GENERAL PRINCIPLE OF DRUG ACTION || PHARMA EASY NOTES|| @PHARMACY



Introduction

What is Drug?

The drug is a chemical molecule or medical agent used for (D, P, Ts, Cd)
Diagnosis
Prevention
Treatment of symptoms
Cure of Disease
  • The desired pharmacological response of the drug can only be achieved if it is present at the site of action in appropriate concentration for a sufficiently long time.
Content 
General Principle of drug action
Introduction
Absorption of drug
Distribution of drug
Protein binding      
Metabolism and Excretion

This appropriate concentration is governed by the following factors-

A&F i) Amount and Frequency of drug administered
R (ii) Route of administration
F- D a,d,e (iii) Factors affecting drug absorption , distribution & elimination

2. Absorption of the drug

The process by which the drug is released in the body from its dosage form is known as absorption.

The factors which affect the rate of absorptions are- (CRPBSD)
C (i) Concentration of the drug
R (ii) Route of administration
P (iii) Physiochemical parameters of the drug
B (iv) Blood circulation to the site of applications
D (v) Dissolution rate for a solid dosage form

The main process by which a drug molecule crosses the natural barrier is -
S (i) Simple Diffusion
D (ii) Diffusion of ions across the membrane
F (iii) Facilitated diffusion
A (iv) Active transport
P (v) Pore transport
P (vi) Phagocytosis 

Note-                     Diffusion- S, D, F                                      
                          Transport- A, P                                                Phagocytosis-P


3. Distribution of drug

  • Once the drug has been absorbed into the blood, it is distributed around the body.
  • The drug in the blood system freely and rapidly distributes into the aqueous fluid surrounding the various tissue and organs.
  • The entry of the drug into the cell depends upon many mechanisms.
  • Aqueous channels- Water molecules and ions diffuse (eg K+, Cl−) through the aqueous channels.
  • Lipid soluble drugs- of any size diffuse freely through the cell membrane.
  • Water-soluble molecule and ions of moderate size including the ionic form of most of the drugs can not enter cells readily, except by special technique.


4. Protein binding

The reversible binding of a drug with a non-specific and non-functional site on the body protein without showing any biological effect is called protein binding. 

Drug  + Albumin ⇌  Drug + Albumin complex
  • Depending upon whether the drug is a weak or strong acid, base, or is neutral, it can bind to a single blood protein to multi proteins.
  • The most significant protein involved in the binding of the drug is albumin, which comprises more than half of blood volume.
  • Albumin interacts with acidic or basic drugs in the plasma by -
Vander-Waal's force
Hydrophobic binding
Hydrogen bonding
Ionic interaction
  • Acid-glycoprotein (AGP) interacts with basic entities and lipoproteins bind with both basic and neutral drugs.
  • Protein binding values are normally given as the percentage of total plasma concentration of the drug that is bound to all plasma proteins. 
Free drug [Df] + Free protein [Pf]  ⇌ Drug/Protein complex [Dp]
  • The total plasma concentration of the drug is expressed as the sum of the present free drug and the percent bound.
Total plasma concentration
[Dt]    =   [Df]  + [Dp]

5 Metabolism and Excretion

  • The termination of the drug effect is caused by biotransformation and excretion.
  • All the substances in the circulatory system, including drugs, metabolism, and nutrients will pass through the liver.
Drugs and their metabolites can be excreted from the body by a number of routes such as via The lungs
The skin
The bile duct
The Kidney
  • Volatile and gaseous drugs can be excreted through the lungs. For example- Gaseous general anesthetics are excreted in this way.
  • A certain proportion of a drug can be excreted through sweat, saliva, breast milk
  • Blood is filtered to remove small molecules (such as drugs and most of the water) quickly reabsorbed setting up concentration gradient leads hydrophobic molecules (reabsorbed into blood supply).
  • Polar molecules remain in the nephron and are excreted in the urine.
  • Drug metabolism makes a drug more polar so that it is less likely to be reabsorbed from the nephrons.
Purpose of this blog- To provide accurate and easy pharma notes ( D. pharm, B. Pharm, M, Pharm. Pharm D) that make your pharmacy study easy. our team covers each and every topic in easy form. For any query plz DM to us.

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