The pharmacokinetics, pharmacological responses and behavioral effects of acepromazine in the horse

Decreased Circulating Red Cell Mass Induced by Intravenous Acepromazine Administration Alters Viscoelastic and Traditional Plasma Coagulation Testing Results in Healthy Horses

Coagulopathy is common in equine critical illness, with its early recognition being crucial for patient management and prognosis. In vitro viscoelastic (VE) hypercoagulability with decreased RCM/PCV has been demonstrated in dogs but not horses. Our objective was to evaluate the effects of acepromazine-induced (0.1 mg/kg IV) decreased RCM on VE and plasma coagulation parameters using a prospective interventional study of eight adult horses. Complete blood count (CBC), fibrinogen, prothrombin time (PT), partial thromboplastin time (PTT), packed cell volume (PCV), total solids (TS), and VCM Vet™ VE testing performed at baseline (T0), 1 h (T1), and 12 h (T2) post acepromazine administration. Splenic volume was determined ultrasonographically. The results were analyzed using one-way repeated measures ANOVA with Tukey's post hoc HSD test to determine the effect of time (sample). PCV decreased 13% points following acepromazine administration from T0 to T1 (p < 0.001), remaining decreased at T2 (p < 0.001). Splenic volume increased from T0 to T1 (p = 0.04) and was not different from baseline at T2. Maximal clot formation (MCF) increased from T0 (p = 0.03). PTT decreased from T0 to T1 and increased at T2 (p = 0.03). No other coagulation parameters were significantly altered. This study demonstrates a non-inflammatory acute model of anemia in horses that impacts VE and plasma-based testing.

A review of equine anesthetic induction: Are all equine anesthetic inductions "crash" inductions?

Horses are the most challenging of the common companion animals to anesthetize. Induction of anesthesia in the horse is complicated by the fact that it is accompanied by a transition from a conscious standing position to uncconconscious recumbency. The purpose of this article is to review the literature on induction of anesthesia with a focus on the behavioral and physiologic/pharmacodynamic responses and the actions and interactions of the drugs administered to induce anesthesia in the healthy adult horse with the goal of increasing consistency and predictability.

A highly efficient and portable laser-scribed graphene-based electrochemical system for forensic-oriented determination of acepromazine

Acepromazine (ACP) is a phenothiazine derivative drug commonly used as a tranquilizer veterinary medication due to its sedative properties. Benefiting from sedative properties, ACP has emerged as a drug of abuse and has been associated with drug-facilitated sexual assaults. Herein, we report, for the first time, the electrochemical behavior of ACP using a miniaturized and environmentally friendly laser-scribed graphene-based (LSG) sensor fabricated on a polyetherimide (PEI) substrate. The LSG device presented high porosity, as demonstrated by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements of the PEI-LSG electrode confirmed the enhanced electroactive area (3.1-fold increase) caused by the rough surface and revealed a low charge transfer resistance of the electrode material, with a heterogeneous electron transfer rate constant (k0) of 8.66 × 10-3 cm s-1 for potassium ferricyanide redox probe. A simple and accurate method was applied to quantify ACP by using square wave voltammetry (SWV) under optimized experimental conditions, which exhibited high sensitivity (0.686 ± 0.008 A L mol-1 cm-2) and a low limit of detection (LOD) of 7.43 × 10-8 mol L-1, with a linear concentration ranging from 0.5 to 100 μmol L-1 ACP. Aiming for on-site analysis, the PEI-LSG sensor was integrated with a miniaturized potentiostat controlled by using a smartphone and applied as proof of applicability to ACP detection in commercial beverage and synthetic urine samples. These studies demonstrated adequate recoveries, ranging from 95.1% to 115.8%. The analytical parameters highlight the robustness and reliability of the proposed method for analyses of ACP directly at a potential crime scene.

Kinematic Patterns in Horses Sedated With Low Doses of Detomidine: An Accelerometric Evaluation

Alpha-2-adrenergic drugs, such as detomidine, are commonly used to sedate lame horses during examination. However, the use of these drugs should be minimized, as they have numerous side-effects, like ataxia. Therefore, we wanted to test the effects, on the locomotor pattern, of low doses of detomidine (0.003 mg/kg). Six horses were sedated with 0.003 mg/kg of detomidine and compared with the same horses administered a saline solution. Using a triaxial accelerometer, data of kinetic, coordination and energetic locomotor parameters and the degree of sedation were collected. The effects were monitored for 60 minutes after treatment administration. No effects on coordination parameters were observed, but some kinetic and energetic parameters were significantly altered after detomidine administration compared to the saline group. These results show that administering low doses of detomidine to lame horses can be a useful sedative solution, ensuring a safe examination with lower side-effects.

