Biomedical Engineering Reference
In-Depth Information
Table 2.2
Formulations for drug delivery to the cardiovascular system
Sustained release preparations
Controlled release preparations
Preparations for targeted delivery
Special preparations
Proteins and peptides
Microparticles and nanoparticles
Liposomes
Cell and gene therapies
Sustained and Controlled Release
These two formulations are used often in cardiology and will be defined. Sustained
release (SR) preparations are not new but several new modifications are being
introduced. They are also referred to as “long acting” or “delayed release” as com-
pared to “rapid” or “conventional” release preparations. The term sometimes over-
laps with “controlled release,” which implies more sophisticated control of release
and not just confined to the time dimension. Controlled release implies consistency
but release of drug in SR preparations may not be consistent. The rationale of
developing SR is:
•
To extend the duration of action of the drug
•
To reduce the frequency of dosing
•
To minimize the fluctuations in plasma level
•
Improved drug utilization
•
Less adverse effects
Limitations of SR products are:
•
Increase of drug cost
•
Variation in the drug level profile with food intake and from one subject to
another
The optimal release form is not always defined and multiplicity of SR forms
•
may confuse the physician as well as the patient
SR is achieved by either chemical modification of the drug or modifying the
delivery system, for example, use of a special coating to delay diffusion of the drug
from the system. Chemical modification of drugs may alter such properties as dis-
tribution, pharmacokinetics, solubility, or antigenicity. One example of this is
attachment of polymers to the drugs to lengthen their lifetime by preventing cells
and enzymes from attacking the drug.
Controlled release implies regulation of the delivery of a drug usually by a
device. The control is aimed at delivering the drug at a specific rate for a definite
period of time independent of the local environments. The periods of delivery are
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