet.
How It Works
Irbesartan (Avapro) is an angiotensin receptor antagonist. Angiotensin II acts as a vasoconstrictor. In addition to causing direct vasoconstriction, angiotensin II also stimulates the release of aldosterone. Once aldosterone is released, sodium as well as water are reabsorbed. The end result is an elevation in blood pressure. Irbesartan binds to the AT1 angiotensin II receptor. This binding prevents angiotensin II from binding to the receptor thereby blocking the vasoconstriction and the aldosterone secreting effects of angiotensin II.
Irbesartan (Avapro) is an orally active agent. This drug is rapidly absorbed with a bioavailability of 60-80%. Peak plasma levels are reached in about 2 hours. The terminal half-life of irbesartan is approximately 11-15 hours. Following oral administration, the drug is metabolized into inactive metabolites and excreted via the biliary and renal routes.
Irbesartan (Avapro): Clinical Tips
In a study conducted by McIntyre and colleagues, 12 normotensive male volunteers were enrolled. The subjects were salt depleted for 3 days before each study day. The authors tested 6 single oral doses for safety and efficacy. The doses of irbesartan of 1, 5, 10, 25, 50, and 100 mg were administered in escalating strength with a placebo randomized within the panel. The authors measured supine and standing blood pressure as well as heart rate, electrolytes, plasma renin activity and angiotensin II in order to assess the effects of irbesartan. They found that there was a dose-related decrease in blood pressure once the dose reached 10 mg and a dose-related increase in plasma renin activity and angiotensin II. The authors also noted that there was no change in heart rate.
In another study, Van den Meiracker et al studied the effects of irbesartan in 86 untreated patients with essential hypertension. Patients were randomized to one of four treatment groups: the 1 mg, 25 mg, 100 mg or placebo group on a once a day regimen. The authors found that the blood pressure of the patients in the 1 mg group did not show an appreciable change from that of the patients in the placebo group. However, there was a favorable effect seen in patients receiving the 25 mg and the 100 mg dose. In those receiving the 25 mg, the blood pressure was 7.0 mm Hg lower than those in the placebo group and for those in the 100 mg dose group, the blood pressure was 12.1 mm Hg lower than the placebo group. Interestingly, the blood pressure of those in the 100 mg dose group was maintained for 24 hours. As in the previous study, there was no change in the heart rate of those that were receiving irbesartan.
As it can be seen from the above studies, irbesartan has a favorable effect on blood pressure. At a dose that is 25 mg or greater, blood pressure was reduced as compared to placebo. Irbesartan (Avapro) may prove to be a valuable option for certain patients whose blood pressure remain unsatisfactorily controlled with other antihypertensive medications.
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