Transdermal fentanyl and its use in ovine surgery

In vivo Assessment of AMP2, a Novel Ceramic-Binding BMP-2, in Ovine Lumbar Interbody Fusion

STUDY DESIGN

Assessment of bone formation in an ovine interbody fusion study.

OBJECTIVE

To compare OsteoAdapt SP, which consists of AMP-2, a modified variant of recombinant human bone morphogenetic protein (rhBMP-2) bound to a tricalcium phosphate-containing carrier, to autologous iliac crest bone graft (ICBG) in a lumbar interbody fusion model.

SUMMARY OF BACKGROUND DATA

Treatment of lumbar disk degeneration often involves spinal fusion to reduce pain and motion at the affected spinal segment by insertion of a cage containing bone graft material. Three graft materials were compared in this study-ICBG and OsteoAdapt SP (low or high dose).

METHODS

The sheep underwent lateral lumbar fusion surgery with PEEK or Titanium interbody cages packed with OsteoAdapt SP (low or high dose) or ICBG. Outcomes were evaluated at 8-, 16- and 26- weeks. Newly formed bone quality, bone mineralization, and fusion were assessed by manual palpation, qualitative and semi-quantitative histopathology, histomorphometry, computed tomography (CT), and micro-CT (mCT) analysis.

RESULTS

OsteoAdapt SP was implanted into 43 animals and ICBG into 21 animals (L3-L4). No group showed evidence of systemic toxicity by multiple assessments. All levels were fused by manual palpation at 26 weeks. Serial CT scans showed increasing fusion scores over time. Both doses of OsteoAdapt SP resulted in robust new bone formation and progression of fusion in the interbody cage. Range of motion tests for treatment groups was lower compared with ICBG at 8- and 16 weeks. Similarly, histology at eight weeks demonstrated more robust new bone formation for both OsteoAdapt SP groups compared to autograft.

CONCLUSION

We have demonstrated the preclinical safety and efficacy of OsteoAdapt SP in a clinically relevant large animal model, supporting faster and more robust new bone formation within the interbody cage, comparable to or better than the gold standard, ICBG, in all measures.

Pain Relief Interventions in Australian Livestock Husbandry: A Review of Animal Welfare and Pain Duration

In veterinary medicine and livestock production, ensuring good animal husbandry is vital for the physical and emotional wellbeing of animals under our care. Pain poses challenges for assessment and mitigation, especially in species unable to express pain overtly. This review examines current pain mitigation interventions in routine husbandry, focuses on the duration of pain after procedures and implications for animal welfare. Pain behaviours have been observed for days or weeks after regular husbandry procedures, and many studies have noted pain-related behaviour persisting until study finalisation, suggesting potential undocumented pain beyond study completion. Current products registered in Australia for pain mitigation in livestock primarily target immediate pain associated with procedures. The future of pain relief in livestock demands longer-acting solutions to address post-procedural pain adequately. Providing pain relief for at least 72 h post surgery is recommended, but current products require retreatment intervals to achieve this, posing practical challenges, especially in livestock. Methods of pain relief provision, such as voluntary consumption of medicated feed, transdermal medication delivery and long-acting formulations offer potential solutions for prolonged pain relief, with research ongoing in these areas. There is a need for further research and development of longer-acting pain relief to ensure optimal welfare of livestock.

An Exploration of Analgesia Options for Australian Sheep

During their lifetime, sheep undergo many painful husbandry and disease processes. Procedures undertaken on the farm, such as tail docking, castration, and mulesing, all cause considerable pain. In addition, sheep may experience painful diseases and injuries that require treatment by veterinary practitioners, and in biomedical research, sheep may undergo painful experimental procedures or conditions. It is important due to ethics, animal welfare, social licence, and, at times, legal requirements for farmers, veterinary practitioners, and researchers to provide pain relief for animals in their care. While there is a heightened awareness of and a greater interest in animal welfare, there remain few licensed and known analgesia options for sheep within Australia. A literature review was undertaken to identify currently known and potential future options for analgesic agents in sheep in farm and biomedical settings. Non-steroidal anti-inflammatories, opioids, local anaesthetics, α2 adrenoreceptor agonists, and NMDA receptor antagonists are some of the more common classes of analgesic drugs referred to in the literature, but few drugs are registered for use in sheep, with even fewer proven to be effective. Only six analgesic product formulations, namely, lignocaine (e.g., Numocaine®), Tri-Solfen®, ketamine, xylazine, and meloxicam (oral transmucosal and injectable formulations), are currently registered in Australia and known to be efficacious in some types of painful conditions in sheep. The gap in knowledge and availability of analgesia in sheep can pose risks to animal welfare, social licence, and research outcomes. This article presents a summary of analgesic agents that have been used in sheep on farms and in clinical veterinary and biomedical research settings along with details on whether their efficacy was assessed, doses, routes of administration, indication for use, and pain assessment techniques (if any) used. The outcome of this research highlights the challenges, gaps, and opportunities for better analgesia options in sheep.

