drug interactions Flashcards
What is a drug interaction?
An interaction is said to occur when the effects of one drug are changed by the presence of another drug, herbal medicine, food, drink or by some environmental chemical agent.
Definition adapted from Stockley’s Drug Interactions 8th Edition
What are the possible outcomes of a drug interaction?
- Harmful
- Loss of clinical effect
- Beneficial
Which patients are most at risk for drug interactions?
- The elderly
- Patients with hepatic or renal disease
- HIV patients
- Epileptics
- Diabetics
- ITU patients
- Transplant patients
- Patients with more than one prescriber
What are the two main types of mechanisms for drug interactions?
- Pharmacokinetic
- Pharmacodynamic
Fill in the blank: Pharmacokinetic refers to _______.
[what the body does to a drug]
What can affect drug absorption?
- Changes to gastric pH
- Adsorption, chelation, and other complexing
- Changes in gastrointestinal motility
- Drug transporter proteins
- Malabsorption
How does ciclosporin affect rosuvastatin?
Ciclosporin inhibits an organic anion-transporting polypeptide (OATP), decreasing the passage of rosuvastatin into the liver for metabolism, causing statin levels to rise.
What is enzyme induction in drug metabolism?
Enzyme induction is when some drugs induce their own metabolism or the metabolism of other drugs, which can take days to weeks to develop and may persist after the inducer has been stopped.
What are some examples of drugs that induce metabolism?
- Tobacco
- Rifampicin
What is enzyme inhibition in drug metabolism?
Enzyme inhibition is more common than induction and leads to the accumulation of the affected drug, resulting in rapid development of toxicity.
What role do genetic factors play in drug metabolism?
Some individuals may be poor or slow metabolizers, while others may be fast or extensive metabolizers, affecting how drugs are processed.
Fill in the blank: Changes to urinary pH can affect drug _______.
[excretion]
What are pharmacodynamic interactions?
Interactions between drugs that have similar or antagonistic pharmacological effects or side effects, which may occur due to competition at receptor sites.
What is a common example of a pharmacodynamic interaction?
NSAIDs cause fluid retention, which affects the action of diuretics.
What should be considered when dealing with drug interactions?
- Pharmacology of drugs
- Risk factors
- Medicines with a narrow therapeutic range (e.g., ciclosporin, lithium, phenytoin, warfarin, digoxin)
What is the first principle to remember when managing drug interactions?
Primum non nocere (first do no harm).
What is an example of a drug interaction involving erythromycin?
Erythromycin markedly increases simvastatin exposure, with several cases of rhabdomyolysis reported.
What is one solution to the interaction between simvastatin and erythromycin?
Stop using erythromycin.
What action should be taken after identifying a drug interaction?
Discuss with the prescriber and consider the patient’s condition.
What are the steps to take when managing a drug interaction?
- Identify the drugs
- Assess the seriousness of the interaction
- List possible solutions
- Consider potential consequences of solutions
- Determine preferred solution
- Take necessary actions following decision
