If your child is having fevers and being treated for an infection like pneumonia, it's essential that he gets the antibiotics in to fight the infection (and thus the fever)! I'd prioritize getting the antibiotics down over the fever-reducer, although both are ultimately important for keeping your child comfortable.
You can talk with your pediatrician's office about alternatives. For example, some medications are dispensed as a liquid but will also come in chewable form that can be easier to get down. Further, there are new fever-reducers that come in "melt-aways" that are easy to chew and melt in your child's mouth. These can be great for children who fight with liquid medications. Ask the pharmacist about these if you have trouble finding them. Also you can have the pharmacist mix medicine with flavors at the pharmacy or at home you can mix it with chocolate syrup. Offer root beer right after the medicine--it works as a great chaser to cover up yucky tastes. Ultimately, if your child isn't able to tolerate the antibiotics by mouth or misses more than one dose, I recommend you see the pediatrician for follow up the next day.
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