SODIUM NITROPRUSSIDE

“SNP”

1) Therapeutic drug action & mechanism(pharmacology)

• Direct effect; affects venous & arteriolar beds equally

• Specific for the relaxation of arteriolar and venous smooth muscle resulting in vasodilation

• See reduced SVR and reduced venous return

2) Indications

• Hypertensive emergencies (reduces BP due to reduced SVR)

• Cardiac failure (increases CO due to reduced afterload)

• Prolonged hypotension during anaesthesia to reduce surgical bleeding

• Effective in producing systemic vasodilation during rewarming on CPB

• Postoperative hypertension

• Used to offset vasoconstriction caused by adrenergic drugs

3) Effects on organs—side effects

4) Toxic effects/ precautions with administration

• Accumulation of cyanide (prolonged infusions eg >week with renal;hepatic failure; > 10 mg/Kg/min infusion)

• Excessive hypotension

• Methemoglobinaemia

• Hypothermia will reduce rate of SNP metabolism

5) Contraindications

• Should not be used for compensatory hypertension eg AV shunts, Coarctation of aorta

• Severe renal failure

7) Loading dose, maintenance dose, frequency & method of administration

• Continuous infusion

• 50 mg/vial in 100 ml D5W [avoid exposure to light]

• Start at 0.5 mg/Kg/min

• Do not exceed 10 mg/Kg/min

8) Drug’s metabolism—Drug’s excretion—Half life (pharmacokinetics)

• Almost immediate onset and short duration of action (2-3 min)

• Distributed directly to site of action (vascular smooth muscle)

• Rapidly metabolised to cyanide & thiocyanate

• Thiocynate is main metabolite- excreted via kidneys

9) Important drug interactions

• Action is augmented by volatile anaethetics; other circulatory depressants