Evaluation of anti infective drugs updated

Markos Tadele: evaluation of anti infective drugs

Evaluation of anti-infective drugs

Chemotherapy & immunopharmacology

By - Markos Tadele


Introduction

• The drug development process starts with the synthesis of novel chemical compounds

• Substances with complex structures may be obtained from various sources– Plants (cardiac glycosides)– animal tissues (heparin)– microbial cultures (penicillin G)– Cultures of human cells (urokinase),

or by means of gene technology (human insulin)


Parameters need to be addressed for drug evaluation

• To decide for which kind of clinical infection the antibacterial drug product should be use, the following information should be developed from

in vitro studies animal models of infection (PK/PD) information from animal and

human studies and clinical trials


I. In vitro anti infective activity evaluation

General considerations for in vitro and in vivo tests

• The goal should be to learn about a drug product’s antibacterial activity in vitro and in animal models of infection

• Tests are recommended to be done in three replication

• QC parameters for in vitro susceptibility tests antimicrobials of certified potency in accordance with standardized procedures (CLSI)


Development of QC Parameters for In Vitro Susceptibility Testing

• should be established before determining the activity of the antibacterial drug product

• to ensure the generation of precise, accurate, and reproducible results

• If susceptibility information provided without proper quality monitoring, the test procedure and test results may be considered invalid.


Anti infective activity Information required A) Antibacterial Spectrum of Activity

• Which type of organisms are affected? genotypes, serotypes, biotypes, isolates

• known mechanisms of resistance should be identified

• internationally approved antibacterial drug products, especially those with the same mechanism of action as the new drug should be used


B. Mechanism of Action

• chemical structure and a description of any structural or biological similarities to known antibacterial drug products

• mechanism of action (e.g., inhibition of cell wall synthesis, lysis of cell membrane, protein synthesis, and inhibition of DNA or RNA replication) should be demonstrated

• helps to understand development of resistance/ if occur lately


C. Intracellular Antimicrobial Concentration Assessment

• The ability of an antibacterial drug product to achieve significant intracellular concentrations may have clinical importance

• when the target organism can reside within the cell (e.g., Listeria, Chlamydophila, Legionella) and phagocytosed pathogens

• Ex vivo studies may be suitable for this kinds of study


E. Minimum inhibitory concentration/ MIC

• The MIC is the lowest concentration of antimicrobial agent that completely inhibits growth of the organism in tubes or micro- dilution

• reported as the concentration of drug necessary to inhibit 50% of strains (MIC50) , 90% of strains (MIC90)

• Since growth and death of Mos are multifactoral the conditions of the medium and the incubation requirements must be standardized


D. Mechanism of Resistance Studies

• Resistance mechanisms may limit the effectiveness of an antibacterial drug product in clinical settings– Mechanisms include alterations of

the drug product by production of enzymes (e.g., β-lactamases, mutation)

– inability to reach the target– changes in the affinity of the

antibacterial for the target site– Drug transporting proteins etc…


F. Minimum lethal concentration/ MLC

• The bactericidal endpoint (MBC) at which 99.9% of the final inoculum is killed

• (MBC) or (MFC), also known as the minimum lethal concentration (MLC)

• MFC is also defined as the lowest concentration of the drug that yields 98% – 99.9% killing effect as compared to the initial inoculum

• Can be expressed like MIC, MBC90, MBC98, MBC99


G. Immunotoxicology Evaluation of New Drugs

Five adverse event categories should be evaluated

1. Immunosuppression: Effects on the immune system that result in decreased immune function

2. Immunogenicity: Immune reactions elicited by a drug and/or its metabolites

3. Hypersensitivity: Immunological sensitization due to a drug and/or its metabolites

4. Autoimmunity: Immune reactions to self-antigens

5. Adverse Immunostimulation: Activation of immune system effector mechanisms


H. Anti infective drug Interactions and Fixed Combination Studies

• Drug interaction studies of antibacterial drug products may provide information (e.g., synergy, antagonism, indifference)

• methods can include – checkerboard titration analyzed by

fractional inhibitory concentration and

– kill curves• These drug interactions are

particularly important for fixed combination drug products (e.g., ß-lactam and ßlactamase inhibitor combination)


drug Interactions….

• Drug interactions also can reflect the additive nature of the pharmacodynamic effect of either drug when taken with the other drug Concomitant medications dietary supplements some foods, such as grapefruit juice,

may alter metabolism and/or drug transport abruptly in individuals

who previously had been receiving and tolerating a particular dose of a drug


I. Post-Antibiotic Effect (PAE)• PAE measures the time to reach

normal logarithmic growth – log10

• The standard equation for PAE is: PAE (hours) = T – C

• T = is the time required for the count of cfu to increase 1 log10 (10-fold) above the count immediately seen after drug treatment

• C = is the time required for the count to increase 1 log10 in an untreated control culture


Post-Antibiotic Effect (PAE)

1

10

100

1000

10000

0 1 2 3 4 5 6

Time (hours)

Removal of Antibiotic

Viab

le C

ount

(cfu

/ml)

Control

1.6 hours to increase 1 log10

1 log10 increase

3.1 hours to increase 1 log10

Antibiotic Induced death

PAE = 3.1 - 1.6 = 1.5 hours Due to antibiotic effect only


Post-Antibiotic Effect

• Precise mechanism is still not understood• Examples of PAE


J. Other Effects of Antibacterial Drug Product

• post antibiotic leukocyte effect• sub-MIC effects• effects on endotoxin• effects on virulence factors and• interactions with the host

immune system.


