GLYCERINE TRINITRATE (NITROGLYCERINE)

GLYCERINE TRINITRATE (NITROGLYCERINE)

CLASSIFICATION

� Potent organic nitrate vasodilator especially of the venous system. Through relaxing the vascular smooth muscles.

� Dose related in dilation of both the arterial and venous beds.

MODE OF ACTION

GTN produces, in a dose related manner � dilation of the venous bed promoting peripheral pooling of blood, decreasing venous return to the heart and reducing left ventricular end diastolic pressure - preload � and dilation of the arterial bed reducing systemic vascular resistance (SVR) and arterial pressure - afterload. This decreased preload and afterload reduces myocardial oxygen demand and the vasodilatory effects of GTN on coronary arteries increases myocardial oxygen supply to ischaemic zones.

INDICATIONS

� Acute episodes of angina pectoris

 � Management of angina pectoris associated with or resulting from coronary insufficiency, coronary artery disease, coronary occlusion, or sub acute myocardial infarction.

� Cardiac failure

� Hypertension

PHARMOCOLOGY

Nitroglycerine is widely distributed in the body and is rapidly metabolized with a short half life of 1 - 4 minutes. It is rapidly metabolized in the liver by hepatic enzymes. Nitroglycerine is excreted mainly by the renal route, with a half life of 3 to 4 hours.

CONTRA INDICATIONS

� Known hypersensitivities

 � Severe anaemia

� Patients with early myocardial infarction

� Hypotension

 � Uncorrected hypovolemia.

PRECAUTIONS

� The use of Nitroglycerine in acute myocardial infarction or congestive heart failure requires careful clinical and/or haemodynamic monitoring.

 � Use with caution in patients with severe liver or renal disease.

 � Anticholinergic agents, tricyclic antidepressants and alcohol may potentiate the hypotensive effects

ADVERSE REACTIONS

� Headache, a result of dilation of cerebral vessels, which occurs in up to 50 % of patients at the beginning of therapy. �

 � Apprehension, restlessness

� Dizziness

� Muscle twitching

� Abdominal and retrosternal pain

� Nausea and vomiting

 � Palpations

 � Tachycardia

 � Excessive hypotension

 PROCEDURE FOR I.V. GTN.

� Remove topical nitrates and withhold oral nitrates whilst infusion in progress.

 � Record baseline H.R, B.P., E.C.G, and rhythm strip if on monitor.

� Monitor B.P./H.R with in first 5 minutes of infusion commencing, then at 15,30 and 60 minutes.

� If B.P. drops to or below 100 mmHg systolic or drops dramatically, reduce infusion by 5 mcg/min or stop it. Elevate legs to 45 degrees. Report to R.M.O

. � Consider haemaccel 100 ml boluses. Recheck B.P. in 2 minutes

. � Recommence infusion as soon as B.P. allows.

 � When patient is haemodynamically stable, monitor B.P. every 4 hours.

� If refractoriness is suspected, or tolerance develops, consider repletion of sulphahydryl drugs with Acetylcysteine (Parvolex) given simultaneously Dramatic return of nitrate sensitivity will necessitate reduction of GTN rate.

� Administer O2, as V/Q abnormalities reducing PaO2 can be provoked.

� When infusion is to be weaned.

� Establish with physician time of oral nitrates +/- topical nitrates to commence, ie before infusion is completely ceased

� Reduce infusion each hour by 1 ml unless other wise specified by R.M.O.

PRESENTATION

Glyceryl Trinitrate - 50 mg in 10 ml ampoules

DOSAGE AND ADMINISTRATION

Nitroglycerine readily migrates into many plastics. To avoid absorption, parental solution containers, should be made in glass solution bottles. Some filters absorb nitroglycerine, therefore all filters should be avoided. A conventional administration set with absorbable tubing (most frequently made of PVC), or a special administration set which will not absorb any significant amount of nitroglycerine from the infusion solution should be used.

ADULTS

VIA GEMINI PUMP (Used at W.G.H)

Mix 50 mg GTN in 500 ml 5% Dextrose (100 mcg/ml) Flush line (50 mls) Begin infusion at 5 mcg/min (3 ml/hr) 10 mcg/min 15 mcg/min 20 mcg/min (6 ml/hr) (9 ml/hr) (12 ml/hr) 30 mcg/min 40 mcg/min 50 mcg/min (18 ml/hr) (24 ml/hr) (30 ml/hr)

VIA SYRINGE PUMP Add 30 mgs GTN to 5% Dextrose to total 50 mls. Final concentration 600 mcg/kg/ml. Infusion rate 1 ml /hr-=10 mcg/ min.

PAEDIATRICS

Add 3 mgs GTN. to 5 % Dextrose to total 50 mls. Final concentration 60 mcg/kg/ml. Infusion rate 1 ml/hr = 1 mcg/kg/min. Usual dose range 1 - 20 mcg/kg/min (1 - 20 ml/hr)

CARDIOVERSIONS

Remove nitroglcerine patches prior to cardioversion to avoid formation of electical arc.