The objective of chemotherapy is to study and to apply the drugs that have highly selective toxicity to the pathogenic microorganisms in the host body and have no or less toxicity to the host, so as to prevent and cure infective diseases caused by pathogens
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1. chemotherapy principles and problems
1. Jagir R. Patel, Asst Prof Dept. Pharmacology, APC
Jagir R. Patel
Assistant Professor
Dept. Pharmacology
2. Chemotherapy
Chemo + Therapy
The use of drugs (chemicals or derived from microorganisms) to treat any
disease or condition.
which has selective toxicity against organisms like virus, bacteria,
Protozoa, Fungi & Helminthes is called Chemotherapy.
Objective
The objective of chemotherapy is to study and to apply the
drugs that have highly selective toxicity to the pathogenic
microorganisms in host body and have no or less toxicity to
the host, so as to prevent and cure infective diseases caused
by pathogens.
3. Cont.…
Bactericidal: A bactericide or bacteriocide, sometimes abbreviated
Bcidal, is a substance that kills bacteria. Bactericides are disinfectants,
antiseptics, or antibiotics.
Bacteriostatic: they inhibit the growth and multiplication of
microorganisms. At high concentration bacteriostatic agents can be
bactericidal.
Minimum Inhibitory Concentration (MIC)
- minimum concentration of antibiotic required to inhibit the growth of
the test organism.
• Minimum Bactericidal Concentration (MBC)
- minimum concentration of antibiotic required to kill the test
organism.
4. Definitions
An antimicrobial agent is any chemical (drug) used to treat an infectious
disease, either by inhibiting or killing pathogens in vivo. Some
antimicrobial agents are antibiotics.
An antibiotic is a substance produced by a microorganism that kills or
inhibits growth of other microorganisms.
Antibiotics that have been chemically modified to kill a wider variety of
pathogens or reduce side effects are called semisynthetic antibiotics;
examples include semisynthetic penicillins such as ampicillin and
carbenicillin.
5. Time dependent and concentration dependent killing
Concentration-Dependent Killing
The rate & extent of killing increases as the peak drug concentration
increases
Eg: drugs inhibiting protein or DNA synthesis, largest
for AMINOGLYCOSIDES & FLUOROQUINOLONES
These drugs also exhibit a “POST-ANTIBIOTIC EFFECT”
or persistent suppression of bacterial growth after limited exposure to
an antibiotic
Proposed mechanisms include:
slow recovery of bacteria after non-lethal damage to cell structures
persistence of the antibiotic at its binding site
a need for bacteria to synthesize new proteins before growth can
continue
CLINICAL SIGNIFICANCE:
Antibiotics with a long post-antibiotic effect can be administered at
longer dosing intervals than would be predicted by their
pharmacokinetic half-life
6. Cont..
Time-Dependent Killing
A property associated with cell wall
synthesis inhibitors e.g. β-LACTAMS
& VANCOMYCIN
Bactericidal activity continues as
long as the plasma concentration is
greater than the minimum
bactericidal concentration (or
MIC).
CLINICAL SIGNIFICANCE:
The concentration of these drugs
should be maintained above the
MIC for the entire time interval
between repetitive doses.
7. Chemotherapeutic index
Chemotherapeutic agents need to act at a concentration that can
be tolerated by the tissues of the host and therefore they must
have a selective toxicity for micro organism compared with the
host.
This selective toxicity expressed in terms of the
“Chemotherapeutic Index” that compress the maximum dose that
can be tolerated by the host without causing death
Chemotherapeutic index defined as the maximum tolerated dose
per kilogram of body weight, divided by minimum dose per
kilogram body weight that will cure the disease.
8. Chemotherapeutic index
Chemotherapeutic Index (CI): the ratio of median lethal dose
(LD50) to median effective dose (ED50).
LD50/ED50 or LD5/ ED95
Generally the bigger the CI of a drug is, the lower its toxicity,
the better its curative effect and the greater its value of clinical
application.
CI = LD50 / ED50
9. Anti microbial classification
Typical bacteria
• Cell wall:
peptidoglycan
• Plasma membrane:
phospholipids no
sterols
• No nucleus
membrane the
genetic material is
single chromosome
• Plasmid : extra
chromosomal DNA
• Flagella: for
movement
• Pilli: sexual organ
during mating and
joints the other
bacteria for DNA
transfer
10. Metabolic pathway in bacterial cell
Class I: the utilization of glucose or some alternative carbon source for the
generation of energy (ATP) and synthesis of simple carbon compounds used
as precursors in the next class of reactions.