A Novel Nanostructured Surface on Titanium Implants Increases Osseointegration in a Sheep Model

BACKGROUND

A nanostructured titanium surface that promotes antimicrobial activity and osseointegration would provide the opportunity to create medical implants that can prevent orthopaedic infection and improve bone integration. Although nanostructured surfaces can exhibit antimicrobial activity, it is not known whether these surfaces are safe and conducive to osseointegration.

QUESTIONS/PURPOSES

Using a sheep animal model, we sought to determine whether the bony integration of medical-grade, titanium, porous-coated implants with a unique nanostructured surface modification (alkaline heat treatment [AHT]) previously shown to kill bacteria was better than that for a clinically accepted control surface of porous-coated titanium covered with hydroxyapatite (PCHA) after 12 weeks in vivo. The null hypothesis was that there would be no difference between implants with respect to the primary outcomes: interfacial shear strength and percent intersection surface (the percentage of implant surface with bone contact, as defined by a micro-CT protocol), and the secondary outcomes: stiffness, peak load, energy to failure, and micro-CT (bone volume/total volume [BV/TV], trabecular thickness [Tb.Th], and trabecular number [Tb.N]) and histomorphometric (bone-implant contact [BIC]) parameters.

METHODS

Implants of each material (alkaline heat-treated and hydroxyapatite-coated titanium) were surgically inserted into femoral and tibial metaphyseal cancellous bone (16 per implant type; interference fit) and in tibial cortices at three diaphyseal locations (24 per implant type; line-to-line fit) in eight skeletally mature sheep. At 12 weeks postoperatively, bones were excised to assess osseointegration of AHT and PCHA implants via biomechanical push-through tests, micro-CT, and histomorphometry. Bone composition and remodeling patterns in adult sheep are similar to that of humans, and this model enables comparison of implants with ex vivo outcomes that are not permissible with humans. Comparisons of primary and secondary outcomes were undertaken with linear mixed-effects models that were developed for the cortical and cancellous groups separately and that included a random effect of animals, covariates to adjust for preoperative bodyweight, and implant location (left/right limb, femoral/tibial cancellous, cortical diaphyseal region, and medial/lateral cortex) as appropriate. Significance was set at an alpha of 0.05.

RESULTS

The estimated marginal mean interfacial shear strength for cancellous bone, adjusted for covariates, was 1.6 MPa greater for AHT implants (9.3 MPa) than for PCHA implants (7.7 MPa) (95% CI 0.5 to 2.8; p = 0.006). Similarly, the estimated marginal mean interfacial shear strength for cortical bone, adjusted for covariates, was 6.6 MPa greater for AHT implants (25.5 MPa) than for PCHA implants (18.9 MPa) (95% CI 5.0 to 8.1; p < 0.001). No difference in the implant-bone percent intersection surface was detected for cancellous sites (cancellous AHT 55.1% and PCHA 58.7%; adjusted difference of estimated marginal mean -3.6% [95% CI -8.1% to 0.9%]; p = 0.11). In cortical bone, the estimated marginal mean percent intersection surface at the medial site, adjusted for covariates, was 11.8% higher for AHT implants (58.1%) than for PCHA (46.2% [95% CI 7.1% to 16.6%]; p < 0.001) and was not different at the lateral site (AHT 75.8% and PCHA 74.9%; adjusted difference of estimated marginal mean 0.9% [95% CI -3.8% to 5.7%]; p = 0.70).

CONCLUSION

These data suggest there is stronger integration of bone on the AHT surface than on the PCHA surface at 12 weeks postimplantation in this sheep model.

CLINICAL RELEVANCE

Given that the AHT implants formed a more robust interface with cortical and cancellous bone than the PCHA implants, a clinical noninferiority study using hip stems with identical geometries can now be performed to compare the same surfaces used in this study. The results of this preclinical study provide an ethical baseline to proceed with such a clinical study given the potential of the alkaline heat-treated surface to reduce periprosthetic joint infection and enhance implant osseointegration.

