Patient Related Factors

Affecting drug absorption

Presented by,Presented by,Hinglajia Hetal RatilalHinglajia Hetal Ratilal

Patient Related Factors

Age

Age

Infants• Gastric pH high

• Intestinal surface low

• Blood flow to GIT low

Elderly persons Altered gastric emptying

Decreased intestinal surface area & GI blood flow

Higher incidents of achlorhydria

Bacterial overgrowth

Altered Absorption pattern

Gastric Gastric emptyingemptying

Gastric emptying

Apart from dissolution of a drug & its permeation through

the bio membrane, the passage from stomach to the small

intestine, called as gastric emptying.

Rate limiting step, because the major site of drug absorption

is intestine.

It increases bioavailability of a drug.

It is first order process.

Rapid gastric emptying Rapid gastric emptying advisable where,advisable where,

Delay gastric emptying advisable where,

Gastric acid quantifying parameters

• Gastric emptying rate is the speed at which the

stomach contents empty into the intestine.

• Gastric emptying time is the time required for the gastric content to empty into the small intestine.• Longer the gastric emptying time , lesser the gastric

emptying rate.

• Gastric emptying t1/2 is the time taken for half the stomach contents to empty.

Factors affecting on gastric emptying

Intestinal transitIntestinal transit

Intestinal transitIntestinal transitSmall intestine- major site for drug absorption, long

intestinal transit is desirable for complete drug

absorption

The residence time depends on the intestine that

occurs due to peristaltic contractions..

It promotes drug absorption by,

Increasing drug intestinal membrane contact,

Enhancing dissolution especially poorly soluble drugs,

through induced agitation.

Delayed intestinal transit is desirable for,

Intestinal transitIntestinal transit

Promotes..

Diarrhea

Laxatives

Drugs like metoclopramide

Demotes..

Food

Pregnancy

Anticholinergics

Gastrointestinal pHGastrointestinal pH

107 fold difference in the H+ ion concentration is observed between the gastric & colon fluids.

Blood Flow To The GIT

The GIT is extensively supplied by blood capillary network & the

lymphatic system.

The blood flow rate to the GIT is 500 to 1000 times (28% of

cardiac output) more than the lymph flow.

GI perfusion rate could be a rate limiting step in the absorption of

lipid soluble drugs.

The perfusion rate increases after meals but absorption is not

influenced significantly.

Disease States

Classes of diseases states, can affect on Bioavailability of drug

Gastrointestinal diseases

Cardiovascular diseases

Hepatic diseases

Gastrointestinal diseasesAltered GI motility

GI diseases & infectionsAchlorhydria – decreased gastric acid secretion &

increased stomach pHMalabsorption syndrome

Celiac diseaseCrohn’s disease

Infections like gastroenteritis, cholera, colitis, amoeviasis & constipation

GI surgery

Cardiovascular diseases:

CHF influence bioavailability of drug viz.

oedema of intestine,

Decreased blood flow to the GIT & gastric

emptying rate,

Altered GI pH, secretion & microbial flora

Hepatic diseases:

Such as hepatic cirrhosis.

Presynaptic metabolism

(First-pass effects)

Before a drug reaches blood circulation, it has to pass for

the first time through organs of elimination namely the

GIT & liver.

The loss of drug through biotransformation by such

eliminating organs during its passage to systemic

circulation is called as FIRST-PASS METABOLISM

Following system affect on FIRST-PASS METABOLISM

Luminal enzymes

Digestive enzymes

Bacterial enzymes

Mucosal / Gut wall enzymes

Hepatic enzymes

What is gastric emptying? Describe its role in drug absorption

Write a note on factors affecting drug absorption.

QUESTIONS QUESTIONS ASKEDASKED

For further reading regarding this topic, please refer the books like Brahmankar, Remington, Alton and another related books…..!