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Basic Pharmacology Principles > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Define Volume of Distribution (Vd)

Is it a physiologic value?

Is Vd an absolute value for any given drug?

A

The apparent volume in the body available to contain the drug

Vd=_             Dose          _   =         _      LD    _

       Plasma [Drug]                    Css

No

No

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2
Q

Define Clearance (Cl)

A

Cl- Volume of blood cleared of the drug per unit time;

Cl= rate of elimination of drug

            plasma [drug]

Total Body Cl= Clhepatic + Clrenal +Clpulmonary +ClOther

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3
Q

Define Half-life (t1/2)

A

Time required for plasma [drug] to decreased by one-half after absorption & distribution are complete

t1/2= .693 * Vd

 Cl
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4
Q

Define Steady State CSS

A

Steady state is reached when the rate of drug influx into the body= the rate of drug elimination out of the body

CSS= plasma concentration of drug at steady state

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5
Q

How much of a drug is left after 2 half-lives?

A

25%

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6
Q

How much of a drug is left after 3 half-lives?

A

12.5%

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7
Q

During constant infusion, what percent of steady state is reach after:

1 half-life?

2 half-lives?

3 half-lives?

4 half-lives?

A

1 half life= 50%Css

2 Half lives= 75% Css

3 Half Lives= 87.5% Css

4 Half Lives= 94% Css

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8
Q

Equation of Infusion Rate (ko)

A

ko= Cl x Css

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9
Q

Loading Dose (LD) equation

A

LD= Vd x Css

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10
Q

Maintenance Dose (MD) Equation

A

MD= Cl x Css x dosing interval

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11
Q

Clearance (Cl) Equation

A

Cl= K x Vd

K= the elimination constant

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12
Q

What happens to the steady state concentration of a drug if the infusion rate is doubled?

A

Steady State Concentration is also doubled

Remember that dose & concentration are directly proportional (linear kinetics)

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13
Q

If there is no active secretion or reabsorption, then renal clearance (Clrenal) is equal to what?

A

Glomerular Filtration Rate (GFR)

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14
Q

If a drug is protein bound, then Clrenal is equal to what?

A

GFR x free fraction (of drug)

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15
Q

What happens to the LD in patients with impaired renal or hepatic function?

A

Stays the same

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16
Q

What happens to the MD in pts with impaired renal or hepatic function?

A

Decreases

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17
Q

Rate of elimination is CONSTANT, regardless of concentration

A

Zero-order elimination

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18
Q

Plasma concentration decreases exponentially with time

A

First-Order Elimination

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19
Q

Rate of elimination is proportional to the drug concentration

A

First-Order Elimination

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20
Q

Plasma concentration decreases linearly with time

A

Zero-Order Elimination

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21
Q

Rate of Elimination is dependent on concentration

A

First-order elimination

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22
Q

Drugs that undergo zero-order elimination?

A

Acetylsalicyclic Acid (ASA) at high/toxic concentrations

Phenytoin

Ethanol

23
Q

Describe Phase I Metabolism

A

Metabolism that generally yeilds more polar, water solubule metabolites (may still be active)

Enzyme activity DECREASES with pt’s age

24
Q

Describe Phase II Metabolism

A

Metabolism that generally yields VERY polar, INACTIVE metabolites (renally excreted)

Enzyme Activity does NOT decrease with pt’s age

25
Q

Phase I (microsomal) metabolism involves what types of reactions?

A

Oxidation

Reduction

Hydrolysis

all carried out by cytochrome P-450 enzymes

26
Q

Phase II (nonmicrosomal) metabolism involves what types of reactions?

A

Glucuronidation

Acetylation

Sulfation

Amidation

Glutathione Conjugation

27
Q

Give examples of drugs that undergo phase II metabolism:

A

Isoniazid (INH)

Morphine

6-MP

Acetaminophen

28
Q

What are the potential consequences of phase I oxiation rxns with regard to drug activity & elimination?

A

Drug activity may or may not change (no rule, ie potentially dangerous outcome)

Drug elimination is usually increased due to greater water solubility

29
Q

What are the potential consequences of phase II rxns with regard to drug activity & elimination?

