I. DRUG ADMINISTRATION

Often the goal is to attain a therapeutic drug concentration in plasma from which drug

enters the tissue (therapeutic window between toxic concentration and minimal effective

concentration).

A. Enteral Routes

1. Sublingual (buccal)

Certain drugs are best given beneath the tongue or retained in the cheek

pouch and are absorbed from these regions into the local circulation.These

vascular areas are ideal for lipid-soluble drugs that would be metabolized

in the gut or liver, since the blood vessels in the mouth bypassthe liver (do

not undergo first pass liver metabolism), and drain directly into the systemic

circulation. This route is usually reserved for nitrates and certain hormones.

2. Oral

By far the most common route. The passage of drug from the gut into the

blood is influenced by biologic and physicochemical factors (discussed in

detail below), and by the dosage form. For most drugs, two- to five-fold

differences in the rate or extent of gastrointestinal absorption can occur,

depending on the dosage form. These two characteristics, rate and

completeness of absorption, comprise bioavailability. Generally, the

bioavailability of oral drugs follows the order: solution > suspension >

capsule > tablet > coated tablet.

3. Rectal

The administration of suppositories is usually reserved for situations in

which oral administration is difficult. This route is more frequently used

in small children. The rectum is devoid of villi, thus absorption is often

slow.

B. Parenteral Routes

1. Intravenous injection

Used when a rapid clinical response is necessary, e.g., an acute asthmatic

episode. This route allows one to achieve relatively precise drug

concentrations in the plasma, since bioavailability is not a concern. Most

drugs should be injected over 1-2 minutes in order to prevent the occurrence

of very high drug concentrations in the injected vein, possibly causing

adverse effects. Some drugs, particularly those with narrow therapeutic

indices or short half-lives, are best administered as a slow IV infusion or

drip.

2. Intra-arterial injection

Used in certain special situations, notably with anticancer drugs, in an effort

to deliver a high concentration of drug to a particular tissue. Typically, the

injected artery leads directly to the target organ.