Distribution of orally administered trimethoprim and sulfadiazine into noninfected subcutaneous tissue chambers in adult ponies

The distribution of trimethoprim (TMP) and sulfadiazine (SDZ) into subcutaneously implanted noninfected tissue chambers was studied in healthy adult ponies. Six ponies were given an oral TMP/SDZ paste formulation at a dose of 5 mg/kg TMP and 25 mg/kg SDZ at 12 h intervals for 2 days in order to reach steady-state concentrations. Plasma concentrations and tissue chamber fluid (TCF) concentrations of both drugs were measured at regular intervals during a period commencing 24 h after the last oral administration. The peak concentration of TMP (mean +/- SD) was 2.92 +/- 0.86 microg/mL for plasma and 1.09 +/- 0.25 microg/mL for TCF. For SDZ, the mean peak concentration was 40.20 +/- 14.74 microg/mL for plasma and 23.48 +/- 5.84 microg/mL for TCF. TMP peak concentrations in plasma were reached at 3.17 +/- 03.48 h and those in TCF at 7.33 +/- 03.72 h. SDZ peak concentrations in plasma were reached at 1.83 +/- 02.04 h and those in TCF at 8.00 +/- 03.10 h. Concentrations of TMP and SDZ in TCF remained above the generally accepted breakpoint for susceptibility (0.5/9.5 for the TMP/SDZ combination) for 12 h. Therefore, in ponies oral administration of TMP/SDZ at a dose rate of 30 mg/kg given twice daily in the form of a paste should be appropriate for effective treatment of infections caused by susceptible bacteria.     

Ketamine, Telazol, xylazine and detomidine. A comparative anesthetic drug combinations study in ponies.

This study was designed to assess the effects of 5 anesthetic drug combinations in ponies: (1) ketamine 2.75 mg/kg, xylazine 1.0 mg/kg (KX), (2) Telazol 1.65 mg/kg, xylazine 1.0 mg/kg (TX), (3) Telazol 2 mg/kg, detomidine 20 micrograms/kg (TD-20), (4) Telazol 2 mg/kg, detomidine 40 micrograms/kg (TD-40), (5) Telazol 3 mg/kg, detomidine 60 micrograms/kg (TD-60). All drugs were given iv with xylazine or detomidine preceding ketamine or Telazol by 5 min. Heart rate was decreased significantly from 5 min to arousal after TD-20 but only at 60 and 90 min after TD-40 and TD-60 respectively. Respiratory rate was decreased significantly for all ponies. Induction time did not differ between treatments. Duration of analgesia was 10 min for KX, 22.2 min for TX, 27.5 min for TD-20, 32.5 min for TD-40, and 70 min for TD-60. Arousal time was significantly longer with detomidine and Telazol. Smoothness of recovery was judged best in ponies receiving KX and TD-40. All ponies stood unassisted 30 min after signs of arousal.     

Controlled test and clinical evaluation of dienbendazole against naturally acquired gastrointestinal parasites in ponies

A controlled test was performed to titrate the anthelmintic dosage of dienbendazole in 24 mixed-breed ponies naturally infected with Strongylus vulgaris, S edentatus, and small strongyle species, as determined by parasitic egg and larval counts in feces. Comparison of results of treatment was made among 3 dienbendazole dosages--2.5, 5, and 10 mg/kg of body weight--and a gum (excipient) mixture given by nasogastric intubation. All ponies were euthanatized and necropsied at 7 or 8 days after treatment. Trichostrongylus axei, Habronema muscae, S vulgaris, S edentatus, small strongyles, and Oxyuris equi were efficaciously eliminated in response to all doses of dienbendazole; Gasterophilus spp were not affected by any dose. There were not sufficient numbers of Draschia megastoma, Anoplocephala spp, or Parascaris equorum in the ponies to evaluate drug effect. Changes in the appearance of the intestinal lining were dose-dependent; in the ponies treated with 5 and 10 mg of dienbendazole/kg, the mucosa appeared clean and smooth, though in ponies given 2.5 mg/kg, it appeared clean, but was nodular and moderately reactive to embedded immature small strongyles. In the gum mixture-treated ponies, the large intestinal mucosa was inflamed, with edematous areas, in response to infections caused by large and small strongyles. A limited clinical titration was done in 12 ponies that were fecal culture negative for S vulgaris larvae, although other strongyles were detected. Two ponies in each of 6 groups were given the following dosages: 0 (gum mixture only), 0.5, 1, 2.5, and 5 mg of dienbendazole/kg. One group of 2 ponies was given 5 mg of fenbendazole/kg as a standard treatment control.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical efficacy of prophylactic administration of trimethoprim/sulfadiazine in a Streptococcus equi subsp. zooepidemicus infection model in ponies

