Gastric Emptying Presentation

GAS TRI C EM PTYI NG

BY: Rahul Jain B.Pharm VI SEM

Overview 

Apart from dissolution of a drug and its permeation through the biomembrane the passage from stomach to the small intestine called as gastric emptying.

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It can also be a rate limiting step in drug absorption because the major site of drug absorption is intestine. Motor events during normal Gastric Emptying

ADVANTAGES OF RAPID AND DELAYED GASTRIC EMPTYING Rapid gastric emptying is advisable where:    

A rapid onset of action is desired e.g. sedatives Dissolution of drug occurs in the intestine e.g. enteric coated dosage forms. The drugs are not stable in the fluids e.g. penicillin G and Erythromycin. The drug is best absorbed from the distal part of the small intestine e.g. vitamin B12

Delay in gastric emptying is recommended in particular where:    

The food promotes drug dissolution and absorption e.g. griseofulvin The drugs dissolve slowly e.g. griseofulvin The drugs irritate the gastric mucosa e.g. .aspirin. pheoylbutazone and nitrofurantoin The drugs are absorbed from the proximal part of the small intes­tine and prolonged drug­absorption site contact is desired e.g.vitamin B2 and vitamin C

Characteristics of GI physiology pH

Membrane

Blood Supply

Surface Area

Transit Time

BUCCAL

approx 6

thin

Good, fast absorption with low dose

small

Short unless controlled

ESOPHAGUS

6

Very thick, no absorption

-

small

short

STOMACH

1-3 decomposition, weak acid unionized

normal

good

small

30 - 40 minutes, reduced absorption

DUODENUM

5-7 bile duct, surfactant properties

normal

good

very large

very short (6" long), window effect

SMALL INTESTINE

6 -7

normal

good

very large. 10 - 14 ft, 80 cm 2 /cm

about 3 hours

LARGE INTESTINE

6.8 - 7

-

good

not very large. 4 - 5 ft

long, up to 24 hr

Factors Affecting Stomach Emptying PROMOTE Gastric volume

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Increased food volume in stomach promotes increased emptying Antral distension stimulates vasovagal excitatory reflexes leading to increased antral pump activity

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Liquid vs solid food

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Clear fluids are empty rapidly. Solids stay in stomach longer. Pylorus is open enough for H2O/fluids to empty with ease. Constriction of the pyloric sphincter to solids until chyme is broken down into small particles and mixed to almost fluid consistency

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Types of food

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Protein empties fastest, followed by carbohydrates. Fats take longest to empty Note: high protein food especially meat stimulate release of gastrin from antral mucosa

Drugs 

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Prokinetic Drugs eg:­ Cisapride, Erythromycin, Domperidone, Bethanchol, Metoclopramide

Body posture 

Gastric emptying is favored while standing and by lying on the right side, since the normal curvature of the stomach provides a downhill path.

INHIBIT 

Duodenal distension  Slow or even stop stomach emptying if the volume of chyme in the duodenum becomes too much

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Osmolarity of chyme  Iso­osmotic gastric contents empty faster than hyper or hypo­osmotic contents due to feedback inhibition produced by duodenal chemoreceptors (hyper more inhibitory than hypo)

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Types of food  Fat and protein breakdown products in the small intestine inhibits gastric emptying

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Acid  pH of chyme in the small intestine of < 3.5­4 will activate reflexes to inhibit stomach emptying until duodenal chyme can be neutralized by pancreatic and other secretions

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Temperature  Cold liquid (40C) empty more slowly

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Hormones  Cholecystokinin released from duodenum in response to breakdown products of fat and protein digestion. Blocks the stimulatory effects of gastrin on the antral smooth muscle  Secretin released from the duodenum in response to acid, has a direct inhibitory effect on the gastric smooth muscles

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Patient factors  Pregnancy delays gastric emptying (progesterone)  Anxiety delays gastric emptying  Elderly  Disease states eg diabetes mellitus

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Drugs  Antacids (Aluminum hydroxide), Anticholinergics (Atropine), narcotic analgesics (morphine)

Conclusion

REFRENCE 

WEBSITES:

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http://digestive.niddk.nih.gov/ddiseases/pubs/rapidgastricemptying

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http://www.pharmacy.wsu.edu/courses/PharS532/Oral/Bio.html#Factors

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http://www.aic.cuhk.edu.hk/web8/gastric_emptying.htm

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BOOKS:

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Textbook of Biopharmaceutics & Pharmacokinetics. III ed. DR. Javed Ali, Alka Ahuja, R.K. Khar, Biopharmaceutics & Pharmacokinetics. D.M. Brahmankar, Sunil B. Jaiswal. Textbook of Gastroenterology. 4th ed. Lippincott Williams and Wilkins.

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