Overdose during chemical restraint in a black rhinoceros (Diceros bicornis)

A juvenile female black rhinoceros (Diceros bicornis) was successfully treated after overdose of drugs used for chemical restraint. Subsequent general anaesthesia for surgical reduction of a recurrent rectal prolapse was uneventful. Over a 25-minute period before transportation to the veterinary hospital, the animal received a total dose of 1.225 mg etorphine, 30 mg acepromazine and 30 mg detomidine. Based on an estimated mass of 200 kg, these corresponded to doses of 6.1 microg kg(-1) etorphine, 150 microg kg(-1) acepromazine, and 150 microg kg(-1) detomidine which constitutes considerable overdose for each drug given separately, notwithstanding the synergy that probably resulted when the three drugs were present concurrently. The estimated body mass may have substantially overestimated the actual body mass and exacerbated overdosage. The animal was recumbent and apnoeic on arrival at the hospital. Heart sounds were auscultated and a weak peripheral pulse was palpated; no pulse deficits were detected, although the heart rate was low. The trachea was intubated, inspired breath was enriched with oxygen and the lungs ventilated manually. Diprenorphine (1.5 mg) was given intravenously and spontaneous breathing resumed 11 minutes later. After induction of general anaesthesia using isoflurane, emergency surgery for correction of rectal prolapse was performed, from which the animal recovered uneventfully. The case highlights some of the practical problems that may be encountered in dealing with dangerous and unfamiliar species.

Hyena disease (premature physeal closure) in calves due to overdose of vitamins A, D3, E

Holstein suckling calves on a farm manifested severe emaciation, generalized alopecia, dome-like cranial deformation, and high mortality (Case 1). Metaphyseal growth plates of the femur were achondroplastic; segmented, partially resorped, and replaced with immature bony trabeculae containing degenerated chondrocytes. The skull was thin and partially replaced with connective tissue. Diffuse and severe fatty degeneration was observed in the hepatic stellate (Ito') cells. After 6 mo, surviving calves manifested unthrifty with short and irregular hindquarters (Case 2). The metaphyseal growth plates were poorly formed, irregular, partially disappeared centrally, and often sealed with thin bony trabeculae. The cartilage matrix was not homogeneous but was finely fibrous, and chondrocytes were flat and degenerated. The bone lesion was diagnosed as chondrodysplasia due to premature physeal closure. These calves had been administered excessive amounts of vitamins A, D3 and E, and blood chemistry of acute case showed hypervitaminosis A and E. Case I demonstrated acute disease, while Case 2 demonstrated chronic sequelae. Hypervitaminosis A was the suspected cause.

Lasalocid toxicosis is inadequately quantified for horses

The current estimate of LD50, 21.5 mg/kg BW, for lasalocid in horses is based on an analysis of 8 data from 4 horses that died at dose levels of 15, 21, 22 and 26 mg/kg. This analysis neglected 14 data from another 6 horses that survived at dose levels of 5, 10,14, 18, 19, 25, 29 and 50 mg/kg, and so was biased by selection of data. An examination of all the data indicates they are insufficient to determine the LD50. In contrast, the whole data set suggests a lowest toxic dose of 15 mg/kg, although this estimate was based on only 1 affected animal in 8 tests from 5 to 15 mg/kg in an unbalanced experiment and thus needs confirmation.

A review of moxidectin overdose cases in equines from 1998 through 2000

Moxidectin is a macrolide endectocide available as a 2% equine oral gel in the US. This report presents clinical signs of moxidectin toxicosis and its treatment in equines as reported to the ASPCA Animal Poison Control Center (APCC) from January 1998 to December 2000. Nine cases of moxidectin overdose in equines occurred: 5 had signs of toxicosis such as coma, dyspnea, depression, ataxia, tremors, seizures, or weakness. The approximate dose of moxidectin at which these signs were observed ranged from 1.0 to 5.1 mg/kg. The 4 equines that ingested moxidectin between 0.9 mg/kg to 1.7 mg/kg did not show signs of toxicosis. Clinical signs were seen within 6-22 h and lasted for 36-168 h. Only 1/5 clinical equines was an adult, the others were < 4 month of age. This study supports earlier report that young foals are more susceptible to moxidectin toxicosis. All 4 equines with known outcomes recovered with treatment that included decontamination, seizure control, thermoregulation, fluid therapy, and supportive care.

