Using molecular similarity to highlight the challenges of routine immunoassay-based drug of abuse/toxicology screening in emergency medicine

Table 2 Drugs that can produce false positives on broad specificity DOA/Tox screening immunoassays

			Cross-Reactivity to Marketed Immunoassays
Drug	Assay¹	Similarity to assay target compound²	Abbott³	Beckman³	Biosite Triage³	Microgenics³	Roche³	Siemens³
Phentermine	AMPH	0.778	No effect	No effect	750,000	No effect		25,000
Levofloxacin	OPIA	0.560	1,700,000	No effect	125,000	60,000	200,000
Dextromethorphan	PCP	0.565	12,900	No effect	500,000	No effect	No effect	12,000
Meperidine	PCP	0.538	34,650	No effect	No effect	No effect	No effect	25,000
Carbamazepine	TCA	0.460	29,972		No effect	No effect		No effect
Cyclobenzaprine	TCA	0.565			2,000	450
Prochlorperazine	TCA	0.630	999	100,000
Quetiapine	TCA	0.485	2,484		No effect	No effect		100,000

¹ Assay abbreviations: AMPH, amphetamines; OPIA, opiates; PCP, phencyclidine; TCA, tricyclic antidepressants.
² Target compounds: AMPH, d-amphetamine; OPIA, morphine; PCP, phencyclidine; TCA, desipramine. Similarity calculated using MDL public keys with Tanimoto coefficient.
³ Concentration of compound in ng/mL that produces cross-reactivity equal to 1,000 d-amphetamine (AMPH assay), 300 ng/mL morphine (OPIA assay), 25 ng/mL phencyclidine (PCP assay), or 1,000 ng/mL desipramine (TCA assay). Blank cells indicate that no cross-reactivity data is reported. For all assays except TCA, marketed assays are Abbott Architect, Beckman, Biosite Triage, Microgenics DRI, Roche cobas c, Siemens Syva EMIT. For TCA, marketed assays are Abbott AxSYM, Biosite Triage, Microgenics DRI serum, and Siemen Syva EMIT. See Additional file 1 (tab T) for more detail.

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