Lecture 2 - Drug interactions Flashcards
What is a drug interaction?
The concurrent administration of other drugs that can alter the response to drugs.
Which populations are at increased risk of drug interactions?
- Elderly patients
- Patients with multiple prescribers
- Patients with chronic illnesses
- Obese patients
- Malnourished patients
- Critically ill patients
- Patients with autoimmune disorders
- Transplant recipients
What are the two general mechanisms by which drugs may interact?
- Pharmacodynamic interaction
- Pharmacokinetic interaction
Fill in the blank: The administration of one drug can alter the action of another by modifying the _______ effect.
[pharmacological]
What can be the consequences of drug interactions?
- No untoward effects
- Severe morbidity
- Death
- Increased medical-legal liability
- Increased healthcare costs
What characterizes a drug with a narrow therapeutic range?
A small reduction in effect will lead to loss of efficacy and/or a small increase in effect will lead to toxicity.
True or False: All drug interactions involve pharmacokinetic processes.
False
What are pharmacodynamic interactions?
Interactions where two drugs produce additive, antagonistic, or synergistic responses.
Give an example of a synergistic drug interaction.
Nitrates plus sildenafil or sulfonamides plus trimethoprim.
What is an antagonistic interaction?
When one drug decreases the potency of another drug by competing with its receptor or producing a blunting effect.
What is a common risk factor for drug interactions?
Use of multiple prescribers and/or multiple pharmacies.
What are the four major processes that determine pharmacokinetics?
- Absorption
- Distribution
- Metabolism
- Excretion
Fill in the blank: Altered gastric pH can affect the absorption of drugs that require an _______ environment.
[acidic]
What is complexation or chelation in drug interactions?
When agents form chemical complexes with drugs, causing lower rates of drug absorption.
How can altered gastrointestinal motility affect drug absorption?
Slowed motility may enhance absorption, while increased motility may decrease absorption.
What role do gut flora play in drug metabolism?
Gut flora metabolize some drugs, and antibiotics can disrupt this process, leading to increased drug concentrations.
What two types of transport proteins are present in the intestinal mucosa?
- Transport proteins for absorption into the bloodstream
- Efflux transporters
What is the effect of drug-induced mucosal damage on drug absorption?
It can increase absorption of other drugs.
What can cause a decrease in blood supply affecting drug absorption?
Vasoconstriction, such as when adrenaline is added to local anaesthetic injections.
What is the main mechanism for drug interactions at the distribution stage?
Displacement of a drug from protein-binding sites.
What are the two main types of hepatic drug metabolism?
- Phase I reactions
- Phase II reactions
What is the role of the cytochrome P-450 (CYP) system?
It mediates phase I oxidative reactions in drug biotransformation.
What is the main organ for drug metabolism?
Liver
Other organs involved include GIT, skin, lung, and WBCs.
What are the two main types of hepatic drug metabolism?
Phase I and Phase II reactions.
