Pharmacologic effects of
alpha-methylfentanyl and
3-methylfentanyl, analogs of
fentanyl, were investigated in mares. The ability of an 125I-labeled
fentanyl radioimmunoassay (125I-RIA) to detect these methylated
fentanyl analogs in individual and pooled urine samples from horses was evaluated. Also, the ability of 7
fentanyl antibodies to react with
fentanyl and
fentanyl derivatives (
sufentanil,
alfentanil, and
carfentanil) was investigated. Mares were studied in a locomotor test to determine the amount of stimulation methylated
fentanyl analogs might induce. Two mares each were given
alpha-methylfentanyl at 1, 2, 4, 8, or 13 micrograms/kg of
body weight, IV, or
3-methylfentanyl at 0.4, 0.7, or 1 microgram/kg IV. The cross-reactivity of
sufentanil,
alfentanil,
carfentanil,
alpha-methylfentanyl, and
3-methylfentanyl with 7
fentanyl antibodies was studied, using the 125I-RIA. All
fentanyl analogs, with the exception of
alfentanil, cross-reacted well with a C1 antibody raised to
fentanyl. Less satisfactory cross-reactivity was determined with 6 other
antibodies raised to
fentanyl derivatives. When the C1 antibody was combined with an iodinated analog to
fentanyl, good detectability of
alpha-methylfentanyl and
3-methylfentanyl, in terms of
fentanyl equivalents, was obtained from urine samples of dosed mares. The ability of the 125I-RIA to detect methylated
fentanyl analogs in forensic urine samples pooled in groups of up to 20 samples was evaluated. When these methylated analogs were administered to mares in doses that induced measurable locomotor stimulation, the analog's presence was readily detected in individual or pooled samples.