Babies range greatly in size, so drug dosages are based on a baby's weight, not his age -- the smaller the baby, the greater the impact of a missed or inaccurate dose. Most of the time your instructions will be given in milliliters (or cc's). Five milliliters (or 5 cc's) technically equals one teaspoon, but don't use an actual teaspoon to determine the amount, because your dose could be off. Instead, use a medicine syringe labeled with milliliters or cc's to be certain that you're measuring out the right amount.
Originally published in American Baby magazine, January 2008. Updated 2009