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OPT 540 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What are the four pharmacokinetic properties that determine the speed of onset of drug action, the intensity of the drug’s effect, and the duration of drug action?

A

Absorption
Distribution
Metabolism
Elimination

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2
Q

Absorption, distribution, metabolism, and elimination determine what?

A

The speed of onset of drug action, the intensity of the drug’s effect, and the duration of drug action.

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3
Q

Which route of administration is safest and most common?

A

Enteral (mouth, sublingual, buccal).

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4
Q

What does enteric coating accomplish, and what is an example of a drug that is commonly coated so?

A

It resists the chemical actions of the stomach but dissolves readily in the upper intestine. Aspirin is one such drug.

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5
Q

What is an example of an extended release drug?

A

Morphine.

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6
Q

Why are parenteral drugs sometimes preferable to other types?

A

If a drug (such as heparin) is poorly absorbed or is unstable in the GI tract (such as insulin), this route allows the drug to bypass these obstacles.

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7
Q

What are some disadvantages of parenteral drugs?

A

They are irreversible, can lead to infections and local tissue damage, and can cause fear and pain in the patient.

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8
Q

Name two examples of drugs delivered by oral inhalation.

A

Albuterol (bronchodilator), fluticasone (corticosteroid).

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9
Q

Name three examples of drugs delivered by nasal inhalation.

A

Oxymetazoline (nasal decongestant), calcitonin (treatment for osteoporosis), desmopressin (treatment for diabetes insipidus).

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10
Q

Name one drug delivered by intrathecal/intraventricular routes.

A

Amphotericin B (treatment for cryptococcal meningitis).

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11
Q

When would a topical drug be desired?

A

For local effect of a drug.

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12
Q

Name one drug delivered topically.

A

Clotrimazole (treatment for dermatophytosis).

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13
Q

When would a transdermal drug be desired?

A

For sustained delivery of a drug.

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14
Q

Name three drugs delivered transdermally.

A

Nitroglycerin (treatment for ischemic heart disease caused by angina pectoris), scopolamine (for motion sickness), nicotine (smoking cessation).

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15
Q

What is the definition of bioavailability?

A

The percentage of drug that gets into the bloodstream.

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16
Q

What are the different methods of drug absorption from the GI tract?

A

Passive diffusion, facilitated diffusion, active transport, and endocytosis/exocytosis.

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17
Q

Which method of drug absorption is most common?

A

Passive diffusion.

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18
Q

What four ideas describe passive diffusion?

A

1: Drug moves from area of high concentration to area of low concentration.
2: Does not involve a carrier.
3: Is not saturable.
4: Shows low structural specificity.

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19
Q

How would you describe facilitated diffusion?

A

Drug enters cell through specialized transmembrane proteins that undergo conformational changes to allow their passage into the cell, moving them down their concentration gradient. It does not require energy, can be saturated, and may be inhibited by compounds that compete for the carrier.

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20
Q

How would you describe active transport?

A

Drugs that closely resemble naturally occurring metabolites may use these carrier proteins. This form of transport requires energy. Drugs may be moved against the concentration gradient. These systems can be saturated, and may be competitively inhibited by other substances.

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21
Q

Name one molecule taken up by endocytosis.

A

Vitamin B12, across the gut wall.

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22
Q

Name one molecule released by exocytosis.

A

Norepinephrine, from membrane-bound vesicles in the nerve terminal.

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23
Q

For a weakly acidic drugs and weakly basic drugs, which forms can permeate through membranes?

A

For weak acids (HA↔H+ + A-), the protonated form HA permeates.
For weak bases (BH+↔ B + H+), the uncharged form B permeates.

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24
Q

What does pKa represent?

A

It measures the strength of the interaction of a compound with a proton. Lower pKa is more acidic, higher pKa is more basic.

