Phentolamine

Source: UK SPC (eMC) for Phentolamine mesilate 10 mg/ml Solution for Injection, §4.2. CONCENTRATION: 10 mg/ml solution for injection; the SPC's volume equivalences confirm this (5 mg = 0.5 ml, 1 mg = 0.1 ml, 3 mg = 0.3 ml). INTRA-OPERATIVE CRISIS (§4.2): 'During surgical tumor removal as part of the treatment of phaeochromocytoma, a hypertensive crisis may occasionally occur, even if the patient has received phentolamine as premedication. In such cases, beta-blockade may be indicated. Use a beta-1-selective beta blocker, such as metoprolol, administered as a slow IV injection.' SECOND SPC INDICATION — DIAGNOSTIC USE (quoted for completeness only; NOT the treatment dose): 'The dosage for adults is 5 mg (0.5 ml) and for children, 1 mg (0.1 ml)' for the intravenous test, given quickly with blood pressure measured every 30 seconds for the first 3 minutes and every 60 seconds for the next 7 minutes; for the intramuscular test 'The dose for adults is 5 mg (0.5 ml) and for children 3 mg (0.3 ml)', with blood pressure every 5 minutes for 30–45 minutes. Test preparation: 'Do not administer sedatives, analgesics or other medications for 24 hours and preferably not even for 48-72 hours prior to testing, except for essential medications (such as digitalis and insulin)... The test should not be conducted on patients with normal blood pressure.' Positive result: 'the blood pressure drops by more than 35 mm Hg systolic and 25 mm Hg diastolic.' §4.4 cautions that this diagnostic use 'has largely been replaced by the commonly available urinalysis of catecholamines or other biochemical tests due to their accuracy and safety. Therefore, the diagnostic use of phentolamine mesilate is not the first choice and should only be used if the other specific tests are not available.' EXCIPIENT WARNING (§4.4): 'This medicinal product contains 0.5 mg sodium metabisulphite in each 1 ml of solution which may rarely cause severe hypersensitivity reactions and bronchospasm' — note hypersensitivity to sulphites is a contraindication. GI CAUTION (§4.4): 'Due to its stimulating effect on the gastrointestinal tract, including gastric acid secretion, phentolamine mesilate should be used with caution in patients with gastritis and peptic ulcers.'

Presentation: 10 mg/ml solution for injection (1 mg = 0.1 ml; 3 mg = 0.3 ml) NO PER-KG PAEDIATRIC DOSE EXISTS IN THIS SOURCE — dosePerKg deliberately left null, and the live page's '0.1 mg/kg SC' is NOT in any fetched source and must not be carried forward. The only paediatric figures in the UK SPC are fixed milligram amounts: TREATMENT of paroxysmal hypertension in phaeochromocytoma, §4.2 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 described as the MINIMUM EFFECTIVE dose, not a recommended or maximum dose, and it is stated only for children over 8 years — the SPC gives nothing for children aged 8 years or under. DIAGNOSTIC TEST (different indication): intravenous test 'for children, 1 mg (0.1 ml)'; intramuscular test 'for children 3 mg (0.3 ml)'. The US openFDA record in this bundle (OraVerse) has paediatric limits — 'In pediatric patients weighing between >=15 kg and <30 kg, the maximum dose of OraVerse recommend is 1/2 cartridge (0.2 mg)... Use in pediatric patients under 3 years of age or weighing less than 15 kg (33 lbs) is not recommended' — but these belong to a 0.4 mg/1.7 mL dental submucosal cartridge for reversing local-anaesthesia soft-tissue numbness and MUST NOT be applied to intravenous phaeochromocytoma or extravasation use. Verify any under-18 use against a children's formulary and with the relevant specialist team.