What Did Preschool Lisdexamfetamine Actually Measure in Plasma? A 24-Child Study With Eight PK Profiles

Quick answer: A 2020 open-label investigation of oral lisdexamfetamine in 24 children aged four to five years recorded clinical safety and symptom ratings, while an eight-child intensive pharmacokinetic subset provided directly measured plasma lisdexamfetamine and active d-amphetamine concentrations. In the five children assigned 30 mg at rich sampling, the mean d-amphetamine plasma peak was 86.20 ng/mL (SD 22.78); it was not a legally collected venous whole-blood concentration. All children received active treatment, so a 26.1-point average symptom-score decrease cannot establish a placebo-adjusted treatment effect. Decreased appetite affected 8 of 24, and two children discontinued after adverse events at the 5-mg dose. These are useful clinical and analytical observations, not validated measures of individual intoxication, driving impairment, or incident causation. The source is the original Childress and colleagues empirical publication.

What was the exact scientific question?

This phase 2 study asked whether a conservatively titrated course of lisdexamfetamine dimesylate could be administered to selected preschool children with ADHD while allowing investigators to describe adverse events, vital signs, symptom-scale changes, and plasma exposure. The trial was conducted at seven U.S. research sites in 2015–2016. Its central evidentiary strengths were prospectively specified clinical visits and chemically specific measurement in a small pharmacokinetic subset. Its central limitation was the absence of a randomized placebo comparison: every enrolled child who received study medication received active lisdexamfetamine. The authors therefore called the symptom measures efficacy-related or clinical effects rather than a blinded controlled superiority result.

A forensic question is different from that clinical one. One might want to know whether a measured chemical in a particular sample identifies a drug, whether two biological matrices can be compared, or whether observed conduct can be ascribed to that drug. This trial supplies published plasma concentrations in a few children at specified visits. It does not supply forensic whole-blood concentrations, independently validated legal thresholds, or individual injury and driving outcomes. Keeping those different questions apart is essential to a scientifically responsible summary.

How many different children were enrolled and evaluated?

The source enrolled 24 children aged four or five years, including 18 boys and six girls. Baseline ADHD Rating Scale-IV Preschool scores averaged 43.6 points (SD 5.54), reflecting a clinically selected symptomatic population. Nineteen of the 24 completed the eight-week active phase. Five did not complete: two discontinued following treatment-emergent adverse events, two withdrew, and one was lost to follow-up. Adverse-event summaries and the reported final symptom change use study-specific denominators, so the same fraction should not be silently attached to every result.

Eight members of the treated cohort, not eight additional recruits, entered the intensive week-seven plasma sampling component. At the relevant dose, one received 10 mg, two received 15 mg and five received 30 mg. That arrangement does not create three parallel randomized drug trials. Repeated weekly office visits, blood sampling time points, and medication steps are nested measurements of the same biological participants. The dose columns in the adverse-event table likewise show participants as they passed through titration, not separate sets of unrelated children.

What oral dose and schedule were actually used?

The administered study agent was lisdexamfetamine dimesylate, a prodrug that yields active d-amphetamine after absorption and conversion. It is neither methamphetamine nor a measured d-amphetamine concentration in blood. Participants began with oral lisdexamfetamine 5 mg once daily. Depending on clinical response and tolerability, weekly steps allowed 10 mg, 15 mg, 20 mg and eventually 30 mg by the fifth treatment week. Six weeks were used for optimization, followed by two weeks at the selected tolerated dose, with subsequent follow-up. A five-milligram starting dose is a prescribed nominal formulation amount, not a five-nanogram-per-milliliter laboratory result.

To designate a dose as optimized, clinicians evaluated both a reduction of at least 30% in the preschool symptom score and a rating of much or very much improved, without unacceptable adverse effects. Ten children reached a 30-mg maximum during titration, but that fact does not imply that all 24 received it or that a given child maintained it for all eight weeks. At week eight the mean prescribed daily dose was 22.9 mg (SD 7.25). Actual specimen collection and chemistry must be examined separately from this dosing sequence.

Which physical biological specimen was assayed?

The investigators collected participant blood samples and analyzed the separated plasma fraction for lisdexamfetamine and d-amphetamine. They described a validated liquid-chromatography tandem-mass-spectrometry method consistent with prior bioanalytical publications. The reported lower limits of quantification were 1.00 ng/mL for lisdexamfetamine and 2.00 ng/mL for d-amphetamine. Those chemical-specific units differ completely from rating-scale points, milligrams dispensed and a clinician’s global impression.

