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Pharmacy Year 2 Semester 2 > Modified release lecture 1/2 > Flashcards

Modified release lecture 1/2 Flashcards

1
Q

What are the potential limitations of giving repetitive conventional peroral dosage forms?

A

1) concentration of drug in plasma fluctuates over successive dosing interviews, even when “steady state” condition is achieved
2) For drugs with short biological half lives, frequent doses are required to maintain ‘steady-state’ concentrations. Maintenance of therapeutic concentration is susceptible to forgotten doses and overnight no-dose period

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2
Q

Define modified release dosage form

A

Those whose drug release characteristics of time course and/or location are chosen to accomplish therapeutic or convenience objectives not offered by conventional forms

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3
Q

Describe features of the ideal dosage regimen

A

provides and then maintains an acceptable therapeutic concentration of drug at the site(s) of action “immediately”

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4
Q

Give 5 Advantages for modified release

A

1) Peaks and troughs minimised - steady state therapeutic levels to better manage disease
2) Improved compliance - less frequency doses
3) Better safety margin - lower side effects
4) efficient use of drug (lower overall amount used)
5) Reduction in healthcare costs - shorter treatment time, less monitoring and dispensing

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5
Q

Main disadvantages of modified release

A
  • risk of dose dumping and instability of drug

- more costly manufacturing process

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6
Q

Define delayed release

A

Drug is not released immediately following administration but at a ,later time
e.g. enteric coated tablets

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7
Q

Define repeat action

A

an individual dose is released soon after administration. 2nd or 3rd doses are released at later intervals

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8
Q

Prolonged release

A

The drug is absorbed over a longer period of time than from a conventional dosage form. Implication is that onset is delayed because of a slower release rate from the dosage form

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9
Q

define sustained action

A

an initial release of drug sufficient to provide a therapeutic dose soon after administration. Then a gradual release over an extended period

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10
Q

define extended release

A

release drug slowly
Plasma concentrations are maintained for a prolonged period of time
(usually 8-12 hours)

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11
Q

define controlled release

A

Release drug at a constant rate and provide plasma concentrations that remain invariant with time

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12
Q

Are prolonged release and sustained release the same as extended release? What should you not confuse them which?

A

Don’t confuse with delayed release

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13
Q

How can a repeat-action tablet be distinguished from sustained-release?

A
  • repeat action does not release the drug in a slow, controlled manner.
  • repeat-action tablets usually contain 2 doses of a drug. The first is released immediately after administration. The second dose is delayed, often by an enteric coat
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14
Q

What are modified release products designed to do?

A

either:
-remaining constant within the therapeutic range of the drug for a prolonged period of time
OR
-declining at such a slow rate that the plasma concentration remains within the therapeutic range for a prolonged period of time

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15
Q

Name 5 attributes that would make a drug suitable for modified release

A
  • biological half life of 2-8 hours
  • high therapeutic window
  • LogP=~2.2-3.3
  • uniformly absorbed and too unstable throughout the GIT
  • moderate potency (require small doses)

NB. physicochemical properties of drug and biological factors are additional considerations to be made

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16
Q

If a drug has
Low solubility and high permeability
which BCS class is it?

A

Class II (2)

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17
Q

If a drug has high solubility and high permeability which BCS class is it?

A

Class I (1)

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18
Q

If a drug has both low solubility and low permeability which BCS class is it in?

A

Class IV (4)

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19
Q

If a drug has high solubility and low permeability which BCS class is it in?

A

Class III (3)

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20
Q

Why is difficult to achieve ideal drug release in mass balance to achieve constant plasma levels? I.e. what factors make this difficult?

A
  • variable physiological conditions of the GIT
  • clearance rate can be patient dependent (age, race etc)
  • Disease status
  • Food/diet intake
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21
Q

How fast/slow do solutions and pellets (<2mm) leave the stomach?

A

They leave it rapidly

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22
Q

How long do single dose units stay in the stomach for after the delivery system is taken with a heavy meal?

A

Single dose units (.7mm) can stay in the stomach for up to 10 hours if the delivery system is taken with a heavy meal

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23
Q

What is the transit time through the small intestine?

