Overview:

Vadher, Patterson and Leaning developed a computerized algorithm for managing patients receiving oral anticoagulants. This routine is for maintenance dosing (not loading) and used the target and current INR to adjust dosage and also to adjust when the next appointment for follow-up care should occur (values that we well below or well above target levels trigger an immediate healthcare provider visit).

The user of this algorithm must select the following:

1. Target INR Value

• 2.0-3.0
• 3.0-4.5

2. Measured INR Value

3. History of alcohol abuse or poor compliance (Yes/No)

Details of the calculation and algorithm:

The calculation is that of a 'V' value, which is:

V = (target INR value)-(current INR value)

• A negative V = Decrease the dose
• A positive V = Increase the dose
• Magnitude of V is degree to which dosing needs to be adjusted

-This routine will select a target INR of 2.5 when the user selects 2.0-3.0 for target and 3.75 when the user select 3.0-4.5 as the target.

-The difference between the target and the actual measured value will determine any recommended dose change

-In the case of alcohol abuse or poor compliance, follow-up visit will be moved to one interval closer

Goal INR 2.0-3.0

• V Value ==> Dose Change (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 or <-1.15   See healthcare provider now
• 0.91-1.15 (or -)   ==> 1 week
• 0.66-0.90 (or -)   ==> 2 weeks
• 0.46-0.65 (or -) ==> 4 weeks
• 0.45 to -0.45 ==> 8 weeks

Goal INR 3.0-4.5

• V Value ==> Dose Change (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 or <-1.45   See healthcare provider now
• 0.91-1.45 (or -) ==> 1 week
• 0.66-0.90 (or -)   ==> 2 weeks
• 0.56-0.65 (or -)   ==> 4 weeks
• 0.55 to -0.55   ==> 8 weeks

Conclusions of use of this algorithm include:

• This algorithm performed better than inexperienced clinicians
• The algorithm performed as well as experienced clinicians if a case was not complicated
• For complicated cases an experienced clinician needs to be consulted
• During initiation and maintenance of oral anticoagulants, quality control is often quite poor
• Use of a computerized decision system, such as his seems to improve quality of anticoagulant therapy in doctors in training
• The median time to achieve a stable dose was significantly lower in the group assisted by this algorithm than in controls, without any increase in over or under treatment
• Patients who were enrolled in the computerized algorithm spent more time in the therapeutic range (whether inpatient or outpatient)

References

Vadher BD, et al. Validation of an algorithm for oral anticoagulant dosing and appointment scheduling. Clin Lab Haematol. 1995;17:339-45.

Vadher B, et al. Evaluation of a decision support system for initiation and control of oral anticoagulation in a randomized trial. BMJ. 26 April 1997;314(7089):1252.