Pharmacology is the science of drugs (Greek: Pharmacon—drug; logos—discourse in). In a broad sense, it deals with interaction of exogenously administered chemical molecules (drugs) with living systems. It encompasses all aspects of knowledge about drugs, but most importantly those that are relevant to effective and safe use for medicinal purposes.
INTRODUCTION
PHARMACOLOGY
Pharmacology is the
science of drugs (Greek: Pharmacon—drug; logos—discourse in). In a broad sense, it deals with interaction of
exogenously administered chemical molecules (drugs) with living systems. It
encompasses all aspects of knowledge about drugs, but most importantly those
that are relevant to effective and safe use for medicinal purposes.
For thousands of years
most drugs were crude natural products of unknown composition and limited
efficacy. Only the overt effects of these substances on the body were rather
imprecisely known, but how the same were produced was entirely unknown.
Pharmacology as an experimental science was ushered by Rudolf Buchheim who
founded the first institute of pharmacology in 1847 in Germany. In the later
part of the 19th century, Oswald Schmiedeberg, regarded as the ‘father of
pharmacology’, together with his many disciples like J Langley, T Frazer, P
Ehrlich, AJ Clark, JJ Abel propounded some of the fundamental concepts in
pharmacology. Since then drugs have been purified, chemically characterized and
a vast variety of highly potent and selective new drugs have been developed.
The mechanism of action including molecular target of many drugs has been elucidated.
This has been possible due to prolific growth of pharmacology which forms the
backbone of rational therapeutics.
The two main divisions
of pharmacology are pharmacodynamics and pharmacokinetics.
Pharmacodynamics
(Greek: dynamis—power) —What the drug does to the body.
This includes
physiological and biochemical effects of drugs and their mechanism of action at
organ system/subcellular/macromolecular levels, e.g.—Adrenaline → interaction with adrenoceptors
→ Gprotein mediated
stimulation of cell membrane bound adenylyl cyclase → increased
intracellular cyclic 3´,5´AMP → cardiac stimulation, hepatic glycogenolysis
and hyperglycaemia, etc.
Pharmacokinetics
(Greek: Kinesis—movement) — What the body does to the drug.
This refers to
movement of the drug in and alteration of the drug by the body; includes
absorption, distribution, binding/localization/storage, biotransformation and
excretion of the drug, e.g. paracetamol is rapidly and almost completely
absorbed orally attaining peak blood levels at 30–60 min; 25% bound to plasma
proteins, widely and almost uniformly distributed in the body (volume of
distribution ~ 1L/kg); extensively metabolized in the liver, primarily by
glucuronide and sulfate conjugation into inactive metabolites which are
excreted in urine; has a plasma half life (t½) of 2–3 hours and a clearance
value of 5 ml/kg/min.
Drug
(French: Drogue—a dry herb) It is the
single active chemical entity
present in a medicine that is used for diagnosis, prevention, treatment/cure of
a disease. This disease oriented definition of drug does not include
contraceptives or use of drugs for improvement of health. The WHO (1966) has
given a more comprehensive definition—“Drug is any substance or product that is
used or is intended to be used to modify or explore physiological systems or
pathological states for the benefit of the recipient.” sense usage is
unfortunate degradation of a time honoured term, and ‘drug’ should refer to a
substance that has some therapeutic/diagnostic application.
Some
other important aspects of pharmacology are:
Pharmacotherapeutics
It is the application
of pharmacological
information together with knowledge of the disease for its prevention,
mitigation or cure. Selection of the most appropriate drug, dosage and duration
of treatment taking into account the specific features of a patient are a part
of pharmacotherapeutics.
Clinical pharmacology
It
is the scientific study of drugs in man. It
includes pharmacodynamic and pharmacokinetic investigation in healthy volunteers
and in patients; evaluation of efficacy and safety of drugs and comparative
trials with other forms of treatment; surveillance of patterns of drug use,
adverse effects, etc.
The
aim of clinical pharmacology is to generate data for optimum use of drugs and
the practice of ‘evidence based medicine’.
Chemotherapy
It is the treatment of
systemic infection/malignancy
with specific drugs that have selective toxicity for the infecting organism/
malignant cell with no/minimal effects on the host cells.
Drugs
in general, can thus be divided into:
Pharmacodynamic agents
These are designed to have pharmacodynamic effects in the
recipient.
Chemotherapeutic
agents
These are designed to inhibit/kill invading parasite malignant
cell and have no/minimal pharmacodynamic effects in the recipient.
Pharmacy
It is the art and
science of compounding and dispensing drugs or preparing suitable dosage forms
for administration of drugs to man or animals. It includes collection,
identification, purification, isolation, synthesis, standardization and quality
control of medicinal substances. The large scale manufacture of drugs is called
Pharmaceutics. It is primarily a
technological science.
Toxicology
It is the study of
poisonous effect of drugs and other
chemicals (household, environmental pollutant, industrial, agricultural, homicidal)
with emphasis on detection, prevention and treatment of poisonings. It also
includes the study of adverse effects of drugs, since the same substance can be
a drug or a poison, depending on the dose.
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