How do Doctors Determine the Best Penicillin Dosage?

Doctors consider many factors when determining the correct penicillin dosage. The patient's weight, health history, and possible drug allergies are important things to consider. The infection being treated will also help determine the correct amount of this antibiotic to be administered. While penicillin is used exclusively to treat bacterial infections, different bacteria will require different dosages. The method of delivery — orally, by injection, or intravenously — will also affect the amount of penicillin given to a patient.

The patient's weight is a primary concern for doctors when determining penicillin dosage. Doctors will prescribe a larger dose for an adult or patient with a higher weight than for smaller adults or children. Children process and interact with drugs differently than adults, and very small children will eliminate the drug from their bodies more slowly than older children and adults. The doctor will reduce the dosage accordingly when administering penicillin to a child.

Other medications being taken by the patient can also affect how a doctor determines the correct penicillin dosage. Different drugs can interact with each other, altering how each drug affects the patient and affecting how each drug performs. Penicillin, for example, can make birth control pills less effective.

Allergies to penicillin or other drugs can affect how much penicillin a doctor will give a patient. An allergy to penicillin itself will prevent a doctor from prescribing penicillin at all. If a patient has an allergy to cephalosporins, which are another type of antibiotic, a doctor may reduce the dosage of penicillin in an effort to avoid a reaction or may avoid prescribing penicillin at all.

Health conditions, either past or present, that are not related to the condition being treated with penicillin, can also have an effect on a doctor's decision regarding a penicillin dosage. Certain health problems such as asthma, kidney disease, bleeding disorders, or any allergy may require a reduction of the dosage. The doctor might also order special tests, under these circumstances, to determine the safety of a particular dose.

The infection being treated will be the final factor the doctor considers when determining a penicillin dosage. Penicillin is used to treat a wide variety of bacterial infections. Each one has a base dosage, based on long years of medical history and case studies, for a patient of a particular weight. Doctors have specialized knowledge of these infections and how much penicillin is required to treat them.