McKenna's Pharmacology for Nursing, 2e

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P A R T 8  Drugs acting on the cardiovascular system

V asodilators If other drug therapies do not achieve the desired reduc- tion in blood pressure, it is sometimes necessary to use a direct vasodilator. Most of the vasodilators are reserved for use in severe hypertension or hypertensive emergencies. These include diazoxide (generic), hydrala- zine ( Alphapress, Apresoline ), minoxidil ( Loniten ) and sodium nitroprusside (generic). Therapeutic actions and indications The vasodilators act directly on vascular smooth muscle to cause muscle relaxation, leading to vasodilation and drop in blood pressure. They do not block the reflex tachycardia that occurs when blood pressure drops. They are indicated for the treatment of severe hyper­ tension that has not responded to other therapy (see Table 43.2). Pharmacokinetics Diazoxide and sodium nitroprusside are used intra­ venously; hydralazine is available for oral and intravenous use; and minoxidil is available as an oral agent only. These drugs are rapidly absorbed and widely distributed. They are metabolised in the liver and prim­ arily excreted in urine. They cross the placenta and enter breast milk (see Contraindications and cautions). Contraindications and cautions The vasodilators are contraindicated in the presence of known allergy to the drug to prevent hypersensi- tivity reactions and with any condition that could be exacerbated by a sudden fall in blood pressure , such as cerebral insufficiency. Caution should be used in people with peripheral vascular disease, CAD, heart failure or tachycardia, all of which could be exacerbated by the fall in blood pressure. Diazoxide must be used with extreme caution in people with functional hypogly­ caemia because this drug increases blood glucose levels by blocking insulin release . These drugs are also contraindicated with preg- nancy unless the benefit to the mother clearly outweighs the potential risk because of the potential for adverse effects on the fetus or neonate. If they are needed by a breastfeeding woman, another method of feeding the baby should be selected, because of the potential for adverse effects on the baby. • Be extremely careful in any situation that might lead to a drop in blood pressure (e.g. excessive sweating, vomiting, diarrhoea, dehydration). If you experience light-headedness or dizziness in any of

Adverse effects The adverse effects most frequently seen with these drugs are related to the changes in blood pressure. These include dizziness, anxiety and headache; reflex tachy- cardia, heart failure, chest pain, oedema; skin rash and lesions (abnormal hair growth with minoxidil); and GI upset, nausea and vomiting. Cyanide toxicity (dyspnoea, headache, vomiting, dizziness, ataxia, loss of conscious- ness, imperceptible pulse, absent reflexes, dilated pupils, pink colour, distant heart sounds and shallow breath- ing) may occur with nitroprusside, which is metabolised to cyanide and also suppresses iodine uptake and can cause hypothyroidism. Clinically important drug–drug interactions Each of these drugs works differently in the body, so each drug should be checked for potential drug–drug interactions before use. these situations, consult your healthcare provider immediately. • Keep this drug, and all medications, out of the reach of children. Prototype summary: Sodium nitroprusside Indications: Severe hypertension, maintenance of controlled hypotension during anaesthesia, acute heart failure. Actions: Acts directly on vascular smooth muscle to cause vasodilation and drop of blood pressure; does not inhibit cardiovascular reflexes and tachycardia; renin release will occur. Pharmacokinetics: Route Onset Peak Duration IV 1–2 mins Rapid 1–10 mins T 1/2 : 2 mins; metabolised in the liver and excreted in urine. Adverse effects: Apprehension, headache, retrosternal pressure, palpitations, cyanide toxicity, diaphoresis, nausea, vomiting, abdominal pain, irritation at the injection site.

Care considerations for people receiving vasodilators

Assessment: History and examination

■ ■ Assess for the following conditions, which could be cautions or contraindications to use