[Or…Why I changed my aspirin dosing schedule]
Henry I. Bussey, Pharm.D., FCCP
I just read one of the most complex and confusing studies that I’ve ever read. This well-written article was complex and confusing because of the amount of data presented and the number of endpoints, dosing regimens, and patient subgroups addressed. The data, however, are important and, I believe, should be practice-changing. After reading the article twice and discussing it with a hematologist on the ClotCare Editorial Board, I made a substantial change in my aspirin dosing schedule; and I believe that there is a good chance that most others taking aspirin for primary prevention are taking a dose that may be ineffective and/or harmful.
If you would like to review the article for yourself, it is available at https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)31307-2/fulltext
Here are some of the key points that I got from this paper that analyzed individual patient data for 117,279 patients who were enrolled in trials of aspirin for primary prevention:
In the primary prevention of cardiovascular events:
- Low-dose aspirin (75 to 100 mg daily) is effective only in individuals who weigh less than 70 Kg (Hazard Ratio, HR = 0.77) with no benefit in those who weigh 70 kg or more (HR = 0.95). Furthermore, for those who weigh 70 Kg or more, there is a trend for low-dose aspirin to increase cardiovascular events if the individual has diabetes, smokes, or is at least 70 years old.
- Low-dose aspirin may be harmful in those who weigh less than 50 Kg. (including an increased risk of sudden death).
- Enteric coated or sustained release aspirin products may be less effective.
- Alternate day dosing may be less effective.
- High-dose aspirin (300 – 325 mg or 500 mg or more) is effective in those who weigh more than 70 Kg (where low-dose is ineffective), but high-dose may be harmful in those who weigh less than 60 Kg.
- Twice a day dosing may be desirable based on (1) the impressive reduction in cardiovascular events (HR = 0.74) among patients weighing less than 70 kg. in the ESPS-2 secondary stroke prevention trial that used a regimen of 25 mg of aspirin twice a day and (2) the theory that systemic availability of aspirin may be necessary to inhibit the 10-15% of new platelets that are released daily. Patients who weighed 70 Kg or more in the ESPS-2 did not exhibit a reduction in cardiovascular events with this regimen which led the authors of the current paper to suggest that 50 – 100 mg twice a day might be effective in heavier individuals. Whether such a twice daily regimen would carry any bleeding risk in those weighing 90 kg or more is uncertain.
In the primary prevention of cancer:
- Low-dose aspirin did not alter the rate of cancer in those who weighed 70 Kg or more.
- Low-dose aspirin in those weighing less than 70 Kg increased cancer rates during the first 3 years of follow-up and this effect was especially evident in those with diabetes (HR = 1.32) and those over 70 years of age (HR = 1.35).
- High-dose aspirin seemed to have a similar impact on cancer rates as that seen with low-dose aspirin.
- Aspirin (regardless of dose or patient age) appeared to reduce the incidence of colorectal cancer at 20 years of follow-up in patients who weighed more than 50 kg and less than 80 Kg. No clear benefit was seen outside of that weight range.
- Women younger than 50 years of age who had diabetes and were taking aspirin had an especially high rate of cancer (HR = 4.35) due in part to a high rate of breast cancer (HR = 2.60).
The risk of major or significant bleeding with aspirin:
- Low-dose aspirin increases major bleeding up to a body weight of 90 Kg, above which bleeding risk disappears.
- High-dose aspirin carried an increased risk of major bleeding that not only persisted but increased at weights above 90 Kg.
Reference:
Rothwell PM, Cook NR, Gaziano JM, et al. Effects of aspirin on risks of vascular events and cancer according to bodyweight and dose: Analysis of individual patient data from randomized trials. The Lancet 2018; 392:387-399. http://dx.di.org/10.1016/S0140-6736(18)31133-4