Antibiotic and antimicrobial resistance through plasmid, conjugation, tranduction. post antibiotic effect

1. Antimicrobial Resistance
And
Post Antibiotic Effect
Ankita Mishra
JR2
Dept. of pharmacology
AMU, Aligarh

2. Antimicrobial resistance
• The WHO defines antimicrobial resistance as a microorganism's resistance
to an antimicrobial drug that was once able to treat an infection by that
microorganism.
• Intrinsic Resistance
• Acquired Resistance

3. Evolutionary Basis of Resistance Emergence
1. Resistance Via Mutation Selection (Chromosomal)
2. Resistance by External Acquisition of Genetic Elements

4. • Mutation refers to change in DNA structure of a gene.
• Spontaneous mutation in bacterial cells at a frequency of one/million
cells.
• Selection of mutants- confering antibiotic resistance.
• Clinical problem in Mycobacterium ,MRSA]=
Resistance via mutation selection

5. External Acquisition of Genetic Elements
• Horizontal transfer of resistance determinants from a donor cell:-
Conjugation Transformation Transduction

6. Mobile Genetic Elements
• Plasmids
• Transposable elements
• Integrons
• Gene cassettes

7. • Reduced entry of antibiotic into pathogen.
• Enhanced export of antibiotic by efflux pumps.
• Alteration of target proteins.
• Release of microbial enzymes that destroy AB.
• Development of alternative pathways to those inhibited by the antibiotic.
Mechanisms of resistance to antimicrobial agents

8. • Resistance Due to Reduced Entry of Drug into Pathogen
• Absence of, mutation in, or loss of a favored porin channel.
• Reduce drug concentration at the target site.
• If target is intracellular and drug requires active transport across cell
membrane, a mutation that slows or abolishes this transport mechanism
can confer resistance.

9. • Resistance Due to Drug Efflux
• Efflux pump overexpression.
• Expulsion of antibiotics to which microbes would otherwise be
susceptible.
• Major facilitator superfamily (MFS) transporters – Tetracycline.
• ATP binding cassette (ABC) transporters- Pfmdr1.

10. • Resistance Due to Destruction of Antibiotic
• Bacterial resistance to aminoglycosides due to production of an
aminoglycoside-modifying enzyme.
• β-lactam antibiotics due to β-lactamase.
• Chloramphenicol inactivated by acetyltransferase.

11. • Resistance Due to Reduced Affinity of Drug to Altered Target Structure
• Single or multiple point mutations cause change in a.a. composition and
conformation of target protein.
• Mutation of natural target (e.g., fluoroquinolone resistance),.
• Target modification (e.g., ribosomal protection type of resistance to
macrolides and tetracyclines).
• Staphylococcal methicillin resistance caused by production of a low-
affinity PBP.

12. • Resistance Due to Enhanced Excision of Incorporated Drug
• NRTI resistance emerges via mutations at a variety of points in the reverse
transcriptase gene.
• Phosphorolytic excision of incorporated chain-terminating nucleoside
analog is enhanced.

13. • Hetero-Resistance
• Subset of total microbial population is resistant.
• There is a baseline mutation rate for each gene.
• Vancomycin in S. aureus,Enterococcus faecium, rifampin, isoniazid, and
streptomycin in M. tuberculosis, and penicillin in S. pneumoniae,
Fluconazole in Cryptococcus neoformans &Candida albicans.
• Viral Quasi Species
• Viral replication is more error prone.
• Viral evolution under drug and immune pressure occurs easily.
• Variants or quasi species that may contain drug-resistant subpopulations.

14. Post Antibiotic Effect
• Persistent suppression of bacterial growth after a brief exposure (1 or 2 h) of
bacteria to an antibacterial agent even in the absence of host defense
mechanisms.

15. • Minimum inhibitory concentrations (MICs) are defined as the lowest
concentration of an antimicrobial that will inhibit the visible growth of a
microorganism after overnight incubation.

