Control of cancer pain in veterinary patients

Anaesthesia in Veterinary Oncology: The Effects of Surgery, Volatile and Intravenous Anaesthetics on the Immune System and Tumour Spread

Throughout the course of oncological disease, the majority of patients require surgical, anaesthetic and analgesic intervention. However, during the perioperative period, anaesthetic agents and techniques, surgical tissue trauma, adjuvant drugs for local pain and inflammation and other non-pharmacological factors, such as blood transfusions, hydration, temperature and nutrition, may influence the prognosis of the disease. These factors significantly impact the oncologic patient's immune response, which is the primary barrier to tumour progress, promoting a window of vulnerability for its dissemination and recurrence. More research is required to ascertain which anaesthetics and techniques have immunoprotective and anti-tumour effects, which will contribute to developing novel anaesthetic strategies in veterinary medicine.

Metabolism, pharmacokinetics and selected pharmacodynamic effects of codeine following a single oral administration to horses

OBJECTIVE

To describe the pharmacokinetics and selected pharmacodynamic variables of codeine and its metabolites in Thoroughbred horses following a single oral administration.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 12 Thoroughbred horses, nine geldings and three mares, aged 4-8 years.

METHODS

Horses were administered codeine (0.6 mg kg-1) orally and blood was collected before administration and at various times until 120 hours post administration. Plasma and urine samples were collected and analyzed for codeine and its metabolites by liquid chromatography-mass spectrometry, and plasma pharmacokinetics were determined. Heart rate and rhythm, step counts, packed cell volume and total plasma protein were measured before and 4 hours after administration.

RESULTS

Codeine was rapidly converted to the metabolites norcodeine, codeine-6-glucuronide (C6G), morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). Plasma codeine concentrations were best represented using a two-compartment model. The Cmax, tmax and elimination t½ were 270.7 ± 136.0 ng mL-1, 0.438 ± 0.156 hours and 2.00 ± 0.534 hours, respectively. M3G was the main metabolite detected (Cmax 492.7 ± 35.5 ng mL-1), followed by C6G (Cmax 96.1 ± 33.8 ng mL-1) and M6G (Cmax 22.3 ± 4.96 ng mL-1). Morphine and norcodeine were the least abundant metabolites with Cmax of 3.17 ± 0.95 and 1.42 ± 0.79 ng mL-1, respectively. No significant adverse or excitatory effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Following oral administration, codeine is rapidly metabolized to morphine, M3G, M6G, C6G and norcodeine in horses. Plasma concentrations of M6G, a presumed active metabolite of morphine, were comparable to concentrations reported previously following administration of an analgesic dose of morphine to horses. Codeine was well tolerated based on pharmacodynamic variables and behavioral observations.

Malignant Transformation of a Canine Papillomavirus Type 1-Induced Persistent Oral Papilloma in a 3-Year-Old Dog

This case report describes a rare case of a persistent canine papillomavirus type 1 (CPV-1)-induced oral papilloma that underwent malignant transformation into an oral squamous cell carcinoma (OSCC) in a 3-year-old Labrador retriever cross. Initially, the patient had multiple and multifocal verrucous lesions populating the oral cavity exclusively. The papillomas persisted despite multiple surgical ablations, azithromycin, interferon α-2b, alternative medicines, and off-label drug use of an immunostimulant. After 1 year and 6 months, an aggressive lesion developed at the level of the left mandibular first molar (309) and progressed to a well-differentiated invasive OSCC. The presence of CPV-1 DNA in the OSCC, and the known oncogenic abilities of CPV-1, suggests that this virus might have played a significant role in the emergence of the OSCC that ultimately led to the patient's euthanasia due to poor quality of life. This is the first well-documented case where OSCC has developed from an oral papilloma caused by CPV-1 in which the presence of coinfection by another papillomavirus was excluded by multiple polymerase chain reaction tests using various primers.

