Jennifer L. Davis

CNS4 is an agonist concentration-biased NMDAR modulator exhibiting GluN2 subtype-dependent activity. Here we evaluated the translational pharmacology of CNS4 across mice, rats, and client-owned surgical oncology dogs. In mice, CNS4 did not produce conditioned place preference, indicating lack of reward liability. CNS4 produced dose-dependent reductions in locomotor activity without motor impairment on accelerating rotarod testing. CNS4 also maintained body temperature 0.5–1°C above the vehicle group in mice and dogs, consistent with NMDAR-dependent thermoregulatory activity and contrasting with hypothermic effects reported for NMDAR channel blockers such as ketamine. In fear-conditioning paradigms, CNS4 did not impair fear learning, memory consolidation, or fear expression. CNS4 reduced acute stress-induced sucrose preference, suggesting modulation of stress-responsive neural circuits. In a rat spinal nerve ligation model of neuropathic pain, both single-dose and three-day repeated CNS4 administration significantly reversed mechanical, pressure, and thermal hypersensitivity, supporting analgesic efficacy with no apparent evidence of rapid tolerance development. In client-owned surgical oncology dogs undergoing standard veterinary procedures, preliminary findings from 14 dogs (8 CNS4-treated, 6 vehicle-treated) demonstrated stable intraoperative mean arterial pressure and heart rate. Postoperatively, CNS4-treated dogs exhibited normal physiological recovery, with respiratory rate, heart rate, and body temperature returning toward the normal canine range, and required approximately 8% less propofol for anesthetic induction. Collectively, these findings support CNS4 as a novel NMDAR modulator with thermoregulatory, anti-agitative, analgesic, and autonomic-stabilizing properties without evidence of abuse liability, supporting continued translational development for neuropathic pain and possibly neuropsychiatric disorders.

Objective: To describe the pharmacokinetics of a single dose of pimobendan (Vetmedin) in healthy adult horses and provide preliminary evidence of the absorption of 2 compounded pimobendan formulations. Methods: From August 2022 through November 2022, 6 healthy adult horses were administered a single dose of 0.5 mg/kg pimobendan orally. A subset of 2 horses was also administered pimobendan, compounded as an oil-based suspension and a capsule formulation. Plasma was collected at times 0, 15, 30, and 45 minutes and 1, 2, 4, 8, 12, and 24 hours after administration. The plasma concentrations of pimobendan and its active metabolite, O-desmethyl-pimobendan, were determined by UPLC-MS-MS. Data were analyzed using noncompartmental pharmacokinetics. Results: Pimobendan reached a mean maximum plasma concentration (C _max ) of 4.96 ± 2.13 ng/mL at time 2.17 ± 0.98 hours, with an area under the concentration-versus-time curve from time 0 to infinity (AUC _0–∞ ) of 22.1 ± 8.8 h·ng/mL. The compounded formulations in the 2 horses receiving them resulted in a C _max ranging from 2.66 to 4.58 ng/mL and an AUC _0–∞ ranging from 11.78 to 16.82 h·ng/mL. O-desmethyl-pimobendan was not detected in any sample. Conclusions: The mean C _max and AUC _0–∞ of pimobendan in the plasma of these horses after administration of Vetmedin and compounded formulations was considerably lower than the C _max reported in dogs administered the same dose. Clinical Relevance: Low plasma concentrations of pimobendan in horses were measured regardless of formulation. Further investigations of other doses and routes are recommended prior to clinical use.