16. • The shape of relationship b/w non-protein-bound antibiotic concentration
(exposure) vs microbial kill is inhibitory sigmoid Emax curve.
• The optimal dose of the antibiotic for a patient is the dose that achieves
EC/IC80 to IC90 exposures at the site of infection.

17. PK/PD Integration
1). t>MIC , i.e., time measured as % of time during which concentration
remains above MIC between two-dosage interval.
2). Cmax/MIC ratio (inhibitory quotient).
3). AUC/MIC ratio; If 24 h AUC is used to deduce this ratio, it is called AUIC(0-
24).

18. Which of the three indices (AUC/MIC, or CPmax/MIC or T>MIC) is the most important to
the outcome being assessed (i.e., microbial kill)?
Can be determined by which of these patterns best approximates a perfect inhibitory
sigmoid Emax curve.

19. • Antibacterial agents classified into 3 gps based
on bactericidal activity pattern as shown by
their CDK or TDK dynamics

20. • Group I. Agents that show concentration dependent killing (CDK) efficacy with
persistent PAE
• Aminoglycosides, fluoroquinolones, rifampicin.
• Eliminate bacteria more rapidly when their concentrations are above the MIC
of organism (Cmax).
• As concentration decreases, the rate of antibacterial activity decreases.
• Display a powerful PAE, duration of which is also concentration dependent.
• Wide dosage intervals can be chosen with this group of drugs.
• Cmax/MIC ratio and AUC/MIC ratio are effective predictors of therapeutic
outcome.

21. • Group II. Agents that show time dependent killing (TDK) efficacy with
minimal PAE
• β-lactam antibiotics, clindamycin, and erythromycin.
• Bacterial killing rate reaches ceiling at concentrations 4 to 5 times MIC.
• Time needed to exceed MIC is an important determinant of efficacy.
• Pharmacodynamic marker: t >MIC imp. for this group.
• Aim of therapy- to maintain serum conc. above MIC as long as possible
during the dosing intervals.

22. • Group III. Agents that show time- (duration) dependent killing (TDK) with
prolonged PAE
• Newer macrolides, e.g. azithromycin, clarithromycin, etc., vancomycin, and
tetracyclines.
• Clinical efficacy is not compromised if concentration falls below the MIC as
they possess persistent PAE.
• Both t > MIC and 24 h AUC/MIC ratio play imp. role in planning dosage
regimens.

23. Summary
• Determinants of success of antimicrobial therapy include proper selection
of antimicrobial therapy based on microbiology results and susceptibility
testing.
• Proper dose and dosing schedule are chosen by integrating PK/PD
information, expected PK variability, and MIC.
• General rule is monotherapy, except in select situations where
combination therapy has been shown to be superior.
• Poor dosing strategies lead to drug-resistance and untoward toxicity

25. Concentration-dependent versus time-dependent killing
(CDK vs TDK)
• Bacterial cell death following antibiotic exposure can be classified as
either concentration-dependent or time-dependent.
• Although the bactericidal activity of a given antibiotic is a function of
several factors, viz. the selected antibacterial drug, the pathogen species,
and the exposure concentration, it is generally accepted that killing profile
is always the same, i.e. the agent always shows CDK.
• However, some antibacterials display a ceiling effect to this CDK, i.e. once
a serum concentration for near maximum effect is reached it is more
important to sustain it rather than increase the concentration. Agents
showing this kind of antibacterial effect have been suggested to exhibit
the TDK dynamics

26. • With respect to aminoglycosides, Cmax/MIC ratio of at least 8 to 10 were
necessary for achieving an optimal clinical response in 90% of patients
treated for Gram-negative bacterial infection.
• Cmax/ MIC ratios of this magnitude in another study prevented the
development of resistance.
• Both Cmax/MIC ratio and AUC/MIC ratio are effective predictors of
therapeutic outcome in patients receiving aminoglycosides.
• Accordingly, to take advantage of CDK and PAE dynamics of
aminoglycosides, the concept of once daily dose regimen has been
introduced in clinical practice.

27. • For fluoroquinolones Forrest et al.32 by using
ciprofloxacin for serious infections found that clinical
and bacteriological response rates of <50% were
achieved (in 7 days) when the AUIC(0- 24) was <125.
However, when a higher AUIC(0- 24) (>250) was
obtained, the response rate rose to 80% within 2 days.
Thus, these results suggest that antibiotics which show
CDK efficacy, an AUIC(0- 24) of >125 can achieve a
better and rapid clinical cure using dosage regimens
that produce high initial concentrations. Further
emergence of resistance can be prevented if doses of
these agents that optimize the values of Cmax/MIC or
AUIC(0-24) are used26,33

28. • Other drug and disease-related pharmacokinetic factors in selection of
antibacterials and their dosage
• Since aminoglycosides have half-lives ranging between 2 and 8 h, it may be
difficult to obtain Cmax/MIC ratio of >8-10 h, i.e. peak concentration 8-10 times
greater than the MIC without reaching toxic concentration. Since, these ratios are
also important in preventing the development of resistance, there is currently a
trend towards single daily administration15,26. This regimen has been shown to
be more effective and possibly less toxic than traditional 8-hourly administration.
• There is also evidence that administration of subsequent aminoglycoside doses,
while there is still detectable aminoglycoside present, may inhibit their bacterial
killing capacity. This phenomenon is called "adaptive resistance after first
exposure". Bacteria are no more sensitive to bactericidal activity for several hours
before gradually returning to their full sensitivity46-47. The mechanism for this
adaptive resistance is thought to be down-regulation of aminoglycoside uptake by
energy dependent drug transport into the bacterial cell46. Accordingly the once
daily dose regimen of aminoglycoside antibiotics appears to be more rational.

29. • Since, the optimal duration of dosage interval for a given antibiotic
varies depending upon the infecting organism, site of infection,
inoculum effect, and immunocompetence of the host, with this
concept, it is clear that the pharmacodynamic marker: t >MIC with
an efficacy break point value of >50% is important for clinical
success with this group of antibiotics; closer is the value towards
100%, greater will be the success rate. For β-lactams with short
halflives, it is important to maintain drug concentrations above the
MIC against infecting pathogens during most of the dosage interval.
This can be done by using smaller fractions of the total daily dose
given at frequent intervals or the use of β-lactams with long serum
half lives such as ceftriaxone (t½ of 6-8hrs.
• n, the continuous infusion regimen was significantly (p=0.03) more
effective (65% cure) than intermittent regimen (21% cure) for the
treatment of infections

30. • As discussed above for β-lactams, it is important to maintain drug concentration
above MIC against the infecting pathogen over much of the dosage interval.
Therefore, agents with long half-lives can be given less frequently (Table 2), e.g.
ceftriaxone which has the longest half-life among the β-lactams (approximately 8-
10 h) can be given once daily. Cefotetan, cefoperazone and cefonicid have t½ of >2
h and can be given twice daily. Cefazolin, cefotaxime, ceftazidime and aztreonam
have short t½ of 1 to 2 h and generally need to be given 3-times daily. Other
cephalosporins and penicillins have a half-life of only 0.5 to 1 h and are generally
required to be given 4 times daily or more frequently.
• The carbapenems (imipenem+cilastatin; meropenem; biapenem) also have short
half-lives of approximately 1 h, thus, 3 times-daily administration may not provide
concentrations above the MIC throughout the dosage interval. However, since
these agents show some amount of PAE albeit of short duration1, this persistent
effect allows a longer dosage interval. Indeed, twice-daily administration of
meropenem has been shown to be as effective as 3-times daily administration in
patients with urinary tract infection or respiratory tract infections48 as has been
twice daily administration of cefazolin for cellulitis.