Class II: the utilization of these precursors in an energy-dependent synthesis
of all the amino acids, nucleotides, phospholipids, amino sugars,
carbohydrates and growth factors required by the cell for survival and growth.
Class III: assembly of small molecules into macromolecules-proteins, RNA,
DNA, polysaccharides and peptidoglycan.
11. Metabolic pathways- promising targets
Class I reactions are not promising targets for two reasons. First, bacterial
and human cells use similar mechanisms (the Embden-Meyerhof pathway and
the tricarboxylic acid cycle) to obtain energy from glucose.
Class II reactions are better targets because some pathways exist in
pathogens, but not human, cells. There are several examples
1. folate synthesis: sulphonamides
2. pyrimidine and purine analogues : fluorouracil /cancer chemotherapy
12. CLASS III REACTIONS
As pathogen cells cannot take up their own unique macromolecules, class
III reactions are particularly good targets for selective toxicity, and there are
distinct differences between mammalian cells and parasitic cells in this
respect.
Eg:
cell wall synthesis: cell wall inhibitors: e.g. penicillins
Protein synthesis: translations and transcription inhibitor: e.g.
aminoglycosides
Nucleic acid synthesis: interference with nucleic acids : Quinolones
18. What is the ideal antimicrobial drug ?
Have highly selective toxicity to the pathogenic
microorganisms in host body
Have no or less toxicity to the host.
Low propensity for development of
resistance.
Not induce hypersensitivies in the host.
Have rapid and extensive tissue distribution
Be free of interactions with other drugs.
Be relatively inexpensive
19. Problems with Antimicrobials
Toxicity:
This arise at the site of application gastric irritation, pain, abscess formation
(i.m.), thrombophlebitis (i.v.) e.g. tetracycline's, cephalosporin's etc.
Systemic toxicity:
Majority of AMAs posses systemic toxicity
High therapeutic index: penicillins
Low therapeutic index: aminoglycosides, tetracycline's, chloramphenicol
Very low therapeutic index: its only used when no suitable alternative is
available e.g.: vancomycin, amphotericin
20. Hypersensitive reactions/ drug resistance
Majority of AMAs posses hypersensitive reactions like rashes and
anaphylactic shock which are dose dependent
E.g. penicillins, cephalosporin's
Drug resistance:
It refers to unresponsiveness of microorganism to an AMAs and causes drug
tolerance
2 types of resistance
Natural resistance: some microbes always been resistant to AMAs
Cause: they lack metabolic process or the target site which is affected by
AMAs. E.g. gram-ve microbes for penicillins M.tuberculosis insensitive to
tetracycline's
21. Cont..
Acquired resistance: it is development of resistance by an organism due to
use of an AMA over period of time
Development of resistance is dependent on the microorganism e.g.
acquisition of resistance, e.g. staphylococci, coliforms, tubercle bacilli for
penicillins
Resistance may be developed by Mutation or gene transfer
22. Antibiotic ResistanceresNatural
Lack of
metabolic
process /
target site
Acquired
Genetic
methods
Chromosomal
methods -
Mutation
Extra
chromosomal
methods –
Plasmids
Within
/between
bacteria
Biochemical
mechanisms
By producing
enzymes
Preventing drug
accumulation
Modifying target
site
Use alternative
pathways
Quorum sensing
Antibiotic Resistance
23. Genetic determinants of Antibiotic resistance
1. Chromosomal determinants : mutations
2. Gene amplification
3. Extrachromosomal determinants: Plasmids
4. The transfer of resistance genes between genetic elements
within the bacterium
5. The transfer of resistance genes between bacteria
“Potential threat to humans”
24. Chromosomal determinants: Mutation
Mutation It is a stable and heritable genetic change that occurs
spontaneously and random among microorganisms.
It is not induced by the AMA.
Any sensitive population of a microbes contains a few mutant cells which
require high concentration of the AMA for inhibition
Single step: A single gene mutation may confer high degree of resistance;
emerges rapidly, e.g. streptomycin, E coli and Staphylococci to rifampicin
Multistep: A number of gene modifications are involved
Sensitivity decreases gradually in a stepwise manner
Resistance to erythromycin, tetracycline's and chloramphenicol developed
by many organisms in this manner
25. Gene amplification
Gene duplication and amplification are important mechanisms for
resistance in some organisms.
