DEVELOPMENT OF A MINIMUM-ANESTHETIC-CONCENTRATION DEPRESSION MODEL TO STUDY THE EFFECTS OF VARIOUS ANALGESICS IN GOLDFISH ( CARASSIUS AURATUS )

Pharmacokinetics of the analgesic and anti-inflammatory drug meloxicam after administration of multiple doses to nursehound sharks (Scyliorhinus stellaris)

OBJECTIVE

To determine the pharmacokinetics of meloxicam in the nursehound shark (Scyliorhinus stellaris) during multiple dose administration.

STUDY DESIGN

Prospective experimental trial.

ANIMALS

A total of eight clinically healthy adult nursehounds (four males, four females).

METHODS

Meloxicam was administered intramuscularly at a dose of 1.5 mg kg-1 once daily for 7 days. Blood samples were collected from the caudal vein for pharmacokinetic analysis at 2.5 hours and 24 hours after drug administration. After a 4 week washout period, meloxicam was administered orally at the same dose at 12 hour intervals for three repeated doses. Blood samples were collected at 1, 2, 4, 6, 8, 12, 24, 36 and 48 hours after the first administration. Sharks were visually monitored during each study and 4 weeks afterwards for side effects or signs of toxicity. Time required to achieve steady state was assessed by visual inspection and statistical comparison of peak and trough concentrations using a Friedman test; comparison between sexes was performed using a Mann-Whitney U test and p-value was set at 0.05.

RESULTS

No animal died or showed clinical signs of toxicity during the study. Meloxicam administered orally did not produce detectable concentrations in plasma. After intramuscular administration, steady state was achieved after five doses, and mean trough and peak plasma concentrations at steady state were 1.76 ± 0.21 μg mL-1 and 3.02 ± 0.23 μg mL-1, respectively. Mean peak concentration accumulation ratio was 2.50 ± 0.22.

CONCLUSIONS AND CLINICAL RELEVANCE

This study shows that intramuscular posology produces plasma concentrations considered therapeutic for other species. However, meloxicam was not detected in plasma after oral administration. These results suggest that meloxicam administered intramuscularly may be a useful non-steroid anti-inflammatory drug in nursehound sharks. Further pharmacodynamic studies are needed to fully evaluate its clinical use in this species.

PHARMACOKINETICS OF MELOXICAM AFTER SINGLE ORAL AND INTRAMUSCULAR ADMINISTRATION IN CHINA ROCKFISH (SEBASTES NEBULOSUS)

Fish species are important for various purposes including aquaculture stock and display animals, but there are significant gaps in the medical knowledge regarding pharmacological parameters and effective pain management. Meloxicam is a nonsteroidal anti-inflammatory drug (NSAID) that has been studied in few teleost species and with several administration routes. However, these species were typically freshwater or euryhaline fish, and evaluation in marine species is lacking. The pharmacokinetic properties of meloxicam were determined in nine adult China rockfish (Sebastes nebulosus), presumed healthy based on physical examination and benign medical histories. Based on a pilot study, China rockfish were given 1 mg/kg meloxicam via IM injection in the epaxial musculature, and, after a 48-h washout period, 1 mg/kg meloxicam was given by PO gavage. Blood samples were collected from the caudal vein at baseline and at nine time intervals over a 48-h time period following administration of meloxicam. Plasma meloxicam concentrations were determined by reverse phase high-performance liquid chromatography, and noncompartmental analysis was performed. The mean peak plasma concentration after IM injection was 4.9 µg/ml, and the mean terminal half-life was 5.0 h. The mean peak plasma concentration after PO administration was 0.07 µg/ml. Based on these findings, IM injected meloxicam reaches plasma levels consistent with therapeutic concentrations in select mammals, and peak levels were maintained for ≤12 h. Single-dose PO administration failed to achieve similar concentrations, and clinical practicality is unknown. Further studies evaluating NSAID multidose regimes and their pharmacodynamic effects may provide additional dosing information.

Treatment of Pain in Fish

This chapter provides an overview of our current understanding of clinical analgesic use in fish. Recently, the efficacy and pharmacokinetics of several analgesic drugs for use in fish have been investigated, and the most important data indicates that μ-opioid agonist drugs (e.g, morphine) are consistently effective as analgesics across fish species. In addition, bath application of some analgesic drugs may be useful, which affords multiple methods for delivering analgesics to fish. Although few published studies of non-steroidal anti-inflammatory drugs administered to fish show promise, we have much to learn about the analgesic efficacy of most drugs in this class.

