Effect of feeding isoniazid and cimetidine on growth and bone development in male broiler chicks.

Because previous studies indicated that cimetidine (CIMET) and isoniazid (ISON) may inhibit vitamin D metabolism in both rats and humans, experiments were conducted to evaluate the influence of these drugs on growth and bone development in male broiler chicks. Chicks were fed a corn and soybean meal basal diet containing various levels of the drugs for 21 days. Body weight gain (BWG), feed consumption per bird (FB), tibia ash (TA), tibia breaking force (TBF), and plasma calcium levels were measured. In birds fed a diet supplemented with 1,100 ICU D3/kg, CIMET at up to 300 ppm resulted in a significant linear decrease in TA as the drug level increased. Birds fed ISON up to 405 ppm had inconsistent responses in TA and TBF. Body weight gain was only depressed with the highest level of ISON (405 ppm). The effects of feeding 0, 150, or 300 ppm CIMET were also investigated when chicks were fed 200 or 1,000 ICU per kg vitamin D3. The interaction between vitamin D3 and CIMET was significant for BWG, FCB, TA, and TBF. These were significantly reduced as the CIMET level increased for birds fed the low vitamin D3 diet but were not significantly affected when fed the high D3 diet. In another study in which chicks were fed a diet with 1,100 ICU vitamin D3, lowering the dietary Ca, or P, or both did not result in any effect of CIMET on the chicks. The results indicate that CIMET possibly interferes with normal bone formation in chicks by altering vitamin D3 metabolism.