Background: Surgical resection of phaeochromocytomas requires careful planning. The Endocrine Society guidelines recommend combined alpha and beta-adrenergic blockade to reduce peri-operative morbidity and mortality. Phenoxybenzamine is the preferred agent for alpha-adrenergic blockade with a recommended starting dose of 10mg BD, and a maximum suggested dose of 1mg/kg/day (1). There is limited evidence for the use of phenoxybenzamine above this dose.
Case: We present the case of a 23-year-old Caucasian male with a 5cm left-sided phaeochromocytoma and severe hypertension (BP>200/130mmHg), complicated by grade 3 hypertensive retinopathy, macroalbuminuria and left ventricular impairment. He was symptomatic with palpitations, diaphoresis, and headaches. His 24-hour urine normetanephrine was 30.2 umol/24hr (0-3.5) and plasma normetanephrine was 7290 pmol/L (<570). Plasma metanephrine and 3-methoxytyramine were not elevated. Ga-68 DOTATATE-PET/CT confirmed the absence of metastatic disease. The patient engaged in recreational drug use consuming marijuana 1.5g daily, occasional LSD and ketamine.
Despite reaching the recommended 1mg/kg/day of phenoxybenzamine, he continued to have significant hypertension with no postural change. Marijuana withdrawal was considered as a potential contributor to his hypertension, and PRN benzodiazepines were administered. Phenoxybenzamine was progressively uptitrated to a dose of 120mg every 6h with additional Amlodipine 10mg every 12h and Metoprolol 100mg every 12h, to achieve the pre-operative BP 100/70mmHg with a significant postural drop. He was also treated with oral and intravenous sodium chloride prior to surgery. The peri-operative course was uneventful with successful surgical resection, discontinuation of all antihypertensive agents post-operatively and no post-operative hypotension.
Conclusion: This case demonstrates high doses of phenoxybenzamine may be required in young adults with a shorter duration of hypertension and greater arterial compliance, and the challenges of managing marijuana withdrawal in the setting of peri-operative adrenergic blockade for phaeochromocytoma. It highlights the safe administration of high dose phenoxybenzamine in a unique circumstance and the importance of individualised care.