Current options for providing sustained analgesia to laboratory animals

Long-Acting Opioid Analgesics for Acute Pain: Pharmacokinetic Evidence Reviewed

Long-acting injectable (LAI) opioid formulations mitigate the harm profiles and management challenges associated with providing effective analgesia for animals. A single dose of a long-acting opioid analgesic can provide up to 72 h of clinically relevant pain management. Yet, few of these new drugs have been translated to products for veterinary clinics. Regulatory pathways allow accelerated drug approvals for generic and biosimilar drugs. These pathways depend on rigorous evidence for drug safety and pharmacokinetic evidence demonstrating bioequivalence between the new and the legacy drug. This report reviews the animal PK data associated with lipid and polymer-bound buprenorphine LAI formulations. Buprenorphine is a widely used veterinary opioid analgesic. Because of its safety profile and regulatory status, buprenorphine is more accessible than morphine, methadone, and fentanyl. This review of PK studies coupled with the well-established safety profile of buprenorphine suggests that the accelerated approval pathways may be available for this new family of LAI veterinary pharmaceuticals.

Anesthesia and analgesia for experimental craniotomy in mice and rats: a systematic scoping review comparing the years 2009 and 2019

Experimental craniotomies are a common surgical procedure in neuroscience. Because inadequate analgesia appears to be a problem in animal-based research, we conducted this review and collected information on management of craniotomy-associated pain in laboratory mice and rats. A comprehensive search and screening resulted in the identification of 2235 studies, published in 2009 and 2019, describing craniotomy in mice and/or rats. While key features were extracted from all studies, detailed information was extracted from a random subset of 100 studies/year. Reporting of perioperative analgesia increased from 2009 to 2019. However, the majority of studies from both years did not report pharmacologic pain management. Moreover, reporting of multimodal treatments remained at a low level, and monotherapeutic approaches were more common. Among drug groups, reporting of pre- and postoperative administration of non-steroidal anti-inflammatory drugs, opioids, and local anesthetics in 2019 exceeded that of 2009. In summary, these results suggest that inadequate analgesia and oligoanalgesia are persistent issues associated with experimental intracranial surgery. This underscores the need for intensified training of those working with laboratory rodents subjected to craniotomies.

Systematic review registration

https://osf.io/7d4qe.

Hystricomorph Rodent Analgesia

Limited information on the analgesic efficacy and safety of even clinically commonly used analgesic drugs in guinea pigs and chinchillas is available. Buprenorphine and meloxicam are currently the most common analgesics routinely used to treat painful conditions in guinea pigs and chinchillas. Hydromorphone has also shown to be an effective analgesic drug in these species, with limited adverse effects. Tramadol in chinchillas does not provide analgesia even at high doses, and no information is available on the efficacy of this drug in guinea pigs. Multimodal analgesic protocols should be considered whenever possible.

Buprenorphine implants: a model for expedited development and approval of new drugs

Regulations for new drug approvals require stringent safety testing and efficacy trial programs. The approval process for generic drugs, however, is significantly streamlined. Bioavailability data can substitute for new rounds of efficacy trials, thereby both decreasing time to approval and reducing the costs required for new studies. This regulatory choice has not been available when generic drugs are offered in a controlled release format such as a subcutaneous depot, transdermal patch or implant. The purpose of this review is to suggest that the approval of generic drugs in inert controlled release envelopes should be eligible for similar regulatory relief. Proof for this concept is provided by the example of the numerous controlled release buprenorphine products. Buprenorphine is a generic opioid used since the 1980s in tablet form to treat pain and to treat opioid addiction. Long-acting, inert delivery vehicles for the drug have become available for the same indications. Safety and bioavailability profiles of the long-acting products are the same or improved over the parent product. A review of the long-acting drugs provides compelling evidence to recommend that generic drug-controlled release products may be eligible for alternative regulatory programs.

Preliminary survey of the attitudes of Brazilian scientists towards pain management and assessment in animals used in science

OBJECTIVE

To investigate the current scenario in Brazil regarding pain assessment and control in experimental animals.

