Benzylpenicillin
A natural penicillin given by injection for streptococcal, pneumococcal and meningococcal infections, syphilis and endocarditis.
Also called penicillin G (US name).
Drug card
- Class
- Penicillin
- How it works
- Blocking the enzymes that cross-link the bacterial cell wall, so bacteria burst
- Used for
- Syphilis, including neurosyphilis
- Meningococcal and pneumococcal meningitis
- Endocarditis
- Pneumonia
- Known for
- Allergic reactions (hypersensitivity)
- Anaphylaxis
- Jarisch-Herxheimer reaction when treating syphilis
- Its name
- -cillin means a penicillin
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does benzylpenicillin work?
Benzylpenicillin is the natural penicillin. It is very active against streptococci, pneumococci, meningococci, clostridia and Treponema pallidum, but not against most Gram-negative bacilli, and penicillinase destroys it, so many staphylococci resist it. It is injected; the benzathine salt is released slowly from muscle, giving low levels that last for weeks.
Like other penicillins: Penicillins carry a beta-lactam ring that binds and inactivates penicillin-binding proteins (PBPs), the enzymes that cross-link peptidoglycan in the bacterial cell wall. The weakened wall gives way and dividing bacteria burst, so penicillins are bactericidal. Bacteria resist them by making beta-lactamases (penicillinases) or by changing their PBPs.
See its molecule in 3DPubChem CID 5904Uses
What is benzylpenicillin used for?
- Syphilis, including neurosyphilis
- Meningococcal and pneumococcal meningitis
- Endocarditis
- Pneumonia
- Streptococcal throat infections
- Sepsis
Side effects
Side effects of benzylpenicillin
- Allergic reactions (hypersensitivity)Known forSerious
- AnaphylaxisKnown forSerious
- Jarisch-Herxheimer reaction when treating syphilisKnown for
- Rash and hives
- C. difficile colitisSerious
- Seizures with massive doses or kidney failureSerious
- High potassium (large IV doses of potassium salt)Serious
- Low potassium (large doses of sodium salt)Serious
- Hemolytic anemiaSerious
- Interstitial nephritis (kidney injury)Serious
- Severe skin reactions (SJS, TEN, DRESS)Serious
- Pain and phlebitis where it is injected
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Benzathine benzylpenicillin is for deep intramuscular injection only: given into a vein it has caused cardiac arrest and death.
- Large IV doses carry much potassium or sodium; give them slowly and check electrolytes, kidney function and blood counts on long courses.
- Kidney impairment slows its clearance, so doses are reduced to avoid convulsions and coma.
Good to know: The long-acting benzathine salt treats early syphilis with one intramuscular dose and is used to stop rheumatic fever coming back.
Remember it
A way to remember it
Penicillins jam the wall builders: only growing bacteria, busy laying new wall, are killed.
The penicillin-binding proteins are the enzymes that link peptidoglycan strands into a firm wall. Penicillins block them, so bacteria die while they multiply; a drug that halts growth, such as a tetracycline, can blunt this effect.
Written for biofideX
Its name
-cillin means penicillin
Marks penicillins (6-aminopenicillanic acid derivatives), including benzylpenicillin. Beta-lactamase inhibitors given with them keep their own names: clavulanic acid, tazobactam.
- Every drug name stem
Its class
Penicillins
Other penicillins with a card:
Easily mixed up with cephalosporins, carbapenems and glycopeptides.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Penicillin G potassium for injection: label (DailyMed)
- Penicillin G benzathine injectable suspension: label (DailyMed)
- Benzylpenicillin sodium 600 mg powder for injection: SmPC (emc)
- Penicillin G (NCI Thesaurus)
- P&S Syphilis: STI Treatment Guidelines (CDC)
- Neurosyphilis, Ocular Syphilis, and Otosyphilis (CDC)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Antibiotics: the cell wall
Benzylpenicillin is one of 12 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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