MUCOSAL DELIVERY Mucoadhesion
is the process by which a drug delivery device is designed to stick to a
part of the gut or other mucosae (buccal cavity, nasal, rectal and
vaginal), thus delivering drug to a precise site in the body for an
extended period. This gives more effective treatment of some
diseases and can also protect drugs from some of the harsh conditions in
the body. Mucoadhesive drug delivery systems are used to treat several
conditions in the mouth and have been investigated as treatments for
stomach ulcers and cancer. The majority of infections affecting man and
animals take place or start in mucous membranes. The ability to retain
pharmacologically-active agents for extended periods of time on any
mucosal epithelium, including those of the nose, mouth, rectum or vagina
confers several potential therapeutic advantages.
TRANSDERMAL DELIVERY Transdermal
drug delivery as a route for systemic drug administration is currently
one of the advancing areas in drug development research.
This
is particularly true for the delivery of such drugs as opiate
painkillers, birth control, nitroglycerin for the prophylaxis of angina,
nicotine for smoking cessation therapy, testosterone for the correction
of male hypogonadism.
The skin route for systemic drug delivery is
especially attractive to formulators, as this integument is the most
readily accessible organ of the body. Clinicians are increasingly
recognising the advantages of controlled continuous intravenous infusion
of drugs, such as the avoidance of hepatic metabolism and the
maintenance of a constant therapeutic level in the body, that can be
obtained by the use of the skin as a portal of drug delivery, without
the risks and costs of intravenous therapy.
Developments
in transdermal, dermal and mucoadhesive drug delivery methods are
paving the way to the future of systemic drug administration.
As
skin is both the largest and most accessible organ in a human body,
pharmaceutical manufacturers are keen to take advantage of it as a drug
delivery platform. The transdermal route helps to reduce the risks and costs of intravenous therapy that can be both traumatic and intrusive. Transdermal
controlled release (CR) systems usually combine a therapeutic component
with an adhesive formulation that ensures a continuous delivery of the
active ingredient through unbroken skin at a constant absorption rate.
Skin adhesion and drug compatibility determine the efficacy of
transdermal applications.
Although
administration via the peroral route is the most commonly targeted goal
of new drug and dosage form research and development, oral
administration is not always feasible or desirable.
The
potential for oral dosage form development is severely limited for
active agents that are poorly absorbed in the upper gastrointestinal
(GI) tract and unstable to proteolytic enzymes. Some agents cause local
stomach or upper GI irritation or require doses in excess of 500mg.
Additionally, treatment of some diseases is best achieved by direct
administration near the affected area, particularly with diseases
involving anorectal tissues. Although oral administration can be used
for drugs targeted for some of these diseased tissues, exposure of the
entire body compartment to the administered drug is inefficient and can
lead to undesired adverse effects.
VAGINAL DELIVERY The vaginal route of administration offers a promising option for local and systemic delivery of drugs.
Suppositories,
creams, gels and tablets are commonly used vaginal drug delivery
systems. These conventional vaginal formulations, however, are
associated with limitations of poor retention, leakage, and messiness,
thereby causing inconvenience to users.
To overcome these limitations,
formulations that adhere to the vaginal mucosa for a sufficient period
of time need to be developed. Bioadhesion and retention are desirable
characteristics of a vaginal formulation to achieve desired efficacy.
These properties can be built in during formulation development by the
use of bioadhesive polymers and tested by similar methods to those
already discussed for bioadhesion. The limitations have also
necessitated the development of other novel drug delivery systems.
OCULAR DELIVERY Treatment
of some diseases is best achieved by direct administration near the
affected area, particularly with diseases involving ophthalmic, optic,
dermal, oral cavity, and anorectal tissues.
Ocular drug
delivery is an interesting and challenging opportunity for
pharmaceutical development. The eye is protected by a series of complex
defense mechanisms, which usually result in poor bioavailability of
drugs administered via the ocular route. These include tear production
and the blinking reflex in addition to short residence time and reduced
drug permeability.
Developments in injectable depots and implants are driven by a desire to decrease the necessity for frequent medication.
Incorporating
polymer technology for slow, long-term release, this route is best
utilised for the treatment of chronic conditions, such as heart disease
and pain management. Hip or knee cap replacements are susceptible to
infection following surgery.
A preventative approach could be
for the doctor to leave behind an implant that could deliver an
anti-infective agent and disintegrate with time. These devices give
localised, high-concentration delivery, and by tuning the ratio of drug
load to polymer the required release rate can be optimised, over two
days or two months.
Pulmonary delivery has been used for years to treat respiratory diseases by delivering drugs locally to the lung. However, the latest advances are seeing drugs being delivered via this route for systemic circulation. The delivery of drugs to the bloodstream via the lungs is an attractive hypothesis, offering a non-invasive and rapid-onset alternative to injections. Inhalation Drug Delivery via Metered-dose Inhalers
Aerosol route of administration targets drugs directly to the lungs and offers advantages of bypassing the first pass elimination, reducing the dosage frequency and minimising the extent of adverse drug reactions.
