Pharmacological and pharmacokinetic differences between donkeys and horses

Pharmacokinetics of Enrofloxacin in Plasma, Urine, and Feces of Donkey (Equus asinus) after a Single Intragastric Administration

Enrofloxacin is a broad-spectrum antimicrobial agent, but the study of its pharmacokinetics/pharmacodynamics (PKs/PDs) in donkeys is rarely reported. The present study aimed to investigate the pharmacokinetics of enrofloxacin administered intragastrically, and to study the pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin in plasma, urine, and feces, and the PK/PD parameters were investigated to provide a rationale for enrofloxacin treatment in donkeys. A total of five healthy donkeys were selected for intragastric administration of 7.5 mg·kg-1 BW of enrofloxacin by gavage, and blood, urine, and fecal samples were collected. The results showed that the elimination half-life of plasma enrofloxacin was 11.40 ± 6.40 h, Tmax was 0.55 ± 0.12 h, Cmax was 2.46 ± 0.14 mg·L-1, AUC0-∞ was 10.30 ± 3.37 mg·L-1·h, and mean residence time (MRT) was 7.88 ± 1.26 h. The Tmax of plasma ciprofloxacin was 0.52 ± 0.08 h, Cmax was 0.14 ± 0.03 mg·L-1, and AUC0-∞ was 0.24 ± 0.16 mg·L-1·h. Urinary Cmax was 38.18 ± 8.56 mg·L-1 for enrofloxacin and 15.94 ± 4.15 mg·L-1 for ciprofloxacin. The total enrofloxacin and ciprofloxacin recovered amount in urine was 7.09 ± 2.55% of the dose for 144 h after dosing. The total enrofloxacin and ciprofloxacin recovered amount in feces was 25.73 ± 10.34% of the dose for 144 h after dosing. PK/PD parameters were also examined in this study, based on published MICs. In conclusion, 7.5 mg/kg BW of enrofloxacin administered intragastrically to donkeys was rapidly absorbed, widely distributed, and slowly eliminated in their bodies, and was predicted to be effective against bacteria with MICs < 0.25 mg·L-1.

A retrospective comparison of postoperative outcomes in ovariectomised jennies (Equus asinus) treated with phenylbutazone or flunixin meglumine

BACKGROUND

Clinically, flunixin meglumine (FM) and phenylbutazone (PBZ) are preferentially selected for the treatment of visceral and musculoskeletal pain, respectively, in horses. In donkeys, there is no information to support or refute this conventional conjecture.

OBJECTIVES

To compare postoperative outcomes in a group of jennies treated with intravenous FM or oral PBZ.

ANIMALS

Fourteen jennies unilaterally ovariectomised by standing left flank laparotomy.

STUDY DESIGN

Retrospective cohort study.

METHODS

Data from medical records of ovariectomised jennies (case details, weight, non-steroidal anti-inflammatory drug [NSAID] protocol, surgery duration, operative sequence, anaesthesia protocol, physical examination findings and outcomes) were collected. From collated data, postoperative adverse events were defined as fever, tachycardia, tachypnea, inappetence, altered mentation, abnormal oral mucous membranes, bruxism, colic, incisional complications (i.e., drainage, oedema, peri-incisional emphysema and pain) and non-survival, then further divided into occurrence during the early (≤24 h) or late (>24 h) postoperative period for data analysis using R software. Chi-squared test was used to compare individual adverse events between groups (PBZ vs. FM) and moments (early vs. late). Significance was set at p ≤ 0.05.

RESULTS

PBZ treatment (8/14) was associated with (odds ratio, 95% confidence interval) more total (2.93, 1.97-4.36), early (3.01, 1.87-4.84) and late (2.69, 1.28-5.63) adverse events than FM treatment (6/14). Tachycardia (37.83, 2.21-646.66), tachypnoea (0.29, 0.13-0.66), altered mentation (2.78, 1.01-7.67), altered mucous membranes (18.38, 1.04-325.23), incisional oedema (44.33, 2.60-754.5) and incisional pain (47.78, 2.81-811.61) were significantly different between groups. Early adverse events significantly different between groups included tachycardia (50.2, 2.9-877.0), altered mentation (3.33, 1.08-10.29) and incisional pain (21.0, 1.2-374.5), with late adverse events being tachypnea (0.07, 0.01-0.62), incisional oedema (32.92, 1.85-584.28) and incisional pain (28.92, 1.62-515.68). Colic (2/8) and non-survival (1/8) were rare events that only occurred in the PBZ cohort and could not be further evaluated for differences.

