Nitroprusside
sodium
Trade names:
Nitropress
Class: Vasodilator antihypertensive drugs
Pregnancy: (Category C)
Action:
Its mechanism of
action appears to be liberation of nitric oxide (NO), converting Hemoglobin to
cyanomethaemaglobin. Nitroprusside also releases cyanide ions which are
converted in the liver to thiocyanate by the enzyme rhodanase, a reaction which
requires a sulfur donor such as thiosulfate.
Thiocyanate is then excreted by the kidney.
In the absence of sufficient thiosulfate, cyanide ions can quickly reach toxic
levels.
The
half-life of nitroprusside is less than 10 minutes although thiocyanate has an
excretion half life of several days. The duration of treatment should not
exceed 72 hours and thiocyanate plasma concentrations should be monitored.
Uses:
• immediate reduction of blood pressure of patients in
hypertensive crises.
• producing controlled hypotension in order to reduce bleeding
during surgery.
• treatment of acute congestive heart failure.
Dose:
• Hypertensive crisis, by intravenous infusion, initially 0.5–1.5
micrograms/kg/minute, then increased in steps of 0.5 micrograms /kg/minute
every 5 minutes within range 0.5–8 micrograms/kg/minute (lower doses in
patients already receiving other antihypertensives); stop if response
unsatisfactory with max. dose in 10 minutes
•
Maintenance
of blood pressure at 30–40% lower than
pretreatment diastolic blood pressure, 20–400 micrograms/minute (lower
doses for patients being treated with other antihypertensives) Contraindications:
should not be used in the treatment of
compensatory hypertension, where the primary homodynamic lesion is aortic
coarctation or arteriovenous shunting.
should not be used to produce hypotension
during surgery in patients with known inadequate cerebral circulation, or in
moribund patients (A.S.A. Class 5E) coming to emergency surgery.
Patients with congenital (Leber's) optic
atrophy or with tobacco amblyopia have unusually high cyanide! thiocyanate
ratios.
Sodium nitroprusside should not be used for
the treatment of acute congestive heart failure associated with reduced
peripheral vascular resistance such as high-output heart failure that may be
seen in endotoxic sepsis.
Side effects:
• allergic reaction: hives; difficulty breathing; swelling of
face, lips, tongue, or throat.
• feeling extremely light-headed, even while lying down;
• confusion, ringing in your ears;
• fainting, breathing that stops;
• gasping or struggling to breathe;
• dizziness with nausea and vomiting, confusion, rapid breathing,
and seizure;
• tremors, chills, bowel or bladder urgency;
• fast, slow, or uneven heart rate;
• easy bruising or bleeding; or muscle pain or weakness, numb or
cold feeling in your arms and legs.
Nursing
considerations:
This drug can cause
very large decreases in blood pressure so proper monitoring, serious injury or
death could result.
Nitroprusside, especially in
larger-than-recommended doses, might cause cyanide poisoning. Therefore, be
sure not to exceed the recommended dose, instructed by the doctors especially
if the patient has kidney problems.
