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First we have to cover the core principles of pharmacology. Let's start!
What is Pharmacology?
The word pharmacology is derived from the Greek word pharmakon, which means drug and logia which means to study. It can simply be defined as the study of interaction of drugs with living organisms.
Does this definition clarify pharmacology? Certainly not. There remains a lot of questions to be answered.
While describing in detail, pharmacology can be defined as a branch of science that includes history, source, physicochemical properties, dosage forms, methods of administration, absorption, distribution, mechanism of action, pharmacological effects, biotransformation, excretion, clinical uses and adverse effects of drugs.
Nowadays pharmacology is considered as an integrated rather than an autonomous science. The techniques and knowledge of several disciplines such as physiology, biochemistry, physics, chemistry, and even mathematics have been incorporated to make the subject more easier and well defined. The synthesis of new drug in the laboratory is mainly on the basis of knowledge on chemistry. Mathematics as well as physics have been applied in understanding pharmacokinetics of a drug. Pharmacology is becoming more and more molecular in its outlook. A knowledge of pharmacology is an essential element in medical practice, and is a basis for the discovery of new drugs.
What is a drug?
Since the term "drug" has been already used in defining pharmacology, it is necessary to explain what it means. The word drug is derived from the French word 'drogue", possibly deriving later into "droge-vate" from Middle Dutch meaning "dry barrels", referring to medicinal plants preserved in them.
A drug may be defined as 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.
Drugs used to be small compounds derived first from natural sources, later from organic chemistry. Today, large proteins mostly produced by molecular biological techniques have been added to the family of drugs. Tomorrow we may see further types of drugs: DNA in the form of oligonucleotide and replacement of defective genes and cells or regenerate defective tissues are the two most likely candidates.
Drugs are simple ions to complex ones. For example, iron is considered as a drug that is used for the treatment of iron deficiency anemia. Even some peptides (captopril, oxytocin, calcitonin, insulin, somatostatin, growth hormone, cyclosporin and ACTH) and proteins (streptokinasem tissue plasminogen activator, interferons, erythroproteins, antibodies and vaccines) are also considered to be drugs.
What are drugs used for?
Drugs can be used to diagnose, prevent, control or cure a disease.
A single drug does not fulfill all the above purposes.
For example, Barium sulfate (a radio-opaque substance) is usually used to fill the gastrointestinal tract so that any defect in the tract can be exposed for X-ray. Here, barium sulfate is used for the diagnosis of disease. It has no role in prevention or cure. Mefloquine (against malaria), aspirin (against myocardial infarction) or immunization is used for prevention (prophylaxis) of disease. Diabetes mellitus is still not a permanently curable disease but it can be controlled by Glebenclamide or insulin. On the other hand, metronidazole is used for the treatment of amoebiasis with the purpose to cure the disease.
The term drug is sometimes replaced by the term medicine or agent. For example anti-hypertensive agent instead of anti-hypertensive drug.
But there is a difference between the terms medicine and drug. A drug is just a drug. But a drug becomes a medicine when the daily dose, frequency and duration of treatment is added to it.
Scope of Pharmacology
The scope of pharmacology is rapidly expanding and provides a rational basis for the therapeutic use of drug. The branch that first achieved professional status was pharmacy. It is concerned with the preparation, compounding and dispensing of chemical agents for therapeutic uses. Nowadays a pharmacy graduate (pharmacist) is no longer called upon to prepare or package drug since this is done by the pharmaceutical company. Pharmacy includes pharmacognosy, pharmaceutical chemistry, and biopharmaceutics. Pharmacognosy deals with the synthesis of new drug. The formulation of drug influences the pharmacokinetic and pharmacodynamic behavior of drug (biopharmaceutics)
Pharmacokinetic and Pharmacodynamic are the two most important parameters necessary to understand the principals of pharmacology. Any drug therapy can fail if the pharmacokinetic or pharmacodynamic parameters are wrong.
