<p>The toxicity of penicillins is generally low, but in a small number of patients penicillin can cause sensitization and allergic reactions. Acute, lifethreatening anaphylactic reactions are rare, but they do occur.<br />
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Intramuscular injection of benzathine penicillin can cause moderate burning discomfort, local pain, and deep muscle soreness and tenderness at the site of injection, lasting for one to three days in about 10% of patients. Some patients had low-grade fever (102˚F) associated with local pain and tenderness. This febrile reaction disappeared within 24 to 48 hours.</p>