OBJECTIVE To compare efficacy and duration of desensitization of oral structures with a lidocaine-bupivacaine mixture administered via a lateral percutaneous or modified infraorbital approach. ANIMALS 6 healthy adult hound-type female dogs. PROCEDURESIn this crossover study, dogs were randomized for side (left or right) and maxillary nerve approach (lateral percutaneous or infraorbital), with a 2-week washout period. Dogs were anesthetized, and a 2-mL mixture of 2% lidocaine and 0.5% bupivacaine (50:50 [vol/vol]) was administered with a 22-gauge, 4.5-cm-long catheter inserted through the infraorbital canal (infraorbital approach) or with a shielded stimulating needle to the maxillary nerve (percutaneous approach). Reflex-evoked motor potentials were measured for the maxillary canine tooth, fourth premolar tooth, second molar tooth, and hard palate mucosa ipsilateral to the injected mixture and for the contralateral maxillary canine tooth (control) at three 10-minute intervals before injection (baseline) and at predetermined times after injection for up to 6.7 hours. For each oral structure, the proportion of dogs with desensitization (efficacy) and time to onset and duration of desensitization were compared between approaches. RESULTS The proportion of dogs with successful nerve blockade did not significantly differ between infraorbital and percutaneous approaches and among the 4 oral structures. Time to onset of desensitization did not differ between approaches, but duration was significantly longer with the infraorbital approach. CONCLUSIONS AND CLINICAL RELEVANCE A modified infraorbital approach with the lidocaine-bupivacaine mixture had similar effects to a lateral percutaneous approach but provided a longer duration of desensitization. Neither approach was universally successful at desensitizing all oral structures.

OBJECTIVE To investigate the in vitro effects of clinically relevant concentrations of the local anesthetics (LAs) bupivacaine, lidocaine, lidocaine with preservative (LP), mepivacaine, and ropivacaine on equine chondrocyte and fibroblast-like synoviocyte (FLS) viability. SAMPLES Chondrocytes and FLSs of the metacarpophalangeal joints of 4 healthy adult horses. PROCEDURES Viability of chondrocytes and FLSs was determined with 3 assays: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH), and trypan blue (TB) exclusion (only FLS). Viability was assessed after 30- and 60-minute exposures to 0.0625%, 0.125%, and 0.25% bupivacaine; 0.25%, 0.5%, and 1% lidocaine; 0.25%, 0.5%, and 1% LP; 0.25%, 0.5%, and 1% mepivacaine; and 0.125%, 0.25%, and 0.5% ropivacaine. RESULTS Viability of chondrocytes was significantly decreased with exposure to 0.25% bupivacaine, 1% lidocaine, 1% LP, 1% mepivacaine, and 0.25% ropivacaine. Viability of FLSs was significantly decreased with exposure to 0.25% bupivacaine, 1% mepivacaine, 1% LP, and 0.5% ropivacaine. CONCLUSIONS AND CLINICAL RELEVANCE Clinically relevant concentrations of LAs had in vitro time- and concentration-dependent cytotoxicity for chondrocytes and FLSs isolated from the metacarpophalangeal joints of healthy horses. Bupivacaine was more toxic to chondrocytes than lidocaine, mepivacaine, and ropivacaine, whereas bupivacaine, LP, mepivacaine, and ropivacaine were more toxic to FLSs than preservative-free lidocaine. Several LAs may negatively affect chondrocyte and FLS viability.