MAIN LIMITATIONS

Small sample size; retrospective study; treatment bias; varied administration routes.

CONCLUSIONS

Oral PBZ may be inappropriate to use following abdominal surgery in donkeys.

CLINICAL RELEVANCE

More prospective and case-controlled studies are needed to evaluate the clinical efficacy of these two NSAIDs in donkeys.

Pharmacokinetic properties of pergolide mesylate following single and multiple-dose administration in donkeys (Equus asinus)

BACKGROUND

Donkeys with clinical signs of pituitary pars intermedia dysfunction are treated with oral pergolide mesylate despite the lack of species-specific pharmacokinetic data.

OBJECTIVE

To evaluate the pharmacokinetics of intragastric and oral pergolide mesylate in healthy donkeys (Equus asinus).

STUDY DESIGN

Pharmacokinetic study.

METHODS

Six healthy donkeys were administered pergolide mesylate (Prascend®) at 2 μg/kg bodyweight (bwt) intragastrically once, then once daily per os (PO) for 5 days. Blood samples were collected at 0, 10, 20, 30 and 45 min and 1, 1.5, 2, 3, 4, 6, 8, 12, 24, 36 and 48 h after the single intragastric dose, once daily immediately before the PO dose, and then again at the above times after Day 5 of once daily oral dosing. Plasma pergolide concentration was quantified via ultra-performance liquid chromatography-tandem mass spectrometry. Pergolide concentration versus time data after the first and last doses were analysed based on noncompartmental pharmacokinetics using commercial software. Paired t-tests were used to compare single and multiple doses (p < 0.05). In a follow-up study, a single oral dose was then administered to two donkeys followed by concurrent blood sampling from the jugular and cephalic veins to evaluate the effect of route of administration on pergolide pharmacokinetics.

RESULTS

Cmax , Tmax AUC, and t½λz differed significantly (p ≤ 0.03) after single and multiple doses, with significantly lower Cmax (0.16 ± 0.16 ng/ml) and t½λz (9.74 ± 1.35 h) after intragastric dosing on Day 1 than after 5 days of oral dosing (3.74 ± 2.26 ng/ml and 16.35 ± 5.21 h, respectively). Pergolide plasma concentrations were higher in jugular vein samples compared to cephalic vein samples after a single oral dose.

MAIN LIMITATIONS

Small sample size; varied administration routes.

CONCLUSIONS

Pergolide mesylate (dosed at 2 μg/kg bwt) is bioavailable in donkeys after intragastric and PO administration. Differences in pharmacokinetics were noted after multiple doses, related to different routes of administration and sublingual absorption of pergolide.

Horse and donkey parasitology: differences and analogies for a correct diagnostic and management of major helminth infections

In June 2022, at the XXXII Conference of the Italian Society of Parasitology, the parallels of the main endoparasitic infections of horses and donkeys were discussed. Although these 2 species are genetically different, they can be challenged by a similar range of parasites (i.e. small and large strongyles, and Parascaris spp.). Although equids can demonstrate some level of resilience to parasites, they have quite distinct helminth biodiversity, distribution and intensity among different geographical locations and breeds. Heavily infected donkeys may show fewer clinical signs than horses. Although parasite control is primarily provided to horses, we consider that there may be a risk of drug-resistance parasitic infection through passive infection in donkeys when sharing the same pasture areas. Knowing the possible lack of drug efficacy (<90 or 80%), it is advocated the use of selective treatment for both species based on fecal egg counts. Adult horses should receive treatment when the threshold exceeds 200–500 eggs per gram (EPG) of small strongyles. Moreover, considering that there are no precise indications in donkeys, a value >300 EPG may be a safe recommendation. We have highlighted the main points of the discussion including the dynamics of helminth infections between the 2 species.

