chemotherapeutics & antibiotics. chemotherapeutics chemicals which are used within the body...
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•Chemotherapeutics
•&
• antibiotics
Chemotherapeutics
•Chemicals which are used within the body tissues to kill or inhibit the growth of pathogenic organisms
The Spectrum of antimicrobial Activity
•**it is easy to find or develop drugs that effective against prokaryotic cells ,& that do not affect the eukaryotic cells of humans
•**the problem is difficult when the pathogen is eukaryotic (fungus, protozoan, helminthes)
•**viral infection more difficult to treat
The Spectrum of antimicrobial Activity
•Prok.**-differ in cell wall
•- differ in fine structure of their ribosome
•- details of their metabolism
•Euk.**resemble the human cell
•**the virus is within the human cells
antibiotics
Antibiotics=are a metabolic products or a constituent of a microorganism which kills or inhibit the growth of another microorganism
Nowadays used are semi synthetic (Ampicillin) or synthetic (Sulfa drugs)
(produced wholly or partly by chemical synthesis(
Low concentrations inhibit the growth of m.o.
Characteristics of a good chemotherapeutic or antibiotic
•1-it must kill or inhibit the growth of the pathogenic organism
•2-it must cause no damage to the host (it must have selective toxicity)
•3-it must cause no allergic reaction
•4-it must be stable in solid or dissolved state
•5-it must remain in the desired tissue for the sufficient length of time (pharmacokinetics)
•6 -it must kill the pathogenic organism quickly before it mutates and
becomes resistant to the drug
•Pharmacokinetics have to be desirable (absorption, disintegration)
•selective toxicity = toxic for the pathogenic organism and not toxic for the host == defined by the therapeutic index
• max. tolerated dose (toxic to the host)
•-------------------------------------------------------------- • min. curative dose (effective therapeutic dose)
•The high the therapeutic index the better the antibiotic is
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Therapeutic Index = Toxic Dose/Therapeutic DoseD
rug
Do
sag
e (p
er K
g B
od
y W
eig
ht)
Small Ratio(dangerous(
ModerateRatio
High Ratio(safe(
Most desirable.
Antibiotics activity
The Spectrum of antimicrobial Activity
•Narrow spectrum = affect only select group of microorganisms
• e.g Penicillin G affects Gram positive bacteria
•Broad spectrum = affect a broad range of Gram positive or Gram negative bacteria
• = affect a more diverse • range of microbes
e.g. Chloramphenicol.
Antibiotics activity
The type of activity
•Bactericidal : direct killing of microorganisms• = kill microorganisms directly
• (Streptomycin(
•Bacteriostatic = inhibit their growth• = prevent microorganism
• from growth (chloramphenicol(
= *#*# Host defenses usually destroy microorganisms by phagocytosis & antibody production
•Combination of
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Mechanisms of Antimicrobial Action
• Bacteria have their own enzymes for– Cell wall formation– Protein synthesis– DNA replication– plasma membrane– Synthesis of essential metabolites
Bacterial protein synthesis inhibitors
• ##initiation of protein synthesis
• ##elongation (=interfere with elongation factors(
Fusidic acid
Bacteriostatic
Gm+ve bacteria only
initiation of protein synthesis inhibitors
Antimicrobial that bind to the 50S ribosomal subunit
Antimicrobial that bind to the 30S ribosomal subunit
Chloramphenicol –
broad rang
LincomycinClindamycin
Restricted range
Tetracyclines
bacteriostatic broad spectrum
Tetracyclin ,Minocycline Doxycycline
Aminoglycosides
Bactericidal
Many gm.-ve bacteria &some gm+ve. Bacteria
StreptomycinKanamycinGentamycinNeomycinTobramycin
MacrolidesGm+ve bacteria &
Mycoplasma
Erythromycin
bacteriostatic
Inhibitors of nucleic acid synthesis & function
Inhibitors of RNA(DNA dependent RNA
polymerase(
Inhibitors of DNA(DNA gyrase(
Rifampin
Rifamycin
Rifampicin
Bactericidal
Wide spectrum Tuberculosis
Quinolones
Nalidixic acid
Ciprofloxacin
Bactericidal
Gm+ve bacteriaurinary tract infection
•Bacterial cell wall synthesis inhibitors
Bacterial cell wall synthesis inhibitors (bactericidal(
penicillins
•Bactericidal•Narrow range
•Effected by Stomach acidity=intramuscularly•Susceptible to penicillinase ( lactamase)
= are enzymes produced by many bacteria (Staph.) that clave the lactam ring
•
•Methicillin
•Oxacillin
•Ampicillin & amoxacillin & Mezlocillin=broad spectrum
• Carbapenems & Monobactam =broad
• Cephalosporins=gm-ve
• Vancomycin Bacitracin =gm+ve
• ++anti mycobacterial agents•Mycobacterium tuberculosis
• Antibiotics that interfere with mycolic acid synthesis or incorporation
– Isoniazid (INH)– Administerd simultaneously with other
drug (rifampin=rifampicin)
•Plasma membrane= phospholipids & protein
•Polymixin B interfere with phospholipids of plasma membrane
•Bactericidal
•Gm. – ve bacteria
Antimetabolite antimicrobials
• ++Inhibitors of folic acid synthesis•(bacteria cannot use pre-formed folic acid, they
synthesize their own folic acid(
bacteriostatic
•antifungal
Antifungal chemotherapeutics
•Fungi are Eukaryotes
•They may be unicellular ( yeast) or multicellular (mold).
