Compare and contrast the pharmacology of sodium nitroprusside and glyceryl trinitrate.
It was expected candidates would address specific aspects of pharmacology such as action,
mechanism of action, half life and duration of effect, route of administration, potential
toxicity and special precautions. These agents lend themselves to comparison and contrast as
several distinct similarities and differences exist and credit was given for highlighting these.
Specific comments should include that both agents result in blood vessel dilation with extra
credit given for detailing the differences in the balance of arterial versus venous effects
between them. For both agents the effect is mediated through nitric oxide and it was
expected candidates would identify that nitroprusside releases NO spontaneously and GTN
requires enzymatic degradation with the resultant effects on smooth muscle mediated via c
GMP. They are both short acting agents when used intravenously and require careful titration
to measured blood pressure for effect.
Extra credit was given for mentioning that routes other than IV are available for GTN (topical
/ oral) but not for nitroprusside. Comments on special precautions such as Nitroprusside
should be protected from light and GTN given via non PVC giving sets gained additional
marks. In addition to the well described adverse effects of each agent, it was expected candidates would mention the potential for cyanide toxicity with nitroprusside and extra marks were awarded for an indication of usual doses.
Syllabus C2b 2e
References Katzung 10th edition, Goodman and Gillman Chp 31 & 32