Inhibitors of Protein Synthesis 1.30S directed: irreversible=cidal aminoglycosides selective toxicity: active transport into bacteria, requires oxid/phos and is affected by pH, O2, cations, no penetration into animal cellsselective toxicity: active transport into bacteria, requires oxid/phos and is affected by pH, O2, cations, no penetration into animal cells 2.50S directed: reversible=static chloramphenicol, erythromycin, (clarithromycin), clindamycin, quinupristin/dalfopristin, linezolid selective toxicity: do not penetrate mito/ poor binding to mitochondrial and animal ribosomesselective toxicity: do not penetrate mito/ poor binding to mitochondrial and animal ribosomes 3.30S directed: reversible=static tetracyclines (doxycycline, minocycline) selective toxicity:energy dependent uptake by sensitive bacteria, animal ribosomes sensitive to high dose but no active transportselective toxicity:energy dependent uptake by sensitive bacteria, animal ribosomes sensitive to high dose but no active transport

Folic Acid Pathway Inhibitors sulfonamides, trimethoprim –selective toxicity: sulfonamides: animal cells do not make folate, we absorb it from the environmentsulfonamides: animal cells do not make folate, we absorb it from the environment trimethoprim: has much higher affinity for the bacterial DHFR than the mammalian DHFRtrimethoprim: has much higher affinity for the bacterial DHFR than the mammalian DHFR

Pathway of tetrahydro- folate cofactor synthesis and role in DNA, RNA, and protein synthesis Trimethoprim inhibits Sulfonamides inhibits

Folic Acid

DHFR thymidylate synthetase

Synergistic combinations of Trimethoprim & Sulfamethoxazole (Bactrim®, Septra®)  Staph sensitivity Sulfamethoxazole MIC = 3 ug/ml Sulfamethoxazole MIC = 3 ug/ml Trimethoprim MIC = 1 ug/ml Trimethoprim MIC = 1 ug/ml combo MIC = 0.3 Sulf & Trim combo MIC = 0.3 Sulf & Trim 20:1 ratio most effective20:1 ratio most effective  Advantages more likely to be cidal more likely to be cidal broader spectrum broader spectrum decreased resistance decreased resistance lower doses = lower toxicity lower doses = lower toxicity

Other mechanisms  Membrane disrupters: Daptomycin Daptomycin lipopeptide that binds bacterial membraneslipopeptide that binds bacterial membranes causes ion leakage and membrane depolarizationcauses ion leakage and membrane depolarization leads to cell death (cidal)leads to cell death (cidal)

Daptomycin action  active against gram+ including methicillin resistant Staph A (MRSA) and vancomycin resistant enterococcus (VRE)  alternative to vancomycin for MRSA (especially important as vancomycin resistant MRSA emerges other alternatives: linezolid, quinupristin/dalfopristin, other alternatives: linezolid, quinupristin/dalfopristin,

Other mechanisms  RNA synthesis inhibitors: rifampin--binds bacterial RNA Polymerase and inhibits rifampin--binds bacterial RNA Polymerase and inhibits selective toxicity: little binding to human RNA polymerase selective toxicity: little binding to human RNA polymerase  DNA gyrase/topoisomerase inhibitors prototype: nalidixic acid prototype: nalidixic acid fluoroquinolones fluoroquinolones ciprofloxacin, norfloxacin: broad spectrum, low toxicityciprofloxacin, norfloxacin: broad spectrum, low toxicity newer derivatives: trovafloxacin, moxifloxacin, levofloxacin have expanded spectrum, longer half life, high oral bioavailabilitynewer derivatives: trovafloxacin, moxifloxacin, levofloxacin have expanded spectrum, longer half life, high oral bioavailability

REPLICATION TRANSCRIPTION TOPO IV GYRASE Function of DNA gyrase and topoisomerase IV in replication and transcription

Mechanism of action of ciprofloxacin and other DNA gyrase/topoisomerase IV inhibitors

Gatifloxacin Ciprofloxacin Nalidixic acid Norfloxacin Levofloxacin Moxifloxacin Quinolones

Metronidazole--mechanism of action  Anaerobic organisms contain ferredoxins that can activate metronidazole to form a reactive nitro radical anion that kills by targeting DNA/other biomolecules  Treatment examples: Giardiasis (protozoal infection) Giardiasis (protozoal infection) also used to treat Clostridium difficile also used to treat Clostridium difficile Giardia lamblia

Risk of Giardia in the mountains? up to 35% of children in daycare test positive for Giardia in stool samples! most asymptomatic

Oral Absorption of Antibiotics Good: Good:sulfonamides chloramphenicol clindamycin trimethoprim isoniazid, pyrazinamide ciprofloxacin doxycycline cycloserine metronidazole linezolid Bad or variable: penicillins (some are, many aren’t) cephalosporins (few are, most are not) erythromycin (estolate conjugate) (clarithromycin is better) Ugly: Ugly: aminoglycosides: gentamicin tobramycin amikacin netilmicin vancomycin quinupristin/dalfopristin meropenem

Therapeutic levels in the CSF? Good: Good: ciprofloxacin sulfonamides, trimethoprim chloramphenicol some 3rd generation cephalosporins (e.g. ceftriaxone, ceftizoxime) meropenem cycloserine, metronidazole pyrazinamide, isoniazid linezolid OK: OK: (esp. when meninges inflamed) ampicillin, ticarcillin vancomycin rifampin Poor:aminoglycosidestetracyclinesclindamycinerythromycincefaclorquinupristin/dalfopristin(synercid)

Distribution of drug into human cells?  Pathogens can enter cells Require intracellular phase Require intracellular phase Rickettsia (cytoplasm)Rickettsia (cytoplasm) Chlamydia (phagosomes)Chlamydia (phagosomes) Can survive both intra and extracellular environment Can survive both intra and extracellular environment Mycobacteria (cytoplasm & phagosomes)Mycobacteria (cytoplasm & phagosomes) Legionella (phagosomes)Legionella (phagosomes) Listeria (cytoplasm)Listeria (cytoplasm) Salmonella (phagosomes)Salmonella (phagosomes)  Question: Do antibiotics need to penetrate animal cell to kill these pathogens? probably not but it may help probably not but it may help

Antibiotic metabolism and excretion 1. excreted unchanged via kidney 2. metabolized by liver  metabolites excreted by kidney  metabolites excreted thru bile Affected by renal/hepatic disease, developmental state, pharmacogenetic traits, and drug/drug interactions

Drug Metabolism and Excretion Excretion by Kidney (primarily) penicillins/cephalosporins (both kidney and liver for some) aminoglycosides tetracyclines (except doxycycline) sulfonamides vancomycin ciprofloxacin trimethoprim pyrazinamide Metabolized by Liver (primary) doxycycline chloramphenicol erythromycin clindamycin isoniazid rifampin metronidazole linezolid quinupristin/ dalfopristin

Chloramphenicol is metabolized in liver and then excreted by kidney

age 1-2 days age 1-11 years

Application of pharmacokinetic principles  Bactrim: 400mg sulfamethoxazole + 80 mg trimethoprim in fixed dose---does this make sense? what basic properties of these two drugs are relevant? what basic properties of these two drugs are relevant? optimal plasma ratio and concentrationoptimal plasma ratio and concentration t1/2t1/2 oral bioavailabilityoral bioavailability volume of distributionvolume of distribution drug interactionsdrug interactions