Pharmacokinetic and Pharmacodynamic
The term pharmacokinetic is derived from the Greek work pharmakon means drug, and kinein means to move.
When a person swallows a drug, it does not remain within the stomach. It will move through the intestine. If it is absorbable, then it will enter the systemic circulation. Sometimes the whole amount of drug is not absorbed. The amount that is not absorbable will be excreted out through the feces. After absorption, the drug usually will not stay within the blood, rather it is distributed throughout the whole body and the distribution of drug depends on the nature of that drug. Later the parent drug will be metabolized mainly in the liver to make the drug more polar so that the metabolite(s) will be excreted out mainly by the kidneys through urine.
So basically speaking pharmacokinetic is what the body does to the drug and it includes absorption, distribution, metabolism (biotransformation) and excretion of a drug.
Pharmacokinetic can be formally defined as the study of the rate process associated with the absorption, distribution, biotransformation, and excretion of drug, i.e. quantitating drug and/or metabolite(s) concentrations in body fluids and excreta at any time from the moment of administration until the elimination from the body is complete.
The primary standard of a pharmacokinetic study is based on the data obtained following intravenous administration of a drug. Since the entire dose is administered directly in the blood, all the potential rate limiting and metabolic factors associated with the drug absorption is absent. So the pharmacokinetic parameters are unaffected by absorption. After obtaining the primary pharmacokinetic parameters the drug absorption parameters following other routes of administration may be evaluated and defined in relation to the intravenous standard.
Pharmacodynamic can be simply defined as what the drug does to the body.
For e.g. aspiring lowers the body temperature in a case of fever. Atenolol reduces the blood pressure. Blood sugar level is reduced by glibenclamide So, lowering temperature, blood pressure or blood sugar are all considered as what the drug does to the body (drug effects or pharmacological effects).
Pharmacodynamic includes mechanism of action and pharmacological effects of a drug. The knowledge if pharmacodynamic is essential for the selection of a drug.
Now the question is where and how are the effects produced? Aspirin acts on the thermoregulatory center present at the medulla to readjust it. Atenolol acts on the heart and blood vessels to reduce cardiac output and peripheral resistance. Glibenclamide on the beta cells of the Islet of Langerhans of the pancreas to release insulin. Here, thermoregulatory center, heart, blood vessels and beta cells of the Islet of Langerhans are the sites of action of drugs.
Besides these, the knowledge about pharmacodynamic would be helpful to know about the genetic factor on the effects of some drugs. About 10% of American black male shows haemolysis after administration of primaquine that is due to hereditary deficiency of glucose-6-phosphate dehydrogenase in red blood cell.
The scope of pharmacology has been extended by introducing biochemical pharmacology, clinical pharmacology, immunopharmacology and behavioral pharmacology.
Biochemical pharmacology describes the action of drug on biochemical processes within the cell.
There is a gap between pharmacology as a basic and a clinical science. Clinical pharmacology integrates therapeutics with the basic principles of pharmacology, research methodology and biostatistics. It evaluates the pharmacological effects of drug, preferred method of administration, and safe range in human by clinical trials.
Immunopharmacology deals with the immunological aspects of drug action, including the effects of drug in immune response and development of antibodies in response to the drug. Any drug that suppresses the immune system play important role in organ transplantation procedure.
Behavioral pharmacology refers to the study of how drug affects the behaviour of a patient. This includes description of the changes in behaviour produced by the drug, and exploration of the mechanism by which the drug produces these changes.
Pharmacoeconomic is the study of the cost of medicine. Pharmacoepidemiology is the study of both beneficial and adverse effects of a drug on a large number of people. While prescribing a drug, it is vital issue about pharmacoeconomics and rational use of drug.
Nowadays we are expecting a drug free permanent solution for many types of diseases. It is based on gene therapy. A drug works from the outside in, and must be continuously re-administered if the disease is chronic. Contrarily, gene therapy works from the inside and should keep working indefinitely.
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