Physiological factors that influence drug absorption include age, gastric emptying rate, intestinal transit time, diseases, blood flow to the gastrointestinal tract, gastrointestinal contents, and pre-systemic metabolism. Drug absorption depends on the movement of the unchanged drug from the site of administration into systemic circulation. It can be affected by factors like age, which impacts gastric acid levels and blood flow. Gastric emptying rate and intestinal transit time determine how quickly a drug enters the small intestine where most absorption occurs. Diseases of the GI tract can impact drug metabolism and permeability. Blood flow is important for removing the drug and maintaining absorption. Food in the GI tract and pre-systemic metabolism in the liver can impact bioavailability.

1. DRUG ABSORPTION-
PHYSIOLOGICAL FACTORS
Department of Pharmaceutics
SREE DATTHA INSTITUE OF PHARMACY
Sheriguda , Ibrahimpatnam , Telangana- 5010510
Presented by
G.DEEKSHA (16U21R0013)
Under the guidance of :
Asst.Professor. Mrs Naga Chandrika
SREE DATTHA INSTITUTE OF PHARMACY 1

2. DRUG ABSORPTION
DEFINITION :
Drug absorption is defined as the process of movement of unchanged drug from its site of
administration into the systematic circulation(blood).
 The rate and extent of absorption are important pharmacokinetic factors determining the dose
of drug and its frequency of administration.
 Drugs given by any route have to cross or pass through one or more semipermeable
membranes before reaching their site of action.
SREE DATTHA INSTITUTE OF PHARMACY
2

3. PHYSIOLOGICAL FACTORS
1. Age
2. Gastric Emptying/ Gastric Motility
3. Intestinal Transit
4. Diseases
5. Blood Flow To GIT
6. Gastrointestinal Contents
7. Pre – Systemic Metabolism / First Pass Effect
SREE DATTHA INSTITUTE OF PHARMACY
3

4. 1. AGE
 The absorption pattern of drugs may vary among different age groups.
 Infants have less acidic GI fluids ,smaller intestinal surface area and comparatively
less blood flow than adults.
 These conditions alter the dissolution and stability pattern of several drugs in
pediatrics.
 In elderly patients, decreased intestinal surface area and blood flow, bacterial
overgrowth in small intestine , altered gastric emptying etc.., may retard the drug
adsorption
SREE DATTHA INSTITUTE OF PHARMACY
4

5. 2. GASTRIC EMPTYING / GASTRIC MOTILITY
 Gastric emptying or gastric motility is the entry of gastric contents into the small intestine.
 The gastric emptying can be quantified using the following factors :
 Gastric emptying rate : it is the rate at which the gastric contents empty into the small
intestine.
 Gastric emptying time: it is the time required for the gastric contents to empty into the small
intestine.
 Gastric emptying time α 1
Gastric emptying rate
SREE DATTHA INSTITUTE OF PHARMACY
5

6. Gastric Emptying may be considered as the rate determining step in the process of absorption.
RAPID GASTRIC EMPTYING
it is required when the consumed drugs
a) Are unstable in gastric PH (E.g : Penicillin G , Erythromycin)
b) Are better absorbed from the small intestine ( E.g : Vit B12)
c) Are required to exhibit a rapid onset of action ( E.g : Sedatives)
d) Undergo dissolution in small intestine( E.g : Enteric – coated tablets )
DELAYED GASTRIC EMPTYING
it is required when
a) The drug dissolve slowly
b) Food enhances the dissolution and absorption of drugs
c) GI fluids promote the disintegration and dissolution of different dosage forms.
d) Drugs causes gastrointestinal irritation (E.g: Aspirin )
SREE DATTHA INSTITUTE OF PHARMACY
6

7. 3. INTESTINAL TRANSIT
The residence time of food/ drug substances in intestine is known as intestinal transit time.
DELAYED INTESTINAL TRANSIT
it is recommended for those drugs which :
a) Exhibit sustained release action ( E.g: Diclofenac sodium )
b) Are enteric coated and hence dissolve only in intestine
c) Are site specific i.e.., absorbed from specific intestinal sites ( E.g: Vit B)
d) Exhibit slow penetrating ability ( E.g: Acyclovir)
e) Are least absorbed from colon
f) Exhibit high ratio of dose to solubility ( E.g : Cholorothiazide)
SREE DATTHA INSTITUTE OF PHARMACY
7

