What is Penicillin? Explain Mechanism of Action. Classify its different types.

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Sir Alexander Fleming discovered penicillin in 1928 from Penicillin notatum. In 1941 penicillin was available for therapeutic use. Penicillins are one of the most important groups of antibiotics. Penicillin is now obtained from the fungus Penicillin chrysogenum for therapeutic use.
MECHANISM OF ACTION:- Beta lactam antibiotics act by inhibiting cell wall synthesis in the bacteria. The rigid cell wall of the bacteria protects the bacteria from lysis. Therefore, cell wall is essential for the survival of bacteria. Peptidoglycon is an important component of the cell wall which gives rigidity to cell wall. The Synthesis of this peptidoglycan requires enzymes called transpeptidases. Beta -Lactam antibiotics inhibit these transpeptidases and thus inhibit the synthesis of peptidoglycon. This results in the formation of bacteria with weak cell wall. Such bacteria undergoes lysis .
CLASSIFICATION:- a. Natural e.g. penicillin
b. Semi-synthetics
Penicillin G (Benzyl Penicillin) :- Anti bacterial spectrum:- Penicillin G has narrow antibacterial spectrum and is effective against gram-positive cocci and bacilli and a few gram negative cocci.
Resistance:- Many Organism like staphylococci produce penicillinase which is a beta –lactamase.It opens the Beta Lactam rings and inactivates penicillin’s.
Penicillin may not bind to the bacteria because of changes in the target proteins. This also leads to resistance.
Pharmacokinetics:- Penicillin G is destroyed by gastric juice, food interferes with its absorption – hence, it is to be given 2 hours after food. It has a short t half life of 30 minutes.
Preparation and Dose:- Penicillin G is mainly given parentrally. Oral penicillin is used only in minor infection.
Adverse effect:- Hypersensitivity:- It is the most common cause of drug allergy.
Jarisc h-Herxheimer Reaction:- When penicillin is injected in a patient with syphilis, there is sudden destruction of spirochetes and release of its lytic products. These triggerers a reaction with fever, myalgia, exacerbation of syphilitics lesions and vascular collapse.

Jishu Baiju
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