The question concerns general information on the interaction between clodronate (Bonefos) and calci

Fråga: The question concerns general information on the interaction between clodronate (Bonefos) and calcium (Calcium-Sandoz). Is there any new documentation that contradicts the recommendation that one should not take both drugs simultaneously when both drugs are used concurrently? The questioner got the information from a colleague that the interaction is of little or no practical consequence.

Sammanfattning: It is unclear to what extent the recommendation not to take clodronate and calcium at the same time when treated with both drugs has any practical consequence in vivo. However, we have not found any in vivo studies concerning interaction between clodronate and calcium, nor any new documentation that would change the present recommendation.

Svar: Clodronate (dichloromethylene bisphosphonate) is a small, highly water-soluble molecule, which inhibits the activity of osteoclasts and slows down the dissolution of bone mineral, apatite crystals. It is used to prevent bone resorption in disorders characterised by excessive bone loss. Clodronate is poorly absorbed when given orally, with a bioavailability of one to four per cent, and the absorption is subject to a large inter- and intraindividual variability. Thus, high oral doses are required to obtain therapeutic effects in humans (1). This poor absorbability is thought to result, at least in part, from formation of unabsorbable polynuclear chelate complexes with calcium. Calcium also plays a role in the binding of clodronate to plasma proteins. Much of the calcium in plasma is protein bound. Clodronate binds to the calcium ions which are associated with plasma proteins (2). However, it is unclear whether this mechanism is of any importance to the interaction. No documentation has been found in the literature, including the databases Medline and Drugline, which revealed any new reports contradicting the present recommendation.