Drug Administration part IV

Dosage Forms for Parenteral ,
Pulmonary , Rectal or Vaginal ,
and Cutaneous Application
Drugs need not always be administered
orally (i.e., by swallowing), but may also
be given parenterally. This route usually
refers to an injection, although enteral
absorption is also bypassed when
drugs are inhaled or applied to the skin.
For intravenous, intramuscular, or
subcutaneous injections, drugs are often
given as solutions and, less frequently,
in crystalline suspension for
intramuscular, subcutaneous, or intraarticular
injection. An injectable solution
must be free of infectious agents,
pyrogens, or suspended matter. It
should have the same osmotic pressure
and pH as body fluids in order to avoid
tissue damage at the site of injection.
Solutions for injection are preserved in
airtight glass or plastic sealed containers.
From ampules for multiple or single
use, the solution is aspirated via a
needle into a syringe. The cartridge ampule
is fitted into a special injector that
enables its contents to be emptied via a
needle. An infusion refers to a solution
being administered over an extended
period of time. Solutions for infusion
must meet the same standards as solutions
for injection.
Drugs can be sprayed in aerosol
form onto mucosal surfaces of body cavities
accessible from the outside (e.g.,
the respiratory tract). An aerosol
is a dispersion of liquid or solid particles
in a gas, such as air. An aerosol results
when a drug solution or micronized
powder is reduced to a spray on being
driven through the nozzle of a pressurized
container.
Mucosal application of drug via the
rectal or vaginal route is achieved by
means of suppositories and vaginal
tablets, respectively. On rectal application,
absorption into the systemic circulation
may be intended. With vaginal
tablets, the effect is generally confined
to the site of application. Usually the
drug is incorporated into a fat that solidifies
at room temperature, but melts in
the rectum or vagina. The resulting oily
film spreads over the mucosa and enables
the drug to pass into the mucosa.

Powders, ointments, and pastes
are applied to the skin surface. In
many cases, these do not contain drugs
but are used for skin protection or care.
However, drugs may be added if a topical
action on the outer skin or, more
rarely, a systemic effect is intended.

Transdermal drug delivery
systems are pasted to the epidermis.
They contain a reservoir from which
drugs may diffuse and be absorbed
through the skin. They offer the advantage
that a drug depot is attached noninvasively
to the body, enabling the
drug to be administered in a manner
similar to an infusion. Drugs amenable
to this type of delivery must: (1) be capable
of penetrating the cutaneous barrier;
(2) be effective in very small doses
(restricted capacity of reservoir); and
(3) possess a wide therapeutic margin
(dosage not adjustable).