Dosing instructions on bottles of liquid Tylenol and Motrin are generally based upon age. However, these medications are more appropriately dosed by weight. The instructions on the bottle tend to *under dose* children. This isn’t necessarily a bad thing, because no one wants to accidentally cause liver failure in a child by giving too much Tylenol (this nearly happened in my house, see below).

How can parents calculate the most accurate dose of commonly used medications for their children?

Arriving at the correct dose of pediatric medications is more challenging than it seems. Although most parents know the approximate weights of their children in pounds, pediatric drugs are dosed on a milligram per kilogram basis. Moreover, young children tend to receive liquid medications, so the drug’s concentration is important for calculating the dose in milliliters.

To get an idea of the math involved, let’s review the steps pediatricians follow when calculating medication doses for children:

- Convert the child’s weight into kilograms by dividing by 2.2.
- Calculate the total daily dose by multiplying the kilogram weight times the milligram per kilogram daily dosage of the medication (for example children usually receive 10 mg/kg of Motrin per dose).
- Divide the total daily dose into a dosing schedule, i.e. two to three times daily, if necessary (for instance, children sometimes receive 85 mg/kg/day of Amoxicillin; the daily dose will need to be converted into a twice daily dosing schedule).
- Convert single doses in milligrams into the correct number of milliliters, based on the drug’s concentration (Children’s Motrin, for instance, has a concentration of 100 mg/5 mL; Infant Motrin, however, is twice is concentrated, so the volume administered would be half that of Children’s Motrin).
- Check to make sure that a single dose or daily dose doesn’t surpass the maximum recommended adult dose (i.e. 400 mg for Motrin).

Does this sound like a lot of work? That’s because it is! To help parents arrive at the correct dose more easily, I’ve condensed steps one through five into a single calculation for some of the most widely used pediatric medications.

**Children’s Motrin (Advil, ibuprofen)**:

**For Children’s Motrin, to obtain the correct dose in milliliters, simply multiply your child’s weight in pounds X .22. The maximum dose is 20 mL (400 mg).**

**Infant Motrin**:

Infant Motrin is twice as concentrated as children’s Motrin; therefore, the volume of infant Motrin required is half that of children’s Motrin.

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**For infant Motrin, to obtain the correct dose in milliliters, multiply your child’s weight in pounds X .11. The maximum dose is 10 mL (400 mg).**

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**Children’s Tylenol (acetaminophen)**:

Tylenol comes in only ONE formulation, 160 mg/5 ml.

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**For Tylenol, to obtain the correct dose in milliliters, multiply your child’s weight in pounds X .21. The maximum dose is 20 mL (650 mg) at one time. **

The active ingredient in Tylenol, acetaminophen, is metabolized through the liver. Tylenol should not be administered more than once every four hours, or four times in one day. My general advice to parents using Tylenol is that they shouldn’t use it for too many days in row. Importantly, an accidental overdose of Tylenol can cause life-threatening liver failure, so be sure to administer the correct dose. In cases of possible overdose, contact your local poison control for further advice. An algorithm can be used to determine whether your child will require NAC (N-acetyl cysteine), the antidote for Tylenol, to prevent liver failure.

Not long ago I was shocked to find myself calling poison control regarding a possible Tylenol overdose for one of my own kids—my youngest, who was six-years-old at the time. My daughter had developed a fever while sleeping at her grandmother’s house. Grandma appropriately found a bottle of children’s Motrin in the cabinet and gave Sarah two pills, which she swallowed without chewing (even at that tender age, Sarah was already an expert at swallowing pills because she took a daily dose of adult Claritin). When I arrived at Grandma’s house the next morning, I happened to check the bottle of Motrin. Instead of finding the usual purple chewable tablets, I discovered the bottle contained red and yellow non-chewable tablets, which were labeled in tiny red letters with the word, “Tylenol.” Someone (don’t ask me who) had filled an empty bottle of children’s Motrin with extra-strength, 500 mg adult Tylenol. And my 40-pound six-year-old had easily swallowed both pills…twice. Grandma had administered two doses, two pills each, once at bedtime and again in the morning. Oy! In a hysterical panic, I called poison control, wondering if my daughter might be headed toward an acute case of liver failure, followed by a transplant. Fortunately, poison control quickly informed me that she was going to be fine and wouldn’t need any treatment. I breathed a huge sigh of relief. Grandma, however, still hasn’t recovered from the emotional trauma of nearly poisoning her youngest grandchild. The big take home lesson from this lovely experience was the following: never switch pills into a bottle with the wrong label.

The active ingredient in Motrin and Advil is ibuprofen, a non-steroidal anti-inflammatory (NSAID) that is metabolized by the kidneys. Fortunately, Motrin generally won’t cause failure of any organs. However, the drug isn’t completely benign. NSAIDS like Motrin and Naprosyn are mild blood thinners, and they can also irritate the lining of the GI tract, causing gastritis and in rare cases, ulcers. Personally, I can’t stomach Motrin without taking an antacid, but most children tolerate NSAIDS without any problems.

When parents are choosing between Tylenol and Motrin, I usually recommend Motrin for three reasons:

- Motrin won’t cause liver failure.
- Motrin has some nice anti-inflammatory effects; it’s great for teething pain and muscle aches.
- Motrin lasts six to eight hours, as opposed to Tylenol, which wears off after four hours. In my opinion, Motrin is the best drug to soothe a sick child during the night—so long as the child doesn’t suffer from GI problems.

Although Motrin is only FDA approved for children six months of age and older, it’s perfectly safe for younger children if given in the correct dose. Just use the calculation listed above, and be sure to double check your math.