Biomedical Engineering Reference
In-Depth Information
a combination of “patch” concept and a sophisticated miniaturized pump operated
by gas generation.
Depot Formulations and Implants
These are usually administered by injection and must ensure protein/peptide stabil-
ity. One of the formulations used is poly(lactide-co-glycide) sustained release.
Implants involve invasive administration and also must ensure protein/peptide sta-
bility. Implantable titanium systems provide drug release driven by osmotic pumps.
This technology has been extended to other proteins such as growth hormone.
Nutropin Depot (Genentech/Alkermes) is the first long-acting form of growth hor-
mone that encapsulates the drug in biodegradable microspheres that release the
hormone slowly after injection. It reduces the frequency of injection in children
with growth hormone deficiency from once daily to once a month.
Poly(Ethylene Glycol) Technology
Poly(ethylene glycol) or PEG, a water soluble polymer, is a well-recognized treat-
ment for constipation. When covalently linked to proteins, PEG alters their prop-
erties in ways that extend their potential uses. Chemical modification of proteins
and other bioactive molecules with PEG − a process referred to as PEGylation can
be used to tailor molecular properties to particular applications, eliminating dis-
advantageous properties or conferring new molecular functions. This approach
can be used to improve delivery of proteins and peptides. Advantages of PEG
technology are:
•
Increase of drug solubility
•
Increase of drug stability
•
Reduction of immunogenicity
•
Increase in circulation lifetime
•
Improvement of release profile
Enzyme deficiencies for which therapy with the native enzyme is inefficient
(due to rapid clearance and/or immunological reactions) can now be treated with
equivalent PEG-enzymes.
Microencapsulation for Protein Delivery
Microencapsulation of recombinant cells is a novel and potentially cost-effective
method of heterologous protein delivery. A “universal” cell line, genetically modi-
fied to secrete any desired protein, is immunologically protected from tissue rejec-
tion by enclosure in microcapsules. The microcapsule can then be implanted in
different recipients to deliver recombinant proteins in vivo.
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