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NURP 424 Adv Pharm > Week 2: Pharmacokinetics > Flashcards

Week 2: Pharmacokinetics Flashcards

1
Q

What is pharmacokinetics?

A

What the body does to the drug

  • absorption
  • distribution
  • metabolism
  • excretion
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2
Q

What is absorption

A

The rate at which a drug leaves the site of administration and passes into systemic circulation

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3
Q

What is distribution

A

The transport of drugs in body fluids from the site of absorption to the receptor site on the cell, a storage site, and the elimination site

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4
Q

How is the drug broken down after distribution?

A

Metabolism - the drug may be biotransformed through metabolism by the liver or the tissues

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5
Q

How does the drug leave the body?

A

Excretion - the drug and its metabolites are eliminated from the body in urine, bile, or feces

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6
Q

What are some factors that can impact pharmacokinetics

A

Age, preganancy, hepatic or renal disease, drug interactions, ethnicity, the rate of metabolism, GI surgeries, nutritional status

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7
Q

Factors that can affect bioavailability of a drug

A
  • how a drug is transported across the membrane
  • how a drug interacts with the gastric acid and enzymes in the GI tract
  • drug formulations - particle size, the salt form, the crystal polymorphisms, enteric coatings, what binders were used by the manufacturer - influences how a drug dissolves in the system
  • *#1 factor that affects bioavailability of a drug - route of administration**
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8
Q

The rate at which the drug leaves the site(s) of administration and passes into systemic circulation

A

absorption

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9
Q

What is bioavailability?

A

measure of how much of the drug gets absorbed and into systemic circulation (blood)
F value = fraction of unchanged drug that reaches systemic circulation
F value = 0.25 this means that 1/4 of the dose get to systemic circulation

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10
Q

3 factors that increase absorption and distribution of a drug

A

1) Lipophilic
2) Low protein binding
3) Low molecular weight

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11
Q

3 factors that decrease absorption and distribution of a drug

A

1) Hydrophilic
2) High protein binding
3) High molecular weight

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12
Q

A molecule that is un-ionized, uncharged, non-polar is considered:

A

lipophilic - are more lipid soluble allowing for increased absorption

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13
Q

A molecule that is ionized, charged, polar is considered:

A

hydrophilic

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14
Q

Where is a basic drug absorbed?

A

In the more basic environment of the small intestines

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15
Q

Where is an acidic drug absorbed?

A

In the more acidic environment of the stomach

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16
Q

What is the first pass effect?

A

Drugs taken orally are absorbed and goes into portal circulation/liver where is may be extensively metabolized before reaching systemic circulation - decreased the bioavailability of oral drugs - limits the efficacy of many oral medications

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17
Q

What affects distribution of a drug?

A
  • cardiac output & local blood flow
  • capillary permeability
  • Tissue volume
  • amount of the drug that become bound to plasma and tissue proteins
  • relative lipophilicity of the drug
18
Q

What is Volume of Distribution (Vd)?

A

The measure of the apparent space in the body available to contain the drug - theoretical - lipophilic drugs will have a larger Vd (larger concentration in the tissues) - hydrophilic drugs will have a smaller Vd (higher concentration in the plasma because it cannot pass as readily into the tissues/cells)

19
Q

Properties affecting distribution

A
  • molecular size (large MW - lower distribution; small MW - greater distribution)
  • Lipid solubility
  • pH of the environment - acidic stays ionized in a basic environment - basic stays ionized in an acidic environment
  • Ionization - polar molecules are hydrophilic
  • Protein binding - albumin - drug bound to protein is inactive - only unbound drug is active and can exert an effect
20
Q

Your patient has had HTN for 5 years and has been taking an anti-hypertensive that is 90% protein bound since his diagnosis without any ADR. Recently, he was diagnosed with a DVT and started on Warfarin which is 99% protein bound. What will happen to his blood pressure?

A

Because Warfarin has a higher affinity to be bound to protein, more of the free antihypertensive medication in the plasma causing the patient’s blood pressure to drop significantly. (went from 10% free HTN medication to 99% free HTN medication)

21
Q

What enzymes are responsible for Phase 1 drug metabolism?

A

CYP450 (cytochrome P450)

22
Q

What is happening during Phase 1 of drug metabolism?

