n. a *penicillin-type antibiotic used mainly to treat urinary-tract infections caused by many Gram-negative bacteria. Possible side-effects include allergic reactions, nausea, and vomiting.
Penicillin is a beta-lactam antibiotic, one of a group of drugs that also includes CEPHALOSPORINS. Drugs of this group have a four-part beta-lactam ring in their molecular structure and they act by interfering with the cell-wall growth of mutliplying bacteria.
Among the organisms to which it has been, and often still is, active are: streptococcus, pneumococcus, meningococcus, gonococcus, and the organisms responsible for syphilis and for gas gangrene (for more information on these organisms and the diseases they cause, refer to the separate dictionary entries). Most bacteria of the genus staphylococcus are now resistant because they produce an enzyme called PENICILLINASE that destroys the antibiotic. A particular problem has been the evolution of strains resistant to methicillin – a derivative originally designed to conquer the resistance problem. These bacteria, known as METHICILLINRESISTANT STAPHYLOCOCCUS AUREUS (MRSA), are an increasing problem, especially after major surgery. Some are also resistant to other antibiotics such as vancomycin.
An important side-e?ect of penicillins is hypersensitivity which causes rashes and sometimes ANAPHYLAXIS, which can be fatal.
Forms of penicillin These include the following broad groups: benzylpenicillin and phenoxymethyl-penicillin; penicillinase-resistant penicillins; broad-spectrum penicillins; antipseudomonal penicillins; and mecillinams. BENZYLPENICILLIN is given intramuscularly, and is the form that is used when a rapid action is required. PHENOXYMETHYLPENICILLIN (also called penicillin V) is given by mouth and used in treating such disorders as TONSILLITIS. AMPICILLIN, a broad-spectrum antibiotic, is another of the penicillins derived by semi-synthesis from the penicillin nucleus. It, too, is active when taken by mouth, but its special feature is that it is active against gram-negative (see GRAM’S STAIN) micro-organisms such as E. coli and the salmonellae. It has been superceded by amoxicillin to the extent that prescriptions for ampicillin written by GPs in the UK to be dispensed to children have fallen by 95 per cent in the last ten years. CARBENICILLIN, a semi-synthetic penicillin, this must be given by injection, which may be painful. Its main use is in dealing with infections due to Pseudomonas pyocanea. It is the only penicillin active against this micro-organism which can be better dealt with by certain non-penicillin antibiotics. PIPERACILLIN AND TICARCILLIN are carboxypenicillins used to treat infections caused by Pseudomonas aeruginosa and Proteus spp. FLUCLOXACILLIN, also a semi-synthetic penicillin, is active against penicillin-resistant staphylococci and has the practical advantage of being active when taken by mouth. TEMOCILLIN is another penicillinase-resistant penicillin, e?ective against most gram-negative bacteria. AMOXICILLIN is an oral semi-synthetic penicillin with the same range of action as ampicillin but less likely to cause side-effects. MECILLINAM is of value in the treatment of infections with salmonellae (see FOOD POISONING), including typhoid fever, and with E. coli (see ESCHERICHIA). It is given by injection. There is a derivative, pivmecillinam, which can be taken by mouth. TICARCILLIN is a carboxypenicillin used mainly for serious infections caused by Pseudomonas aeruginosa, though it is also active against some gram-negative bacilli. Ticarcillin is available only in combination with clarulanic acid.... penicillin
Prolonged use may cause weight gain.... pityriasis rosea
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