Commercial diet induced hypothyroidism due to high iodine. A histological and radiological analysis

A number of puppies of the School Hospital of the Faculty of Veterinary Science-UBA showed bone changes. Measurement of the iodine content of the commercial diet showed a significant increase in its content. Iodine excess causes alterations in thyroid function and morphology, and its hormones have a direct action on bone formation. Three groups of puppies were fed on different diets: a home-prepared diet, a commercial diet (containing 5.6 mg potassium iodide/kg dry food), and a home-prepared diet supplemented with 5.6 mg potassium iodide/kg dry food. Groups B and C developed hypothyroidism. A significant decrease (p<0.05) in the styloid apophyseal surface was found in groups B and C vs. A, determined by radiography. Histologically, the hypertrophied cartilage was shorter in groups B and C than in group A (p<0.0001). The present results suggest that commercial diets with a high iodine content may cause hypothyroidism and changes in bone metabolism.

Effects of intravenous lidocaine overdose on cardiac electrical activity and blood pressure in the horse

This study aimed to identify blood serum lidocaine concentrations in the horse which resulted in clinical signs of intoxication, and to document the effects of toxic levels on the cardiovascular and cardiopulmonary systems. Nineteen clinically normal mature horses of mixed breed, age and sex were observed. Lidocaine administration was initiated in each subject with an i.v. loading dose of 1.5 mg/kg bwt and followed by continuous infusion of 0.3 mg/kg bwt/min until clinical signs of intoxication were observed. Intoxication was defined as the development of skeletal muscle tremors. Prior to administration of lidocaine, blood samples for lidocaine analysis, heart rate, mean arterial blood pressure, systolic blood pressure, diastolic blood pressure, respiratory rate and electrocardiographic (ECG) data were collected. After recording baseline data, repeat data were collected at 5 min intervals until signs of intoxication were observed. The range of serum lidocaine concentrations at which the clinical signs of intoxication were observed was 1.85-4.53 microg/ml (mean +/- s.d. 3.24 +/- 0.74 microg/ml). Statistically significant changes in P wave duration, P-R interval, R-R interval and Q-T interval were observed in comparison to control values, as a result of lidocaine administration. These changes in ECG values did not fall outside published normal values and were not clinically significant. Heart rate, blood pressures and respiratory rates were unchanged from control values. This study establishes toxic serum lidocaine levels in the horse, and demonstrates that there were no clinically significant cardiovascular effects with serum lidocaine concentrations less than those required to produce signs of toxicity.

Pharmacokinetics and dosage regimen of 2-pyridine aldoxime in Bubalus bubalis intoxicated with fenitrothion

In the present study, the pharmacokinetics of 2-pyridine aldoxime (2-PAM, 30 mg/kg, i.v.) alone and in conjunction with atropine (0.3 mg/kg; 1/4 i.v., 3/4 i.m.) was investigated in 10 Bubalus bubalis intoxicated with a single oral lethal dose of fenitrothion (435 mg/kg). Based on the kinetic parameters, an appropriate dosage regimen of 2-PAM in B. bubalis was calculated. There was no significant difference between plasma levels and pharmacokinetic parameters of 2-PAM in the two groups of animals, given 2-PAM alone and in conjunction with atropine. The peak plasma concentration of 2-PAM at 1 min was in the range of 189.5-196.6 microg/mL which declined to 9.22-9.98 microg/mL at 4 h. The values of elimination half-life, Vd(area) and total body clearance were 2.41-2.67 h, 0.77-0.95 L/kg and 227.5-245.7 mL/kg/h, respectively. The binding capacity of 2-PAM to plasma proteins of fenitrothion-intoxicated buffalo calves and dissociation rate constant of protein drug complex were 0.015 x 10(-6) mol/g and 2.367 x 10(-6) mol, respectively. Approximately 63% of 2-PAM was bound with plasma proteins. In the treatment of organophosphate insecticide (OPI) toxicity in B. bubalis, an appropriate i.v. dosage regimen of 2-PAM in conjunction with atropine would be 18 mg/kg followed by 15 mg/kg at 4 h interval.

[Moxidectin poisoning in a foal?]

A 2 day old foal was presented with central nervous depression (coma) after moxidectin overdose. Moxidectin belongs to the milbemycin anthelmintics which elicit their working mechanism through a GABA (gamma-aminobutyric acid)-stimulatory mode of action. The foal developed profound hypothermia, bradycardia and hypoventilation. Absence of urine voiding and mild abdominal distension suggested a ruptured bladder, which was confirmed by transabdominal ultrasound and clinical-pathologic parameters. Repeat auscultation of the ventral lung parts and the occurrence of gastric reflux were suggestive of an aspiration pneumonia. The foal underwent surgical bladder repair, however, did succumb due to mixed acidosis and early signs of sepsis postoperatively. The findings in this foal are suggestive for moxidectin overdosing. The GABAergic working mechanism of moxidectin does explain the development of profound central nervous depression and its sequels hypothermia, bradycardia, hypoventilation and paralytic ileus. Dyssynergia was unexpected, however, has to be related to a central nervous problem, rather than a peripheral nervous problem.