A

approx 3 hours

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24
Q

Give 4 examples of single-unit dosage forms

A
  • tablets
  • coated tablets
  • matrix tablets
  • some capsules
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25
Q

Give 4 example of multiple-unit dosage forms

A
  • granules
  • beads
  • capsules
  • microcapsules
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26
Q

Give 5 examples of modified-release dosage forms

A
  • inert soluble matrices
  • hydrophilic matrices
  • ion-exchange resins
  • osmotically-controlled formulations
  • reservoir systems
27
Q

Name 3 main classes of oral modified release delivery systems

A
  • monolithic or matrix systems
  • reservoir or membrane-controlled systems
  • osmotic pump systems
28
Q

What are the 2 main mechanisms controlling drug release?

A
  • dissolution of the active drug component

- diffusion of dissolved or solubilized specieis

29
Q

Within the context of the 2 main mechanisms controlling drug release, what are the 4 processes within these?

A
  • hydrating of the system (swelling of the hydrocolloid or dissolution of the channeling agent)
  • diffusion of water into the system
  • dissolution of the drug
  • diffusion of the dissolved (or solubilised) drug out of the system
30
Q

What formulation techniques are used to build the barrier into the peroral dosage form? Name 5

A
  • the use of coatings
  • embedding of the drug in a wax or plastic matrix
  • microencapsulation
  • chemical binding to ion-exchange resin
  • incorporation in an osmotic pump
31
Q

What the the components of a oral MR release system? Name 7

A
  • active drug
  • release control agent(s)
  • filler
  • matrix or membrane modifier
  • solubilizer, pH modifier
  • lubricant and flow aid
  • supplementary coatings
32
Q

Does a matrix system usually give zero order release?

A

No

33
Q

How do wax matrix systems work?

A

1) the drug is contained in a hydrophobic matrix which remains intact during release of the drug
2) In contact with aqueous media, the channeling agent dissolves and leaches out of the compact leaving a porous matrix of tortuous capillaries
3) the drug dissolves out of the system via the capillaries made

34
Q

In a wax matrix system, what is the rate of release governed by?

A

Both:

-the dissolution and diffusion of the channeling agent and the drug

35
Q

Name some matrix-forming agents for Wax matrices

A
  • hydrogenated vegetable oil type 1
  • Carnauba wax
  • Microcrystalline waxes
  • Stearic acid
  • Beeswax
36
Q

Describe a channeling agent for a wax matrix delivery system

A
  • almost any water-soluble pharmaceutically acceptable SOLID material
  • in some cases the drug may act as its own channeling agent
37
Q

In a wax matrix delivery system, how much of the system does the channeling agent usually comprise?

A

20-30%

38
Q

examples of channeling agents for wax matrix delivery systems

A
  • salts (e.g. NaCl)
  • sugars
  • plyols
39
Q

How do hydrophilic matrix delivery systems function?

A
  • hydrophillic colloids swell in contact with water to form a hydrated matrix
  • the outer hydrated matrix layer will erode as it becomes more dilute; the rate of erosion will depend on the nature of the colloid
40
Q

For hydrophilic matrix delivery systems, what does the system comprise?

A
  • mixture of drug
  • hydrophillic glidant
  • release modifiers
  • lubricant/glidant
41
Q

In hydrophilic matrix delivery systems

1) What controls the further diffusion of water into the matrix?
2) What controls the rate of release of the drug?

A

1) the hydrated matrix layer

2) diffusion of drug through the hydrated matrix layer

42
Q

What 2 main components are the reservoir system made up of?

A
  • the drug in a core completely enclosed by membrane

- rate controlling membrane

43
Q

In a reservoir system what is in the core component?

A
  • active drug
  • filler or substrate
  • solubilizer
  • lubricant/glidant
44
Q

In a reservoir system what is in the coating?

A
  • membrane polymer
  • plasticizer
  • membrane modifier
  • colour/opacifer
45
Q

What dosage forms are reservoir systems usually in for oral use?

A

Pellets or multiple units

46
Q

In reservoir systems

1) what is the requirement of the release controlling membrane polymer?
2) Name some typical polymers for this use

A

1) The requirement is that the polymer remain intact for the period of release i.e. no swelling with subsequent erosion as in hydrophilic matrices
2) Ethyl cellulose, acrylic polymers e.g. Eudragitt RL and RS grades, Shellac, Zein

47
Q

How do membrane controlled delivery systems work?