Long-Lasting Analgesia With Transdermal Fentanyl: A New Approach in Rat Neonatal Research

Background: With advances in neonatal care, management of prolonged pain in newborns is a daily concern. In addition to ethical considerations, pain in early life would have long-term effects and consequences. However, its treatment remains inadequate. It was therefore important to develop an experimental model of long-lasting analgesia for neonatal research. Materials and Methods: Experiments were performed in six groups of rats with transdermal fentanyl 0, 3, 12, 50, 100, or 200 μg/kg/h from second postnatal day (P2) until weaning. Assessment of analgesia was carried out at P21, with behavioral scores (ranging from 0 to 3) using a 4% formalin test. Plasma levels of fentanyl were determined by UPLC/TQD at P22. Growth rate was investigated. Results: Fentanyl 100 and 200 μg/kg/h reduced scores of formalin-evoked behavioral pain. They increased time spent in pain score 0 (8 min 55 s and 6 min 34 s versus 23 s in controls) as in low pain scores 1 and 2, and decreased time in the most severe pain score 3 (19 min 56 s and 17 min 39 s versus 44 min 15 s). Fentanylemia increased in a dose-dependent manner from 50 μg/kg/h (2.36 ± 0.64 ng/ml) to 200 μg/kg/h (8.66 ± 1.80 ng/ml). Concerning growth, no difference was observed except weaker growth from P17 to P22 with 200 μg/kg/h. Clinically, we noticed no visible side effect from 3 to 100 μg/kg/h. Concomitantly, 200 μg/kg/h was responsible for ophthalmological side effects with appearance of corneal bilateral clouding in 90% pups. No difference was observed between male and female rats. Conclusion: Altogether, results indicate that transdermal fentanyl 100 μg/kg/h is an efficient therapeutic for long-lasting analgesia in lactating pups. This new model provides a useful tool for protection and welfare, and future opportunity for studying long-term health consequences of sustainable neonatal analgesia.

Pharmacokinetic Profile of Fentanyl in the Koala (Phascolarctos cinereus) after Intravenous Administration, and Absorption via a Transdermal Patch

Simple Summary

Koalas can be injured by cars and bushfires, and be affected by painful infectious diseases. When koalas undergo surgery to repair broken bones, they require analgesia. Fentanyl is a potent opioid that can be administered during surgery to provide analgesia. This study describes the rate of elimination of fentanyl in koalas’ blood when administered as a single intravenous injection and consequently calculates the dose rate to administer a constant rate fentanyl infusion into the koalas’ veins to provide short-term pain control. Fentanyl can also be absorbed via the skin into the circulation when applied as a transdermal patch. Although the data for transdermal fentanyl patch absorption is from two koalas only, the results demonstrate that when a patch is applied, pain control is likely to occur 12 h after application to koalas’ skin. Fentanyl may provide effective pain control to koalas either as an intravenous infusion or as a transdermal patch.

Abstract

Fentanyl was administered as a single intravenous bolus injection at 5 µg/kg to five koalas and fentanyl plasma concentrations for a minimum of 2 h were quantified by an enzyme-linked immunosorbent assay (ELISA). The median (range) fentanyl elimination half-life and clearance were 0.53 (0.38–0.91) h, and 10.01 (7.03–11.69) L/kg/h, respectively. Assuming an analgesic therapeutic plasma concentration of 0.23 ng/mL (extrapolated from human studies), an intravenous constant infusion rate was estimated at approximately between 1.7 to 2.7 µg/kg/h (using the clearance 95% confidence intervals). A transdermal fentanyl patch was applied to the antebrachium of an additional two koalas for 72 h. Fentanyl plasma concentrations were determined during the patch application and after patch removal at 80 h. The fentanyl plasma concentration was greater than 0.23 ng/mL after 12 to 16 h. While the patch was applied, the maximum fentanyl concentration was approximately 0.7 ng/mL from 32 to 72 h. Fentanyl plasma concentrations increased to 0.89 ng/mL 1 h after the patch was removed, and then decreased to a mean of 0.47 ng/mL at 80 h. The transdermal fentanyl patch is likely to provide some level of analgesia but should be initially co-administered with another faster acting analgesic for the first 12 h.

High-strength, porous additively manufactured implants with optimized mechanical osseointegration

Optimization of porous titanium alloy scaffolds designed for orthopedic implants requires balancing mechanical properties and osseointegrative performance. The tradeoff between scaffold porosity and the stiffness/strength must be optimized towards the goal to improve long term load sharing while simultaneously promoting osseointegration. Osseointegration into porous titanium implants covering a wide range of porosity (0%-90%) and manufactured by laser powder bed fusion (LPBF) was evaluated with an established ovine cortical and cancellous defect model. Direct apposition and remodeling of woven bone was observed at the implant surface, as well as bone formation within the interstices of the pores. A linear relationship was observed between the porosity and benchtop mechanical properties of the scaffolds, while a non-linear relationship was observed between porosity and the ex vivo cortical bone-implant interfacial shear strength. Our study supports the hypothesis of porosity dependent performance tradeoffs, and establishes generalized relationships between porosity and performance for design of topological optimized implants for osseointegration. These results are widely applicable for orthopedic implant design for arthroplasty components, arthrodesis devices such as spinal interbody fusion implants, and patient matched implants for treatment of large bone defects.