Presumed moxidectin toxicosis in three foals

Outcome and complications associated with administration of moxidectin gel to 3 foals < 4 months old are described. Two foals became comatose but survived following supportive treatment. One foal died following loss of consciousness associated with moxidectin administration. Risk of moxidectin overdose exists, because horse owners often fail to read or comprehend the package insert instructions pertaining to use of the syringe-locking mechanism. In addition, moxidectin should not be administered to foals < 4 months old, because it is likely that treated foals will become comatose.

Ivermectin toxicosis in a zebra

A 3-mo-old zebra was accidentally given 2.08 mg ivermectin/kg bw orally. Ataxia, blindness and depression developed within a few hours and resolved with symptomatic and supportive treatment by the fifth day post-exposure. These effects were similar to those reported in horses, including the temporary blindness.

Insulin overdose in dogs and cats: 28 cases (1986-1993)

OBJECTIVE

To characterize the frequency, medical history, clinical signs, methods of treatment, and outcome of insulin-induced hypoglycemia and to identify predisposing factors.

DESIGN

Retrospective study.

ANIMALS

8 dogs and 20 cats with diabetes mellitus that developed hypoglycemia because of insulin overdose.

PROCEDURE

Medical records of dogs and cats receiving insulin for treatment of diabetes mellitus were reviewed. Medical records of dogs and cats that had an episode of hypoglycemia were reviewed in detail.

RESULTS

Overdosing of insulin was more common in cats than in dogs. Median weight of diabetic cats that became hypoglycemic was significantly greater than that of the hospital population of diabetic cats at diagnosis. Eighty percent of cats that became hypoglycemic were receiving insulin doses > 6 U/injection, administered once or twice daily. Dose and type of insulin did not correlate with duration or severity of hypoglycemia. In 7 of 8 dogs and 10 of 20 cats, management factors or concurrent medical problems were considered to be predisposing causes for insulin overdose. Two dogs and 2 cats did not have clinical signs of hypoglycemia, despite documented low concentrations of glucose in their blood.

CLINICAL IMPLICATIONS

Diabetic cats, especially if obese, are at greater risk of insulin overdose than are diabetic dogs. The reason for overdose may not be evident. Diabetic dogs and cats may become hypoglycemic without developing autonomic warning signs of hypoglycemia, or these signs may not be recognized (hypoglycemia unawareness).

Magnesium toxicosis in two horses

Magnesium sulfate, a saline laxative, is often used for treatment of intestinal impactions in horses. Clinical signs of hypermagnesemia are an uncommon complication following oral administration of magnesium sulfate. Overdose of magnesium sulfate in combination with renal insufficiency, hypocalcemia, or compromise of intestinal integrity may predispose horses to magnesium toxicosis. Establishment of diuresis with fluids and IV administration of calcium may provide successful treatment of magnesium toxicosis in horses.

Measurement of serum acetylsalicylic acid in a porcine model of aspirin overdose

Although the pharmacokinetics of acetylsalicylic acid (ASA) absorption and metabolism in therapeutic doses are well described, there is little information for overdose. A porcine model was developed to study ASA pharmacokinetics in overdose and to establish the feasibility of using area-under-the-curve (AUC) for serum ASA vs time rather than salicylate vs time as an indirect method of quantifying total drug absorption. Such a model could be useful in comparing the effectiveness of different methods of gastrointestinal decontamination in poisoning. The hydrolysis of ASA to salicylate, known to be a first-order process in therapeutic doses, was confirmed to remain first-order at high serum concentrations using iv aspirin in 2 pigs. Five simulated overdoses were then carried out in 4 pigs using 500 mg ASA/kg administered enterally as intact tablets. Serial determinations of both serum ASA and salicylate concentration were carried out over 72 h. Plots of ASA concentration vs time for each of the trials revealed delayed, multiple and erratic peaks consistent with a bolus effect from sudden dissolution of aspirin concretions, suggesting our model accurately simulates human overdose. Despite the variable peaks, the AUC of ASA concentration vs time for the 5 trials revealed a coefficient of variation of only 13%, compared with 27% for salicylate concentration vs time AUC. This suggests that serial measurements of serum ASA in a porcine ASA overdose model can be used to measure total drug absorption and thereby compare the effectiveness of different methods of gastrointestinal decontamination.

