Determination of highest no effect dose (HNED) for local anaesthetic responses to procaine, cocaine, bupivacaine and benzocaine

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This report evaluates the pharmacological responses, urinary detection and mass spectral confirmation of ropivacaine in horses. Ropivacaine, a potent local anesthetic (LA) recently introduced in human medicine, has an estimated highest no-effect dose (HNED) of about 0.4 mg/site as determined in our abaxial sesamoid block model. Apparent ropivacaine equivalents were detectable by ELISA screening using a mepivacaine ELISA test after administration of clinically effective doses. Mass spectral examination of postadministration urine samples showed no detectable parent ropivacaine, but a compound indistinguishable from authentic 3-hydroxyropivacaine was recovered from these samples. The study shows that ropivacaine is a potent LA in the horse, that clinically effective doses can be detected in postadministration samples by ELISA-based screening, and that its major post administration urinary metabolite is 3-hydroxyropivacaine.

Section: Methodssupporting

confidence: 58%

Ropivacaine in the horse: its pharmacological responses, urinary detection and mass spectral confirmation

Harkins

Karpiesiuk

Lehner

et al. 2001

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“…In this way, a family of dose response curves ( Fig. 4) and HNEDs have been identified for bupivacaine , ropivacaine (Harkins et al, 1999a), mepivacaine (Harkins et al, 1999c;Woods et al, 1998), lidocaine (Harkins et al, 1998a), procaine, cocaine and benzocaine (Harkins et al, 1996a), Sarapin 1 (Harkins et al, 1997a), and fentanyl (Harkins & Tobin, 1999). Some of these agents are highly potent, some are of intermediate potency, and some are pharmacologically inactive in this model.…”

Section: The`highest No Effect Dose'mentioning

confidence: 91%

“…The classic example is procaine. Based on research by our group, the estimated plasma`cut-off' for procaine would be & 1 ng/mL (Harkins et al, 1996a), well below the limit of quantitation of current routine analytical methods. A second problem with procaine is that it is hydrolyzed very rapidly by plasma esterases.…”

Section: Further Analytical/pharmacological Relationshipsmentioning

confidence: 98%

Testing for therapeutic medications: analytical/pharmacological relationships and 'limitations' on the sensitivity of testing for certain agents

Tobin

Harkins²,

Samś³

1999

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Proper veterinary care of horses requires that horses in training have access to modern therapeutic medication. However, the sensitivity of equine drug testing now allows for detection of pharmacologically insignificant concentrations of many therapeutic medications. In 1995, the Association of Racing Commissioners International (ARCI) resolved that members 'address trace level detection so as not to lead to disciplinary action based on pharmacologically insignificant traces of these substances'. The rationale behind this approach is to prevent overly-sensitive testing from inhibiting the proper and appropriate veterinary care of performance horses. This review describes a scientific approach to implement this resolution using local anaesthetics as a model system and compares this approach with others currently in place. For the purpose of this discussion, a 'trace' concentration is defined as a pharmacologically-insignificant concentration. Initially, the target pharmacological effect (e.g. local anaesthesia) was identified, and the dose response relationship was quantified. The 'Highest No Effect Dose' (HNED) was estimated and then administered to horses. Next, the target analyte was identified, synthesized, if necessary, and quantified in blood or urine; the concentrations observed after administration of the HNED are, by definition, true concentrations and hence are pharmacologically insignificant. The key to this approach has been the synthesis of a unique series of authentic equine metabolite standards, which has allowed scientific identification of the concentration at which the pharmacological effect was indistinguishable from control values. Traces found at less than this concentration are, by definition, 'no effect limits', 'no effect traces' (NETs), 'no effect cut-offs', 'no effect limitations on the sensitivity of testing', or 'subtherapeutic residues'. Conversely, this approach will also identify potent medications for which the sensitivity of testing may need to be improved. Within the context of these experiments, the data create an analytical/pharmacological database that should assist industry professionals in interpreting the significance of trace concentrations of these medications or their metabolites in official samples. The most favourable outcome of this research is more medically appropriate use of therapeutic medications in performance horses, yielding substantial benefits to the health and welfare of these horses.

“…For the LAR experiments, dose and time response relationships for mepivacaine were determined with a heat projection lamp described previously (Harkins et al ., 1996). Briefly, focused radiant light/heat was used as a noxious stimulus and was directed onto the pastern of the horse to elicit the classic flexion‐withdrawal reflex.…”

Section: Methodsmentioning

confidence: 99%

Mepivacaine: its pharmacological effects and their relationship to analytical findings in the horse

Harkins

Karpiesiuk

Woods

et al. 1999

Mepivacaine is a local anaesthetic drug that is widely used in equine medicine and is classified by the Association of Racing Commissioners International (ARCI) as a Class 2 foreign substance that may cause regulators to impose significant penalties if residues are identified in post-race urine samples. Therefore, an analytical/pharmacological database was developed for this agent and its metabolites. Using an abaxial sesamoid local anaesthetic model, it was determined that the highest no-effect dose (HNED) for its local anaesthetic effect was 2 mg. Using enzyme-linked immunosorbent assay (ELISA) screening, it was determined that subcutaneous (s.c.) administration of the HNED of mepivacaine to eight horses yielded a peak urinary concentration of apparent mepivacaine of 63 ng/mL 2 h after injection. The major identified metabolite recovered from equine urine after dosing with mepivacaine is 3-hydroxymepivacaine. Therefore, 3-hydroxymepivacaine was synthesized, purified and characterized, and a quantitative mass spectrometric method was developed for this metabolite as isolated from horse urine. Following subcutaneous injection of the HNED of mepivacaine, the concentration of 3-hydroxymepivacaine recovered from horse urine reached a peak of about 64.6 ng/mL at 4 h after administration as measured by GC/MS. The concentration of mepivacaine or its metabolites after administration of a HNED dose are detectable by mass spectral techniques. Within the limits of this research, the study suggests that recovery of concentrations less than about 65 ng/mL of 3-hydroxymepivacaine from post-race urine samples may not be associated with a recent LA effect of mepivacaine.