It's 2 a.m., your baby has a fever, and you reach for the Infants' Tylenol. But you're not sure what the right dose is. Though the recently revised labels warn that too much of the drug could pose serious risks (such as liver damage), they don't give the recommended doses for kids 2 years and under, suggesting instead that you call your doctor.

McNeil Consumer Products (the makers of Tylenol, which is acetaminophen), the American Association of Poison Control Centers (AAPCC), and drug and medical experts are working with the Food and Drug Administration to change labels on acetaminophen and ibuprofen. McNeil wants dosing instructions for babies 6 months and up; the AAPCC for those 2 months and older. An FDA policy change could take up to two years, so in the meantime, parents should ask their doctor for a dosage chart.Parents and caregivers should always be careful when giving the drug. "Until recently, people regarded acetaminophen as so safe that they could give it without concern," says Dr. Hyman Zimmerman, of the Armed Forces Institute of Pathology, in Washington, D.C. "Now we know that it can be toxic. Parents must be scrupulous about sticking to the recommended doses."

How much is too Much?

Typically, twice the total recommended dose given over several days is toxic, says Dr. Toby Litovitz, executive director of the AAPCC. Signs of poisoning include nausea, vomiting and abdominal pain. Call your poison-control hotline if you suspect an overdose.

Call your doctor before giving the medication to any child for more than a day. To help use acetaminophen more safely:

- Never give the infant drops to an older child. The infant formula is 31/2 times more potent than the children's formula so that smaller doses can be given with a dropper to babies who can't handle a cup; the new labels now clearly state that the formula is concentrated.

- Use acetaminophen only if your child has a fever or is clearly in pain from teething or an ear infection, not when he's cranky or appears to be coming down with a bug.

- Write down when and how much of the drug you've given (especially important when more than one person is administering it).

- Use only the dropper or cup that comes with the product.

- If your child spits up or spills the drug, only re-administer if almost all of the dose hasn't been swallowed.