Transdermal Flunixin Meglumine as a Pain Relief in Donkeys: A Pharmacokinetics Pilot Study

Recent approval of transdermal flunixin meglumine (FM) (Banamine^®) in cattle has opened the door for the drug's potential application in other species. Transdermal FM could provide a safe and effective form of pain relief in donkeys. In order to evaluate the pharmacokinetics and effects of FM on anti-inflammatory biomarkers in donkeys, a three-way crossover study design was employed. In total, 6 healthy donkeys were administered transdermal (TD) FM at a dosage of 3.3 mg/kg, and oral (PO) and intravenous (IV) doses of 1.1 mg/kg body weight. Blood samples were collected over 96 h to determine the concentration of flunixin, 5OH flunixin, and eicosanoids (TXB2 and PGF2 alpha) using LC-MS/MS. The results indicated that both flunixin and 5OH flunixin were detectable in blood samples collected during TD. The elimination of the drug was slower following the TD route compared to PO and IV. TD administration significantly decreased TXB2 levels in non-stimulated serum from 1 to 96 h post-administration, while IV and PO resulted in TXB2 reduction for 1 to 8 h. A significant reduction in PGF2 alpha was observed in PO and IV 1 h after administration, while TD resulted in a gradual decline from 4 to 72 h. The study concluded that the off-label use of transdermal FM at 3.3 mg/kg could be effective in controlling inflammation in donkeys.

Pharmacokinetics of butorphanol following intravenous and intramuscular administration in donkeys: A preliminary study

The pharmacokinetics of butorphanol after intravenous (IVB) and intramuscular (IMB) administration in donkeys were determined in this preliminary study. Healthy male gelded donkeys (n = 5), aged 6–12 years old, were administered 0.1 mg/kg butorphanol IV or IM in a randomized, crossover design. Blood samples were obtained at predetermined intervals for 24 h (IVB) and 48 h (IMB) after administration. Plasma butorphanol concentrations were determined by high performance liquid chromatography and pharmacokinetic parameters were calculated. Following IVB administration, mean (± SE) apparent volume of distribution, elimination half-life, total body clearance, and area under the plasma concentration time curve from time 0 to infinity (AUC_0−∞) were 322 ± 50 mL/kg, 0.83 ± 0.318 h, 400 ± 114 mL/h/kg, 370 ± 131 h·ng/mL, respectively. After IMB administration, a maximum plasma drug concentration of 369 ± 190 ng/mL was reached at 0.48 ± 0.09 h. The IMB AUC_0−∞ was 410 ± 60 h·ng/mL. Bioavailability of IMB was 133 ± 45%. The pharmacokinetics of butorphanol in healthy donkeys was characterized by faster elimination half-life compared to values from the equine literature.

Analgesic Effect of Butorphanol during Castration in Donkeys under Total Intravenous Anaesthesia

Pain management is necessary for all surgical procedures. Little scientific evidence about drug efficacy in donkeys is available. The aim of this study was to evaluate the analgesic effect of butorphanol in donkeys undergoing orchiectomy under total intravenous anaesthesia with guaifenesin-ketamine-detomidine. A randomized blinded prospective clinical trial (Protocol n. 2021/0000338), was carried out on 18 clinically healthy donkeys undergoing bilateral orchiectomy. Patients were assigned to Group D (n = 8) or Group DB (n = 10) if receiving intravenous detomidine or detomidine-butorphanol respectively, before induction of general anaesthesia with ketamine-diazepam. Intraoperative muscle relaxation, nystagmus, palpebral reflex, heart and respiratory rate, and non-invasive blood pressure were evaluated every 2 min; time to prepare the patient, duration of surgery and anaesthesia and recovery score were recorded. Group D had significantly longer surgical time, higher heart rate, higher systolic and mean blood pressure (p < 0.05; repeated measure ANOVA), increased muscle rigidity and expression of palpebral reflex (p < 0.05; Mann-Whitney U test) than group DB. Top-ups with thiopental were statistically higher in Group D. Butorphanol and detomidine together produced a more stable anaesthetic plan. The low dosage of opioid and alpha-2-agonists and reduced rescue anaesthesia are responsible for a safer and more superficial anaesthesia, which is mandatory under field conditions.