Tissue chambers, implanted subcutaneously in the neck in six ponies, were inoculated with Streptococcus equi subsp. zooepidemicus in order to determine the clinical efficacy of prophylactic administration of trimethoprim/sulfadiazine (TMP/SDZ) against this infection. The TMP/SDZ treatment consisted of one intravenous (i.v.) injection of 5 mg/kg TMP and 25 mg/kg SDZ and the same dose of TMP/SDZ per os (p.o.), both given 3 h before inoculation. The oral dose was then repeated every 12 h for 5 days. TMP/SDZ concentrations in tissue chamber fluid (TCF) were above 10 times MIC at the moment of inoculation, and they were maintained at this level or higher throughout the duration of treatment. Trimethoprim/sulfadiazine treatment resulted in a marked reduction of viable bacteria in the tissue chamber but did not eliminate the infection, resulting in abscessation from day 19 onwards in all six ponies. This shows that, even when TCF is not yet purulent, TMP/SDZ is unable to eliminate the streptococci. Therefore, TMP/SDZ should not be the antimicrobial treatment of choice in infections in secluded sites in horses.     

Critical tests with oxibendazole against gastrointestinal parasites of ponies.

Twenty ponies were allotted to 4 groups of 5 ponies each, and oxibendazole was orally administered at dose levels of 5, 10, 15, and 20 mg/kg. In the 3 groups of ponies given the largest doses, efficacy against 3 species of Strongylus was between 92 and 100% and that against small strongylids of the genera Cyathostomum, Cylicocyclus, Cylicodontophorus, and Cylicostephanus was more than 99%. All adults and 95 to 100% of larvae of the pinworm Oxyuris equi were removed. In the group of ponies given 5 mg/kg, 86 to 100% of the large strongylids and 84 to 100% of the small strongylids were removed, as were all larval and adult pinworms. Trichostrongylus axei was found only in 4 of the 5 ponies given 5 mg/kg; results were encouraging, but not consistent. Almost all of the Parascaris equorum were found in this group of ponies; no anthelmintic activity was detected at this dose level. Oxibendazole removed approximately 99% of small strongylid 4th-stage larvae. No efficacy against the larval stages of Gasterophilus intestinalis and against Habronema spp and Setaria equina was observed.     

Acute experimentally induced aflatoxicosis in the weanling pony

Nineteen weanling ponies and 1 adult pony were given a single oral dose of aflatoxin B1 (AFB1). Dosages were: 0, 0.5, 1, 2, 4, 5, 6, and 7.4 mg of AFB1/kg of body weight. Vital signs were monitored, and whole blood and serum collected for analysis of serum enzymes, prothrombin time, blood cell counts, and serum urea nitrogen. Ponies that died were examined for gross lesions, and tissues were collected for histopathologic examination and analysis of AFB1 and AFM1 residues. Two of the 4 ponies given the 2 mg/kg dose and all ponies given the larger dosages died within 76 hours. Clinical signs included increased rectal temperature, faster heart and respiratory rates, abdominal straining, bloody feces, and tetanic convulsions. At necropsy, ponies that died of acute aflatoxicosis showed visceral petechiae and hepatic focal lesions. Histopathologic changes included severe hepatic necrosis, vacuolation, and bile duct hyperplasia. Aflatoxins B1 and M1 were recovered from liver, kidney, skeletal muscle, and gastrointestinal contents. One other pony given the 2 mg/kg dose died 32 days after dosing, and 1 control pony died after 70 days. Continuous elevations in prothrombin time and serum aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyl transpeptidase levels were observed in ponies dosed at 4 mg/kg or more. Significant (P less than 0.05) elevations in these values, which peaked 2 to 3 days after dosing, were seen in ponies given the 2 mg/kg dose. This group also had significant increases over controls in PCV and hemoglobin concentration 5 days after dosing.     

