THE CONTEXT
Anti-anginal therapy seeks symptom control with a simple regimen that avoids side-effects. Nitrates reduce oxygen demand and increase oxygen supply through vasodilatation.
Starting and escalating treatment
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Five main drug groups are used, with little evidence that one group is more effective than another.
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Conventional initial treatment consists of sublingual glyceryl trinitrate (GTN) and a β-blocker.
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A calcium channel antagonist or a long-acting nitrate can be added if needed.
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If two drugs do not produce an acceptable symptomatic response, further drug classes offer modest additional benefit and coronary revascularisation should be considered.
How nitrates relieve angina
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Nitrates act directly on vascular smooth muscle, causing venous and arteriolar dilatation.
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Reduced preload and afterload lower myocardial oxygen demand.
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Coronary vasodilatation increases myocardial oxygen supply.
GTN for acute relief and longer action
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Sublingual GTN is used for acute attacks and relieves symptoms in 2–3 minutes. It can also be taken before exercise to prevent symptoms.
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Sublingual preparations include a metered-dose aerosol delivering 400 μg per spray and tablets containing 300 or 500 μg.
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Sublingual GTN has a short duration of action. Adverse effects include headache, symptomatic hypotension and, rarely, syncope.
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Longer effects can be obtained with a transcutaneous patch delivering 5–10 mg daily or a slow-release buccal tablet of 1–5 mg four times daily.
Oral nitrates and tolerance
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Oral options include isosorbide dinitrate 10–20 mg three times daily and isosorbide mononitrate 20–60 mg once or twice daily.
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These preparations can be given by mouth, unlike GTN, which undergoes extensive liver metabolism.
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Headache is common with oral nitrates but tends to diminish with continued treatment.
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Continuous nitrate therapy can cause pharmacological tolerance. A 6- to 8-hour nitrate-free interval can prevent this, preferably at night when the patient is inactive.
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If nocturnal angina predominates, long-acting nitrates can be taken at the end of the day.