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PHARMACOLOGICAL ACTIVITIES - TOXICOLOGY - DRUG INTERACTIONS

Calcium (Citrate)

Calcium is a major structural element in bones and teeth. The amount of calcium absorption in
dogs ranges from 25 to 90 percent, depending on the amount of intake and the age of the animal
(Ettinger & Feldman, 2000a). Calcium deficiency in dogs is characterized by rickets in normal
dogs, milk fever syndrome in pregnant or lactating dogs and a condition known as nutritional
secondary hyperparathyroidism (NSHP). Chronic dietary calcium deficiency causes major
decreases in bone material content, which can result in significant skeletal abnormalities including
fractures. Calcium intake is tied directly to the calcium-phosphorus ratio (1.5:1) in the body. A
diet high in calcium and low in phosphorus may lead to problems metabolizing the calcium. It
will cause bone deformities and hip dysplasia. Calcium deficiency in kittens demonstrated bone
rarefaction, especially in the lumbar vertebrae which tended to curve and collapse, and in the
pelvis (NRC, 2006).

TOXICOLOGY Toxicity for calcium citrate has not been documented in dogs and cats when administered orally in therapeutic
doses. LD of calcium citrate is not documented. Oral LD for calcium carbonate is 6,450 mg/kg of body
50
50
weight in rats (Sciencelab, 2010a).

DRUG Significant interactions have been observed between calcium and certain antibiotics namely
INTERACTIONS tetracyclines and fluoroquinolones (Pfizer, 1990; Bayer, 2002). Calcium decreases the bioavailability
of levothyroxine (Abbott, 2002). Combining calcium with thiazide diuretics increases the risk of
developing hypercalcemia. High doses of supplemental calcium could increase the likelihood of
abnormal heart rhythms in people taking digitalis for heart failure (Vella et al., 1999). Intravenous
calcium salts can prevent hypotension associated with intravenous verapamil (Moser et al., 2000).
Calcium citrate when taken with aluminum-containing antacids, the amount of aluminum absorbed
into the blood may be increased significantly. Bile acid sequestrants such as cholestyramine, colestipol,
and colesevelam may interfere with calcium absorption and increase the loss of calcium in the urine
(UMMC, 2012f).

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