Drug Interactions Flashcards
Define the Object Drug?
The drug whose activity is effected by an interaction
Define the precipitant?
The agent which precipitates a drug interaction
Give a case of a drug interactions that isn’t detrimental?
Parkinsonism is treated wiht levodopa & carbidopa.
The carbidopa prevents the 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
- Concomitant Disease
- Genetic Polymorphisms
List the drug specific risk factors:
- Polypharmacy
- Narrow Therapeutic Range
- HIgh Doses
What other risk factors are there for drug interactions? [non drug or patient specific]
- Multiple Prescribing physicians
- Self-Prescription (both naughty doctors & 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
- are elderly
- are young
- Critically Ill
- Liver or renal impairment
- Epileptic
- Asthmatic
- Diabetes Mellitus (diabetic)
AEDtic
What are the characteristics of drugs involved in serious interactions?
- Steep Dose-Response Curves
- Narrow Therapeutic Indexs
- Very high protein binding
- Can Alter Renal Clearence
- Induce/inhibit hepatic enzyme
Name some foods that can interact with drugs?
- Veg (Boccoli, spinach, cabbage)
- Herbals (ginseng, Green Tea)
- ‘Misc’ (avocado, fish oil)
What are the 3 types of mechanisms for drug interactions?
Pharmacokinetic Interactions
Pharmaceutical
Pharmacodynamic
What are pharmaceutical interactions?
Those involving mixing two drugs in the same solution
What is a pharmacodynamic interaction?
Pharmacodynamic interactions are where one drug alters anothers 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?
In direct interactions one drug alters the others effect directly by actin on hte same receptor.
In indirect interactions they act on different receptors.
How do synergistic interactions occur?
2 drugs with the same pharmacological effect acting on the same receptor are given concurrently
What are the 4 areas affected by pharmacokinetic drug interactions?
Absorption
Distribution
Metabolism
Elimination/Excretion
How do drug interactions affect absorption rates?
- They can form insoluble complexes (erythromicin & iron)
- Alter pH causing another drug to ionise
- Drugs can effect GIT motility
- One drug can alter bacterial flora
How do drug interactions affect drug distribution?
One drug can displace a plasma protein-bound drug possibly causing a massive change in its bioavailability
What normally protects pateints from protin-binding displacement interactions?
Metabolism & excretion
How do drug interactions affect metabolism rates?
- Inhibit the cytochrome P450 system in the liver
- Induces liver enzyme activity (takes 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