Distribution of penicillins into subcutaneous tissue chambers in ponies

The distribution of penicillins into a tissue chamber implanted subcutaneously in ponies was studied. Ampicillin sodium (equivalent to 15 mg/kg ampicillin) was administered intravenously. Pivampicillin, a prodrug of ampicillin, was administered by nasogastric tube to fed ponies at a dose of 19.9 mg/kg (equivalent to 15 mg/kg ampicillin). Procaine penicillin G was administered intramuscularly at a dose of 12 mg/kg (equivalent to 12 000 IU/kg). Six ponies were used for each medication. Antibiotic concentrations in plasma and tissue chamber fluid (TCF) were measured for 24 h after administration. Mean peak concentrations of ampicillin in TCF were 7.3 μg/mL, reached at 1.7 h, and 1.3 μg/mL, reached at 2.7 h, after administration of ampicillin sodium and pivampicillin respectively. The mean peak concentration of penicillin G of 0.3 μg/mL was reached 12.3 h after administration of procaine penicillin G. Concentrations in TCF remained above the minimum inhibitory concentration of Streptococcus zooepidemicus for the proposed dosing intervals of 8, 12 and 24 h for ampicillin sodium, pivampicillin and procaine penicillin G respectively.     

Clinical efficacy of intravenous administration of marbofloxacin in a Staphylococcus aureus infection in tissue cages in ponies

Tissue cages (TC), implanted subcutaneously in the neck in eight ponies, were inoculated with Staphylococcus aureus (S. aureus) to determine the clinical efficacy of marbofloxacin in the treatment of this infection. From 21 h after inoculation, marbofloxacin (6 mg/kg) was administered intravenously (i.v.) once daily for 7 days. Samples of the tissue cage fluid (TCF) were taken to determine marbofloxacin concentrations (days 1, 3 and 7), using high-pressure liquid chromatography, and numbers of viable bacteria [colony forming units (CFU)] (days 1, 3, 7, 14 and 21). Statistical analysis was used to compare CFU before and after treatment. Clinical signs and CFU were used to evaluate the efficacy of treatment. Although, there was a slight decrease in CFU in all TC initially, the infection was not eliminated by marbofloxacin treatment in any of the ponies and abscesses formed. As the MIC (0.25 microg/mL) did not change during treatment and the concentration of marbofloxacin during treatment (mean concentration in TCF was 0.89 microg/mL on day 1, 0.80 microg/mL on day 3 and 2.77 microg/mL on day 7) was above MIC, we consider that the treatment failure might be attributable to the formation of a biofilm by S. aureus. Based on the present results, i.v. administration of marbofloxacin alone is not suitable for the elimination of S. aureus infections from secluded sites.     

Clinical efficacy of trimethoprim/sulfadiazine and procaine penicillin G in a Streptococcus equi subsp. zooepidemicus infection model in ponies

