1.
TOPIC : DRUG
ABSORBTION
NAME- DEBABRATA DINDA
ROLL NO- 20801920056
SUBJECT- BIOPHARMACEUTICS &
PHARMACOKINETICS
SUBJECT CODE- PT604

2.
CONTENTS INTRODUCTION
INTRODUCTION
BIOLOGICAL
MEMBRANE
DRUG TRANSPORT
ABSORPTION OF
DRUG IN GIT
FACTOR AFFECTING
DRUG ABSORPTION
EFFECT OF pH ON
DRUG KINETICS
BIOAVALABILITY
FIRST PASS
METABOLISM
REFERENCE

3.
INTRODUCTION
DRUG ABSORBTION?
Drug absorbtion is defined as the process of movement of unchanged form
of drug from the site of administration to systemic circulation .
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Minimum effective concentration (MEC)
Subtherapeutic level
Time
Plasma
Drug
Concentration
Therapeutic level
Therapeutic success of a rapidly
and completely absorbed drug
Therapeutic failure of a
slowly absorbed drug
Fig- Plots showing significance of rate and extend of absorbtion in drug therapy

4.
BIOLOGICAL MEMBRANE

5.
DRUG TRANSPORT
Drugs need to pass through one or more cell membrane to reach their site of action.
Drugs transport by-
(1) PASSIVE DIFFUTION -
Drug transport in the direction of concentration gradient.
More lipid soluble drug diffuse quickly.
No energy and carrier required.
(2) FILTRATION – trough paracellular space in membrane.
(3) SPECIALIZED TRANSPORT –
(a) Active transport-
Drug movement against concentration gradient.
Energy and carrier reguired
Symport(cotransport)
Antiport(Exchange transport)
(b) Facilitated Diffusion-
Transport of glucose across muscle cell membrane by a trans porter GLUT.
Drug transport in the direction of concentration gradient.
No energy and carrier required.

6.
ABSORPTION ACIDIC AND BASIC DRUG IN GIT
Weakly acidic drugs
Unionised form
Better absorbtion
from stomach
(Aspirin) Weakly basic drug
(Morphine , Quinine)
Unionised form
Better absorbtion from stomach
Acidic pH
Basic pH
So,acidic drug more readily absorbed from stomach and
basic drug more readily absorbed from intestine.

7.
FACTORS AFFECTING DRUG ABSORPTION
Aquous solubility – Solution absorbed faster than solid.
Concentration of drug – Concentrated solution absorbed faster than dilute solution.
Area of absorption sueface – More area faster absorption.
Blood flow – Increase blood flow removes the drug from the site of absorption so reduce absorption.
Empty stomach – Increase absorption of drug.
Presence of food – Retard drug absorption.
Ionization of drug – Drug are absorbed in unionized state so ionization decreases drug absorption.

8.
EFFECT OF pH ON DRUG KINETICS
Most drugs are weak electrolytes, i.e. their ionization is pH dependent.
The ionization of drug is given by:
pH = pKa + log[A^-1]/[HA]
pKa – Numerically equal to the pH at which the drug is ionized.
[A^-1] – Concentration of ionized drug.
[HA] – Concentration of unionized drug.

9.
BIOAVALABILITY
It is the fraction of a drug that reaches systemic circulation.
eg – If 100 unit of a drug is administered by any route and 70% unit reaches
In the systemic circulation , than bioavailability of the drug is 70%.
Bioavailability is i.v. route is 100%.
Disintegration time and dissolution rate – affect bioavailability.
Calculated by relating area under curve plasma concentration – time for i.v.
route and that particular route.
Bioavailability=
AUC oral
AUC injected
X 100

10.
FIRST PASS METABOLISM
When drugs are administered orally,they have to pass
Gut Wall – Portal vein – Liver – Systemic Circulation.
Drugs via high hepatic 1st pass metabolism are –
Salbutamol,Verapamil,Propranolol, Lignocaine,Isoprenaline.

11.
REFERENCE
Brahmankar D M and Jaiswal .Sunil B,Drug absorbtion ,Biopharmaceutics
and Pharmacokinetics.