Nonlinear Mixed-Effect Pharmacokinetic Modeling and Distribution of Doxycycline in Healthy Female Donkeys after Multiple Intragastric Dosing-Preliminary Investigation

Doxycycline (DXC) is a broad-spectrum antibacterial antimicrobial administered to horses for the treatment of bacterial infections which may also affect donkeys. Donkeys have a different metabolism than horses, leading to differences in the pharmacokinetics of drugs compared to horses. This study aimed to describe the population pharmacokinetics of DXC in donkeys. Five doses of DXC hyclate (10 mg/kg) were administered via a nasogastric tube, q12 h, to eight non-fasted, healthy, adult jennies. Serum, urine, synovial fluid and endometrium were collected for 72 h following the first administration. Doxycycline concentration was measured by competitive enzyme immunoassay. Serum concentrations versus time data were fitted simultaneously using the stochastic approximation expectation-maximization algorithm for nonlinear mixed effects. A one-compartment model with linear elimination and first-order absorption after intragastric administration, best described the available pharmacokinetic data. Final parameter estimates indicate that DXC has a high volume of distribution (108 L/kg) as well as high absorption (10.3 h^-1) in donkeys. However, results suggest that oral DXC at 10 mg/kg q12 h in donkeys would not result in a therapeutic concentration in serum, urine, synovial fluid or endometrium by comparison to the minimum inhibitory concentration of common equine pathogens. Further studies are recommended to identify appropriate dosage and dosing intervals of oral DXC in donkeys.

Helminth infections in Italian donkeys: Strongylus vulgaris more common than Dictyocaulus arnfieldi

Donkeys have been used as working animals for transport and farm activities worldwide. Recently, in European countries, there has been an increasing interest in donkeys due to their use as pets, onotherapy or milk production. During 2014-2016, a countrywide survey was conducted to determine prevalence and risk factors of principal helminth infections in 1775 donkeys in 77 Italian farms. A questionnaire on management and parasite control practices was filled out for each farm. Faecal samples were examined using a modified McMaster technique, a centrifugation/flotation method and a sedimentation technique. Pooled coprocultures were performed for differentiation of strongylid eggs. Strongyles were the most common parasites detected (84.9%), followed by Dictyocaulus arnfieldi (6.9%), Oxyuris equi (5.8%), Parascaris spp. (3.6%), Anoplocephala spp. (1.0%), Strongyloides westeri (0.3%). Coprocultures revealed an omnipresence of cyathostomins (100%), followed by Strongylus vulgaris (31.0%), Poteriostomum spp. (25.0%), Triodontophorus spp. (9.0%), Strongylus edentatus (7.0%), Strongylus equinus (5.0%). Logistic regression analysis identified breed, co-pasture with horses, living area, herd size and number of treatments as significantly associated with strongyles. Sex, age, living area and herd size were significantly associated with Parascaris spp. Dictyocaulus arnfieldi was significantly associated with sex, grass, co-pasture with horses, living area and herd size. Strongylus vulgaris was significantly associated with living area and herd size. The mean number of anthelmintic treatments/year was 1.4; most of the donkeys (71.8%) were dewormed using an ivermectin drug. It is important to design parasite programs to specifically address both D. arnfieldi and S. vulgaris in donkeys, and this is especially important if donkeys co-graze with horses.

Pituitary Pars Intermedia Dysfunction and Metabolic Syndrome in Donkeys

Simple Summary

Donkeys are one of the six species of the equid family. Even though they may look similar to horses, there are optical, behavioral, and physiological differences between the two species. The most important endocrine diseases in horses (equine metabolic syndrome and pituitary pars intermedia dysfunction: PPID) also exist in donkeys. The key symptoms of asinine metabolic syndrome (AMS), similar to horses, are obesity, insulin dysregulation, and laminitis. It can be diagnosed with either basal glucose and insulin concentration or dynamic tests. The intravenous glucose tolerance test and the combined glucose insulin tolerance test were evaluated for donkeys. The therapy of AMS is aimed at weight and exercise management. Donkeys suffering from PPID are often laminitic. Other authors have reported on hypertrichosis as a cardinal sign. Donkey-specific differences in shedding compared to horses have to be considered. The PPID can be diagnosed with donkey-specific reference values or dynamic testing. The dexamethasone suppression test, the thyrotropin releasing hormone (TRH) test, and the combined dexamethasone suppression/TRH test were evaluated for donkeys.