The study did not report drug concentrations in an unseparated forensic venous whole-blood sample. Plasma is collected after processing blood; whole blood contains the cellular fraction and requires its own validated interpretation and calibration. Neither a plasma ng/mL observation nor a known oral dose can be converted automatically into a whole-blood value by assuming the matrices are interchangeable. The protocol also did not generate laboratory evidence on urine, oral fluid, hair, sweat, vitreous humor or breath for the purpose of determining a person’s driving ability, last dose or disputed incident conduct.

Why is the eight-person rich PK subset the analytical focus?

Intensive pharmacokinetic sampling was undertaken in eight children during week seven, after the titration period. The sequence included a predose sample followed by draws at 1, 2, 3, 4, 6 and 8 hours after dosing. Less intensive predose measurements were taken at selected visits in the wider treated sample. Noncompartmental analysis produced the reported peak concentration, time of peak, area under a dosing-interval curve and terminal half-life estimates. These outputs require multiple time-linked chemical observations; they are not single-point forensic cutoffs.

The intensively sampled eight were unequally distributed: one child at 10 mg, two at 15 mg and five at 30 mg. Several derived PK parameters have even smaller usable denominators than their dose group’s peak concentration. For 30 mg, the d-amphetamine peak summaries represent five, while AUC and half-life represent four. Source figures show the individual trajectories instead of eight independent averages per dose. Its 24-hour points on the figure were estimated from the next predose measurement rather than separately observed 24-hour postdose draws. Precision and external validity are limited accordingly.

What exactly did the plasma peaks demonstrate?

Peak plasma d-amphetamine concentration increased across the observed 10-, 15- and 30-mg regimen groups, but those groups contained one, two and five children. The reported mean d-amphetamine peaks were 24.10, 47.40 and 86.20 ng/mL, respectively. In contrast, the prodrug lisdexamfetamine peaked relatively early, with mean plasma peaks of 5.45, 13.20 and 49.86 ng/mL. The resulting patterns illustrate the difference between the administered parent prodrug and its converted active moiety, with no implication that the two species are interchangeable assay targets.

The investigators discussed increasing exposure across doses. A pharmacokinetic trend from such sparse observational strata is not a reliable estimate of what every four-year-old will reach at an identical dose, much less a validated forensic threshold. Individual sample times, collection methods, assay performance, maturation, body mass and drug handling matter. A plasma Cmax is the highest concentration within the measured profile, not a continuous measurement of what the child’s whole blood contained at every instant or evidence about dose actually ingested by some other individual on another day.

How should time to peak and half-life be read?

For the active d-amphetamine analyte, mean reported time to peak was approximately 4.00 hours at 10 mg, 4.23 hours at 15 mg and 4.00 hours at 30 mg. The corresponding terminal half-life estimates were 7.18, 8.43 and 8.46 hours. These are plasma-derived pharmacokinetic values in small treatment strata, not hours for which a child remains behaviorally impaired. The parent prodrug peaked earlier, approximately one hour after dosing, and had a much shorter reported plasma terminal phase under the available sampling window.

A terminal half-life describes the modeled slope of drug decline over a selected interval under the source’s assumptions. It does not equal the time a person last swallowed medication, the time until an individual’s blood level is zero, or the duration of a symptom-score improvement. The source explicitly notes that quantifying rapidly eliminated lisdexamfetamine was constrained by the sampling schedule and assay quantification limit. Without a contemporaneous specimen, a reliable full exposure history and matrix-specific validation, backward calculation from those pediatric mean values to an individual’s purported use time would be unsound.

Numerical evidence: actual preschool plasma assays

The table below independently reorganizes the original publication’s dense pharmacokinetic table into analyte-specific units and denominator information. Each row is a treatment dose in the same eight-person intensive cohort; it is not a randomized comparison of eight subjects per row. The peaks are concentrations physically analyzed in plasma by LC–MS/MS. The AUC and terminal half-life values are model-derived from serial plasma observations, and the 30-mg derived parameters have four evaluable profiles instead of five. Single-person values do not carry a population standard deviation.

All concentrations refer to separated plasma. Different rows contain different children; 30-mg AUC and half-life analyses excluded one profile. For this noncompartmental analysis, late concentrations depend on assumptions about the dosing interval and terminal phase. The figure’s 24-hour points were estimated from subsequent predose samples, not directly measured 24-hour venipunctures.

Why are the plasma and whole-blood distinction legally important?

