Question

What are the four steps of pharmacokinetics?

Answer 1

The way the body deals with the absorption, distribution, metabolism and the excretion of drugs under investigation expressed in mathematical terms is called Pharmacokinetics. The effects and the duration of action of drugs are also considered. The study of pharmacokinetics is usually carried out in healthy volunteers or patients. The data obtained from studies are used for designing and conduct of subsequent clinical trials. Clinical pharmacokinetics is the application of pharmacokinetics studies to clinical practices.

Complete answer:
Steps involved in the pharmacokinetics study are:
1. Absorption: Medicines, when travel from the site of administration into the body’s circulation are absorbed. Most common ways of drug administration are oral (such as swallowing an aspirin tablet), intramuscular (getting a flu shot in an arm muscle), subcutaneous (injecting insulin just under the skin), intravenous (receiving chemotherapy through a vein) or transdermal (wearing a skin patch). When medicines are taken by mouth they are shuttled via a special blood vessel leading from the digestive tract to the liver, where a large amount of medicines is broken down. Other routes of drug administration bypass the liver, either entering the bloodstream directly or via lung or skin.
2. Distribution: Mostly the bloodstream acts as the vehicle for carrying the medicines throughout the body. In this step, side effects can occur if medicines act on different sites other than the target site. Drugs which are destined for the central nervous system face a nearly impenetrable barrier called blood brain barrier that protects the brain from poisons or viruses. Fortunately, pharmacologists have devised various ways to sneak some drugs past the blood-brain barrier. Other Factors influencing distribution include fat and protein molecules in the blood that can put drug molecules out of commission by latching onto them.
3. Metabolism: After medicines have been distributed and its function has achieved the drug is broken down or metabolized. Everything that enters the bloodstream is carried to the body’s chemical processing plant, the liver. After reaching the liver, substances are chemically pummeled, twisted, cut apart, stuck together and transformed by proteins called enzymes. Products of the enzymatic breakdown are chemically less active than the original molecule. Genetic differences alter the enzyme actions, affecting their ability to metabolize drugs.
4. Excretion: The inactive drug undergoes the final stage called excretion. The removal happens via the urine or feces. By measuring the amount of a drug in urine as well as in blood clinical pharmacologists can calculate how a person is processing a drug, perhaps resulting in a change to the prescribed dose or even medicines. For example, if a drug is eliminated relatively quickly, the higher dose may be required for that particular drug.

Note:
Pharmacokinetics is the branch of medicinal pharmacology. It deals with the effects of drugs administered externally. It is derived from the Greek word ‘pharmakon’ (drug) and ' kineticos’ (motion). In other words, pharmacokinetics is the study of relation between dose, plasma concentrations, effects of drugs. The four main stages of Pharmacokinetics i.e., absorption, distribution, metabolism and excretion are collectively referred to as ADME.