dose response relationship

1. DOSE RESPONSE
RELATIONSHIP,
HALF LIFE,
WITHDRAWAL
PERIOD,POTENCY,
EFFICACY
By-Joy

2. DOSE
◦ Dose by definition is the amount of a substance administered at one time.
However, other parameters are needed to characterize the exposure to
xenobiotics. The most important are the number of doses, frequency, and
total time period of the treatment.
◦ Some examples:
◦ 500 mg Asperin as a single dose
◦ 500 mg Penicillin every 8 hours for 10 days
◦ 15 mg DDT per day for 60 days
◦ They are 1) the administered or external dose,(observational
epidemiological studies. )
◦ 2) the internal (absorbed) dose (consequence of absorption, distribution,
metabolism and excretion) and
◦ 3) the target or tissue dose. (distributed to and present in a specific tissue
of interest)

3. RESPONSE
Effect seen following exposure in
vivo or in vitro.
“Responses can be either adaptive or adverse. Adverse effects are
defined as a change in the morphology, physiology, growth,
development, reproduction or life span of An organism or subsystem
(e.g. subpopulation of cells) that results in an impairment of functional
capacity, an impairment of the capacity to compensate for additional
stress or an increase in susceptibility to other influences”-
(IPCS,WHO 2004)

4. Relationship
◦ The dose–response relationship, or exposure–response
relationship, describes the magnitude of the response of
an organism, as a function of exposure (or doses) to
a stimulus or stressor (usually a chemical) after a
certain exposure time.Dose–response relationships can
be described by dose–response curves

5. CONSEQUENCES
◦ Knowledge of the dose-response relationship:
◦ - Establishes causality that the chemical has in fact
induced the observed effects
◦ - Establishes the lowest dose where an induced
effect occurs – the threshold effect
◦ - Determines the rate at which injury builds up - the
slope for the dose response.
For example, the
◦ Development of cirrhosis in the liver may not
result in a clinical effect
◦ Until over 50% of the liver has been replaced by
fibrous tissue.

7. HALF LIFE
◦ The drug half-life (t1/2) is the time required for a drug concentration to decrease by 50%. Half-life is a first-order kinetic process
because the same proportion, 50%, of the drug is removed during equal periods.

8. WITHDRAWL PERIOD
◦ Withdrawal period refers to the minimum period of time from administering the last dose of medication and the production of
other animal-derived products for food.
◦ The time it takes the body to break down the antibiotic until it is no longer functional or present is called the withdrawal
time (or withdrawal period). Once the withdrawal period has passed the antibiotic has been eliminated from the animal’s system.

9. POTENCY
◦ In the field of pharmacology, potency is a measure of
drug activity expressed in terms of the amount
required to produce an effect of given intensity.[1] A
highly potent drug
(e.g., fentanyl, alprazolam, risperidone) evokes a given
response at low concentrations, while a drug of lower
potency (meperidine, diazepam, ziprasidone) evokes
the same response only at higher concentrations.
Higher potency does not necessarily mean more side
effects.

10. EFFICACY
◦ Efficacy is the ability to get a job done to a satisfactory degree. The word comes from the same roots as effectiveness
◦ In pharmacology, efficacy (Emax) is the maximum response achievable from an applied or dosed agent, for instance, a small
molecule drug.

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