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25
How do pH and pKa relate in terms of acidic and basic drug permeability?
If the environmental pH is less than the drug's pKa, the drug will trend toward its protonated forms (HA or BH+). If the environmental pH is greater than the drug's pKa, the drug will trend toward its deprotonated forms (A- or B).
26
Does low pH environment favor acidic or basic drugs?
Low pH favors acidic drugs (depending on the individual drug's pKa) since the protonated form HA is not charged, thereby allowing it to cross the membrane.
27
Does high pH environment favor acidic or basic drugs?
High pH favors basic drugs (depending on the individual drug's pKa) since the deprotonated form B is not charged, thereby allowing it to cross the membrane.
28
What are some factors (apart from pH) affecting absorption?
Blood flow to site, total surface area, contact time at the surface, and expression of P-glycoprotein.
29
What is the purpose of P-glycoprotein?
It is a multidrug transmembrane transporter protein that transports many kinds of molecules across cell membranes (out of the cell). In the liver, it transports drugs into bile for elimination; in the kidneys, it pumps drugs into urine for excretion; in brain capillaries, it pumps drugs back into blood, limiting their access to the brain.
30
What is meant by the term "first-pass metabolism"?
When a drug enters portal circulation (such as when taken orally) and as such is exposed to the liver and/or gut first. If the drug is rapidly metabolized there, the amount of drug that enters systemic circulation unchanged is severely limited.
31
How does a drug's solubility affect its absorption?
Drugs that are very hydrophilic are poorly absorbed due to their inability to cross the cell membrane. Drugs that are very hydrophobic are also poorly absorbed since they are insoluble in body fluids and therefore cannot gain access to the surface of cells. Drugs must be mostly hydrophobic with some solubility in aqueous solutions. (This is why many drugs are either weak acids or weak bases.)
32
What is bioequivalence?
It is a term used to describe two drugs if they show comparable bioavailability and similar times to achieve peak blood concentration.
33
What is therapeutic equivalence?
When two drugs are pharmaceutically equivalent with similar clinical and safety profiles.
34
What are some factors that can influence drug distribution?
Cardiac output and regional blood flow, capillary permeability, tissue volume, degree of binding of drug to plasma and tissue proteins, and relative hydrophobicity of drug.
35
How does blood flow affect drug distribution?
Some areas, such as the brain, liver, kidneys, and eyes, receive high flow of blood. Thus, many drugs will affect these areas first. The effect will decrease as the drug is further distributed to lower blood flow areas.
36
How does capillary permeability affect drug distribution?
Some areas, like the kidney and liver, have capillaries that are discontinuous. Drugs are more easily able to enter these types of areas than the brain, where the capillaries are tightly junctioned.
37
How do plasma proteins affect drug distribution?
Plasma proteins (such as albumin) may reversibly bind to drugs. This keeps the drug from diffusing out of the bloodstream but also acts as a drug reservoir, since the bound drug is not being excreted or eliminated.
38
How can tissue proteins affect drug distribution?
Tissue proteins (or lipids or nucleic acids) can bind drugs and act as a reservoir within tissues. This can prolong the action of the drug, or can cause local drug toxicity.
39
Give one example of local drug toxicity due to tissue protein reservoirs.
Acrolein (the metabolite of cyclophosphamide) is toxic to the kidney when it accumulates there.
40
What are the three major routes of elimination?
Hepatic metabolism Elimination in bile Elimination in urine
41
Most drugs eliminated are eliminated according to which order of kinetics?
First-order kinetics.
42
What is meant by "apparent volume of distribution?"
It can be thought of as the fluid volume that is required to contain the entire drug in the body at the same concentration measured in the plasma.
43
What equation describes the apparent volume of distribution?
Vd = (Dose)/(C0), where C0 is the plasma concentration at time zero.
44
What are the three water compartments of the body?
The intracellular compartment, and the plasma compartment, and the interstitial compartment. (These last two together make up the extracellular space.)
45
In what compartment(s) can drugs with large molecular weights be found?
The plasma compartment. Due to the large nature of the molecules, these drugs cannot move out of the slit junctions of the capillaries and are effectively trapped in the plasma. Heparin is one such drug.
46
About how much of the total body weight is plasma?
About 6%, which is about 4L in a 70kg person.
47
In what compartment(s) can low molecular weight and hydrophilic drugs be found?
The plasma and interstitial compartments. Due to their small nature, these drugs can move out of the slit junctions of the capillaries, entering the interstitial compartment. Due to their hydrophilic nature, however, they cannot enter the intracellular compartment, effectively limiting them to the plasma and interstitial compartments. Gentamicin is one such drug.
48
About how much of the total body weight are the plasma and interstitial compartments together?
About 20%, which is 14L in a 70kg person.
49
In what compartment(s) can low molecular weight and hydrophobic drugs be found?
