Pharmacology is the science of drugs, derived from the Greek words ‘pharmacon’ which means drug and ‘logos’ which means discourse. In the broadest sense, pharmacology deals with the interaction of exogenously administered chemical molecules with living systems. Any single chemical substance that can produce a biological response is referred to as a drug. Pharmacology encompasses all aspects of knowledge about drugs, but most importantly, those that are relevant to the effective and safe use of drugs for medicinal purposes. In this article, we provide a comprehensive overview of pharmacology and its different aspects.
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. Animal experiments, primarily aimed at understanding physiological processes, were started in the 18th century. These were pioneered by F. Magendie and Claude Bernard, who also adapted them to study the effects of certain drugs. 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 (founder of modern pharmacology) and 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 the molecular target of many drugs, has been elucidated. This has been possible due to the prolific growth of pharmacology, which forms the backbone of rational therapeutics.
Pharmacodynamics (Greek: dynamis-power) is what the drug does to the body. This includes the physiological and biochemical effects of drugs and their mechanism of action at organ system/subcellular/macromolecular levels. For instance, adrenaline interacts with adrenoceptors, which results in G-protein-mediated stimulation of cell membrane-bound adenylyl cyclase. This leads to an increase in intracellular cyclic 3 ‘,5’ AMP, resulting in cardiac stimulation, hepatic glycogenolysis, and hyperglycemia.
Pharmacokinetics (Greek: Kinesis-movement) is what the body does to the drug. This refers to the movement of the drug in and alteration of the drug by the body. This includes absorption, distribution, binding/localization/storage, biotransformation, and excretion of the drug. For example, paracetamol is rapidly and almost completely absorbed orally, attaining peak blood levels at 30-60 min. It is 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 the urine. It has a plasma half-life (t½) of 2–3 hours and a clearance value of 5 ml/kg/min.
A drug is defined as the single active chemical entity present in a medicine that is used for the diagnosis, prevention, treatment/cure of a disease. This disease-oriented definition of drug does not include contraceptives or the use of drugs for the improvement of health. The World Health Organization (1966) has given a more comprehensive definition – “Drug is any substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefit of the recipient.”
Disclaimer: This article is for informational purposes only and should not be taken as medical advice. Always consult with a healthcare professional before making any decisions related to medication or treatment.