Objective: To evaluate the pharmacokinetics of mirtazapine (MRZ) after single-dose oral administration in healthy adult alpacas and compare concentrations at 2 venous sampling sites. Methods: This study was conducted during the weeks of January 29, 2024, and February 15, 2024. A single dose of 2 mg/kg MRZ was administered orally via syringe to 7 healthy adult alpacas. Blood was collected from jugular vein (JV; n = 7) and cephalic vein (CV; 5) catheters immediately prior to and at predetermined times for 24 hours after administration. Plasma MRZ concentrations were determined by UPLC-MS-MS. Pharmacokinetic parameters were determined for each sampling site, and statistical analysis was performed by paired t tests. Results: Mean maximum plasma concentrations (C _max ) from JV samples (183 ± 95.2 ng/mL) occurred at time 0.0281 ± 0.029 hours and were significantly higher than CV samples’ C _max (4.84 ± 2.37 ng/mL), which occurred at time 0.464 ± 0.093 hours. Comparison of dose-corrected C _max and area under the concentration-time curve from time zero extrapolated to infinity with those previously reported show the C _max from JV samples in alpacas is similar to cats (166 ng/mL), but the C _max from the CV samples failed to reach that reported in dogs (140 ng/mL) and people (123 ng/mL). Conclusions: Plasma concentrations of MRZ were significantly different between sampling sites, resulting in different interpretations for potential use in alpacas. Clinical Relevance: Additional information is needed before using oral MRZ in alpacas, including studies of different doses, formulations, or routes of administration.

Objective: To characterize the effects of pioglitazone (2 mg/kg, PO, either q 24 h [PIO-SID] or q 12 h [PIO-BID]) in equids with severe hyperinsulinemia. Methods: 17 client-owned equids with severe resting hyperinsulinemia (> 100 µIU/mL) were assigned to PIO-SID or PIO-BID in a prospective cohort study with rolling enrollment over an 11-month study period (December 13, 2022, to November 17, 2023). Basal insulin, total and high-molecular-weight adiponectin concentrations, and plasma pioglitazone concentrations were measured over 70 days. Oral sugar tests (OSTs) were performed on days 0 and 28. Results were analyzed via a mixed-effects linear regression model. Results: Mean (95% CI) resting insulin concentrations decreased from day 0 (PIO-SID, 191.2 µIU/mL [10.1 to 372.1 µIU/mL]; PIO-BID, 113.0 µIU/mL [46.9 to 179.2 µIU/mL]) to day 70 (PIO-SID, 183.4 µIU/mL [–44.6 to 411.4 µIU/mL]; PIO-BID, 66.7 µIU/mL [28.8 to 104.5 µIU/mL]) equivocally in both treatment groups; however OST insulin did not change in either. The high-molecular-weight adiponectin increased in PIO-BID between day 0 (3.5 µg/mL [–0.3 to 7.2 µg/mL]) and day 70 (15.0 µg/mL [6.9 to 23.0 µg/mL]), but not in PIO-SID (day 0 = 0.7 µg/mL [0.2 to 1.3 µg/mL]; day 70 = 4.0 µg/mL [–3.0 to 11.1 µg/mL]). Plasma pioglitazone concentrations on day 70 were 291.8 ng/mL (–40.1 to 623.7 ng/mL [PIO SID]) and 739.7 (453.0 to 1,026.3 ng/mL [PIO-BID]). Conclusions: Pioglitazone did not affect OST insulin and failed to normalize resting insulin. With PO administration every 12 hours, plasma concentrations exceeded the reported human therapeutic threshold (617 ng/mL), and adiponectin significantly increased. Clinical Relevance: Although not effective as a sole treatment for severe hyperinsulinemia, pioglitazone increases adiponectin, a potentially beneficial effect that warrants further investigation.

Background: Phenazopyridine is used for ancillary pain management in the treatment of goats with obstructive urolithiasis. However, there are no published studies on the pharmacokinetics, safety, or efficacy of phenazopyridine in goats. Hypothesis/Objectives: Determine the pharmacokinetic parameters of phenazopyridine after oral administration in goats with obstructive urolithiasis after tube cystostomy surgery. Animals: Six male goats, ages 3 months to 4 years. Methods: Prospective, observational study. Goats presenting to a veterinary institution diagnosed with obstructive urolithiasis underwent a tube cystostomy surgery. After surgery, phenazopyridine (4 mg/kg PO q12h) was administered. Plasma and urine samples were collected at predetermined intervals, and the concentration of phenazopyridine and clinically relevant metabolites was determined using ultra high-performance liquid chromatography with mass spectrometry. The pharmacokinetic parameters were determined using non-compartmental analysis. Results: The harmonic mean terminal elimination plasma half-life (T1/2), geometric mean maximum plasma concentration (Cmax), and area under the curve (AUC) were 0.5 h (0.22–1.57 h), 263.4 ng/mL (137.35–1047.88 ng/mL), and 0.69 h*ng/mL (0.10–2.99 h*ng/mL), respectively for phenazopyridine. The concentration of phenazopyridine in urine samples was below the limit of assay detection (1.5 ng/mL) in all but one sample. Conclusions and Clinical Importance: Phenazopyridine was rapidly eliminated from plasma and did not concentrate at detectable levels in the urine after oral administration.

