Anesthetic and pathological changes following high doses of ketamine and xylazine in Sprague Dawley rats

Ketamine, an Old-New Drug: Uses and Abuses

Ketamine as an old-new drug has a variety of clinical implications. In the last 30 years, ketamine has become popular for acute use in humans. Ketamine in standard doses is principally utilized for the induction and maintenance of surgical procedures. Besides its use in anesthesia and analgesia, recent studies have shown that ketamine has found a place in the treatment of asthma, epilepsy, depression, bipolar affective disorders, alcohol and heroin addiction. Ketamine primarily functions as a noncompetitive antagonist targeting the N-methyl-D-aspartate (NMDA) receptor, but its mechanism of action is complex. It is generally regarded as safe, with low doses and short-term use typically not leading to significant adverse effects. Also, ketamine is known as a powerful psychostimulant. During the past decade, ketamine has been one of the commonly abused drugs.

Formulation and Evaluation of Novel Additive-Free Spray-Dried Triamcinolone Acetonide Microspheres for Pulmonary Delivery: A Pharmacokinetic Study

This work aimed to establish a simple method to produce additive-free triamcinolone acetonide (TAA) microspheres suitable for pulmonary delivery, and therefore more simple manufacturing steps will be warranted. The spray-drying process involved the optimization of the TAA feed ratio in a concentration range of 1-3% w/v from different ethanol/water compositions with/without adding ammonium bicarbonate as a blowing agent. Characterization of the formulas was performed via scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and powder X-ray diffraction. Our results indicated that the size and morphology of spray-dried TAA particles were dependent on the feed and solvent concentrations in the spray-dried formulations. Furthermore, adding the blowing agent, ammonium bicarbonate, did not produce a significant enhancement in particle characteristics. We prepared additive-free TAA microspheres and found that TAA formulation #1 had optimal physical properties in terms of diameter (2.24 ± 0.27 µm), bulk density (0.95 ± 0.05), tapped density (1.18 ± 0.07), and flowability for deposition during the pulmonary tract, from a centric airway to the alveoli as indicated by Carr's index = 19 ± 0.01. Hence, formulation #1 was selected to be tested for pharmacokinetic characters. Rats received pulmonary doses of TAA formula #1 and then the TTA concentration in plasma, fluid broncho-alveolar lavage, and lung tissues was determined by HPLC. The TAA concentration at 15 min was 0.55 ± 0.02 µg/mL in plasma, 16.74 ± 2 µg/mL in bronchoalveolar lavage, and 8.96 ± 0.65 µg/mL in lung homogenates, while at the 24 h time point, the TAA concentration was 0.03 ± 0.02 µg/mL in plasma, 1.48 ± 0.27 µg/mL in bronchoalveolar lavage, and 3.79 ± 0.33 µg/mL in lung homogenates. We found that TAA remained in curative concentrations in the rat lung tissues for at least 24 h after pulmonary administration. Therefore, we can conclude that additive-free spray-dried TAA microspheres were promising for treating lung diseases. The current novel preparation technology has applications in the design of preparations for TAA or other therapeutic agents designed for pulmonary delivery.

Novel and simple method using cable ties to induce intestinal strangulation in a rat model

BACKGROUND The pathogenesis of intestinal fibrosis after strangulation in abdominal surgery is not fully understood. Developing an experimental and reliable method is needed to overcome this problem. This study aimed to develop an effective method for intestinal strangulation leading to fibrosis, which might induce intestinal obstruction. METHODS This study was conducted from 2018 to 2019 at the Department of Pharmacology, Faculty of Medicine, Universitas Indonesia. A total of 24 Sprague Dawley rats were used in this study. Artificial intestinal strangulation using cable ties made of durable plastic, which is generally used to ligate objects, was applied, and rats were further classified into control, 6-hour, and 24-hour strangulation groups. At the end of the study, the rats were sacrificed, intestinal tissues were collected, and histomorphological changes were observed using hematoxylin and eosin stain. Moreover, Masson’s trichome staining was used to assess collagen density. RESULTS Median collagen density score of the 24-hour strangulation group was higher than the control. A significant difference in collagen density was found between the submucosal layer of the 24-hour strangulation group and the control (45.4 [11.4] versus 32.4 [14.0], p<0.001) and between the mucosa of the 6- and 24-hour strangulation groups and the control (26.9 [17] versus 6.46 [4.3], p = 0.01 and 24.9 [8] versus 6.46 [4.3], p = 0.004, respectively). CONCLUSIONS The simple use of cable ties adequately promotes intestinal strangulation.

