Absorption of drug | Factor affecting absorption | b pharmacy

 ABSORPTION

• When we take oral drug then it goes Into the stomach and after disintegration and dissolution it absorb into blood.

• Absorption is the first step of pharmacokinetics.

• In disintegration step drug break into small particle in the presence of gastric HCl.

• After disintegration drug dissolve into gastric HCl and absorb into systemic circulation.

Factor affecting drug absorption :

Drug absorption is depends upon following factor -

(1) Physiochemical properties of drug

(2) Physiological factor

(3) Nature of dosage form

(4) Route of drug administration

(5) Bioavailability

(1) PHYSIOCHEMICAL PROPERTIES OF DRUG :

(A) Particle size -

• The absorption of of drug is inversely proportional to the particle size.

• As well as the particle size of drugs increase the rate of absorption is decreased.

• And when the particle size is decrease then the rate of absorption is increase.

(B) Nature of dosage form of drug -

• The nature of any powder is of two types amorphous or crystalline.

• The amorphous powder is dissolved very easily because it takes less energy.

• And in the crystalline form they require high energy for dissolution because they have crystal lattice structure.

• So the rate of absorption is the high for amorphous powder and rate of absorption is the low for crystalline powder.

(C) Solubility / Dissolution -

The rate of absorption of any drug is also depends on the solubility factor because our gastric media is hydrophilic in nature so hydrophilic drug more easily can dissolve into the gastric HCl than lipophilic drug. So the rate of absorption is high for hydrophilic drug and the rate of absorption is low for lipophilic drug.

(D) Salt form of drug -

• The strong acidic and strong basic drug can easily dissociate into the solvent.

• So their dissolution rate and the absorption rate is very high but in the case of weak acid and weak basic drug their dissociation rate is low so they absorb very slowly.

(E) Ionisation rate -

• Those drugs which are in ionic form, can be dissolved easily but they cannot cross the cell membrane.

• But in the case of non ionic form of drug they cannot be associated easily but their rate of absorption is high.

• So we make any drug in such a way that at the time of dissolution they are in ionic form and at the time of absorption they should be in non ionic form.

(2) PHYSIOLOGICAL FACTORS :

(A) Gastric emptying time -

• The absorption of drug is also depends upon the gastric emptying time.

• The drug whose gastric emptying time is less, their rate of absorption is high.

(B) Surface area -

• Surface area of any drug is directly proportional to the rate of absorption.

• If the surface area is increased then the more number of drug will be absorb proper.

(C) Blood flow -

• The rate of drug absorption is directly proportional to the blood flow.

• When the blood flow in body is increased then the rate of drug absorption is also increase.

(D) Effect of food -

• The rate of drug absorption is also depends upon the food which is present in the stomach.

• If the food is present in stomach then it dilute the drug and rate of absorption will decrease.

(E) First pass metabolism - 

• When the drug directly goes into the liver without reaching into the receptors and systemic circulation, this is called first pass metabolism.

• And for those drug which first pass metabolism is high, the rate of drug absorption is slow

(3) NATURE OF DOSAGE FORM :

• The rate of drug absorption is also depends upon the nature of dosage form.

• If the drug is taken orally then some part of drug is metabolized so their rate of absorption is slow.

• But when the drug is given parenterally, their bioavailability is 100% and rate of absorption is 100%.

• In the case of oral, the absorption of liquid dosage form is greater than solid dosage form.

(4) ROUTE OF DRUG ADMINISTRATION :

The rate of absorption is also depend upon the route of drug administration(We have already discussed in detail).

(5) BIOAVAILABILITY :

• It is the actual amount of the drug which reach into the systemic circulation this is called bioavailability of the drug.

• The dose drug bioavailability is high, their rate of absorption is also high.

MCQ CORNER

Spironolactone increase plasma digoxin concentration 

(A) True

(B) False

Ans : (A) True

The percentage of filtered sodium excreted in case of furosemide is 

(A) 10 percent

(B) 25 percent

(C) 40 percent

(D) 80 percent

Ans : (B) 25 percent

Example of Natriuretic are 

(A) Thiazide

(B) Amiloride

(C) Both A and B

(D) Indomethacin

Ans : (C) Both A and B

Lypressin is found in 

(A) Swine

(B) Goat

(C) Fish

(D) Rabbit

Ans : (A) Swine

Thiazide Act as (In case of Diabetes Insipidus) 

(A) Diuretic

(B) Antidiuretic

Ans : (B) Antidiuretic

Vasopressin is 

(A) GPCR

(B) Ion Chanenl

(C) Symporter

(D) All of the above

Ans : (A) GPCR

Which of the following is not a subtype of vasopressin receptors (Tick)

(A) V1

(B) V2

(C) V3

(D) V4

Ans : (C) V3