Long-Term Analgesia following a Single Application of Fentanyl Transdermal Solution in Pigs

INTRODUCTION

In animal research, obtaining efficient and constant pain control is regulatory but challenging. The gold standard pain management consists of opioid analgesic administration, such as buprenorphine or fentanyl extended-release patches. However, as in all drugs with a short half-life time, repeated buprenorphine administrations are needed, leading to multiple injections that affect the research protocol. On the other hand, fentanyl patch efficacy is discussed in some species. These elements highlight the need of an optimal formulation of analgesic drugs for laboratory animals. In this study, we investigated how Recuvyra®, a fentanyl transdermal solution (FTS), validated in dog perioperative pain management, could provide sustained analgesia after a single topical administration in pigs in a surgical context.

METHODS

A total of 11 minipigs were used in this study. As a preliminary experiment, two different doses were tested as a single application on five pigs: two pigs at full dose (2.6 mg/kg) and three pigs at half dose (1.3 mg/kg). Plasma fentanyl dosages were performed during 4 consecutive days, using liquid chromatography with tandem mass spectrometry detection. The efficacy of FTS was then evaluated in a perioperative period. Six minipigs benefited from a surgical intervention comprising a laparotomy. The FTS was blotted on the skin in a single application 20 min before the surgical incision and plasma fentanyl dosages, clinical examination (body weight, food intake, heart rate, and body temperature) and pain assessment were performed for 7 consecutive days.

RESULTS

During the preliminary experiment, all fentanyl concentrations reached the minimum effective concentration (MEC) extrapolated in pigs (fentanylemia ≥0.2 ng/mL) throughout the 4 days. The half dose was chosen for the next step of the study. After the surgical intervention, all plasma fentanyl concentrations remained above the MEC up to 7 days post administration. Pig clinical examinations and pain evaluations showed efficient and constant pain control at the half dose, and few adverse events were observed.

DISCUSSION AND CONCLUSION

This study confirms the pharmacological and clinical efficacy of FTS at 1.3 mg/kg in pigs throughout at least 7 postoperative days following laparotomy. The clinical analgesic effect of FTS appears more efficient and well-tolerated than the one observed with repeated injections of buprenorphine. This analgesic drug formulation could be universally used in animal research to provide optimal perioperative pain management and long-term analgesia.

Analgesia for Sheep in Commercial Production: Where to Next?

Simple Summary

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on industry to alleviate pain associated with husbandry practices, injury and illness. Although a number of analgesic solutions are now available for sheep, providing some amelioration of the acute pain responses, this review has highlighted a number of potential areas for further research.

Abstract

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on livestock production industries to alleviate pain associated with husbandry practices, injury and illness. Over the past 15–20 years, there has been considerable research effort to understand and develop mitigation strategies for painful husbandry procedures in sheep, leading to the successful launch of analgesic approaches specific to sheep in a number of countries. However, even with multi-modal approaches to analgesia, using both local anaesthetic and non-steroidal anti-inflammatory drugs (NSAID), pain is not obliterated, and the challenge of pain mitigation and phasing out of painful husbandry practices remains. It is timely to review and reflect on progress to date in order to strategically focus on the most important challenges, and the avenues which offer the greatest potential to be incorporated into industry practice in a process of continuous improvement. A structured, systematic literature search was carried out, incorporating peer-reviewed scientific literature in the period 2000–2019. An enormous volume of research is underway, testament to the fact that we have not solved the pain and analgesia challenge for any species, including our own. This review has highlighted a number of potential areas for further research.

Pain Management in Small Ruminants and Camelids: Applications and Strategies

Small ruminants are increasing in popularity as production and companion animals in the United States, and among sheep, goats, and camelids there are many disease processes and management techniques that have the potential to result in painful or noxious stimuli. In these species, many medications and therapeutic techniques can be used to reduce or eliminate the long-term consequences of pain. In this second portion of the review, we focus on the application of pain management in these species. These strategies include mono- and multimodal and the use of precision pain management, such as epidural drug administration, regional perfusions, and transdermal applications.

