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Why is penicillin G usually given by injection rather than by mouth?
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Penicillin G is typically administered by intramuscular injection because it possesses poor stability in acid. When taken orally, a significant portion of the drug is broken down by digestive acids as it passes through the stomach, which limits its effectiveness when given by mouth.1
In contrast, other forms of the antibiotic, such as penicillin V or certain semisynthetic penicillins, are more resistant to these digestive acids and can be effectively administered as oral medication.1