toxicology Screening methods Gastrointestinal tract

1. Presented by : Rushikesh STidake
M.PHARM II SEM
Pharmacology
RSCP , BULDANA 1

2.  Objectives of the guidelines –These guidelines were
developed to help protect clinical trails participants &
patients receiving marketed products from potential
adverse effects of pharmaceutical , while avoiding
unnecessary use of animal & other resources.
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3.  2-3% discontinuation of drug project
 Related ADRs & AEs are not life threatening but
hampers quality of life for patients
 18% of total ADRs
 Overuse of NSAIDs in US is a reason behind >1,00,000
hospitalization & 17000 deaths in year (2003)
 Hence there is a need for improved & more extensive
GI screening
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5.  Assessment of gastric emptying & intestinal
motility
 Assessment of Gastric Secretions
 Models of Nausea & Emesis
 Models of Gastrointestinal Absorption
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6. Assessment of gastric Emptying &
intestinal Motility
InVitro models :
•subcellular, cellular, tissue, or whole organ to study the pharmacological
effects and mechanism of action of drugs on GIT
• Stomachs or isolated segments of GIT from small laboratory animals can be
suspended in organ baths to investigate the mechanisms underlying a novel
drug target and to validate physiological or pharmacological responses.
Typically muscular strips or whole segments from the GIT are suspended in
organ baths containing a suitable nutrient solution held at 37⁰ C and gassed
with carbogen
•study the enteric nerves is done by measuring changes in motility caused by
electrical field stimulation (EFS)
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7. In Silico Organ Modeling :
•Computational fluid dynamic (CFD) techniques (Ferrua and Singh 2010) predict
the dynamic effects of luminal contents onGl motility, luminal content mixing,
and propulsion
•This model showed a complex and highly three-dimensional flow profile during
gastric contraction
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8. InVivo Models
• In rodents by administering meals containing markers such as
phenol red, barium sulfate (BaSO4), or charcoal, subsequent to the
administration of the test compound.The test meals can be used
either as an indicator of liquid (phenol red) or solid transport
(charcoal, BaSO4).
• For gastric emptying assessment, the stomach is weighed, after
definite time as its weight directly correlates with its content.Any
difference in the gastric weight between treatment groups indicates
altered gastric emptying.
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9. •For intestinal motility assessment, the intestines are removed (usually from
duodenum to ileum) and the length of intestine filled with charcoal or BaSO4
is measured and compared to the full gut length by visual inspection.
•The percentage of intestinal length filled by the test meal is proportional to
the intestinal transit. Any difference between treatment groups indicates an
alteration in the intestinal motility (increase or decrease).
•With phenol red, the intestinal transit is evaluated by measuring the spectral
absorbance in specific subparts of the gut.
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10. Assessment of Gastric Secretion InVitro Models
•performed on mucosal cell preparation from stomach mucosa obtained by
enzyme dispersion and separated by centrifugation to separate parietal cells
(H+ secreting cells)
•Measures the H+ concentration and pepsin secretion in the gastric effluent
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11. InVivo Models
Pyloric ligation method
•Rats fasted for 24hrs prior ligation
•Randomly divided into 5 groups of 3 animal each .
•Group I : Control vehicle
• Group II: Standard drug (Omeprazole)
•Group III: 'x' concentration of test drug
•Group IV: '2x' concentration of test drug
•GroupV: 4x' concentration of test drug
•Drugs administered once for 2 days and 30 mins prior to ligation
• Rats anesthetized with ether.
• Pyloric ligation procedure done.
• Rats placed in separate cages and allowed to recover.
•19 hrs after pyloric ligation, animals sacrificed by decapitation.
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12. Models of Nausea and Emesis
In vivo models
•assessed in conscious animal models
•Ferrets and dogs are typically considered to be the best species for the
evaluation of emesis, dogs being usually more sensitive to emetic stimuli
compared to humans
•Rats and mice are not able to vomit, but can display some behavioural
reactions that can represent nausea, such as gasping or pica
•Emesis evaluation in dogs, ferrets, or nonhuman primates usually consists
of visual recordings of retching and vomiting events, and possibly
premonitory signs such a licking, during a defined period following
compound administration
•The number of events and the latency are the most frequent parameters
reported.
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13. Models of Gastrointestinal Absorption
In vitro models
•Cell culture-based permeability screening models are used for the rapid
assessment intestinal permeability of drug candidates
•The human monolayer of colon adenocarcinoma cells (Caco-2) model used to
predict the intestinal absorption of orally administered drugs or measurement of
flux of a marker molecule or active ion transport across epithelial cells.
•NSAID-induced mucosal damage has been demonstrated in gastric mucosa
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14. In vivo models
•In situ absorption models have been used in the anesthetized rat, with
intraluminal administration of the test drug and collection of inflow
and outflow of an isolated segment of the gut
•In parallel, arterial blood is sampled and the disappearance rate of the
substance is evaluated
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