Drug discovery and clinical trials Drug discovery Most new drugs or drug products are discovered or developed through one of the following methods: Identification or elucidation of a new drug target. Rational drug design based on an understanding of biological mechanisms, drug receptor structure, enzymes sites etc. Chemical modification of an existing molecule. Screening for biologic […]
“Any noxious change which is suspected to be due to a drug at normal doses, requires treatment or decrease in dose or caution in future use of the drug”
Factors that affect drug action Body size, Age, Sex, Species, Race, Diet and plane of nutrition, Genetics, Route of administration, Environment, Psychological, Disease states, Enzyme inhibitors and inducers are factors that affect drug action in animals. Body size influence the conc. achieved at the site of action. Doses are normally given for adults of medium
Dose response curve As the name indicates this refers to the plotting of the dose vs response, with the dose in X axis and response in some measurable units in the Y axis. The features of the curve so obtained will provide useful information about the action of the drug or in comparison among drugs.
Receptors Receptor theories 1. Occupation theories A.J.Clark propounded the occupation theory which assumes that the extent to which a tissue is dependent on the proportion of its receptor population that has been occupied by a drug and maximal response is reached when all the receptors are occupied. He presumed that each occupied receptor delivered a constant
Pharmacodynamics of drugs Pharmacodynamics is the study of the biochemical and physiological effects of drugs and their mechanism of action. It is the response of the organism to the action of a drug in the absence of a disease. Pharmacodynamics is ‘what the drug does to the body’. Principles of drug action Drugs do not impart new
Excretion of drugs Drugs are excreted mainly by the kidneys into the urine and by the liver into the bile and subsequently into the feces. Alveolar elimination is of major significance when inhalant anesthetics are used. The main factors governing elimination by this route are concentration in plasma and alveolar air and the blood/gas partition
Bio-transformation of drugs The chemical alteration of drugs in the body Sequelae of biotransformation reactions General Pattern of biotransformation is biphasic. these phase 1 and phase 2 described below- 1. Phase-I Biotransformation – oxidation reactions and others Although every tissue has some ability to metabolize drugs, the liver is the principal organ of drug metabolism.
Distribution of drugs Distribution of drug is the drugs taken throughout the body by bloodstream Once absorbed, it gets distributed to other tissues which had no drug. Factors that govern distribution of drug Blood flow rate limiting step in distribution – Highly perfused organs such as Liver, Kidney, GI tract, Brain, Lungs receive rapidly high levels
Absorption of drugs Absorption is the movement of drug from the site of administration to circulation. Often the entire quantity of administered drug does not reach the systemic circulation. Only the fraction of drug that was absorbed is available for action. During the process of absorption, the quantity of drug absorbed and also the rate
