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A look through the recent international literature on managing pain

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01 May 2014, at 1:00am

Efficacy and safety of meloxicam administered as a transmucosal oral spray 

Elizabeth Cozzi and Michael Spensley, Abbot Laboratories, Abbott Park, Illinois 

Oral transmucosal delivery of drugs has a number of potential advantages over conventional oral formulations in terms of ease of administration, rapid absorption through the mucous membranes and elimination of the first pass effect (in which part of the dose is lost during passage through the intestinal wall and liver).

The authors examined the potential value of a novel transmucosal formulation of the non-steroidal anti-inflammatory drug meloxicam, developed as the first veterinary drug for administration by this route. The drug was administered to 280 client-owned dogs with osteoarthritis in a multi- centre, randomised placebo- controlled trial in which the patients were treated once daily for 28 days.

Client pain scores were significantly lower at 14 and 28 days for the treated group although veterinary assessments of pain on palpation were no different between groups. There was some evidence of gastrointestinal adverse effects but the transmucosal formulation of meloxicam appears to be a safe and effective method for controlling pain in dogs with osteoarthritis. 

Journal of Veterinary Pharmacology Therapeutics 36 (6): 609-616.

Absorbable gelatin sponges for pain control following eye enucleation in dogs 

Christina Ploog and others, University of Illinois

Although removal of the globe following disease or trauma is a common surgical procedure in veterinary practice, maintaining good post-operative analgesia remains a challenge.

The authors compared the quality of pain control achieved with lidocaine-bupivacaine-infused absorbable gelatin haemostatic sponges in comparison with retrobulbar injections of the same local anaesthetic agents in dogs following this procedure.

While there were differences over time in heart rate, response to touch, total pain scores, etc., there were no significant overall differences between the two groups. Thus, the impregnated gelatin sponges were a satisfactory method for achieving local anaesthesia.

Journal of the American Veterinary Medical Association 244 (1): 57-62.

Cardiovascular and respiratory effects of intramuscular alfaxalone in cats

Tamara Grubb and others, Washington State University 

Anaesthetic induction using intravenous agents in fractious cats can be extremely challenging and while reliance on inhaled agents for both induction and maintenance is feasible, it does create increased mortality risks. 

The authors investigated the potential use of alfaxalone as an intramuscular induction agent. A total of 12 healthy adult cats were sedated with either dexmedetomidine or dexmedetomidine/hydromorphone before receiving 5mg/kg bodyweight of alfaxalone. Satisfactory anaesthesia was achieved in both groups but recovery was prolonged with excitement, ataxia and hyper- reactivity, so this formulation is not recommended for surgery in cats. 

Journal of Feline Medicine and Surgery 15 (10): 858-865.

Effect of fluconazole on anaesthetic recovery times in horses undergoing ocular surgery 

Stephanie Krein and others, Tufts University, North Grafton, Massachusetts 

General anaesthesia is often required when carrying out ocular surgery in horses as sedation and local anaesthesia may be inadequate for such delicate procedures. The authors examined the clinical records for 81 horses undergoing ocular procedures in search of factors that might be associated with the potential hazards of prolonged recovery times. 

They found that those horses that had received treatment with the antifungal fluconazole before induction with ketamine and midazolam were more likely to experience a prolonged anaesthetic recovery. Duration of anaesthesia and premedication with acepromazine were also identified as risk factors for prolonged recovery time. 

Journal of the American Veterinary Medical Association 244 (5): 577-581.

Low-dose medetomidine infusion for healthy dogs undergoing ovariohysterectomy

Eva Rioja and others, University of Guelph, Ontario, Canada 

Balanced anaesthesia involving the co-administration of multiple agents offers the potential advantage of requiring a smaller total dose and minimising the risks of adverse effects. The authors investigated the value of providing a low dose infusion of medetomidine as a 1mg/kg bolus and at a constant rate of 1mg/kg per hour in dogs maintained on isoflurane anaesthesia for routine ovariohysterectomy. 

They found that this combination provided acceptable and stable cardiovascular performance with lower isoflurane concentrations and a smooth anaesthetic recovery.

Canadian Veterinary Journal 54 (9): 864-868.

Long term pharmacokinetics of meloxicam in rabbits 

Katie Delk and others, Kansas State University

Few analgesic drugs have been approved for long-term use in veterinary patients. In rabbits requiring pain medication, meloxicam is a popular choice for off-label use as it is available in a palatable oral formulation, is not a controlled substance and is known to be well tolerated in many mammalian species. 

