Effects of cyclosporine on magnesium metabolism in rats

Earlier studies have revealed hypomagnesemia with cyclosporine treatment in renal and bone marrow transplant recipients. The present study was designed to investigate the possible effect of cyclosporine on Mg metabolism in normal rats. Sprague-Dawley rats were randomized into the cyclosporine group, which was given 15 mg/kg/day cyclosporine by gastric gavage, and the control group, which received the vehicle alone. Food intake, body weight, serum concentration, urinary excretion, fecal excretion, and tissue content of Mg were determined weekly for 3 weeks. In addition, intestinal absorption of Mg was determined by using in vivo perfusion. Serum Mg concentration fell significantly after 1 week of cyclosporine treatment and remained low throughout the observation period. This was associated with reduced food intake and renal Mg conservation during the first week but normal food intake and severe renal Mg wasting thereafter. In vivo perfusion studies performed at 1 and 3 weeks showed no significant difference in intestinal absorption of Mg between the two groups, thereby excluding intestinal malabsorption as a possible culprit. Likewise, fecal Mg excretion showed no significant difference in the two groups. It was surprising that tissue Mg content (in muscle, liver, and kidney) was increased in the cyclosporine-treated group at 3 weeks. We conclude that cyclosporine administration in rats leads to a fall in serum Mg concentration primarily as a result of renal Mg wasting and possibly as a result of a shift of Mg to the tissue compartments with no discernible effect on gastrointestinal handling of Mg.