DRUG DEVELOPMENT

• Stages of drug development

  • Preliminary studies
  • Preclinical studies & clinical trials
  • Approval by the regulatory board
  • Post-marketing surveillance stage
• Preliminary studies

  1. Synthesis or discovery of a new drug compound

  2. Determine potential drug's safety and efficacy

  3. Tests include computer models, in vitro studies, tests on simple organisms
• Approaches to drug discovery


  • Identification of a new potential drug target
  • Chemical modification of a known drug molecule
  • Design and synthesis of a new drug based on understanding of biologic mechanisms, drug receptor structure, & drug structure
  • Combinations of known drugs to obtain additive or synergistic effects
  • Screening for biologic activity of natural products, chemical entities, organic molecules, etc.
  • Biotechnology & gene cloning to produce peptides & proteins
• Reasons for molecular modification

  • To enhance the specificity of a drug for a particular body target site
  • To increase its potency
  • To improve its rate and extent of absorption
  • To modify its time course in the body
  • To reduce its toxicity
  • To change its physical or chemical properties (e.g. solubility)
• Preclinical studies


  1. Involve laboratory animal testing

  2. Determine a drug's efficacy and safety

  3. Tests include acute toxicity test, chronic toxicity test
• Acute toxicity test

  Examines adverse effects of a substance within 24 h or less, such as seizures, paralysis, depressed respiratory rate, reduced heart rate, death
• Chronic toxicity test


  1. 24 month duration, tests for organ system toxicity/damage, reproductive effects, carcinogenicity, teratogenicity
• Clinical trials

  1. Determine a drug's safety and efficacy on the target species

  2. Also note toxic/adverse effects, tissue residue levels, withdrawal time
• Clinical trial phases

  • Phase 1 (dose-finding)
  • Phase 2 (efficacy)
  • Phase 3 (comparative)
• Withdrawal time/period


  The number of days that must pass after the last drug treatment before the animal can be considered safe for human consumption
• Drug approval for marketing

  1. If test results are favorable, the drug is approved by the regulatory board for marketing

  2. Common reasons for non-approval include side-effects, less effective drug, lack of financial viability
• Post-marketing surveillance


  1. Product monitoring after the drug is marketed

  2. Objectives are to monitor safety and efficacy, and detect adverse drug reactions
• Pharmacovigilance

  The science and activities relating to the detection, assessment, understanding and prevention of adverse effects or any other medicine/vaccine related problem
• Drug development is lengthy and expensive
• Drugs with adverse effects can be approved by the regulatory board if the drug's benefits outweighs the adverse effects
• Local regulatory agencies involved in animal health products (Philippines)

  • Food and Drug Administration (FDA)
  • Bureau of Animal Industry (BAI)
• Requirements for drugs with a satisfactory history of use in developed countries

  • Target animal safety studies
  • Toxicity tests
  • Reproductive studies
• Toxicity test


  1. Objective is to determine the margin of safety

  2. Administer market formulation of the drug to the most sensitive animal in the species at 0, 1x, 3x and 5x the max proposed dose for 3x the max duration of use

  3. Monitor clinical signs, hematological parameters, serum biochemical tests
• Reproductive studies

  For females: administer 2x the maximum proposed drug dose at different stages of ovulation, early pregnancy, and 2nd/3rd trimesters

  For males: administer 2x proposed max dose every other day for 30 days before the breeding season

  Objective is to determine drug effect on breeding & development of the embryo/fetus
• Efficacy studies

  Conduct trials in animals diagnosed with the disease

  Design experiments to evaluate differences within an animal species such as weight, sex, breed, age & condition

  Quantitative measurements include antimicrobial susceptibility tests, serological and lab tests, morbidity and mortality rates

  Qualitative measurements include isolation of etiological entities, presence of disease signs, severity of signs