Phentolamine

SCOPE - THIS DRAFT COVERS ONE OF THE PAGE'S TWO ROUTES ONLY. The page is titled 'IV (crisis) or local infiltration (extravasation)'. The IV crisis route is sourced above. THE EXTRAVASATION / LOCAL INFILTRATION ROUTE IS NOT COVERED BY THIS SOURCE: this SPC contains no subcutaneous or local-infiltration regimen for extravasation of a vasopressor, and its §4.2 method of administration admits only the intravenous and intramuscular routes. Do not infer an infiltration dose or dilution from the figures above - that regimen needs its own source. DIAGNOSTIC USE IN PHAEOCHROMOCYTOMA (recorded for completeness, a separate indication from the crisis dose): intravenous test - adults 5 mg (0.5 ml), children 1 mg (0.1 ml), injected quickly with blood pressure measured immediately after injection at 30-second intervals for the first 3 minutes and 60-second intervals for the next 7 minutes; intramuscular test - adults 5 mg (0.5 ml), children 3 mg (0.3 ml), with blood pressure measured every 5 minutes for 30-45 minutes. The SPC cautions that 'the diagnostic use of phentolamine mesilate is not the first choice and should only be used if the other specific tests are not available', having 'largely been replaced by the commonly available urinalysis of catecholamines or other biochemical tests'. BETA-BLOCKADE: during surgical tumour removal a hypertensive crisis may occasionally occur even if the patient has received phentolamine as premedication; in such cases beta-blockade may be indicated, using a beta-1-selective beta blocker such as metoprolol administered as a slow IV injection. RENAL IMPAIRMENT: no pharmacokinetic studies have been performed in patients with renal impairment; caution is advised.

FIXED DOSE, NOT WEIGHT-BASED - dosePerKg is deliberately null because this SPC expresses the paediatric figure as a flat milligram dose, not per kilogram. Do not derive a per-kg figure. HYPERTENSIVE CRISIS, verbatim: 'For children over 8 years old, the minimum effective dose is 1 mg. The dosage should be further adjusted based on the clinical condition.' Note this is stated as a MINIMUM EFFECTIVE dose, not a recommended or maximum dose, and the SPC gives no figure at all for children aged 8 years or under for this indication. DIAGNOSTIC TEST DOSES IN CHILDREN (a different indication): intravenous test 1 mg (0.1 ml); intramuscular test 3 mg (0.3 ml).