Vadher et al developed an algorithm for managing patients receiving oral anticoagulants. It used the target and current INR to adjust dosage and for scheduling the next appointment for followup care. The authors are from the Whittington Hospital Highgate Hill in London.
V =
= (target INR value) – (current INR value)
The authors used the absolute value for V to determine the magnitude of change, and the sign to determine the type of change. A negative V was associated with the need to decrease the dose, while a positive V indicated the need to increase the dose.
If a person had a history of alcohol abuse or poor compliance, then the suggested interval for the next appointment was reduced by one level (page 340).
INR 2.0 to 3.0
target INR value = 3.0 according to paper (see Note)
NOTE: I used 2.5 for the spreadsheet. I did this for several reasons:
(1) The target INR for range 3.0 to 4.5 is 3.8, which is the midpoint of the range.
(2) When I tested the spreadsheet with a target of 3.0, you could have an INR of 3.69 before your reduced the dose.
(3) An INR of 1.5, which one would expect to be encountered with some frequency, required direct physician intervention even though it was only 0.5 INR from the lower end of the intended range.
|
V value |
dosage change in mg/day |
|
-1.15 to –0.92 |
-1.0 mg/day |
|
-0.91 to –0.70 |
-0.5 mg/day |
|
-0.69 to 0.69 |
no change |
|
0.70 to 0.91 |
+0.5 mg/day |
|
0.92 to 1.15 |
+1.0 mg/day |
|
V value |
next visit |
|
> 1.15 |
see doctor |
|
0.91 to 1.15 |
1 week |
|
0.66 to 0.90 |
2 weeks |
|
0.46 to 0.65 |
4 weeks |
|
0.45 to –0.45 |
8 weeks |
|
-0.46 to -0.65 |
4 weeks |
|
-0.66 to -0.90 |
2 weeks |
|
-0.91 to -1.15 |
1 week |
|
< -1.15 |
see doctor |
INR 3.0 to 4.5
target INR value = 3.8
|
V value |
dosage change in mg/day |
|
-1.45 to –1.12 |
-1.0 mg/day |
|
-1.11 to –0.70 |
-0.5 mg/day |
|
-0.69 to 0.69 |
no change |
|
0.70 to 1.11 |
+0.5 mg/day |
|
1.12 to 1.45 |
+1.0 mg/day |
|
V value |
next visit |
|
> 1.45 |
see doctor |
|
0.91 to 1.45 |
1 week |
|
0.66 to 0.90 |
2 weeks |
|
0.56 to 0.65 |
4 weeks |
|
0.55 to –0.55 |
8 weeks |
|
-0.56 to -0.65 |
4 weeks |
|
-0.66 to -0.90 |
2 weeks |
|
-0.91 to -1.45 |
1 week |
|
< -1.45 |
see doctor |
Performance:
• The algorithm performed better than inexperienced clinicians.
• The algorithm performed as well as experienced clinicians if a case was not complicated.
• For complicated cases an experience clinician would need to be consulted.
Specialty: Hematology Oncology, Clinical Laboratory, Pharmacology, clinical
ICD-10: ,
