750D9 Part 3

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Modified release dosage forms Introduction

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Have some special type of release not offered by conventional release dosage forms

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Delayed release

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Delayed release: releases drug at time other than promptly after the administration

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Extended release

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Extended release: allows at least a two-fold reduction in dosing frequency

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Prolonged release

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Prolonged release: release drug for absorption over a longer period of time

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Sustained release

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Sustained release: gradual release over an extended period

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Repeat action

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Contain two single doses of medication, one for immediate release and the second for delayed release

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Targeted release

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Directed toward isolating or concentrating a drug in a body region, tissue, or site for absorption or for drug action

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Controlled Release

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Designed to release drug in a controlled manner, at a predetermined rate, duration & location to achieve and maintain optimum therapeutic levels of drug.

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Temporal Controlled Release

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Control over rate of drug release

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Spatial Controlled Release

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Control overlocation (space) of drug release

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Advantages for Modified release dosage forms

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1 Reduced dosing frequency
2 Reduction in blood level fluctuations
3 Reduction in overall side effects
4 Reduction in overall healthcare casts
5 More patient compliance

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Disadvantages for Modified release dosage forms

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1 High cost
2 GI transit time is limited
3 Possible dose dumping
4 Reduced potential for dose change or withdrawal in the event of toxicity, allergy, or poisoning

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Types of Controlled Release Systems

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1 Dissolution controlled systems
2 Diffusion controlled systems
A. Monolithic (matrix) systems
B. Reservoir systems
3 Ion-exchange resin systems
4 Osmotically controlled systems
5 Environmentally controlled systems

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Dissolution Controlled - Reservoir System 1

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1 Employing drug dissolution as the rate controlling step in drug release
2 Decrease in dissolution rate leads to a decrease in drug release
3 Drugs with poor aqueous solubility such as mefenamic acid & digoxin can act as natural controlled release products

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Dissolution Controlled - Reservoir System 2

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1 Release rate of drug is dependent on its diffusion through an inert membrane barrier, usually a water-insoluble polymer
2 Two types
A. Monolithic (matrix)
B. Reservoir

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Monolithic (Matrix) system (Dissolution Controlled)

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1 Drug dispersed homogeneously throughout an inert polymer matrix
2 Drug in the outer layer exposed to aqueous solution dissolved and diffuses out of the matrix
3 This process continues with the interface between the aqueous solution and the solid drug moving toward the interior
e.g. Oxycontin®

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Advantages of Reservoir System

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1 Easier to produce than reservoir devices
2 Can deliver high molecular-weight compounds

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Disadvantages of Reservoir System

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1 Cannot obtain zero-order release
2 Removal of remaining matrix is necessary for implanted systems

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Reservoir System

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1 Characterized by a core of drug, the reservoir surrounded by a polymeric membrane
2 Nature & thickness of the membrane determines the rate of release of the drug from the system
e.g. Wellbutrin XL®

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Ion-exchange Systems

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1 Ionic drugs bind to the oppositely charged functional groups of resins to form complexes
2 Drug release from this complex is by ion-exchange
e.g. Tussionex® pennkinetic®

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Advantages for Ion-exchange Systems

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1 High drug loading
2 pH independent (i.e., sulfonated resin)

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Disadvantages for Ion-exchange Systems

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Severe tailing later stage of release

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Osmotically Controlled Systems

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1 These are special type of reservoir systems into which osmotically active agents are incorporated
2 These osmotic agents act to absorb water from the surrounding medium through the semi-permeable membrane
3 Utilize osmotic pressure as the driving force to release drug at a constant rate
OROS® system and OROS®Push-PullTM system

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Advantages for Osmotically Controlled Systems

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1 Release of drug is independent of environment of the system
2 Zero order release is obtainable

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Disadvantages for Osmotically Controlled Systems

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1 Systems can be very expensive
2 Quality control is more extensive

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Environmentally Controlled Systems

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1 The polymers can swell or shrink depending upon the change in environment surrounding the delivery system
2 The environmental change can involve pH, temperature, or ionic strength

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(Patient Considerations) Patient must be:

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1 Instructed not to use drug interchangeably or concomitantly with immediate release forms of the same drug
2 Informed that modified release capsules or tablets should not be crushed or chewed
3 Advised if an empty shell or ghost will remain intact throughout the GIT and may appear in the feces
4 Patients stabilized on a modified-release product should not be changed without considering existing blood level concentrations of the drug