Methicillin

Meticillin
Clinical data

Routes of administration	IV
ATC code	J01CF03 (WHO) QJ51CF03 (WHO)
Pharmacokinetic data
Bioavailability	Not orally absorbed
Metabolism	hepatic, 20–40%
Biological half-life	25–60 minutes
Excretion	renal
Identifiers
IUPAC name (2S,5R,6R)-6-(2,6-dimethoxybenzamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid
CAS Number	61-32-5^Y
PubChem (CID)	6087
DrugBank	DB01603^Y
ChemSpider	5862^N
UNII	Q91FH1328A^N
ChEMBL	CHEMBL575^N
ECHA InfoCard	100.000.460
Chemical and physical data
Formula	C₁₇H₂₀N₂O₆S
Molar mass	380.42 g/mol
3D model (Jmol)	Interactive image
SMILES OC(=O)[C@@H]2N3C(=O)[C@@H](NC(=O)c1c(OC)cccc1OC)[C@H]3SC2(C)C
^NY (what is this?)

Meticillin (INN), also known as methicillin (USAN), is a narrow-spectrum β-lactam antibiotic of the penicillin class. It should not be confused with the antibiotic metacycline.

Meticillin was discovered in 1960.

Compared to other penicillins that face antimicrobial resistance due to β-lactamase, it is less active, can be administered only parenterally, and has a higher frequency of interstitial nephritis, an otherwise-rare adverse effect of penicillins. However, selection of meticillin depended on the outcome of susceptibility testing of the sampled infection, and since it is no longer produced, it is also not routinely tested for any more. It also served a purpose in the laboratory to determine the antibiotic sensitivity of Staphylococcus aureus to other penicillins facing β-lactam resistance; this role has now been passed on to other penicillins, namely cloxacillin, as well as genetic testing for the presence of mecA gene by PCR.

At one time, meticillin was used to treat infections caused by certain gram-positive bacteria including Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, and Streptococcus pneumoniae. Meticillin is no longer effective against these organisms due to resistance.

Resistance to meticillin is conferred by activation of a new bacterial penicillin binding protein (PBP) mecA gene. This encodes protein PBP2a. PBP2a works in a similar manner to other PBPs, but it binds β-lactams with very low affinity, meaning they do not compete efficiently with the natural substrate of the enzyme and will not inhibit cell wall biosynthesis. Expression of PBPA2 confers resistance to all β-lactams.

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Wikipedia