Antibiotic Drugs

Since the days when chloramphenicol was more commonly used, it has been recognized that many antimicrobial drug are associated with severe blood dyscrasias, such as aplastic anemia, neutropenia, agranulocytosis, throm-bocytopenia, and hemolytic anemia. Information on this association has come predominantly from case series and hospital surveys (38^. Some evidence can be extracted from population-based studies that have focused on aplastic anemia and agranulocytosis and their association with many drugs, including antimicrobial drugs. The incidence rates of blood dyscrasias in the general population have been estimated in a cohort study with a nested case-control analysis, using data from a General Practice Research Database in Spain.

Clarithromycin is a commonly used macrolide antibiotic and is a regular part of regimens for the eradication of Helicobacter pylori, often in combination with a nitromidazole antibiotic as well, in addition to a proton pump inhibitor. Variable rates of adverse events (4-30%) have been reported with clarithromycin.

For amebiasis there is still discussion about the use of a single high dose versus repeated lower doses, both as regards efficacy and adverse effects. The use of metronidazole against infections with anerobic bacteria has increased over the years, and with this indication the use of metronidazole in combination with many other drugs used by patients with conditions likely to develop secondary anaerobic bacterial infections. With increased use there is also a widespread and increasing incidence of resistance of various strains of bacteria. The use of metronidazole as an added medication merely “to make assurance double sure” is to be discouraged.

Metronidazole has a disulfiram-like effect in users of alcohol, sufficient to justify a warning. An unusual Antabuse-type reaction reported on one occasion seems to have been due to an interaction of metronidazole with the alcohol present in X-Prep. An interaction with metronidazole and ciclosporin, in which ciclosporin blood concentrations rise, has been suggested, though only in isolated case histories. It has been confirmed that metronidazole can produce a two-fold increase in blood concentrations of ciclosporin and tacrolimus, with a subsequent increase in serum crea-tinine in both cases.

Central nervous system symptoms can occur with standard doses of metronidazole, but they are mainly seen with high doses and especially when such doses are given for a long time. Under the latter conditions, there was a 25% incidence of such symptoms as headaches, dizziness, tremor, ataxia, and confusion.

Cipro (ciprofloxacin) is an antibiotic that belongs to a class of drugs called fluoroquinolones. It is used to treat a variety of bacterial infections by stopping the growth of bacteria.

The anthracyclines are composed of a tetracyclic ring with adjacent quinone-hydroquinone moieties and a short side chain with a carbonyl group at C-13; an aminosugar is attached by a glycosidic bond to the C-7 of the tetracyclic ring. Doxorubicin (DOX) and daunorubicin (DNR) differ in the side chain terminus (-CH2OH or-CH3, respectively).

Nafcillin shares the uses of other parenteral penicillinase-resistant penicillins (e.g., oxacillin) and generally is used only in the treatment of infections caused by, or suspected of being caused by, susceptible penicillinase-producing staphylococci. For specific information on the uses of nafcillin, see Uses in the Penicillinase-Resistant Penicillins General Statement 8:12.16.12. Nafcillin sodium is administered by IM injection or by IV injection or infusion. Although nafcillin also has been administered orally, the drug is poorly absorbed from the GI tract and an oral preparation of the drug is no longer commercially available in the US.

Meropenem is a synthetic carbapenem antibiotic. Unlike imipenem, meropenem has a methyl group at position 1 of the 5-membered ring, which confers stability against hydrolysis by dehydropeptidase 1 (DHP 1) present on the brush border of proximal renal tubular cells and therefore does not require concomitant administration with a DHP-1 inhibitor such as cilastatin.

Carbacephems are b-lactam antibiotics structurally and pharmacologically related to cephalosporins; however, carbacephems contain a methylene group instead of sulfur in the dihydrothiazine ring of the cephalosporin nucleus, resulting in a tetrahydropyridine ring. This structural modification does not affect microbiologic activity, but substantially improves stability in aqueous solution and in serum, plasma, and other body fluids. Loracarbef is the carba analog of cefaclor, a second generation cephalosporin. SumMon® (see Users Guide).