What is the Difference Between Crystalline Penicillin and Benzylpenicillin?

Crystalline penicillin and benzylpenicillin are both antibiotics belonging to the penicillin group, which is derived from fungal species P. chrysogenum and P. rubens. They are used to treat different bacterial infections, but there are some differences between the two:

1. Indications: Crystalline penicillin mainly treats pediatric bacterial infections, while benzylpenicillin mainly treats bacterial infections in adults.
2. Formulation: Aqueous crystalline penicillin G is administered intravenously at dosages of 6-20 million units daily, either in 4-6 divided doses or by continuous infusion. Benzylpenicillin is available as a sodium or potassium salt, providing 20 meq of sodium or 1.7 meq potassium per 1 million unit. The potassium salt is most often used clinically, except in patients with severe renal failure, where the sodium salt may be more appropriate.
3. Administration: Crystalline penicillin G in aqueous solution has been used intramuscularly, subcutaneously, intravenously, and intrathecally. Benzylpenicillin should not be administered subcutaneously due to severe reactions.
4. Jarisch–Herxheimer Reaction: This reaction takes place during the administration of benzylpenicillin but does not happen due to crystalline penicillin.
5. Essential Medicine: According to the World Health Organization, benzylpenicillin is an essential medicine.

Comparative Table: Crystalline Penicillin vs Benzylpenicillin

Crystalline Penicillin and Benzylpenicillin are both antibacterial drugs. Crystalline Penicillin is simply referred to as Penicillin G, while Benzylpenicillin is a derivative of Penicillin G. The main difference between the two lies in their chemical structure and stability in acidic conditions. Here is a table comparing the two:

In summary, Benzylpenicillin is a derivative of Penicillin G with a phenylacetamido group at position 6 of the penam ring, making it stable in acidic conditions. This stability allows Benzylpenicillin to be used for oral administration, unlike Penicillin G.