According to this idea, treatment with antibiotics can induce an increased
number of copies for pre-existing resistance genes such as antibiotic-
destroying enzymes and efflux pumps.
26. Extrachromosomal determinants: plasmids
In addition to the chromosome itself, many species of bacteria contain
extrachromosomal genetic elements called plasmids that exist free in the
cytoplasm.
These are also genetic elements that can replicate independently. Structurally,
they are closed loops of DNA that may comprise a single gene or as many as
500 or even more.
Plasmids that carry genes for resistance to antibiotics (r genes) are referred to
as R plasmids.
Much of the drug resistance encountered in clinical medicine is plasmid-
determined. It is not known how these genes arose.
The whole process can occur with frightening speed. Staphylococcus aureus,
for example, is a past master of the art of antibiotic resistance. Having become
completely resistant to penicillin through plasmid-mediated mechanisms, this
organism, within only 1–2 years, was able to acquire resistance to its
replacement, methicillin
27. The transfer of resistance genes between genetic
elements within the bacterium: Transposons
Some stretches of DNA are readily transferred (transposed) from
one plasmid to another and also from plasmid to chromosome or vice
versa.
This is because integration of these segments of DNA, which are
called transposons, into the acceptor DNA can occur
independently of the normal mechanism of homologous genetic
recombination.
Unlike plasmids, transposons are not able to replicate independently,
although some may replicate during the process of integration
resulting in a copy in both the donor and the acceptor DNA
molecules.
28. Transposons may carry one or more resistance genes and can ‘hitch-
hike’ on a plasmid to a new species of bacterium.
Even if the plasmid is unable to replicate in the new host, the
transposon may integrate into the new host’s chromosome or into its
indigenous plasmids.
This probably accounts for the widespread distribution of certain of
the resistance genes on different R plasmids and among unrelated
bacteria
29.
30. Transfer of genes between bacteria
1.Conjugation
2.Transformation
3.Transduction
31. Gene transfer
Conjugation is the process by
which one bacterium transfers
genetic material to another through
direct contact.
During conjugation,
one bacterium serves as the donor
of the genetic material, and the
other serves as the recipient.
The donor bacterium carries a
DNA sequence called the fertility
factor, or F-factor.
Chloramphenicol resistance of
typhoid bacilli,
streptomycin resistance to E coli
32. Transformation
A resistant bacterium may release the
resistance carrying DNA into the
medium.
This may be imbibed by another
sensitive organism-becoming
unresponsive to the drug
This mechanism is probably not
clinically significant except
isolated instances of Pneumococcal
resistance to penicillin G due to
altered penicillin binding protein
33. Transduction
Transduction is the process by which foreign DNA is introduced into a cell by
a virus or viral vector. An example is the viral transfer of DNA from
one bacterium to another. E.g. staphylococcus strains for penicillins
erythromycin and Chloramphenicol
34. Biochemical mechanisms of resistance
to antibiotics
The production of an enzyme that inactivates the
drug
Alteration of drug-sensitive or drug-binding site
Decreased drug accumulation in the bacterium
Alteration of enzyme pathways
35.
36. Biochemical Mechanisms of
Resistance
Production of drug-
inactivating
enzymes
Change in the
antibiotic target site
. Reduction in
cellular
permeability to the
antibiotic:
Switch to alternative
metabolic pathways
unaffected by the
drug:
Increased
production of
essential metabolite
37. Examples
1. Production of enzymes that inactivate the drug: for example, β-
lactamases, which inactivate penicillin; acetyltransferases, which inactivate
chloramphenicol; kinases and other enzymes, which inactivate
aminoglycosides.
2. Alteration of the drug-binding sites: this occurs with aminoglycosides,
erythromycin, penicillin.
3. Reduction of drug uptake by the bacterium: for example, tetracyclines.
4. Alteration of enzyme pathways: for example, dihydrofolate reductase
becomes insensitive to trimethoprim.
38. Quorum sensing
Microbes communicate with each other and exchange signaling
chemicals (Autoinducers)
These autoinducers allow bacterial population to coordinate gene
expression for virulence, conjugation, apoptosis, mobility and
resistance.