PHARMACOKINETICS OF MELOXICAM AFTER A SINGLE 1.5 MG/KG INTRAMUSCULAR ADMINISTRATION TO NURSEHOUND SHARKS (SCYLIORHINUS STELLARIS) AND ITS EFFECTS ON HEMATOLOGY AND PLASMA BIOCHEMISTRY

A single-dose meloxicam pharmacokinetic (PK) study was performed with eight clinically healthy nursehound sharks (Scyliorhinus stellaris) maintained under human care. Meloxicam was administered IM at a dosage of 1.5 mg/kg to six animals; two animals were administered elasmobranch physiological saline solution (EPSS) IM as a negative control group. Blood samples were obtained prior to and at 12 predetermined times during the first 36 h after administration. Effects on hematology and plasma biochemistry were compared prior to and 24 h after administration. No animal died or showed clinical signs during the study. A significant increase in creatinine kinase and aspartate aminotransferase was found in both EPSS and meloxicam groups and could be considered a direct consequence of sampling and handling required for the PK study. Observed mean time to maximum plasma concentration ± SEM was 2.58 ± 0.47 h and observed mean maximum plasma concentration ± SEM was 806 ± 66 ng/ml; mean terminal half-life ± SEM was 15.97 ± 1.20 h; mean residency time ± SEM was 23.40 ± 2.25 h. Area under the plasma concentration-versus-time curve extrapolated to infinity ± SEM was 15.52 ± 1.70 h·µg/ml. This study suggests that meloxicam 1.5 mg/kg IM in nursehound sharks is likely to result in clinically relevant plasma levels for periods of 24 h without producing significant alterations in blood analytics, although further PK studies with meloxicam IV in sharks are needed. Future PK and pharmacodynamic studies with different drugs and doses are needed in elasmobranchs to establish safe and effective treatment protocols.

Fish Sedation and Anesthesia

Veterinarians often need to sedate or anesthetize fish to perform physical examinations or other diagnostic procedures. Sedation may also be required to transport fish. Painful procedures require complete anesthesia with appropriate antinociceptive agents. Regulations and withdrawal times apply to food animal species in many countries. Specific protocols are therefore warranted in commercial fish versus ornamentals. Tonic immobility of elasmobranchs and electric anesthesia should never be used to perform painful procedures. Anesthetic monitoring in fish remains challenging. This review summarizes ornamental fish anesthesia and discusses techniques used in the commercial fish industry and in field conditions.

PHARMACOKINETIC, PHARMACODYNAMIC, AND TOXICOLOGY STUDY OF ROBENACOXIB IN RAINBOW TROUT (ONCORHYNCHUS MYKISS)

Postoperative antinociception control in fish is currently suboptimal, as commonly used antiinflammatory drugs last for only a few hours at tested temperatures. Therefore, long-acting anti-inflammatory drugs, such as robenacoxib, could improve the welfare of fish. The pharmacokinetics, duration of antinociceptive action, and potential adverse effects of robenacoxib were evaluated through two prospective randomized blinded trials in rainbow trout (Oncorhynchus mykiss). Six healthy rainbow trout received a single IM administration of robenacoxib (2 mg/kg), and two control fish received the same volume of saline IM. Blood samples were collected at predetermined time points for 5 d. Plasma robenacoxib concentrations were measured using high-performance liquid chromatography-high-resolution hybrid orbitrap mass spectrometry and noncompartmental pharmacokinetic analysis. Ten additional rainbow trout received an intralabial injection of 0.05 ml of 2% acetic acid following a previously validated nociceptive model. The treated group (n = 6) received 2 mg/kg of robenacoxib IM and the control group (n = 4) received an equivalent volume of saline IM. The behavior, appetite, and opercular rate of the fish were evaluated every hour for 5 h, then once daily for 3 d. All 12 treated trout and 6 controls underwent histopathologic evaluation. Average maximum plasma concentration (C_max) was 329.9 ± 137.3 ng/ml observed at 2.1 ± 0.7 h (T_max) and terminal half-life was 12.6 ± 2.27 h. Plasma concentrations described as antinociceptive in domestic carnivores were measured for 3-4 d. This dose was associated with a significant decrease in rocking behavior (P = 0.017). No adverse effects were detected clinically nor on histopathology. Robenacoxib administered IM at 2 mg/kg appears to be safe and may provide an antinociceptive effect in rainbow trout. This study presents a new therapeutic option to provide long-lasting antinociception in rainbow trout.

