Read the product information first

EDITOR—Peter et al describe hypocalcaemia after intravenous bisphosphonate administration.1 Reference to the recommendations given in the summary of product characteristics for the products in question may have abrogated the occurrence of this well known and well documented side effect.

The patient in case 1 had a low adjusted serum calcium concentration before zoledronic acid was given, and no calcium and vitamin D supplementation was given at the start of treatment despite the recommendation in the summary of product characteristics.

Hypercalcaemia was treated very effectively with zoledronic acid in case 2. The summary of product characteristics gives the incidence of hypocalcaemia as an adverse event as 1-10%. The patient developed this common, documented side effect. Hypomagnesaemia is also listed as an uncommon side effect. This patient had a low magnesium concentration before treatment. Early correction may have mitigated the hypocalcaemia.

The patient in case 3 was treated with 60 mg pamidronate for an adjusted calcium concentration of 2.96 mmol/l, yet the summary of product characteristics recommends a dose of 15-30 mg for this calcium value. This relative overdose may have resulted in, or at least contributed to, the subsequent hypocalcaemia.

The patient in case 4 was treated appropriately with 90 mg pamidronate for hypercalcaemia. On the following day another 60 mg pamidronate was administered against the advice in the summary of product characteristics to wait before giving a further dose. This overdose may have contributed to the ensuing hypocalcaemia.

The responsibility lies with prescribers to familiarise themselves with all available information on medicines that they prescribe.