Effect of patient-specific factors on weekly warfarin dose

Figures & data

Table 1 Descriptive statistics for the sample of 131 patients

Continuous variables	Mean value	Standard deviation
TWD (mg/week)	36.61	16.03
Age (years)	66.91	13.06
Weight (kg)	83.91	20.91
Height (cm)	172	10.3
BMI (kg/m^2)	28.39	6.34
Vitamin K consumption (mcg/week)***	1764.93	1745.91
Ethnicity	Percentage
Caucasian	71.0%
African American	29%
Dichotomous variables	Percentage
Female	55.0%
Amiodarone use	12.1%
Aspirin use	36.6%
Tobacco use	9.9%
Alcohol use	22.1%
CYP inducer	7.7%
Multivitamin use**	21.5%
History of CHF	16.8%
History of Hypothyroidism	14.6%
LFT 3× ULN*	1.6%
Target INR 2.5–3.5	12.9%

* Notes: Data only available for 129 patients

** Data only available for 130 patients

*** Data only available for 77 patients

Table 2 Descriptive statistics – Indications for warfarin therapy (n = 131)

Indications	Mean value
History of atrial fibrillation	49.6%
History of deep vein thrombosis	24.5%
History of pulmonary embolism	12.2%
Prosthetic valve	10.8%
Other indication for warfarin therapy	21.6%

Table 3 Pearson correlation coefficients between TWD and patient specific variables

Variable	Correlation coefficient
Demographics
Age	−0.241**
BMI	0.076
Caucasian	−0.109
Female	−0.050
Medication use
Amiodarone	−0.066
Aspirin	−0.019
CYP inducer	0.300**
Multivitamin	−0.084
LFT 3× ULN	0.042
Comorbidities
CHF	−0.095
Hypothyroidism	−0.112
Prior embolism	0.108
Other patient characteristics
Target INR 2.5–3.5	0.068
Vitamin K consumption	0.026
Tobacco use	−0.004
Alcohol use	0.108

** Notes: Statistically significant at the 1% level.

Table 4 Comparison of high and low warfarin dose patient populations

Variable	Low (≤25mg) warfarin dose (n = 35)	High (≥50mg) warfarin dose (n = 26)	P-value from a two sample t-test or chi-squared test
Demographics
Average TWD	19.4 mg	60.7 mg	<0.0001**
Age	72.3	61.6	0.001**
BMI	27.1	29.3	>0.10
Caucasian (%)	0.77	0.62	>0.10
Female (%)	0.63	0.50	>0.10
Medication use
Amiodarone (%)	0.08	0.09	>0.10
Aspirin (%)	0.37	0.35	>0.10
CYP Inducers (%)	0.0	0.15	0.016*
Multivitamin (%)	0.26	0.23	>0.10
LFT 3× ULN (%)	0.03	0.04	>0.10
Comorbidities
CHF (%)	0.20	0.17	>0.10
Hypothyroidism (%)	0.23	0.12	>0.10
Prior Embolism (%)	0.43	0.50	>0.10
Other patient characteristics
Target INR 2.5–3.5 (%)	0.11	0.19	>0.10
Vitamin K consumption	1881.5	2040.4	>0.10
Tobacco use (%)	0.11	0.04	>0.10
Alcohol use (%)	0.17	0.27	>0.10

* Notes: Statistically significant at the 5% level

** Statistically significant at the 1% level.

Table 5 Ordinary least squares regression of weekly warfarin dose explained by patient specific variables (n = 130)

Variable	Coefficient	Standard error
Demographics
Age	−0.24	0.12*
BMI	0.026	0.233
Caucasian	−2.75	3.42
Female	−2.55	3.08
Medication use
Amiodarone	−3.35	6.60
Aspirin	−1.62	2.86
CYP inducer	17.19	5.41**
Comorbidities
CHF	−2.66	3.78
Hypothyroidism	−1.99	4.22
Prior embolism	−0.36	3.01
Other patient characteristics
Tobacco use	−5.17	4.74
Alcohol use	3.32	3.46

Notes: R-squared = 0.1676. Adjusted R-squared = 0.0822

* Statistically significant at the 5% level

** Statistically significant at the 1% level.