Olmesartan

Olmesartan medoxomil is a prodrug converted in the gut wall to olmesartan, an angiotensin receptor blocker. It treats hypertension. It has a distinctive rare adverse effect, sprue like enteropathy, that must be considered in patients with chronic diarrhoea and weight loss.

Classification. Angiotensin receptor blocker (AT1); prodrug.

Mechanism. Blocks the AT1 receptor, reducing vasoconstriction and aldosterone release.

Pharmacodynamics. Onset within 1 to 2 hours; full blood pressure effect over 2 to 4 weeks; duration 24 hours.

Pharmacokinetics. Bioavailability about 26%; food has no effect. Half life 13 hours. Excreted unchanged: about 40% in urine and 60% in faeces.

Hypertension, adult.

• Start 20 mg once daily (10 mg if volume depleted).

• Increase after 2 to 4 weeks to 40 mg once daily.

• Maximum 40 mg daily.

Children aged 6 to 16 years. 20 to under 35 kg: 10 mg once daily, increase to a maximum 20 mg; 35 kg and over: 20 mg once daily, maximum 40 mg. Specialist.

Contraindications. Pregnancy; bilateral renal artery stenosis; hyperkalaemia; severe hepatic impairment and biliary obstruction; hypersensitivity; aliskiren in diabetes or kidney impairment.

Warnings. Sprue like enteropathy: severe chronic diarrhoea with weight loss months to years after starting; stop the drug if no other cause is found. Hypotension, hyperkalaemia and kidney function decline. Angioedema is rare. Sick day rule: hold during dehydrating illness.

Adverse effects. Dizziness, hypotension, hyperkalaemia, creatinine rise, back pain, diarrhoea, rarely enteropathy or angioedema.

Interactions. Potassium supplements, potassium sparing diuretics, trimethoprim: hyperkalaemia. Non steroidal anti-inflammatory drugs: kidney injury. Lithium: toxicity. Colesevelam reduces absorption; separate by 4 hours.

Special groups.

• Pregnancy: contraindicated; stop when pregnancy is confirmed.

• Breastfeeding: avoid; no data.

• Patients of African ancestry: smaller response as monotherapy; combine with a calcium channel blocker or thiazide like diuretic.

• Older adults: no adjustment; monitor.

• Kidney impairment: creatinine clearance under 20 mL/min: use with caution, maximum 20 mg daily.

• Liver impairment: moderate: start 10 mg and keep to a maximum of 20 mg daily; severe: avoid.

Formulations. Tablets 10, 20, 40 mg; combinations with amlodipine or hydrochlorothiazide.

Administration. Oral once daily, with or without food.

Baseline. Blood pressure, creatinine and eGFR, potassium, liver function, pregnancy status.

Monitoring. Creatinine and potassium 1 to 2 weeks after starting or each dose increase, then every 6 to 12 months. Accept a creatinine rise up to 30%; reduce or stop if over 30% or potassium is over 6.0 mmol/L; review contributors if potassium is over 5.5 mmol/L. Bowel habit and weight at each visit.

Stopping. Stop for pregnancy, angioedema, unexplained chronic diarrhoea with weight loss, or creatinine rise over 30% or potassium over 6.0 mmol/L.

Common prescribing errors. Missing olmesartan enteropathy in a patient with chronic diarrhoea; use in pregnancy; omitting potassium and creatinine checks; giving with colesevelam without spacing.