A 56 year old man was admitted to hospital with a two day history of nausea and vomiting. Admission calcium was 4.1 mmol/l with a PTH of 146.5 pmol/l and creatinine of 227 umol/l. Primary hyperparathyroidism was diagnosed 4 months earlier with a calcium of 3.22 mmol/l and PTH of 24.4 pmol/l. He had prior outpatient treatment with intravenous disodium pamidronate and cinacalcet. He was waiting SPECT CT due to indeterminant imaging. Past history included right tonsillar carcinoma in 2004 treated with surgery including right neck dissection, chemotherapy and radiotherapy. Initial treatment was intravenous normal saline 0.9% 166 ml/h and plan for disodium pamidronate if eGFR >30. Within 24 h, calcium rose to 4.35 mmol/l and creatinine was 320 umol/l. Fluids were increased to 250 ml/h. Ultrasound of renal tract was unremarkable and urine output good. Pharmacy consulted the Renal Drug Handbook and noted that the same dose of disodium pamidronate could be given as in normal renal function if GFR was above 10 ml/min. Calculated creatinine clearance was 22 ml/min and patient was prescribed 90 mg in 500 ml normal saline 0.9% over 5 h. After discussion with endocrine surgeons, transfer was arranged for urgent SPECT CT and parathyroidectomy. SPECT CT revealed a 3.2 cm left sided parathyroid adenoma. Four days post pamidronate, calcium was 2.82 mmol/l and creatinine 248 umol/l. Surgery was performed the following day. Histology was consistent with parathyroid adenoma. Post operatively, there was a rapid improvement in renal function, almost normalising by 3 weeks. He remains normocalcaemic with GFR 81 more than 12 months later. This case highlights the need for intensive medical and surgical treatment in severe hypercalcaemia due to parathyroid disease, and also the use of the renal drug handbook.