The Effect of Nano-chitosan and Nano-curcumin on Radiated Parotid Glands of Albino Rats: Comparative Study

Decreasing the salivary flow rate manifested by xerostomia occurs early during the irradiation treatment. The duration of depressed salivary function varies among patients. Various histopathological changes occur in the salivary glands. The current study was performed to investigate and compare between the possible anti-radiotherapeutic effect of the gamma rays-synthesized curcumin nanoparticles (Cur NPs), and chitosan nanoparticles (Cs NPs). They were utilized to overcome the histopathological changes associated with radiation therapy in albino rats’ parotid glands. Sixty adult male Albino rats were utilized, fifteen as control group, fifteen as radiated group and thirty as Cur NPs and Cs NPs treatment groups. The parotid glands were dissected and examined histologically, immunohistochemically for vascular endothelial growth factor (VEGF) as well as histo-morphometrically. The histological results proved the antiradio-therapeutic effect of Cur NPs, and Cs NPs, with the least degenerative changes in the Cur NPs treated group. A high significant increase in VEGF was recorded in the radiated group as compared to the other treated groups. Cs NPs have proved to be an anti-radiotherapeutic and anti-oxidant substrate in treating the histopathological changes in radiated parotid glands of albino rats. However, it was lagging behind Cur NPs in all analyses but non-significant differences between them have been recorded.

Graphical Abstract

Effects of general anaesthesia with an inhalational anaesthetic agent on the expression of exosomes in rats

Background: We hypothesized that the expression of exosomes under general anaesthesia with an inhalational anaesthetic agent would be changed. The study was designed to confirm the effect of general anesthesia with an inhalational anaesthetic agent on the expression of exosomes in rats. Methods: After intraperitoneal administration for the mixture of ketamine and xylazine, tracheal intubation was performed. Just before the connection to ventilator, Control group and Anaesthesia group, according to anaesthesia with isoflurane, were allocated. The expressions of exosomes were checked in bronchoalveolar lavage (BAL), the blood and the tissues from the lung and the brain. Cytokines in the blood were also assessed. Results: The expressions of cluster of differentiation (CD)63 and CD81 as markers for the exosomes in the blood was increased after anaesthesia with isoflurane (CD63, 0.078 ± 0.057 % in Control group vs. 0.180 ± 0.036 % in Anaesthesia group, p = 0.02; CD81, 0.028 ± 0.034 % in Control group vs. 0.245 ± 0.054 % in Anaesthesia group, p < 0.01). However, the increased expression of them were not checked in BAL, and the tissues from the lung and the brain. The cytokines in the blood did not show any significant difference before and after anaesthesia with isoflurane. Conclusion: General anaesthesia with an inhalational anaesthetic agent increased the expression of exosomes in the blood. However, the change was limited in the blood, not the alveoli and the brain.

Context-Specific Tolerance and Pharmacological Changes in the Infralimbic Cortex-Nucleus Accumbens Shell Pathway Evoked by Ketamine

Like other drugs, ketamine is abused due to its ability to act as a positive reinforcer in the control of behavior, just as natural reinforcers do. Besides, through Pavlovian conditioning, tolerance to drug effects can become conditioned to specific contextual cues showing that environmental stimuli can act as powerful mediators of craving and relapse. In the present study, we shall investigate the effects of long-term ketamine administration and withdrawal on behavioral measures and emotionality, the drug-context-specific influence on the tolerance to the sedative effects of an anesthetic dose of ketamine, and the neuropharmacological events underlying this phenomenon, in rats conditioned with 10 mg/kg of ketamine and later challenged with a dose of ketamine of 80 mg/kg in a familiar and non-familiar environment. Variations in dopamine and serotonin efflux in the infralimbic cortex-nucleus accumbens shell circuitry (IL-NAcSh) was further recorded in the same conditions. Our results highlight that besides its well-known reinforcing properties, ketamine also shares the ability to induce behavioral and pharmacological conditioned tolerance, associated with increases in cortical (IL), and decreases in striatal (NAcSh) dopamine release. To our knowledge, we are presenting the first set of behavioral and neurochemical data showing that, like other drugs of abuse, ketamine can induce learned context-specific tolerance.

