The differences between procaine penicillin and penicillin are different onset of action times, different main ingredients, and different side effects. 1. Different onset of action. Procaine penicillin’s onset of action can take up to 48 hours, while penicillin’s onset of action can take up to 72 hours. 2. The main ingredients are different. Procaine penicillin is mainly composed of procaine penicillin and penicillin sodium, add appropriate suspension and buffer made of sterile powder. The main component of penicillin is penicillin alkane, extracted from penicillin culture fluid, belongs to the β-lactam antibiotics. 3. Side effects are different. Side effects of procaine penicillin include severe anaphylaxis, serum sickness type reactions, and other symptoms of allergic reactions such as hemolytic anemia, drug rash, contact dermatitis, asthma attacks, and so on. Penicillin side effects can act on the gastrointestinal flora, which can irritate the stomach and cause diarrhea and possibly gastrointestinal dysfunction. Drugs have certain side effects, it is recommended that patients should use drugs under the guidance of a doctor to avoid discomfort.