Abstract

Appropriate medical care for donkeys is challenging despite being important working animals in non-industrialized countries and pets in first world countries. Although the same principles of diagnosis and therapy as in horses are commonly applied, there are differences in reference values and physiologic reaction to dynamic tests. However, donkeys seem to suffer from typical equine diseases, such as metabolic syndrome and pituitary pars intermedia dysfunction (PPID). Asinine metabolic syndrome (AMS) comprises obesity, insulin dysregulation, and laminitis. The principles of diagnosis are similar to horses. Donkey-specific reference ranges for insulin and glucose have been evaluated previously. Examinations regarding dynamic testing revealed differences in the intravenous glucose tolerance test and the combined insulin tolerance test compared to horses. The therapy of AMS is based mainly on weight loss and exercise. There are conflicting data regarding the incidence of PPID in donkeys. Laminitis and hypertrichosis were described as the main clinical signs. Species-specific and seasonal reference ranges were defined to diagnose PPID in donkeys. Furthermore, the dexamethasone suppression test, the thyrotropin releasing hormone (TRH) test and the combined dexamethasone suppression/TRH test were evaluated. Pergolide is commonly recommended for treatment.

Development of a Donkey Grimace Scale to Recognize Pain in Donkeys (Equus asinus) Post Castration

The objectives of this study were to establish a donkey ethogram, followed by a donkey grimace scale to be applied to donkeys pre- and post-castration and to test if there was a notable difference in scores based on observer knowledge, gender, and experience, which could reveal possible discomfort/pain. Nine healthy male adult donkeys were surgically castrated. Fifty-four photos were selected from frontal, lateral, and body views taken pre- and post-castration. Observers ranging from minimal to extensive knowledge and levels of experience based on education and hours/month spent with donkeys scored six photos/donkey on a scale of 0-2 (0 = not present, 1 = moderately present, 2 = obviously present). Scores were based on body language and facial parameters: Ears down, ears back, eye white showing, glazed look, orbital tightening, eyes round shape, nostril tension, eyes narrow shape, muzzle tension, and abnormal stance and overall perception of the animal being in pain. Level of experience and knowledge, as well as gender significantly (p < 0.001), affected observers' ability to accurately score images. The study suggests that the most significant indicators of pain in donkeys are overall appearance and abnormal body stance provided their sensitivity, specificity and accuracy values of 63.18%, 62.07%, and 62.60%, respectively.

Anthelmintic Efficacy and Pharmacokinetics of Ivermectin Paste after Oral Administration in Mules Infected by Cyathostomins

Ivermectin (IVM) is an anthelmintic compound commonly used off-label in mules due to its broad-spectrum of activity. Despite the general use of IVM in mules with the same dose and route of administration licensed for horses, significant pharmacokinetic differences might exist between horses and mules, as already observed for donkeys. The aim of the present study was to evaluate the pharmacokinetic profile and anthelmintic efficacy of an oral paste of IVM in mules naturally infected with cyathostomins. Fifteen adult mules with fecal egg counts (FEC) ≥200 eggs per gram (EPG), with exclusive presence of cyathostomins, were included in the study. All mules were orally treated with IVM according to the manufacturer's recommended horse dosage (200 µg/kg body weight). FECs were performed before (day-10 and day-3) and after treatment at days 14 and 28 by using a modified McMaster method. The FEC reduction (FECR%) was also calculated. Blood samples were collected from five animals at various times between 0.5 h up to 30 days post treatment to determine pharmacokinetic parameters. The maximum IVM serum concentration (Cmax) was 42.31 ± 10.20 ng/mL and was achieved at 16.80 ± 9.96 hours post-treatment (Tmax), area under the curve (AUC) was 135.56 ± 43.71 ng × day/mL. FECR% remained high (>95%) until the 28th day.

