Pharmacology

• Preclinical trials

  Research using animals to find out if a drug, procedure, medical device or treatment is likely to be useful. Preclinical studies take place before any testing in humans is done.
• Preclinical studies


  • Providing evidence for the desired biological effect of a drug (pharmacodynamics)
  • Providing insight into potential toxicities to establish a human starting dose at which no serious adverse events are expected to occur
  • Allow for monitoring of any undesired effects in human trials
• Preclinical Pharmacology

  Aims at discovering complications or sequelae arising from the pharmacological actions of a drug and any unexpected side-effects

  
• Ethical issues to be considered in animal studies

  • Animals cannot give consent or express pain
  • Animals are killed or kept in captivity
  • Some substances tested, may never be used for anything useful
  • It is very expensive
  • Animals and humans are never exactly the same
• The 3Rs in pre-clinical studies

  • Replacement: Use non-animal methods
  • Reduction: Reduce the number of animals
  • Refinement: modification of experiment to minimize pain and distress, and to enhance the welfare of an animal

  
• Non-whole animal methods


  • In silico models
  • Using previous study data for baseline determination

  
• Whole animal methods


  • Rodents
  • Zebra fish
• Mice are the most widely used in clinical research as they are small, inexpensive and easy to handle
• Preclinical tests


  • Safety Pharmacology
  • Preliminary toxicological testing
  • Pharmacokinetic testing
• In vitro studies


  • Provide information on mechanism(s) of action of a drug
  • Provides an early indication of the potential for some kinds of toxic effects, allowing a decision to terminate a development program before spending too much money
• Bioassay


  A "live" system that can be used to measure drug effect. It may be a culture of cells or organs or a whole animal.
• Pharmacokinetics


  Focused on defining the key ADME components of drug delivery, exposure and disposition in the well-tolerated and pharmacologically active dose range
• ADMET


  • Absorption
  • Distribution
  • Metabolism
  • Excretion
  • Toxicity
• Pharmacodynamics

  Actions of the drug being developed relevant to the therapeutic use
• ED50


  The dose that gives 50% of the maximum effect
• Toxicology studies


  • Single dose studies: for acute toxicology
  • Repeated dose studies: Subacute, Intermediate and Chronic (long-term toxicology)
• Types of toxicology studies

  • Systemic toxicology studies
  • Reproductive toxicology studies
  • Local toxicity studies
  • Hypersensitivity studies
  • Genotoxicity studies
  • Carcinogenicity studies
• LD50

  Median Lethal dose - the dose that is lethal in 50% of the population (only measured in animals)
• Therapeutic index


  LD50/ED50 - not considered a useful guide to the safety of a drug in clinical use as LD50 does not reflect the incidence of adverse effects in the therapeutic setting
• Repeated-dose Toxicity Studies


  1. 14 days [oral administration]

  2. Wherever applicable, include a Control group

  3. 3 other groups are formed

  4. Highest dose: Observable toxicity [Minimum toxic dose, MTD]

  5. Lowest dose: No observable toxicity /no observed adverse effects level [NOAEL]

  6. Intermediate dose: Some symptoms; not gross toxicity or death placed logarithmically between doses
• Other parameters


  • Symptoms, signs and mode of death
  • LD 50 value, preferably with 95 % CI
  • Genetic effects if any
• Repeat dose toxicity studies establish

  • Minimum lethal dose (MLD)
  • Maximum tolerated dose (MTD)
  • Target organ of toxicity (if possible)
• Therapeutic index


  • Therapeutic index= LD50/ED50
  • LD50= dose that is lethal in 50% of the population (only measured in animals)
  • ED50 = dose that is 'effective' in 50
• Therapeutic index is not considered as a useful guide to the safety of a drug in clinical use for several reasons
• Parameters monitored and recorded in Repeated Dose Studies/Sub-acute or Chronic Toxicity

  • Behavioral
  • Physiological
  • Biochemical
  • Microscopic observations
• Tests included in Reproduction studies


  • Gametes (male and female)
  • Fertility
  • Implantation
  • Intrauterine growth
  • Parturition
  • Post-natal development
  • Growth and behaviour
  • Second generation effects
• Thalidomide disaster-10,000 babies affected
• Phocomelia- 'seal extremities' was caused by the drug thalidomide, which had not been tested in pregnant animals
• Male Fertility study

  1. 3 dose groups taken (each with 6 adult males), 1 control

  2. Drug treatment by clinical route for 28-72 days

  3. Mated with females in 1:2 ratio

  4. Females getting pregnant should be examined

  5. All male animals sacrificed

  6. Weights of testis, epididymus recorded and examined for their histology

  7. Sperms examined for motility and morphology
• Segments of Reproductive toxicology studies

  • Segment I: Fertility and general reproductive performance study
  • Segment II: Teratogenicity
  • Segment III: Peri- and post-natal study
• Female Fertility study


  1. Drug administered to both males (28days) and females (14 days) before mating

  2. Implantation

  3. Embryogenesis
• Types of local toxicity studies

  • Dermal toxicity studies
  • Dermal photo-toxicity studies
  • Vaginal toxicity studies
  • Rectal tolerance studies
  • Ocular toxicity studies
  • Parenteral drugs
  • Inhalation toxicity studies
• Allergic/hypersensitivity studies


  1. Guinea Pig Maximization test

  2. Local lymph node assay

  3. Determination of Maximum non irritant or minimum irritant dose

  4. Evaluation of Erythema and oedema
• In vitro Genotoxicity tests

  • Test for gene mutation in Bacteria
  • Cytogenetic evaluation of chromosomal damage in mammalian cells
• In vivo Genotoxicity tests

  • Chromosome damage in rodent hematopoietic cells
• Carcinogenicity (oncogenicity) studies


  1. Group sizes of 50 animals/sex at each of 3 dose levels

  2. Control group is of double size

  3. Record for onset of tumor development

  4. Usually carried out for 24 months in rats and 18 months in mice (life span studies)
• Why not full carcinogenicity studies done with every new compound?
• Evaluation of Carcinogenicity/oncogenicity studies

  • Incidence of cancers in control and test
  • Trend towards increasing incidence with increasing doses
  • Number of animals with single/multiple tumors
  • Macroscopic changes observed by autopsy
  • Histopathology of organs and tissues
• Adverse effects not uncovered in preclinical studies

  • Skin reactions, subjective reactions such as nausea, headache, dizziness
  • Effects ignored or not looked for, e.g. ototoxicity of aminoglycoside antibiotics, teratogenicity of thalidomide
  • Immunological reactions, idiosyncratic reactions
  • Insufficient exposure in animal studies
  • Species-specific metabolites
• Limitations of preclinical testing

  • Toxicity testing is time-consuming and expensive
  • Large numbers of animals may be needed to obtain valid preclinical data
  • Extrapolations of therapeutic index and toxicity data from animals to humans are reasonably predictive for many but not for all toxicities
  • For statistical reasons, rare adverse effects are unlikely to be detected