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Angina Treatment (Organic Nitrates (Drugs:
Glyceryl trinitrate (GTN),…
Angina Treatment
Organic Nitrates
Drugs:
- Glyceryl trinitrate (GTN), Isosorbide mononitrate, Nitric oxide
Mechanism of action:
- Organic nitrates react with sulfhydryl groups in endothelial cells to release nitric oxide
- Nitric oxide diffuses into smooth muscle cells causing smooth muscle relaxation
Clinical effects
Low doses: Venorelaxation with little effect on arterial resistance thus increasing coronary perfusion and decreasing cardiac workload & O2 demand
High doses: Vasodilation further increasing coronary perfusion and decreasing cardiac workload & O2 demand
Clinical use:
- Treatment & prevention of angina attacks
Dosage forms:
Sublingual GTN tablets & sprays: Rapidly absorbed with an onset of 30 seconds, lasts for 30 minutes and not destroyed by first pass metabolism
Oral isosorbide mononitrate tablets: Taken once a day for prevention of angina attacks
Transdermal GTN patches: Contains a drug reservoir that is slowly released and used for the prevention of angina attacks. Should be used for no longer than 12 hours daily
IV GTN injections: Used for treatment of acute angina attacks unresponsive to sublingual tablets or sprays
Adverse effects:
- Headache, flushing, reflex tachycardia, palpitations, postural hypotension, fainting, peripheral oedema
Drug interactions:
- PDE5 inhibitors for erectile dysfunction will increase organic nitrate effects which can lead to severe hypotension
Beta-blockers
Drugs:
- Metoprolol, Atenolol
(Cardioselective)
Mechanism of action:
- Inhibits beta-receptors thus opposing SNS outflow to the heart
Clinical effects:
- Decreased HR, AV conduction & contractility resulting in increased coronary perfusion and decreased cardiac workload and O2 demand
Clinical use:
- Prevention of angina attacks (1st line prevention)
- Also tachyarrhythmias, hypertension, heart failure
Adverse effects:
- Bradycardia, fatigue, cold extremities, bronchoconstriction, nightmares, hypoglycaemia
Calcium channel blockers
Verapamil:
- Cardioselective
- Decreases HR & contractility thus decreasing cardiac workload & O2 demand
Adverse effects: - Bradycardia, constipation
Diltiazem:
- Non-selective
- Decreases HR & contractility and causes vasodilation thus increasing coronary perfusion and decreasing cardiac workload & O2 demand
Adverse effects:
- A combination of cardioselective & vascular smooth muscle selective
Amlodipine, Felodipine, Lercandipine, Nifedipine, Nimodipine:
- Vascular smooth muscle selective
- Causes vasodilation thus increasing coronary perfusion and decreasing afterload, cardiac work load & O2 demand
Adverse effects: - Headache, flushing, peripheral oedema, reflex tachycardia
Clinical use:
- Prevention of angina attacks if beta-blockers are contraindicated
- Also hypertension, SVT, atrial flutter, AF
Nicorandil
Mechanism of action:
- K+ channel agonist thus hyperpolarising vascular smooth muscle cells and causing relaxation and vasodilation
- Also stimulates the release of nitric oxide further causing vasodilation
Clinical effects:
- Vasodilation --> increased coronary perfusion and decreased cardiac workload & O2 demand
Clinical use:
- Prevention of angina attacks if beta-blockers & Ca2+ channel blockers are contraindicated
Adverse effects:
- Headache, dizziness, flushing, ulcers & fistulae (only heals after stopping nicorandil)
Ivabradine
Mechanism of action:
- Blocks hyperpolarisation-activated Na+ channels in the SA node thus inhibiting a current regulating the intervals between depolarisations
Clinical effects:
- Reduced HR without affecting BP, conduction or contractility
- Lowers cardiac workload and O2 demand
Clinical use:
- Prevention of angina attacks
-
Perhexiline
Mechanism of action:
- Inhibits mitochondrial enzyme carnitine palmitoyltransferase which results in an inhibition of mitochondrial uptake of long-chain fatty acids
- This shifts the metabolic process towards more energy efficient pathways such as glucose
Clinical effects:
- More oxygen & energy available for the heart to use
Clinical use:
- Last line treatment for the prevention of angina
Adverse effects:
- Narrow therapeutic window & high pharmacokinetic variability
- Toxic effects such as peripheral neuropathy & hepatic damage