Losartan and its primary metabolite block the angiotensin receptor found in many tissues primarily in vascular smooth muscle. Angiotensin formed by the action of angiotensin converting enzyme ACE is a powerful chemical that causes blood vessel narrowing vasoconstriction which can lead to elevated blood pressure hypertension.

Losartan may be given with or without food. Losartan is metabolized in the liver by cytochrome P450 enzymes to an active metabolite that is responsible for most of the drug activity. Reduction in dose by 50 is suggested in patients with impaired liver function.

In studies of over 4000 patients including 1200 treated for over 6 months and 800 for over 1 year the overall incidence of side effects was similar to placebo. Losartan is generally well tolerated. Side effects reported included diarrhea muscle cramps dizziness insomnia and nasal congestion.

Losartan must be used with caution in patients who are volume depleted due to excessive decreases in blood pressure after use. Losartan may compromise kidney function in patients dependent on angiotensin activity to maintain kidney blood flow similar to ACE inhibitors. This is sometimes seen in diabetic patients with some degree of kidney impairment as well as in patients with narrowings in one of the main arteries supplying one kidney.

No significant drug interactions have been found in any studies but inhibitors of cytochrome P450 such as ketoconazole Nizoral have been shown in lab studies to inhibit the formation of the active drug metabolite. Therefore caution should be used when adding losartan to a patient taking Nizoral as reduced activity of losartan would be expected.

Losartans safety and efficacy in children has not been established.

Losartan is indicated for the treatment of hypertension. It may be used alone or in combination with other agents. It has less of an effect in black patients similar to ACE inhibitors such as captopril Capoten enalapril Vasotec and lisinopril Zestril.

Tablets should be stored at room temperature in a tightly closed light resistant container.