Telmisartan

Telmisartan is a long acting angiotensin receptor blocker with the longest half life in its class and mainly biliary elimination. It treats hypertension and reduces cardiovascular events in high risk patients who cannot take an angiotensin converting enzyme inhibitor. It also has partial agonist activity at PPAR gamma receptors, of uncertain clinical importance.

Classification. Angiotensin receptor blocker (AT1); non prodrug.

Mechanism. Blocks the AT1 receptor with high affinity and slow dissociation.

Pharmacodynamics. Onset within 3 hours; full effect over 4 weeks; duration over 24 hours (blood pressure control through the missed dose period).

Pharmacokinetics. Bioavailability 42 to 58% (dose dependent); food lowers exposure slightly. Half life about 24 hours. Conjugated in the liver and excreted in faeces (over 97%).

Hypertension, adult.

• Start 40 mg once daily (20 mg in mild hepatic impairment, older or frail patients).

• Increase after 4 weeks to 80 mg once daily.

• Maximum 80 mg daily.

Cardiovascular risk reduction in patients unable to take an angiotensin converting enzyme inhibitor (aged 55 or over with established vascular disease or high risk diabetes), adult. 80 mg once daily; use 40 mg if low blood pressure.

Children. Not established.

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

Warnings. Hypotension, hyperkalaemia and kidney function decline. Angioedema is rare. Sick day rule: hold during dehydrating illness. In hepatic impairment, accumulation raises exposure. Not for combination with an angiotensin converting enzyme inhibitor in routine practice.

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

Interactions. Digoxin: levels rise about 20%; monitor. Potassium supplements, potassium sparing diuretics, trimethoprim: hyperkalaemia. Non steroidal anti-inflammatory drugs: kidney injury. Lithium: toxicity. Ramipril: raised ramipril exposure.

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, but monitor.

• Kidney impairment: no adjustment because elimination is biliary; monitor creatinine and potassium; not dialysable.

• Liver impairment: mild to moderate: maximum 40 mg daily; severe: avoid.

Formulations. Tablets 20, 40, 80 mg; combinations with hydrochlorothiazide or amlodipine.

Administration. Oral once daily, with or without food; keep tablets in the blister until use because they are hygroscopic.

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. Digoxin levels where used.

Stopping. Stop for pregnancy, angioedema, or creatinine rise over 30% or potassium over 6.0 mmol/L.

Common prescribing errors. Using it in biliary obstruction; use in pregnancy; omitting digoxin level checks; exceeding 40 mg in liver impairment.