The effect of
calcium citrate on intestinal
aluminum absorption, assessed by the increment in urinary
aluminum excretion, was evaluated in eight normal men. Baseline urinary
aluminum excretion was determined for 2 days; thereafter, subjects ingested
aluminum hydroxide for 3 days. In a cross-over study, subjects were given either
calcium citrate, 950 mg four times a day, or placebo during the 3 days of
aluminum hydroxide ingestion (2.4 g/d). Plasma
aluminum levels were measured on the second control day and the third day of
aluminum hydroxide ingestion. Baseline urinary
aluminum excretion was 0.02 +/- 0.004 (6.5 +/- 1.1 micrograms/g
creatinine) and 0.03 +/- 0.005 mumol/mmol
creatinine (7.4 +/- 1.3 micrograms/g
creatinine). These values increased during
aluminum hydroxide therapy, but values were much greater when
calcium citrate was ingested with
aluminum hydroxide. On 3 consecutive days, urinary
aluminum excretion levels were 11.1 +/- 3.23, 8.8 +/- 2.9, and 5.3 +/- 0.7 times greater during the administration of
calcium citrate with
aluminum hydroxide than with
aluminum hydroxide alone. Plasma
aluminum levels did not differ in the two treatment groups. Thus,
calcium citrate markedly enhances the absorption of
aluminum from
aluminum hydroxide and the two must not be prescribed together in patients with
renal failure.