Antibacterial drugs, mechanisms orally active

Clarithromycin is derived from erythromycin by addition of a methyl group and has improved acid stability and oral absorption compared with erythromycin. Its mechanism of action is the same as that of erythromycin. Clarithromycin and erythromycin are virtually identical with respect to antibacterial activity except that clarithromycin is more active against Mycobacterium avium complex (see Chapter 47 Antimycobacterial Drugs). Clarithromycin also has activity againstM leprae and Toxoplasma gondii. Erythromycin-resistant streptococci and staphylococci are also resistant to clarithromycin. 

Paromomycin shares the same mechanism of action as neomycin and kanamycin (binding to the 30S ribosomal subunit) and has the same spectrum of antibacterial activity. Paromomycin is available only for oral use in the United States. Following oral administration, 100% of the drug is recovered in the feces, and even in cases of compromised gut integrity, there is little evidence for clinically significant absorption of paromomycin. Parenteral administration carries the same risks of nephrotoxicity and ototoxicity seen with other aminoglycosides. 

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