Pharmcokinetics Flashcards

1
Q

Drug efficacy is defined as

A

A drug in its therapeutic concentration.

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2
Q

Pharmacokinetics

A

Gets the drug there so pharmacodynamics (drug action) happens

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3
Q

Pharmacokinetics in Four easy Pieces

A
  1. Absorption
  2. Distribution
  3. Metabolism (drug molecule altered: activated/inactivated, made toxic or nontoxic).
  4. Elimination (broken down or excreted)
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4
Q

Non-absorption, why would you want this?

A

Drug given for localized effect, don’t want it to be absorbed.
May be well tolerated b/c it doesn’t have systemic effects
**GI infection drugs, skin and mucosal infections, lung infections (inhalants), or local anesthetics

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5
Q

Basic pharmacokinetic plot

A

X-axis is time
Y axis is [drug] (C) in blood (expressed as a log)
Absorption is the up slope: the appearance and increase of drug in blood

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6
Q

Factors that affect absorption:

A
  1. Drug Molecule
  2. Site of Administration
  3. Patient Factors
  4. Miscellaneous Factors
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7
Q

Chemical nature of the drug determines what?

A

Absorption, elimination, distribution, and metabolism.

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8
Q

Most important property of the drug:

A

Lipophilicity

  1. Lipophilic=fat-soluble=hydrophobic (goes better through cell membrane)
  2. Hydrophilic=water soluble=lipophobic
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9
Q

Lipophilic drug life cycle

A

Easily pass through cell membranes and tissue barriers.
Are generally more readily absorbed and better distributed throughout the body.
Generally must be metabolized before elimination by the kidneys.
***Easy in, easy around, hard out (stored in body fat)

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10
Q

Weak Acids/Weak Bases

A

60% of drugs

Can exist in either charged or uncharged forms.

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11
Q

Charged or uncharged weak acids/bases: What determines this?

A

The its pKa and the pH of the environment

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12
Q

Henderson-Hasselbach for weak acids/bases

A
  1. Weak acid: log HA/A-=pKa-pH
    weak acid @low pH=more unionized so more cross the barrier.
  2. Weak base: log H+A/A=pKa-pH
    weak base @high pH=more unionized so cross barrier
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13
Q

Example of a weak acid with a pKa of 7.3

A
  1. In breast milk (pH 6.3): log HA/A-=7.3-6.3=1
  2. Log 10^1 HA/A=10 parts HA (unionized), 1 part ionized
    Basically, a weak acid in a strong acid has more unionized, and vice versa.
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14
Q

Ion trapping

A

When drugs are charged they have difficulty passing through tissue barriers, they are trapped.
**Will be trapped in an environment opposite its pKa

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15
Q

Ion trapping of a weak acid

A

(Amphetamines)

Will be trapped in a basic environment.

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16
Q

Ion trapping of a weak base

A

(Barbituates)

Will be trapped in an acidic environment.

17
Q

Other properties of drugs that affect absorption

A
  1. Size: smaller drugs are more easily absorbed
  2. Formulation: more easily absorbed if they are easily dissolved
    Liquid suspensions more quickly absorbed, some are give in forms that delays or prolongs absorption (XR capsule
18
Q

Site of Absorption

A

Second most important determinant of absorption.
Tight junctions: skin, mucous membranes, sublingual, stomach (excludes better)
Open junctions: intestines, subcutaneous, intramuscular, intrapleural (absorbs better)

19
Q

Blood flow and surface area:

A

Higher the blood flow to absorptive site, the more quickly the drug gets absorbed.
Larger surface area=more rapid drug transfer (alveoli for example).