What are the 4 stages of pharmacokinetics?

Stages of Pharmacokinetics

Definition:-

The word pharmacokinetics is formed of two word “Pharmacon” means “Drug” and “Kinetics” means “Movement” thus literally mean of pharmacokinetic is the study of drug movement in and out of the body.

Pharmacokinetics explains that what the body do to the drug or the body ‘s response for drug. Body’s response is called Pharmacokinetic Effect.

Pharmacokinetics includes the process of absorption of drug, distribution of drug , biotransformation (Metabolism) and excretion of drug.

The pharmacokinetic process:-

 Route of Administration:-

The way or path by which drug moves and gives its pharmacological action is called route of administration.

Using of route of administration in percentage form:-

Membrane Transport:-

1.    Membrane transport refers to the collection of mechanism which regulate passage of solute like ion and small molecule through biological membrane.

2.    Which are lipid bilayer containing protein embedded in them.

3.    Water soluble substances are passed through protein.

4.    Separete substances of distinct chemical nature.

5.    Only pass the specific substances.

Transport type:-

1.    Active transport.

2.    Passive transport.

Passive transport:-

1.    Movement of ion and other atomic / molecular substance across cell membrane.

2.    Without the input of metabolic energy.

3.    Rate of passive transport depends upon the permeability of cell membrane of the cell.

1.    Diffusion:-

Movement of the molecule from an area of high concentration to an area with lower concentration.

2.    Facilitated diffusion:-

·       Carrier mediated Osmosis

·       Movement of the molecules across cell membrane via special transport proteins embedded within the cell membrane

3.    Filtration:-

·       Filtration is the movement of water and solute molecule across the cell membrane due to the hydrostatic pressure generated by cardiovascular system.

·       Depending upon the size of membrane pores.

·       Solute may pass through it e.g sodium potassium passes through membrane pore of the bowman’s capsule.

Active transport:-

·       The drug form a complex with a component of the biological membrane.

·       Characterized by selectively , saturability and competitive inhabitation.

·       Requires the energy.

·       Moves against the concentration gradient.

If the process uses energy in the form of ATP it is primary active transport e.g Sodium Potassium Pump.

Secondary transport involves uses of an electrochemical gradient.

Bioavailability:-

The rate and extent of drug absorbed from its dosage form and reached to the serum of the blood.

Intaveinous have 100% bioavailability as compared to oral route.

Depends upon the following:-

3.    Route of Administration.

4.    Formulation.

5.    Chemical properties of drug.

Distribution of drug:-

1.Once a drug is absorbed in systemic circulation it can be carried throughout the body this process is called distribution.

2.The delivery of drug from the blood stream to the site of action depends on the flow, degree of binding to blood and tissue protein .The molecule bind with receptor and other molecule again back into the bloodstream.

3.It is reversible process.

4.Blood flow to the different organ of the body is inequal.

5.Most vital organ like brain, liver, kidney, heart receive greatest supply of blood.

Factors:-

1.Blood Flow:-

1) Greater organ i.e brain ,liver, kidney, heart will receive greater amount of blood.

2) Lower organ i.e skeletal muscle, Adipose tissue will receive low amount of blood.

2. Capillary permeability depends upon:-

Capillary structure:-

If there is junction between the cell then drug will distribute more but if there is no junction so drug can’t be distributed.

3. Plasma protein binding:-

When drug combine with plasma protein then the size increases and can’t come out from capillary. It is irreversible if free drug becomes finished then this bind drug will detach from plasma protein.

Acid Drug bind with protein albumin.

Basic drug bind with alpha-acid glycoprotein

4.lipophilicity:-

1.Lipid soluble drug can easily cross membrane.

2.Charged or lipid insoluble drug can’t cross the membrane.

5.Volume of distribution(V):-

Apparent volume of distribution is defined as the volume that would accommodate all the drugs in the body, if the concentration was the same as in plasma.

Expressed as:- In liters 𝑉= 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑑𝑟𝑢𝑔 𝑖𝑛 𝑏𝑜𝑑𝑦 𝑃𝑙𝑎𝑠𝑚𝑎 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛

Blood brain barrier:-

1.Capillary endothelial cells in the brain have tight junction and lack large intracellular pores and above that there is a layer of neural tissues.

2.In choroid plexus, capillary are line by choroidal epithelium with tight junction blood CSF barrier.

Metabolism of drug:-

1. Metabolism is defined as the larger particle molecule are converted into small particle.

2. Conversion of one molecule of drug into another suitable molecule of drug is called biotransformation or metabolism.

Purpose of metabolism:-

To convert the drug into more water soluble component.

Primary site of Drug metabolism:-

Liver, kidney, intestine, lungs and plasma.

Metabolic Enzymes:-

Drug metabolizing enzyme is divided into two types:-

·       Microsomal Enzymes.

·       Non Microsomal Enzymes. 

Both of them develops partially in first month and completely in 3rd month.

Microsomal Enzyme:-

·       Located in smooth ER primarily in liver , also in kidney, intestinal mucosa and lungs.

·       Catalyze most of Oxidation , reduction , hydrolysis and glucouronide conjugation.

·       Example:- Monooxygenase, cytochrome P 450, Glucouronyl transferase. 

Non- Microsomal Enzyme:-

·       Located in cytoplasm and mitochondria of hepatic cells as well as in other tissue including plasma.

·       Some oxidation and reduction reactions, many hydrolytic reactions and all conjugating except glucoronidization.

·       Esterase , amidase , flavoprotein oxidases.

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