General Definitions used on 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  -> G-protein 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 (t1/2) 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.”

The term ‘drugs’ is being also used to mean addictive /abused / illicit substances. However, this restricted and derogatory 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 is 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 recipients.

Chemotherapeutic agents These are designed to inhibit/kill invading parasite/ malignant cells and have no / minimal pharmacodynamic effect 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.