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15 Cards in this Set

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Define bioavailability.
The fraction of the dose of drug that reaches the systemic circulation
What is the "first pass" effect?
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)
What are the factors that affect drug absorption?
1. Blood flow to the site of administration
2. Surface area for diffusion
3. Ionization state of the drug
4. Lipophilicity of the drug
What types of drug administration eliminate the "first pass" effect?
Sublingual and rectal
What is the definition of intrathecal administration?
Entry of drug into CSF and central nervous system
What are the factors that affect oral absorption of a drug?
1. Acid secretion
2. Stomach emptying
3. Intestinal transit
4. Bile and mucus flow
What are the factors that affect drug absorption of the stomach?
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
What are the factors that affect drug absorption of the small intestine?
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
What are the factors the favor the absorption of a weak acid from the small intestine?
1. Large surface area
2. High blood flow
3. pH in the blood favors the ionized form (i.e. ion trapping)
What can be done to reduce dissolution of a drug into GI fluids?
Coating particles with wax or other water-insoluble material OR embedding the drug in the matrix
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?
1. Hydrophobicity of drug
2. Rate of capillary blood flow
Describe the mechanism of action of a local anesthetic.
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
When giving a drug intramuscularly, how does pH affect absorption?
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.
Describe ways that non-intravenous parenteral preparations have been formulated to provide sustained blood levels.
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
How can plasma protein binding drugs contribute to toxicity?
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.