If a legal case contains a venous whole-blood amphetamine result, this preschool study cannot by itself establish the same numerical value in whole blood after an equal oral dose. Blood-cell partitioning, hematocrit, sample preparation, anticoagulant and extraction can affect the relationship between fractions. The investigators explicitly measured plasma; that narrow claim is stronger than saying simply that the trial measured drug in blood. A reliable forensic opinion should name the precise matrix and validated analytical approach reflected in the actual evidence.

The work is also not a method-validation trial of courtroom specimens. It does not report an adjudicative chain of custody, independent confirmatory laboratory comparison, roadside test performance, false-positive rates, a population-based impairment threshold, or d-/l-amphetamine isomer attribution in a disputed sample. An observed plasma peak after a prescribed prodrug dose may inform broad physiology but cannot establish whether a different whole-blood specimen came from prescribed treatment, nonprescribed use or a distinct compound without case-specific validated testing. A concentration alone is not a credibility test or accident reconstruction.

What did the preschool ADHD symptom scale record?

Mean baseline total ADHD-RS-IV Preschool score was approximately 43.6. At the final on-treatment assessment, the mean within-study total-score change was −26.1 points with a reported 95% confidence interval from −32.2 to −20.0. Subscale average changes were −13.6 points for inattention and −12.5 for hyperactivity/impulsivity, each with source-reported confidence intervals. The Clinical Global Impressions–Improvement measure categorized 20 of 24 participants, approximately 83%, as much or very much improved at their final treatment assessment.

These observations describe changing ratings during an intervention, not a verified randomized treatment effect. There was no assigned placebo group, no blinding to active treatment and no formal placebo-adjusted mean difference from which to draw a between-group efficacy p value. Expectation, developmental change, regression toward the mean, rater behavior, and supportive follow-up could contribute to observed improvement. The confidence interval around a within-group mean change does not eliminate those alternative explanations. Clinical change is a different outcome from a d-amphetamine plasma value, and neither is a direct measure of driving performance or a legal impairment criterion.

Could drug concentrations explain an individual clinical improvement?

The publication did not fit or validate an individual clinical response equation that predicts an ADHD score from a particular plasma dextroamphetamine concentration. Its rich PK subset was only eight participants, and those profiles were obtained at week seven. The overall symptom changes were calculated across the broader clinical treatment experience. Connecting the group mean chemical peak directly to a specific child’s decrease in inattention would require linked individual concentration–response analyses, relevant temporal alignment and a suitable design to address confounding and treatment expectations.

Even if a separate clinical trial established a robust average exposure–response relationship, the conclusion would remain probabilistic rather than a direct reconstruction of a disputed incident. The 24 preschool children were selected on diagnosis and safety criteria, including exclusion of important cardiac risks and low baseline weight. Their physiologic responses do not function as a reference interval for adult motorists, witnesses, injured persons or toxicology samples obtained long after an alleged event. No method or data in this paper support a forensic conversion from questionnaire benefit to legal impairment.

What adverse events were actually observed?

At least one treatment-emergent adverse event occurred in 19 of 24 participants (79%). Fourteen children (58%) had at least one event considered related to treatment. Decreased appetite was the most common named event, affecting 8 of 24 (33%). Insomnia and upper-respiratory infection each affected 4 of 24 (17%). Other reported events included irritability, affect lability, abdominal symptoms and decreased weight. These are actual reported clinical observations; an event’s appearance during treatment does not automatically prove that medication caused each occurrence.

Two participants stopped the drug while still taking 5 mg because of adverse events. One experienced increased hyperactivity and worsened sleep; another experienced manic-like symptoms. The source described those discontinuation events as treatment related and resolving after discontinuation. The trial recorded no serious or severe treatment-emergent adverse events and no deaths, but this is not a comparative safety noninferiority result. With only 24 subjects and roughly eight weeks of active treatment, an absence of certain observed events provides little power to exclude rare or long-term harms. Positive symptomatic changes and tolerability problems can coexist within the same study.

Why can dose-specific adverse-event columns mislead?

The original adverse-event table has columns for exposure while taking 5, 10, 15, 20 and 30 mg. Their denominators are 24, 23, 18, 12 and 10. Summing those denominators would create 87 apparent participants from a study with only 24 independently enrolled children. In reality, these are successive treatment stages or dose exposures of overlapping participants. Any event counted under a particular dose is linked to when that child experienced it, not to an unrelated randomized group.

