Core Concepts in Pharmacology

Chapter 5Pharmacokinetics

Therapeutic effect and target cells

• What is the relationship between therapeutic effect and target cells?

• What is the greatest barrier to achieving the therapeutic effect?

• What physiologic processes hinder the achievement of therapeutic effects?

Substance Passage Through Plasma Membranes

• What role does diffusion play in achieving the therapeutic effect?

• Compare and contrast the two processes involved in diffusion.

Four Components of Pharmacokinetics

• Absorption• Distribution• Metabolism • Excretion

What do you remember about these processes?

What do you think?

• What other organs are involved in excretion?

• What effect will liver or kidney impairment have on the pharmacokinetics of medication.

• What are the implications for the prescriber?

• What are the implications for the nurse administering the prescribed drugs?

First Pass Effect

• Figure 5.4

What is the problem with the first pass effect?

What can be done to bypass the first pass effect?

Plasma Proteins and Drug Distribution

• Drugs bind with plasma proteins– Drug protein complexes– Capillary membranes impermeable– Drug does not reach target cells

• Drugs and other agents compete for plasma proteins– Affinity– Increasing blood levels• Toxicity

Therapeutic response and plasma drug level

• Direct relationship

• What nursing responsibility is essential when administering drugs with low safety profiles?

• Define:– Minimum effective concentration– Toxic concentration– Therapeutic range

Achieving and Maintaining Therapeutic Concentrations

• Repeated dose scheduling• Drug accumulates in blood stream• Plateau reached• Amount administered = amount excreted

Differentiate between Loading Dose and Maintenance Dose

• Loading Dose– Higher amount of given

drug

What is the benefit to administering a loading dose?

• Maintenance Dose– Doses administered at

intermittent (scheduled) times

What is the purpose of maintenance doses?

Plasma half-life (t ½)

• Describes drugs duration of action

• Describe h0w the frequency of dosing differs depending upon the drugs half-life.

• How does renal or liver disease affect drug half-life?

Application problem

• ciprofloxacin hydrocholride (Cipro) has a half-life of 4 hours.

• You administer a 500 mg oral dose of ciprofloxacin. How long will it take to have less than 1o mg of that dose circulating?