NEOMYCIN & KANAMYCIN
Neomycin and kanamycin are closely related. Paromomycin is also a member of this group. All have similar properties.
Drugs of the neomycin group are active against gram-positive and gram-negative bacteria and some mycobacteria. P aeruginosa and streptococci are generally resistant. Mechanisms of antibacterial action and resistance are the same as with other aminoglycosides. The widespread use of these drugs in bowel preparation for elec-tive surgery has resulted in the selection of resistant organisms and some outbreaks of enterocolitis in hospitals. Cross-resistance between kanamycin and neomycin is complete.
Drugs of the neomycin group are poorly absorbed from the gas-trointestinal tract. After oral administration, the intestinal flora is suppressed or modified, and the drug is excreted in the feces. Excretion of any absorbed drug is mainly through glomerular filtration into the urine.
Neomycin and kanamycin are now limited to topical and oral use. Neomycin is too toxic for parenteral use. With the advent of more potent and less toxic aminoglycosides, parenteral administration of kanamycin has also been largely abandoned. Paromomycin has recently been shown to be effective against visceral leishmaniasis when given parenterally , and this serious infec-tion may represent an important new use for this drug.
Solutions containing 1–5 mg/mL are used on infected surfaces or injected into joints, the pleural cavity, tissue spaces, or abscess cavities where infection is present. The total amount of drug given in this fashion must be limited to 15 mg/kg/d because at higher doses enough drug may be absorbed to produce systemic toxicity. Whether topical application for active infection adds anything to appropriate systemic therapy is questionable. Ointments, often formulated as a neomycin-polymyxin-bacitracin combination, can be applied to infected skin lesions or in the nares for suppression of staphylococci but they are largely ineffective.
In preparation for elective bowel surgery, 1 g of neomycin is given orally every 6–8 hours for 1–2 days, often combined with 1 g of erythromycin base. This reduces the aerobic bowel flora with little effect on anaerobes. In hepatic encephalopathy, coliform flora can be suppressed by giving 1 g every 6–8 hours together with reduced protein intake, thus reducing ammonia production. Use of neomycin for hepatic encephalopathy has been largely supplanted by lactulose and other medications that are less toxic.
All members of the neomycin group have significant nephrotoxic-ity and ototoxicity. Auditory function is affected more than ves-tibular function. Deafness has occurred, especially in adults with impaired renal function and prolonged elevation of drug levels.
The sudden absorption of postoperatively instilled kanamycin from the peritoneal cavity (3–5 g) has resulted in curare-like neu-romuscular blockade and respiratory arrest. Calcium gluconate and neostigmine can act as antidotes.
Although hypersensitivity is not common, prolonged applica-tion of neomycin-containing ointments to skin and eyes has resulted in severe allergic reactions.