Aminoglycosides

The aminoglycosides are first-line therapy for a limited number of very specific, often historically prominent infections, such as plague, tularemia, and tuberculosis; they also are frequently used to treat infections caused by aerobic gram-negative bacteria. Their clinical roles have diminished as less toxic alternatives have become available. Unlike most inhibitors of microbial protein synthesis, which are bacteriostatic, the aminoglycosides are bactericidal. Resistance most commonly arises from acquisition of plasmids or transposons encoding genes for aminoglycoside-metabolizing enzymes or from impaired transport of drug into the cell; cross-resistance is common.

These agents are polycations whose polarity affects their shared pharmacokinetic properties: none is absorbed adequately after oral administration, inadequate concentrations are found in cerebrospinal fluid (CSF), and all are excreted relatively rapidly by the normal kidney. All members of the group also share the same spectrum of toxicity, most notably nephrotoxicity and ototoxicity.

The aminoglycosides consist of two or more amino sugars joined in glycosidic linkage to a hexose nucleus (Figure 45-1). Different aminoglycosides are distinguished by the amino sugars attached to the aminocyclitol. Streptomycin differs from the other aminoglycoside antibiotics in that it contains streptidine rather than 2-deoxystreptamine, and the aminocyclitol is not in a central position.

The aminoglycosides consist of two or more amino sugars joined in glycosidic linkage to a hexose nucleus (Figure 45-1). Different aminoglycosides are distinguished by the amino sugars attached to the aminocyclitol. Streptomycin differs from the other aminoglycoside antibiotics in that it contains streptidine rather than 2-deoxystreptamine, and the aminocyclitol is not in a central position.

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