Angiotensin receptor blockers or Angiotensin receptor antagonists are also known as ‘ARBs’, ‘AT1 receptor blockers’ or ‘sartans’. ARBs have similar hypotensive effects that of ACE inhibitors. These drugs mainly use in patient with hypertension or following myocardial infarction. It case vasorelaxation. ARBs are preferred than other antihypertensive agents in diabetic patient because these drugs reduce the risk of diabetic nephropathy. It is less expensive than ACE inhibitors.
ARBS are also available with other diuretics to enhance antihypertensive effects like hydrochlorothiazide and amlodipine.
| GENERIC NAME | BRAND NAME |
| Losartan | Cozar |
| Valsartan | Diovan |
| Candesartan | Atacand |
| Irbesartan | Avapro |
| Olmesartan | Benicar |
| Telmisartan | Micardis |
MECHANISM OF ACTION
Renin is an enzyme released from the kidney in response to reduced renal arterial pressure, sympathetic neural stimulation or increased sodium concentration in DCT of nephron. Renin acts upon on Angiotensinogen, an enzyme released from the liver and convert it into angiotensin I. Angiotensin I is then converted into Angiotensin II with the help of Angiotensin converting enzyme. Angio II acts as ligand to AT1 receptor and promote its biological action. Angio II receptor (AT1 receptor) are predominantly located in vascular smooth muscles.
Angiotensin receptor blockers act by selectively blocking the AT1 receptor. This blocking action inhibits the major effects of Angio II i.e. vasoconstrictor and sodium retaining activity. ARBs also inhibit aldosterone release which is also stimulated by Angio II
PHARMACOKINETICS
ARBs are given orally and well tolerated. Candesartan has high AT1 receptor affinity and losartan has lesser than all ARBs. Protein binding of all ARBs is high > 98%. The major route of elimination of ARBs is hepatic clearance which is 60-90% while some clearance also occurs via kidney i.e. 12-35%. Losartan, candesartan and olmesartan has active metabolites which are more potent than its original form.
INDICATIONS
- Hypertension
- Diabetic nephropathy (only irbesartan, losartan)
- Stroke prophylaxis (only losartan)
- Heart failure (valsartan)
CONTRAINDICATIONS
- Non diabetic renal disease
- Pregnancy
SIDE EFFECTS & ADVERSE EFFECTS
- First dose hypotension
- Functional renal failure (patient with renal arterial stenosis)
- Fetal renal toxicity
- Angio oedema (less common)
- Oliguria
- Progressive azotemia
- Hyperkalemia (patient with renal disease)
- Anaphylaxis
- Abnormal hepatic function
- Neutropenia
- Leukopenia
DRUG INTERACTION
- Potassium supplements or potassium rich diets can cause cardiac arrhythmias and hyperkalemia when given with ARBs
- ARBS increase the toxicity of Lithium when given concurrently
- ARBs when given with insulins can enhance the hypoglycemic effects
- K-sparing diuretics can cause hyperkalemia when given with ARBs
- Aspirin and NSAIDS may reduce the hypotensive effects of ARBs
- Beta blockers enhance the hypotensive effects of ARBs when given concurrently
NURSING INTERVENTION
- Avoid given first dose at night due to increase hypotensive risk.
- Monitor blood pressure and pulse frequently.
- Enquire the complete health history of patient specially any renal disease
- Check patient s/s for angioedema.
- Monitor electrolytes specially sodium and potassium levels, uric acid levels and CBC
PATIENT EDUCATION
- Avoid potassium rich diet and supplements when taken ARBs
- Do not breast feed when taken ARBs
- Inform patients the s/s of hypotension.
- Inform HP about pregnancy if conceived
- Take plenty of water to avoid dehydration