Aminoglycoside antibiotics

Aminoglycoside antibiotics

The aminoglycoside antibiotics contain one or more amino sugars linked to an aminocytitol ring by glycosidic bonds. These are broad-spectrum antibiotics; in general, they have greater activity against gram-negative than gram-positive bacteria. The development of streptomycin, the first antibiotic of this group, was a well-planned work of Waksman (1944) and his associates, who isolated it from a strain of Streptomyces griseus.

The aminoglycoside can produces severe adverse effects, which include nephrotoxity, ototoxicity, and neuro effects. These properties have limited the use of aminoglycoside chemotherapy to serious systemic indications. Some aminoglycosides can be administered for ophthalmic and topical purposes.

Mode of action: The aminoglycosides exhibit bactericidal effects as a result of several phenomena. Ribosomal binding on 30s and 50s subunits as well as the interface produces misreading; this disturbs the normal protein synthesis. Cell membrane damage also plays an integral part in ensuring bacterial cell death. Some examples of aminoglycoside antibiotics are listed in Table 4.1.

a. Streptomycin and dihydrostreptomycin

Properties and uses: Streptomycin sulphate is a white hygroscopic powder, very soluble in water, and practically insoluble in ethanol. The organism, S. griseus, releases the other substances, such as hydroxystreptomycin, mannisidostreptomycin, and cycloheximide, but do not reach up to the required activity/potency level. The development of resistant strains of bacteria and chronic toxicity constitutes major drawbacks of this category. It is an aminoglycoside antibacterial also used as an antitubercular drug.

Assay: It is assayed by microbiological method.

Dosage forms: Streptomycin injection B.P.

b. Gentamycins

Properties and uses: Gentamycin is a mixture of C₁, C₂, and C₁A compounds, obtained commercially from Micromonospora purpurea. Gentamycin sulphate exists as white hygroscopic powder, soluble in water, and practically insoluble in alcohol, although it is a broad-spectrum antibiotic. It is used in the treatment of infections caused by gram-negative bacteria of particular interest and has a high degree of activity against

P. aeruginosa, where the important causative factor is burned skin. It is used topically in the treatment of infected bed-sores, pyodermata, burns, and in the eye infection.

Assay: It is assayed by microbiological method.

Dosage forms: Gentamicin cream B.P., Gentamicin ear drops B.P., Gentamicin and Hydrocortisone acetate ear drops B.P., Gentamicin eye drops B.P., Gentamicin injection B.P., Gentamicin ointment B.P.

c. Neomycin

Properties and uses: Neomycin sulphate is a white or yellowish-white hygroscopic powder, very soluble in water, very slightly soluble in alcohol, and practically insoluble in acetone. Neomycin is a mixture of closely related epimers, neomycin B, and C. Neomycin B differ from neomycin C by the nature of the sugar attached terminally to _D-ribose, this sugar called neosamine. B1 differs from neosamine C in its stereochemistry. In neomycin B₁ , the neobiosamine moiety contains. β-_L-iodopyranosyl, whereas in neomycin C the configuration is inverted and it is 2-_D-glucopyranosyl. It is photosensitive and its main use is in the treatment of the ear, eye, and skin infections; these include burns, wounds, ulcer, and infected dermatoses.

Assay: It is assayed by microbiological method.

Dosage forms: Dexamethasone and Neomycin ear spray B.P., Hydrocortisone and neomycin cream B.P., Hydrocortisone acetate and Neomycin ear drops B.P., Hydrocortisone acetate and Neomycin eye drops B.P., Neomycin eye drops B.P., Hydrocortisone acetate and Neomycin eye ointment B.P., Neomycin eye ointment B.P., Neomycin oral solution B.P., Neomycin tablets B.P.

d. Kanamycin

Properties and uses: Kanamycin sulphate is a white crystalline powder, soluble in water, practically insoluble in acetone and in alcohol. The mixture consists of three related structures, that is, Kanamycin A, B, and C. The kanamycins do not possess _D-ribose molecule that is present in neomycins and paramomycins. The use of kanamycins is restricted to infections of the intestinal tract and to systemic infections.

Assay: It is assayed by microbiological method.

e. Amikacin

Properties and uses: Amikacin is a semisynthetic drug derived form kanamycin A. It retains 50% of the original activity of kanamycin A. _L-Isomer is more active than _D-isomer. It resists attack by most bacterialinactivating enzyme. Therefore, it is very effective and less ototoxic than other aminoglycosides.

Dosage forms: Amikacin sulphate injection I.P.

f. Tobramycin

Properties and uses: Its activity is similar to gentamycin. The superior activity of tobramycin against P. aeruginosa may make it useful in the treatment of bacterial oesteromyelitis, and pneumonia caused by P. species.

Dosage forms: Tobramycin injection I.P.

g. Netilmicin (1-N-ethylsisomicin)

Properties and uses: Netilimycin sulphate is a white or yellowish-white hygroscopic powder, very soluble in water, practically insoluble in acetone and alcohol. It is similar to gentamycin and tobramycin. The majority of the aminoglycoside inactivating enzymes do not metabolize it. It is useful for the treatment of serious infections due to susceptible enterobacteria and other aerobic gram-negative bacilli.

Assay: It is assayed by microbiological method.