Download Pharmacokinetics

PHARMACOKINETICS
ABSORPTION→DISTRIBUTION→METABOLISM→EXCRETION
Chapter 26 – Fundamentals
NUR 152
Denise Turner, MS-N.Ed, CCRN, RN

Overview of the principles of pharmacotherapy

Pharmacodynamics/pharmacokinetics

Discuss half life and therapeutic levels

Types of medication effects
OBJECTIVES
• Pharmaceutical Factors
– Rate of dissolution
– Lipid/water solubility
- pH
– Route
• Clinician/Patient Factors
– Blood flow
– Route
– Competition
ABSORPTION
PG 609/614
FIGURE 26-3

Elevation of gastric pH (makes it more alkaline) by antacids –
Increases the absorbance of basic drugs; decreases that of
acidic drugs

• Laxatives – Increase peristalsis and decrease GI transit time
PHARMACOKINETIC EFFECTS ON
ABSORPTION

Blood Flow – Target organ/area

Protein binding

Free drugs-body can use the “free or unbound” drug
DISTRIBUTION (TRANSPORTATION)
PG 614

Remaining unbound drug is chemically inactivated, broken into
metabolites and excreted once it reaches its target organ and is
finished doing its job

First Pass Effect:

Effectively, the drug has been metabolized before it ever reaches
the systemic circulation and/or its target organ
METABOLISM-BIOTRANSFORMATION
PG 615

In order for a drug to “stop” performing its actions it must be
excreted. Metabolism is the start of this process (which is
dependent on “functioning” organs of metabolism).

Liver, lungs, kidneys, GI tract
EXCRETION
PG 615

Decreased function in any of the areas of excretion can cause
delays:


Renal disease

Dehydration/decreased fluid intake

Increased creatinine
Liver/GI tract disorders/probs

Increased peristalsis = ↑

Decreased peristalsis


Decreased activity, diet = ↑
Lungs disorders/probs
EXCRETION DELAYS
The client has been on a low-protein diet. This will most likely affect
which pharmacokinetic process?
a.
Absorption
b.
Excretion
c.
Distribution
d.
Metabolism
CLICKERCHECK
Correct answer: C
A low-protein diet may lead to an inadequate level of plasma
proteins, which will affect availability of “free” drug.
CLICKERCHECK (CONT’D)
The nurse is having difficulty deciphering the medication prescription written by
the provider. What is the best strategy to clarify the information?
a.
Ask the patient what medication the provider prescribed.
b.
Call the pharmacist and ask him or her to read
the prescription.
c.
Ask the nurse who knows the provider’s handwriting to read the
prescription.
d.
Call the provider and ask him or her to clarify
the prescription.
CLICKERCHECK
Correct answer: D
All other answers increase the risk of a medication error.
CLICKERCHECK (CONT’D)
When administering a drug via a parenteral route, the drug would
be absorbed fastest if given per the IM route.
a.
True
b.
False
CLICKERCHECK
Correct answer: B
Absorption refers to the “movement” of the drug from the site of
administration into the bloodstream. Therefore, the IV, parenteral
route leads to “instant” absorption.
CLICKERCHECK (CONT’D)
PHARMACODYNAMICS
Pg 618

Onset, peak, and duration of action

Agonists and antagonists
Two Drug Agonists Attach to the Receptor Site.
The drug agonist that has an exact fit is a strong agonist and is more
biologically active than the weak agonist.

Therapeutic Effects



The desired effect we are expecting
Side Effects

Unintended but we are aware they can happen

If the S/E is pronounced we will stop or decrease the dose
Adverse Reactions:

Harmful, not expected and unpredictable

Usually end up stopping the medication

Depending on reaction, may require contacting the FDA and filing a
report
PG 619

Toxic reactions:



Must monitor therapeutic levels on some medications

Nurses need to know what s/s of toxicity are for particular medications
Allergic reactions:


Blood levels are too high or not therapeutic
Rash, anaphylaxis
Idiosyncratic:

Abnormal or odd response


Sensitivity or an opposite effect of the therapeutic response expected.
Cumulative effects:

Client may not be able to metabolize or excrete a medication effectively with
end result of too much medication in their system or toxicity.