Recovery after General Anaesthesia in Adult Horses: A Structured Summary of the Literature

Simple Summary

Recovery is the most dangerous phase of general anaesthesia in horses. Numerous publications have reported about this phase, but structured reviews that try to reduce the risk of bias of narrative reviews/expert opinions, focussing on the topic are missing. Therefore, the aim of the present article was to publish the first structured review as a summary of the literature focussing on the recovery phase after general anaesthesia in horses. The objective was to summarise the available literature, taking into account the scientific evidence of the individual studies. A structured approach was followed with two experts in the field independently deciding on article inclusion and its level of scientific evidence. A total number of 444 articles, sorted by topics and classified based on their levels of evidence, were finally included into the present summary. The most important findings were summarised and discussed. The present structured review can be used as a compilation of the publications that, to date, focus on the recovery phase after general anaesthesia in adult horses. This type of review tries to minimise the risk of bias inherent to narrative reviews/expert opinions.

Abstract

Recovery remains the most dangerous phase of general anaesthesia in horses. The objective of this publication was to perform a structured literature review including levels of evidence (LoE) of each study with the keywords “recovery anaesthesia horse”, entered at once, in the search browsers PubMed and Web of Science. The two authors independently evaluated each candidate article. A final list with 444 articles was obtained on 5 April 2021, classified as: 41 “narrative reviews/expert opinions”, 16 “retrospective outcome studies”, 5 “surveys”, 59 “premedication/sedation and induction drugs”, 27 “maintenance with inhalant agents”, 55 “maintenance with total intravenous anaesthesia (TIVA)”, 3 “TIVA versus inhalants”, 56 “maintenance with partial intravenous anaesthesia (PIVA)”, 27 “other drugs used during maintenance”, 18 “drugs before/during recovery”, 18 “recovery systems”, 21 “respiratory system in recovery”, 41 “other factors”, 51 “case series/reports” and 6 “systems to score recoveries”. Of them, 167 were LoE 1, 36 LoE 2, 33 LoE 3, 110 LoE 4, 90 LoE 5 and 8 could not be classified based on the available abstract. This review can be used as an up-to-date compilation of the literature about recovery after general anaesthesia in adult horses that tried to minimise the bias inherent to narrative reviews.

Assessment of Inhibition of Bovine Hepatic Cytochrome P450 by 43 Commercial Bovine Medicines Using a Combination of In Vitro Assays and Pharmacokinetic Data from the Literature

BACKGROUND

There has been a lack of information about the inhibition of bovine medicines on bovine hepatic CYP450 at their commercial doses and dosing routes.

OBJECTIVE

The aim of this work was to assess the inhibition of 43 bovine medicines on bovine hepatic CYP450 using a combination of in vitro assay and Cmax values from pharmacokinetic studies with their commercial doses and dosing routes in the literature.

METHODS

Those drugs were first evaluated through a single point inhibitory assay at 3 μM in bovine liver microsomes for six specific CYP450 metabolisms, phenacetin o-deethylation, coumarin 7- hydroxylation, tolbutamide 4-hydroxylation, bufuralol 1-hydroxylation, chlorzoxazone 6-hydroxylation and midazolam 1'-hydroxylation. When the inhibition was greater than 20% in the assay, IC50 values were then determined. The potential in vivo bovine hepatic CYP450 inhibition by those drugs was assessed using a combination of the IC50 values and in vivo Cmax values from pharmacokinetic studies at their commercial doses and administration routes in the literature.

RESULTS

Fifteen bovine medicines or metabolites showed in vitro inhibition on one or more bovine hepatic CYP450 metabolisms with different IC50 values. Desfuroylceftiour (active metabolite of ceftiofur), nitroxinil and flunixin have the potential to inhibit one of the bovine hepatic CYP450 isoforms in vivo at their commercial doses and administration routes. The rest of the bovine medicines had low risks of in vivo bovine hepatic CYP450 inhibition.

CONCLUSION

This combination of in vitro assay and in vivo Cmax data provides a good approach to assess the inhibition of bovine medicines on bovine hepatic CYP450.

A comparative study of the cardiopulmonary and sedative effects of a single intramuscular dose of ketamine anesthetic combinations in rabbits

The aim of this prospective, randomized, blinded crossover study was compare the cardiopulmonary and sedative effects of ketamine in combination with acepromazine, diazepam, dexmedetomidine, midazolam or xylazine, injected intramuscularly in rabbits, using eight one-year-old male New Zealand rabbits (4.1 ± 0.40 kg). All treatments included ketamine (K; 30 mg/kg) in combination with one of the following: acepromazine 0.5 mg/kg (treatment KA); diazepam 1 mg/kg (KD); dexmedetomidine 0.025 mg/kg (KDex); midazolam 1 mg/kg (KM); or xylazine 3 mg/kg (KX) mixed in the same syringe and injected intramuscularly. Cardiopulmonary variables, blood gases and sedative scores were measured before injection (T0 or baseline) and every 10 min thereafter, over a 60-min period. There were reductions in heart rate, compared with the baseline, at all evaluation times in treatment KX. Treatments KDex, KM and KX presented reductions in respiratory rate at all evaluation times, in comparison with the baseline. There were reductions in mean arterial pressure in KA and KX at times T10-T60 and in PaO2 in KDex, KM and KX at T10-T50. The sedation scores were similar in KA, KDex, KM and KX at T10-T20. Ketamine in combination with acepromazine, dexmedetomidine, midazolam or xylazine promoted similar sedative effects for twenty minutes, but the α2-agonists can promote hypoxemia.