Tissue chambers, implanted subcutaneously on both sides of the neck in eight ponies, were inoculated with Streptococcus equi subsp. zooepidemicus in order to compare the clinical efficacy of trimethoprim/sulfadiazine (TMP/SDZ) and penicillin G treatment in a purulent infection. The TMP/SDZ treatment consisted of one intravenous (i.v.) injection of 5 mg/kg TMP and 25 mg/kg SDZ and the same dose of TMP/SDZ per os (p.o.), both given 20 h after inoculation. The oral dose was then repeated every 12 h for 21 days. The penicillin treatment consisted of one i.v. injection of 20 000 IU/kg sodium penicillin G and intramuscular (i.m.) injection of 20 000 IU/kg procaine penicillin G, both given 20 h after infection. The i.m. dose was then repeated every 24 h for 21 days. Eight ponies, each with two tissue chambers, were used in a cross over design; in the first experiment the left tissue chamber (TC) was infected and in the second experiment the right. TMP/SDZ treatment resulted in a limited reduction of viable bacteria in the TC but did not eliminate the infection, resulting in abscessation in 10-42 days in all eight ponies. However, penicillin treatment eliminated the streptococci in seven of eight ponies, and only one pony suffered abscessation on day 10. This constitutes a significantly better efficacy of the penicillin treatment in this model. The most probable cause of the failure of TMP/SDZ to eliminate the streptococci is inhibition of the action of TMP/SDZ in the purulent TCF. Therefore, TMP/SDZ should not be used to treat purulent infections in secluded sites in horses.     

Effects of phenobarbital treatment on 3-methylindole toxicosis in ponies

To study the role of cytochrome P-450-dependent mixed function oxidase reactions in equine 3-methylindole (3MI) toxicosis, ponies were given 20 mg of phenobarbital/kg of body weight at 72, 60, 48, 36, and 24 hours before 100 mg of oral 3MI/kg to induce cytochrome P-450 or no treatment (controls). Maximal 3MI plasma concentration was decreased and clearance was faster in phenobarbital-treated ponies. Plasma 3MI was still detectable 12 and 36 hours after dosing in phenobarbital-treated and control ponies, respectively. Phenobarbital treatment induced a distribution phase with transition from a 1-compartment to a 2-compartment extravascular model. Bronchiolitis occurred in all ponies 72 hours after 3MI, but was more severe in those treated with phenobarbital. Appearance of a distribution phase, increased total body clearance, and more severe bronchiolitis in phenobarbital-treated ponies indicated that mixed function oxidases are involved in metabolism and conversion of 3MI to a toxic metabolite.     

The Effect of Sedation on Gastric Emptying of a Liquid Marker in Ponies

OBJECTIVE: The effect of sedation on gastric emptying was evaluated in six ponies by monitoring serum concentrations of acetaminophen (AP) after intragastric administration. EXPERIMENTAL DESIGN: Prospective randomized experimental study. ANIMALS: Six adult ponies, 135 to 275 kg. METHODS: Fifteen minutes after the intravenous administration of xylazine (1 mg/kg), butorphanol (0.05 mg/kg), acepromazine (0.05 mg/kg) or saline, ponies were given AP (20 mg/kg in 350 mL water) by stomach tube. Blood for AP analysis was collected at baseline and 15, 30, 45, 75, 90, 105, and 120 minutes after AP administration. The time (Tmax) to reach peak serum concentration (Cmax), and the area under the AP serum concentration versus time curve (AUC) were determined for each treatment group. RESULTS: Tmax was 31 mins in the control group, and this increased significantly (P<.05) after sedation. Cmax decreased (P<.05) after xylazine administration, and AUC decreased (P<.05) after acepromazine. CONCLUSIONS: This study indicated that sedation has a significant effect on the gastric emptying rate of a liquid in ponies.     

A Preliminary Comparison of Lidocaine and Xylazine as Epidural Analgesics in Ponies

Xylazine (0.35 mg/kg) or lidocaine (0.35 mg/kg) was injected into the epidural space of six ponies to compare their effectiveness as epidural analgesics. Each pony received both treatments at 1 week intervals with the order of treatments randomized. Xylazine produced analgesia of significantly longer duration (247 +/- 58 minutes) than that produced by an equal dose of lidocaine (135 +/- 22 minutes). Mild transient ataxia of no clinical significance developed in all ponies with both treatments. Spinal cords were removed from two ponies and examined histologically. No discernible pathologic changes were noted.     