STUDY DESIGN

Prospective survey.

METHODS

A confidential questionnaire was available online and sent by e-mail to Brazilian scientists working with animal experimentation in Brazil. Data collection was conducted from October 2016 to October 2017. The exclusion criteria included blank questionnaires or with <80% completed responses, researchers not performing experiments involving animals and foreign scientists.

RESULTS

A total of 96 questionnaires from 104 respondents were analyzed. The Fisher's exact test showed a disparity between the proportions of scientists who recognized the importance of analgesia and their application of analgesic techniques in painful procedures (p < 0.0003), and also for the researchers who assumed that experiments inflicted pain and their classification of the degree of invasiveness (p < 0.0001), indicating their insufficient knowledge of these topics. Overall, 77% of institutions did not offer specific training to assess pain in experimental animals, and 24% of respondents had no training to work with animal experimentation. In total, 62% of the studies inflicted pain, 48% of respondents used pain scales, and the drugs administered most frequently for pain management were morphine (44%), meloxicam (43%) and tramadol (37%); 15% of respondents did not include analgesics even though their studies inflicted pain. Commonly used animals were rats (33%), mice (29%) and rabbits (8%).

CONCLUSIONS AND CLINICAL RELEVANCE

The results of this preliminary survey indicated that in Brazil there is a gap in the knowledge and training on pain assessment and management of experimental animals. Therefore, there is a necessity for an educational program to prepare and train scientists to assess and manage pain in laboratory or experimental animals. Further studies using a psychometrically validated survey instrument are warranted.

Clinical Management of Pain in Rodents

The use of effective regimens for mitigating pain remain underutilized in research rodents despite the general acceptance of both the ethical imperative and regulatory requirements intended to maximize animal welfare. Factors contributing to this gap between the need for and the actual use of analgesia include lack of sufficient evidence-based data on effective regimens, under-dosing due to labor required to dose analgesics at appropriate intervals, concerns that the use of analgesics may impact study outcomes, and beliefs that rodents recover quickly from invasive procedures and as such do not need analgesics. Fundamentally, any discussion of clinical management of pain in rodents must recognize that nociceptive pathways and pain signaling mechanisms are highly conserved across mammalian species, and that central processing of pain is largely equivalent in rodents and other larger research species such as dogs, cats, or primates. Other obstacles to effective pain management in rodents have been the lack of objective, science-driven data on pain assessment, and the availability of appropriate pharmacological tools for pain mitigation. To address this deficit, we have reviewed and summarized the available publications on pain management in rats, mice and guinea pigs. Different drug classes and specific pharmacokinetic profiles, recommended dosages, and routes of administration are discussed, and updated recommendations are provided. Nonpharmacologic tools for increasing the comfort and wellbeing of research animals are also discussed. The potential adverse effects of analgesics are also reviewed. While gaps still exist in our understanding of clinical pain management in rodents, effective pharmacologic and nonpharmacologic strategies are available that can and should be used to provide analgesia while minimizing adverse effects. The key to effective clinical management of pain is thoughtful planning that incorporates study needs and veterinary guidance, knowledge of the pharmacokinetics and mechanisms of action of drugs being considered, careful attention to individual differences, and establishing an institutional culture that commits to pain management for all species as a central component of animal welfare.

Bone morphogenetic protein and activin membrane-bound inhibitor overexpression inhibits gastric tumor cell invasion via the transforming growth factor-β/epithelial-mesenchymal transition signaling pathway

