Nitroglycerine Tablets

Mechanism

Nitroglycerine forms free radical nitric oxide (NO) which activates guanylate cyclase, resulting in an increase of guanosine 3'5' monophosphate (cyclic GMP) in smooth muscle and other tissues. These events lead to dephosphorylation of myosin light chains, which regulate the contractile state in smooth muscle and result in vasodilatation. It works by relaxing the blood vessels which decreases the oxygen demand of the heart and reduces its workload, thereby preventing/treating attacks of angina (chest pain).

Pharmacokinetics

• Absorption: Rapid oral and sublingual absorption
• Distribution: Widely distributed, high affinity for vascular tissues
• Metabolism: Extensive hepatic metabolism via nitrate reductases
• Elimination: Renal excretion of metabolites
• Half-life: 1–4 minutes (very short, rapid onset)

Side Effects

• Headache (common)
• Dizziness
• Hypotension
• Flushing
• Reflex tachycardia

Contraindication

• Severe hypotension
• Concomitant use with PDE5 inhibitors
• Increased intracranial pressure
• Severe anemia

Interaction

• PDE5 inhibitors (sildenafil, tadalafil, vardenafil) — risk of severe hypotension
• Antihypertensives — additive blood pressure lowering
• Alcohol — enhances vasodilatory effects
• Ergot alkaloids — may reduce anti-anginal efficacy

Warning and Precautions

• Monitor blood pressure during therapy
• Use cautiously in patients with hypovolemia
• May cause tolerance with prolonged use — follow dosing schedule