Effects of aflatoxins in young ponies

Sixteen clinically normal, healthy ponies were randomly assigned to 4 groups and given aflatoxin B1 in doses of 0.045, 0.030, 0.015, and 0 (control) mg/kg of body weight per day for 21 days (or total doses of 0.945, 0.630, 0.315, and 0 mg/kg). The animals were allowed to recover for 3 months and then were reassigned to 4 treatment groups such that each group during the 2nd trial included a pony from each of the groups of the 1st trial. The animals in the new groups were intubated and were given aflatoxin in doses of 0.4, 0.2, 0.1, and 0 (control) mg/kg/day for 5 days ( or total doses of 2.0, 1.0, 0.5, and 0 mg/kg). Venous blood samples were drawn every other day to monitor for toxicosis; examinations were made for RBC and WBC counts, hemoglobin concentration, PCV, serum urea nitrogen, prothrombin time, and serum concentrations of aspartate aminotransferase, iditol dehydrogenase, alkaline phosphatase, albumin, gamma-glutamyl transferase, and arginase. There were no significant differences between treatment groups and controls (given no aflatoxin) in the toxicologic values examined for during the 1st trial. During the 2nd experiment, 2 of the ponies in the large-dose treatment gorup (2.0 mg/kg) demonstrated increased serum enzyme activities. These animals had been in the large-dose (0.945 mg/kg) and median-dose (0.63 mg/kg) groups during the 1st trial. Arginase, iditol dehydrogenase, and gamma-glutamyl transpeptidase activities became increased on the 4th day of treatment and continued to increase until the 6th day of the experiment (1 day after treatment was terminated). These enzymes approached control group values at 10 days after cessation of treatment. These increases were indicative of hepatocellular toxicity. It was concluded that the possibility of equine aflatoxicosis exists although ponies given high quality rations appear to be less susceptible than some other species. Prior exposure to aflatoxins may predispose to clinical toxicity on subsequent exposure, despite lack of expression of clinical signs.     

Flunixin meglumine attenuation of endotoxin-induced damage to the cardiopulmonary vascular endothelium of the pony

Endotoxic shock was induced in 5 ponies by intraperitoneal injections of 20, 40, 60, 80, and 80 micrograms of Escherichia coli endotoxin (LPS)/kg of body weight at 0, 6, 12, 18, and 24 hours, respectively. At 24 hours, the ponies also were given 20 micrograms of LPS/kg via catheter in the left ventricle of the heart. A 2nd group of 4 ponies was given 1.1 mg of flunixin meglumine (FM)/kg, IV, at 6, 12, 18, and 24 hours just before the corresponding LPS injection. Two hours after the 24-hour LPS injection, the ponies in both groups were anesthetized, the lungs were perfused with fixative, and portions of the pulmonary arteries and veins and right and left ventricles were prepared for scanning and transmission electron microscopy. In ponies that were given only LPS, some areas of pulmonary vascular endothelium appeared normal when compared with untreated controls, but other areas had disoriented endothelial cells or had varying amounts of sloughing, which ranged from focal areas of a few cells to large areas of denuded endothelium. Ponies treated with FM before LPS had less severe and less extensive endothelial cell damage. In both groups, leukocytes were attached to areas of the vessel wall; endothelial cell damage was greater in these regions. Administration of FM before LPS administration attenuated the LPS-induced endothelial cell damage.     