Single autoinducer from single microbe is incapable of inducing any
such change
But when its colony reaches a critical density(quorum), threshold of
autoinduction is reached and gene expression starts
QS signal molecules AHL, AIP, AI-2 & AI-3 have been identified
in Gm-ve bacteria AI-2 QS –system is shared by GM+ve bacteria also
39. WHY INHIBIT QUORUM SENSING ??
Proved to be very potent method for bacterial virulence inhibition.
Several QS inhibitors molecules has been synthesized which
include AHL, AIP, and AI-2 analogues
QS inhibitors have been synthesized and have been isolated from
several natural extracts such as garlic extract.
QS inhibitors have shown to be potent virulence inhibitor both in
in-vitro and in-vivo, using infection animal models.
40. Drug Tolerant & Drug destroying
Drug tolerant: Loss of affinity of the target biomolecule of the
microorganism for a particular AMA
e.g. penicillin-resistant pneumococcal strains have altered penicillin binding
proteins
Trimethoprim-resistance results from plasmid-mediated synthesis of a
dihydrofolate reductase that has low affinity for trimethoprim.
Drug destroying: The resistant microbe elaborates an enzyme which
inactivates the drug
E.g. B-lactamases are produced by staphylococci, Haemophilus, gonococci,
etc. which inactivate penicillin G.
The B-lactamases may be present in low quantity but strategically located
periplasmically (as in gram-negative bacteria) so that the drug is inactivated
soon after entry, or may be elaborated in large quantities (by gram-positive
bacteria) to diffuse into the medium and destroy the drug before entry.
41. Enzymatic inactivation
&
Modification of target sites
Enzymatic inactivation : The ability to destroy or inactivate the
antimicrobial agents can confer resistance on microorganisms.
E.g. β-lactamases destroy many penicillins and cephalosporin's
Modification of target sites
The β-lactams can resist to organism by alteration of the target site that is
penicillin binding protein(PBP) and mutation of dihydrofolate reductase
which is less sensitivity to inhibition in organism resistant to trimethoprim.
42. Drug impermeable & cross resistance
Drug impermeable :
Many hydrophilic antibiotics gain access into the bacterial cell through
specific channels formed by proteins called 'porins', or need specific transport
mechanisms. These may be lost by the resistant strains
e.g. penicillin-resistant gonococci are less permeable to penicillin G
Cross resistance:
Acquisition of resistance to one AMA conferring resistance to another AMA,
to which the organism has not been exposed, is called cross resistance.
resistance to one sulfonamide means resistance to all others, and resistance to
one tetracycline means insensitivity to all others.
44. Superinfection or supra infection
This refers to the appearance of a new infection as a result of antimicrobial
therapy for another infection
The causative organism may be different from that of primary diseases
E.g. broad spectrum antibiotics like tetracycline's, and chloramphenicol,
alter normal bacterial flora as a result of which the host defense mechanism is
impaired
Hence pathogenic organisms invade the host multiply and produce
Superinfection e.g. bacteria or fungi
45. Pathogenesis of Superinfection
It is associated with suppression or change in flora in the body following
treatment of certain AMAs
46. Factors predisposing to Superinfection
Superinfection is due to immunocompromised conditions such as diabetes,
AIDS, malignancy etc.
Can be minimized by
1. using special antimicrobials
2. avoid unnecessary use of AMAs
3. use of probiotics e.g.. Lactobacillus
47. Nosocomial/ hospital acquired infections
A hospital-acquired infection (HAI), also known as a nosocomial
infection, is an infection that is acquired in a hospital or other health
care facility.
To emphasize both hospital and nonhospital settings, it is sometimes instead
called a health care–associated infection (HAI or HCAI).
Such an infection can be acquired in hospital, nursing home, rehabilitation
facility, outpatient clinic or other clinical settings.
Spreading of infection
By health care staff, infected patient etc.
Infection due to contamination of reused patients bed, surgicals, plastic
equipment's ( like syringe, needle etc.)
49. In some cases the microorganism originates from the patient's own skin
microbiota, becoming opportunistic after surgery or other procedures that
compromise the protective skin barrier.
Contact transmission, airborne transmission, common vehicle transmission,
vector born transmission
Source of contamination can not be ensured
Prevention: QA/QC measures
Isolation, sterilization, hand washing, surface sanitation
Treatment
Among the categories of bacteria most known to infect patients are the
category MRSA (resistant strain of S. aureus), member of gram-positive
bacteria and Acinetobacter (A. baumannii), which is gram-negative.
