February 14, 2012 — Although adults prescribed the attention-deficit/hyperactivity disorder (ADHD) medication methylphenidate may be at increased risk for adverse cardiovascular events, this association may not be causal, new research suggests.
In a cohort study of almost 220,000 individuals, new users of methylphenidate had almost twice the risk for sudden death or ventricular arrhythmia than age-matched control participants had. They also had a significantly higher risk for all-cause death.
However, the medication dosage "was inversely associated with risk," meaning it lacked a dose-response relationship, report the investigators.
"We were surprised by the risk findings. But the inverse associations leads us to be somewhat skeptical," coinvestigator Sean Hennessy, PharmD, PhD, associate professor of epidemiology and pharmacology at the Perelman School of Medicine at the University of Pennsylvania in Philadelphia, told Medscape Medical News.
"Ordinarily, if a drug increases the risk of adverse outcomes, that increase is going to be dose-dependent. We didn't see that, and in fact, found an inverse relationship for death and other outcomes," he explained.
Dr. Hennessy said that this could be due to "frail, elderly patients who have other things going on" and who are prescribed low-dose methylphenidate.
"Maybe baseline differences in those patients that aren't captured in the medical claims data are responsible for the elevated risk of adverse outcomes we were seeing rather than it being a causal effect of the methylphenidate itself," he opined.
"So I would say to wait for these findings to be replicated and clarified in other research before they are acted on clinically."
The study is published in the February issue of the American Journal of Psychiatry.
According to the investigators, methylphenidate and other ADHD medications are used by almost 1.5 million adults in the United States — even though these medications have been shown to raise blood pressure and heart rate.
"Given these effects, case reports of sudden death, stroke, and myocardial infarction have led to regulatory and public concern about the cardiovascular safety of these drugs," write the researchers.
However, in May 2011, and reported by Medscape Medical News at that time, the same group of researchers published a study in Pediatrics that showed no increased risk for cardiovascular events in children treated with ADHD medications.
In addition, researchers from Kaiser Permanente Northern California published a study in December 2011 in the Journal of the American Medical Association that examined risks in adults younger than age 65 years who were taking methylphenidate, amphetamine, atomoxetine, or pemoline.
The combined group of ADHD medication users showed no increased risk for serious cardiovascular events, including myocardial infarction, sudden cardiac death, or stroke, compared with the group of nonusers.
For this analysis, investigators examined records from Medicaid and commercial databases, representing 19 states, for adults in a broader age range. Included were 43,999 new users of methylphenidate and 175,955 individuals who did not use methylphenidate, amphetamines, or atomoxetine (for both groups, 55.4% were women).
In each group, 67.3% of the participants were between the ages of 18 and 47 years, 23.2% were between the ages of 48 and 64 years, and 9.5% were aged 65 years or older.
Primary cardiac events assessed included sudden death or ventricular arrhythmia, myocardial infarction, stroke, and a combination of stroke/myocardial infarction. All-cause death was a secondary measure.
Results showed that the adjusted hazard ratio (HR) for sudden death/ventricular arrhythmia for the methylphenidate users compared with the nonusers was 1.84 (95% confidence interval [CI], 1.33 - 2.55). For all-cause death, the HR was 1.74 (95% CI, 1.60 - 1.89).
Adjusted HRs for myocardial infarction and stroke (alone or in combination) were not statistically different between the 2 treatment groups.
For the participants who experienced a cardiovascular event, the mean treatment dosage was 20 mg/day. No significant association was found for sudden death/ventricular arrhythmia between the patients who took more or less than 20 mg/day of methylphenidate.
"However, there were unexpected inverse associations" between high methylphenidate dosage and stroke, myocardial infarction, stroke/myocardial infarction, and all-cause death compared with low dosage, report the researchers. They add that this lack of a dose-response association discredits a causal relationship.
"Furthermore, the inverse relationships...may suggest that lower dosages were prescribed to the frailest patients, who might have had a greater risk of all-cause death and sudden death — that is, the results may have been affected by unmeasured confounding," write the investigators.
Other limitations cited included the fact that the study was not randomized and that administrative databases do not include potential confounders such as smoking, blood pressure, substance use, and exercise use/nonuse.
Dr. Hennessy reported that the investigators also assessed cardiovascular risks in their study participants who were also taking amphetamines or atomoxetine. They will be publishing those results soon.
Findings "Generally Reassuring"
Christopher J. Kratochvil, MD, from the University of Nebraska Medical Center in Omaha, writes in an accompanying editorial that this and other studies are "generally reassuring and demonstrate movement in the right direction, with systematic retrospective analyses better informing us of issues related to cardiovascular safety with ADHD pharmacotherapy."
"While gaps persist in the methodical and comprehensive assessments of the safety of ADHD medications, these studies add valuable information to our already large repository of safety and efficacy data...and better inform the risk-benefit analysis of their use," writes Dr. Kratochvil, who was not involved with this research.
He adds that establishing a "robust" national electronic health records system containing detailed data elements will also offer considerable help to clinicians.
These large and more accessible databases "will allow us to improve our identification and understanding of rare but serious adverse effects and better address these questions of public health significance," he concludes.
The study was funded through a sponsored research agreement with Shire Development, Inc., and by a Clinical and Translational Science Award from the National Institutes of Health. The study authors all receive salary support from Shire through their employers. All financial disclosures for the study authors and Dr. Kratochvil are listed in the original article.
Medscape Medical News © 2012 WebMD, LLC
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Cite this: Mixed Results for ADHD Meds and Cardiovascular Risk - Medscape - Feb 14, 2012.