, NR565 Week 1 Study Outline
Chapter 2: Review of Basic Principles of Pharmacology
How Drugs are Developed
Drugs are developed by pharmaceutical companies to help patients and to make
money
The early part of the drug development process is called the preclinical stage
Pharmaceutical companies will identify a drug target, starting sometimes with
ingredients isolated from a plant (or organism in the case of antibiotics) with
desirable medicinal properties, sometimes with a molecular target identified in
the body to produce the desired response, and sometimes with a disease in
need of treatment.
Many drugs are examined as pharmaceutical companies seek the elusive
perfect drug with just the right combination of properties. Preclinical studies
are performed on cells, isolated tissues and organs, and in laboratory animals
to identify promising compounds
Drugs approved by the Food and Drug Administration (FDA) must be both safe
and effective and are screened by pharmacologists specializing in various
aspects of drug activity.
Ideally, drugs will produce their desired effects at dosages well below those
needed to produce toxicity.
During the clinical stage of new drug development, pharmaceutical companies
must establish the safety and effectiveness of new products in humans.
Phase I clinical trials typically establish biological effects as well as safe
dosages and pharmacokinetics in a small number of healthy patients.
o During phase II clinical trials, new drugs are used to treat disease in a small
number of patients and to establish the n potential of the drug to
improve patient outcomes.
If the drug still looks promising, phase III clinical trials will compare the new
medication to standard therapy in a larger number of patients studied by at
sites across the country.
New drugs must be at least as good as, and it is hoped better than, other
available therapies. Throughout the process, pharmaceutical companies work
with the FDA.
After being approved by the FDA, drugs are continuously monitored through post-
marketing surveillance, in which health professionals are encouraged to report
adverse events, which are studied by both pharmaceutical companies and the
FDA.
Drug Responses
Homeostasis is the tendency of a cell, tissue, or the body not to respond to drugs
but instead to maintain the internal environment by adjusting physiological
processes.
, Before a medication can produce a response, it often must overcome
homeostatic mechanisms.
Drug effects depend on the amount of drug that is administered.
o If the dose is below that needed to produce a measurable biological
effect, then no response is observed; any effects of the drug are not
sufficient to overcome homeostatic capabilities.
o If an adequate dose is administered, there will be a measurable biological
response. With an even higher dose, we may see a greater response.
At some point, however, we will be unwilling to increase the dosage further, either
because we have already achieved a desired or maximum response or because
we are concerned about producing additional responses that might harm the
patient.
Because pharmacology is the study of substances that produce biological
responses, measurement of what happens when we administer
medications is important.
Two types - these responses differ in how they are measured and dictate dosing
decisions to achieve the desired effect.
, o Quantal
Responses that may or may not occur
Ie: convulsions, pregnancy, rash, sleep, death
A quantal response to a drug is observed in a population, and is either
present or absent in any single individual.
Quantal dose-response graphs plot the rate of an outcome
occurrence in a population against the drug dose.
o Graded
Biological effects that can be measured continually up to the
maximum responding capacity of the biological system
Most drug responses are graded
ie: changes in BP are measured in millimeters of mercury (mm
Hg); HR, diuresis; bronchodilation; FEV1; pain; coma scale
Graded responses are easier to manage clinically because we can see
how each patient responds to a particular dose of medication and, if
appropriate, alter the dosage to achieve a greater or less response
Expression Drug Responses
o Pharmacologists show the relationship between dose or concentration and
drug effect using graphs that show the dose–response relationship, or
dose–response curve.
Vertical axis - drug responses
Horizontal axis - concentration
o Dose-response curves provide information on the relationship between
dosage or concentration and responses for one more more drugs
o To “read” a concentration–effect or dose– response curve, move from left to
right along th e horizontal axis; this represents an increasing dosage or
concentration.
At each dosage, the level of effect is shown by the vertical height of
the curve. When concentration–response data are shown for two
drugs or two responses on the same graph, we can compare the
effects at each dose level.
o Pharmacologists compare drugs and their actions in several ways,
including potency, efficacy, intrinsic activity, and selectivity.
Potency is the expression of how much drug is needed to produce a
biological response.
Potency describes the difference in concentration or dosage of
different drugs required to produce a similar effect. Drugs that
are more potent require a lower dosage or concentration to
produce the same response
o Efficacy expresses the ability of a drug to produce a maximum effect at
any dosage. Efficacy is the expression of the maximum effect a drug can
produce.
Drugs with high efficacy can produce greater effects than lower-
efficacy drugs can.
o Intrinsic activity is very similar to efficacy in that it represents the ability of
a drug to produce a large response. Intrinsic activity, however, is used to
describe the ability of a drug to produce a response once it has occupied
specific receptors.
Some drugs produce the maximum receptor stimulation once they
occupy receptors; their response is limited by how many drug
molecules occupy receptor sites.
Drug Selectivity
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