Flunixin meglumine is a nonsteroidal anti-inflammatory drug (NSAID). Banamine Transdermal is a pour-on formulation of flunixin approved for pain control in beef and dairy cattle, but not for calves and some classes of dairy cattle or swine. Violative flunixin residues in edible tissues in cattle and swine have been reported and are usually attributed to non-compliant drug use or failure to observe an appropriate withdrawal time. This project aimed to develop a physiologically based pharmacokinetic (PBPK) model for flunixin in cattle and swine to predict withdrawal intervals (WDI) after exposures to different therapeutic regimens of Banamine Transdermal. Due to the lack of comprehensive skin physiological data in cattle, the model was initially developed for swine and then adapted for cattle. Monte Carlo simulation was employed for population variability analysis. The model predicted WDIs were rounded to 1 and 2 d for liver and muscle in cattle, respectively, under FDA tolerance levels, while under EU maximum residue limits, the WDIs were rounded to 1, 3, 2, and 2 d for liver, kidney, muscle, and fat, respectively, following a labeled single transdermal 3.3 mg/kg dose in cattle. The model was converted into a user-friendly interactive PBPK (iPBPK) interface. This study reports the first transdermal absorption model for drugs in cattle. This iPBPK model provides a scientifically based tool for the prediction of WDIs in cattle and swine administered with flunixin in an extra-label manner, especially by the transdermal route.

NMDAR channel blockers produce analgesic and antidepressant effects by preferentially inhibiting the GluN2D subtype at lower doses. Given the distinct physiological role of GluN2 subunits, we hypothesized that compounds capable of simultaneously modulating GluN2A and GluN2D subtypes in opposite directions could serve as effective analgesics with minimal cognitive adverse effects. In this translational study, we investigated the in vivo effects of CNS4, a recently discovered glutamate concentration-dependent NMDAR modulator. Pharmacokinetic data revealed that CNS4 reaches peak plasma and brain concentrations within 0.25 hours post-intraperitoneal injection, with brain concentrations reach values up to 8.4% of those in plasma (64.9 vs. 5.47 µg/ml). Preliminary results showed that CNS4, a non-opioid compound, increased escape latency in mice during a hotplate assay by 1.74-fold compared to saline. In a fear conditioning (FC) experiment, CNS4 anecdotally reduced the electric shock sensation and significantly decreased stress-related defecation (fecal pellets: males, 21 vs. 1; females, 19 vs. 3). CNS4 also improved hyperarousal behavior (25 vs. 4 jumps), without affecting fear memory parameters such as freezing episodes, duration, or latency. CNS4 caused no changes in locomotion across 8 of 9 parameters studied. Remarkably, approximately 50 hours after FC training, CNS4 prevented stress-induced excessive sucrose drinking behavior by more than 2-fold both in male and female mice. These findings suggest that CNS4 penetrates brain tissue and produces pharmacological effects like those of NMDAR-targeting drugs but with a distinct mechanism, avoiding the undesirable side effects typical of traditional NMDAR blockers. Therefore, CNS4 holds potential as a novel non-opioid analgesic, warranting further investigation. Significance: NMDA-subtype glutamate receptors are an attractive target for chronic pain and PTSD treatments as they play a critical role in forming emotional memories of stressful events. In this translational pharmacology work, we demonstrate the central analgesic and stress-mitigating characteristics of a novel glutamate concentration-biased NMDA receptor modulator, CNS4. Visual