INFLUENCE OF CALCIUM ACETATE OR CALCIUM CITRATE ON INTESTINAL ALUMINUM ABSORPTION

The risk of aluminum (Al) accumulation in patients with chronic renal failure has led to use of non-Al phosphate binders. Frequently, Al and non-Al phosphate binders are co-administered. Unfortunately, calcium citrate (Ca citr), when given with Al-gel, markedly enhances Al absorption. To determine whether calcium acetate (Ca acetate) also augments Al absorption, 10 normal volunteers were each given orally, three-day courses of the following drug combinations dosed four times daily: 1) aluminum hydroxide gel (Al[OH]3) (5 ml) alone; 2) Al[OH]3 (5 ml) plus Ca acetate (1330 mg); 3) Al[OH]3 (5 ml) plus Ca citr (950 mg). A nine day wash-out occurred between each course. Al levels were measured using flameless atomic absorption spectrophotometry. Daily urine Al excretion was measured during a two-day baseline before each course and during each three-day drug course. Plasma Al was obtained during each baseline and drug course. Mean 24-hour Al excretion (μg/g creatinine/day) at baseline versus treatment for each combination was: 1) 5.9 ± 3.2 versus 42.0 ± 40.7 (mean ± SD); 2) 5.7 ± 3.0 versus 40.3 ± 28.6: 3) 6.3 ± 3.4 versus 175.8 ± 103.3. Al excretion was significantly greater with combination 3 than with either 1 or 2 (P < 0.05). The difference between 1 and 2 was not significant. Plasma Al (μg/liter) at baseline versus treatment for each combination was: 1) 5.3 ± 4.2 versus 8.1 ± 2.5 (mean ± SD); 2) 3.1 ± 2.2 versus 7.3 ± 2.9; 3) 3.0 ± 2.3 versus 12.0 ± 6.1. Comparing baseline to treatment differences, the increment in plasma Al with combination 3 was significantly greater than with either 1 or 2 (P < 0.05). The difference between 1 and 2 was not significant. We conclude that in normal subjects, standard doses of Ca citr markedly enhance Al absorption from Al[OH]3, whereas Ca acetate does not augment Al absorption. Theoretically, use of Ca acetate may be associated with less risk than Ca citr for Al absorption and accumulation in patients with chronic renal failure, concurrently treated with Al-gel.