Endocrine Abstracts

Patients receiving parenteral forms of treatment for osteoporosis (e.g. denosumab (DMAB) and zoledronic acid (ZOL)) should be vitamin D replete prior to administration, to minimise the risk of hypocalcaemia. Most patients receiving DMAB or ZOL take supplemental (calcium and) vitamin D but it is widely accepted that adherence to calcium and vitamin D is poor. Frequency of testing 25-hydoxyvitamin D (25OHD), calcium and renal function varies widely between centres in the UK. In recent times, our local protocol has been to check these variables ~ 2 months prior to each injection/infusion and only proceed to treatment when the 25OHD is ≥50 nmol/l. This audit was established to determine the value of this intensive monitoring protocol and whether it informs practice.

Case records of 240 patients who received DMAB (60) or ZOL (180) were reviewed. In the DMAB group, prior to first treatment, 27.3% (12) had 25OHD <50 nmol/l, (7% were <30) and 58% were already taking calcium/vitamin D supplements. In the ZOL group, 40% had 25OHD <50 nmol/l (15% were <30 nmol/l) prior to the 1st infusion; 33% were already taking calcium/vitamin D supplements. Prior to administration of the second dose of ZOL/DMAB 17–24% still had 25OHD <50 nmol/l. Prior to the third and fourth doses of ZOL/DMAB, 26–12 and 20-0% respectively had 25OHD <50 nmol/l, despite ongoing Ca/D supplementation. In those with low 25OHD, adjustments to vitamin D intake were made so as to achieve the target 25OHD concentration of 50 nmol/l.

Despite prescription of Ca/D, 25OHD levels are frequently suboptimal prior to drug administration. The proportion of those with 25OHD <50 nmol/l falls with subsequent dosing and time but even after the 3rd dose of ZOL, 20% patients had 25OHD <50 nmol/l. The data justifies an aggressive approach to pre-treatment testing of 25OHD. We believe this is important for patient safety and to mitigate risks of post-treatment hypocalcaemia.