Drug Interactions Flashcards
Define the Object Drug?
Risk of drug-drug interaction increases with number of drugs used
The drug whose activity is effected by interactions is the Object Drug
Define the precipitant?
The agent which precipitates a drug interaction
Modifies object drugs ADME
Give a case of a drug interactions that isn’t detrimental?
Parkinsonism is treated with levodopa & carbidopa.
Carbidopa prevents systemic side effects of levodopa
What are the 5 types of drug interaction?
Drug
Herbal
Food/Drink
Pharmacogenetic
List the patient specific risk factors for drug interaction:
Old Age
Multiple different illness at same time
Genetic Polymorphisms
List the drug specific risk factors:
Polypharmacy (use of multiple drugs)
Narrow Therapeutic Range
High Doses
What other risk factors are there for drug interactions? [non drug or patient specific]
Multiple Prescribing physicians
Self-Prescription (over counter drugs)
Prolonged stays in hospital
Patients with what characteristics are most susceptible to severe (life threatening) drug interactions?
many meds
undergoing complex surgery
elderly/young
Critically Ill
Liver/renal impairment
Epileptic
Asthmatic
Diabetes Mellitus (diabetic)
What are the characteristics of drugs involved in serious interactions?
Steep Dose-Response Curves
Narrow Therapeutic Index
Very high protein binding
Can Alter Renal Clearance
Induce/inhibit hepatic enzyme
What are the 3 types of mechanisms for drug interactions?
Pharmacokinetic Interactions
Pharmaceutical
Pharmacodynamic
What are pharmaceutical interactions?
Involving mixing two drugs in the same solution
What is a pharmacodynamic interaction?
One drug alters another’s effect at its site of action
What are the subtypes of pharmacodynamic interaction?
Additive/Synergistic or antagonistic
Direct or indirect
Whats the difference between direct & indirect pharamcodynamic interactions?
Direct - one drug alters others effect directly by acting on the same receptor
Indirect - act on different receptors
How do synergistic interactions occur?
2 drugs acting on the same receptor with the same pharmacological effect are given at the same time
How do drug interactions affect absorption rates?
Form insoluble complexes (erythromicin & iron)
Alter pH causing another drug to ionise
Effect GUT motility
Alter bacterial flora
How do drug interactions affect drug distribution?
One drug can displace a plasma protein-bound drug and change its bioavailability
What normally protects patients from protein-binding displacement interactions?
Metabolism & excretion
How do drug interactions affect metabolism rates?
Inhibit cytochrome P450 system in liver
Induces liver enzyme activity (weeks to build up)
How do drug interactions affect elimination?
Some drugs affect Glomerular Filtration Rate or tubular secretion
What do loop diuretics do?
Loop Diuretics increase tubular reabsorbtion
