Table 2.

Incidence rate of myocardial infarction (MI) with incident allopurinol exposure* (yes versus no) and different allopurinol use duration periods

	Person-days of follow-up	MI cases	MI incidence rate per 1,000,000 person-days
Allopurinol use
Yes	12,877,451	937	73
No	8,327,742	607	73
Allopurinol use duration
0 days	8,327,742	607	73
1–180 days	5,902,851	514	87
181 days to 2 years	5,127,382	326	64
>2 years	1,847,218	97	53

*Baseline period was defined as 365 days during which patients could not have had an MI; baseline period for allopurinol was also 365 days before the index allopurinol prescription during which the patient could not have had a filled/refilled allopurinol prescription

Allopurinol use duration of “0 days” use represents the period where a person was not using allopurinol. This could be because they had not received their first prescription when we started observing them or because they went more than 30 days without getting a new prescription; they would begin contributing to the “0 days” category on day 31 of interruption of their allopurinol prescription