Both are beta lactams. However, benzylpenicillin, which is also called penicillin G i.e. narrow group antibiotic. I have now in both the following as a mechanism of action

Binds to PBP in bacterial cell wall, causing deficit in the cell wall and causing cell death.

where I would like to differentiate clearly benzylpenicillin from amocillin.

How is benzylpenicillin better in bacterial meningitis than amoxicillin?

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    $\begingroup$ As the term meningitis is pretty broad, you should probably narrow this down to bacterial meningitis. There I would say the antibiotic is used to which the bacteria are sensitive. $\endgroup$
    – Chris
    Jun 8, 2015 at 14:00
  • $\begingroup$ @Chris I narrowed it. Specificity of course, but this is a general question. If you have those drugs, give their indications. I see bacterial meningitis in benzylpenicillin as indication, but not in amoxicillin. However, googling shows that amoxicillin has induced some meningitis but I do not know if it has been used in bacterial-meningitis. $\endgroup$ Jun 8, 2015 at 14:03
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    $\begingroup$ Can you share your source that penicillin G is better than amoxicillin? You also stated in your initial revision that you have read about amoxicillin induced meningitis; that amoxicillin can induce aseptic meningitis seems like penicillin G has an advantage. m.cid.oxfordjournals.org/content/46/4/642.1.full $\endgroup$
    – canadianer
    Jun 8, 2015 at 19:15
  • $\begingroup$ @canadiane No, this is a class note. Yes, it may be related to the fact that amoxicillin can even induce meningitis, probably because the increased resistance of the drug (wider spectrum than penicillin G but more resistance also). Good link! Make it an answer with a small summary, please. $\endgroup$ Jun 8, 2015 at 19:37

2 Answers 2


Amoxicillin is just penicillin with a hydroxyl group off the ring and an extra amine group..

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Their mechanisms of action are the same. Their ability to cross the blood-brain barrier are the same. They can both cause seizures.

Both are used to treat to meningitis. The selection of one over the other would be based on the sensitivity of the infecting organism, and the ability to cross the blood-brain barrier in inflamed meninges.

There are better drugs to treat meningitis.

Penetration of Drugs through the Blood-Cerebrospinal Fluid/Blood-Brain Barrier for Treatment of Central Nervous System Infections

  • $\begingroup$ Excellent idea to explain this by structure! Do both work in the similar analogue in Syphilis? Similarly, I think better drugs for that. $\endgroup$ Jun 9, 2015 at 6:18

benzylpenicillin is actively transported into the brain via the oat‐3 transporters. Amox is only poorly diffuses through the blood brain barrier. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1471-4159.2009.06451.x


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