Pharmacokinetics of Ketoprofen in Nile Tilapia (Oreochromis niloticus) and Rainbow Trout (Oncorhynchus mykiss)

The objective of this study was to document the pharmacokinetics of ketoprofen following 3 mg/kg intramuscular (IM) and intravenous (IV) injections in rainbow trout (Oncorhynchus mykiss) and 8 mg/kg intramuscular (IM) injection in Nile tilapia (Oreochromis niloticus). Plasma was collected laterally from the tail vein for drug analysis at various time intervals up to 72 h following the injection of ketoprofen. In trout, area under the curve (AUC) levels were 115.24 μg hr/mL for IM and 135.69 μg hr/mL for IV groups with a half-life of 4.40 and 3.91 h, respectively. In both trout and tilapia, there were detectable ketoprofen concentrations in most fish for 24 h post-injection. In tilapia, there was a large difference between the R- and S-enantiomers, suggesting either chiral inversion from R- to S-enantiomer or more rapid clearance of the R-enantiomer. AUC values of the S- and R-enantiomers were 510 and 194 μg hr/Ml, respectively, corresponding to a faster clearance for the R-enantiomer. This study shows that there were very high plasma concentrations of ketoprofen in trout and tilapia with no adverse effects observed. Future studies on the efficacy, frequency of dosing, analgesia, adverse effects, and route of administration are warranted.

Anaesthetics and analgesics used in adult fish for research: A review

The number of fish used in research has increased in the last decades. Anaesthesia is required when fish must be held immobile and it is crucial to promote fish welfare, because these vertebrates can show signs of stress and/or pain during handling, transport, tagging, sampling and invasive procedures. The use of an inadequate anaesthetic protocol can compromise not only the welfare of the fish, but also the reliability of the research results. Thus, the development of suitable anaesthetic regimes for each fish species is important. This article reviews the main anaesthetic and analgesic agents used in adult fish in a research setting.

Lack of postexposure analgesic efficacy of low concentrations of eugenol in zebrafish

OBJECTIVE

To test the postexposure analgesic efficacy of low doses of eugenol in zebrafish.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 76 large adult zebrafish (Danio rerio).

METHODS

Fish swimming behavior (median velocity, freeze time, high-speed swimming and distance moved in the vertical direction) was recorded in a 1.6 L video arena before and after exposure to eugenol (0, 1, 2, 5, 10 and 20 mg L^-1). In a second experiment, fish were anesthetized with 2-phenoxy-ethanol and treated with an injection of 5% acetic acid (noxious stimulus), and then exposed to 0, 1, 2 and 5 mg L^-1 eugenol. The fish swimming behavior was also recorded.

RESULTS

The higher doses (10 and 20 mg L^-1) reduced the median velocity, high-speed swimming and distance moved in the vertical direction, and increased the freeze time. Zebrafish behavior was not altered by eugenol (1, 2 and 5 mg L^-1) after noxious stimulation.

CONCLUSIONS AND CLINICAL RELEVANCE

The change in the behavior of zebrafish associated with a noxious stimulus can be monitored and is a good model for studying analgesia in fish. Eugenol (10 and 20 mg L^-1) induced zebrafish sedation. The response after a noxious stimulus was not affected by postexposure to lower doses, and thus we cannot recommend its use as an analgesic.

Evidence-Based Advances in Aquatic Animal Medicine

Fish and aquatic invertebrates deserve evidence-based medicine. Pharmacologic information is available; most pharmacokinetic studies are derived from the aquaculture industry and extrapolated to ornamental fish. Conversely, advanced diagnostics and information regarding diseases affecting only ornamental fish and invertebrates require more peer-reviewed experimental studies; the examples of carp edema virus, sea star wasting disease, seahorse nutrition, and gas bubble disease of fish under human care are discussed. Antinociception is also a controversial topic of growing interest in aquatic animal medicine. This article summarizes information regarding new topics of interest in companion fish and invertebrates and highlights some future avenues for research.

