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gi tract - year one > rectal administration of drugs > Flashcards

rectal administration of drugs Flashcards

1
Q

where does blood flow in the superior rectal vein

A

to the liver

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2
Q

where does blood flow in the middle rectal vein and the inferior rectal vein

A

to the heart

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3
Q

why should you aim to keep dosage in the lower part of the rectum

A

because it avoids 1st pass metabolism

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4
Q

what is the structure of the rectum

A

its a hollow organ with a one cell layer thick epithelium

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5
Q

what does the rectum membrane contain

A

epithelial, cylindrical and goblet cells (secrete mucous)

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6
Q

is there villi in the rectum

A

no which means decreased surface area

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7
Q

what is the pH of the rectum

A

7-8

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8
Q

do the same principles of drug absorption apply to the rectum like they do the GI tract

A

yes BUT no active transport in the rectum, only diffusion

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9
Q

advantages of rectal drug administration

A
  • absorption not affected by food or gastric emptying
  • avoids pH changes in GI tract
  • avoids action of gastric juices on drug
  • avoids (partially) 1st pass metabolism
  • no problems with flavouring
  • can be used while vomiting
  • can be used in unconsciousness
  • can be used for specific patient population eg infants
  • quick systemic response
  • useful with upper GI disease
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10
Q

disadvantages of rectal drug administration

A
  • patient acceptability (cultural influence)
  • irritation of mucus membrane
  • small surface area
  • less fluid content than small intestine leading got dissolution problems and pain
  • drug degradation by rectal bacterial flora
  • bowel movements can interupt absorption
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11
Q

what are the rectal formulations

A
  • enema
  • foams
  • gels
  • creams
  • ointments
  • suppositories
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12
Q

where in the colon do enemas spread to

A

in a 30ml dose
- 99% in sigmoid colon

in a 100ml dose
66% sigmoid colon
25% descending colon

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13
Q

what is the vehicle on a suppository

A

the base

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14
Q

what are the characteristics of a suppository vehicle

A
  • fatty
  • water soluble, water-miscible vehicle
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15
Q

what are the requirements of a vehicle

A
  • melts, disperses or dissolves at 36 degrees
  • rapid solidification and narrow melting range
  • easily released from suppository mould
  • convenient to handle
  • non irritating, non toxic
  • physically and chemically stable
  • compatible with drug
  • have viscosity to prevent over sedimentation of drug but allows flow into mould and also over membranes during application
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16
Q

what is the characteristics of the fatty base of a suppository

A
  • made of theobroma oil (cocoa butter)
  • melting point 34.5 degrees
  • non-irritant
17
Q

what are the challenges with the traditional fatty base

A

polymorphism, theobroma oil exists in different crystal forms

  • a-crystal, melts 23 degrees
  • y-crystal, melts 19 degrees
  • B-crystal, melts 34.5 degrees
18
Q

what influences the form of the theobroma oil that is used

A
  • degree of heating (up to 36 degrees)
  • cooling process (slow)
19
Q

characteristics of the fatty bases used nowadays in suppository’s

A
  • natural, semi and fully synthetic fat mixtures
  • melting point can be titrated
20
Q

type A way to make gelatin

A

acid hydrolysis to gelatin cationic

21
Q

type B way to make gelatin

A

alkaline hydrolysis to make gelatin anionic

22
Q

how is gelatin made

A

purified from skin/bones from hydrolysis

two ways - type A and B

23
Q

what is the melting point of PEG (polyethylene glycol)

A

various melting points, approx 50 degrees

24
Q

why should you dip suppositories with PEG base before insertion

A

only 3ml of liquid/mucus present in rectum and more water sometimes needed

if not dipped can be osmotic pain

25
Q

how does PEG bases work

A

the base disperses in rectal fluid/mucus to release the drug

26
Q

which base would you choose for
LOW fat and HIGH water solubility

A

fatty base

27
Q

which base would you choose for:
HIGH fat and LOW water solubility

A

aqueous base

28
Q

which base would you choose for
LOW fat and LOW water solubility

A

indeterminate

29
Q

how are suppository moulds calibrated

A
  • they’re filled volumetrically as volume-weight relationship is base dependent
  • generate a number of perfectly formed suppositories containing only base
  • determine average weight per suppository
30
Q

does the drug have the same density to the base material

A

no

31
Q

what is the displacement of value of a drug

A

the number of parts by weight of drug which displaces 1 part by weight of the base

32
Q

what is the displacement value of the base dependent on

A

the drug

33
Q

equation for density

A

density=mass/volume

34
Q

does the density of the drug need to be the same as the base

A

yes, as the mould is calibrated by volume

gi tract - year one (25 decks)

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