8. 4. DISEASES
a) GI diseases and infections
 Abnormalities associated with celiac disease which reduces the drug absorption include
1 Altered intestinal drug metabolism
2 Increased GI permeability
3 Increased gastric emptying rate
4 Decreased enterohepatic cycling of bile salts
 Abnormalities associated with crohn’s disease which also influence the drug absorption
pattern include
1 Decreased gut surface area
2 Decreased intestinal transit time
3 Altered gut wall microbial flora
SREE DATTHA INSTITUTE OF PHARMACY
8

9.  Decreased gastric acid secretion ( achlorhydria) and increased gastric PH reduces the absorption
( E.g: Asprin )
 Malabsorption of drugs may also occur due to GI infections like gastroenteritics , food
poisoning, cholera, shigellosis and intake of alcohol and antineoplastics .
b) GASTROINTESTINAL SURGERY
gastrointestinal surgery especially gastrectomy ( surgical removal of the entire or part of the
stomach) may cause drug dumping in the intestine , decreased intestinal transit time and osmotic
diarrhea , thereby resulting in altered drug absorption.
c) OTHER DISEASES
CVS disorders ,hepatic diseases, Parkinson’s disease, HIV –AIDS etc.., results in altered /impaired
drug absorption and first pass metabolism of certain drugs.
SREE DATTHA INSTITUTE OF PHARMACY
9

10. 5) BLOOD FLOW TO GIT
Blood and lymph serves as an important means for the transportation of drug molecules to various
body parts. As GIT is the major site of drug absorption it is therefore richly supplied with blood and
lymph vessels
Increase in the blood flow to the site of absorption (GIT), increases the drug absorption as rapid
removal of drug from its absorption site helps to maintain sink conditions i.e, concentration gradient .
Decrease in splanchic blood flow as in hypovolemic states results in decreased absorption and
bioavailability of drugs.
SREE DATTHA INSTITUTE OF PHARMACY
10

11. 6) GASTROINTESTINAL CONTENTS
Presence of food ( Food –Drug Interaction)
Presence of food alters the gastrointestinal transit time and thus effects the absorption of many drugs.
Presence of food either increases, decreases or has no effect on drug absorption.
Usually, drugs are rapidly absorbed when given on empty stomach , but sometimes food aids in the
absorption of certain drugs or helps to overcome any gastric irritation.
Drugs like chloroquine, griseofulvin, nitrofurantoin, diazepam, actively absorbed water –soluble
vitamins, spironolactone etc.., are well absorbed in the presence of food.
SREE DATTHA INSTITUTE OF PHARMACY
11

12. 7) PRE –SYSTEMATIC METABOLISM / FIRST – PASS EFFECT
A drug administered via oral route shows decreased bioavailability owning to ,
a) Decreased adsorption because of precipitation ,poor solubility , complexation etc.
b) Destruction of the drug
c) Pre-systematic or first –pass metabolism
A drug when administered orally, passes through the GIT and liver where it undergoes extensive
metabolism before reaching the systematic circulation , thereby leading to decreased bioavailability. This
phenomenon is termed as first-pass effect or pre-systematic metabolism.
when the drug undergoes hepatic first-pass effect , the resulting metabolite is less potent than the parent
drug . Hence, the dose of the drug needed for oral administration is larger than that needed for i.v or i.m
administration to attain the same therapeutic effect.
SREE DATTHA INSTITUTE OF PHARMACY
12

13. REFERENCES
 BOOK NAME : BIOPHARAMACEUTICS AND PHARMACOKINETICS
( AUTHORNAME : BRAHMANKAR )
SREE DATTHA INSTITUTE OF PHARMACY
13

14. SREE DATTHA INSTITUTE OF PHARMACY
14