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Pharm304 > Lecture 6: Oral drug delivery I > Flashcards

Lecture 6: Oral drug delivery I Flashcards

1
Q

What is biopharmaceutics?

A

study of how the physicochemical properties of drugs, dosage forms and routes of administration affect the rate and extent of drug absorption

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2
Q

What is pharmacokinetics?

A

the study of ADME

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3
Q

What is the relationship between pharmacokinetics and pharmacokinetics

A

While PK studies the effects of the body on the drug,

PD studies the effects of drug on the body.
e.g. side effects, toxicity, ADRs

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4
Q

What is the bioavailability for IV? other routes?

A

IV = 100%

Other routes = administered dose which reaches systemic circulation in an unchanged form.

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5
Q

how is absolute bioavailability determined?

A

relative to an IV bolus injection

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6
Q

What are the main characteristics of the oral route?

A

most frequently used
usually for systemic effect
generally considered the simplest, most convenient and safest
drug needs to be able to survive acid conditions of stomach, and be resistant to enzymatic attack to be absorbed across GIT membrane

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7
Q

What is the GIT?

A

the gastrointestinal tract is a muscular tube approx 6m long with FOUR main anatomical areas.

absorption is increased by surface roughness
the majority of the epithelium is covered by a mucous layer

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8
Q

What are the 4 main anatomical areas of the GIT?

A

oesophagus
stomach
small intestine
large intestine/colon

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9
Q

What is mucous?

A

a viscoelastic translucent aqueous gel
It has a large water component (approx 95%)
~5-500um thickness

it is constantly removed and replenished due to abrasion from acid and enzymatic break down

estimated turnoever of 4-5 hours.

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10
Q

What does mucous contain?

A

mucin

  • large glycoproteins
  • protein backbone of ~800 amino acids long
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11
Q

What is the oesophagus?

A

tube that links mouth to stomach
pH between 5-6
material moved by swallowing (commonly impaired in elderly) and peristalsis
assisted by gravity in upright position.
rapid transit time (5-15 seconds)

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12
Q

What is the stomach?

A

temporary reservoir to deliver food to duodenum at controlled rate.

  • reduces solids to chyme via acid and enzymes
  • reduces risk of noxious agents reaching intestine
  • capacity of ~1.5L with mainly gastric secretions (though may be 50mL if fasting)
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13
Q

What are the main gastric secretions of the stomach?

A
  • acid secreted by parietal cells (pH 1-3.5)
  • gastrin (hormone) stimulates gastric acid secretions. gastrin is stimulated by peptides
  • pepsins break down proteins at low pH
  • mucous, protects gastric mucosa from acid and pepsins
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14
Q

What is the small intestine?

A

longest and most convoluted part of the GIT
~4-5m
-divided into duodenum, jejunum and ileum
-main site of absorption
-well supplied with blood and lymphatic vesels (~1/3 of CO)
-pH ~ 6-7.5

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15
Q

What are the main functions of the small intestine?

A
  • digest (completes enzymatic digestion from stomach)

- absorb (major site of absorption)

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16
Q

How long is the duodenum?

A

200-300mm

17
Q

How long is the jejunum?

A

2m

18
Q

How long is the ileum ?

A

3m

19
Q

How is the small intestine vasculated?

A
  • blood flows IN through superior mesenteric artery
  • blood LEAVES via hepatic portal vein (to liver)
  • vasculature from lymphatic system is important in absorption of fats
  • surface area increased around 600x due to villi
20
Q

What are the different secretions in the small intestine?

A
  • brunner’s glands in duodenum secrete bicarbonate
  • intestinal cells throughout the SI secrete mucous and enzymes
  • pancreas secretes bicarbonate, proteases (about 1-2L/day)
  • hepatocytes secrete bile. This is concentrated in the gallbladder and hepatic biliary system to form an aqueous mixture
21
Q

What are the main components of bile?

A

organic solutes: bile acids, phospholipids, cholesterol, bilirubin

inorganic compounds: sodium, potassium, plasma electrolytes

22
Q

What is the main function of bile?

A

aid absorption of dietary fat, e.g. fatty acids, cholesterol via emulsification and micellar solubilisation

23
Q

What are the two types of movement in the small intestine?

A

propulsive and mixing

24
Q

What does propulsive movement determine?

A

the transit time and residence time
This is typically 3.5-4.5hours in healthy volunteers

Research into attempts to extend transit time

Presence of fat delays transit time modestly (30-60mins)

25
Q

What is the colon?

A

Last portion of GIT
1.5m long
surface area increased 10-15x by microvilli and crypts
however only 1/30th of surface area of the small intestine

colonised by microflora (mainly lactobacillus)
pH caecum: 6-6.5 increases to 7-7.5
transit time ~24 hours

26
Q

What are the main functions of the colon?

A

absorption of Na, Cl, water
exchange bicarbonate and potassium ions
storage and compaction of faeces

27
Q

What is the relationship between colonic absorption and formulation of drugs?

A

for most formulations, colonic absorption of drugs is the only real opportunity to increase the interval between doses because it takes so long to reach the colon. Thus sustained release opportunity.

Some interest in using bacterial enzymes to target drug delivery to this area

28
Q

What are the main GIT characteristics relevant to drug delivery?

A

residence time and absorption area
pH
enzymes
FPM

29
Q

What is residence time?

A

the length of time during which the drug molecules are in contact with the absorption surface

  • determines amount of absorption, and rate of absorption
  • increases down the GIT
  • useful in the design of SR products and estimating the amount of absorption.
30
Q

what is the significance of the GIT pH?

A

gradually increases along GIT
determines stability and ionisation which in turn affects passive diffusion and solubility

can be used to design dosage forms and estimate drug absorption

31
Q

What is the significance of the GIT enzymes?

A
  • break down nutrients
  • several different types.

some are detoxifying enzymes which metabolise xenobiotics.

  • these determine FPM, stability of drug molecules and drug interactions
  • can be used to predict FPM and stability which is critical in the design of dosage forms
32
Q

What is first pass metabolism?

A

Everything from the stomach below will go through the liver (aside from rectum)

FPM determines absorption rate and liver fpm
It is useful for the selection of route of administration

Pharm304 (21 decks)

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