Compounds commonly used in equine medicine inhibits the voltage-gated potassium channel Kv11.1

BACKGROUND

The voltage-gated K⁺-channel K_v11.1 has a central role in cardiac repolarization. Blockage of K_v11.1 has been linked to severe cardiovascular side effects, such as acquired long QT syndrome (aLQTS), torsade de pointes arrhythmia and sudden cardiac death (SCD). K_v11.1 is susceptible to unspecific drug interactions due to the presence of two aromatic amino acids residing in the inner vestibule of the pore. These aromatic residues are also present in the equine orthologue of K_v11.1. This suggests that equine K_v11.1 may also be prone to high-affinity block by a range of different chemical entities, which potentially could cause severe cardiac side effects and SCD in horses.

AIM

To screen a series of commonly used drugs in equine medicine for interaction with K_v11.1.

METHODS

High-throughput screening of selected compounds on human K_v11.1 expressed in a mammalian cell line was performed using an automated patch clamp system, the SyncroPatch 384PE (Nanion Technologies, Munich, Germany). Results were validated on equine K_v11.1 expressed in CHO-K1 cells by manual patch clamp.

RESULTS

Acepromazine maleat (IC₅₀ = 0.5 μM) trimethoprim (IC₅₀ = 100 μM), diphenhydramine hydrochloride (IC₅₀ = 2 μM) and cyproheptadine hydrochloride (IC₅₀ = 1.84 μM) inhibited equine K_v11.1 current at clinically relevant drug concentrations.

CONCLUSION

The results suggest that drug interaction with K_v11.1 can occur in horses and that some drugs potentially may induce repolarization disorders in horses.

Pharmacokinetics, pharmacodynamics, and metabolism of acepromazine following intravenous, oral, and sublingual administration to exercised Thoroughbred horses

Acepromazine is a tranquilizer used commonly in equine medicine. This study describes serum and urine concentrations and the pharmacokinetics and pharmacodynamics of acepromazine following intravenous, oral, and sublingual (SL) administration. Fifteen exercised adult Thoroughbred horses received a single intravenous, oral, and SL dose of 0.09 mg/kg of acepromazine. Blood and urine samples were collected at time 0 and at various times for up to 72 hr and analyzed for acepromazine and its two major metabolites (2-(1-hydroxyethyl) promazine and 2-(1-hydroxyethyl) promazine sulfoxide) using liquid chromatography-tandem mass spectrometry. Acepromazine was also incubated in vitro with whole equine blood and serum concentrations of the parent drug and metabolites determined. Acepromazine was quantitated for 24 hr following intravenous administration and 72 hr following oral and SL administration. Results of in vitro incubations with whole blood suggest additional metabolism by RBCs. The mean ± SEM elimination half-life was 5.16 ± 0.450, 8.58 ± 2.23, and 6.70 ± 2.62 hr following intravenous, oral, and SL administration, respectively. No adverse effects were noted and horses appeared sedate as noted by a decrease in chin-to-ground distance within 5 (i.v.) or 15 (p.o. and SL) minutes postadministration. The duration of sedation lasted 2 hr. Changes in heart rate were minimal.

Effects of dobutamine hydrochloride on cardiovascular function in horses anesthetized with isoflurane with or without acepromazine maleate premedication

OBJECTIVE To determine the effects of acepromazine maleate premedication on cardiovascular function before and after infusion of dobutamine hydrochloride for 30 minutes in isoflurane-anesthetized horses. ANIMALS 6 healthy adult horses. PROCEDURES Each horse was anesthetized once following premedication with acepromazine (0.02 mg/kg, IV) administered 30 minutes prior to anesthetic induction (ACP+ treatment) and once without premedication (ACP- treatment). Anesthesia was induced with IV administration of xylazine hydrochloride (0.8 mg/kg), ketamine hydrochloride (2.2 mg/kg), and diazepam (0.08 mg/kg). Horses were positioned in right lateral recumbency, and anesthesia was maintained via inhalation of isoflurane delivered in oxygen. End-tidal isoflurane concentration was adjusted to achieve a target mean arterial blood pressure of 60 mm Hg (interquartile range [25th to 75th percentile], 57 to 63 mm Hg) for at least 15 minutes. Cardiac index, oxygen delivery index, and femoral arterial blood flow indices were determined 60 minutes after anesthetic induction (baseline). Dobutamine was then infused to achieve a target mean arterial blood pressure of 80 mm Hg (interquartile range, 76 to 80 mm Hg). Data collection was repeated 30 minutes after the start of dobutamine infusion for comparison with baseline values. RESULTS Complete data sets were available from 5 of the 6 horses. Dobutamine administration resulted in significant increases in oxygen delivery and femoral arterial blood flow indices but no significant change in cardiac index for each treatment. However, at baseline or 30 minutes after the start of dobutamine infusion, findings for the ACP+ and ACP- treatments did not differ. CONCLUSIONS AND CLINICAL RELEVANCE In isoflurane-anesthetized horses, dobutamine administration increased oxygen delivery and femoral arterial blood flow indices, but these changes were unaffected by premedication with acepromazine.