A

Drug products of phase II rxns are usually inactive & their renal elimination is enhanced

30
Q

Where are cyt P-450 enzymes found?

A

Smooth ER of cells

mainly in liver, but also in the GI tract, kidney, & lungs

31
Q

Phase 1 in clinical drug development tries to accomplish what?

A

Safety in HEALTHY individuals

drug pharmacokinetics

32
Q

What is Phase II with respect to clinical development of a drug?

A

Efficacy in DISEASED individuals

SMALL-scale trials

single-double-blind

33
Q

What is phase III in clinical drug development?

A

Efficacy in DISEASED individuals

small scale trials

single OR double blind

34
Q

What is phase IV in clinical drug development?

A

Postmarketing surveillance (monitored release)

35
Q

What is the first-pass effect?

A

After oral administration, many drugs are absorbed intact from the small intestine & transported first to the liver via the portal system

In the liver they undergo extensive metabolism, therefore usually decreasing the bioavailability of certain oral medications

36
Q

What is the most common plasma protein that drugs bind to?

A

Albumin

37
Q

Displacing a drug that is bound to plasma proteins will increase its what?

A

Its free fraction (therefore may possibly increase the risk of toxicty bc the plasma concentration of active drug has been increased)

However, depending on the drug, an increase in free fraction may actually increase its metabolism bc more drug is available to metabolizing enzymes

38
Q

What is the mechanism of passive diffusion?

A

No energy required

No carrier

Not saturable (proportional to concentration gradient)

39
Q

Mechanism of Facilitated Diffusion?

A

No energy required

CARRIER REQUIRED

SATURABLE

40
Q

Mechanism of Active Transport?

A

Against concentration/electrical gradient

Energy required

Carrier required

Saturable

41
Q

Permeation of drugs across cellular membranes is dependent on what?

A

Drug Properties:

  • Drug Solubility
  • Drug concentration
  • Drug ionization

Local Properties:

  • Surface Area
  • Vascularity
42
Q

ACIDIFICATION of urine will increase renal elimination of what types of drugs?

A

WEAK BASES (ionized form of drug, BH+) will be trapped in the renal tubules & excreted in the urine

43
Q

Acidification of urine will decrease renal elmination of what types of drugs?

A

Weak Acids (nonionized, HA form of drug) can cross membranes

44
Q

Alkalinization of the urine will increase renal elmination of what types of drugs?

A

Weak ACIDS (ionized, A- form of drug) will be trapped in the renal tubules & excreted in the urine

45
Q

Alkalinization of urine will decrease renal elmination of what types of drugs?

A

Weak Bases (nonionized, B form of a drug) can cross membranes

46
Q

What agents are used to acidify urine?

A
  • NH4Cl (Ammonium Cloride)
  • HIGH dose of vitamin C
47
Q

What agents are used to alkalinize urine?

A
  • NaHCO3 (Sodium Bicarbonate)
  • ACETAZOLAMIDE
48
Q

Example of a weakly acidic drug?

A

ASA

Barbiturates

49
Q

Example of a weakly basic drug?

A

Amphetamines

50
Q

Inducers of cyt P-450 enzymes

A
  • Phenytoin
  • Carbamazepine
  • Griseofulvin
  • Barbiturates
  • Chronic Alcohol Use
  • St. John’s Wart
  • Rifampin
51
Q

Inhibitors of cyt P-450 enzymes

A
  • Quinidine= Queen Dining
  • Ciprofloxacin= Sip Rope Sippy cup
  • Isoniazid= Ice knight w a zit squeezing grapefuit
  • Grapefruit Juice
  • Acute Alcohol Use
  • Erythromycin (Macrolides)= Earth throwing mice
  • Macrolides
  • Amiodarone
  • Ritonavir
  • Ketoconazole
  • Sulfonamides
  • Gemfibrozil
52
Q

What tpe of elimination involves a CONSTANT FRACTION of drug eliminated per unit time?

A

First-Order Elimination

53
Q

What type of elimination involves a constant AMOUNT of drug eliminated per unit time?

A

Zero-Order Elimination

Basic Pharmacology Principles (1 decks)

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