For example, the 30-mg column lists six affected among ten exposed children, while the 5-mg column lists ten among 24. That does not establish that the 30-mg dose has a greater causal event risk than 5 mg. Dose progression is conditioned on earlier tolerability and observed response; participants who could not tolerate low doses may never reach the highest dose. This selection, together with changing exposure duration, makes raw dose-column frequencies poor causal dose–risk estimates. The overall 19/24 safety observation avoids mistakenly treating the same person as several independent cases.

What did the vital signs and weight data contribute?

At the end-of-treatment or early-termination assessment, source mean change in systolic blood pressure was −1.1 mmHg (SD 7.31), diastolic pressure +1.5 mmHg (SD 6.93), and pulse −0.8 beats per minute (SD 12.75). Mean weight change was −0.41 kg (SD 0.824), and two participants lost at least 7% of baseline weight. These descriptively measured clinical variables are not drug concentrations. Without a parallel untreated group, the changes should not be stated as placebo-adjusted physiologic effects or assumed to predict a particular child’s medical response.

The investigators themselves described variability in these findings and noted that early automated blood-pressure cuffs were not calibrated for the preschool age range; readings were subsequently obtained manually. That procedural issue affects interpretation of small mean blood-pressure shifts. Two blood-pressure-related treatment-emergent events were reported. None of these measurements determines the child’s dexamphetamine plasma concentration, and no one measurement yields a legally validated intoxication threshold. A courtroom assessment of pulse, weight or pressure requires the case’s actual examination and contextual evidence, not substitution of averages from this small noncomparative study.

Which study findings were nonsignificant—or not tested at all?

This experiment is not a placebo-controlled trial with a set of prespecified drug-versus-placebo hypothesis tests. Its key symptom and safety summaries are descriptive; reporting a confidence interval for a change does not transform the design into a controlled comparison. It would be equally misleading to fabricate a significant efficacy p value or a nonsignificant placebo contrast. The source reports no inferential test showing that serious adverse events occur equally frequently with and without treatment, and its observation of zero serious events cannot be relabeled a tested null finding.

Several topics were not measured as trial endpoints: legally collected whole-blood d-amphetamine levels, oral-fluid or urine time-course detection, on-road driving, individual decision-making under emergency conditions, eyewitness accuracy, validated use-time reconstruction and future incident causation. An unmeasured outcome is not the same as a nonsignificant result. Other outcomes such as measured plasma peaks and clinical rating changes are positive observations, while their causal significance is limited by sample size and study design. That careful distinction prevents both overclaiming and unfair dismissal of what the trial genuinely measured.

What uncertainty comes from the small pharmacokinetic subgroups?

Dose-stratified rich sampling included only one child at 10 mg, two at 15 mg and five at 30 mg. At 30 mg, complete modeling of the AUC and d-amphetamine terminal half-life drew on four individuals. Means drawn from one or two profiles are simply an overview of those profiles, not an adequate basis for estimating interindividual dispersion or defining a forensic reference range. In the five 30-mg Cmax observations, the reported standard deviation 22.78 ng/mL itself indicates substantial between-person variation relative to the mean 86.20 ng/mL.

A further uncertainty is the sampling window. The source’s illustrated d-amphetamine value at 24 hours was an extrapolation from the next predose value, not a direct 24-hour draw. Short-lived LDX was especially hard to characterize in the available schedule given the assay’s quantification floor. The paper contains no empirical test showing that these sparse preschool profiles predict plasma peaks in other age groups, disease states, products or doses. A dose-level difference in sampled concentration cannot be converted into an individual causal effect without independent validation.

What was learned—and not learned—about pediatric safety?

The selected sample provided preliminary direct observations on appetite, sleep, mood-related complaints, pulse, blood pressure and body mass over an eight-week course. It therefore contributes to early-stage safety characterization, particularly at doses beginning as low as 5 mg. The two treatment-related discontinuations remain part of the evidence even though many participants showed improved symptom ratings. The study’s eligibility criteria excluded children with various cardiac risks and other clinical concerns, which limits how broadly its observations can be applied.

The trial did not determine long-term growth trajectories, rare serious adverse-event rates, safety beyond the observed treatment horizon or optimal management for every child. It also did not establish that 30 mg is preferable to another target dose, because this was one dose-optimization arm without randomized dose groups. The sponsor supported the study and medical writing, as acknowledged in the original, which is context for scrutiny rather than a reason to discard data automatically. A full appraisal should preserve the observed findings, the deliberately conservative regimen and the substantial limits to comparative inference.

How would forensic testing of an actual individual differ?

