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Pharm 202 > Booklet 8: Routes of Administration > Flashcards

Booklet 8: Routes of Administration Flashcards

1
Q

What is pharmaceutics?

A

The science of dosage form design

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2
Q

What is a fomulated preparation made out of?

A
  1. Biologically active entity

2. Additives (excipients)

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3
Q

What are the advantages of the oral route?

A
  1. Simplest, most convenient and safest
  2. For systemic or local effects
  3. Drug needs to be able to survive acid conditions of the stomach, resistant to enzymatic attack and absorbed across GIT membrane
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4
Q

What are the disadvantages of the oral route?

A
  1. Relatively slow onset of action
  2. Irregular absorption due to interaction with food
    Eg. Tetracycline with calcium
  3. GI secretions and digestive enzymes (oral insulin)
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5
Q

How long is the muscular tube in the gastrointestinal tract?

A

6cm

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6
Q

What are the 4 main anatomical areas in the gastro intestinal tract?

A
  1. Oesophagus
  2. Stomach
  3. Small Intestine
  4. Large intestine or colon
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7
Q

How is the surface area for absorption increased?

A
  1. By its surface toughness

2. Majority of epithelium covered by mucus layer

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8
Q

The Oesophagus

  1. Where
  2. pH
  3. How is material moved?
  4. Transit time
  5. Impairment
A
  1. Mouth to stomach
  2. pH 5-6
  3. Swallowing and peristalic wave of contraction assisted by gravity in an upright position
  4. Transit time rapid (5-15s)
  5. Swallowing impairment common in elderly
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9
Q

The Stomach

  1. Where
  2. Capacity
A
  1. Temporary reservoir to deliver to duodenum at controlled rate
  2. Approx 1.5L (fasting may only be less than 50mL because it is mainly gastric secretions)
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10
Q

What are gastric secretions of the stomach?

A
  1. Hormone gastrin
  2. Pepsins- secreted from peptic cells in the form of its precursor pepsinogen (peptidase)
  3. Mucus (protection to the gastric mucosa)
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11
Q

Small intestine

  1. How long?
  2. Main functions (2)
  3. Division (3)
  4. Purpose
A
  1. 4-5m long
    • Digest: complete enzymatic digestion from the stomach
    • Absorb: major site for absorption of most drugs and nutrients
    • Duodenum (200-300mm)
    • Jejunum (2m)
    • Ileum (3m)
  4. Main site of absorption for most drugs and nutrients
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12
Q

How is the surface area of the small intestine increased?

A
  1. Folds of Kerchring
  2. Villi- approx 0.5-1.5mm long by 0.1mm diameter
  3. Microvilli - 600-1000 each villus
    - Provide largest increase in surface area
    - Covered by fibrous substance (glycocalyx)
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13
Q

What is in the structure of a villus in the small intestine?

A 
Outer
- Microvilli
- Fats and partially digested fats
- Basement membrane
- Capillaries
- Lymph vessel
Inner
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14
Q

What is the transit time of the small intestine?

A
  1. 5-4.5 hours in healthy volunteers

- presence of fat does delay but only modest (30-60 minutes)

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15
Q

Colon

  1. How long is it?
  2. How is the surface area increased?
  3. Main functions (3)
A
  1. 1.5m
  2. Irregularly folded mucosae: increase 10-15 times that of a simple sylinder (1/30th of small intestine)
    • Absorption: Na+, Cl-, water
    • Exchange: bicarbonate and K+
    • Storage and compaction of faeces
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16
Q

What is the colon colonised by?

A

A variety of bacteria

17
Q

What is the pH of the Caecum?

A

6-6.5, increases to 7-7.5

18
Q

What is the transit time of the colon?

A 
24 hours (about) 
- proteolytic activity very low compared to that of the small intestine
(time controlled release formulation, pH dependent release dosage forms)
19
Q

Mechansims of Drug Absorption

2

A

Transcellular

  • accross cells
  • passive diffusion
  • carrier mediated :active transport, facilitated diffusion
  • Endocytosis

Paracellular
- between cells

20
Q

Passive diffusion (driving force, eg)

A
  1. Concentration difference and proceed from high to low concentration
  2. Small lipophillic mechanisms, many drugs
21
Q

Active Transport

A
  1. Require energy as driving force and proceed from low concentration to high concentration
  2. May become saturated
  3. May be competition for same transport system by similar substance
22
Q

Facilitated diffusion

A
  1. Still requires concentration gradient as driving force as in passive diffustion
  2. Faster rate than anticipated
  3. Saturable and subject to inhibition
  4. Very minor route for drug absorption
23
Q

Endocytosis

A
  1. Primary mechanism to absorb macromolecules

Eg. Vaccine (polio) absorption

24
Q

Paracellular drug absorption

A
  1. Via aq pours between cells
  2. Small intestine relatively leaky
  3. Important for transport of sugars, ions, amino acids, and peptides at concentrations above capacity of their carriers
  4. Route for small hydrophilic and charged drugs
25
Q

Efflux of drugs from intestine

A
  1. Efflux proteins expel specific drugs back into GIT

2. Key counter transport proteins = P-glycoprotein

26
Q

What are some barriers to drug absorption in the lumen?

A
  1. Chemical degradation
  2. Enzymatic degradation
  3. Complexation
  4. Absorption
27
Q

What are some barriers to drug absorption in the unfiltered water layer?

A
  1. Complexion to mucous

2. Water and mucous diffusion

28
Q

Gastro intestinal membrane barriers

A
  1. Transcellular transport
  2. Paracellular transport
  3. Efflux

Pharm 202 (2 decks)

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