Acute acepromazine overdose: clinical effects and toxicokinetic evaluation

INTRODUCTION

Acepromazine is a phenothiazine that is used exclusively in veterinary medicine for multiple purposes. Human overdoses are rarely reported and toxicokinetic data has never been reported. We present a case of intentional acepromazine overdose resulting in central nervous system and cardiovascular toxicity with confirmatory toxicokinetic data.

CASE REPORT

A 54-year-old woman intentionally ingested 950 mg of her dog's acepromazine. Within 3 h of ingestion, she developed central nervous system and respiratory depression along with hypotension requiring non-invasive ventilation and vasopressors. Clinical toxicity resolved over the following 8 h. Serial plasma acepromazine levels were determined using gas chromatography/mass spectrometry. The initial acepromazine level (1-h post-ingestion) was 63 ng/ml. Follow-up levels at 8-, 10.5-, and 13.5-h post-ingestion were 8.9 ng/ml, 7.6 ng/ml, and 6.3 ng/ml, respectively.

DISCUSSION

Human acepromazine toxicity is rarely reported but results in clinical toxicity (central nervous system depression, respiratory depression, hypotension) are similar to other phenothiazines. Compared to other phenothiazines, it appears to have a short elimination half-life that may account for the brief duration of clinical toxicity with relatively rapid improvement. No significant human cardiac toxicity has been reported. Treatment is supportive.

CONCLUSION

This case highlights the unique toxicity of acepromazine in demonstrating rapid improvement of severe toxicity within 8 h consistent with a short elimination half-life.

The use of low doses of acepromazine as an aid for lameness diagnosis in horses: An accelerometric evaluation

OBJECTIVES

The aim of the present study was to quantify by accelerometry the trotting pattern of adult horses sedated with two different doses of acepromazine, in order to assess the use of this drug in equine lameness evaluations.

METHODS

Seven mature horses were used and three treatments were administered to each horse: saline solution, acepromazine (0.01 mg/kg), and acepromazine (0.02 mg/kg). The portable gait analyzer used consisted of three orthogonal accelerometers that measure accelerations along the dorsoventral, longitudinal, and lateral axes. Baseline values were obtained and after treatment, accelerometric recordings were repeated every five minutes during the first 20 minutes after the injection and then every 10 minutes thereafter for two hours. Ground-to-lip distance was also measured.

RESULTS

Administration of acepromazine decreased some of the variables investigated and differences between doses were observed. Speed, stride frequency, and stride length were significantly reduced following treatments. For coordination parameters, no significant differences among values were observed. Energetic variables suffered only weak reductions whereas ground-to-lip distance values were significantly decreased up to 120 minutes after treatment.

CLINICAL SIGNIFICANCE

Acepromazine produces significant alterations in the gait pattern with differences between doses, but it does not affect coordination variables in normal unexcited horses, and at a dose of 0.01 mg/kg may be the tranquilizer of choice for evaluating lameness in this setting.

Low-residue euthanasia of stranded mysticetes

Euthanasia of stranded large whales poses logistic, safety, pharmaceutical, delivery, public relations, and disposal challenges. Reasonable arguments may be made for allowing a stranded whale to expire naturally. However, slow cardiovascular collapse from gravitational effects outside of neutral buoyancy, often combined with severely debilitating conditions, motivate humane efforts to end the animal's suffering. The size of the animal and prevailing environmental conditions often pose safety concerns for stranding personnel, which take priority over other considerations. When considering chemical euthanasia, the size of the animal also necessitates large quantities of euthanasia agents. Drug residues are a concern for relay toxicity to scavengers, particularly for pentobarbital-containing euthanasia solutions. Pentobarbital is also an environmental concern because of its stability and long persistence in aquatic environments. We describe a euthanasia technique for stranded mysticetes using readily available, relatively inexpensive, preanesthetic and anesthetic drugs (midazolam, acepromazine, xylazine) followed by saturated KCl delivered via custom-made needles and a low-cost, basic, pressurized canister. This method provides effective euthanasia while moderating personnel exposure to hazardous situations and minimizing drug residues of concern for relay toxicity.

Nociceptive thermal threshold testing in horses - effect of neuroleptic sedation and neuroleptanalgesia at different stimulation sites

Background

Aim of the study was to compare the effect of neuroleptic sedation with acepromazine and neuroleptanalgesia with acepromazine and buprenorphine on thermal thresholds (TT) obtained at the nostrils and at the withers. The study was carried out as a randomized, blinded, controlled trial with cross-over design. Thermal thresholds were determined by incremental contact heat applied to the skin above the nostril (N) or the withers (W). Eleven horses were treated with saline (S), acepromazine (0.05 mg/kg) (ACE) or acepromazine and buprenorphine (0.0075 mg/kg) (AB) intravenously (IV). Single stimulations were performed 15 minutes prior and 15, 45, 75, 105, 165, 225, 285, 405 and 525 minutes after treatment. Sedation score, gastrointestinal auscultation score and occurrence of skin lesions were recorded. Data were analysed with analysis of variance for repeated measurements.