A genuine forensic toxicology interpretation would begin with the actual material submitted to the laboratory: whole blood, separated plasma, serum, urine, oral fluid, hair, sweat, vitreous or another identified matrix. It would require documented collection conditions, analyte identity, chain of custody when applicable, method validation, calibration and quality-control results. If the issue concerns prescribed lisdexamfetamine versus another amphetamine source, the exact chemical species and potential stereochemistry may matter; this small pediatric trial was not a source-attribution validation study.

The temporal and functional questions demand equally specific evidence. A person’s concentration at a known draw time does not, without more, establish driving impairment, the precise time of ingestion, witness accuracy or causal responsibility for an incident. Fatigue, medical condition, age, coexposures and contemporary behavioral observations can be relevant to an individual assessment. For foundational distinctions see the site’s existing biological specimen matrices guide and confirmatory testing guide; neither changes the actual data measured by this study.

What is the strongest defensible bottom line?

The study has two complementary but differently weighted results. First, it measured genuine lisdexamfetamine and d-amphetamine exposure in plasma with a chemical instrument, generating useful preliminary concentration-time and PK estimates. Second, it recorded symptom improvement and adverse events during an open-label treatment course in 24 preschool-aged children. The source’s appropriate claim is about preliminary clinical and pharmacokinetic characterization, not placebo-proven superiority or a validated forensic impairment framework.

The evidence is narrower when applied to an individual. Eight intensive profiles cannot guarantee a personal peak level, and zero severe adverse events in this short cohort cannot rule out rare adverse outcomes. A Cmax obtained from plasma cannot substitute for an observed legal whole-blood concentration. A lower ADHD rating score cannot certify a driver’s safety or explain a prior injury. Keeping these distinctions explicit preserves the utility of the source without asking it to answer forensic, epidemiological or causal questions its actual design did not test.

Frequently asked forensic-science questions

1. How many unique children were studied, and how many had intensive drug measurement?

Twenty-four children started oral treatment, nineteen completed the eight-week phase, and eight of those in treatment supplied week-seven rich plasma pharmacokinetic profiles. At 10, 15 and 30 mg, the rich-sampling dose groups contained one, two and five children. Repeated weekly samples did not create more independent children.

2. Was the reported 86.20 ng/mL amphetamine result measured in whole blood?

No. It was the group mean peak d-amphetamine concentration in plasma among five children at a 30-mg oral LDX regimen. The study did not publish a chemically assayed forensic venous whole-blood d-amphetamine value or a validated conversion between the two matrices.

3. Did every participant take 30 mg lisdexamfetamine?

No. All began with 5 mg orally, with dose optimization according to response and tolerance; some never reached 30 mg. There were ten children exposed to 30 mg during titration, but just five at 30 mg in intensive week-seven PK sampling. The mean daily dose at week eight was approximately 22.9 mg.

4. What do d-amphetamine peak time and half-life mean here?

The source reported a roughly four-hour plasma peak time and approximate 7.18–8.46-hour terminal half-life in the small dose-stratified subsets. These are descriptive drug concentration-time parameters, not personal behavioral-impairment durations, exact ingestion times, or forensic elimination constants established in whole blood.

5. Did the study prove lisdexamfetamine better than placebo for four-year-olds?

No. All participants received active treatment in this open-label phase 2 dose-optimization study. A mean symptom-score improvement and a confidence interval were reported, but no concurrent randomized placebo contrast existed. The clinical finding is preliminary and cannot be relabeled a blinded drug-efficacy test.

6. Were there no adverse or safety concerns because no serious TEAE was observed?

No. Nineteen of twenty-four reported at least one treatment-emergent event, eight had decreased appetite and two discontinued because of drug-related adverse experiences at 5 mg. Zero observed severe or serious events in this small short trial is a descriptive count, not proof that such events cannot occur.

7. Can these plasma concentrations establish intoxication or the cause of an incident?

No. The cohort consisted of selected preschool patients in treatment; it included no validated impairment threshold, on-road driving, witness-reliability, injury-reconstruction or individual case-causation experiment. A case-specific opinion requires actual specimen identity, matrix-specific confirmed results and independently relevant contemporaneous evidence.

Original primary research

Childress AC, Findling RL, Wu J, Kollins SH, Wang Y, Martin P, Robertson B. Lisdexamfetamine Dimesylate for Preschool Children with Attention-Deficit/Hyperactivity Disorder. Journal of Child and Adolescent Psychopharmacology. 2020;30(3):128–136. Read the full original empirical study. The published trial documents open-label clinical observations and a limited plasma PK analysis; it does not provide forensic whole-blood quantitation or prove individual impairment.