NEW YORK: Multiple courses of commonly used antibiotics may have a significant impact on children’s development, shows a study. It found female mice treated with two classes of widely used childhood antibiotics gained more weight and developed larger bones than untreated mice. However, both of the antibiotics also disrupted the gut microbiome, the trillions of microbes that inhabit the intestinal tract. The mice were given three short courses of amoxicillin (a broad-spectrum antibiotic), tylosin or a mixture of both drugs. “The number of courses of antibiotics matters. We get a little interruption of maturation process after second course of antibiotics, and we have even more interruption after three courses,” said lead co-author Laura M Cox from the department of medicine at NYU School of Medicine. Short, high-dose pulses of tylosin had the most pronounced and long-lasting effect on weight gain, while amoxicillin had the biggest effect on bone growth — a prerequisite for increased height. The drugs altered not only the bacterial species, but also relative numbers of microbial genes linked to specific metabolic functions. Antibiotic-exposed microbiomes may be less adaptable to environmental changes, said the study. The more pronounced effects of tylosin on weight gain and microbiome disruption are worrisome, given the increasing popularity of macrolide antibiotic prescriptions for children. The evidence highlights the need for better awareness of potential downsides of antibiotic overuse, the authors said. The study appeared online in Nature Communications.