Results

There were no significant differences in TT between N and W with all treatments. The TT remained constant after S and there was no difference in TT between S and ACE. After AB there was a significant increase above baseline in TT until 405 minutes after treatment. Restlessness occurred 30–90 minutes after AB in 7 horses. All horses had reduced to absent borborygmi after AB administration for 165 to 495 minutes.

Conclusion

Thermal stimulation at both described body areas gives comparable results in the assessment of cutaneous anti-nociception in horses. There is no differential influence of neuroleptic sedation or neuroleptanalgesia on TTs obtained at N or W. Buprenorphine combined with acepromazine has a long lasting anti-nociceptive effect associated with the typical opioid induced side effects in horses.

A Bayesian approach for estimating detection times in horses: exploring the pharmacokinetics of a urinary acepromazine metabolite

We describe the population pharmacokinetics of an acepromazine (ACP) metabolite (2-(1-hydroxyethyl)promazine) (HEPS) in horses for the estimation of likely detection times in plasma and urine. ACP (30 mg) was administered to 12 horses, and blood and urine samples were taken at frequent intervals for chemical analysis. A bayesian hierarchical model was fitted to describe concentration-time data and cumulative urine amounts for HEPS. The metabolite HEPS was modelled separately from the parent ACP as the half-life of the parent was considerably less than that of the metabolite. The clearance (Cl/F(PM)) and volume of distribution (V/F(PM)), scaled by the fraction of parent converted to metabolite, were estimated as 769 L/h and 6874 L, respectively. For a typical horse in the study, after receiving 30 mg of ACP, the upper limit of the detection time was 35 h in plasma and 100 h in urine, assuming an arbitrary limit of detection of 1 lg/L and a small (≈0.01) probability of detection. The model derived allowed the probability of detection to be estimated at the population level. This analysis was conducted on data collected from only 12 horses, but we assume that this is representative of the wider population.

Experimental Pharmacodynamics and Analgesic Efficacy of Liposome-Encapsulated Hydromorphone in Dogs

The purpose of this study was to determine the experimental side effects of liposome-encapsulated hydromorphone (LE-Hydro) in beagles and to evaluate LE-Hydro analgesia in dogs undergoing ovariohysterectomies (OVH). Beagles were injected subcutaneously with 1–3 mg/kg LE-Hydro or 0.1 mg/kg hydromorphone. Dogs were evaluated for sedation, temperature, respiratory rate, and heart rate. OVH dogs were injected with 2 mg/kg LE-Hydro subcutaneously or 0.2 mg/kg morphine and 0.05 mg/kg acepromazine intramuscularly. Side effects of LE-Hydro were within clinically acceptable limits. The analgesic efficacy was superior in dogs administered LE-Hydro at 12 hr postsurgically. LE-Hydro provided adequate, durable analgesia in dogs undergoing OVH.

Contemporary use of acepromazine in the anaesthetic management of male horses and ponies: a retrospective study and opinion poll

REASON FOR PERFORMING STUDY

Current use of acepromazine in the anaesthetic management of male horses and ponies and associated risks are largely unknown.

OBJECTIVES

To explore anaesthetic acepromazine use and related adverse effects in the male horse.

METHODS

Of 8533 anaesthetised horses and ponies medical records of male animals treated perianaesthetically with acepromazine were reviewed. Demographic data, time and dose of acepromazine administration, co-administered drugs, quality of induction and recovery from anaesthesia, arterial blood pressures, and occurrence of penile dysfunction were recorded. Practising ACVA and ECVAA diplomates were polled on the use of acepromazine and its effects on blood pressure and penile dysfunction in the equine.

RESULTS

Of all animals, 12% females and 11% males (n=575 including 42% stallions) received perianaesthetic acepromazine, predominantly for premedication. Anaesthetic induction was smooth in 566 animals. Lowest mean arterial pressures averaged 65±9 mmHg. Recovery was good or very good in 70% of all animals and 74% stood after 1-2 attempts. In 14 horses (2.4%; 7 stallions, 7 geldings), penile prolapse occurred for 0.5-4 h and in one stallion (0.2%) for >12 but <18 h post recovery. Most surveyed anaesthesiologists use acepromazine in stallions (occasionally 63%; frequently 17%) but more frequently in geldings (occasionally 34%; frequently 59%) and mares (occasionally 38%; frequently 59%), primarily for premedication with other sedatives and analgesics. Persistent intraoperative hypotension was not frequently reported. Only 5% of surveyed anaesthesiologists recall penile prolapse post acepromazine administration lasting for >12 h and only one recalls 3 cases of irreversible penile prolapse in 20 years of anaesthesia practice.

CONCLUSIONS AND POTENTIAL RELEVANCE

The extremely low risk of permanent penile dysfunction (≤1 in 10,000 cases) does not justify more restricted use of acepromazine in the intact male vs. geldings and mares.