Inhibition of growth of canine-derived vascular endothelial cells by non-steroidal anti-inflammatory drugs and atrial natriuretic peptide

This study investigated the direct effects of non-steroidal anti-inflammatory drugs (NSAIDs) and atrial natriuretic peptide (ANP) on canine-derived vascular endothelial cells (VECs). VECs were isolated and cultured from canine arteries and veins. The mRNA expressions of vascular endothelial growth factor receptor 2, cyclooxygenase-2, and natriuretic peptide receptor 1 were detected in the cultured VECs. The viability of the cultured VECs was reduced in a dose-dependent manner by meloxicam, carprofen, and robenacoxib. By contrast, dose escalations of ANP had only marginal influence on the viability of cultured VECs. NSAIDs may potentially serve as not only analgesic agents against cancerous and perioperative pain but also as adjuvant anti-angiogenic drugs in dogs with malignant tumors.

Oral Coadministration of Fluconazole with Tramadol Markedly Increases Plasma and Urine Concentrations of Tramadol and the O-Desmethyltramadol Metabolite in Healthy Dogs

Tramadol is used frequently in the management of mild to moderate pain conditions in dogs. This use is controversial because multiple reports in treated dogs demonstrate very low plasma concentrations of O-desmethyltramadol (M1), the active metabolite. The objective of this study was to identify a drug that could be coadministered with tramadol to increase plasma M1 concentrations, thereby enhancing analgesic efficacy. In vitro studies were initially conducted to identify a compound that inhibited tramadol metabolism to N-desmethyltramadol (M2) and M1 metabolism to N,O-didesmethyltramadol (M5) without reducing tramadol metabolism to M1. A randomized crossover drug-drug interaction study was then conducted by administering this inhibitor or placebo with tramadol to 12 dogs. Blood and urine samples were collected to measure tramadol, tramadol metabolites, and inhibitor concentrations. After screening 86 compounds, fluconazole was the only drug found to inhibit M2 and M5 formation potently without reducing M1 formation. Four hours after tramadol administration to fluconazole-treated dogs, there were marked statistically significant (P < 0.001; Wilcoxon signed-rank test) increases in plasma tramadol (31-fold higher) and M1 (39-fold higher) concentrations when compared with placebo-treated dogs. Conversely, plasma M2 and M5 concentrations were significantly lower (11-fold and 3-fold, respectively; P < 0.01) in fluconazole-treated dogs. Metabolite concentrations in urine followed a similar pattern. This is the first study to demonstrate a potentially beneficial drug-drug interaction in dogs through enhancing plasma tramadol and M1 concentrations. Future studies are needed to determine whether adding fluconazole can enhance the analgesic efficacy of tramadol in healthy dogs and clinical patients experiencing pain.

Anti-tumour efficacy of etoposide alone and in combination with piroxicam against canine osteosarcoma in a xenograft model

Osteosarcoma (OSA) in dogs is locally invasive and highly malignant. Distant metastasis is the most common cause of death. To date, the survival rate in dogs with OSA remains poor. The cytotoxic effects of etoposide against canine OSA cell lines, either alone or in combination with piroxicam, have been previously demonstrated in vitro. The aim of this study was to evaluate the anti-tumour effect of etoposide alone and in combination with piroxicam on canine OSA using murine models. Etoposide single agent treatment significantly delayed tumour progression with a marked reduction in Ki-67 immunoreactivity in tumour tissue. Concomitant treatment with piroxicam did not enhance the anti-tumour efficacy of etoposide. Etoposide single agent treatment and combination treatment with piroxicam down-regulated survivin expression, but was not followed by increased apoptotic activity. These findings indicate that etoposide might be a promising novel therapeutic for canine OSA. Further investigations into its potential for clinical application in veterinary oncology are warranted.