Pharmacokinetics of low-dose methotrexate in horses

This study aimed to investigate both the pharmacokinetic behavior and tolerance of methotrexate (MTX) in horses to design a specific dosing regimen as a new immunomodulatory drug for long-term treatment. To determine the primary plasma pharmacokinetic variables after single intravenous, subcutaneous or oral administration, six horses were administered 0.3 mg/kg MTX in a crossover design study. After a 10-week washout, MTX was administered subcutaneously to three of the six previously treated horses at a dose of 0.3 mg/kg once per week for 3 months. In both studies, MTX and metabolite concentrations were measured using LC-MS/MS. The absolute bioavailability of MTX was 73% following subcutaneous administration but less than 1% following oral administration. The plasma clearance was 1.54 ml min^-1  kg^-1 (extraction ratio = 2%). After 24 hr, plasma concentrations were below the LOQ. No adverse effects were noted except for a moderate reversible elevation in liver enzymes (GLDH). With regards to the main metabolites of MTX, very low concentrations of 7-hydroxy-MTX were found, whereas polyglutamated forms (mainly short chains) were found in red blood cells. A subcutaneous dose of 0.2 mg kg^-1  week^-1 may be safe and relevant in horses, although this has yet to be clinically confirmed.

Clinical Pharmacology in Donkeys and Mules

Donkeys and mules show several pharmacodynamic and pharmacokinetic idiosyncrasies that have to be fully considered by any clinician dealing with these species. Because they possess an increased metabolic rate and cellular water content compared with horses, higher doses (or shorter dosing intervals) are usually recommended for those drugs where pharmacologic studies have been performed. Nonetheless, owing to the lack of species-specific information, this assumption cannot be arbitrarily applied. Thus, when a drug protocol published for horses is extrapolated to a donkey or a mule, a close monitoring is required to detect any secondary effect or subdosing.

Sedative and cardiorespiratory effects of low doses of xylazine with and without acepromazine in Nordestino donkeys

BACKGROUND

Information on appropriate protocols for sedation of Nordestino donkeys is scarce.

OBJECTIVES

To evaluate the sedative and cardiorespiratory effects of low doses of intravenous (i.v.) xylazine with and without acepromazine in 'Nordestino' donkeys.

STUDY DESIGN

Seven healthy female Nordestino donkeys (150 ± 18 kg) were included in this blinded, randomised, crossover experiment.

METHODS

Four treatments were administered, consisting of two i.v. injections, at baseline (T0, 1st injection) and 15 min later (T15, 2nd injection). Treatments included acepromazine 0.05 mg/kg bwt + saline (AS), saline + xylazine 0.5 mg/kg bwt (SX0.5), acepromazine + xylazine 0.25 mg/kg bwt (AX0.25) or acepromazine + xylazine 0.5 mg/kg bwt (AX0.5). Sedative and cardiorespiratory parameters were evaluated before T0 and 15, 20, 30, 45, 60, 75 and 90 min after treatment. Degree [height of head above ground (HHAG)] and quality of sedation [ataxia, responses to stimuli and visual analogue scale (VAS) scoring] and respiratory rate were evaluated by the main investigator in situ, and heart rate was measured by an assistant investigator. Three experienced evaluators assessed vídeos for ataxia and responses to stimuli. Normal data were analysed by repeated measures ANOVA, and non-normal by Kruskal-Wallis (P<0.05).

RESULTS

HHAG was lower than baseline for 15 min after xylazine administration in AX0.25 and for 30 min in SX0.5 and AX0.5 groups. All treatments with xylazine increased VAS and ataxia scores in situ for 15 min after xylazine administration, with no differences between groups. Ataxia scores in situ were higher in SX0.5 and AX0.5 groups than AS for 15 and 30 min after xylazine administration, respectively.

MAIN LIMITATIONS

Absence of a negative control group (saline-saline).

CONCLUSION

Acepromazine added to xylazine at 0.25 mg/kg bwt produced briefer and milder sedation than xylazine at 0.5 mg/kg bwt.

Evaluation of cardiorespiratory and biochemical effects of ketamine-propofol and guaifenesin-ketamine-xylazine anesthesia in donkeys (Equus asinus)

OBJECTIVES

To evaluate the cardiorespiratory and biochemical effects of ketamine-propofol (KP) or guaifenesin-ketamine-xylazine (GKX) anesthesia in donkeys.

STUDY DESIGN

Prospective crossover trial.

ANIMALS

Eight healthy, standard donkeys, aged 10 ± 5 years and weighing 153 ± 23 kg.