The authors investigated the pharmacokinetics of this agent when administered at a daily oral dose of 1mg/kg bodyweight for 29 days. Plasma concentrations were similar to those reported in rabbits treated for up to five days, indicating that the dose would be safe for long-term treatment in this species. 

American Journal of Veterinary Research 75 (2): 195-199.

Intramuscular injections of dexmedetomidine and hydromorphone for sedating dogs

Jennifer Carter and others, Ross University, St Kitts, West Indies 

Intravenous administration of pre- anaesthetic and anaesthetic drugs may be impractical in some canine patients because of temperament, small vein diameter, etc. The authors compared the onset time and quality of sedation achieved with intramuscular injections of dexmedetomidine and hydromorphone into different muscle groups. 

Resting pulse and respiratory rates were not significantly different in dogs sedated with IM injections into the semimembranosus, cervical, gluteal or lumbar muscle groups. However, semimembranosus muscle inoculations resulted in significantly higher sedation scores and there was a shorter time to onset of sedation. 

Journal of the American Veterinary Medical Association 243 (11): 1,569- 1,572. 

Sedation of hyperthyroid cats with subcutaneous alfaxalone and butorphanol 

Sue Ramoo and others, Advanced VetCare, Kensington, Victoria

Cats with increased circulating thyroid hormone can be difficult to handle and while a number of sedation strategies have been used in such patients, full details of the physiological effects are usually lacking. 

The authors assessed the cardiovascular, respiratory and sedative effects of a combination of 3mg/kg alfaxalone and 0.2mg/kg butorphanol administered subcutaneously in 20 client-owned hyperthyroid cats. The maximum sedation score was recorded 45 minutes after treatment and the combination was deemed to provide satisfactory sedation in cats undergoing short duration procedures.

Australian Veterinary Journal 91 (4): 131- 136.

Pharmacokinetics of intravenous midazolam in horses 

John Hubbell and others, Ohio State University

Midazolam is a water-soluble benzodiazepine used to control seizures and to enhance muscle relaxation in horses but there are no published data describing the pharmacokinetics of the agent in this species. 

The authors administered midazolam intravenously at 0.05 and 0.1mg/kg doses in six healthy horses. Their findings showed that the mean terminal half-life was 216 minutes and 408 minutes at the lower and higher dose, respectively. Cardiorespiratory parameters and sedation scores were unchanged but several horses showed evidence of agitation, postural sway and weakness while one given the higher dose became recumbent. 

Equine Veterinary Journal 45 (6): 721-725.

Effects of intravenous lidocaine on isoflurane anaesthesia in rabbits 

Rodney Schnellbacher and others, Kansas State University

The local anaesthetic lidocaine is used in human and veterinary medicine to reduce the concentration of inhalant anaesthetic needed for surgery and reduce the risks of haemodynamic depression. 

The authors investigated the effects of a continuous rate infusion of 50 or 100ug/kg/minute lidocaine (following a loading dose of 2mg/kg) on the minimum alveolar concentration of isoflurane required to maintain adequate anaesthesia in five 12-month-old New Zealand white rabbits. At both doses, the co- administration of lidocaine significantly reduced the MAC of isoflurane needed to eliminate any response to the application of a tail clamp.

American Journal of Veterinary Research 74 (11): 1,377-1,384.

Future approaches to the treatment of neuropathic pain in dogs 

Sandra Sanchis-Mora and others, Royal Veterinary College, London

Neuropathic pain is considered to be one of the most painful and challenging chronic pain conditions in human medicine and is even more difficult to recognise and treat in veterinary patients. The authors review knowledge on the assessment and treatment of these disorders in dogs and examine the potential options for future treatment. 

They conclude that a multimodal strategy involving a combination of agents such as non- steroidal anti-inflammatories, anticonvulsants such as a gabapentin, opioids including tramadol and methadone, and tricyclic antidepressants such as amitriptyline may help improve quality of life in affected animals.

Companion Animal 19 (1): 8-13.

Propofol or propofol/ketamine anaesthesia for evaluating laryngeal function in dogs

Kelci McKeiman and others, Oklahoma State University 

Laryngeal paralysis is a common acquired condition in older, large breed dogs. Thiopental has been the favoured anaesthetic agent for investigations of laryngeal function in this species but that compound is no longer commercially available. 

The authors compare the use of propofol and propofol/ketamine as local anaesthetics in healthy dogs undergoing laryngoscopy. They found that ketamine did not allow for a reduction in the propofol dose and caused increased respiratory depression, making it a poor addition to propofol for investigations of laryngeal function. 

Journal of the American Animal Hospital Association 50 (1): 19-26.