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Pharmaceutics 2 Winter Final > 6 - Rectal > Flashcards

6 - Rectal Flashcards

1
Q

Rectal formulation should display….

A
  • Rapid absorption
  • Consistent interpatient bioavailability
  • Prolonged maintenance of effective concentrations
  • Minimal side effects
  • Ease of dose preparation and administration
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2
Q

When should rectal administration be considered?

A
  • Px is vomiting or convulsing

- Oral intake is restricted (ex: post-surgery)

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3
Q

How long is the rectum?

A

12-20 cm

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4
Q

What is the surface area of the rectum?

A

200-400 cm^2

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5
Q

Does the rectum contain fluid?

A

Small amount (3-5 mL) spread as a thin film

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6
Q

How long is the anal canal?

A

About 4 cm

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7
Q

What happens to drugs applied to the anal canal?

A

Only act locally; not absorbed systemically

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8
Q

What are the sections of the anal canal?

A
  • Upper 2/3 – mucosa lined by simple columnar epithelium; supplied by superior rectal artery
  • Lower 1/2 – ends are joined together by anal valves; lined by stratified squamous epithelium; relatively impermeable to drugs; supplied by inferior rectal artery
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9
Q

What is the superior rectal artery a branch of?

A

Inferior mesenteric artery

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10
Q

What is the inferior rectal artery a branch of?

A

Internal pudendal artery

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11
Q

Rectal route bypasses around ____ of first-pass metabolism. Why?

A
  • 2/3

- Rectum’s venous drainage is 2/3 systemic (middle and inferior rectal vein) and 1/3 hepatic (superior rectal vein)

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12
Q

How are drugs absorbed in the rectum?

A

Paracellular, transcellular, and transport-assisted

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13
Q

What does absorption in the rectum depend on?

A
  • Lipophilicity
  • Molecular weight
  • Water solubility
  • Degree of ionization
  • Formulation
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14
Q

Is there a wide bioavailability range for the rectal route?

A

Yes

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15
Q

What is the pH of the rectum?

A
  • 7.2 for adults

- 9.6 for children

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16
Q

Does the rectum have good buffer capacity?

A

No

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17
Q

What is the difference in absorption for enemas and suppositories?

A
  • Enemas show prompt absorption
  • Suppositories show slower absorption, and depend on nature of drug used, physicochemical nature of drug, and presence of additives or excipients
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18
Q

What are disadvantages to the rectal route?

A
  • Variability of absorption
  • Absorption problems in px w/ diarrhea or rectal disease
  • Social-cultural reluctance to use rectal dose forms
  • Some drugs may cause mucosal irritation
19
Q

What are the possible dose forms for the rectum? Which is most common?

A
  • Suppository (most common)
  • Solutions
  • Suspensions
  • Gels
  • Ointments
  • Foams
  • Creams
20
Q

How is drug released from a suppository?

A

Base will melt at body temp or dissolve in rectal fluid and release drug

21
Q

What is the normal weight of suppositories?

A
  • 2g for adults

- 1g for children

22
Q

Are suppositories used for local effect or systemic delivery?

A

May be used for both

23
Q

What determines the selection of a base for a suppository?

A
  • Physicochemical nature of drug

- Desired pattern of drug release

24
Q

What properties of a base are required for a suppository?

A

Should be solid at room temp and either melt at body temp or dissolve

25
Q

What are the 2 general types of suppository bases?

A
  • Oleaginous or fatty

- Water soluble or water miscible

26
Q

What are typically used as fatty bases for suppositories?

A

Cocoa butter or theobroma oil (composed of saturated and unsaturated fatty acids, but can form polymorphs which are liquid at room temp)

27
Q

What are some excipients commonly used in oleaginous suppository bases?

A
  • Surfactants (ex: glyceryl monostearate)

- Suspending agents (ex: colloidal silica)

28
Q

How are different types of drugs released from oleaginous bases?

A
  • Lipophilic and unionized drugs released slowly

- Water soluble and hydrophilic drugs released quickly

29
Q

Do oleaginous suppository bases cause irritation?

A

No, they have emollient properties so are soothing

30
Q

Why is cocoa butter a good base to use for a suppository that is intended for local effect?

A

Soothing and keeps drug in the area it is applied

31
Q

What are examples of water soluble or miscible suppository bases?

A

PEG (polyethylene glycol) and glycerinated gelatin

32
Q

Do water soluble/miscible suppository bases release drug slow or fast?

A

Slow

33
Q

Molecules w/ higher ______ tend to be harder and slower to dissolve

A

Melting point

34
Q

What is important to note about suppositories w/ a PEG base?

A

PEG is hygroscopic, so must dip in water prior to insertion to avoid stinging w/ moisture being absorbed from tissues

35
Q

Are glycerinated gelatin bases common? Why or why not?

A

No b/c release drugs very slowly

36
Q

Release of drug and onset of action are functions of:

A
  • Liquefication of suppository base
  • Dissolution of active components
  • Passage of drug through mucosal layers
37
Q

How are different types of drugs released from water soluble suppository bases?

A
  • Lipophilic drugs released at moderate rate
  • Hydrophilic drugs released more rapidly
  • *Release rate depends on water solubility
38
Q

What is in a diazepam suppository? What is the benefit to each ingredient? What is the tmax?

A
  • Propylene glycol and ethanol so drug is in solution and absorption is good
  • Peak levels achieved in about 90 mins
39
Q

What can rectal enemas contain?

A
  • Preservatives
  • Cosolvents
  • Buffers
  • Viscosity increasing agents
40
Q

Do enemas or suppositories spread over larger areas?

A

Enemas

41
Q

What is the propellant used for aerosol rectal dose forms?

A

Propane

42
Q

What is a benefit to rectal foams over enemas?

A

Foams tend to cover mucosa more evenly w/ better adhesion

43
Q

What is an advantage to rectal ointments/creams? Which drugs are used in the dose form?

A
  • Little systemic absorption

- Corticosteroids, anti-pruritics, local anesthetics

Pharmaceutics 2 Winter Final (9 decks)

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