Ampicillin Dosage: What You Need to Know

Ampicillin is a common penicillin‑type antibiotic used for many infections. Getting the dose right matters – too little may not clear the bug, too much can cause side effects. Below you’ll find the most common dosing schedules, plus tips for special cases like children or kidney problems.

Standard Adult Dosage

For most adults, doctors prescribe 250 mg to 500 mg every 6 hours. If the infection is more severe, the dose can go up to 1 g every 6 hours. The total daily amount usually stays between 1 g and 4 g, split into equal doses. Take the pills with a full glass of water and try to keep the timing consistent – it helps keep steady levels of the drug in your blood.

Special Situations: Kids, Kidney Issues, Pregnancy

Children: Dosing for kids is based on weight, not age. The usual range is 25 mg to 50 mg per kilogram of body weight per day, divided into doses every 6 hours. For a 20 kg child, that works out to roughly 500 mg to 1 g spread over the day.

Kidney problems: If you have reduced kidney function, the doctor will lower the dose or space the doses farther apart. This prevents the drug from building up and causing toxicity. Always tell your provider about any kidney issues before starting ampicillin.

Pregnancy and breastfeeding: Ampicillin is generally considered safe, but the exact dose should follow a doctor’s advice. The medication does pass into breast milk, so monitoring the baby for any unusual symptoms is a good idea.

Other factors that can change the dose include the type of infection (e.g., urinary tract vs. respiratory) and whether you’re taking other medicines that affect kidney function.

When you get a prescription, check the label for the exact amount and frequency. If you miss a dose, take it as soon as you remember—unless it’s almost time for the next one. In that case, skip the missed dose and continue with the regular schedule. Never double up to make up for a missed pill.

Side effects like nausea, diarrhea, or rash are common but usually mild. If you notice a severe reaction—such as trouble breathing, swelling of the face, or a high fever—stop the drug and seek medical help right away.

Finally, finish the entire course even if you feel better early. Stopping too soon can let the infection come back and may make the bacteria resistant to antibiotics in the future.

Got more questions about your specific dose? Talk to your pharmacist or doctor. They can adjust the plan based on your health history and make sure you get the most out of ampicillin while staying safe.