Lincosamides, including clindamycins

This chaj)ter discusses three groups of broad-spectrum antibiotics the tetracyclines, tlie macrolid, and the lincosamides. Example of the tetracycline include doxycycline (Vibramycin), minocycline (Minocin), and tetracycline (Sumycin). Examples of the macrohde include azithromycin (Zitliromax), clarithromycin (Biaxin), and erytliromycin (E-Mycin). The lincosamides include clindamycin (Cleocin) and lin-comycin (Lincocin). The Summary Drug Table Tetracyclines, Macrolide, and Lincosamide describe the lyi es of broad-spectrum antibiotics discussed in tliis chapter. 

The lincosamide family of antibiotics includes lin-comycin (Lincocin) and clindamycin (Cleocin), both of which inhibit protein synthesis. They bind to the SOS ri-bosomal subunit at a binding site close to or overlapping the binding sites for chloramphenicol and erythromycin. They block peptide bond formation by interference at either the A or P site on the ribosome. Lincomycin is no longer available for human use in the United States. 

The macrolide antibiotics include erythromycin, clarithromycin, azithromycin, tylosin, tilmicosin and tiamulin. Clindamycin and lincomycin are related lincosamides. Susceptible bacteria include staphylococci, streptococci, Campylobacter jejunii, Clostridium spp., R. equi, Mycoplasma pneumoniae and Chlamydia spp. Drugs in this group are only effective against a few Gram-negative bacteria in cattle, namely some strains of Pasteurella and Haemophilus spp. Macrolides and lincosamides are associated with causing colitis in horses, so their use is usually restricted to p.o. erythromycin for the treatment of R. equi infections in foals. Subantimicrobial doses of erythromycin are administered i.v. to horses for gastrointestinal prokinetic action. 

Examples of antibiotics that attack bacteria by inhibiting protein synthesis at the ribosomal level include the following tetracycline antibiotics (e.g. chlortetracycline) aminoglycoside antibiotics (e.g. neomycin, streptomycin) macrolide antibiotics (e.g. erythromycin, clarithromycin, azithromycin) also chloramphenicol, fusidic acid and lincosamides (e.g. clindamycin). 

Erythromycin estolate in conjunction with rifampin (both drugs administered orally) can be recommended for the treatment of Rhodococcus equi pneumonia in foals. Early diagnosis of the infection and prompt initiation of therapy considerably increase the effectiveness of treatment. Apart from this specific indication, macrolide antibiotics (including erythromycin) and lincosamides (lincomycin and clindamycin) are contra-indicated in horses. Antimicrobial agents in these classes can cause severe disturbance of the balance between commensal bacterial flora in the colon of the horse. 

A. Classification and Pharmacokinetics The lincosamides lincomycin and clindamycin inhibit bacterial protein synthesis via a mechanism similar to that of the macrolides, though they are not chemically related. Mechanisms of resistance include methylation of the binding site on the 50S ribosomal subunit and enzymatic inactivation. Cross-resistance between lincosamides and macrolides is common. Good tissue penetration occurs after oral absorption. The lincosamides are eliminated partly by metabolism and partly by biliary and renal excretion. 

The lincosamide class of antimicrobial drugs includes lincomycin, clindamycin, and pirlimycin two of these drugs—lincomycin and pirlimycin—are approved for use in food-producing species. Lincosamides are derivatives of an amino acid and a sulfur-containing galactoside. Lincomycin was isolated in 1962 from the fermentation product of Streptomyces lincolnensis subsp. lincolnensis. Clindamycin is a semi-synthetic derivative of lincomycin, and pirlimycin is an analog of clindamycin. 

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