All of the water compartments. Small, hydrophobic drugs can cross the slit junctions and cross cell membranes, effectively opening up all of the total body water to them. Ethanol is one such drug.
50
About how much of the total body weight is the total body water?
About 60%, or 42L in a 70kg person.
51
What effect does a large Vd have on the half-life of a drug?
A large Vd indicates that most of the drug is not in the plasma but in the extraplasmic space, and since elimination depends on blood flow to the kidney and liver, the half-life is extended.
52
What is meant by "clearance" as it applies to metabolism?
It is an estimation of the amount of drug removed from the body per unit of time.
53
What equation can be used to find clearance?
CL = 0.693 x Vd/t1/2
54
What is the equation of velocity used for first-order kinetics?
v = Vmax[C]/Km
55
What is the equation of velocity used for zero-order kinetics?
v = Vmax[C]/[C], that is, v = Vmax
56
True or false: In first-order kinetics, the rate of elimination is independent of drug dose.
False. First-order kinetics are directly proportional to drug dose.
57
True or false: In zero-order kinetics, the rate of elimination is independent of drug dose.
True. The enzyme has been saturated with a high dose and therefore elimination proceeds at a constant pace.
58
What are three drugs that obey zero-order kinetics?
Aspirin, ethanol, and phenytoin.
59
Why can't the kidney readily eliminate lipophilic drugs?
The drugs readily cross cell membranes and so can be reabsorbed in the distal convoluted tubules.
60
What is the general purpose of Phase I of drug metabolism?
To convert lipophilic molecules into more polar molecules by introducing or unmasking a polar functional such as -OH or -NH2.
61
Most Phase I reactions are catalyzed by what system?
The cytochrome P450 system.
62
True or false: Phase I metabolism always decreases the drug's pharmacologic activity?
False. It can increase, decrease, or leave unaltered the drug's pharamacologic activity.
63
Cytochrome P450 is designated as CYP. Which P450 isozymes are responsible for most P450 reactions?
CYP3A4/5, CYP2D6, CYP2C8/9, and CYP1A2.
64
Why is codeine a poor choice of analgesic for some people?
Some people lack the CYP2D6 that activates the drug.
65
The P450 isozyme CYP219 is required to activate what prodrug?
Clopidogrel.
66
What can inducers do to the expression of CYP isozymes?
Inducers increase the expression of CYP isozymes, and therefore increase the metabolism of drugs. This leads to decrease plasma drug concentration, decrease drug activity if metabolite is inactive, increase drug activity if the metabolite is active, and decreased therapeutic drug effect.
67
Name three inducers of CYP isozymes.
Phenobarbital, rifampin, and carbamazepine.
68
Name five inhibitors of CYP isozyme acitivity.
Omeprazole, erythromycin, ketoconazole, ritonavir, and cimetidine.
69
What does cimetidine do?
It blocks the metabolism of theophylline, clozpine, and warfarin.
70
Grapefruit and its juice inhibits which CYP isozyme?
CYP3A4
71
Grapefruit and its juice leads to decreased metabolism of what drugs?
Nifedipine, clarithryomycin, and simvastatin.
72
What is the purpose of Phase II metabolism?
It causes a conjugation reaction of the drug with an endogenous substrate such as glucuronic acid, sulfuric acid, acetic acid, or an amino acid, resulting in a more water-soluble compound.
73
Which conjugation system is the most important and most common?
Glucuronidation.
74
What is the effect of chloramphenicol in neonates?
Chloramphenicol is inactivated by addition of glucuronic acid. It results in gray baby syndrome since neonates are deficient in the glucuronidation conjugation system.
75
True or false: all drugs undergo Phase I and Phase II reactions in that order.
False. Isoniazid is first acetylated (Phase II) and then hydrolyzed to isonicotinic acid (Phase I).
76
What is normal glomerular filtration rate?
125mL/min, or about 20% of renal plasma flow.
77
What types of drugs are actively transported into the proximal tubule?
Weak acids and weak bases, since they are cations and anions.
78
What happens as a drug moves toward the distal convoluted tubule, and what is the kidney's response?
The drug's concentration increases, and if it is uncharged, it may diffuse back out into systemic circulation. This can be countered by manipulating the pH of the urine. This process is called "ion trapping."
79
In the distal tubular portion, how would the pH change in order to more effectively eliminate weak acids?
The pH would increase (alkalinization) in order to increase the ionized form (HA -->A- + H+).
80
Give an example of ion trapping acidification alkalinization.
Phenobarbital overdose can be treated with bicarbonate, increasing its elimination.
81
In the distal tubular portion, how would the pH change in order to more effectively eliminate weak bases?
The pH would decrease (acidification) in order to increase the ionized form (B + H+ -->BH+).
82
Give an example of ion trapping through acidication.
Amphetamine overdose can be treated with NH4Cl, which acidifies the urine.
83
Give an example of a drug eliminated by the lungs?
Halothane.
84
What is meant by the term "steady state?"
It is the point at which rate of administration equals that of elimination.
85
How long does it take for a drug to reach steady state?
About four half-lives.
86
When is a loading dose desirable?
When the therapeutic benefit of the drug is required immediately, such as lidocaine for arrhythmias.

OPT 540 (12 decks)

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