Chemotherapeutic Agents

Topics: Penicillin, DNA, Reverse transcriptase inhibitor Pages: 16 (1260 words) Published: August 25, 2013
CHEMOTHERAPEUTIC AGENTS
Anti-microbials

Paul Ehrlich

Father of chemotherapy
- Salvarsan or 606 or arsphenamine

Chemotherapeutic agents

-have selective toxicity (killing pathogens without harming the host)

Choice of chemotherapeutic agent depends on the following:

Identity & sensitivity of the organism
Empiric therapy
Definitive therapy

2. Host factors
Immune status:
immunocompromised
immunocompetent
Renal and hepatic function
Pregnancy and lactation
Age

4. Drug factors
Narrow/broad spectrum
Safety
Cost

Antibacterials

Classifications:
Inhibitors of cell wall synthesis
β-lactams, Vancomycin

Inhibitors of protein synthesis
Tetracycline, Aminoglycoside, Marolide, Clindamycin, Chloramphenicol

Inhibitor of folate synthesis
Sulfonamides, Trimethoprim

Inhibitor of nucleic acid synthesis
Rifampicin, Quinolones
INHIBITORS OF CELL WALL SYNTHESIS
β-lactam antibiotics
activity due to β-lactam ring

Penicillin
- inhibits transpeptidation or cross linking
- rupture of the cell wall
1. natural
Penicillin G (Benzylpenicillin)
Susceptible to β-lactamase
acid-labile
Pneumococcal pneumonia, rheumatic fever, syphilis
Procaine, Benzathine Penicillin G (depot): IM

Penicillin V (Phenoxymethylpenicillin)
acid-stable
Same spectrum as Penicillin G

2. Penicillinase-resistant
Methicillin, Oxacillin, Cloxacillin, Nafcillin
S. Aureus
Methicillin-resistant S. Aureus (MRSA), Vancomycin

3. Aminopenicillin
Amoxicillin, Ampicillin
Extended spectrum against gram (-) (H. Influenzae, E. Coli, S. Typhi)

Anti-pseudomonal
Carbenicillin, Piperacillin, Ticarcilli, Mezlocillin

Side Effects:
Hypersensitivity
Diarrhea
Nephritis (Methicillin)
Hemorrhage (anti-pseudomonal)
Electrolyte imbalance

Drug Interactions
-Probenecid: inhibits renal excretion of Penicillin
-Static drug: antagonism

β- Cephalosporins
Same Mode of Action
More resistant to β-lactamase
Increase gram (-) activity
GENERATIONS
1st Generation – Proteus, E. Coli, Klebsiella

Cefazolin
Cefadroxil
Cefalexin
Cephapirine
Cephalothin

2nd Generation – H. Influenzae, Enterobacter, Neisseria

Cefuroxime
Cefoxitin
Cefprozil
Cefamandole
Cefaclor
Loracarbef

3rd Generation – Serratia, Salmonella, Shigella

Cefoperazone
Ceftriaxone
Cefetamet
Cefixime
Ceftazidime
Cefotaxime
Ceftibuten
Moxalactam

4th Generation – greater activity against gram (+) cocci, Enterobacter, Pseudomonas than 3rd Generation

Cefepime
Cefpirome

Side effect
Allergy
Disulfiram-like reaction

Carbapenems
Resist β-lactamase
Broad spectrum for multi-drug resistant bacteria
Imipenem, Meropenem
Imipenem + Cilastatin (inhibits dehydropeptidase in kidney prevents formation of toxic metabolite)

S/E: seizures

Monobactams
Aztreonam
Against gram (-) aerobic bacteria: E. Coli, Serratia, Proteus, Salmonella, Hemophillus, Klebsiella, Pseudomonas

β-lactamase Inhibitors
Clavulanic Acid + Amoxicillin
Sulbactam + Ampicillin
Tazobactam + Piperacillin
ii. VANCOMYCIN
MRSA
Pseudomembrane colitis (Clostridium difficile)
S/E: red man syndrome
INHIBITORS OF PROTEIN SYNTHESIS
Bacteria:70s ribosome (50s & 30s subunits)

Human: 80s ribosome (60s & 40s)

Tetracycline
Bind to 30s
Static
Tetracycline, Doxycycline, Minocycline, Demeclocycline
Chlamydua, Mycoplasma pneumoniae, H. Pylori, rocky mountain spotted fever, lyme disease

Side effects
Gastric distress
Teeth discoloration, enamel dysplasia
Phototoxicity (Demeclocycline)
Hepatic necrosis
Fanconi-like syndrome

Drug Interactions:
+ Ca (dairy products), Mg & Al (antacids); complexation

Exception: Doxycycline, Minocycline

II. Aminoglycosides
bind to 30s
Cidal
Streptomycin, Gentamycin, Amikacin, Neomycin, Tobramycin, Kanamycin Pseudomonas, E. Coli & Klebsiella pneumoniae
Streptomycin: TB, plague, viridans endocarditis

Side effects
ototoxicity: Neomycin, Kanamycin, Amikacin...
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