DRUG DELIVERY AND ADMINISTRATION

Prior to discussing basic pharmacology and pharmacokinetics, some exposure
to pharmaceutics is helpful. This area of pharmacy knowledge focuses on dosage
forms and routes of administration. Knowledge of pharmaceutics is required in order
to begin to understand how drugs work.
For a medication to be effective, it first needs to reach a target location in the
organism. Some type of delivery system is needed for this to occur. This requires
use of a specific route of administration. Routes of administration are more numerous
than people outside the medical professions would think. Thanks to technological
advances, both routes for drug administration and dosage forms (a term describing
the specific physical form of the drug’s active and inactive ingredients) exhibit more
variety today than ever before.
Three major routes are used for drug delivery: topical, enteral, and parenteral.
The topical route (cutaneous) can be used to apply a drug for its local activity at
the area of application. Antifungal medications, such as miconazole creams for
athlete’s foot, serve as examples. Drugs may also be applied topically (transcutaneous)
to a site from which they can be absorbed to exert a systemic effect. Nitroglycerin
ointment or patches, used to prevent angina pain, are examples of this route.
Vaginal creams and suppositories are examples of topical drugs used in contact with
mucous membranes rather than the epidermis. Topical drugs are also used for the
eye (ophthalmic), ear (otic), and nose (intranasal). Finally, certain topical drugs can
be delivered into the lung (inhalation) for both local and systemic effects.
The most common and convenient route for drug administration is via the gastrointestinal
tract. The oral route (per os, PO) is the most common enteral route, but
not the sole one. Medication may be administered sublingually (SL), using tablets
formulated for SL administration. Nitroglycerin is available as a sublingual tablet. This dosage form is rapidly absorbed into the bloodstream. Medication can also be administered
buccally (in contact with the oropharyngeal mucosa), as in the case of nystatin
oral suspension; and rectally. When medication is given via the gastrointestinal tract,
mechanisms usually involved in the absorption of nutrients are “borrowed” to transport
the drug into the body. In effect, the gastrointestinal tract takes on an added function.
This is possible because absorbable drugs have some chemical features in common
with nutrients. This facilitates the active or passive absorption of the drug. The nasoenteric
and percutaneous enteral tubes, familiar to many for delivery of nutrition, may,
with appropriate precautions, also be pressed into service for enteral drug delivery.
The most invasive route for drug administration is the parenteral route. Whereas,
technically, parenteral means not via the gastrointestinal tract, it is commonly used
to refer to routes requiring some form of injection. Once again, a variety of routes
come under this umbrella. The routes include injection into the bloodstream, most
commonly intravenously (IV), or into a vein. This can be done rapidly (IV push),
over a limited time (IV piggyback), or over a longer time (IV infusion). Occasionally,
the blood vessel may be an artery instead of a vein. Arteries are sometimes used as
the injection site for provision of intrahepatic chemotherapy. This is referred to as
intraarterial injection.
Medication can be injected into the subcutaneous tissue (SQ), muscle tissue
(intramuscularly, IM), or the skin (intradermal). Medication may also be injected into
the spinal canal or into the dura surrounding the spinal cord. This is done mainly for
pain control. The techniques here are intrathecal and subdural, respectively. Occasionally,
chemotherapy for cancer or infection is given intrathecally in an attempt to
decrease systemic side effects while maximizing central nervous system (CNS) effectiveness
or to compensate for poor passage of many medications across the
blood/brain barrier from the bloodstream into the cerebrospinal fluid. Antiinflammatory
steroids, used for severe arthritis, may be injected into the space within a joint.
This is called synovial injection. Occasionally medication, particularly hydration
fluids, may be given by slow infusion subcutaneously rather than into a vein. This is
called hypodermoclysis, and it is no longer commonly used for large volumes. Small
volumes are sometimes given this way. An example of this would be insulin delivered
by a pump. Medication can also be given directly into the peritoneum (intraperitoneal),
directly into the wall of the heart or into one of its chambers (intracardiac),
and sprayed into the trachea (intratracheal). The latter two routes may be used during
cardiopulmonary resuscitation. Occasionally, drugs can be given via catheter into the
ventricles of the brain. This is called intraventricular administration. During gestation,
drugs may even be administered to a fetus in utero or into the amniotic fluid, referred
to as intrauterine injection. Finally, there is a route of injection called intraosseous,
where the injection is done into the bone marrow of long bones such as the tibia.
This may be useful in children with poor veins and relatively soft bones.