Absorption Distribution Metabolism & Elimination of Drug
for the specific effect of drug, it have absorbed well. After absorption drug get distributed via blood to all over body & its fraction amount of drug reaches to site of action. Then shows therapeutic effect. With this activity drug get metabolized & excretion. Thus the study of absorption, distribution, metabolism, excretion are important.
Absorption of Drug
Hence, Absorption is the process in which drug enters from site of administration to systemic circulation. Absorption further classified on the basis of their mechanism.
1. Simple/Passive diffusion: In simple diffusion drug crosses the permeable/cell/mucous membrane through aqueous pores & lipid soluble drug directly dissolved in membrane. For the simple diffusion the particle size not more than 800 gm/mole. (As per soil science society of America).
2. Active transport mechanism: In active transport drug crosses the cell membrane through carrier molecule, which present on membrane. For active transport energy is required. In active transport drug bind with carrier & cross the cell membrane.
3. Pinocytosis/phagocytosis: as you knows cell performs his own daily activity like food intake, etc. the mechanism which similar to food intake of cell known phagocytosis.
• Factors affects on Absorption of Drug:
1. Physical state: absorption of drug changes with there physical state like liquid gets easily absorbed than solid. Oily substances get fast absorbed than water-soluble substances.
2. Particle size: Absorption of solid substances varies with particle size, because the smaller particle size improves better absorption.
3. Concentration: Higher the concentration higher the absorption of drug.
4. Absorbing surface: The physiology of Absorbing surface is very important for absorption of drug, if the highly vascular membrane is available then higher the absorption.
5. GIT: if the peristaltic action increased then absorption of drug decreased. If git is free from food then absorption is better.
6. Ph: The Ph of GI tract is different in stomach & Intestine. The Ph of stomach is acidic hence absorption of acidic drug is better than basic drug, while large & small intestinal Ph is basic hence absorption of basic drug is better.
7. Formulation: Now a days medicine come in different dosage forms like, tablet, capsules, syrups, suspension, mixture, powders, etc. it means different type of formulation varies in absorptoin.
1st drug absorbed from GIT. After absorption Drug get DISTRIBUTED through out the body via blood. Distributed drug reaches to all body include Liver, when Drug come in contact with Liver then undergoes different chemical changes known as Metabolism. This process continues with absorption & metabolism. Metabolized drug is less toxic than active form and it’s ready for Excretion through kidney in form of urine, lungs, etc.
Distribution of Drug
After absorption drug enters in systemic circulation known as Blood & drug bind on Plasma proteins to transfer one place to other. Distribution defined as the process which transports drug to site of action, to the storage sites, to the organs of metabolism & excretion. Free drug enters in contacted tissue or cell & show his specific activity. In the distribution drug get distributed through out the body. It includes blood, extracellular fluids, etc. Distributed drug also have cross some barriers like BBB (Blood-Brain-Barrier), Placental barriers, etc.
Distribution of drug is very important for desired action of drug with respect to time limit of drug. The Maximum time of drug presence in blood provide longer effect of drug.
The specific action of Drug due to fraction amount of drug reaches to a specific area.
Factors affect on Distribution:
• Plasma protein binding property of drug.
• Chemical Property of Drug.
• Active transport system.
• Barriers of the body
Metabolism of Drug
The metabolism of drug is process which convert active drug into inactive form. This inactive form of drug is less toxic to excretion organs than active form. The metabolism of drug is simply detoxification process also known as Biotransformation of drug. The drug undergoes lots of chemical changes with the help of hepatic microsomal enzymes which present in Liver. The processes of metabolism occur along with Absorption & Distribution of drug. Some drugs get activated after metabolism knows as Prodrug.
The maximum type of drug metabolized in Liver due to presence of certain enzyme in liver. The metabolism of drug happened in different reactions known as Phase reaction. They are….
• Phase I reactions: this reaction also known as Nonsynthetic reactions because there is no any synthesis happened. in this reactions include,
1. Oxidation Reactions
2. Reduction Reactions
3. Hydrolysis Reactions
For this reaction certain enzymes are required like, Cytochrome P 450, NADPH, etc.
• Phase II reactions: This reaction known as synthetic reactions, because the reaction yield a synthetic product which is in good soluble form & its very helpful to excretion. In this reactions include…
1. Gluconide synthesis reactions
2. Methylation Reactions
3. Acetylation Reactions
For this reaction certain enzymes are required like, Glucuronyl transferase, Catechol-O-Methyl transferase, N-acetyl transferase.
Elimination of Drug
After the Biotransformation of drug it get eliminated through out the body via lungs, kidneys, bile, intestine etc called Excretion of drug. The drug eliminated in the active/inactive form.
• Kidneys: the elimination of drug through urine.
• Lungs: the elimination of drug through Breath.
• Skin: the elimination of drug through Sweat.
• Intestine: the elimination of drug in faeces.
• Saliva & milk: the drug excreted in milk & saliva.
• Bile: the drug excreted in bile.
Vilas k Sonagre
Lecturer (KDPCP Saoner)
For privet circulation only.
Absorption Distribution Metabolism & Elimination of Drug