ALPHA-ADRENERGIC CRISIS DEFINITION Stimulation of alpha-adrenergic receptors due to exposure to partial or pure alpha agonists, resulting in a syndrome characterised predominantly by vasoconstriction and hypertension. TOXIC CAUSES Phenylpropanolamine Phenylephrine Ephedrine Mephentermine Metaraminol Methoxamine Pseudoephedrine. CLINICAL FEATURES Hypertension, bradycardia (reflex) and mydriasis. Hypertension is typically accompanied by headache and, exceptionally, may result in intracranial haemorrhage. Life-threatening ventricular arrhythmias (including AV block and ventricular tachycardia) may also occur. Convulsions, myocardial infarction and acute renal failure have been reported. DIFFERENTIAL DIAGNOSIS Acute hypertension of non-toxic origin. Monoamine oxidase inhibitors (in overdose or in combination with certain drugs or tyramine-containing). Substances with sympathomimetic or anticholinergic effects. RELEVANT INVESTIGATIONS Routine clinical chemistry, including serum creatinine. Creatine phosphokinase activity, including measurement of isoenzymes if indicated. Electrocardiogram. CT Scan of head if indicated (focal neurological signs or persistent headache). TREATMENT In mild asymptomatic cases, simple observation with close monitoring of vital signs is sufficient. Where the diastolic blood pressure remains above 120 mmHg or there is evidence of end-organ damage, specific therapy with one of the following short-acting parenteral hypotensive agents should be instituted. Aim to carefully lower the diastolic blood pressure to 100 mmHg. Sodium Nitroprusside Direct generalised vasodilator. Dose: Commence continuous IV infusion at 0.5 µg/kg/min. Titrate to blood pressure to a maximum dose of 10 µg/kg/min. Must be administered under close observation, ideally with continuous blood pressure monitoring. Solution and tubing must be covered to prevent photodegradation. Phentolamine Competitive alpha-adrenoreceptor blocker. Dose: 2.5 - 5 mg (0.05 - 0.1 mg/kg) IV every 5 minutes until desired effect achieved. Thereafter, continuous infusion of 25 to 100 mg/12 hours with close monitoring of blood pressure. Caution: Atropine and beta blockers are contraindicated. Treat ventricular arrhythmias and convulsions. CLINICAL COURSE MONITORING The course is usually self-limiting and a full recovery is to be expected. Until clinical features resolve, monitoring should include vital signs (pulse, blood pressure, temperature), cardiac rhythm and fluid and electrolyte balance. LONG-TERM COMPLICATIONS Unusual unless there are complications of a severe hypertensive crisis. These potentially include intracranial haemorrhage, myocardial infarction and retinal haemorrhage. AUTHOR(S)/PEER REVIEW Author: Albert J. Nantel, Directeur, Centre de Toxicologie du Quebec, Quebec, Canada. Peer Review: Cardiff September 1996: J-F. Deng, L. Fruchtengarten, L. Lubomirov, T. Meredith, H. Persson.