METHODS

Donkeys were premedicated with 1.0 mg kg(-1) of xylazine (IV) in both treatments. Eight donkeys were administered ketamine (1.5 mg kg(-1)) and propofol (0.5 mg kg(-1) for induction, and anesthesia was maintained by constant rate infusion (CRI) of ketamine (0.05 mg kg(-1) minute(-1)) and propofol (0.15 mg kg(-1) minute(-1)) in the KP treatment. After 10 days, diazepam (0.05 mg kg(-1)) and ketamine (2.2 mg kg(-1)) were administered for induction, and anesthesia was maintained by a CRI (2.0 mL kg(-1) hour(-1)) of ketamine (2.0 mg mL(-1), xylazine (0.5 mg mL(-1)) and guaifenesin (50 mg mL(-1)) solution. Quality of anesthesia was assessed along with cardiorespiratory and biochemical measurements.

RESULTS

Anesthetic induction took longer in GKX than in KP. The induction was considered good in 7/8 with KP and in 6/8 in GKX. Anesthetic recovery was classified as good in 7/8 animals in both treatments. Xylazine administration decreased heart rate (HR) in both treatments, but in KP the HR increased and was higher than GKX throughout the anesthetic period. Respiratory rate was higher in GKX than in KP. PaO(2) decreased significantly in both groups during the anesthetic period. Glucose concentrations [GLU] increased and rectal temperature and PCV decreased in both treatments. Arterial lactate [LAC] increased at recovery compared with all time points in KP. [GLU] and calcium were higher in GKX than in KP at recovery.

CONCLUSION AND CLINICAL RELEVANCE

These protocols induced significant hypoxemia but no other cardiorespiratory or metabolic changes. These protocols could be used to maintain anesthesia in donkeys, however, they were not tested in animals undergoing surgery.

Persistence of α-cypermethrin residues in milk of lactating donkeys (Equus asinus) using UHPLC-MS/MS

The aim of this study was to measure the persistence of residues of the pyrethroid insecticide α-cypermethrin (ACYP) in the milk of lactating donkeys following pour-on treatment. Milk was collected from animals (n = 7) before the treatment and at 12, 24, 36, 48, 60, 72 and 84 h post-treatment. The last sampling was taken 7 days post-treatment (168 h). Milk samples were analysed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The analytical method was validated following requirements of Commission Decision 2002/657/EC. All samples showed levels of ACYP below the maximum residue limit (MRL) of 20 μg kg(-1) established for bovine milk (Commission Regulation (EU) No. 37/2010). The results demonstrate that there is minimal partitioning of ACYP into milk in lactating donkeys from pour-on treatment.

The effects of intravenous romifidine on intraocular pressure in clinically normal horses and horses with incidental ophthalmic findings

DESIGN

Original study.

OBJECTIVE

To evaluate the effect of sedation with romifidine hydrochloride 1% (Sedivet: Boehringer-Ingelheim) on intraocular pressure (IOP) in the normal horse and horses with incidental ophthalmic findings as measured by applanation tonometry.

ANIMALS

Nineteen clinically normal horses (13 geldings, six mares) and eight horses (three geldings, five mares) with incidental ophthalmic findings were included in this study.

PROCEDURES

All horses underwent complete ophthalmic examination with pharmacologic mydriasis a minimum of 2 weeks prior to IOP evaluation. Baseline intraocular pressure values were obtained following auriculopalpebral nerve block and topical anesthetic. Immediately thereafter, romifidine was administered intravenously (75 µg/kg) and the IOP recorded at 5, 15, 30, 45 and 60 min postsedation in both eyes. Five successive readings were obtained at each time point, the low and high value discarded, and three remaining readings averaged for a mean.

RESULTS

The changes with time were consistent between eyes and OD and OS results were pooled. The mean IOP at baseline was 26.35 ± 5.57 mmHg. Mean IOP values were significantly lower than baseline at 5 (P < 0.0001), 15 (P < 0.0001), 30 (P = 0.0003), 45 (P < 0.0001) and 60 (P = 0.0005) minutes. The largest change from baseline (16.7%) was noted at t = 15 min.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of romifidine significantly decreased the IOP from baseline at all time points measured. The greatest decline in IOP was noted at 15 min postsedation. Results are consistent with other studies noting a decline in IOP with administration of α-2 agonists.

