CHAPTER 10 – ADVERSE DRUG REACTIONS AND DRUG INTERACTIONS Flashcards
Mrs MH, an active 80-year-old lady, lives in a residential aged care facility and regularly enjoys bowls and social outings. She generally enjoys good health and for the last 5 years has taken warfarin for atrial fibrillation. Her INR has been checked regularly and usually is within the range of 2-3. Despite repeated tests over the last week the INR values reported have been 1. The dose was increased 3 days ago to 5mg/daily but the latest INR was 1.4.
Mrs MH, an active 80-year-old lady, lives in a residential aged care facility and regularly enjoys bowls and social outings. She generally enjoys good health and for the last 5 years has taken warfarin for atrial fibrillation. Her INR has been checked regularly and usually is within the range of 2-3. Despite repeated tests over the last week the INR values reported have been 1. The dose was increased 3 days ago to 5mg/daily but the latest INR was 1.4.
- Make a list of possible factors that may explain the low INR.
- Make a list of possible factors that may explain the low INR.
Possible factors that could be decreasing her INR could be:
• Other medications – oral contraceptives, hormone replacement therapy
• OTC drugs – vitamin K, nutritional supplements
• Certain food she may be ingesting- beef, pork, liver, green tea, soybeans
Mrs MH shows you her ‘warfarin book’ and the dated entries confirm she has recorded her dose and the time she took the drug. In further conversation with you she reluctantly admits that she may have done the wrong thing as she had bought some tablets from the health food store. She insists that they are harmless and are just a ‘little pick me up’ to help her not feel so sad after the death of her friend. She agrees to show you the tablets and you immediately recognise that she has bought St John’s wort and has been taking it for the last 3 weeks.
Mrs MH shows you her ‘warfarin book’ and the dated entries confirm she has recorded her dose and the time she took the drug. In further conversation with you she reluctantly admits that she may have done the wrong thing as she had bought some tablets from the health food store. She insists that they are harmless and are just a ‘little pick me up’ to help her not feel so sad after the death of her friend. She agrees to show you the tablets and you immediately recognise that she has bought St John’s wort and has been taking it for the last 3 weeks.
- Explain the mechanistic basis for the interaction between warfarin and St John’s wort
SJW reduces the anticoagulant effect
- Discuss the most appropriate course of action at this stage
Stop taking SJW and monitor closely INR levels to check if it rises. The dose of warfarin may need adjusting till it reaches normalised range ‘2-3’.
Arrange for alternative treatments such as counselling to aid in how she is feeling.