PROPOFOL AS AN IMMERSION ANESTHETIC AND IN A MINIMUM ANESTHETIC CONCENTRATION (MAC) REDUCTION MODEL IN GOLDFISH (CARASSIUS AURATUS)

Propofol is a novel immersion anesthetic in goldfish ( Carassius auratus ). Objectives were to characterize propofol as an anesthetic and assess its suitability in a minimum anesthetic concentration (MAC) reduction model. Using a crossover design, eight goldfish were submerged in 1, 5, or 10 mg/L propofol. Data included induction time, recovery time, heart rate, opercular rate, and response to supramaximal stimulation. Baseline MAC (Dixon's up-and-down method) was determined, and 15 fish were anesthetized with propofol on 4 consecutive days with MAC determination on the fifth day, weekly, for 1 mo. Using a crossover design, MAC of propofol (n = 15) was determined 1 hr following administration of i.m. butorphanol 0.05, 0.5, and 1 mg/kg, dexmedetomidine 0.01, 0.02, and 0.04 mg/kg, ketoprofen 0.5, 1, and 2 mg/kg, morphine 5, 10, and 15 mg/kg, or saline 1 ml/kg. Comparisons were performed with Wilcoxon signed-rank tests (P < 0.05) and Tango's score confidence interval. Propofol at 1 mg/L did not produce anesthesia. Induction time with 10 mg/L (112, 84-166 s) was faster than 5 mg/L (233, 150-289 s; P = 0.0078). Heart and opercular rates for 5 and 10 mg/L were 36 (24-72) beats/min, 58 (44-68) operculations/min and 39 (20-48) beats/min, 57 (48-80) operculations/min, respectively. Recovery time was 249 (143-396) s and 299 (117-886) s with 5 and 10 mg/L, respectively. Response to supramaximal stimulation was not significantly different with 5 mg/L (1/8) compared with 10 mg/L (0/8). Baseline and weekly MAC following daily exposure was 8.4 and 9.0, 8.1, 8.1, and 8.7 mg/L, respectively. MAC reduction was no more than 8% following any drug or dosage. Propofol at 5 and 10 mg/L produced anesthesia, and anesthetic needs were similar following repeated exposure. Propofol was not suitable to test MAC reduction in goldfish in this study.

TRICAINE METHANESULFONATE (MS-222) SEDATION AND ANESTHESIA IN THE PURPLE-SPINED SEA URCHIN (ARBACIA PUNCTULATA)

The purple-spined sea urchin ( Arbacia punctulata ) is commonly found in shallow waters of the western Atlantic Ocean from the New England area of the United States to the Caribbean. Sea urchins play a major role in ocean ecology, echinoculture, and biomedical research. Additionally, sea urchins are commonly displayed in public aquaria. Baseline parameters were developed in unanesthetized urchins for righting reflex (time to regain oral recumbency) and spine response time to tactile stimulus. Tricaine methanesulfonate (MS-222) was used to sedate and anesthetize purple-spined sea urchins and assess sedation and anesthetic parameters, including adhesion to and release from a vertical surface, times to loss of response to tactile stimulus and recovery of righting reflex, and qualitative observations of induction of spawning and position of spines and pseudopodia. Sedation and anesthetic parameters were evaluated in 11 individuals in three circumstances: unaltered aquarium water for baseline behaviors, 0.4 g/L MS-222, and 0.8 g/L MS-222. Induction was defined as the release from a vertical surface with the loss of righting reflex, sedation as loss of righting reflex with retained tactile spine response, anesthesia as loss of righting reflex and loss of tactile spine response, and recovery as voluntary return to oral recumbency. MS-222 proved to be an effective sedative and anesthetic for the purple-spined sea urchin at 0.4 and 0.8 g/L, respectively. Sodium bicarbonate used to buffer MS-222 had no measurable sedative effects when used alone. Anesthesia was quickly reversed with transfer of each individual to anesthesia-free seawater, and no anesthetic-related mortality occurred. The parameters assessed in this study provide a baseline for sea urchin anesthesia and may provide helpful comparisons to similar species and populations that are in need of anesthesia for surgical procedures or research.

Fish Oncology: Diseases, Diagnostics, and Therapeutics

The scientific literature contains a wealth of information concerning spontaneous fish neoplasms, although ornamental fish oncology is still in its infancy. The occurrence of fish neoplasms has often been associated with oncogenic viruses and environmental insults, making them useful markers for environmental contaminants. The use of fish, including zebrafish, as models of human carcinogenesis has been developed and knowledge gained from these models may also be applied to ornamental fish, although more studies are required. This review summarizes information available about fish oncology pertaining to veterinary clinicians.

