The amino bisphosphonate ibandronate prevents vitamin D toxicity and inhibits vitamin D-induced calcification of arteries, cartilage, lungs and kidneys in rats.

Experiments were carried out to determine whether the doses of the amino bisphosphonate ibandronate that inhibit bone resorption inhibit soft tissue calcification and death in rats treated with a toxic dose of vitamin D. These studies were prompted by the recent discovery that ibandronate doses that inhibit bone resorption potently inhibit artery calcification induced by treatment with the vitamin K antagonist warfarin. All 16 rats treated with the toxic dose of vitamin D (12.5 mg cholecalciferol x kg(-1)) died by d 6 after the first vitamin D injection (median survival: 4.5 d), whereas the 12 rats treated with vitamin D plus ibandronate (0.25 mg x kg(-1) x d(-1)) were alive and in good health at d 10. Rats treated with vitamin D alone and examined at d 4 had extensive Alizarin red staining for calcification in the aorta, the carotid, hepatic, mesenteric, renal and femoral arteries, kidneys and lungs, whereas rats treated with vitamin D plus ibandronate had no evidence for calcification at any of these tissues when examined at d 7 and 10. Ibandronate treatment also inhibited the dramatic increase in the levels of calcium and phosphate seen in the abdominal aorta, kidneys, lungs and trachea of the vitamin D-treated rats (P < 0.001). Serum calcium levels were, however, not different in rats treated with vitamin D alone (3.4 +/- 0.2 mmol x L(-1)) and in rats treated with vitamin D plus ibandronate (3.5 +/- 0.2 mmol x L(-1)). Treatment with vitamin D alone increased levels of matrix Gla protein, an inhibitor of soft tissue calcification, in the arteries, kidneys, lungs and trachea by 10- to 100-fold, and ibandronate treatment prevented this increase. The importance of these studies in the rat model is that they identify a class of drugs in current clinical use that can be used to treat patients with vitamin D toxicity and that they identify the dose of the drug that is predicted to be effective, namely the dose that inhibits bone resorption. Because there is no other known treatment for vitamin D toxicity, there would seem to be good reason to try bisphosphonates such as ibandronate in future studies aimed at treating patients who have been exposed to toxic levels of vitamin D.