Influence of Caralluma adscendens Var. attenuata cold cream on UV-B damaged skin epidermal cells: a novel approach

Ultraviolet radiation-induced sunburns are characterized by pigmented, wrinkled, and dried skin, with rashes and red spots. Chemical sunscreen lotion shows beneficial effects, but it shows the adverse side effect while in continuous usage. Natural substances of plant origin are deemed a possible cause of UV radiation through sunscreen resources. On this basis, we formulated the cold cream from the Caralluma adscendens Var. attenuata (CAVA) plant extract. The phytocompounds were studied by using GC-MS. The antioxidant potential of the plant extract was determined, and the CAVA showed cytotoxicity on A375 skin melanoma cells determined by MTT assay. The FT-IR spectra analysis confirmed the chemical nature of crude and crosslinking between cold creams. The cream was applied topically to rats pre-exposed to UV-B radiation (32,800 J/m2) four times/week (on alternate days). UV-B exposed without any treatment rats showed increased red spots or wrinkles (5 cm2). In contrast, the cold cream treatment application on irradiated skin has significantly reduced the size of rashes and red spots and the wound was contracted in a dose-dependent manner. Furthermore, histopathology of the experimental rat skin confirmed that CAVA cream treatment significantly reduced the epidermal thickening, damage in dermis and epidermis layers, and restructured the hair follicles. This study suggests that the cream formulated using CAVA can alleviate the damages caused by the UV-B-irradiation at a high level and safeguard the skin tissues.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02694-y.

Curcumin can prevent the loss of sinoatrial node cells in methionine-treated rats: A stereological study

Methionine (MET) rich diets, smoking, coffee and alcohol consumption, low physical activity, and aging are related to high plasma concentrations of homocysteine, which can jeopardize the heart health. Although hyperhomocysteinemia has been considered a recognized risk factor for cardiac dysrhythmia, the structural changes of the conductive system, including Sinoatrial (SA) node of the heart involved in the disorder, have not been completely clarified. Curcumin is the main component of turmeric and has shown some cardioprotective effects. This study aimed to evaluate the effect of curcumin on the structural changes of the SA node in L-MET-treated rats. These alterations were evaluated by means of stereological techniques, namely cavalieri principle for volume estimation and optical disector counting technique for cell counting. Both techniques used two-dimensional images for obtaining three-dimensional parameters. The rats were divided into four groups, including control, MET-treated (1 g/kg/day), curcumin-treated, (100 mg/kg/day), and MET + curcumin. The treatments were performed for 28 days. On the final day, SA nodes were dissected out for stereological investigation. Compared to the control rats, the volume of SA node, total volume of grape-like cell clusters, and number of SA node cells were respectively decreased by 42%, 34%, and 37% in the MET-treated group (p < 0.04). However, collagen density remained constant in all the study groups. Furthermore, treatment with curcumin could protect the SA node from cellular decline in the MET + curcumin group (p < 0.01). It can be concluded that curcumin could prevent the structural changes of the SA node in the rats treated with methionine.

Auditory brainstem responses in aging dark agouti rats

The present study examined auditory function across age in the dark agouti (DA) rat strain. Auditory brainstem responses (ABRs) were measured for frequencies 8, 16, and 32 kHz in male and female DA rats from 3 to 18 months of age. Hearing thresholds and absolute and interpeak latencies (IPLs) were analyzed. Male hearing thresholds remained stable for the first year of life and then significantly increased at 18 months across all frequencies; female hearing remained stable at all tested ages out to 18 months. At 12 months, male DA rats showed significantly longer absolute latencies by age (i.e., compared with 3-month-old males) and sex (compared with 12-month-old females), with no differences in IPLs. At 18 months, female DA rats showed significantly longer absolute latencies with age (compared with 3-month-old females) and sex (compared with 18-month-old males), particularly for the later waves. Female IPLs were also significantly longer with age and by sex for the later waves. This report supports the feasibility of using male DA rats in studies to investigate age-related hearing loss (ARHL; presbycusis).

