Istin

Istin is a brand of amlodipine, a long-acting dihydropyridine calcium channel blocker widely used in the UK for the treatment of hypertension (high blood pressure) and stable angina pectoris (chest pain due to reduced blood flow to the heart). It is one of the most commonly prescribed antihypertensive medicines in the UK and has an extensive evidence base spanning decades of clinical use.

How Amlodipine Works

Amlodipine blocks L-type calcium channels in vascular smooth muscle and cardiac muscle cells. In blood vessels, this causes vasodilation and reduces peripheral vascular resistance, lowering blood pressure. In the coronary arteries, vasodilation improves blood flow to the heart muscle, relieving angina. Amlodipine has a very long half-life (35–50 hours), enabling reliable once-daily dosing and a smooth, sustained blood pressure reduction without the peak-and-trough effect seen with shorter-acting agents.

Cardiovascular Outcomes

Major clinical trials including ASCOT-BPLA have demonstrated that amlodipine reduces the risk of stroke, myocardial infarction, and cardiovascular death in hypertensive patients. It is recommended by NICE as a first-line treatment for hypertension, particularly in patients over 55 and in patients of Afro-Caribbean origin.

How to Take Istin

Take one Istin tablet once daily at the same time each day. It can be taken with or without food. Swallow the tablet whole with water. The effect of amlodipine on blood pressure is gradual and reaches its maximum over 7–14 days, so do not expect an immediate large drop in blood pressure when starting.

Dose Adjustment

Treatment usually begins at 5 mg once daily. If blood pressure or angina is not adequately controlled after two to four weeks, the dose may be increased to 10 mg once daily, which is the maximum recommended dose. Do not stop amlodipine suddenly, as this can cause a rebound increase in blood pressure or worsening of angina.

Istin (amlodipine) tablets are available in 5 mg and 10 mg strengths. Take once daily. The maximum dose is 10 mg once daily. Dose reduction to 2.5 mg may be considered in patients with hepatic impairment or frail elderly patients. Several combination tablets containing amlodipine with other antihypertensives (e.g. amlodipine + valsartan, amlodipine + perindopril) are also available for patients requiring combination therapy.

Common Side Effects

Ankle oedema (fluid retention causing swelling of the feet and ankles) is the most frequently reported side effect of amlodipine, affecting up to 10% of patients. It is more common at higher doses. It occurs because vasodilation increases fluid leak from capillaries, rather than from fluid retention by the kidneys. This distinguishes it from heart failure-related oedema and means it usually does not respond well to diuretics. Reducing the dose or switching to a different antihypertensive may be necessary if oedema is troublesome.

Other common side effects include flushing, headache, palpitations, and dizziness, particularly at the start of treatment or after a dose increase. These often improve over time.

Amlodipine should be used with caution in patients with severe hepatic impairment (reduced clearance means dose adjustment is required) and in patients with severely impaired left ventricular function. It is not recommended in cardiogenic shock. Grapefruit juice should be avoided, as it can increase amlodipine plasma concentrations and enhance hypotensive and side effects. Monitor patients for excessive peripheral vasodilation when initiating therapy.

Istin is contraindicated in patients with known hypersensitivity to amlodipine, other dihydropyridines, or any excipient, and in patients with severe hypotension or cardiogenic shock. Not recommended during breastfeeding. Use in pregnancy should be avoided unless clearly necessary.