Conventional forms of drug administration generally rely on pills, eye drops, ointments, and
intravenous solutions. Recently, a number of novel drug delivery approaches have been developed.
These approaches include drug modification by chemical means, drug entrapment in small vesicles
that are injected into the bloodstream, and drug entrapment within pumps or polymeric materials
that are p dace in desired bodily compartments (for example, the eye or beneath the skin). These
techniques have already led to delivery systems that improve human
health, and continued research may revolutionize the way many drugs are delivered.
A drug could be chemically modified to selectively alter properties like biodistribution,
pharmacokinetics, solubility, or anti-
genicity.Drugs are been also attached to soluble macromolecules like proteins,polysaccharides,or
synthetic polymers through degradable linkages.This process changes drug’s size and other
properties,resulting in variety of pharmacokinetics and biodistribution.
Many polymers ,like polyethylene glycol(peg),are attached to drugs to lengthen their lifetime or
change their immunogenicity.Drug’s longevity and immunogenicity might also be affected by
biological approaches,like proteins engineering and changing glycosylation patterns.
These are microparticulates/colloidal carriers composed of substances like
proteins.lipids,carbohydrates or synthetic polymers.Vesicles may be aimed either passively or
actively.In passive targeting natural uptake by cells that scavenge foreign microparticulates like
reticuloendothelial cells,which are are concentrated in tissues like liver or spleen,or circulating
monocytes.Active targeting involves placing recognition onto vesciles such that it is more
frequently taken up by certain cell types, than others.
This type of system delivers drug at a predetermined rate for a definite time period.Generally
release rates are independent of environmental conditions(pH,etc.).These can be selectively released
only in certain body part,like if we want it to dissolve in intestine but not in stomach,we can have
enteric coatings.
Advantages of this system:
i)delivery to specific part of body
ii)preserve drug till it is needed in body
iii)less follow up care
iv)enhanced comfort
v)improved compliance
Earlier proteins being large molecules(difficulty of diffusion) were not under controlled release
systems.A recent discovery of matrices of solid hydrophobic polymers having macro-molecues
enabled any size permeability for more than hundred days.Such examples are vinyl acetate
copolymer & lactic-glycolic acid coplymers.
Mechanism of release is through complex porous path in polymer matrix.These are used in insulin
nowadays,and also treatment of prostate cancer.
But still challenges exist like encapsulated protein remain in body for a long time.Which causes loss
of biological activity and effect immunogenicity.TRANSCENDERMAL CONTROLLED RELEASE SYSTEMS
In this system,delivery is through skin.Hence loss due to lever metabolism are reduced.Skin has
primarily keratin and lipids,and drugs to penetrate should have low molecular weight and soluble in
water and oil.The main obstacle in this process is to increase variety of drugs.Four methods are
Electrically(iontophoresis)-charged particles penetrate skin.
Ultrasound-removes lag times
Chemical modification-lipophilic drug
Penetration enhancers-azone,dimethly sulfoxide,dimethly formamide
The only degradable polymer used is lactic acid-glycolic acid co-polymers which causes bulk
degradation of interior.To prevent surface degradation drug degradation should be less than
surface.Efforts are being on to develop ideal polymer which is hydrophobic but should have water-
labile linkages connecting monomers.
Several different surface-eroding polyorthoester systems are synthesized.Here additives are inside
polymer matrix,because of which surface degrades at different rate than drug.
Sometimes it is necessary to increase drug level when needed.Here we use open-loop and closed-
loop.Open-loop has drug ans small magnetic beads in polymer matrix.Release rates are increased by
oscillating external magnetic field.
Research is done to find self-triggered release drugs like narcotic antagonists in multicomponent
systems having polymers,antibodies and enzymes.
This paper discusses effect of carrier on drug level,location,longevity and antigenicity.Research is
also done on novel anatomical delivery pathways such as nose or lungs.Also possibility to insert
gene into cells is also carried.Finally development in material science and chemical engineering
should improve substances to be effectively in drug delivery.