Tramadol metabolism to O-desmethyl tramadol (M1) and N-desmethyl tramadol (M2) by dog liver microsomes: Species comparison and identification of responsible canine cytochrome P-450s (CYPs)

Tramadol is widely used to manage mild to moderately painful conditions in dogs. However, this use is controversial since clinical efficacy studies in dogs showed conflicting results, while pharmacokinetic studies demonstrated relatively low circulating concentrations of O-desmethyltramadol (M1). Analgesia has been attributed to the opioid effects of M1, while tramadol and the other major metabolite (N-desmethyltramadol, M2) are considered inactive at opioid receptors. The aims of this study were to determine whether cytochrome P450 (CYP) dependent M1 formation by dog liver microsomes is slower compared with cat and human liver microsomes; and identify the CYPs responsible for M1 and M2 formation in canine liver. Since tramadol is used as a racemic mixture of (+)- and (-)-stereoisomers, both (+)-tramadol and (-)- tramadol were evaluated as substrates. M1 formation from tramadol by liver microsomes from dogs was slower than from cats (3.9-fold), but faster than humans (7-fold). However, M2 formation by liver microsomes from dogs was faster than from cats (4.8-fold) and humans (19-fold). Recombinant canine CYP activities indicated that M1 was formed by CYP2D15, while M2 was largely formed by CYP2B11 and CYP3A12. This was confirmed by dog liver microsomes studies that showed selective inhibition of M1 formation by quinidine and M2 formation by chloramphenicol and CYP2B11 antiserum, and induction of M2 formation by phenobarbital. Findings were similar for both (+)-tramadol and (-)-tramadol. In conclusion, low circulating M1 concentrations in dogs is explained in part by low M1 formation and high M2 formation, which are mediated by CYP2D15 and CYP2B11/CYP3A12, respectively.

Acrolein scavengers, cysteamine and N-benzylhydroxylamine, reduces the mouse liver damage after acetaminophen overdose

Our previous study suggested that the highly toxic α,β-unsaturated aldehyde acrolein, a byproduct of oxidative stress, plays a major role in acetaminophen-induced liver injury. In this study, to determine the involvement of acrolein in the liver injury and to identify novel therapeutic options for the liver damage, we examined two putative acrolein scavengers, a thiol compound cysteamine and a hydroxylamine N-benzylhydroxylamine, in cell culture and in mice. Our results showed that cysteamine and N-benzylhydroxylamine effectively prevented the cell toxicity of acrolein in vitro and acetaminophen-induced liver injury in vivo, which suggested that acrolein is involved in the liver damage, and these two drugs can be potential therapeutic options for this condition.

Management of acute pancreatitis in dogs: a critical appraisal with focus on feeding and analgesia

Knowledge about acute pancreatitis has increased recently in both the medical and veterinary fields. Despite this expansion of knowledge, there are very few studies on treatment interventions in naturally occurring disease in dogs. As a result, treatment recommendations are largely extrapolated from experimental rodent models or general critical care principles. General treatment principles involve replacing fluid losses, maintaining hydrostatic pressure, controlling nausea and providing pain relief. Specific interventions recently advocated in human medicine include the use of neurokinin-1 antagonists for analgesia and early interventional feeding. The premise for early feeding is to improve the health of the intestinal tract, as unhealthy enterocytes are thought to perpetuate systemic inflammation. The evidence for early interventional feeding is not supported by robust clinical trials to date, but in humans there is evidence that it reduces hospitalisation time and in dogs it is well tolerated. This article summarises the major areas of management of acute pancreatitis in dogs and examines the level of evidence for each recommendation.

Feline Oral Squamous Cell Carcinoma: Clinical Manifestations and Literature Review

Squamous cell carcinoma (SCC) is the most commonly encountered malignant oral tumor in cats. The etiology of this locally invasive tumor is likely multifactorial. Several risk factors have been identified, including the use of flea collars, and a history of feeding canned food and canned tuna. Clinical signs vary depending on tumor location. The tumor commonly arises from the gingiva and mucosa of the maxilla, mandible, tongue, sublingual area, or tonsillar region. Maxillary SCC commonly presents clinically as an ulcerative lesion, whereas mandibular SCC is commonly proliferative, expansile, and firm. Lingual/sublingual SCC may be ulcerative, necrotic, infiltrative, or proliferative. In general, feline oral SCC is an invasive and malignant neoplasm regardless of its location. Surgery, radiation therapy, chemotherapy and combinations thereof have been attempted with rarely a satisfactory response. Currently, cures are obtained only in a small subset of cats whose tumors are amenable to complete resection, or where resection with microscopic residual disease is followed by definitive radiation therapy. A multimodal treatment approach likely offers the best chance of success. For cats with advanced disease, palliative care may improve patients' quality of life, albeit transiently. Sequelae associated with tumor progression and local tissue destruction often result in euthanasia of feline patients with oral SCC.

