Two oral-fluid collection devices can give similar average findings without being proven interchangeable for every specimen. A controlled l-methamphetamine study illustrates how collection order, specimen volume and assay target complicate that comparison.
What was administered, and to whom?
Newmeyer and colleagues studied sixteen healthy adults, twelve men and four women, under controlled conditions. Participants used a historical Vicks VapoInhaler formulation containing l-methamphetamine: two inhalations per nostril every two hours for six doses on the first day, followed by a seventh dose the next morning.
The paper describes an estimated 0.16–0.60 mg delivered per four-inhalation dose, rather than a precisely measured absorbed dose for each participant. Specimens were collected before dosing and through 32 hours after the first dose, approximately eleven hours after the final dose. These historical formulation and administration details should not be generalized to every product currently sold under a similar name.
How were the collectors compared?
Oral fluid was collected with Quantisal and Oral-Eze, with different pad positions and processing procedures. Quantisal was always collected first. Each collection stopped when the volume indicator changed or five minutes elapsed. Low-volume specimens were analyzed without weight-based volume correction.
The study collected 432 oral-fluid specimens for each device. After dosing, there were 88 low-volume Quantisal collections and 130 low-volume Oral-Eze collections. Because order was fixed, the greater number with the second device cannot cleanly be attributed to that device alone. Prior collection may affect the fluid available for subsequent collection.
What were the positive and null results?
All sixteen participants had measurable oral-fluid l-methamphetamine at the method’s 1 µg/L quantification limit. Median maximum concentrations were 14.8 µg/L with Quantisal and 16.1 µg/L with Oral-Eze, with ranges of 5.2–380 and 4–182 µg/L, respectively. The paired maximum-concentration comparison was nonsignificant, p = 0.535.
First detection and last detection comparisons were also nonsignificant. The median last positive specimen occurred eight hours after the seventh dose for both devices. Seven participants remained positive with both at the final collection. Nonsignificant differences on these endpoints do not constitute a prespecified equivalence demonstration or establish exact agreement for an individual specimen.
Why did the on-site screen remain negative?
The DrugTest 5000 screening assay targeted d-methamphetamine, whereas the administered drug was the l-enantiomer. All screening results were negative; chiral laboratory testing detected no d-methamphetamine or d-amphetamine in oral fluid.
A negative d-targeted screen alongside a positive laboratory l-methamphetamine measurement is not automatically a false negative for the screen’s intended analyte. The target, cross-reactivity, cutoff and confirmatory identification must be examined together. The study does not establish performance for all d-methamphetamine concentrations or every real-world drug mixture.
Could oral fluid be converted to plasma concentration?
Only two participants had detectable plasma l-methamphetamine, with observed maxima of 10.0 and 6.3 µg/L. Their oral-fluid/plasma ratios varied substantially both within and between individuals. No plasma d-methamphetamine or either amphetamine enantiomer was detected.
Those observations do not supply a dependable oral-fluid-to-plasma conversion factor. Plasma must also remain distinct from whole blood. Applying a proposed analytical cutoff is a separate question from inferring a person’s concentration in another specimen or functional state.
What does the study support?
It supports broadly similar selected collector outcomes under one small controlled protocol, while documenting substantial individual variation and collection limitations. The study was not an impairment experiment, did not randomize collector order and followed only seven doses. A defensible comparison preserves specimen volume, sequence, processing, isomer and observation window instead of treating all oral-fluid results as interchangeable.
Source
Newmeyer MN et al. Oral Fluid with Three Modes of Collection and Plasma Methamphetamine and Amphetamine Enantiomer Concentrations After Controlled Intranasal l-Methamphetamine Administration. Drug Testing and Analysis. 2015;7:877–883. doi:10.1002/dta.1784. Historical controlled human administration study.
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