Inhibitors of Protein SynthesisInhibitors of Protein Synthesis1.1. 30S directed: irreversible=cidal30S directed: irreversible=cidal

aminoglycosidesaminoglycosides• selective toxicityselective toxicity: active transport into bacteria, requires oxid/phos and is affected by pH, O2, : active transport into bacteria, requires oxid/phos and is affected by pH, O2,

cations, no penetration into animal cellscations, no penetration into animal cells

2.2. 50S directed: reversible=static50S directed: reversible=staticchloramphenicol, erythromycin, (clarithromycin), clindamycin, quinupristin/dalfopristin, chloramphenicol, erythromycin, (clarithromycin), clindamycin, quinupristin/dalfopristin,

linezolidlinezolid• selective toxicityselective toxicity: do not penetrate mito/ poor binding to mitochondrial and animal ribosomes: do not penetrate mito/ poor binding to mitochondrial and animal ribosomes

3.3. 30S directed: reversible=static30S directed: reversible=statictetracyclines (doxycycline, minocycline)tetracyclines (doxycycline, minocycline)

• selective toxicityselective toxicity:energy dependent uptake by sensitive bacteria, animal ribosomes sensitive :energy dependent uptake by sensitive bacteria, animal ribosomes sensitive to high dose but no active transportto high dose but no active transport

Folic Acid Pathway InhibitorsFolic Acid Pathway Inhibitorssulfonamides, trimethoprimsulfonamides, trimethoprim– selective toxicityselective toxicity: :

• sulfonamides: animal cells do not make folate, we sulfonamides: animal cells do not make folate, we absorb it absorb it from the environment from the environment

• trimethoprim: has much higher affinity for the bacterial trimethoprim: has much higher affinity for the bacterial DHFR than the mammalian DHFRDHFR than the mammalian DHFR

Pathway of tetrahydro-Pathway of tetrahydro-folate cofactor synthesisfolate cofactor synthesisand role in DNA, RNA,and role in DNA, RNA,and protein synthesisand protein synthesis

Trimethoprim inhibitsTrimethoprim inhibits

Sulfonamides inhibitsSulfonamides inhibits

Folic Acid

DHFRDHFR

thymidylate synthetasethymidylate synthetase

Synergistic combinations of Synergistic combinations of Trimethoprim & SulfamethoxazoleTrimethoprim & Sulfamethoxazole

(Bactrim®, Septra®) (Bactrim®, Septra®) Staph sensitivityStaph sensitivity

Sulfamethoxazole MIC = 3 ug/mlSulfamethoxazole MIC = 3 ug/ml Trimethoprim MIC = 1 ug/mlTrimethoprim MIC = 1 ug/ml combo MIC = 0.3 Sulf & 0.015 Trimcombo MIC = 0.3 Sulf & 0.015 Trim

• 20:1 ratio most effective20:1 ratio most effective

AdvantagesAdvantages more likely to be cidalmore likely to be cidal broader spectrumbroader spectrum decreased resistancedecreased resistance lower doses = lower toxicitylower doses = lower toxicity

Other mechanismsOther mechanisms

Membrane disrupters: Membrane disrupters: DaptomycinDaptomycin

• lipopeptide that binds bacterial lipopeptide that binds bacterial membranesmembranes

• causes ion leakage and causes ion leakage and membrane depolarizationmembrane depolarization

• leads to cell death (cidal) leads to cell death (cidal)

Daptomycin actionDaptomycin action

active against gram+ including methicillin resistant Staph A active against gram+ including methicillin resistant Staph A (MRSA) and vancomycin resistant enterococcus (VRE)(MRSA) and vancomycin resistant enterococcus (VRE)

alternative to vancomycin for MRSA (especially important alternative to vancomycin for MRSA (especially important as vancomycin resistant MRSA emergesas vancomycin resistant MRSA emerges other alternatives: linezolid, quinupristin/dalfopristin, other alternatives: linezolid, quinupristin/dalfopristin,

Other mechanismsOther mechanisms RNA synthesis inhibitors:RNA synthesis inhibitors:

rifampin--binds bacterial RNA Polymerase and rifampin--binds bacterial RNA Polymerase and inhibitsinhibits

selective toxicity: little binding to human RNA selective toxicity: little binding to human RNA polymerasepolymerase

DNA gyrase/topoisomerase inhibitorsDNA gyrase/topoisomerase inhibitors prototype: nalidixic acidprototype: nalidixic acid fluoroquinolonesfluoroquinolones

• ciprofloxacin, norfloxacin: broad spectrum, low toxicityciprofloxacin, norfloxacin: broad spectrum, low toxicity• newer derivatives: trovafloxacin, moxifloxacin, levofloxacin newer derivatives: trovafloxacin, moxifloxacin, levofloxacin

have expanded spectrum, longer half life, high oral have expanded spectrum, longer half life, high oral bioavailability bioavailability

REPLICATIONREPLICATION

TRANSCRIPTIONTRANSCRIPTION

TOPO IVTOPO IVGYRASEGYRASE

Function of DNA gyrase and topoisomerase Function of DNA gyrase and topoisomerase IV in replication and transcriptionIV in replication and transcription

