Pharmacology is a science which deals with the detailed study of the physiological effects, history, properties, mechanism of action (Pharmacodynamics), absorption, distribution, metabolism, excretion (Pharmacokinetics) and uses of drugs.
• Pharmacodynamics: how the drugs, affect the body
• Pharmacokinetics: How the body, well or sick, affects drugs.
Mechanism of drug action:
A drug may produce its effect by a number of mechanisms like combining with enzymes, receptors, cell membranes and other components of a cell. A fundamental concept of pharmacology is that to initiate an effect in a cell. This molecular structure is called a receptor. Receptor: It is the hypothetical component of the cell with which a drug interacts. The receptor may be on the cell membrane or inside the cell. It may be a protein or enzyme.
Many receptors are capable of initiating a chain of events involving second messengers.
Absorption of drugs: A drug can enter into a systemic circulation and reach the site of action only after absorption. The absorption of a drug involves its passage across cell membranes.
Distribution of drugs: After a drug is absorbed, it is distributed to various fluids and body tissues. Drugs which easily pass through the cell membrane to achieve a wide distribution.
Metabolism: Alteration of a drug in a living organism is known as xenobiotics or biotransformation. In this process, a drug may either be converted or inactivated into more active compounds.
Methods of biotransformation:
Excretion of drugs: It decreases its duration of action. This in turn decreases the toxicity. The drugs can be eliminated through various routes are kidneys, lungs, skin, intestine, bile and saliva.
PHASES OF CLINICAL INVESTIGATION: The clinical development of a novel drugs usually takes place in phases or steps described as clinical investigation (phase I), clinical investigation (phase II), clinical trials (phase III), and post-marketing studies (phase IV).
Phase I: For certain types of drugs, such as anticancer drugs, it is not appropriate to use healthy subjects The studies generally have been conducted in healthy volunteers in between the age of 18 and 45 years, this practice is coming under the assessment of safety. because the risk of injury is too high. The purpose of phase I studies is to assess the dose level at which the signs of toxicity first appear, Administration of a single dose of the test drug and closely observing the subject in a hospital or clinical pharmacology unit with emergency facilities. If no side effects occur, the dose is increased progressively until a pre-determined dose is reached. Phase I studies are usually confined to a group of 20 to 80 subjects. If no untoward effects occur from single doses, short-term multiple-dose studies are initiated.
Phase II: If the reports of phase I studies showed that it is safe to continue, the new drug is administered to patients for the first time. Ideally, these individuals should have no medical problems other than the condition for which the new drugs are intended. Here, the efficacy of drugs can be estimated. The dose–response studies are a critical part of phase II studies. The number of volunteers in phase II studies is usually between 80 and 100.
Phase III: In this phase, the number of subjects may range from several hundred to several thousand, depending on the drug. The purpose of phase III studies is to verify the safety and efficacy of the drug and to detect effects that may not have surfaced in the phase I and II trials. A new drug application is submitted at the end of phase III.
Phase IV: After the approval of drug, Controlled and uncontrolled studies are often conducted and marketed. Such studies are intended to the experience with the drug and compare it with other drugs.
Pharmacokinetics, pharmacodynamics, clinical trail
