Resistance: R-factor mediated resistance resulting in 1. adenylation; 2. phosphorylation; 3. acetylation.

Pharmacokinetics: All are very poorly absorbed from GI tract (given before surgery for bowel sterilization); excreted almost entirely from the kidney via filtration; can reach very high levels in urine (alkaline environment improves effectiveness); do not pass thru BBB (although can be administered intrathecally).

Toxicity: Hypersensitivity (neomycin can produce contact dermatitis); curare-like effect on peritoneum; ototoxicity; nephrotoxicity.

MOA: Streptomycin binds to the 30S subunit and blocks initiation of protein synthesis and causes misreading of the genetic code, resulting in synthesis of fraudulent proteins because of incorporation of false amino acids. Bactericidal/static depending on concentration.

Spectrum: Mainly used as an adjuvant in tuberculosis therapy. Also used for plague and in combination with penicillin against enterococci.

Resistance: Develops explosively.

Toxicity: 8th nerve toxicity (vestibular), high frequency sounds are lost first; renal damage; curare-like effect; skin rashes.

Therapeutic place: Miliary tuberculosis, S. faecalis (with penicillin), uncommon infections (with tetracycline).

Tobramycin – Similar to gentamicin.

Viomycin – Second line drug in treatment of tuberculosis.

Netilmicin – New.

Spectinomycin – Not officially an aminoglycoside; indicated only in the treatment on N. gonorrhoea; takes just one dose; no renal or ototoxicity.

Gentamicin-Carbenicillin – BAD combination.

Gentamicin-Cephalothin – Additive nephrotoxicity.

Gentamicin-Polymixin B – Increased nephrotoxicity.

Gentamicin/Kanamycin-Ethacrynic acid – Increased oxotoxicity.

Category: Pharmacology Notes