A study in 1972, a comparison of the toxicity of Ergocalciferol and Cholecalciferol was done on Rhesus Monkeys. Oral doses of 50,000, 100,00 & 200,000 IU given demonstrated that Cholecalciferol was significantly more toxic than ergocalciferol. All animals given cholecalciferol developed hypercalcemia, died and had extensive soft tissue mineralization.
Hypercalcemia occurred in ergocalciferol supplemented monkeys, but the animals survived and comparable soft tissue mineralization was not evident after sacrifice. A unique feature of the lesion of cholecalciferol toxicity was the deposition of crystals resembling urates with an associated granulmatous reaction.
Moving forward, further studies have shown that known side effects caused by ergocalciferol and cholecalciferol administration include damage/impairment in the renal system. This may include polyuria, polydipsia, reversible azotemia, generalized vascular calcification, which may result to sever kidney damage or even death.
The prior available forms of nutritional vitamin D therapy for patients with CKD were ergocalciferol and cholecalciferol. Studies examining the bioequivalence of ergocalciferol and cholecalciferol are inconclusive, but suggest that ergocalciferol may be less potent.
There is also controversy as to the effectiveness of vitamin D supplementation with ergocalciferol and cholecalciferol in patients with CKD. One study showed that CKD patients treated with cholecalciferol experienced treatment resistance in increasing serum 25(OH)D levels to a pre-selected target level, while data from the CRIC study showed that increased vitamin D supplementation was associated with greater serum 25(OH)D levels, with a dose response relationship.
Patients with vitamin D resistance tend to have lower initial estimated glomerular filtration rate (eGFR), higher PTH, lower albumin, higher serum phosphate, and lower 25(OH)D levels.
In contrast, the modified release oral calcifediol produced gradual increases in both serum 25(OH)D and calcitriol without inducing FGF23 or CYP24A1. The CKD patients who received modified release oral calcifediol also had improved plasma PTH levels. A study of patients with CKD stages 2-4 with SHPT and vitamin D deficiency showed that treatment with 30, 60 or 90µg over 6 weeks of modified-release calcifediol increased serum 25(OH)D levels to >30ng/ml in more than 90% of subjects and reduced plasma PTH by >30% in more than 60% of subjects at dosages >60 µg/d.