IONIZED AND TOTAL MAGNESIUM LEVELS IN CYCLOSPORINE-TREATED RENAL-TRANSPLANT RECIPIENTS - RELATIONSHIP WITH CHOLESTEROL AND CYCLOSPORINE LEVELS

1. Ionized magnesium, measured using a newly developed ion-selective e lectrode, total magnesium, and ionized and total calcium were evaluate d in 39 stable, long-term, cyclosporin-treated renal transplant recipi ents and compared with those of age-matched, nontransplanted control s ubjects. Total cholesterol, cyclosporin trough level, serum creatinine , time after-transplant and the ratio of ionized calcium to ionized ma gnesium were also measured in renal transplant recipients and the rela tionships between these variables and ionized and total magnesium were evaluated. 2. Renal transplant recipients exhibited marked deficits i n ionized magnesium, with a mean value of 0.54 +/- 0.01 mmol/l as comp ared with 0.61 +/- 0.006 mmol/l for normal control subjects (P less-th an-or-equal-to 0.05), with a more moderate deficit in total magnesium. Values for ionized and total calcium did not differ. By stepwise line ar multiple regression analysis, ionized magnesium was significantly r elated to cyclosporin trough level and total cholesterol but not to se rum creatinine, time after transplant or the dose of cyclosporin. Ioni zed magnesium correlated inversely with cyclosporin trough level and d irectly with total cholesterol. The ratio of ionized calcium to ionize d magnesium was elevated in renal transplant recipients when compared with control subjects and correlated positively with the cyclosporin t rough level. 3. Deficits in ionized magnesium are common during the la te post-transplant period in cyclosporin-treated renal transplant reci pients. Ionized magnesium may be a more sensitive clinical parameter t han total magnesium in this population, in whom total magnesium may be only mildly decreased in the setting of a severe deficit in ionized m agnesium. 4. Ionized magnesium correlates with the cyclosporin level. Renal transplant recipients with high cyclosporin levels demonstrate t he most severe deficits in ionized magnesium, and this finding could c ontribute to cyclosporin-induced hypertension and nephrotoxicity. The direct correlation between ionized magnesium and total cholesterol may result from a 'masked magnesium deficiency', as has been suggested in animal models, and requires further study. 5. Accelerated atheroscler osis observed after renal transplantation may relate to alterations in ionized magnesium and elevated ratios of ionized calcium to ionized m agnesium, which are associated with atherogenesis in other models.