Principles of Drug Action

Question 1

Direct chemical interaction between drug and biologic mediator, which inactivates the drug. An example is chelation of toxic metals by a chelating agent.

Answer 1

Chemical antagonism

Question 2

Can occur when two drugs each produce an effect, and the two effects cancel each other. For example, methacholine can stimulate parasympathetic (muscarinic) receptors in the airways,
causing bronchoconstriction; epinephrine can stimulate beta 2 receptors in the airways, causing
bronchodilation.

Answer 2

Functional antagonism

Question 3

Occurs when a drug has affinity for a receptor but no efficacy and at the same time blocks the active agonist from binding to and stimulating the receptor. For example, fexofenadine is a competitive antagonist to histamine on specific receptors (H1) on bronchial smooth muscle and the nasopharynx and is used to treat allergies to pollens.

Answer 3

Competitive antagonism

Question 4

Occurs when two drugs act on a target organ by different mechanisms of action, and the effect
of the drug pair is greater than the sum of the separate effects of the drugs.

Answer 4

Synergism:

Question 5

Occurs when two drugs act on the same receptors, and the combined effect is the simple linear
sum of the effects of the two drugs, up to a maximal effect.

Answer 5

Additivity:

Question 6

special case of synergism in which one drug has no effect but can increase the activity of
the other drugs.

Answer 6

Potentiation:

Question 7

Effect that is the opposite of, or unusual, or an absence of effect, compared with the predicted usual effect in an individual.

Answer 7

Idiosyncratic effect

Question 8

Allergic or immune-mediated reaction to a drug, which can be serious, requiring airway
maintenance or ventilatory assistance.

Answer 8

Hypersensitivity:

Question 9

Decreasing intensity of response to a drug over time.

Answer 9

Tolerance:

Question 10

Rapid decrease in responsiveness to a drug.

Answer 10

Tachyphylaxis:

Question 11

refers to hereditary differences in the way the body handles specific drugs. Several examples can be given from drugs commonly seen in respiratory and critical care:

Answer 11

PHARMACOGENETICS:

Question 12

Antituberculosis drug that varies in its rate of metabolism and inactivation among individuals,
with rapid and slow inactivators seen. The proportion of rapid versus slow inactivators is about 50/50
among white and black individuals, but Inuit and some Asian people tend to be rapid inactivators

Answer 12

Isoniazid:

Question 13

Neuromuscular paralyzing agent used during surgery. It is normally metabolized by a butyrylcholinesterase enzyme (pseudocholinesterase). Approximately 1 in 3000 individuals has a genetically determined variant of this enzyme. As a result, a patient may take several hours to recover from
the drug and begin to breathe spontaneously, rather than the several minutes usually seen. Mechanical ventilatory support would be required until spontaneous breathing is adequate.

Answer 13

Succinylcholine:

Question 14

Inhalation anesthetic that (similar to several other, related anesthetics) can cause malignant hyperthermia in genetically susceptible individuals. Patients with an atypical variant of a calcium release channel can die as a result of this serious complication of general anesthesia, which involves a rapid
increase in body temperature and increased oxygen consumption.

Answer 14

Isoflurane: