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What is Benzylpenicillin and explain in detail?
Benzylpenicillin, also known as penicillin G (PenG) or BENPEN, and in military slang "Peanut Butter Shot" is an antibiotic used to treat a number of bacterial infections. This includes pneumonia, strep throat, syphilis, necrotizing enterocolitis, diphtheria, gas gangrene, leptospirosis, cellulitis, and tetanus. It is not a first-line agent for pneumococcal meningitis. Benzylpenicillin is given by injection into a vein or muscle. Two long-acting forms benzathine benzylpenicillin and procaine benzylpenicillin are available for use by injection into a muscle.Side effects include diarrhea, seizures, and allergic reactions including anaphylaxis. When used to treat syphilis or Lyme disease a reaction known as Jarisch–Herxheimer may occur. It is not recommended in those with a history of penicillin allergy. Use during pregnancy is generally safe in the penicillin and β-lactam class of medications.Benzylpenicillin is on the World Health Organizations List of Essential Medicines.

Medical uses
Antimicrobial potency
As an antibiotic, benzylpenicillin is noted to possess effectiveness mainly against gram-positive organisms. Some gram-negative organisms such as Neisseria gonorrhoeae and Leptospira weilii are also reported to be susceptible to benzylpenicillin.

Adverse effects
Adverse effects can include hypersensitivity reactions including urticaria, fever, joint pains, rashes, angioedema, anaphylaxis, serum sickness-like reaction. Rarely CNS toxicity including convulsions (especially with high doses or in severe renal impairment), interstitial nephritis, haemolytic anaemia, leucopenia, thrombocytopenia, and coagulation disorders. Also reported diarrhoea (including antibiotic-associated colitis).
Benzylpenicillin serum concentrations can be monitored either by traditional microbiological assay or by more modern chromatographic techniques