The effects of detomidine, romifidine or acepromazine on echocardiographic measurements and cardiac function in normal horses

OBJECTIVE

To evaluate by echo- and electrocardiography the cardiac effects of sedation with detomidine hydrochloride, romifidine hydrochloride or acepromazine maleate in horses.

STUDY DESIGN

An experimental study using a cross-over design without randomization.

ANIMALS

Eight clinically normal Standardbred trotters.

MATERIALS AND METHODS

Echocardiographic examinations (two-dimensional, guided M-mode and colour Doppler) were recorded on five different days. Heart rate (HR) and standard limb lead electrocardiograms were also obtained. Subsequently, horses were sedated with detomidine (0.01 mg kg(-1)), romifidine (0.04 mg kg(-1)) or acepromazine (0.1 mg kg(-1)) administered intravenously and all examinations repeated.

RESULTS

Heart rate before treatment with the three drugs did not differ significantly (p = 0.98). Both detomidine and romifidine induced a significant decrease (p < 0.001) in HR during the first 25 minutes after sedation; while acepromazine had a varying effect on HR. For detomidine, there was a significant increase in LVIDd (left ventricular internal diameter in diastole; p = 0.034) and LVIDs (left ventricular internal diameter in systole; p < 0.001). In addition, a significant decrease was found in IVSs (the interventricular septum in systole; p < 0.001), LVFWs (the left ventricular free wall in systole; p = 0.002) and FS% (fractional shortening; p < 0.001). The frequency of pulmonary regurgitation was increased significantly (p < 0.001). Romifidine induced a significant increase in LVIDs (p < 0.001) and a significant decrease in IVSs (p < 0.001) and FS% (p = 0.002). Acepromazine had no significant effect upon any of the measured values.

CONCLUSIONS

and clinical relevance The results indicate that sedation of horses with detomidine and to a lesser extent romifidine at the doses given in this study has a significant effect on heart function, echocardiographic measurements of heart dimensions and the occurrence of valvular regurgitation. Although the clinical significance of these results may be minimal, the potential effects of sedative drugs should be taken into account when echocardiographic variables are interpreted in clinical cases.

A Retrospective Study on the Use of Acepromazine Maleate in Dogs With Seizures

Use of acepromazine (i.e., acetylpromazine) maleate in dogs with a history of seizures is reportedly contraindicated because of the risk of decreasing the seizure threshold in these animals. In this retrospective study, acepromazine was administered for tranquilization to 36 dogs with a prior history of seizures and to decrease seizure activity in 11 dogs. No seizures were seen within 16 hours of acepromazine administration in the 36 dogs that received the drug for tranquilization during hospitalization. After acepromazine administration, seizures abated for 1.5 to 8 hours (n=6) or did not recur (n=2) in eight of 10 dogs that were actively seizing. Excitement-induced seizure frequency was reduced for 2 months in one dog.

Effects of acepromazine on three-phase 99mTc-MDP bone imaging in 11 horses

Horses undergoing skeletal scintigraphy can have decreased radiopharmaceutical bone uptake in the limbs. This reduces the diagnostic value of the scan. The aim of the present study was to measure the changes in count density caused by vasodilatation and increased blood flow associated with intravenous injection of acepromazine during bone scintigraphy in normal horses. A three-phase bone scan was performed twice in 11 adult horses to study the effects of acepromazine on the count density of the resultant scintigrams. With acepromazine, there was a statistically significant mean difference of 12 s for initial blood flow and 21 s for peak flow. The time to initial blood flow and time to peak flow occurred earlier for the scans in which acepromazine was used. There were no significant differences in the bone to soft tissue ratios during the soft tissue and bone phases of the scan between procedures. Intravenous administration of acepromazine increases peripheral blood flow causing an earlier onset of the vascular phase during the three-phase bone scan. Acepromazine did not increase the count density of the bone phase scintigrams. As expected, the vasodilatation and increased blood flow associated with intravenous injection of acepromazine affected the count density of the vascular phase of the bone scan.

Effects of acepromazine on pulmonary gas exchange and circulation during sedation and dissociative anaesthesia in horses

OBJECTIVE

To study pulmonary gas exchange and cardiovascular responses to sedation achieved with romifidine and butorphanol (RB) alone, or combined with acepromazine, and during subsequent tiletamine-zolazepam anaesthesia in horses.

ANIMALS

Six (four males and two females) healthy Standardbred trotters aged 3-12 years; mass 423-520 kg.

STUDY DESIGN

Randomized, cross-over, experimental study.

MATERIALS AND METHODS

Horses were anaesthetized on two occasions (with a minimum interval of 1 week) with intravenous (IV) tiletamine-zolazepam (Z; 1.4 mg kg(-1)) after pre-anaesthetic medication with IV romifidine (R; 0.1 mg kg(-1)) and butorphanol (B; 25 microg kg(-1) IV). At the first trial, horses were randomly allocated to receive (protocol ARBZ) or not to receive (protocol RBZ) acepromazine (A; 35 microg kg(-1)) intramuscularly (IM) 35 minutes before induction of anaesthesia. Each horse was placed in left lateral recumbency and, after tracheal intubation, allowed to breathe room air spontaneously. Respiratory and haemodynamic variables and ventilation-perfusion (; multiple inert gas elimination technique) ratios were determined in the conscious horse, after sedation and during anaesthesia. One- and two-way repeated-measures anova were used to identify within- and between-technique differences, respectively.

