How do doctors determine antibiotic dosages for babies?

Per kilo body weight: Most antibiotics have dosages by milligrams per kilo body weight per day; amoxicillin, for example, is 40-100 mg/kg/day, so an 11-pound (5-kilo) baby would get up to 500 mg per day, usually in 2 doses, so that's 250 mg twice a day, maximum.

Weight and age: Dosage for antibiotics are given by the weight and age of the child. Each antibiotic has a specific amount that is given depending on the weight of the child. This dose increases until a specific amount or maximum for that particular antibiotic.

Based on weight: Doctors know the right dose for your baby based on his or her current weight. Some medications (such as eye or ear drops) have a standard dosage. But most other antibiotics require specific dosing. If your child is on other medications or has problems with his/her liver or kidney, the dosage may need to be adjusted to accommodate for those special circumstances that may affect the dose.

By weight/reason: In addition to using your child's body weight and factoring in other medical problems such as kidney or liver disease, your doctor doses antibiotics based upon the reason they are being prescribed. For example, the dosage of Amoxicillin that is used for ear infections (if antibiotics are needed, of course) is different from that used to treat strep throat.