Can Small Average Pulse Changes Hide Lisdexamfetamine Outliers? A Historical Safety Review

A small average change in pulse does not establish that every participant had a small change. A 2014 lisdexamfetamine safety review reported modest mean cardiovascular changes alongside individual threshold crossings in clinical trials. The average, the number of people meeting a criterion and the persistence of those findings are different parts of the safety evidence.

Coghill and colleagues reviewed lisdexamfetamine dimesylate, a prodrug converted to active d-amphetamine. It is distinct from methamphetamine. This article examines a specific adult trial described in that historical review, without treating a short trial as a complete assessment of long-term or individual cardiovascular risk.

Which studies did the review cover?

The authors searched PubMed for English-language literature through September 16, 2013. Of 129 identified references, 35 contained safety and tolerability data in patients with ADHD. The review brought together short-term parallel-group trials, crossover studies, open-label extensions and other reports; it was not one experiment with a common denominator for every result.

The adult example here is study 303, a four-week randomized, double-blind, placebo-controlled trial in people aged 18–55 years. Its reported safety populations were 119 assigned to a 30-mg lisdexamfetamine target dose, 117 to 50 mg, 122 to 70 mg and 62 to placebo.

Did every participant receive the target dose for four weeks?

No. The review describes forced titration with once-daily administration. Participants assigned to 30 mg received that dose throughout. Those assigned to 50 mg received 30 mg during week one and 50 mg during weeks two through four. Those assigned to 70 mg received 30 mg in week one, 50 mg in week two and 70 mg in weeks three and four.

The assigned dose is therefore the target regimen, not proof of four full weeks at the highest listed dose. These milligram quantities refer to lisdexamfetamine treatment, not a measured d-amphetamine concentration in blood.

What did the mean pulse results show?

Table 2 of the review reports least-squares mean changes from baseline to endpoint. The reported pulse changes were 2.8 beats per minute at 30 mg, 4.2 at 50 mg and 5.2 at 70 mg, compared with approximately zero for placebo. Their reported standard errors were 0.83, 0.83, 0.82 and 1.14 beats per minute, respectively.

These are adjusted group summaries with standard errors, not ranges containing every individual response. A standard error describes precision of an estimated mean; it should not be read as the variability of individual patients or relabeled a standard deviation.

Endpoint was the last post-randomization on-treatment visit with a valid assessment. That timing also differs from asking whether a participant crossed a threshold at any visit during the trial.

How many participants reached 100 beats per minute?

The review’s Table 3 reports the following outlier analysis for study 303. The criterion was a pulse rate of at least 100 beats per minute. Counts are people meeting the specified criterion, not the number of separate readings.

The criterion’s wording matters. “At least two time points” is not the same as continuous elevation, two consecutive weeks or a diagnosis of an arrhythmia. Likewise, the any-time count does not by itself establish a new-onset abnormality caused by treatment in each person.

Does the 70-mg group have lower risk because it had fewer crossings?

That conclusion does not follow from these counts. The mean pulse change increased across the target doses, while the count of people crossing this particular threshold did not. Mean change and threshold crossing measure different features of the data.

The threshold count depends on absolute pulse values and the selected cutoff; the mean-change analysis concerns change from each participant’s baseline. Neither summary supplies a complete comparison of every cardiovascular outcome. The review does not provide a definitive statistical demonstration that the 70-mg regimen was safer than 50 mg on the basis of these small counts.

Similarly, no crossings among 62 placebo recipients during four weeks does not establish that such a reading is impossible without the drug. It is the observed zero under that study’s conditions and follow-up.

Were these clinical cardiac events?

A pulse reading meeting an analysis threshold is a physiological measurement. It is not automatically a heart attack, sustained tachyarrhythmia, structural heart injury or serious adverse event. Those outcomes need their own definitions, assessment and denominators.

The review characterized cardiovascular-related serious events and discontinuations as rare in the lisdexamfetamine clinical program and generally described mean changes as modest. It also acknowledged that small, relatively short trials were unlikely to detect rare events or events emerging only after prolonged treatment. Both observations belong in the interpretation.

Who might the trial evidence miss?

The review notes that the trials excluded major cardiovascular and neurological conditions, certain psychiatric comorbidities and extremes of weight; participants were generally in good health. Long-term extensions also tended to select people who responded to or tolerated treatment. These design features limit application to the full range of patients seen in practice.

All clinical trials described in the review were manufacturer-sponsored, and three review coauthors disclosed employment and stock or stock options with the manufacturer. These disclosures are relevant context, not proof that any particular result is false.

The historical lesson is to report several levels of evidence together: mean change, individual threshold counts, repeated findings, actual clinical events and the population studied. None of these measurements establishes a person’s drug concentration, impairment or cause of an unrelated incident. This article interprets a historical evidence source and does not provide individualized treatment advice or current prescribing standards.

Scientific source

Coghill DR, Caballero B, Sorooshian S, Civil R. A systematic review of the safety of lisdexamfetamine dimesylate. CNS Drugs. 2014;28(6):497–511. doi:10.1007/s40263-014-0166-2. Full-text review. Historical systematic review with search coverage through September 16, 2013. Study 303 dosing, means and outlier counts above are reported through the supplied review’s methods and Tables 1–3; no individual-level reanalysis was performed.