AMINOGLYCOCIDES

Gentamicin;Tobramycin; Amikacin;Streptomycin

• A group of bactericidal drugs sharing chemical, antimicrobial, pharmacologic and toxic characteristics

• ‘-mycin’: extracted from Streptomyces sp; ‘micin’: extracted from a Micromonospora sp.

• Inhibit protein synthesis in bacteria

• Potentially ototoxic and nephrotoxic: as are excreted via kidneys, dose must be reduced in renal failure

• Used most widely against gram negative bacteria

• Used for severe systemic infections

• Poorly absorbed from GIT therefore given IV

• Synergistic activity with penicillins: most streptococci are resistant to gentamicin, however, such streptocci can be killed by the concommitant use of a cell wall-active drug (eg penicillin)

• Problems of resistance

TETRACYCLINES

Tetracycline; Doxycycline

• Large group of antibiotics with a common basic structure and activity

• Extracted from Streptomyces aureofaciens

• Generally are bacteriostatic than bactericidal in action

• Inhibit protein synthesis in susceptible organisms by binding to ribosomes

• Broad antimicrobial spectrum: active against most gram-positive that are sensitive to penicillin and also against gram-neg that are not susceptible to penicillin

• Due to their effectiveness against a variety of microbes, they have often been used indiscrimately esoecially in the treatment of respiratory tract infections resulting in resistant organisms

ERYTHROMYCIN

• Produced by Stretomyces erythreus

• Inhibits protein synthesis in susceptible organisms by binding to ribosomes & inhibiting polypeptide synthesis

• More effective against gram-positive

• One of the safest & least toxic of the antibiotics

VANCOMYCIN

• Isolated from Streptomyces orientalis

• Unrelated to other commercial antibiotics

• Binds rapidly & reversibly to the cell walls of sensitivr bacteria, thereby inhibiting cell wall synthesis

• Only effective against gram positive

• Resistance to vancomycin does not appear to develop during therapy

• No cross-resistance with other antibiotics

• Excreted by kidneys

• Ototoxicity & nephrotoxicity are the most serious side effects

• Only indication is serious staphylococcal infection or endocarditis not responding to other treatment

CHLORAMPHENICOL

• First broad spectrum antibiotic discovered

• Originally isolated from Strptomyces venezuelae

• Now produced synthetically

• Inhibits protein synthesis by binding to ribosomes

• Wide antibacterial spectrum

• Aplastic anaemia is a rare complication; is generally low toxicity

METRONIDAZOLE

• Effective against susceptible anaerobic bacteria and protozoa (eg Trichomoniasis; Giardiasis)

• Metabolites bind to DNA of organism thereby inhibiting its synthesis

CARBAPENEM

Imipenem

• Beta-lactam antibiotic

• Wide spectrum with good activity against gram-neg, gram-positive and anaerobes

• Resistant to beta-lactamases

• Inactivated by dihydropeptidases in renal tubules: therefore is administered with Cilastin [inhibitor of renal dihydropeptidase]

MONOBACTAMS

Aztreonam

• Beta-lactam antibiotic

• Resistant to beta-lactamases

• Active against gram-negative rods

• No activity against gram-positive bacteria or anaerobes

CLAVULANIC ACID

eg Augmentin (Amoxicillin + clavulanate)

• Resemble beta-lactam molecules but have weak antibacterial action

• Are potent inhibitors of bacterial beta-lactamases

• Thus are given with Amoxycillin or Ticarcillin to treat beta-lactamase producing bacteria