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Pharmacology: Meixam is a synthetic penicillin of the isoxazolyl group. It is stable to penicillinase and is highly active against Streptococci, Pneumococci and Staphylococci irrespective of their sensitivity to other penicillins.
Meixam is bactericidal to all gram-positive organisms except Streptococcus faecalis but is primarily of interest for its activity against Staphylococci that are resistant to penicillin G.
Meixam can be given in combination with ampicillin (1:1) in infections due to β-lactamase-producing microorganism, since it may inhibit the destruction of ampicillin. It shows a marked synergistic action by the combination of the 2 antibiotics, cloxacillin and ampicillin. It is useful in treating serious mixed infections due to unidentified bacteria and the toxicity is of a very low order.
Pharmacokinetics: Absorption is more complete when given by IM injection and peak plasma concentrations of about 15 mcg/mL have been observed 30 min after a dose of 500 mg. About 94% of cloxacillin in the circulation is bound to plasma proteins.
Meixam is acid-stable and is well absorbed when given orally and is active for 4-6 hrs. Effective blood tissue and urine levels are readily achieved and the peak serum levels are obtained about 1 hr after administration. Doubling the dose doubles the serum concentration.
Meixam is predominantly excreted by glomerular filtration and renal tubular secretion in similar manner to the other penicillins.
