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Queen's University
Pharmacology and Toxicology
PHAR 100
Hisham Elbatarny

Antimicrobial, Antifungal and Antiviral Drugs History • Paul Ehrlich – Father of chemotherapy, used organoarsenicals – syphilis • Domagk – sulfonamides • Fleming – penicillin from a mold • Waksman – streptomycin • Antibiotic: a substance produced by an microorganism that suppress the growth of other organisms • synthetic compounds would be called antimicrobial. • Gram positive and negative: bacteria that take up gram’s stain are G+, and those that do not are G– ◦ cell wall is different: G- cell wall doesn't take up gram stain, while G+ lacks a component of the cell wall and ca Current Issues • Emergence of resistant strains: ◦ Longstanding problem. ◦ Due to organism mutating to have different properties. ◦ Over-use or under-use? ▪ prescribe usually for 8-10 days ▪ usually people feel better after ~5 days ▪ and stop taking drug: but organism still in body, more resistant ones! • Most of the current drugs take advantage of a difference between the host and the organism • All these targets have been discovered (common ones) • New targets will be more difficult to develop and hence the appearance of drugs that act via novel mechanisms could be rare ◦ Vancomysin resistant bacteria: problem b/c was main backu[ Classification • Narrow spectrum: e.g. penicillin acts on G+ only. • Broad spectrum: acts on both G+ and G–. • Bactericidal: kill the organism • Bacteriostatic: prevent multiplication of organism and defense mechanism of the host remove organism Penicillin • bacteria have rigid cell walls: have high osmotic pressure • mammalian cells do not have cell walls • thus, penicillin inhibits an enzyme involved in cell wall synthesis and bacteria are formed without cell walls and cannot maintain the pressure, break open ◦ selective toxicity: penicillin resembles D-alanyl-D-alanine and thus inhibits the enyzme (transpeptidation reaction- cross links the peptide chains) that would be used to make the cell wall Gram negative ← Grampositive does not have this layer D-ald-alacts onpeptidogyglan: inhibits the synthesis ofthis layer Resistance:some organisms can produce enzyme beta- lactamase that breaks down penicilin Classification of Penicillins • Penicillin G ◦ extracted from penicillium mold. ◦ narrow spectrum mainly G+ organisms. ◦ pneumoniae, middle ear infections and skin infections, meningitis, and syphilis. • Penicillin V – semisynthetic ◦ altered to make the molecule resistant to acid in the stomach ◦ more bioavailable than Pen G • Cloxacillin • penicillin developed to become resistant to beta-lactamase • bacteria become resistant to antibiotics by developing an enzyme that destroys the antibiotic. ◦ betalactamase or penicillinase – an adaptive enzyme produced by penicillin resistant organisms (staphylococcus aureus). • Ampicillin and Amoxicillin ◦ broader spectrum than Pen G, include some G– bacteria ◦ useful in urinary tract infections and E. coli. • Carbenicillin ◦ broad spectrum penicillin derivative, effective in severe infections caused by G– organisms ◦ problem: use where penicillin G would be sufficient • Augmentin ◦ combination of amoxacillin and clavulinic acid (ie an inhibitor of penicillinase) ◦ can be used for penicillinase producing organisms Adverse Effects of Penicillins • one of safest drugs • allergic reactions – most common: ◦ rash, tongue and face swell, urticaria (wheels) ◦ also get difficulty in breathing and fall in blood pressure if severe • diarrhea ◦ most antiobiotics cause diarrhea ◦ antibiotic destroy normal gut flora ◦ also if take antiobiotics with oral contraceptives, sometimes interfere with efficacy partially b/c of diarrhea Cephalosporins • Similar to penicillin in mechanism of action, but are more resistant to penicillinase. • first generation: Cephalothin, good against G+ less effective against G–. • CefamandoleL second generation, increased activity against G–. • third generation: less active against G+ than first generation, but increased activity against G–. ◦ gonorrhea • fourth generation: broader spectrum Fluoroquinolones highly abused b/c it is broad spectrum, lots of • Ciprofloxacin resistance ◦ broad spectrum G+ and G– ◦ inhibits DNAGyrase (ie topoisomerase II) and protein synthesis Erythromycin and Congeners • Severe G+ infections. • Inhibits protein synthesis • Used where individual allergic to penicillin. • Also used for some G– infections. Gonococci and legionnaires bacillus (people caught at a legionnaire conference when air conditioning unit was infected) • Azithromycin and clarithromycin. • Chemically modified from erythromycin, more effective than erythromycin but more expensive. Tetracyclines • Broad spectrum – bacteriostatic: don't kill organism, but stop their growth • Resistance is a problem due to over use • Inhibits bacterial protein synthesis • High affinity for calcium in bone and teeth → can't use in children (teeth and bone formation) and pregnant women Oxygens/hydroxyls on rings can bind calcium chloramphenicol Macrolides (?) Tetracycline Chloramphenicol • Broad spectrum, bacteriostatic antimicrobial
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