A comparative study of xylazine-induced mechanical hypoalgesia in donkeys and horses

OBJECTIVE

To compare the effects of xylazine on mechanical nociceptive thresholds in donkeys and horses.

STUDY DESIGN

Randomized, controlled, crossover, Latin-square, operator-blinded design.

ANIMALS

Six 3.1 ± 0.89 year old standard donkeys weighing 145.0 ± 30.5 kg and six 9.6 ± 4.4 year old Thoroughbred horses weighing 456.0 ± 69.0 kg.

METHODS

Each animal received one of four doses of xylazine (0.5, 0.7, 0.9, and 1.1 mg kg(-1) ), or acepromazine (0.05 mg kg(-1) ) or saline solution (0.9%) intravenously and mechanical nociceptive thresholds were assessed over 90 minutes. The areas under the threshold change versus time curve values for 60 minutes (AUC(0-60) ) post-drug administration were used to compare the effect of treatment. A 1-week interval was allowed between successive trials on each animal.

RESULTS

All doses of xylazine, but not acepromazine or saline, increased mechanical thresholds for up to 60 minutes. Xylazine-induced hypoalgesia was dose-dependent and corresponding AUC(0-60) values for each treatment were not significantly different between donkeys and horses (p ≥ 0.0697).

CONCLUSION

The hypoalgesic effects of xylazine at four different doses were not different between donkeys and horses.

CLINICAL RELEVANCE

Xylazine induced a similar degree of mechanical hypoalgesia in donkeys and horses suggesting that similar doses are needed for both species with regard to analgesia.

Species differences in pharmacokinetics and pharmacodynamics

Veterinary medicine faces the unique challenge of having to treat many types of domestic animal species, including mammals, birds, and fishes. Moreover, these species have evolved into genetically unique breeds having certain distinguishable characteristics developed by artificial selection. The main challenge for veterinarians is not to select a drug but to determine, for the selected agent, a rational dosing regimen because the dosage regimen for a drug in a given species may depend on its anatomy, biochemistry, physiology, and behaviour as well as on the nature and causes of the condition requiring treatment. Both between- and within-species differences in drug response can be explained either by variations in drug pharmacokinetics (PK) or drug pharmacodynamics (PD), the magnitude of which varies from drug to drug. This chapter highlights selected aspects of species differences in PK and PD and considers underlying physiological and patho-physiological mechanisms in the main domestic species. Particular attention was paid to aspects of animal behaviour (food behaviour, social behavior, etc.) as a determinant of interspecies differences in PK or/and PD. Modalities of drug administration are many and result not only from anatomical, physiological and/or behavioural differences across species but also from management options. The latter is the case for collective/group treatment of food-producing animals, frequently dosed by the oral route at a herd or flock level. After drug administration, the main causes of observed inter-species differences arise from species differences in the handling of drugs (absorption, distribution, metabolism, and elimination). Such differences are most common and of greatest magnitude when functions which are phylogenetically divergent between species, such as digestive functions (ruminant vs. non-ruminant, carnivore vs. herbivore, etc.), are involved in drug absorption. Interspecies differences also exist in drug action but these are generally more limited, except when a particular targeted function has evolved, as is the case for reproductive physiology (mammals vs. birds vs. fishes; annual vs. seasonal reproductive cycle in mammals; etc.). In contrast, for antimicrobial and antiparasitic drugs, interspecies differences are more limited and rather reflect those of the pathogens than of the host. Interspecies difference in drug metabolism is a major factor accounting for species differences in PK and also in PD (production or not of active metabolites). Recent and future advances in molecular biology and pharmacogenetics will enable a more comprehensive view of interspecies differences and also between breeds with existing polymorphism. Finally, the main message of this review is that differences between species are not only numerous but also often unpredictable so that no generalisations are possible, even though for several drugs allometric approaches do allow some valuable interspecies extrapolations. Instead, each drug must be investigated on a species-by-species basis to guarantee its effective and safe use, thus ensuring the well-being of animals and safeguarding of the environment and human consumption of animal products.