Mechanism of actionof ciprofloxacin and otherDNA gyrase/topoisomerase

IV inhibitors

N

NH

CH3N

O

OH

O

F

OCH3

N

O

OH

O

N

NH

F

N

NH

N

O

OH

O

F

CH3

N N

O

OH

O

CH3

CH3

Gatifloxacin

CiprofloxacinNalidixic acid

Norfloxacin Levofloxacin

Moxifloxacin

N

N

O

OH

O

F

O

N

CH3CH3

S

N

O

OH

O

F

NNH

H

H

OCH3

S

S

Quinolones

Metronidazole--mechanism of actionMetronidazole--mechanism of action

Anaerobic organisms Anaerobic organisms contain ferredoxins that can contain ferredoxins that can activate metronidazole to activate metronidazole to form a reactive nitro radical form a reactive nitro radical anion that kills by targeting anion that kills by targeting DNA/other biomoleculesDNA/other biomolecules

Treatment examples:Treatment examples: Giardiasis (protozoal infection)Giardiasis (protozoal infection) also used to treat Clostridium also used to treat Clostridium

difficiledifficile

Giardia lamblia

Risk of Giardia in the mountains?Risk of Giardia in the mountains?

up to 35% of children in daycare test positive forGiardia in stool samples! most asymptomatic

Oral Absorption of AntibioticsOral Absorption of Antibiotics

Good:Good: sulfonamideschloramphenicolclindamycintrimethoprimisoniazid, pyrazinamideciprofloxacindoxycyclinecycloserinemetronidazolelinezolid

Bad or variable:Bad or variable: penicillins (some are, many aren’t)cephalosporins (few are, most are

not)erythromycin (estolate conjugate)

(clarithromycin is better)

Ugly:Ugly: aminoglycosides:gentamicintobramycinamikacinnetilmicin

vancomycinquinupristin/dalfopristinmeropenem

Therapeutic levels in the CSF?Therapeutic levels in the CSF?

Good:Good: ciprofloxacinsulfonamides, trimethoprimchloramphenicolsome 3rd generation cephalosporins

(e.g. ceftriaxone, ceftizoxime)meropenemcycloserine, metronidazolepyrazinamide, isoniazidlinezolid

OK:OK: (esp. when meninges inflamed)ampicillin, ticarcillinvancomycinrifampin

Poor:Poor:aminoglycosidesaminoglycosidestetracyclinestetracyclinesclindamycinclindamycinerythromycinerythromycincefaclorcefaclorquinupristin/dalfopristinquinupristin/dalfopristin

(synercid)(synercid)

Distribution of drug into human cells?Distribution of drug into human cells?

Pathogens can enter cells Pathogens can enter cells Require intracellular phaseRequire intracellular phase

• Rickettsia (cytoplasm)Rickettsia (cytoplasm)• Chlamydia (phagosomes)Chlamydia (phagosomes)

Can survive both intra and extracellular environmentCan 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 Question: Do antibiotics need to penetrate animal cell to kill these pathogens?to kill these pathogens? probably not but it may helpprobably not but it may help

Antibiotic metabolism and excretionAntibiotic metabolism and excretion

1.1. excreted unchanged via kidneyexcreted unchanged via kidney

2.2. metabolized by liver metabolized by liver metabolites excreted by kidneymetabolites excreted by kidney metabolites excreted thru bilemetabolites excreted thru bile

Affected by renal/hepatic disease, developmental Affected by renal/hepatic disease, developmental state, pharmacogenetic traits, and drug/drug state, pharmacogenetic traits, and drug/drug interactionsinteractions

Drug Metabolism and ExcretionDrug Metabolism and Excretion

Excretion by Kidney (primarily)Excretion by Kidney (primarily)penicillins/cephalosporins

(both kidney and liver for some)

aminoglycosidestetracyclines (except

doxycycline)sulfonamidesvancomycinciprofloxacintrimethoprimpyrazinamide

Metabolized by Liver (primary)Metabolized by Liver (primary)doxycyclinechloramphenicolerythromycinclindamycinisoniazidrifampinmetronidazolelinezolidquinupristin/

dalfopristin

Chloramphenicol is metabolized in liver andChloramphenicol is metabolized in liver andthen excreted by kidneythen excreted by kidney

age 1-2 daysage 1-2 days

age 1-11 yearsage 1-11 years

Application of pharmacokinetic Application of pharmacokinetic principlesprinciples

Bactrim: 400mg sulfamethoxazole + 80 mg Bactrim: 400mg sulfamethoxazole + 80 mg trimethoprim in fixed dose---does this make trimethoprim in fixed dose---does this make sense?sense? what basic properties of these two drugs are what basic properties of these two drugs are

relevant?relevant?• optimal plasma ratio and concentrationoptimal plasma ratio and concentration• t1/2t1/2• oral bioavailabilityoral bioavailability• volume of distributionvolume of distribution• drug interactionsdrug interactions