Canine mammary tumours, an overview

Canine mammary tumours (CMTs) are the most common neoplasms in intact female dogs. Although the prevalence of these tumours decreases in regions where preventive ovari(ohyster)ectomy is performed, it remains an important disease entity in veterinary medicine. Moreover, treatment options are limited in comparison with human breast cancer. Nevertheless, recent human treatment protocols might have potential in bitches suffering from CMTs.

Pharmacokinetics of subcutaneous fentanyl in Greyhounds

The purpose of the study was to describe the pharmacokinetics of subcutaneous fentanyl (15μg/kg) in six healthy Greyhound dogs. Fentanyl plasma concentrations were determined by a liquid chromatography with mass spectrometry method. Non-compartmental pharmacokinetic analysis was used. Fentanyl was rapidly absorbed with a mean peak concentration (C(MAX)) of 3.56ng/mL at 0.24h. The mean terminal half-life, volume of distribution per bioavailability, and clearance per bioavailability were 2.97h, 7.09L/kg, 27.60mL/min/kg, respectively. Pain occurred on injection in all six dogs, but addition of 8.4% sodium bicarbonate (1mL per 20mL fentanyl) resulted in no pain on injection in 3/3 dogs but similar C(MAX) values. The subcutaneous route may be an alternative route of fentanyl administration if intravenous administration is not practical.

Where do we go from here? Future treatment strategies for chronic pain

Many of the tools that can be used to alleviate chronic pain in our patients are readily available to all practitioners, but they are not used with appropriate frequency. Thus, the immediate future of chronic pain therapy is simply to do more of what we are already doing. There are also drugs and techniques currently used in human medicine that may be available to us in the near future and many drugs and techniques on the research bench that might make it to our patients in the more distant future. Because of the magnitude of the chronic pain problem in human medicine, research on the treatment of chronic pain is intense, and the hope is that both human and veterinary patients will eventually benefit.

Pharmacokinetics of acetaminophen, codeine, and the codeine metabolites morphine and codeine-6-glucuronide in healthy Greyhound dogs

The purpose of this study was to determine the pharmacokinetics of codeine and the active metabolites morphine and codeine-6-glucuronide after i.v. codeine administration and the pharmacokinetics of acetaminophen (APAP), codeine, morphine, and codeine-6-glucuronide after oral administration of combination product containing acetaminophen and codeine to dogs. Six healthy Greyhound dogs were administered 0.734 mg/kg codeine i.v. and acetaminophen (10.46 mg/kg mean dose) with codeine (1.43 mg/kg mean dose) orally. Blood samples were collected at predetermined time points for the determination of codeine, morphine, and codeine-6-glucuronide plasma concentrations by LC/MS and acetaminophen by HPLC with UV detection. Codeine was rapidly eliminated after i.v. administration (T(1/2) = 1.22 h; clearance = 29.94 mL/min/kg; volume of distribution = 3.17 L/kg) with negligible amounts of morphine present, but large amounts of codeine-6-glucuronide (C(max) = 735.75 ng/mL) were detected. The oral bioavailability of codeine was 4%, morphine concentrations were negligible, but large amounts of codeine-6-glucuronide (C(max) = 1952.86 ng/mL) were detected suggesting substantial first pass metabolism. Acetaminophen was rapidly absorbed (C(max) = 6.74 microg/mL; T(max) = 0.85 h) and eliminated (T(1/2) = 0.96 h). In conclusion, the pharmacokinetics of codeine was similar to other opioids in dogs with a short half-life, rapid clearance, large volume of distribution, and poor oral bioavailability. High concentrations of codeine-6-glucuronide were detected after i.v. and oral administration.