•Cell wall compose of chitin
•Sterols in plasma membrane = ergosterol
AntifungalsMacrolide PolyenesAmphotericin B –mimic lipids, most versatile & effective, topical & systemic treatmentsNystatin – topical treatment
•Azole•Synthetic azoles – broad-spectrum;
ketoconazole, clotrimazole, miconazole (topical treatment of athlets foot)
•Allylamine•Recently developed antifungal=inhibit
ergosterols
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Antifungal drugs• Flucytosine – analog of cytosine;
coetaneous mycoses or in combination with amphotericin B for systemic mycoses
• **interfere with RNA biosynthesis
•Antiviral drugs
Antiviral drugs•Attachment
•Penetration
•Uncoating
•Nucleic acid synthesis (polymerases inhibitors(
•Assembly
•release
•Nucleoside & nucleotide analoges•(acyclovir, ribavirin, lamavudine(
•Lamavudine ==nucleoside analog=cytidine•Hepatitis B virus
•Reverse transcriptase inhibitor==HIV
Antiviral drugsAcyclovair=Zovirax=acycloguanosine=ACVGuanosine analogus
**Herpes simplex virus infection ) Genital, oral & eye(
**varicilla zoster virus) Shingles & Chickenpox in immunocompromised
patients(
###viral thymidine kinase phosphorelate the drug==this inactivate DNA polymerase
@@activity only inside virally infected cells@@
•Ribavirin==guanosin analoge
•stop viral RNA synthesis & mRNA
•===nucleoside inhibitor
•***hepatitis C virus
•***respiratory syncytial virus
•Amantadine ==symmetrel•***uncoating of influenza virus
•Tamiflue…..neuraminidase
•HIV inhibitors•Reveres transcriptase enzyme
inhibitors=retrovirus= nucleoside analoge•Protease inhibitors
•(Indinavir, saquinavir, ritonavir(•Zidovidine=rv.tr. inhibitor
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Interferon=protein(cytokines( produced by virally infected cells, that inhibit spread of the virus & protect other cells
***by the activation of the cell to produce certain enzyme
==prevent viral protein
synthesis
==kill virally infected cells
==the same way in which cancer
cells be killed (cancers) • (Viral hepatitis)
Antiviral Drugs
•Protozoa are unicellular Eukaryotic microbes
•Have variety of shapes ,
•Lives free or as parasite•They absorb or ingest organic compounds from
their environment
•Anti protozoa chemotherapeutics
•Anti malaria
•Malaria is an entirely preventable & treatable disease
•treatment==rapid & complete elimination of the parasite ------chronic & anemia
•prevention== of the spread & emerging resistance
Drugs used for malaria prophylaxis can work in one of three ways:
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Kill parasites in the liverCausal prophylaxisprimaquine ++++malarone ++
Kill asexual parasites in RBCs Suppressive prophylaxischloroquine ++++malarone ++++mefloquine ++++doxycycline ++++Kill sexual parasites
(gametocytes) in RBCsGametocytocidal prophylaxisprimaquine ++++
Mosquito Human
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Antihelminthic Drugs• Helminths are
macroscopic multicellular eukaryotic organisms: tapeworms, roundworms, pinworms, hookworms
Praziquantel
Albendazole
Surgery
Clinical uses of antimicrobial drugs
Clinical uses of antimicrobial drugs
•Inappropriate Antimicrobial Use Prescription not taken correctly
Antibiotics for viral infections
Antibiotics sold without medical supervision
Spread of resistant microbes in hospitals due to lack of hygiene
Proper selection of antimicrobial agent is based on a number of factors
•-**the identity of the pathogen•-**potential toxicity to the patient
•-**pharmacokinetics & pharmacodynamics of the agent
•-**site of infection•-**rout of administration
•-**drug resistance•-**possible drug interaction
•-**host factors•-**cost
•Drug selection should be based on it’s activity against infecting pathogen
•pathogen may be predictably susceptible to a particular drug
•Therefore lab. guidance is essential for safe prescribing
•Culture & sensitivity test
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Susceptibility Tests
Agar diffusion = disk-diffusion test Kirby-Bauer Disk Diffusion Test
Sensitive
Intermediate
resistant
(cont’d)
32 ug/ml 16 ug/ml 8 ug/ml 4 ug/ml 2 ug/ml 1 ug/ml
Sub-culture to agar medium
MIC = 8 ug/mlMBC = 16 ug/ml
Minimal Inhibitory Concentration (MIC)=the lowest concentration of drug capable of preventing bacterial growth
vs.Minimal Bactericidal Concentration (MBC)=the lowest concentration of chemotherapeutic agent that kills bacteria
•Minimum inhibitory concentration (MIC) •is determined when
•**a patient does not respond to treatment
•**thought to be adequate,
•**relapses while being treated
•**when there is immunosuppression.