Cisapride toxicosis in dogs

Cisapride is an oral prokinetic agent used to facilitate or restore motility in the gastrointestinal tract. The National Animal Control Center has received 17 reports of accidental overexposure of dogs to cisapride since 1994. Doses of 640 mg/kg in dogs were reported to be lethal, but severe clinical signs have been noted at acute exposures as low as 18 mg/kg. The most common signs include diarrhea, muscle tremors and fasciculations, ataxia and incoordination, and hyperthermia. Available treatment is symptomatic and supportive. Activated charcoal is effective in reducing plasma cisapride levels.

Vitamin D toxicosis in cats: natural outbreak and experimental study

A pathological study on 5 of 21 cats affected naturally with systemic calcinosis was performed. The animals ranged in age from 1 to 9 years. Hematology and serum chemistry analyses showed the elevated values of phosphorus, blood urea nitrogen and serum creatinine. X-ray examination disclosed the increased density of systemic bones. Histologically, marked calcification was present at the vascular walls of almost all the organs including the lungs, trachea, kidneys, heart, aorta, alimentary tracts, choroid plexus and bones. In the lungs, kidneys and stomach, the calcified lesions were associated with deposition of oxalate crystals. Serum chemistry showed more elevated values of 25-hydroxycholecalciferol (vitamin D) of the affected cats than the normal level. Retrospective examination revealed that these cats had been fed the commercial pet foods containing a large amount of vitamin D (6,370 IU/100 g diet) from their young age, and its value was about ten times as much as that of the control food (680 IU/100 g diet). Pathological changes found in the cats from the experimental vitamin D3 toxicosis were similar to those in the natural cases. In addition, tissue levels of calcium, phosphorous and zinc in the lungs and kidneys were markedly elevated in both natural and vitamin D-intoxicated cases. These findings suggest that long-term feeding of the pet food containing excessive vitamin D was responsible for the outbreak of the systemic calcinosis in the cats.

Treatment of acute isoniazid overdose in dogs

The National Animal Poison Control Center received 28 calls of isoniazid (INH) exposures in dogs and cats between 1987 and 1993. The ingestion of a single 300 mg INH tablet was the most common complaint. Isoniazid has a low therapeutic margin and produces life threatening signs in dogs ingesting single 300 mg human tablets. The LD50 of INH in dogs is estimated at 50 mg/kg bw, which is probably similar to that for humans. However, rodents are among the species most resistant to INH and thus are not good animal models for toxic dose extrapolation. The more consistent clinical signs reported were recurrent clonic-tonic seizures followed by a stuporous state with poor response to stimulus. Ideal treatment combines vitamin B6 given as a single i.v. bolus at an equivalent dose to the amount of INH ingested and anticonvulsants such as 1 mg diazepam/kg bw. This combination acts synergistically to improve GABAergic transmission in the CNS and has proved effective in protecting animals from further convulsions and death, even after several seizure episodes, as often encountered in clinical situations.

Closantel intoxication in a dog

A case of overdosage with closantel, a salicynalide derivative, in a dog is described. The dog received 6 times the recommended dosage. Closantel induced optic neuritis, retinal degeneration, partial deafness, hepatotoxicosis and myopathy. Only the blindness was irreversible. The therapy included albumin administration to reduce the acute toxicity of closantel.

Loperamide intoxication in a seven-week-old pup

A 7-w-old Samoyed-cross pup was presented with central nervous system signs approximately 18 h following administration of the second of 2 doses of loperamide. Circling, vocalization, head pressing and unreactive pupils were present. There was no history of trauma. Improvement was seen shortly following administration of activated charcoal and 0.2 ml naloxone. Naloxone treatment was repeated at 2-h intervals over 12-h. Approximately 20 h following the initial clinical evaluation, the puppy was released to the owner for home care and observation.

Nephrotoxicosis associated with topical administration of gentamicin in a cat

A 4-year-old cat was referred for treatment of a large, open wound. The wound had been lavaged twice, approximately 12 hours apart, with approximately 10 ml of 5% gentamicin solution prior to referral, because of infection caused by Pseudomonas spp. Results of initial serum biochemical analyses were within reference ranges, and the cat was anesthetized for surgical wound debridement and closure. Two days later, the cat was azotemic (SUN concentration, 113 mg/dl; serum creatinine, concentration, 9.8 mg/dl) and had a urine specific gravity of 1.008. Granular casts were seen in the urine. The azotemia became more severe over the next 2 1/4 hours, despite treatment for acute renal failure, and the cat was euthanatized. Severe acute proximal tubular necrosis, consistent with gentamicin-induced nephrotoxicosis, was diagnosed histologically. Retrospectively, serum samples obtained for biochemical analyses were assayed for gentamicin concentration. Serum concentration of gentamicin 8 hours after topical lavage was 58.07 micrograms/ml. This was approximately 6 times greater than the desired peak concentration for gentamicin and suggested that gentamicin had been absorbed systemically following topical application.