Table 1.

Characteristics of cases and controls

Variable	Cases (n = 796)	Controls (n = 3148)	Standardized difference†	P value
Age (median, IQR) (years)	75 (70–80)	74 (70–80)	0.00	0.8475
66–75	438 (55.0%)	1,757 (55.2%)	0.00	0.8672
76–85	294 (36.9%)	1,196 (37.6%)	0.01	0.5628
≥86	65 (7.8%)	230 (7.3%)	0.02	0.1505
Male	367 (46.1%)	1,468 (46.1%)	0.00	1.0000
Number of years of phenytoin treatment (median, IQR)	1 (0–3)	2 (1–5)	0.37	<0.0001
Residence in a long-term care facility, n (%)	116 (14.6%)	832 (26.1%)	0.27	<0.0001
Number of prescription drugs in previous year, (median, IQR)	11 (7–15)	9 (6–13)	0.27	<0.0001
Previous hospitalization for phenytoin toxicity (1 year)	8 (1.0%)	≤5 (0.1%)	0.17	0.0005
Chronic liver disease in preceding year	8 (1.0%)	12 (0.4%)	0.09	0.0316
Chronic renal disease in preceding year	36 (4.5%)	58 (1.8%)	0.18	<0.0001
Chronic alcoholism in preceding year	53 (6.7%)	92 (2.9%)	0.20	<0.0001
Malignancy in preceding year	52 (6.5%)	112 (3.5%)	0.15	0.0001
Medication use in preceding 90 days
CYP2C8/2C9 inhibitors	89 (11.2%)	272 (8.5%)	0.09	0.0205
CYP2C8/2C9 inducers	106 (13.3%)	390 (12.2%)	0.03	0.4100
CYP2C19 inhibitors	152 (19.1%)	484 (15.2%)	0.11	0.0073
CYP2C19 inducers	32 (4.0%)	82 (2.6%)	0.09	0.0286
Income quintile, n (%)
1 (lowest)	211 (26.5%)	652 (20.5%)	0.15	0.0003
2	155 (19.5%)	681 (21.4%)	0.05	0.2371
3	156 (19.6%)	690 (21.7%)	0.05	0.1965
4	140 (17.6%)	556 (17.5%)	0.00	0.9336
5	117 (14.7%)	544 (17.1%)	0.06	0.1013
Missing	17 (2.1%)	61 (1.9%)	0.02	0.6780

^†Difference between cases and controls divided by standard deviation.