Intraperitoneal Alfaxalone and Alfaxalone-Dexmedetomidine Anesthesia in Sprague-Dawley Rats (Rattus norvegicus)

Due to their unpredictability and variable effects, injectable anesthetic regimens in laboratory rodent species warrant refinement. In our study we sought to evaluate alfaxalone, which has gained recent popularity in veterinary medicine, alone and in combination with dexmedetomidine to evaluate their anesthetic ability in Sprague-Dawley rats when administered intraperitoneally. Three doses of alfaxalone only and 4 dose combinations of alfaxalone-dexmedetomidine were tested in males and female rats. The time to induction, anesthetic duration, pulse rate, respiratory rate, temperature, and time to recovery were recorded by a blind observer. The level of anesthesia induced by the various anesthetic protocols was assessed by using pedal withdrawal reflex to a noxious stimulus and scored according to the response. Dependent on the treatment group, atipamezole or saline was administered intraperitoneally once animals reached 60 min of anesthesia. Regardless of the dose, alfaxalone alone achieved only a sedative level of anesthesia, whereas all alfaxalone-dexmedetomidine combinations led to a surgical level of anesthesia in all animals. Anesthesia regimens using alfaxalone alone and in combination with dexmedetomidine demonstrated sex-associated differences, with female rats maintaining longer durations of sedation or anesthesia than their male counterparts. Both male and female rats displayed decreases in physiologic parameters consistent with the effects of dexmedetomidine. Given the results described herein, we recommend 20 mg/kg alfaxalone for sedation and 30 mg/kg alfaxalone combined with 0.05 mg/kg dexmedetomidine for surgical anesthesia in female rats. Appropriate doses of alfaxalone only and alfaxalone-dexmedetomidine for male rats were not determined in this study and need further evaluation.

Multimodal imaging reveals transient liver metabolic disturbance and sinusoidal circulation obstruction after a single administration of ketamine/xylazine mixture

A ketamine/xylazine (K/X) mixture is widely used before and during experiments in rodents. However, the impact of short-term use of K/X mixture and its influences on data interpretation have rarely been discussed. In this study, we administered one shot of a K/X mixture and examined acute hepatic responses using biochemical analysis, histopathological examination, and non-invasive imaging to determine the delay required prior to further assessment of the liver to avoid confounding effects triggered by anaesthesia. After the K/X injection, aspartate aminotransferase (AST) in serum was significantly elevated from 3 to 48 h. Obstructed sinusoidal circulation lasting for 24 or 36 h was revealed by DCE-MRI and drug distribution analysis, respectively. Metabolic alterations were detected at 3 h by NMR analysis and FDG-PET. Moreover, ultrasonography showed that lipid droplet accumulation increased from 1 to 16 h and declined thereafter. Taken together, our findings show that the K/X mixture induces acute hepatotoxicity and metabolic disturbance, and these disturbances cause hemodynamical disorders in the liver. The required time interval for recovery from K/X impact was dependent on the chosen assay. It took at least 16 h for metabolic recovery and 36 h for recovery of sinusoidal circulation. However, the liver was not fully recovered from the injury within 48 h.

Oxygen inhalation improves postoperative survival in ketamine-xylazine anaesthetised rats: An observational study

OBJECTIVE

A simple but reliable and safe anaesthetic procedure is required for surgical interventions in small rodents. Combined ketamine and xylazine injections are often used in rats for less invasive surgery, possibly with spontaneous breathing and without airway management. However, there are important pitfalls to be avoided by special precautions and monitoring, as shown subsequently.

STUDY DESIGN

Observational study.

ANIMALS

Twenty-four anaesthetic procedures for bile duct ligation, sham operation or carotid artery dilatation in 20 male Sprague-Dawley rats, preoperatively weighing between 440 and 550 g.

METHODS

Intolerable high mortality rates occurred in the first 7 postoperative days while establishing a new experimental model in rats using ketamine-xylazine anaesthesia. Rats were spontaneously breathing ambient air during the first 12 surgeries without airway management. An observed high mortality rate in these animals led to a change in the trial protocol: the insufflation of 2 litres of oxygen per minute via nose cone during the following 12 rat surgeries. Retrospective comparison of the outcome (without oxygen vs. with oxygen insufflation) was conducted.

