Olmesartan

• Hypertension in adults and children 6 years and older
• Alternative to ACE inhibitors in patients with cough
• Component of combination antihypertensive therapy

Olmesartan is an angiotensin II receptor blocker (ARB) used for the treatment of hypertension. By selectively blocking the AT1 receptor, it prevents the cardiovascular effects of angiotensin II while avoiding the cough that commonly occurs with ACE inhibitors, making it an important option for patients requiring renin-angiotensin-aldosterone system blockade.

Mechanism of Action

Olmesartan medoxomil is a prodrug that is rapidly converted to the active form, olmesartan, during absorption from the gastrointestinal tract. Olmesartan selectively blocks the binding of angiotensin II to the AT1 receptor in vascular smooth muscle and other tissues. This blockade prevents angiotensin II from causing vasoconstriction, aldosterone release, and sympathetic activation. Unlike ACE inhibitors, ARBs do not affect bradykinin metabolism, which explains the lower incidence of cough with this class of medications.

The AT2 receptor, which may have protective cardiovascular effects, is left unblocked by olmesartan. The increased circulating angiotensin II that results from AT1 blockade can stimulate AT2 receptors, potentially contributing to cardiovascular benefits.

Available Formulations

Olmesartan medoxomil (Benicar) is available as oral tablets in 5 mg, 20 mg, and 40 mg strengths. It is also available in fixed-dose combinations with hydrochlorothiazide (Benicar HCT), with amlodipine (Azor), and in a triple combination with both amlodipine and hydrochlorothiazide (Tribenzor) for patients requiring more intensive blood pressure control.

FDA-Approved Indications

Olmesartan is FDA-approved for the treatment of hypertension in adults and pediatric patients 6 years of age and older, either alone or in combination with other antihypertensive agents. While not specifically indicated for heart failure or diabetic nephropathy (unlike some other ARBs), it provides effective blood pressure control that is fundamental to cardiovascular protection.

Dosing Guidelines

For adults with hypertension, the recommended starting dose is 20 mg once daily when used as monotherapy. The dose may be increased to 40 mg once daily after 2 weeks if further blood pressure reduction is needed. For patients with possible volume depletion (those on diuretics or with reduced oral intake), consider starting at a lower dose. For pediatric patients 6 years and older, dosing is weight-based: 10 mg once daily for those weighing 20-35 kg, and 20 mg once daily for those weighing more than 35 kg.

Sprue-Like Enteropathy

A unique safety concern with olmesartan is the development of severe, chronic diarrhea with substantial weight loss, termed sprue-like enteropathy. This condition may develop months to years after starting therapy and is characterized by intestinal villous atrophy. Symptoms typically resolve after discontinuing olmesartan. If severe diarrhea develops during treatment, consider this diagnosis and discontinue the medication if no other etiology is identified.

Important Safety Considerations

Olmesartan carries a boxed warning for fetal toxicity; it should be discontinued immediately when pregnancy is detected. Hypotension may occur, especially in volume-depleted patients. Hyperkalemia can develop, particularly in patients with renal impairment or those taking potassium supplements. Renal function should be monitored in patients with renal artery stenosis, severe heart failure, or volume depletion.

Drug Interactions

NSAIDs may reduce the antihypertensive effect and increase renal impairment risk. Potassium supplements and potassium-sparing diuretics increase hyperkalemia risk. Avoid dual blockade of the renin-angiotensin system with ACE inhibitors or aliskiren (especially in diabetic patients) due to increased adverse effects. Lithium levels should be monitored if used concomitantly.

Judging Whether Olmesartan Is Working

A blood pressure medication is judged on readings taken properly, and most apparent failures of an ARB turn out to be measurement problems rather than pharmacology. Office readings taken immediately after walking in, with the arm unsupported or a cuff too small for the arm, overstate pressure by enough to prompt an unnecessary dose increase. A week of home readings, twice in the morning and twice in the evening, taken after five minutes seated with the arm supported at heart level, gives a far better estimate. It also separates the two patterns a single office visit cannot: white coat elevation, where office readings are high and home readings normal, and masked hypertension, where the reverse is true and the risk is underestimated. Our articles on home blood pressure monitoring the right way and on white coat vs masked hypertension describe both patterns.

When the readings are reliable and hypertension (high blood pressure) is still not controlled, the usual explanations are dietary sodium, alcohol, NSAIDs, decongestants, untreated sleep apnea, and missed doses, in roughly that order of frequency. Sodium matters particularly for this class, because renin-angiotensin blockade works less well against a high-salt diet; our article on hidden sodium and blood pressure covers where most of it actually comes from. Adding a second agent from a different class generally lowers pressure more than doubling a single one, which is why the fixed-dose combinations with a thiazide such as hydrochlorothiazide or with amlodipine exist at all.

Olmesartan Compared With the Other ARBs

The angiotensin receptor blockers are close to one another in blood pressure effect, and the practical differences lie in the evidence supporting indications beyond hypertension, in duration of action, and in cost. Losartan is the least expensive and the shortest-acting, sometimes needing twice-daily dosing to hold pressure overnight, and it lowers uric acid slightly, which occasionally matters in a patient who also has gout. Valsartan and candesartan carry heart failure indications that olmesartan does not. Irbesartan and losartan carry the older diabetic kidney disease evidence. Olmesartan's strength is a dependable twenty-four-hour effect from a single daily dose; what it lacks is outcome evidence outside blood pressure, which is why a patient with heart failure or albuminuric kidney disease is often placed on an ARB that was studied in that setting instead.

The other consideration specific to this agent is the enteropathy described above. It is rare, but it is worth keeping in mind for a patient who has taken olmesartan for a year or longer and develops unexplained watery diarrhea and weight loss, because a malabsorption workup can otherwise run a long way, including a celiac evaluation that comes back negative, before the medication is suspected. Kidney function and potassium are checked after starting and after each dose increase, as with any renin-angiotensin blocker, and our article on chronic kidney disease and eGFR explained covers how those numbers are interpreted over time. The MedlinePlus olmesartan monograph lists what patients should report, and the NHLBI guidance on treating high blood pressure sets out where medication fits alongside diet and activity.

Special Populations

No dosage adjustment is needed for mild to moderate hepatic impairment or for renal impairment, although closer monitoring may be warranted. Use with caution in patients with bilateral renal artery stenosis. Olmesartan is contraindicated during pregnancy. Safety and efficacy have been established in pediatric patients 6 years of age and older for hypertension.

Learn more at MedlinePlus