(Mode of Action of Drugs)

PharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamicsPharmacodynamics

Chapter

1.4

Chapter

9.4 Aminoglycosides Antibiotics

Aminoglycosides are group of bactericidal
antibiotics originally obtained from various
Streptomyces species.

All aminoglycosides act by inhibiting
protein synthesis of bacteria by directly
combining with ribosomes. They penetrate
the outer cytoplasmic membrane and inhibit
protein synthesis. Streptomycin combines
with the bacterial 30S ribosomes and
inteferes with the mRNA-ribosome
combination. Other aminoglycosides bind
to additional sites on 50S subunit as well as
to 30S-50S interface.

All aminoglycosides are poorly
absorbed after oral administration, are more
active in alkaline pH and are excreted
unchanged by glomerular filtration. Since

Aminoglycosides

Antibiotics

excretion is principally via the kidney,

accumulation occurs in renal impairment.

All the aminoglycosides produce

cochlear and vestibular damage (ototoxicity)

which is a dose and duration of treatment

related side effect. Another serious side

effect is nephrotoxicity. Aminoglycosides

also reduce the acetylcholine release from

the motor nerve endings and cause

neuromuscular blockade.

Aminoglycoside antibiotics are

classified as in table 9.4.1.

STREPTOMYCIN

The aminoglycoside antibiotic, obtained

from Streptomyces griseus is the first

antitubercular drug.

Table 9.4.1: Classification of aminoglycoside antibiotics.

Streptomycin (AMBISTRYN-S) 0.75-1 g/day IM

Gentamicin (TAMIACIN) 3-5 mg/kg/day IM; 0.1-0.3% topical (eye drop, skin ointment/cream)

Tobramycin (TOBACIN) 3-5 mg/kg/day IM/IV

Amikacin (NOVACIN) 15 mg/kg/day IM

Kanamycin (KANSIN) 0.5-1 g/day IM

Neomycin (as sulphate) 0.3-0.5% topical (eye/ear drop, ointment/powder)

Framycetin (SOFRAMYCIN) 0.5-1.0% topical (eye drop/ointment, skin cream)