RESULTS

During sedation with RB, arterial oxygen tension (PaO(2)) decreased compared to baseline and increased mismatch was evident; there was no O(2) diffusion limitation or increase in intrapulmonary shunt fraction identified. With ARB, PaO(2) and remained unaffected. During anaesthesia, intrapulmonary shunt occurred to the same extent in both protocols, and mismatching increased. This was less in the ARBZ group. Arterial O(2) tension decreased in both protocols, but was lower at 25 and 35 minutes of anaesthesia in RBZ than in ARBZ. During sedation, heart rate (HR) and cardiac output (Qt) were lower while arterial-mixed venous oxygen content differences and haemoglobin concentrations were higher in RBZ compared with ARBZ. Total systemic vascular resistance, mean systemic, and mean pulmonary arterial pressures were higher during anaesthesia with RBZ compared to ARBZ.

CONCLUSIONS AND CLINICAL RELEVANCE

Acepromazine added to RB generally improved haemodynamic variables and arterial oxygenation during sedation and anaesthesia. Arterial oxygenation was impaired as a result of increased shunt and mismatch during anaesthesia, although acepromazine treatment reduced disturbances and falls in PaO(2) to some extent. Haemodynamic variables were closer to baseline during sedation and anaesthesia when horses received acepromazine. Acepromazine may confer advantages in healthy normovolaemic horses.

Pharmacologic considerations in the treatment of neonatal septicemia and its complications

This article focuses on the pharmacologic properties of drugs commonly used in the treatment of neonatal septicemia and its complications. Rational therapy demands an awareness of not only the pharmacology of individual drugs but also the interactions and anticipated fate of such drugs in the rapidly changing physiologic environment of the neonate. Further research in the area of equine neonatal pharmacology should greatly assist our understanding of the impact of the disease state on the unique physiology of the newborn and should allow us to better predict the ultimate fate of drugs commonly used for such purposes. Careful dosing and close monitoring of pharmacologic effects are critical for a successful outcome. In the future, newer therapeutic strategies that are safe and efficacious may provide a means to circumvent many of the problems currently encountered with treating the septicemic newborn foal.

Drug residue considerations for anesthetics and adjunctive drugs in food-producing animals

This article is a summary of residue concerns for anesthetics and anesthetic adjuncts used in food animals. The risks associated with residues of these drugs in food-producing animals, as well as the veterinarian's responsibility to reduce this risk, are discussed. The potential for residues and suggestions for prevention in each of the major anesthetic drug classes are described. Suggested withdrawal times are proposed for nonapproved drugs used off label. Each class of drug is summarized in the tables.

Pharmacokinetic values of drugs frequently used in performance horses

Tables of values of pharmacokinetic variables (volume of distribution, total body clearance, and plasma elimination half-life) of drugs frequently administered to performance horses are accompanied by explanatory notes. Drugs described include the nonsteroidal anti-inflammatory drugs, corticosteroids, anabolic steroids, central nervous system-modifying drugs, respiratory system drugs, diuretics, local anesthetics, and antibacterial drugs.

Sedatives, tranquilizers, and stimulants

Drugs of relevance to equine practice that modify the central nervous system (CNS) can be broadly classified as depressants or stimulants. The pharmacologic mechanisms of action, uses, and side effects of selected CNS depressant and stimulant drugs in horses are reviewed. Knowledge of the way these CNS-modifying drugs may affect performance is limited.

Disposition, bioavailability and clinical efficacy of orally administered acepromazine in the horse

The pharmacokinetics and pharmacological efficacy of orally (p.o.) administered acepromazine were studied and compared with the intravenous (i.v.) route of administration in a cross-over study using six horses. The oral kinetics of acepromazine can be described by a two-compartment open model with first-order absorption. The drug was rapidly absorbed after p.o. administration with a half-life of 0.84 h, tmax of 0.4 h and Cmax of 59 ng/ml. The elimination was slower after p.o. administration (half-life 6.04 h) than after i.v. injection (half-life 2.6 h). The bioavailability of the orally administered drug formulation was 55.1%. After p.o. administration of 0.5 mg/kg acepromazine, the parameters of the sedative effect were similar to those obtained after i.v. injection of 0.1 mg/kg. The effect of the drug on blood cell count and haemoglobin content was similar after both p.o. administration and injection, while the effects on the parameters of penile prolapse and on the mean arterial blood pressure were less pronounced after p.o. administration than after injection. After p.o. administration, no significant effects on haematocrit-level as well as on the heart and respiratory rates were observed, while these parameters were significantly affected after injection. It is concluded that the high initial plasma level of the drug after i.v. injection may play a role in producing adverse effects of acepromazine.

