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PHAR 124* > MRDFs > Flashcards

MRDFs Flashcards

1
Q

What is the meaning of the acronym MTC?

A

Maximum therapeutic concentration

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2
Q

What is the meaning of the acronym MEC?

A

Minimum effective concentration

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3
Q

What is the therapeutic window?

A

This is the range of drug concentration in the body that is within the MTC (maximum therapeutic concentration) to the MEC (minimum effective concentration)

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4
Q

What is the duration of action?

A

This is the time spent when drug concentration is above MEC (minimum effective concentration)

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5
Q

What are some challenges associated with conventional release?

A

Do not maintain blood concentration within therapeutic window for an extended period of time

AND

Controlled drug release is not possible

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6
Q

What is the rational for MRDFs?

A

To prolong or control drug availability or release with the intent of improving efficacy of drug therapy

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7
Q

What are the different types of MRDFs?

A

Sustained release (SR)
TImed release (TR)
Time Delay (TD)
Prolonged action (PA)
Controlled release (CR)
Repeat action
Extended release (ER)
Long acting (LA)
Targeted release

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8
Q

Describe extended release systems

A

Allow reduction in dosing frequency from that necessitates by a conventional dosage form

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9
Q

Describe delayed-release systems

A

They release the drugs at a time other than promptly after administration. They delay may be influenced by pH (like enteric formulations)

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10
Q

What is targeted release (TR)?

A

This formulation effectively isolates or concentrates drugs in a specific body region, tissue, or organ (tumour therapy may employ this formulation)

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11
Q

What is repeat action in terms of drug release systems?

A

They usually contain two or more single doses of the drug, one for immediate release and the second for delayed release

Ex. Concerta

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12
Q

What are some examples of a delayed action formulation?

A

Enteric coated

Rheumatoid arthritis

Morning sickness (releases during sleep so it is effective in the morning)

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13
Q

What is the rationale for extended release formulations?

A

These formulations provide an immediate release of drug (“loading dose-ish” brings drug concentration above MEC), and it is followed by gradual and continual release of additional amounts of drug to maintain its effect over a period of time

This effectively reduces the frequency of dosing

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14
Q

What is the difference between controlled and extended release?

A

Controlled release: constant rate of release

Extended release: variable rate of release (faster at start, gradual over time)

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15
Q

What is the difference between sustained release and extended release?

A

It is the duration of action

Extended release is usually a higher dose, but remains effective for a longer period of time vs. the sustained release formulation

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16
Q

What are some advantages of MRDFs?

A

Less fluctuation in drug levels

Reduced dosing frequency

Enhanced patient adherance

Reduction in adverse side effects

Potential reduction in indirect health care costs due to the above advantages

17
Q

What are some limitations of MRDFs?

A

Initial cost is high

Immediate termination of drug action is not possible

Contain higher amount of active ingredient (abuse potential)

Higher probability for drug-excipient interaction

More complex formulation design

Not suitable when rapid action is required

Not flexible (cannot split)

18
Q

What are some variables that are considered in the design of MRDFs?

A

All of the following variables are interrelated:

Route of delivery

Type of delivery system

Disease being treated

The patient (age, sex, individual variation)

Length of therapy

Properties of the drug (physiochemical, biological)

19
Q

What is the desired water solubility in MRDFs?

A

We need to use drugs with intermediate water solubility

If low solubility, takes too long to dissolve and have hard time diffusing through polymer shell

If high solubility = hard to reduce dissolution rate

20
Q

What is the significance of partition coefficient in MRDFs?

A

It is the potential of drugs to cross biological membrane (ratio of drug in lipid vs. aqueous phase)

This property affects the ability of the drug to diffuse through the polymers used in the design of MRDFs

21
Q

What is stability requirements for MRDFs?

A

The drug needs to remain stable in the dosage form while OUTSIDE the body

The drug also needs to be stale in the dosage form INSIDE the body (penetrating fluids should not degrade the drug)

22
Q

What pharmacokinetic properties are preferred in MRDFs?

A

Intermediate ADME is preferred

Slow kinetics (do not need to formulate into MRDFs)

Fast kinetics (very short half-life, need large amounts of drug to design MRDFs bc by extending duration of action, that is more time for the unreleased drug to be subject to ADME)

23
Q

Are drugs that bind to plasma proteins good candidates for formulation into MRDFs?

A

No, only free unbound drug can diffuse through tissues and hence can be controlled

24
Q

Are drugs with wide therapeutic indexes ideal fro formulation into MRDFs?

A

Yes, there is not a concern about accidental immediate release

Avoid using drugs that have narrow therapeutic indices

25
Q

Are oral MRDF doses smaller or bigger compared to conventional release oral formulations?

A

They are bigger because MRDFs must store more drug in a larger tablet or capsule.

A larger tablet/capsule may increase difficulty of swallowing = reduced patient compliance

26
Q

What is the principle of dissolution systems in MRDFs?

A

Controlled release products are prepared by controlling the dissolution rate of drugs that are readily soluble

27
Q

What are the two types of dissolution systems in MRDFs?

A

Membrane dissolution systems

Matrix dissolution systems

28
Q

Describe Membrane Dissolution Systems

A

Type 1:
Different groups of particles with different membrane thickness and composition are made and contained in a tablet/capsule

Type 2:
A layer of drug is coated on a sugar core and then coated with slowly dissolving membrane (alternating membrane and drug, like Matryoshka doll). The outer-most layer is a layer of drug that can be immediately releases as the loading dose

Due to these difference, each granule will release drug at different rates or times

29
Q

Describe Matrix Dissolution Systems

A

Drug is disperse in a series of different sized granules (no discernible core) made of the matrix material

These matrix granules often are combines with granules with no matrix material (effectively providing a loading dose)

30
Q

What is the principle behind diffusion systems?

A

Release rate of drug is determined by its diffusion through a water-insoluble polymer

31
Q

What are the two types of diffusion systems?

A
  1. Membrane Diffusin (Reservoir devices): core is surrounded by a polymeric membrane
  2. Matrix Diffusion (Matrix device): drug is distributed uniformly in an inert polymeric matrix
32
Q

What are matrix diffusion devices?

A

The drug is dispersed homogeneously in the matrix which DOES NOT dissolve or erode (unlike dissolution systems)

The drug diffuses from the matrix to outside

33
Q

How do osmotic systems control the release rate of drug?

A

Osmotic pressure is used to swell a membrane, causing it to push drug through an orifice. The rate at which the membrane expands and the size of the orifice can impact drug release rate

34
Q

Can immediate release and MRDFs formulations of the same drug be used interchangeably?

A

No, patients stabilized on a MRDF should not be changes to an immediate release product without consideration of any existing blood level concentrations of the drug

35
Q

Can MRDFs be crushed to chewed for easier swallowing?

A

No, this will compromise the unique drug release features

36
Q

Are empty shells in stool while on MRDFs an issue?

A

No, they are usually non-erodible and it is common to see them in the stool

37
Q

What is the only situation where pharmacists can switch a patient from one MRDF to another MRDF of the same drug?

A

When the prescribed MRDF is unavailable, we may use another MRDF as a temporary substitute

Use the MRDF substitute that can give the most similar dose vs. time curve

PHAR 124* (12 decks)

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