Potassium citrate has been shown to be effective prophylaxis against recurrent calcium oxalate nephrolithiasis, but its use is limited because of gastrointestinal side effects. Studies suggest that recurrent calcium oxalate stones may be related to magnesium deficiency. In response to these two issues, a formulation of potassium–magnesium citrate was developed by clinical investigators. This formulation has a lower concentration of potassium and may reduce the incidence of gastrointestinal side effects. Ettinger and colleagues studied the effectiveness of potassium–magnesium citrate in the prevention of nephrolithiasis in patients with recurrent stone formation.

Patients were included in the placebo-controlled study if they had a history of two or more calcium oxalate calculi in the previous five years and at least one episode within the previous two years with no secondary causes. One group of 31 patients received potassium–magnesium citrate therapy, which provided a daily dosage of 42 mEq of potassium, 21 mEq of magnesium and 63 mEq of citrate. The placebo group included 33 patients. Initial assessment included 24-hour urine studies, blood chemistries, evaluation for the possibility of current stones and assessment of previous nephrolithiasis. The 24-hour urine studies and blood chemistries were repeated five months later and then every four months during the three years of the study. Side effects of treatment were evaluated at each visit.

At the end of three years, only 13 percent of the treatment group had recurrent nephrolithiasis, compared with 64 percent of the placebo group. Approximately one half of the patients in the treatment group dropped out of the study, but only 16 percent did so because of adverse side effects.

The authors conclude that the potassium–magnesium citrate formulation is effective as prophylaxis against recurrent calcium oxalate stones. This formulation did not cause hypocitraturia, so this parameter would not need monitoring. Gastrointestinal side effects were less frequent with potassium–magnesium citrate than with potassium citrate, but the authors note that the incidence of side effects should be studied further.