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Prilosec (Omeprazole) Plus Calcium Carbonate Decreases Calcium Absorption In Elderly Women: Presented at AGS

By Anne Jacobson
Special to DG News

WASHINGTON, DC -- May 15, 2002 -- The concomitant use of Prilosec (omeprazole) with calcium carbonate and no food decreases calcium absorption in most elderly women.

"Of our 18 patients, 16 had decreased fractional calcium absorption and two subjects had increased fractional calcium absorption on omeprazole," said Dr. Mary Beth O'Connell, PharmD, from University of Minnesota, in Minneapolis, Minnesota, United States. She reported findings here Friday at the annual scientific meeting of the American Geriatrics Society in Washington, DC.

Calcium carbonate needs an acidic medium for disintegration and digestion. To determine if acid suppression induced by omeprazole would result in decreased calcium absorption, Dr. O'Connell and colleagues conducted a placebo-controlled, double-blind crossover study in 18 women aged 65-89 (76±6.5 years).

In the first arm of the study, subjects were randomly selected to receive seven days of the proton pump inhibitor omeprazole or placebo. Beginning one week prior to study day 1, subjects took vitamin D 400 IU/day throughout the study period. Calcium carbonate supplements were held one week before each study day.

On study day 1, subjects ingested radioactively labeled calcium carbonate (45-CaCO3) 1.25 gm and the study drug. Blood samples were drawn prior to 45-CaCO3 and five hours later. Subjects fasted from the previous night until the five-hour sample.

Calcium concentrations were determined by atomic absorption spectrophotometry. Fractional calcium absorption was calculated based on serum concentrations of radioactively labeled calcium carbonate, height, and weight.

In the second arm of the study, the procedure was repeated with the other drug after a washout period lasting at least three weeks.

At the end of the study period, Dr. O'Connell and her colleagues found that the mean fractional calcium absorption decreased from 9.1±5.1 percent on placebo to 3.5±3.9 percent on omeprazole (p=0.003). Sixteen women achieved a decrease in fractional calcium absorption on omeprazole, while two women had increases in fractional calcium absorption on concomitant omeprazole and calcium carbonate.

The mean difference in fractional calcium absorption was -5.5±-6.9 percent and ranged from -18.6 percent to 12.1 percent.

Though no period effect was seen, age did seem to play a role in fractional calcium absorption, Dr. O'Connell noted. "Age correlated with fractional calcium absorption while on omeprazole, but not for placebo or the difference," she said.

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