Hello...i understand your concern. Can you tell me how old he is? Does he have such memory lapses frequently or was this the first time this has happened? Without jumping to conclusions there are a few things that need evaluation. It is possible that he is developing alzheimers disease which commonly presents with memory disturbances initially. He could be also be having age related dementia. It is best that you get him examined by a neurologist. He will probably need an mri scan of the brain to look for age related changes of cerebral atrophy. It is very unlikely that an antibiotic caused the memory lapse. Hope this helps.... Regards,