Those beginning diclofenac had a 50% increased 30-day risk for a composite outcome of major adverse cardiovascular events (MACE) compared with individuals who didn’t initiate an NSAID or acetaminophen (95% confidence interval for incidence rate ratio, 1.4-1.7).
The risk was still significantly elevated when the study’s first author, Morten Schmidt, MD, and his colleagues compared diclofenac initiation with beginning other NSAIDs or acetaminophen. Compared with those starting ibuprofen or acetaminophen, the MACE risk was elevated 20% in diclofenac initiators (95% CI, 1.1-1.3 for both). Initiating diclofenac was associated with 30% greater risk for MACE compared with initiating naproxen (95% CI, 1.1-1.5).
“Diclofenac is the most frequently used NSAID in low-, middle-, and high-income countries and is available over the counter in most countries; therefore, its cardiovascular risk profile is of major clinical and public health importance,” wrote Dr. Schmidt and his coauthors.
In all, the study included 1,370,832 individuals who initiated diclofenac, 3,878,454 ibuprofen initiators, 291,490 naproxen initiators, and 764,781 acetaminophen initiators. Those starting diclofenac were compared with those starting other medications, and with 1,303,209 individuals who sought health care but did not start one of the medications.
The researchers used the longstanding and complete Danish health registry system to their advantage in designing a cohort trial that was modeled to resemble a clinical trial. For each month, beginning in 1996 and continuing through 2016, Dr. Schmidt and his collaborators assembled propensity-matched cohorts of individuals to compare each study group. The study design achieved many of the aims of a clinical trial while working within the ethical constraints of studying medications now known to elevate cardiovascular risk.
For each 30-day period, the investigators were then able to track and compare cardiovascular outcomes for each group. Each month, data for a new cohort were collected, beginning a new “clinical trial.” Individuals could be included in more than one month’s worth of “trial” data as long as they continued to meet inclusion criteria.
The completeness of Danish health data meant that the researchers were confident in data about comorbidities, other prescription medications, and outcomes.
Dr. Schmidt and his colleagues performed subgroup and sensitivity analyses to look at the extent to which preexisting risks for cardiovascular disease mediated MACE risk on diclofenac initiation. They found that diclofenac initiators in the highest risk group had up to 40 excess cardiovascular events per year – about half of them fatal – that were attributable to starting the medication. Although that group had the highest absolute risk, however, “the relative risks were highest in those with the lowest baseline risk,” wrote the investigators.
In addition to looking at rates of MACE, secondary outcomes for the study included evaluating the association between medication use or non-use and each individual component of the composite primary outcome. These included first-time occurrences of the nonfatal endpoints of atrial fibrillation or flutter, ischemic (but not hemorrhagic) stroke, heart failure, and myocardial infarction. Cardiac death was death from any cardiac cause.
“Supporting use of a combined endpoint, event rates consistently increased for all individual outcomes” for diclofenac initiators compared with those who did not start an NSAID, wrote Dr. Schmidt and his colleagues.
Individuals were excluded if they had known cardiovascular, kidney, liver, or ulcer disease, and if they had malignancy or serious mental health diagnoses such as dementia or schizophrenia. Participants, aged a mean 48-56 years, had to be at least 18 years of age and could not have filled a prescription for an NSAID within the previous 12 months. Men made up 36.6%-46.3% of the cohorts.
Dr. Schmidt, of Aarhus (Denmark) University, and his collaborators said that in comparison with other NSAIDs, the short half-life of diclofenac means that a supratherapeutic plasma concentration of diclofenac soon after initiation achieves not just cyclooxygenase-2 (COX-2), but also COX-1 inhibition. However, after those high levels fall, patients taking diclofenac spend a substantial period of time with unopposed COX-2 inhibition, a state that is known to be prothrombotic, and also associated with blood pressure elevation, atherogenesis, and worsening of heart failure.
Diclofenac and ibuprofen had similar gastrointestinal bleeding risks, and both medications were associated with a higher risk of bleeding than were ibuprofen, acetaminophen, or no medication.
“Comparing diclofenac initiation with no NSAID initiation, the consistency between our results and those of previous meta-analyses of both trial and observational data provides strong evidence to guide clinical decision making,” said Dr. Schmidt and his coauthors.
“Considering its cardiovascular and gastrointestinal risks, however, there is little justification to initiate diclofenac treatment before other traditional NSAIDs,” noted the investigators. “It is time to acknowledge the potential health risk of diclofenac and to reduce its use.”
The study was funded by the Department of Clinical Epidemiology Research Foundation, University of Aarhus, and by the Program for Clinical Research Infrastructure, funded by the Lundbeck Foundation, Novo Nordisk Foundation, and the Danish Research Council. The authors reported that they had no relevant conflicts of interest.
SOURCE: Schmidt M et al. BMJ 2018;362:k3426