Magnesium concentration in saliva -- an indicator of digitalis toxicity. ?

In a prospective study salivary magnesium was measured by atomic absorption spectrophotometry in 168 patients on chronic digoxin therapy. Magnesium concentration in saliva was correlated with clinical data and plasma digoxin levels. A significant elevation in salivary magnesium concentration was caused by digoxin therapy (0.58 +/- 0.39 mmol/l, n = 93) in comparison to patients with no digitalis treatment (0.17 +/- 0.07 mmol/l, n = 35). Magnesium concentrations in saliva were significantly higher in toxic patients (1.1 +/- 0.68 mmol/l, n = 32) than in nontoxic patients. Possibly toxic patients showed a magnesium level of saliva of 0.63 +/- 0.39 mmol/l (n = 40). In 89% of the intoxicated patients salivary magnesium concentrations were higher than 1.0 mmol/l. The overlap of magnesium between toxic and nontoxic patients was less as compared to calcium and potassium concentrations in saliva. No changes were noted in serum magnesium levels. Magnesium concentration in saliva was influenced by chronic digoxin therapy only. No significant increase of magnesium in saliva was observed within 24 h after i.v. injection of 1.0 mg digoxin in four healthy volunteers. It is concluded that salivary magnesium concentration is a valid method for monitoring digoxin therapy in addition to plasma digoxin levels.