Host factors play an important part in proper selection of antimicrobial drug
•-**age
•-**circulating & tissue phagocyte activity•e.g. hematological malignancy=acute
leukemia•Bactericidal= amino glycosides
• broad spectrum penicillins• cephalosporin
• quinolones
Pharmacological factors•By achieving satisfactory drug concentration at the site
of infection•Standard pharmacokinetics =absorption• distribution• metabolism
• excretion•Oral---- G.I. absorption should be satisfactory
• interaction with food• vomiting (surgery)
•***Parenteral agent will be required
Site of infection
•---lipid solubility of the drug•Amino glycosides are poorly lipid –soluble
=penetrate CSF poorly (bacterial meningitis(•Meningeal inflammation also affect drug
penetration into the tissues
•Beta-lactam agents achieve satisfactory concentration within CSF but the inflammation subsides drug concentration
super infection•Normal flora (skin & mucous membrane)
•Microbial overgrowth of resistant pathogen•Oral & vaginal candidiasis
•Broad spactrum-(ampicillin or tetracycline)
•Pseudo-membranous colitis•Toxin-producing strain of clostridium
•Following the use of clindamycin•Managed by oral vancomycin
•surgery
Proper selection of antimicrobial agent is based on a number of factors
•-**the identity of the pathogen•-**potential toxicity to the patient
•-**pharmacokinetics & pharmacodynamics of the agent
•-**site of infection•-**rout of administration
•-**drug resistance•-**possible drug interaction
•-**host factors•-**cost
Drug resistance
•Intrinsic= inherent properties of bac. are responsible for preventing antibiotic action ==always chromosomally mediated
• 0r
•Acquired= occurs when bac. which were previously susceptible then become resistance
• ==occur by mutation in the chromosome or by acquisition of genes coding for resistance from external source (plasmid(
•Plasmid mediated resistance has been recognized among Gm.-ve bact.== can code for multiple resistant ##cephalosporins, chloromphinicol, amino glycosides
•==enzymatic inactivation
•hospitals & intensive care units
Multi-drug resistance
•Methicillin resistant Staph.aureus (MRSA)
•=resist to many antibiotics
•Hospitals, intensive care units, burn ,cardiothoracic units
•Glycopeptides , vancomycin
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Enzymatic destruction of drug (B lactamase( Drug inactivation – penicillinases
Prevention of penetration of drug to its target site within the bacteria (tetracycline resistance( Decreased permeability to drug or increased elimination of drug from cell
Mechanisms of Antibiotic Resistance
Mechanisms of Antibiotic Resistance
Alteration of drug's target site(a.a changes in the ribosome( Change in metabolic patterns
Rapid ejection of the drug Change in drug receptors
•Efflux pump= antibiotic is rapidly extracted from the cell by an energy-dependent mechanism ( tetracyclines & macrolides)
• ++Inpaired cell wall or cell envelope penetration
• ++Enzymatic inactivation
• ++Altered binding sites• ++Efflux pump= antibiotic is rapidly
extracted from the cell by an energy-dependent mechanism( tetracyclines & macrolides)
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What Factors Promote Antimicrobial Resistance?
Exposure to sub-optimal levels of antimicrobial
Exposure to microbes carrying resistance genes
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To lower Antimicrobial Resistance Development
• Use more narrow spectrum antibiotics
• Use antimicrobial cocktails
Effects of combinations of drugs
• SynergismPenicillin and streptomycin, Sulfa and trimethoprim
• AntagonismPenicillin and tetracycline
• Addition
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Com
bina
tion
of
Dru
gs
For antibiotics “A” and “B” used in combination:
Actual killing rate = A + B Additive
Actual killing rate > A + B Synergistic
Actual killing rate < A + B Antagonistic
Typically bacteriostatic agents are antagonistic to bactericidal agents.
Bacteriocidal agents can be synergistic (think of the latter as one antibiotic weakens more bacteria than it kills, making the not-killed bacteria more susceptible to additional insult by the second antibiotic).
Additive means that the two (or more) antibiotics neither hinder nor help each other’s ability to kill.
Also relevant to rates of mutation to resistance.
•Second term exam.•Good luck