text: what if a tablet contains 5 mg antibiotics. if the doctor orders .15 g of antibiotics how many tab.are needed? what will be the answer, if a tablet contains 5 mg antibiotics. and if the doctor orders .15 g of antibiotics, how many tablets are needed? don't, i repeat, don't ever mess with perscription drugs on your own. don't take drugs prescribed for someone else (you could have a sensitivity to them). it's very dangerous. get to a clinic and get your own. they'll tell you what to take and how much.