Pharmacology - Drug Absorption

Front 1

Define bioavailability.

Back 1

The fraction of the dose of drug that reaches the systemic circulation

Front 2

What is the "first pass" effect?

Back 2

The removal of a significant portion of a drug dose by metabolism during the first pass of the drug through the gastrointestinal mucosa and liver

(factors can influence the amount of drug reaching the systemic circulation AFTER the drug has penetrated the intestinal wall)

Front 3

What are the factors that affect drug absorption?

Back 3

1. Blood flow to the site of administration
2. Surface area for diffusion
3. Ionization state of the drug
4. Lipophilicity of the drug

Front 4

What types of drug administration eliminate the "first pass" effect?

Back 4

Sublingual and rectal

Front 5

What is the definition of intrathecal administration?

Back 5

Entry of drug into CSF and central nervous system

Front 6

What are the factors that affect oral absorption of a drug?

Back 6

1. Acid secretion
2. Stomach emptying
3. Intestinal transit
4. Bile and mucus flow

Front 7

What are the factors that affect drug absorption of the stomach?

Back 7

1. Properties of drug (solubility in aqueous GI fluids, stability in acid and digestive enzymes)
2. Binding of drugs to food particles
3. Surface area
4. Blood flow
5. Gastric emptying time

Front 8

What are the factors that affect drug absorption of the small intestine?

Back 8

1. Properties of drug (susceptibility to digestive enzymes and GI flora, solubility in aqueous GI fluids)
2. Binding of drug to food particles
3. Surface area
4. Blood flow

Front 9

What are the factors the favor the absorption of a weak acid from the small intestine?

Back 9

1. Large surface area
2. High blood flow
3. pH in the blood favors the ionized form (i.e. ion trapping)

Front 10

What can be done to reduce dissolution of a drug into GI fluids?

Back 10

Coating particles with wax or other water-insoluble material OR embedding the drug in the matrix

Front 11

Direct placement of a drug into the blood stream ensures bioavailability because of the bypassing of the skin barrier. What are the factors that regulate the rate of entry into capillaries?

Back 11

1. Hydrophobicity of drug
2. Rate of capillary blood flow

Front 12

Describe the mechanism of action of a local anesthetic.

Back 12

A vasoconstrictor is added to the drug which decreases blood flow to the injection site, therefore, slowing the absorption of the drug and increasing the duration of action of the drug

Front 13

When giving a drug intramuscularly, how does pH affect absorption?

Back 13

When you give a drug intramuscularly, the drug has to be water soluble (for example, at a pH of 12); however, when injected, the tissue fluids act as buffers and the pH decreases, causing a shift in the equilibrium between the ionized and free non-ionized from (HA) of the drug. The HA form, which is poorly water soluble, and precipitates at the site of the injection is is absorbed very slowly.

Front 14

Describe ways that non-intravenous parenteral preparations have been formulated to provide sustained blood levels.

Back 14

1. Insoluble salts
2. Suspensions (solutions in non-aqueous vehicles)
3. Procaine salt of penicillin is poorly soluble
a. duration of action of penicillin can be further slowed by suspending the procaine penicillin in oil containing aluminum stearate
b. OIL prevents contact of the salt with an aqueous medium, thereby retarding dissolution and the ALUMINUM STEARATE further delays dissolution by INCREASING VISCOSITY

Front 15

How can plasma protein binding drugs contribute to toxicity?

Back 15

The fraction of drug unbound in plasma increases after binding sites are completely filled (i.e. saturated). An increase in plasma concentration due to a subsequent dose will result in a greater fraction of unbound drug and therefore, more drug will move into tissues and create a greater than normal response.