II. Animal Therapeutic and Pharmacological Studies

Why animals used in research

• in vitro activity of antibacterial drug products may not translate into significant activity in vivo

• Animal models of human disease can be studied in induced animals– provide potential efficacy and safety of

antibacterial drug products in humans.


Why animals used in research

• The basic cell processes are the same in all animals, and they perform similar vital functions

• Simple animals can be used to study complex biological systems

• will mimic the infection of interest and the pharmacokinetics of the drug product in humans

• what happens in the body following treatment with certain drugs (ADME)


Animals mostly used in research


Mammals in in researches


DIFFERENCE BETWEEN RATS AND MICE

• The rat is much larger in size and has greater body weight as compared to the mouse.

• The mouse has a pointed face when compared to the rat

• The rat has a thick and heavy tail. On the other hand, a mouse has a very thin tail

• The rat has a higher pair of chromosomes, ie 22 pairs. On the contrary, the mouse has only a 20 pairs

• The rats have a longer gestation period compared with the mice.


Animal experiment

• should at a minimum obtain information on: – the natural history of the disease or

condition in humans and animals (is it the same?)

– the etiologic agent and– the proposed intervention (can work

on both?)

• Results can be reported as (ED50), (PD50), (CD50)


III. Human Pharmacological Studies and Clinical Trials

Steps to indicate the effectiveness and toxicity of the agent– investigation in vitro– study effects in laboratory animals

(studies in cell culture- antivirals)

• The in vitro studies and the in vivo studies in animals lead to investigational studies in man

• 4 phases


Clinical Study: Phase 1 (Human Pharmacology)

• Normal subjects; occasionally use patients (eg. Hypertensive patients, highly toxic drugs)

• See if/how pharmacokinetics data from animal studies extrapolates to human data

• Usually open label with ascending doses; establish dose-range

• Build safety profile: monitor adverse effects


Studies conducted in Phase I typically involve one or a combination of the following aspects:

a) Estimation of Initial Safety and Tolerability dose range expected to be needed for

later clinical studies and to determine the

nature of adverse reactionsb) Pharmacokineticsc) Assessment of Pharmacodynamics

For PK/PD studies may be conducted to estimate dosage regimen and doses

d) Early Measurement of Drug Activity Preliminary studies of activity or

potential therapeutic benefit


Phase II (Therapeutic Exploratory)

• In Phase II primary objective is to explore therapeutic efficacy in patients

• patients who are selected by relatively narrow criteria (relatively homogeneous)

• An important goal for this phase is to determine the dose(s) and regimen for Phase III trials.

• Confirm dose range is similar in such people; if not, re-define range

• Blinding, randomization, controls used


Phase III (Therapeutic Confirmatory)

• primary objective is to demonstrate, or confirm therapeutic benefit safety and efficacy profiles claimed in Phase II

• Conducted on intended users, May have slightly broader entry criteria - age, severity of disease

• Conducted between efficacy of the medicine is demonstrated and New Drug Application (NDA)

• intended to provide an adequate basis for marketing approval.


Phase III (Therapeutic Confirmatory)

Phase III may also further explore– the dose-response relationship– explore the drug's use in wider

populations– Drug performance in different stages of

disease– combination effect with another drug

(For drugs intended to be administered for long periods)

– trials involving extended exposure to the drug are ordinarily conducted in Phase III, although they may be started in Phase II


Phase IV (Therapeutic Use/PM surveilance)

• Phase IV begins after drug approval• Therapeutic use studies go beyond the

prior demonstration, provide additional details about the medicine's efficacy or safety profile

• New age groups, races, and other types of patients can be studied

• previously unknown or inadequately quantified adverse reactions and related risk factors are an important aspect of many Phase IV studies




Subjects used in clinical studies

• Overall investigation Plan– Phase 1 - Normal subjects: usually < 50

subjects, at one facility, safety parameters– Phase 2 - Patients: about 50 - 100 subjects;

at two sites; may do some dose-range assessment; safety and some initial efficacy

– Phase 3 - Patients: few hundred to several thousand; multiple sites; main support study

– Phase 4 - Patients (post-marketing): varies



References • CLSI, 2009, Development of In Vitro Testing Criteria and

Quality Control Parameters; Approved Standard, CLSI document M23-A3.

• CLSI, 2007, Methods for Antimicrobial Testing of Anaerobic Bacteria; Approved Standard, CLSI document M11-A7.

• Background and History of Animal Testing Author: Ian Murnaghan B.Sc (hons), M.Sc - Updated: 28 April 2015

• www.aboutanimaltesting.co.uk • Spilker, Bert. Guide to Clinical Trials, Raven Press, 1984.• Luellman, color atlas of pharmacology, 2005• FDA, 2009, Microbiological Data for Systemic Antibacterial

Drug Products — Development, Analysis, and Presentation

Health & Medicine

Evaluation of anti infective drugs updated