able for absorption. Drugs contain an active ingredient and inactive ingredients.
The active ingredient is the substance that causes the pharmaceutical response. The
inactive ingredient, called excipient, is the substance that has no pharmaceutical
response but helps in the delivery of the drug. These are fillers and inert sub-
stances that give the drug its shape and size. The coating around tiny particles of
a capsule that causes a timed-release action of the drug is an inactive ingredient.
Nearly 80% of all drugs are administered orally (P.O.) and are carried to the
small intestine by the gastrointestinal tract where the drug is absorbed into the
bloodstream. The time necessary for the drug to disintegrate and dissolve so it
can be absorbed is called the rate limiting time.
A drug has a higher rate limiting time (Table 2-1) if it is absorbed in acidic
fluids rather than alkaline fluids. Children and the elderly have a lower pH in their
GI tract and therefore drugs are absorbed more slowly than in a healthy adult.
Some drugs are more effective if absorbed in the small intestine rather than
the stomach. However, the stomach is more acidic than the small intestine.
Therefore, pharmaceutical manufacturers place an enteric coating around the
drug that resists disintegration in the stomach. The coating disintegrates in the
alkaline environment of the small intestine. Enteric coating is also used to delay
the onset of the pharmaceutical response and to prevent food in the stomach
from interfering with the dissolution and absorption of the drug.
Tip: Never crush a capsule that contains enteric release beads or is coated
for timed-release.
The form of a drug influences the drug’s pharmacokinetics and pharmaco-
dynamics.
CHAPTER 2 Drug Action and Drug Interactions^25
Preparation Absorption Rate (fastest to slowest)
Lipid soluble non-ionized liquids, elixirs, syrups 1
Water soluble ionized liquids, elixirs, syrups 2
Suspension solutions 3
Powders 4
Capsules 5
Tablets 6
Coated tablets 7
Enteric-coated tablets 8Table 2-1. Rate limiting time rating for drug forms.