Pediatric acepromazine poisoning: the importance of child-resistant packaging for veterinary drugs

The first reported case of acepromazine ingestion in a pediatric patient is presented. It is an aliphatic phenothiazine that is structurally similar to chlorpromazine (thorazine). In our case, a 2 1/2-year-old male ingested 3 to 4 of his 80-pound Doberman's 25-mg tablets. The pills were stored in a vial without a child-resistant closure. The child displayed signs and symptoms of phenothiazine toxicity. There is no federal law which requires veterinary medicines to be dispensed in special packaging. All prescription medications should require child-resistant packaging.

Effect of acepromazine, xylazine and thiopentone on factor VIII activity and von Willebrand factor antigen concentration in dogs

The effect of acepromazine maleate, xylazine and thiopentone on the packed cell volume, plasma protein content, factor VIII activity and von Willebrand factor antigen concentration of blood was studied in normal dogs. The same variables were measured in dogs with haemophilia A given acepromazine maleate and thiopentone. Both the packed cell volume and plasma protein content decreased after the administration of either acepromazine maleate or xylazine. Values were not changed further after administration of thiopentone. Changes in the haemostatic variables measured were generally small. Consequently, blood samples collected from dogs under the influence of premedicant doses of acepromazine maleate or xylazine, and when subsequently anaesthetised with thiopentone, are adequate for the assay of factor VIII activity and von Willebrand factor antigen concentration for establishing an animal's haemophilia A and von Willebrand's disease status.

Reactivity of equine palmar digital arteries and veins to vasodilating agents

Palmar digital arteries and veins removed surgically from healthy horses under general anesthesia were cut into 4 mm vascular rings, suspended in tissue baths, and attached to force displacement transducers for continuous measurement of vascular tension. In vitro vascular responses were determined for acetylcholine, acepromazine, isoxsuprine hydrochloride (isoxsuprine), prostaglandin E2 (PGE2), and prostaglandin I2 (prostacyclin). After preconstriction with norepinephrine hydrochloride (norepinephrine), or prostaglandin F2 alpha (PGF2 alpha), the concentrations needed to produce 50% maximum relaxation (EC50) and the maximum percentage of relaxation were determined for each drug. Acetylcholine was the most potent arterial vasodilator (smallest EC50 value) and PGE2 was the least potent. Prostacyclin was the least potent venodilator (highest EC50 value); there were no differences between acetylcholine, acepromazine, isoxsuprine, and PGE2. Isoxsuprine produced greater arterial relaxation than all other agents. Isoxsuprine and acepromazine produced significantly greater venous relaxation than did acetylcholine and PGE2. Prostacyclin produced minimal vasodilation of arteries or veins. Acepromazine and isoxsuprine relaxed the veins significantly more than the arteries. When PGF2 alpha was used instead of norepinephrine to preconstrict the arteries and veins, the potency and effectiveness of acepromazine and isoxsuprine to produce vasodilation were significantly decreased. Results indicate that acepromazine and isoxsuprine can relax the equine digital vasculature but their effectiveness varies depending on the origin of the constriction.

Cardiorespiratory and sedative effects of a combination of acepromazine, xylazine and methadone in the horse

Cardiorespiratory and sedative effects of a combination of acepromazine, xylazine and methadone were studied in the horse. Acepromazine and xylazine produced cardiovascular effects whereas methadone mainly affected respiratory rate. Decreases in heart rate, arterial blood pressure and respiratory rate were seen. Sedation was superior to that of acepromazine, xylazine or a combination of these. No serious side effects were seen.

Principles of drug disposition in the horse

This article is intended to give the reader an understanding of the mathematic and conceptual framework underlying equine pharmacology. The methods by which the veterinary practitioner determines drug concentrations, disposition, and bioavailability are discussed.

Disposition of anesthetic and anesthetic-related agents in ruminants

Many factors may influence the actions and fates of anesthetic and anesthetic-related agents in ruminant animals. These considerations need to be taken into account when these drugs are employed clinically. Some of the major principles governing the disposition of CNS-active drugs are reviewed, with special emphasis on the uniqueness of ruminant animals. General pharmacokinetic considerations are also covered as a preamble to a commentary on the kinetic characteristics of anesthetic and anesthetic-related agents that are commonly used in domesticated ruminants.

Cardiovascular and respiratory effects of acetylpromazine and xylazine on halothane-anesthetized horses

Circulatory and respiratory effects of intravenously administered acetylpromazine (0.033 and 0.067 mg/kg) and xylazine (0.5 and 1.0 mg/kg) were studied in drug cross-over fashion in eight laterally recumbent horses anesthetized only with halothane (1.06%, end-tidal) in O2. Both doses of acetylpromazine caused a significant and sustained elevation in cardiac output via a rise in stroke volume. Xylazine produced an initial significant fall in cardiac output followed by a return to control levels. Halothane anesthesia did not prevent xylazine-related atrioventricular conduction block. All treatments caused a similar significant fall in arterial blood pressure (acetylpromazine, total peripheral resistance-related; xylazine, cardiac output-related). PaCO2 significantly increased after all treatments. PaCO2 decreased significantly only following xylazine treatment. One horse (not included in the tabulation) developed ventricular fibrillation and died 15 min after receiving its first injection (0.5 mg/kg) of xylazine.