Antagonism of xylazine-pentobarbital anesthesia by yohimbine in ponies

Effects of yohimbine on xylazine-pentobarbital anesthesia were evaluated in ponies. Five minutes after the IV injection of xylazine (1.1 mg/kg of body weight), pentobarbital sodium (12.7 mg/kg, IV) and additional xylazine (2.2 mg/kg, IM) were given and produced anesthesia in 12 ponies for 64.0 +/- 16.4 minutes (mean +/- SD) as well as immobilization for 89.8 +/- 34.2 minutes. Eleven ponies were given yohimbine (0.1 mg/kg, IV) 50 minutes after pentobarbital dosing. In these 11 ponies, durations of anesthesia and immobilization were shorter, 52.0 +/- 1.4 and 65.5 +/- 14.8 minutes, respectively. The xylazine-pentobarbital combination caused bradycardia that was reversed by yohimbine injection. Xylazine-pentobarbital produced a small, but steady, decrease of mean arterial blood pressure, which was compounded by yohimbine administration and was evident for approximately 2 minutes. Within a minute after yohimbine injection, the ponies' respiratory rate decreased and the length of inspiration and expiration and thoracic breathing increased. This lasted approximately 2 to 3 minutes and was followed by an increase in respiratory rate. The anesthesia also produced a decrease in PaO2 that gradually returned to base line in 12 control ponies, but was more pronounced in 11 ponies given yohimbine. The PaCO2, although remaining moderately high in control ponies, returned to base line after yohimbine injection. An increased pHa was seen 60 minutes after induction of anesthesia and was especially noticeable after yohimbine administration. Decreases in the number of WBC, hemoglobin content, PCV, plasma protein and serum aspartate transaminase resulting from xylazine-pentobarbital were reversed by yohimbine. Conversely, serum glucose values and creatine kinase activities were increased by xylazine-pentobarbital.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of butorphanol, flunixin, levorphanol, morphine, and xylazine in ponies

The analgesic and behavioral effects of butorphanol (0.22 mg/kg), flunixin (2.2 mg/kg), levorphanol (0.033 mg/kg), morphine (0.66 mg/kg), and xylazine (2.2 mg/kg), given IM were observed in 8 ponies. These ponies were instrumented to measure response objectively to painful superficial and visceral stimuli. Effects on the cardiopulmonary system and rectal temperature also were evaluated in 6 of these ponies. Observations were conducted before drug injection (base-line values) and after injection at 30, 60, 120, 180, and 240 minutes. Xylazine provided the highest pain threshold for the first 60 minutes and a sedative effect for 105 minutes. The effects for superficial pain and visceral pain persisted 3 hours and 4 hours, respectively. Morphine produced good analgesia for superficial pain (30 minutes), whereas butorphanol provided good effect for visceral pain (4 hours). A slight degree of analgesia for visceral pain was obtained after morphine (1 hour) and levorphanol (4 hours); flunixin did not induce analgesia. Butorphanol, levorphanol, and morphine stimulated motor activity. Behavioral effects did not occur after flunixin was given. Xylazine decreased systolic, diastolic, and mean blood pressures. Marked increases in these pressures, heart rate, and respiratory rate were observed after morphine was given. Changes of central venous pressure, rectal temperature, and blood gas values remained within base-line limits after both drugs were given. Butorphanol increased heart rates for 1 hour; flunixin and levorphanol did not alter any of the above values.     

A comparison of N-butylscopolammonium bromide and butorphanol tartrate for analgesia using a balloon model of abdominal pain in ponies.

The analgesic effect of N-butylscopolammonium bromide (0.3 mg/kg) using a balloon-induced model of colic in ponies was evaluated and compared with butorphanol tartrate (0.1 mg/kg). Eight adult ponies were used and each received both treatments during the two different trials. The order in which the treatment was received was randomly assigned. At the start of each trial, moderate abdominal pain was induced by inflation of a balloon placed in the lumen of the caecum. The ponies were evaluated every 5 minutes, and a cumulative pain score (CPS) was assigned. Two baseline measurements were recorded, followed by the administration of one of the two treatments. Assessments were continued for 60 minutes, or until moderate abdominal pain returned. Three ponies out of 8 responded to treatment with butorphanol tartrate, while 6 out of 8 ponies responded to N-butylscopolammonium bromide. There were no statistical differences in the CPS or duration of drug action between treatments.     

Lincomycin-induced severe colitis in ponies: association with Clostridium cadaveris.

