Download ADME: Absorption/Administration By: Laura Duffin Student Number

ADME: Absorption/Administration
By: Laura Duffin
Student Number: 100340824
Prof: Dr. Jan Matejovic
Drug absorption refers to the route or method by which a drug reaches the blood supply. First, we must
look at how the drug is administered. There are seven ways this is done; oral administration, absorption
through mucous membranes, rectal administration, topical administration, inhalation, injection and
implants.
Oral administration refers to drugs taken by the mouth, usually in the form a tablet, capsule, caplet or
liquid. A certain amount of orally administered drugs are absorbed in the stomach, but most is absorbed
by the upper intestine. Absorption through mucous membranes happens in the nose and mouth. Nasal
sprays and sublingual tablets dissolved under the tongue are examples of these. Eye drops also fall into
this category. Rectal administered drugs are in the form of suppositories and are taken if the patient
cannot swallow or they are unconscious. Topical administration drugs are applied to the skin. They can
come in the form of creams or patches. The drug is absorbed through the skin and reaches the blood
stream and is generally slow release. Inhalation is another way drugs can be administered. It is absorbed
through the cell lining of the respiratory tract and then into the blood stream. Anti-asthmatics are
widely used inhaled drugs. Injections are administered directly into a vein, into a muscle, under the
surface of the skin, into the spinal cord or into the abdomen.
If the drug is administered orally, it travels through the gastrointestinal tract which consists of the
mouth, throat, stomach and intestines. A percentage of the drug, depending on which drug it is and how
it is made, can be absorbed through the mucosal membrane of the mouth. The drug moves from the
mouth down to the stomach where it can be broken down and digested in the gastric juices. Drugs that
are still intact after encountering these acidic juices then make their way to the intestines through the
cells lining the gut wall. The drug then passes between the cells lining the blood vessels and enter the
blood stream. Through the blood stream the drug meets its next destination, the liver, where it is then
metabolized.
In order for a drug to make it to the liver for metabolism, there are many important characteristics it
must possess. If it is not chemically stable enough, it will be broken down by the acids in the stomach. It
must also be metabolically stable to pass metabolism in the gastrointestinal tract to avoid the digestive
enzymes encountered along the tract as well as in the liver. It is also important to keep in mind the
solubility of the drug. The drug will not be able to pass the gut and enter the intestines if it is too polar,
or hydrophilic. If it happens to be too hydrophobic, it will end up dissolving in fat globules before it
reaches the intestines. It is important to note that molecular weight does not affect the ability of a drug
to be absorbed, but rather the solubility as previously described.
Another important characteristic for a drug to contain is amine functional groups. The main importance
of these groups is in respect to the drugs ability to bind to its target and to permit good water solubility.
Amines are weak bases, and with a pKa between 6 and 8, the ionized and non-ionized form are in
equilibrium at blood pH. This allows the drug to cross through cell membranes in their non-ionized form
and be water soluble in their ionized form as well as good binding interactions with the target site.