Published in:
01-08-2014
The effect of somatostatin analogs on vitamin D and calcium concentrations in patients with acromegaly
Published in: Pituitary | Issue 4/2014
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Purpose
The goals of this study were to determine: (1) 25OH vitamin D (25OHD) and calcium levels in patients with acromegaly and their association with insulin-like growth factor (IGF-1) and (2) whether somatostatin analog (SSA) therapy effects calcium and 25OHD levels.
Methods
125 patients with acromegaly were studied. Serum calcium and 25OHD levels were compared prior to and after vitamin D supplementation between patients receiving versus not receiving SSA in whom medical therapy included pegvisomant and/or dopamine agonists. Calcium and 25OHD levels were also evaluated longitudinally prior to and during short-term (mean 3 months, range 1–5) and long-term (mean 49 months, range 7–180) SSA administration. Vitamin D2 50,000 units weekly were given to 3 patients in the cross sectional and 1 in the longitudinal group; 400–4,000 units/day of D3 were given to 11 and 5 in respective groups.
Results
In patients with a comparable mean IGF-1 index and season of testing, mean serum levels of 25OHD prior to vitamin D supplementation did not differ in patients receiving versus not receiving SSA (30 ± 3 vs. 30 ± 1 ng/ml, p = 0.99) and the prevalence of vitamin D sufficiency was similar between SSA and non SSA groups (42 vs. 57 %, p = 0.20), prior to vitamin D supplementation. In patients with a comparable mean IGF-1 index and season of testing, mean serum 25OHD levels in patients increased after vitamin D supplementation in both those who were (37 ± 2 ng/ml, N = 23, p = 0.007) and were not receiving SSA (35 ± 1 ng/ml, N = 69, p = 0.005) compared to pre-D supplementation levels but were not different between these groups, p = 0.95) after D supplementation. Calcium and albumin were normal throughout longitudinal follow up. Calcium correlated with IGF-1 index (ρ = 0.29, p = 0.001, N = 125). In the longitudinal subset, serum calcium decreased transiently, in patients receiving short-term SSA (pretreatment 9.9 ± 0.1 mg/dl vs. short-term SSA 9.5 ± 0.1, p = 0.004). After long-term SSA therapy, calcium increased compared to levels on short-term therapy (9.8 ± 0.1 mg/dl vs. 9.5 ± 0.1, p = 0.017) and were unchanged compared to baseline. Mean vitamin D levels were sufficient at baseline prior to SSA therapy (33 ± 5.0 ng/ml), and did not change during short term (29 ± 6 ng/ml, p = 0.85) and long term SSA therapy (35 ± 5 ng/ml, p = 0.43).
Conclusions
Prior to and after vitamin D supplementation, patients with acromegaly receiving long-term SSA had vitamin D levels similar to those receiving other therapies, suggesting that long-term SSA therapy does not affect serum vitamin D. However, given the limitations of this retrospective study, further prospective studies evaluating the impact of SSA on vitamin D levels are necessary to confirm these findings definitively. Calcium levels are positively associated with IGF-1 index in patients with acromegaly. There is a transient decrease in calcium levels with short-term SSA use. The acute effect of SSA on calcium does not appear to be mediated by albumin, 25OHD or PTH and resolves with long-term SSA treatment. The transient decrease in calcium with short-term SSA use resolved with long-term SSA therapy.