RESULTS

The perioperative mortality rate could be significantly reduced from 58% (7/12) to 17% (2/12) (p = 0.036) by oxygen insufflation via nose cone. Significantly different levels of intraoperative oxygen saturation (SpO2; 89 ± 4% [without oxygen] vs. 97 ± 0.5% [with oxygen], p < 0.0001), but no significant differences in heart rate (HR; 267 ± 7 beats minute-1 [bpm] [without oxygen] vs. 266 ± 6 bpm [with oxygen], p = 0.955) were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

In summary, rats under ketamine-xylazine anaesthesia are susceptible to hypoxia. This may lead to increased delayed mortality related to hypoxia induced lung failure. Apparently, this is an underestimated problem. We highly recommend using additional oxygen insufflation in spontaneously breathing rats under ketamine-xylazine anaesthesia with basic monitoring such as measurement of oxygen saturation.

Diaphragmatic recovery in rats with cervical spinal cord injury induced by a theophylline nanoconjugate: Challenges for clinical use

Context: Following a spinal cord hemisection at the second cervical segment the ipsilateral hemidiaphragm is paralyzed due to the disruption of the rostral ventral respiratory group (rVRG) axons descending to the ipsilateral phrenic motoneurons (PN). Systemically administered theophylline activates a functionally latent crossed phrenic pathway (CPP) which decussates caudal to the hemisection and activates phrenic motoneurons ipsilateral to the hemisection. The result is return of function to the paralyzed hemidiaphragm. Unfortunately, in humans, systemically administered theophylline at a therapeutic dose produces many unwanted side effects.Design and setting: A tripartite nanoconjugate was synthesized in which theophylline was coupled to a neuronal tracer, wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), using gold nanoparticles as the coupler. Following intradiaphragmatic injection of the nanoconjugate, WGA-HRP selectively targets the theophylline-bound nanoconjugate to phrenic motoneurons initially, followed by neurons in the rVRG by retrograde transsynaptic transport.Participants: (N/A)Interventions: (N/A)Outcome Measures: Immunostaining, Electromyography (EMG).Results: Delivery of the theophylline-coupled nanoconjugate to the nuclei involved in respiration induces a return of respiratory activity as detected by EMG of the diaphragm and a modest return of phrenic nerve activity.Conclusion: In addition to the modest return of phrenic nerve activity, there were many difficulties using the theophylline nanoconjugate because of its chemical instability, which suggests that the theophylline nanoconjugate should not be developed for clinical use as explained herein.

Diaphragm muscle activity across respiratory motor behaviors in awake and lightly anesthetized rats

Respiratory muscles such as the diaphragm are active across a range of behaviors including ventilation and higher-force behaviors necessary for maintenance of airway patency, and minimal information is available regarding anesthetic effects on the capacity of respiratory muscles to generate higher forces. The purpose of the present study was to determine whether diaphragm EMG activity during lower-force behaviors, such as eupnea and hypoxia-hypercapnia, is differentially affected compared with higher-force behaviors, such as a sigh, in lightly anesthetized animals. In adult male rats, chronically implanted diaphragm EMG electrodes were used to measure the effects of low-dose ketamine (30 mg/kg) and xylazine (3 mg/kg) on root mean square (RMS) EMG amplitude across a range of motor behaviors. A mixed linear model was used to evaluate the effects of ketamine-xylazine anesthesia on peak RMS EMG and ventilatory parameters, with condition (awake vs. anesthetized), behavior (eupnea, hypoxia-hypercapnia, sigh), side (left or right hemidiaphragm), and their interactions as fixed effects and animal as a random effect. Compared with the awake recordings, there was an overall reduction of peak diaphragm RMS EMG across behaviors during anesthesia, but this reduction was more pronounced during spontaneous sighs (which require ~60% of maximal diaphragm force). Respiratory rates and duty cycle during eupnea and hypoxia-hypercapnia were higher in awake compared with anesthetized conditions. These results highlight the importance of identifying anesthetic effects on a range of respiratory motor behaviors, including sighs necessary for maintaining airway patency. NEW & NOTEWORTHY Respiratory muscles accomplish a range of motor behaviors, with forces generated for ventilatory behaviors comprising only a small fraction of their maximal force generating capacity. Induction of anesthesia exerts more robust effects on the higher-force diaphragm motor behaviors such as sighs compared with eupnea. This novel information on effects of low, sedative doses of a commonly used anesthetic combination (ketamine-xylazine) highlights the importance of identifying anesthetic effects on a range of respiratory motor behaviors.