Gastric carcinoma is one of the most common human malignancies and remains the second leading cause of cancer-associated mortality worldwide. Gastric carcinoma is characterized by early-stage metastasis and is typically diagnosed in the advanced stage. Previous results have indicated that bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) overexpression has been demonstrated to inhibit growth and metastasis of gastric cancer cells. However, the molecular mechanisms of the BAMBI-mediated signaling pathway in the progression of gastric cancer are poorly understood. In the present study, to assess whether BAMBI overexpression inhibited the growth and aggressiveness of gastric carcinoma cells through regulation of transforming growth factor (TGF)-β/epithelial-mesenchymal transition (EMT) signaling pathway, the growth and metastasis of gastric carcinoma cells were analyzed following BAMBI overexpression and knockdown in vitro and in vivo. Molecular changes in the TGF-β/EMT signaling pathway were studied in gastric carcinoma cells following BAMBI overexpression and knockdown. DNA methylation of the gene regions encoding the TGF-β/EMT signaling pathway was investigated in gastric carcinoma cells. Tumor growth in tumor-bearing mice was analyzed after mice were subjected to endogenous overexpression of BAMBI. Results indicated that BAMBI overexpression significantly inhibited gastric carcinoma cell growth and aggressiveness, whereas knockdown of BAMBI significantly promoted its growth and metastasis compared with the control (P<0.01). The TGF-β/EMT signaling pathway was downregulated in BAMBI-overexpressed gastric carcinoma cells; however, signaling was promoted following BAMBI knockdown. In addition, it was observed that BAMBI overexpression significantly downregulated the DNA methylation of the gene regions encoding the TGF-β/EMT signaling pathway (P<0.01). Furthermore, RNA interference-mediated BAMBI overexpression also promoted apoptosis in gastric cancer cells and significantly inhibited growth of gastric tumors in murine xenografts (P<0.01). In conclusion, the present findings suggest that BAMBI overexpression inhibited the TGF-β/EMT signaling pathway and suppressed the invasiveness of gastric tumors, suggesting BAMBI may be a potential target for the treatment of gastric carcinoma via regulation of the TGF-β/EMT signaling pathway.

Lack of adverse effects during a target animal safety trial of extended-release buprenorphine in Fischer 344 rats

Extended-release buprenorphine is an effective analgesic in laboratory animals, and its safety has been established in mice but not in rats. The authors used a target animal safety trial to evaluate the safety of extended-release buprenorphine in rats. Fischer 344 rats received post-surgical subcutaneous injections of 1.3 mg, 3.9 mg or 6.5 mg buprenorphine per kg body weight (two times, six times or ten times the intended dose, respectively), and their body weight, clinical signs and symptoms, clinical pathology and histopathology were monitored for 4 d. Body weight was not significantly different in rats that received buprenorphine compared with control rats. Signs of nausea-related behavior were observed in 25% of the rats treated with buprenorphine. Clinical pathology results for all rats were normal, and gross and microscopic histopathology examinations identified no substantial abnormalities, suggesting that this behavior was of minor consequence. Other adverse events previously reported to occur with opiate therapy, including weight loss and dermal lesions at drug injection sites, were not observed in this study. The results of this study show that post-surgical administration of an extended-release buprenorphine product is safe in Fischer 344 rats and does not necessarily cause substantial adverse effects, confirming that opiate therapy is a viable choice in laboratory animal medicine.

Subcutaneous Implants of a Cholesterol-Triglyceride-Buprenorphine Suspension in Rats

A Target Animal Safety protocol was used to examine adverse events in male and female Fischer F344/NTac rats treated with increasing doses of a subcutaneous implant of a lipid suspension of buprenorphine. A single injection of 0.65 mg/kg afforded clinically significant blood levels of drug for 3 days. Chemistry, hematology, coagulation, and urinalysis values with 2- to 10-fold excess doses of the drug-lipid suspension were within normal limits. Histopathology findings were unremarkable. The skin and underlying tissue surrounding the drug injection were unremarkable. Approximately 25% of a cohort of rats given the excess doses of 1.3, 3.9, and 6.5 mg/kg displayed nausea-related behavior consisting of intermittent and limited excess grooming and self-gnawing. These results confirm the safety of cholesterol-triglyceride carrier systems for subcutaneous drug delivery of buprenorphine in laboratory animals and further demonstrate the utility of lipid-based carriers as scaffolds for subcutaneous, long-acting drug therapy.