We are from the U.S. but are currently living in Buenos Aires, Argentina. We have a 9 month old daughter who currently has a double ear infection. The Argentine doctor has prescribed her Amoxicillin, and on the box it states that each dose (5 ml) contains 250 mg of Amoxicilina. In Spanish it states: "Cada dosis (5 ml) de suspension preparada contiene Amoxicilina (como trihidrato) 250 mg." The doctor indicated that we give her 2.5 ml (1/2 teaspoon) three times a day. Our daughter weighed in yesterday at 8.4 kg (approx 18.9 lbs). When we were in the US this last February, a US doctor prescribed Apothecon Amoxicillin 125mg/5ml for a previous ear infection. 3/4 teaspoon, three times a day. I don't remember her weight then. My question is: Is the concentration and dosage of the Argentine prescription the same as you would prescribe in the US? Being in a different country from home, we sometimes have our doubts. I'd really appreciate your help.

I can certainly understand your concern and confusion over the drug dosages given to your daughter. Medication errors can be a real problem. The issues you've raised aren't restricted, though, to crossing national boundaries. I frequently hear the same concern from parents who have just gone across the street to our after-hours pediatric service or down the hall and seen another doctor in my own practice. Today, I met two adorable twin girls who had just moved here from Oregon. When I prescribed amoxicillin, I learned (when Mom asked about the dose) that the dose was different (less) than they had received before.

Many adult medications come in "one-size-fits-all" formulations. With most medicines for children, however, the dose varies with the child's weight. Because the weights of children change a great deal with the years, these medicines often come in a variety of forms. Many of the liquid antibiotics come in two different concentrations. As you've noted, amoxicillin comes in 125 mg per teaspoon (5mL) or 250 mg per teaspoon (5mL). One teaspoon of the 125 mg strength is equal to one-half teaspoon of the 250 mg strength of the amoxicillin. (So in your case, your daughter got a slightly higher dose this time than previously.) The different concentrations make it easier to measure the appropriate amount to give to smaller children, while making sure that larger children don't need to swallow too much liquid in order to get the correct dose.

In addition to the difference in strengths of the two formulations, there is a wide range of correct dosages for amoxicillin. The dose recommendations for children on amoxicillin range from 20 to 90 milligrams per kilogram of body weight per day . Thus two children could be on appropriate doses of amoxicillin, each weighing the same amount, and yet one is receiving over four times as much as the other.

Physicians will select where to dose a child, within the acceptable range, based on several factors:

• The individual history of the child
• The type of infection being treated
• The physician's personal philosophy of antibiotic usage

As you might expect, smaller doses are not quite as powerful as the larger doses, but have the advantage of fewer side effects. If a child has had a history of problems with diarrhea or yeast infections, a physician might opt for a lower dose. If the child has had a history of infections that don't clear up easily, but the child has not had much in the way of side effects, a physician might opt for the larger end of the dosing scale.

Also, different infections tend to be treated at different ends of the dosage spectrum due to the antibiotic's ability to fight a particular infection. While strep throat can make children very sick, it is an easy infection to clear using the correct antibiotics. Amoxicillin kills strep throat readily, and a 20 mg per kg, per day dosage should be sufficient. With more stubborn infections, such as ear infections, the 40 mg per kg is a standard dose. But whenever resistant bacteria are suspected, high dose treatment with 60 to 100 mg per kg per day might be best. These high doses might also be important for serious bacterial infections.