Glyceryl Trinitrate [GTN], Isosorbide Dinitrate, Isosorbide Mononitrate
Issues for Surgery
For treatment of angina – exacerbation of symptoms if omitted.
Risk of tachycardia and hypotension if continued.
Advice in the Perioperative period
Elective and Emergency Surgery
Continue – monitor heart rate and blood pressure (BP).
Restart post-operatively as soon as next dose is due.
Interaction(s) with Common Anaesthetic Agents
Nitrates can increase the risk of hypotension when used concomitantly with inhalational or intravenous anaesthetics1, 2.
Isosorbide dinitrate can act as a physiological antagonist to noradrenaline / norepinephrine3.
Interaction(s) with other Common Medicines used in the Perioperative Period
Nitrates can increase the risk of hypotension when used concomitantly with the antiemetics droperidol and prochlorperazine1, 2, 3.
Many patients on long-acting or transdermal nitrates rapidly develop tolerance (with reduced therapeutic effects). Reduction of blood-nitrate concentrations to low levels for 4-12 hours each day usually maintains effectiveness. If tolerance is suspected during use of transdermal patches, they should be left off for 8-12 hours (usually overnight)1, 4.
For patients on modified-release (MR) isosorbide dinitrate or standard release isosorbide mononitrate (ISMN), the second of the two daily doses should be given no later than 8 hours after the morning dose. MR preparations of ISMN should only be given once daily, and used in this way do not produce tolerance1.
Ensure that nitrate-based medicines are prescribed accurately and appropriately.