A
  • the rate controlling part of the system is a membrane through which the drug must diffuse.
  • to allow the drug to diffuse out, the membrane has to be permeable, e.g. through hydration of water normally present in the GIT or by the drug being soluble in a membrane component such as the plasticizer
  • unlike a hydrophilic matrix, the membrane polymer DOES NOT swell on hydration to form a hydrocolloid matrix and does not erode
48
Q

What kind of dosage system is an osmotically-controlled system?
How do they generally work?

A

Single unit dosage systems

Osmotic pressure is used as the driving force of drug release

49
Q

Describe the OROS

A
  • elementary osmotic pump
  • simplest osmotically-controlled system
  • the pump is presented as a tablet dosage form and consists of a core of a drug, usually combined with an osmotically-active agent
  • It is coated with a rigid, non-swelling semi-permeable membrane e.g. cellulose acetate
  • the membrane permits the passage of GI fluid but not drug or electrolyte
50
Q

How does a drug get released from an OROS?

A

-an orifice is laser-drilled into the membrane and allows dissolved drug to be pumped out at a rate until the concentration of osmotically active salt in the system falls below saturation

51
Q

In OROS, describe the external surface of the system

A

May be coated the a bioerodible polymer to modify the rate of permeation of the GI fluid.

52
Q

In Osmotically-controlled delivery systems, describe how a movable partition would help

A

The core may be modified to include a movable partition which separates a compartment containing osmotically active agent from the drug reservoir

53
Q

Describe the mode of action of a osmotic pump delivery system

A

1) The drug is included in the tablet core which soluble, and which will solubiliize or suspend the drug in the presence of water
2) The core is coated with a semi-permeable membrane which allows water to pass through into the core which dissolves
3) As the core dissolves , a hydrostatic pressure builds up which forces (pumps) drug solution (or suspension) through the hole in the coating

54
Q

what is the rate of release governed by in an osmotic pump delivery system?

A

-the rate at which water is able to pass through the membrane and how fast drug solution (or suspension) can pass out

55
Q

What can 2 chamber osmotic pump delivery systems accommodate?

A

-accommodate less soluble molecules
and/or
-higher drug loading

56
Q

describe the general way the 2 chamber osmotic pump system works

A

In the GIT, water is imbibed through the semi-permeable membrane into both layers as a result of osmosis.
-when water is drawn in, the push layer expands and forces the drug out from the drug layer

57
Q

Describe an osmotic pump concept whereby there is no delivery orifice and how it works
What does the time before drug release depend on?

A

The build up of hydraullic pressure as GI fluid is imbibed eventually causes the wall of the device to break, releasing the drug
Time before drug release depends on area and thickness of the membrane

58
Q

What has been found by incorporating a number of “osmotic bursting devices” into matrix formulation, whereby there is no delivery orifice?

A

it has been to show to provide a constant rate of drug release

59
Q

Advantages of an osmotic pump system

A

The diffusing species is water:

  • well characterised an understood
  • modification of the rate of water diffusion is more straight-forward than for many drugs
  • release mechanism is not dependent on drug
  • the coating technology is straightforward
  • suitable for a wide range of drugs
  • typically gives a zero order release profile after an initial lag.
60
Q

Drugs that require protection from degradation

A
  • PPIs (omeprazole, pantoprazole)

- Antibiotics (penicillin, erythromycin)

61
Q

drugs that irritate the stomach

A
  • NSAID e.g.:
  • acetylsalicylic acid (aspirin)
  • naproxen
62
Q

drugs designed to act locally in the intestine

A
  • anthelmintics e.g:
  • mebendazole
  • piperazine
63
Q

disadvantages to colon-specific drug delivery

A
  • If delivered to the colon, the drug is exposed to first-pass metabolism by the liver (hepatic portal vein)
  • microorganisms in colon may produce side-reactions that are not known about (microbiota metabolism of drug)
64
Q

For what types of drugs is the colon a less hostile environment than the stomach and small intestine?

A

Peptide and protein drugs

Pharmacy Year 2 Semester 2 (33 decks)

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