Photobiomodulation reduces abdominal adipose tissue inflammatory infiltrate of diet-induced obese and hyperglycemic mice

Systemic inflammation is closely related to the development of insulin resistance and type-2 diabetes, since the activation of pro-inflammatory pathways leads to inhibition of insulin signaling. Although photobiomodulation (PBM) has proven beneficial effects on the treatment of inflammatory disorders, the phototherapeutic approach to manage the chronic inflammatory component of obesity and hyperglycemia had never been explored. In this work, obese and hyperglycemic mice are treated with PBM, and their body mass, glycemia and inflammatory infiltrate of abdominal adipose tissue are evaluated. During four weeks, irradiated animals are exposed to six irradiation sessions using an 843 nm LED (5.7 J cm^-2 at 19 mW cm^-2 per session). Non-irradiated control animals display inflammatory areas almost five times greater than the treated group (p < 0.001). This result on inflammatory infiltrate may have caused impacts on the significant lower blood glucose level from irradiated animals (p = 0.04), twenty-four hours after the last irradiation session. PBM on obese and hyperglycemic mice reduced five times the areas of inflammatory infiltrate within abdominal adipose tissue (a, b), whereas dense inflammatory regions were a common finding amidst non-irradiated animals (c). The asterisks on (c) correspond to the inflammatory infiltrate permeating adipocytes.

Intraperitoneal co-administration of low dose urethane with xylazine and ketamine for extended duration of surgical anesthesia in rats

Procedures involving complex surgical techniques in rats, such as placement of abdominal aortic graft require extended duration of surgical anesthesia, which often can be achieved by repeated administrations of xylazine-ketamine combination. However such repeated anesthetic administration, in addition to being technically challenging, may be associated with potential adverse events due to cumulative effects of anesthesia. We report here the feasibility of using urethane at low dose (~1/10 the recommended anesthetic dose) in combination with a xylazine-ketamine mix to achieve an extended duration of surgical anesthesia in rats. The anesthesia induction phase was quick and smooth with an optimal phase of surgical anesthesia achieved for up to 90 minutes, which was significantly higher compared to that achieved with use of only xylazine-ketamine combination. The rectal temperature, heart rate and respiratory rate were within the physiological range with an uneventful recovery phase. Post surgery the rats were followed up to 3 months without any evidence of tumor or any other adverse effects related to the use of the urethane anesthetic combination. We conclude that low dose urethane can be effectively used in combination with xylazine and ketamine to achieve extended duration of surgical anesthesia up to 90 minutes in rats.

Physiological, pharmacokinetic and liver metabolism comparisons between 3-, 6-, 12- and 18-month-old male Sprague Dawley rats under ketamine-xylazine anesthesia

The main objective of this study was to compare the physiological changes (withdrawal and corneal reflexes, respiratory and cardiac frequency, blood oxygen saturation, and rectal temperature) following intraperitoneal administration of ketamine (80 mg/kg) and xylazine (10 mg/kg) to 3-, 6-, 12- and 18-month-old male Sprague Dawley rats (n=6/age group). Plasma pharmacokinetics, liver metabolism, and blood biochemistry were examined for a limited number of animals to better explain anesthetic drug effects. Selected organs were collected for histopathology. The results for the withdrawal and corneal reflexes suggest a shorter duration and decreased depth of anesthesia with aging. Significant cardiac and respiratory depression, as well as decreased blood oxygen saturation, occurred in all age groups however, cardiac frequency was the most affected parameter with aging, since the 6-, 12-, and 18-month-old animals did not recuperate to normal values during recovery from anesthesia. Pharmacokinetic parameters (T_1/2 and AUC) increased and drug clearance decreased with aging, which strongly suggests that drug exposure is associated with the physiological results. The findings for liver S9 fractions of 18-month-old rats compared with the other age groups suggest that following a normal ketamine anesthetic dose (80 mg/kg), drug metabolism is impaired, leading to a significant increase of drug exposure. In conclusion, age and related factors have a substantial effect on ketamine and xylazine availability, which is reflected by significant changes in pharmacokinetics and liver metabolism of these drugs, and this translates into shorter and less effective anesthesia with increasing age.