Question 1

Absorption

Accepted Answer

Absorption is defined as the movement of a drug from its site of administration into the blood.

Question 2

Distribution

Accepted Answer

Distribution is defined as drug movement from the blood to the interstitial space of tissues and from there into cells.

Question 3

Metabolism

Accepted Answer

Metabolism (biotransformation) is defined as enzymatically mediated alteration of drug structure.

Question 4

Excretion & Elimination

Accepted Answer

Excretion is the movement of drugs and their metabolites out of the body. The combination of metabolism plus excretion is called elimination.

Question 5

Crossing the Membrane: Channel

Accepted Answer

Very few drugs cross membranes via channels or pores. The channels in membranes are extremely small (approximately 4 angstroms), and are specific for certain molecules. Consequently, only the smallest of compounds (molecular weight below 200 daltons) can pass through these channels, and then only if the channel is the right one. Compounds with the ability to cross membranes via channels include small ions, such as potassium and sodium.

Question 6

Crossing the Membrane: Transport Protein P-Glycoprotein, deserves special mention.

Accepted Answer

Transport systems are carriers that can move drugs from one side of the cell membrane to the other. Some transport systems require the expenditure of energy; others do not. All transport systems are selective: They will not carry just any drug. Whether a transporter will carry a particular drug depends on the drug's structure. P-glycoprotein is a transmembrane protein that transports a wide variety of drugs out of cells. This transporter is present in cells at many sites, including the liver, kidney, placenta, intestine, and capillaries of the brain. In the liver, P-glycoprotein transports drugs into the bile for elimination. In the kidney, it pumps drugs into the urine for excretion. In the placenta, it transports drugs back into the maternal blood, thereby reducing fetal drug exposure. In the intestine, it transports drugs into the intestinal lumen, and can thereby reduce drug absorption into the blood. And in brain capillaries, it pumps drugs into the blood, thereby limiting drug access to the brain

Question 7

Crossing the Membrane: Direct Penetration

Accepted Answer

For most drugs, movement throughout the body is dependent on the ability to penetrate membranes directly. Why? (1) most drugs are too large to pass through channels or pores, and (2) most drugs lack transport systems to help them cross all of the membranes that separate them from their sites of action, metabolism, and excretion. A general rule in chemistry states that “like dissolves like.” Membranes are composed primarily of lipids; therefore, to directly penetrate membranes, a drug must be lipid soluble (lipophilic). Certain kinds of molecules are not lipid soluble and therefore cannot penetrate membranes. This group consists of polar molecules and ions.

Question 8

Polar Molecule

Accepted Answer

``` Polar molecules are molecules with uneven distribution of electrical charge. That is, positive and negative charges within the molecule tend to congregate separately from one another. Water is the classic example. The electrons (negative charges) in the water molecule spend more time in the vicinity of the oxygen atom than in the vicinity of the two hydrogen atoms. As a result, the area around the oxygen atom tends to be negatively charged, whereas the area around the hydrogen atoms tends to be positively charged. ``` Gentamicin (Fig. 4–3B), an antibiotic, is an example of a polar drug. The hydroxyl groups, which attract electrons, give gentamicin its polar nature.

Question 9

Ion

Accepted Answer

Ions are defined as molecules that have a net electrical charge (either positive or negative). Except for very small molecules, ions are unable to cross membranes.

Question 10

Quaternary ammonium compound

Accepted Answer

Quaternary ammonium compounds are molecules that contain at least one atom of nitrogen and carry a positive charge at all times. The constant charge on these compounds results from atypical bonding to the nitrogen. In most nitrogen-containing compounds, the nitrogen atom bears only three chemical bonds. In contrast, the nitrogen atoms of quaternary ammonium compounds have four chemical bonds (Fig. 4–4A). Because of the fourth bond, quaternary ammonium compounds always carry a positive charge. And because of the charge, these compounds are unable to cross most membranes.

Question 11

ph Dependent ionization

Accepted Answer

Unlike quaternary ammonium compounds, which always carry a charge, many drugs are either weak organic acids or weak organic bases, which can exist in charged and uncharged forms. Whether a weak acid or base carries a charge is determined by the pH of the surrounding medium. - An acid is defined as a compound that can give up a hydrogen ion (proton). Put another way, an acid is a proton donor. - A base is defined as a compound that can take on a hydrogen ion. That is, a base is a proton acceptor. - -When an acid gives up its proton, which is positively charged, the acid itself becomes negatively charged. Conversely, when a base accepts a proton, the base becomes positively charged.

Question 12

Ion trapping

Accepted Answer

The process whereby a drug accumulates on the side of a membrane where the pH most favors its ionization is referred to as ion trapping or pH partitioning. Figure 4–6 shows the steps of ion trapping using aspirin as an example. Because the ionization of drugs is pH dependent, when the pH of the fluid on one side of a membrane differs from the pH of the fluid on the other side, drug molecules will tend to accumulate on the side where the pH most favors their ionization. Accordingly, since acidic drugs tend to ionize in basic media, and since basic drugs tend to ionize in acidic media, when there is a pH gradient between two sides of a membrane, • Acidic drugs will accumulate on the alkaline side. • Basic drugs will accumulate on the acidic side.

Question 13

5 factors affecting drug absorption

Accepted Answer

1. Rate of Dissolution, 2. Surface Area 3. Blood Flow, 4. Lipid Solubility 5. pH Partitioning

Question 14

IV: 1. Absorption Pattern 2. Advantages 3. Disadvantages

Accepted Answer

1. Absorption Pattern - Instantaneous and complete 2. Advantages - Rapid onset, and hence ideal for emergencies, (Precise control over drug levels, Permits use of large fluid, Permits use of irritant drugs.) 3. Disadvantages Irreversible (Expensive, Inconvenient, Difficult to do, and hence poorly suited for self-administration; Risk of fluid overload, infection, and embolism; Drug must be water soluble.

Question 15

IM: 1. Absorption Pattern 2. Advantages 3. Disadvantages

Accepted Answer

1. Absorption Pattern - Rapid with water-soluble drugs; Slow with poorly soluble drugs. 2. Advantages - Permits use of poorly soluble drugs; Permits use of depot preparations. 3. Disadvantages - Possible discomfort, Inconvenient, Potential for injury.

Question 16

subQ: 1. Absorption Pattern 2. Advantages 3. Disadvantages

Accepted Answer

1. Absorption Pattern - Rapid with water-soluble drugs; Slow with poorly soluble drugs. 2. Advantages - Permits use of poorly soluble drugs; Permits use of depot preparations. 3. Disadvantages - Possible discomfort, Inconvenient, Potential for injury. Same as IM

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Chapter 4 - (Pharmacokinetics) Flashcards

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