Pharmacokinetics III: Drug Interactions & Individual Variation to Drug Responses Flashcards

1
Q

What are Drug Interactions?

A

A change in the magnitude or duration of response of one drug due to presence of a second drug

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2
Q

Are drug interactions chemical or physiological interactions?

A

Physiological

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3
Q

What is a rare example of a chemical interaction between two drugs?

A

Thiopental + Suxamethonium = Precipitate

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4
Q

What are the TWO potentially dangerous effects of drug interactions?

A
  1. Additive - Drug B BOOSTS Drug A effects
  2. Negating Effect - Drug B DECREASES Drug A effect
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5
Q

What is the equation for the Therapeutic Index for a drug?

A
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6
Q

What are the some pharmacodynamic considerations for drugs with NARROW therapeutic ranges?

A
  • Small REDUCTION in drug plasma -> Loss of efficacy
  • Small INCREASE in drug plasma -> Toxicity
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7
Q

What is a pharmacokinetic consideration if the concentration-response for a drug is STEEP?

A

Small change in drug plasma -> Big change in effect

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8
Q

Where do Pharmacodynamic Drug Interactions occur?

A

At the receptor

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9
Q

How is gastrointestinal absorption affected by drugs that inhibit gastric emptying?

A

Slowed absorption

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10
Q

How is gastrointestinal absorption affected by drugs that speed up gastric emptying?

A

Accelerated absorption

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11
Q

Which drug do Ca2+ and Fe2+ form insoluble complexes with in the GI tract?

A

Tetracycline

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12
Q

Which TWO drugs does Colestyramine (bile acid-binding resin) bind in the GI tract?

A

Warfarin and Digoxin

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13
Q

What effect does complex formation in the GI tract cause?

A
  • DECREASED drug absorbance
  • DECREASED drug plasma concentrations
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14
Q

What happens to the levels of free drugs in the plasma with concurrent administration of two drugs with high binding to plasma proteins?

A

INCREASED free drug levels for both drugs

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15
Q

What is Enzyme Induction?

A

Increase in enzyme activity caused by a foreign compound (inducer)

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16
Q

Does Enzyme Induction occur slowly or fast?

A

Slowly

17
Q

TRUE OR FALSE:
Enzyme Induction requires a single exposure to the inducer?

A

False.
Requires repeated / prolonged exposure

18
Q

What are the THREE roles of Enzyme Induction in drug interactions?

A
  1. Accelerates clearance
  2. Reduces drug action
  3. Increases formation of toxic metabolites
19
Q

What inducer enhances the metabolism of Barbiturates, Estradiol, Phenytoin, and Quinine?

A

Barbiturates

20
Q

What inducer enhances the metabolism of Dexamethasone, Digitoxin, and Theophylline?

A

Phenytoin

21
Q

What inducer enhances the metabolism of Anticoagulants, and Oral Contraceptives?

A

Rifampicin

22
Q

What is Enzyme Inhibition?

A

Decreased enzyme activity caused by a foreign compound

23
Q

Does Enzyme Inhibitions occur slowly or fast?

A

Fast

24
Q

What are the THREE roles of Enzyme Inhibition in drug interactions?

A
  1. Requires on a single dose
  2. Impairs drug clearance
  3. Prolongs drug action
25
Q

What inhibitor inhibits the metabolism of Diazepam and Warfarin?

A

Cimetidine

26
Q

What inhibitor inhibits the metabolism of Antipyrine, Ethanol, Phenytoin, and Warfarin?

A

Disulfiram

27
Q

What inhibitor inhibits the metabolism of Methanol?

A

Ethanol

28
Q

How does Hepatic blood flow affect the rate of drug metabolism?

A

Reduced hepatic blood flow = Reduced metabolism

29
Q

Which types of drugs are particularly susceptible to changes in hepatic blood flow?

A

First-Pass metabolism drugs

30
Q

What are the THREE main mechanisms of renal excretion?

A
  1. DECREASED protein binding would INCREASE filtration and elimination
  2. Inhibition of tubular secretion
  3. Alter urine flow and/or urine pH
31
Q
A