Immunoassays for the Detection of Cannabis Abuse

Efavirenz interference in urine screening immunoassays for tetrahydrocannabinol

“…Being low-molecular-weight compounds, cannabinoid haptens (typically 11-nor-Δ 9 -THC-9-carboxylic acid) require linkage to carrier proteins to produce immunogens for antibody generation. 2,3 Steric hindrance by carrier proteins results in the generation of antibodies directed towards exposed functional groups remote from the site of carrier protein linkage. Linkage to positions C1-, C2- or C5′ elicits antibodies with high selectivity for the cyclohexyl ring, which translates to lower sensitivity to C8- and C11-hydroxylated metabolites and their glucuronides (Figure 1).…”

“…3 Antibodies generated by C8- to C11-linked and benzpyran immunogens therefore offer superior detection for clinical purposes, because THC is extensively metabolized at these positions prior to urinary excretion. 2 Inspection of the cross-reactivity data (albeit incomplete) for the 10 assays in Table 1 reveals that some assays, which are subject to EFV interference, exhibit comparatively lower sensitivities to C8- and C11-hydroxylated metabolites. Our postulate that antibodies used in these assays may have been elicited using immunogens with carrier protein linkage to C1-, C2- or C5′ could not be verified, because vendor and proprietary restrictions prevent access to detailed information about immunogen composition.…”

“…Bold arrows indicate published linkage sites for carrier proteins to cannabinoid haptens (from ref. 2 ) …”

“…3 Conversely, linkage to the cyclohexyl ring generates antibodies with greater cross-reactivity to C8-, C9-and C11-substituted moieties. 2 This concept was taken one step further by Roche Diagnostic Systems with the development of a non-cannabinoid immunogen containing only the benzpyran core. 3 By eliminating the antigenic determinants of the cyclohexyl ring completely, antibodies with two to three times higher cross-reactivity to C8-and C11-hydroxylated metabolites than even the C9-linked .............................................................................................................................................…”