A

Oxidation (lose an electron), reduction (gain an electron), and hydrolysis (making something hydrophilic more hydrophilic) - oxidation is the most common enzyme reaction in Phase 1

23
Q

What do oxidation, reduction and hydrolysis do to a drug?

A

prepares the drug for further metabolism by making it more polar - this can increase or decrease the pharmacologic activity of a drug

24
Q

What P450 enzyme is responsible for metabolizing close to 50% of drugs?

A

CYP3A4

25
Q

Phase 1 enzymes are responsible for:

A
  • CYP 450 enzyme Induction/Inhibition
  • oxidation, reduction, hydrolysis
  • making drug more polar for further metabolism
26
Q

What is a prodrug?

A

An inactive drug that must go metabolism in order to be activated - examples: Codeine and Plavix

27
Q

If a drug is a CYP 450 inducer, what could it do to another drug that is also processed by the same enzyme?

A

the inducing drug causes an increase in the rate of metabolism of the first drug, causing the first drug to be less effective

28
Q

If a drug is a CYP 450 inhibitor, what could it do to another drug that is also processed by the same enzyme?

A

The inhibiting drug causes a decrease in the rate of metabolism of the first drug, causing an increase in the concentration of the first drug in the blood because it is not being metabolized as quickly - causes the first drug to hang around longer in systemic circulation

29
Q

Your patient is taking an ace inhibitor which is a CYP3A4 substrate. She volunteers at a homeless shelter and recently contracted TB from working there. She was started on Ryfampin which is a CYP450 inducer. What will this drug-to-drug interaction cause to happen?

A

The metabolism of the ace inhibitor will be increased, which will cause it to be used up more quickly and will have decreased effectiveness, causing the patient’s blood pressure to go up (LESS DRUG=LESS EFFECTIVE)

30
Q

Your patient is currently taking an antihypertensive medication that is a CYP3A4 substrate. He goes to the gym and gets a severe case of athlete’s foot. He is prescribed Econazole which is an CPY3A4 inhibitor. What will this drug-to-drug interaction cause to happen?

A

The metabolism of the antihypertensive will be decreased which will cause an increase in the concentration of free antihypertensive medication in the bloodstream leading to a potentially significant drop in the patient’s blood pressure or hypotension. (MORE DRUG=MORE EFFECTIVE)

31
Q

What happens during Phase II of drug metabolism?

A

a conjugation reaction in which something is added to the drug to synthesize it into a new compound which will make it easier to excrete.

32
Q

The proximal tubule of the kidney is the site of elimination for:

A

Drugs with low molecular weight including conjugated metabolites, many of which are produced by phase 1 and phase 2 metabolism in the liver

33
Q

What types of drugs are reabsorbed in the kidneys back into the blood stream?

A

Lipophilic drugs

34
Q

You are working in the ER and a patient presents with a heroin overdose. Heroin is an acidic drug. What medication can be given in order to trap the heroin in the urine causing increase excretion?

A

Sodium bicarbonate - causes the urine to become more basic which traps acidic molecules of heroin in the urine. (ION TRAPPING)

35
Q

What medication can be given when you have a patient who has overdosed on a basic drug which causes the urine to be more acidic leading to increased excretion of the drug in the urine?

A

Ammonium chloride

36
Q

What things do you need to know about your patient in order to figure their creatinine clearance?

A

Weight in kg
sex
age
serum creatinine level

37
Q

The time it takes the peak drug level in the bloodstream to drop by half is known as the drug’s:

A

Half life

38
Q

At what level of creatinine clearance should you start thinking about the need for dosage adjustments because of decreased kidney function?

A

Less than 50mL/min - at or less than 30mL/min would definitely need dosage adjustment or possibly not giving that drug

39
Q

What is steady state?

A

steady state is reached when the rate of drug elimination is equal to the rate of drug administration such that plasma and tissue levels remain relatively constant

40
Q

How many half lives does it take to reach steady state?

A

4 to 5

41
Q

What can be done in order to reach steady state faster?

A

Give a loading lose (ex.: Z-pack - 500mg on day 1 and then 250mg on days 2-5)

NURP 424 Adv Pharm (63 decks)

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