Professor Dave again, let’s take some drugs.
Before we dive into the specifics of all the different classes of drugs, we have some more
basic information to go over.
First, let’s talk about precisely how drugs are administered.
There are many different ways that a drug can enter the body, and the method selected
has to do primarily with precisely where in the body we need the drug to go, but also
how quickly we need its effects to set in.
This is determined by various healthcare professionals, each of which have a different role, so to
better understand their perspective, let’s go over a basic overview of this information now.
Drug delivery, or the method by which a drug is administered to achieve a specific therapeutic
effect, is quite complicated, as one might imagine.
Administering the wrong drug, or the right drug in the wrong way, can have serious consequences
for a patient, and there are many factors at play.
These include the age and weight of the individual, their medical history, and so forth, and the
wrong decision can result in an adverse reaction to a drug, such as allergic or anaphylactic reactions.
These are acquired hyperresponses of natural bodily defenses to a foreign substance called
an allergen, with anaphylaxis being the more severe version, where massive amounts of histamine
and other mediators of inflammation are released throughout the body, which can be life-threatening.
For reasons such as these, the safe delivery of medications must follow the six rights
of drug administration.
These are basic guidelines that good health professionals obey, and they are as follows.
Right patient, right medication, right dose, right route of administration, right time
of delivery, and right documentation.
Some of these guidelines fall into the realm of highly specific medical training, so we
won’t discuss them in this series, but the route of administration will be of interest
to us, so let’s examine that aspect.
The main methods of drug administration we will discuss are the enteral, topical, and
parenteral routes, each of which have numerous subcategories.
Starting first with the enteral route, this involves drugs being administered orally,
which means through the mouth, or through either nasogastric or gastronomy tubes, which
are essentially feeding tubes that route directly to the stomach, either through the nostril
in the case of the former, or through the belly in the case of the latter.
In any of these cases, the drug ends up in the stomach, with oral ingestion being preferred,
leaving tubes to be utilized only if there is some issue preventing oral ingestion, such
as when the patient is unconscious and thus unable to swallow.
If administered through the mouth, this is typically done with tablets or capsules, and
this is arguably the easiest way to introduce a drug to the body.
If we can recall some things about the digestive system, most of the absorption of nutrients
occurs in the small intestine, which means that these drugs must first make it through
the ultra-acidic environment of the stomach in order to maximize absorption and reach
as many cells as possible.
This is why most tablets have a hard, waxy coating that withstands acidic environments,
but will specifically dissolve in the basic environment of the intestine, so as to be
absorbed thoroughly.
Apart from tablets and capsules, enteral drug administration can involve the sublingual
or buccal routes.
These mean that the patient does not swallow, but keeps the pill either under the tongue
or in the oral cavity between the gum and the cheek.
The mucosa of the oral cavity is highly absorptive, so drugs can enter the bloodstream this way,
avoiding the acidic conditions of the stomach in the process.
With the enteral route covered, let’s move on to the topical route.
This involves the application of drugs to the skin or the membranous linings of various orifices.
So obviously any kind of cream that is rubbed onto the skin falls into this category, as
well as transdermal patches.
In addition there is ophthalmic administration to treat the eyes, such as with eye drops.
Otic administration treats the ear, such as with ear drops.
Nasal administration means through the nostrils, such as with various sprays, and then some
drugs can be administered through the vagina or rectum, typically in the form of a suppository.
The topical route has a number of advantages, namely that drug delivery is more targeted,
as absorption is slow, and very little of the drug makes it into areas of the body other
then where the drug was applied, with the exception of the nostrils and the rectum,
which allow for a drug to circulate through the bloodstream once absorbed.
So some topical drugs have a highly local effect, and others have a systemic effect.
Finally there is the parenteral route.
This is essentially any route other than what we have already mentioned, and it typically
involves a needle, which makes this a more invasive method of administrating drugs.
There are a few different ways to make the injection.
The intradermal route deposits drugs into the skin itself, and thus to the blood vessels within.
The subcutaneous route is similar, the only difference is that intradermal is more shallow,
with injection into the dermis occurring at a very shallow angle, while subcutaneous is
deeper, with injection occurring at more of a 45 degree angle.
Then there is the intravenous route, where drugs are injected directly into the bloodstream,
and the intramuscular route, where the drugs are injected into muscle tissue.
To offer a brief comparison, intravenous administration allows for high levels of the drug in the
bloodstream immediately, which then decrease over time as it is excreted, whereas oral
administration starts off with zero concentration in the bloodstream and slowly increases as
absorption occurs, and then eventually also decreases due to excretion.
So between the enteral route, topical route, and parenteral route, we have completed an
introduction to the various ways in which drugs can enter the body.
The criteria for preferring one route over another will continue to become more clear
as we begin to look at specific drugs later in the series, so for now, let’s move on
to some more key concepts.