Pharmacology Unit 1

Question 1

Discuss the 3 phases of drug actions.

Answer 1

pharmaceutic (dissolution), pharmacokinetic, and pharmacodynamics—as drug actions occur. In the pharmaceutic phase, the drug becomes a solution so that it can cross the biologic membrane. When the drug is administered parenterally by subcutaneous (subQ), intramuscular (IM), or intravenous (IV) routes, there is no pharmaceutic phase. The second phase, the pharmacokinetic phase, is composed of four processes: absorption, distribution, metabolism, (or biotransformation), and excretion (or elimination). In the pharmacodynamic phase, a biologic or physiologic response results.

Question 2

Define the pharmaceutical phase and the role of excipients.

Answer 2

The pharmaceutic phase (dissolution) is the first phase of drug action. In the gastrointestinal (GI) tract, drugs need to be in solution so they can be absorbed. A drug in solid form (tablet or capsule) must disintegrate into small particles to dissolve into a liquid, a process known as dissolution. Drugs in liquid form are already in solution (figure 1­1 pharmaceutic phase of a tablet). Tablets are not 100% drug. Fillers and inert substances, generally called excipients, are used in drug preparation to allow the drug to take on a particular size and shape and to enhance drug dissolution. Some additives in drugs, such as the ions potassium (K) and sodium (Na) in penicillin potassium and penicillin sodium, increase the absorbability of the drug. Penicillin is poorly absorbed by the GI tract because of gastric acid. However, by making the drug a potassium or sodium salt, penicillin can then be absorbed. An infant’s gastric secretions have a higher pH (alkaline) than those of adults; therefore infants can absorb more penicillin.

Question 3

Discuss the dissolution, disintegration and rate limiting and factors affecting these processes.

Answer 3

Disintegration is the breakdown of a tablet into smaller particles. Dissolution is the dissolving of the smaller particles in the GI fluid before absorption. Rate limiting is the time it takes the drug to disintegrate and dissolve to become available for the body to absorb it. Drugs in liquid form are more rapidly available for GI absorption than are solids. Generally, drugs are both disintegrated and absorbed faster in acidic fluids with a pH of 1 or 2 rather than in alkaline fluids. Both the very young and older adults have less gastric acidity; therefore drug absorption is generally slower for those drugs absorbed primarily in the stomach. Enteric­coated drugs resist disintegration in the gastric acid of the stomach, so disintegration does not occur until the drug reaches the alkaline environment of the small intestine. Enteric­coated tablets can remain in the stomach for a long time; therefore their effect may be delayed in onset. Enteric­coated tablets or capsules and sustained­release (beaded) capsules should not be crushed. Crushing would alter the place and time of absorption of the drug. Food in the GI tract may interfere with the dissolution and absorption of certain drugs. However, food can also enhance absorption of other drugs; thus some drugs should be taken with food. Some drugs irritate the gastric mucosa, so fluids or food may be necessary to dilute the drug concentration and to act as
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