Four groups of two ponies, free of fecal Salmonella and Clostridium cadaveris, were treated as follows: Group A, control group; B, single nasogastrically administered dose of lincomycin (25 mg/kg) followed 48 h later by 3 L of C. cadaveris (10(9) organisms/mL); C, the same dose of lincomycin as group B; D, the same dose of C. cadaveris as group B on each of three occasions at 12 h intervals. Groups A and D remained healthy, but groups B and C developed severe colitis 48-56 h (B) or 72 h (C) after administration of lincomycin. Three ponies were euthanized and one in group B died. Clostridium cadaveris was isolated at about 10(6)/mL of colonic contents from these ponies, but one pony in group B also yielded Salmonella typhimurium from the colon. Subsequent challenge of group A ponies (3 L of C. cadaveris 10(9)/mL, three times at 12 h intervals) did not produce colitis. Nasogastric administration of lincomycin (25 mg/kg) to group A and D ponies, 20 days after administration of C. cadaveris, resulted in severe colitis in all ponies within 48-72 h. Salmonella agona was isolated from the colonic contents of one pony and C. cadaveris (10(6)/mL) from all four ponies. Clostridium cadaveris was not isolated from the colonic content of 45 healthy horses examined immediately after death. These studies confirm the potential for lincomycin to induce severe enterocolitis in ponies and implicate C. cadaveris further as a cause of "idiopathic colitis" in ponies.     

The effect of guaiphenesin on romifidine/ketamine anaesthesia in ponies

The purpose of this study was to investigate the effect of a single dose (50 mg/kg) of guaiphenesin on recumbency time, surgical conditions and the ‘quality’ of anaesthesia in ponies anaesthetised for castration. Sixteen ponies were sedated with romifidine 100 μg/kg and anaesthetised with ketamine (2.2 mg/kg). Ponies allocated to Group A received no treatment and those in Group B were given 50 mg/kg of a 15% guaiphenesin solution. Guaiphenesin was given as a rapid iv injection immediately after induction of anaesthesia. All ponies were subsequently castrated. The mean (± se) time of recumbency in Group A was 20.9 ± 1.37 min and in Group B 27.2 ± 2.1 min to (P<0.05). Subjective assessment scores for the quality of surgical conditions and anaesthesia itself were significantly greater (indicating better conditions) in ponies receiving guaiphenesin, although there was no difference between groups in the quality of recovery.     

Neuromuscular and cardiovascular effects of atracurium in ponies anesthetized with halothane

Atracurium besylate, a recently developed, intermediate-duration acting, neuromuscular-blocking agent, was given to 15 halothane-anesthetized ponies to produce surgical relaxation (95% to 99% reduction of hoof twitch). All 15 ponies were given 3 injections; 8 of the 15 ponies were given 2 additional injections. Initial dosage of 0.11 +/- 0.01 mg/kg (mean +/- SD) and all subsequent injections of 0.052 mg/kg produced desired relaxation. Paralysis phase (maximum twitch reduction to 10% twitch recovery) lasted 24 +/- 5 minutes for the initial injection. Paralysis from subsequent injections lasted for a slightly shorter time. Recovery phase (10% to 75% twitch recovery) was similar for all injections (initial and repeated) and lasted approximately 11 minutes. Cardiovascular side effects were not seen. Reversal of effects of atracurium with administration of 0.5 mg of edrophonium/kg was achieved when the evoked digital extensor tension (twitch height) had returned to 95% of base line after the last atracurium injection. Edrophonium caused systolic blood pressure to increase 121% +/- 7% of base-line pressure, which was 133 +/- 18 mm of Hg. Heart rate changed to 93% +/- 9% of base line after edrophonium was given, which was 49 +/- 7 beat/min, but this change did not occur until after the blood pressure increased. Recovery to standing was smooth and strong. Five ponies stood on their first attempt to rise, 5 on the 2nd attempt, 2 on the 3rd, and 1 on the 4th. Seven ponies stood within 30 minutes after transportation to the recovery stall, 7 within an hour.(ABSTRACT TRUNCATED AT 250 WORDS)