Pharmacokinetics and Pharmacodynamics in Older Adults

What type of response can occur when two drugs interact pharmacodynamically?

Which of the following is most likely to inhibit GI absorption of other drugs?

How might drug competition for binding sites affect therapeutic outcomes?

What is a characteristic of enzyme inducers in drug metabolism?

Which of the following drugs is known as an enzyme inhibitor affecting drug metabolism?

What complicates metabolism in older patients receiving multiple medications?

Which scenario illustrates a drug interaction that can lead to significant adverse effects due to competitive binding?

What characteristic of a drug would make it more vulnerable to adverse effects when displaced from protein binding sites?

Which cytotoxicity risk is associated with concurrent use of drugs metabolized by P450 3A4?

What effect do substances like cholestyramine have on drug absorption?

Pharmacodynamics in Older Persons

Responses to drugs can be additive (enhancing effects) or antagonistic (reducing effects).
Therapeutic uses include antihypertensives, cancer chemotherapy, and pain management.
Harmful effects may occur in patients taking multiple drugs with anticholinergic properties.

Pharmacokinetics in Older Persons

Absorption

Gastrointestinal (GI) absorption can be inhibited by:
- Medications with large surface area, such as antacids.
- Binding resins like cholestyramine.
- Drugs affecting GI motility.
- Agents altering GI pH (e.g., antacids, iron, kaolin-pectin).

Distribution

Drugs may compete for binding sites on proteins and tissues, impacting pharmacokinetics for several days.
Clinically significant displacement occurs when:
- The displaced drug has high protein binding.
- It has a limited volume of distribution (VoD).
- Elimination is slow.
- It possesses a low therapeutic index.
Example: Phenylbutazone can dramatically displace warfarin from protein binding sites, enhancing bleeding risk.

Metabolism

Drug metabolism can be altered by concurrent medication administration leading to varying effects:
- Enzyme inducers, like Barbiturates, Carbamazepine, and Phenytoin, may enhance metabolism (effects evident in 1-3 weeks).
- Enzyme inhibitors (primarily affecting P450 3A4) can lead to increased drug concentration and possible toxicity. Common inhibitors include:
  - Amiodarone, fluoxetine, cimetidine, erythromycin, and others.
Inhibition of drug metabolism typically begins rapidly and reaches maximum effect by the time steady-state concentrations are achieved.

Explore the critical concepts of pharmacokinetics and pharmacodynamics specifically tailored for older persons. This quiz covers therapeutic effects, harmful interactions, and absorption challenges related to medications in this population. Test your knowledge on how aging influences drug efficacy and safety.