Methicillin



Methicillin
Systematic (IUPAC) name
6-(2,6-dimethoxybenzamido)-3,3-dimethyl-
7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-
2-carboxylic acid
Identifiers
CAS number 61-32-5
ATC code J01CF03
PubChem 6087
Chemical data
S 
Mol. mass 380.42
Pharmacokinetic data
Bioavailability (not orally-absorbed)
Metabolism hepatic, 20–40%
Half life 25–60 minutes
Excretion renal
Therapeutic considerations
Pregnancy cat.

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Legal status
Routes IV

Methicillin (penicillins.

Mode of action

Main article: Beta-lactam antibiotic

Like other beta-lactam antibiotics, methicillin acts by inhibiting the synthesis of bacterial cell walls. It inhibits cross-linkage between the linear peptidoglycan polymer chains that make up a major component of the cell wall of Gram-positive bacteria. It does this by binding to and competitively inhibiting the transpeptidase enzyme used by bacteria to cross-link the peptide (D-alanyl-alanine) used in peptidogylcan synthesis. Methicillin and other beta-lactam antibiotics are structural analogs of D-alanyl-alanine, and the transpeptidase enzymes that bind to them are sometimes called penicillin binding proteins (PBPs). (Gladwin and Trattler, 2004)

Medicinal chemistry

Methicillin is insensitive to beta-lactamase (also known as penicillinase) enzymes secreted by many penicillin-resistant bacteria. The presence of the ortho-dimethoxyphenyl group directly attached to the side chain carbonyl group of the penicillin nucleus facilitates the β-lactamase resistance, since those enzymes are relatively intolerant of side-chain steric hindrance. Thus it is able to bind to penicillin binding proteins (PBPs) and inhibit peptidoglycan crosslinking, but is not bound by or inactivated by β-lactamases.

Clinical use

Methicillin is not commonly used in clinical practice, but serves a purpose in the laboratory to determine antibiotic sensitivity in microbiological culture.

See also

References

  • Mitscher LA. Antibiotics and antimicrobial agents. In: Williams DA, Lemke TL, editors. Foye's Principles of medicinal chemistry, 5th edition. Philadelphia: Lippincott Williams & Wilkins; 2002.
  • Gladwin M., Trattler B. Clinical Microbiology made ridiculously simple. 3rd edition. Miami: MedMaster, Inc.; 2004.
 
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