PHARMACOKINETIC EVALUATION OF MELOXICAM AFTER INTRAVENOUS AND INTRAMUSCULAR ADMINISTRATION IN NILE TILAPIA (OREOCHROMIS NILOTICUS)

Critically evaluating the pharmacokinetic behavior of a drug in the body provides crucial information about how to effectively treat a patient. Pharmacokinetic studies that exist in fish have primarily focused on drugs used to treat infectious disease, with minimal attention given to analgesic drugs. The objective of this study was to determine the pharmacokinetics of meloxicam (1 mg/kg) in Nile tilapia ( Oreochromis niloticus ) (n = 12). A single dose of meloxicam was administered either i.v. or i.m. Blood samples were obtained at predetermined times after drug injection. Plasma meloxicam concentrations were determined by a validated liquid chromatography/mass spectrometry method, and noncompartmental pharmacokinetic analysis was performed. The mean peak plasma concentration after i.m. injection was 1.95 μg/ml. The mean terminal half-life of meloxicam after i.v. and i.m. administration was 1.36 and 1.8 hr, respectively. The area under the plasma concentration-versus-time curve extrapolated to infinity was 11.26 hr·μg/ml after i.v. administration and 5.72 hr·μg/ml after i.m. administration. Bioavailability of meloxicam after i.m. administration was approximately half that of i.v. administration. Elimination was rapid in both the i.m. and i.v. routes of administration, suggesting that maintaining clinically relevant plasma concentrations may be difficult using this dose. This study represents the first pharmacokinetic evaluation of a nonsteroidal anti-inflammatory drug in a fish species, and further studies evaluating efficacy are needed.

Evaluation of the anesthetic efficacy of alfaxalone in oscar fish (Astronotus ocellatus)

OBJECTIVE

To evaluate effects of alfaxalone on heart rate (HR), opercular rate (OpR), results of blood gas analysis, and responses to noxious stimuli in oscar fish (Astronotus ocellatus).

ANIMALS

6 healthy subadult oscar fish.

PROCEDURES

Each fish was immersed in water containing 5 mg of alfaxalone/L. Water temperature was maintained at 25.1°C, and water quality was appropriate for this species. The HR, OpR, response to noxious stimuli, and positioning in the tank were evaluated, and blood samples for blood gas analysis were collected before (baseline), during, and after anesthesia.

RESULTS

Immersion anesthesia of oscar fish with alfaxalone (5 mg/L) was sufficient for collection of diagnostic samples in all fish. Mean ± SD induction time was 11 ± 3.8 minutes (minimum, 5 minutes; maximum, 15 minutes), and mean recovery time was 37.5 ± 13.7 minutes (minimum, 20 minutes; maximum, 55 minutes). There was a significant difference in OpR over time, with respiratory rates significantly decreasing between baseline and anesthesia and then significantly increasing between anesthesia and recovery. There was no significant difference in HR over time. Median lactate concentrations were significantly increased in all anesthetized fish. Other physiologic or blood gas variables did not change significantly.

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone should be considered as a readily available and easy-to-use anesthetic for oscar fish. Because it is more likely to be found in veterinary hospitals than other traditional anesthetics for fish, its value as an anesthetic for other species of fish should also be considered.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Evaluation of the effects of tricaine methanesulfonate on retinal structure and function in koi carp (Cyprinus carpio)

OBJECTIVE

To determine whether repeated exposure to clinically relevant concentrations of tricaine methanesulfonate (MS-222) would alter retinal function or induce histologically detectable retinal lesions in koi carp (Cyprinus carpio).

DESIGN

Prospective, controlled, experimental study.

ANIMALS

18 healthy koi carp.

PROCEDURES

2 fish were euthanized at the start of the study, and eyes were submitted for histologic evaluation as untreated controls. Anesthesia was induced in the remaining fish with 200 mg of MS-222/L and maintained with concentrations of 125 to 150 mg/L for a total exposure time of 20 minutes daily on 1 to 13 consecutive days. On days 1, 7, and 13, electroretinography of both eyes was performed in all fish remaining in the study, and 2 fish were euthanized immediately after each procedure for histologic evaluation of the eyes. Median b-wave amplitudes were compared among study days for right eyes and for left eyes via 1-way repeated-measures ANOVA with a Bonferroni correction for multiple comparisons.

RESULTS

Median b-wave amplitudes on days 1, 7, and 13 were 17.7, 20.9, and 17.6 μV, respectively, for right eyes and 15.1, 16.9, and 14.3 μV, respectively, for left eyes. No significant differences in b-wave amplitudes were detected among study days. No histopathologic abnormalities were identified in the retinas of any fish treated with MS-222 or in control fish.

CONCLUSIONS AND CLINICAL RELEVANCE

Short-term exposure of koi carp to clinically relevant concentrations of MS-222 daily for up to 13 days was not associated with changes in retinal structure or function as measured in this study.