Undercut macrostructure topography on and within an interbody cage improves biomechanical stability and interbody fusion

BACKGROUND CONTEXT

The interface and interactions between an interbody cage, graft material, and host bone can all participate in the fusion. Shortcomings of Poly(aryl-ether-ether-ketone) interbody cages have been addressed with novel titanium surfaces. Titanium surfaces paired with macroscale topography features on the endplates and within the aperture may provide additional benefits.

PURPOSE

To evaluate the influence of cage design parameters on interbody fusion in a large animal preclinical model.

STUDY DESIGN/SETTING

A comparative preclinical large animal model was performed to evaluate how macroscale topography features of an interbody cage can facilitate early integration between the host bone, graft material, and interbody cage and these effects on biomechanical stability and fusion.

METHODS

Forty single level interbody fusions (L4-L5) using iliac crest autograft and bilateral pedicle screw fixation were performed in adult sheep to evaluate the effect of undercut macrostructure topography features of an interbody cage on the endplates and within the aperture. Fusions were evaluated at 6 and 12 weeks (n=10 per group) using radiography, microcomputed tomography, biomechanical integrity, and histology endpoints.

RESULTS

The presence of the undercut macrostructures present on the endplates and within the aperture statistically improved biomechanical integrity at 6 and 12 weeks compared with controls. Microcomputed tomography and histology demonstrated bony interdigitation within the endplate and aperture features contributing to the improvement in properties.

CONCLUSIONS

The present study demonstrates that Poly(aryl-ether-ether-ketone) implants with titanium surfaces can be augmented by undercut macrostructures present on the endplates and within the aperture to provide opportunities for a series of anchoring points that, with new bone formation and remodelling, result in earlier and improved biomechanical integrity of the treated level.

CLINICAL SIGNIFICANCE

This preclinical study showed that bone interdigitation with the undercut macrostructures present on the endplates and within the aperture resulted in improved fusion and biomechanical stability in a clinically relevant spinal fusion model. Future clinical study is warranted to evaluate such implants' performance in humans.

Fentanyl Plasma Concentrations after Application of a Transdermal Patch in Three Different Locations to Refine Postoperative Pain Management in Rabbits

Simple Summary

Fentanyl patches offer “stress free” postoperative pain management in rabbits. It has been shown that fentanyl uptake is dependent on exogenous and endogenous factors of the area where the patch is applied. The purpose of the study was to investigate three different locations (neck, inner and outer surface of the ear) to obtain reliable fentanyl plasma concentrations above those previously shown to be analgesic. The fentanyl plasma concentration was measured at several time points after patch application. In addition, the practicability of the proposed methods was evaluated. The group with application on the neck had the fastest uptake and equal to or over the analgesic plasma concentration for up to 72 h. The outer surface of the ear had slightly slower uptake and shorter analgesic duration whereas fentanyl uptake at the inner surface of the ear was insufficient to provide plasma analgesic concentration. The preparation of the neck proved to be the most laborious because of the thin and dense fur and the removal of the patch resulted in erythema. In conclusion, depending on how long potent analgesia is required, either the neck or the outer surface of the ear are suitable for patch application enabling “stress free” and reliable postoperative analgesia in rabbits.

Abstract

Transdermal patches allow a noninvasive and “stress free” analgesia in rabbits. As fentanyl uptake is dependent on exogenous and endogenous factors of the area where the patch is applied, this study investigated three different locations (neck, inner and outer surfaces of the ear) for fentanyl patch application to provide adequate and reliable fentanyl plasma concentrations above those previously shown to be analgesic. Fentanyl plasma concentration was measured at different time points (3, 6, 9, 12, 18, 24, 36, 48, 72, 96, 120 h) and rabbits were assessed for their general conditions and treatment-related side effects. Practicability of the proposed methods was evaluated. Following patch application on the neck, fentanyl plasma concentrations equal to or above the analgesic value were measured in all rabbits between 6 and 72 h. Comparable concentrations were reached between 9 and 48 h in all animals for the outer ear surface. However, for the inner ear surface, analgesic concentrations were not reached, even if practicability was considered the best for this location. Preparation of the neck skin was judged as the most cumbersome due to the clipping of the dense fur and patch removal resulted in erythema. In summary, the application of the fentanyl patch on the neck and outer ear surface allowed the reach of reliable plasma concentrations above the analgesic threshold in rabbits. When applied on the neck, fentanyl patches provided the longest duration of analgesic plasma concentrations, whereas patch application and removal were easier on the outer ear surface.

Transdermal Fentanyl Uptake at Two Different Patch Locations in Swiss White Alpine Sheep

Simple Summary

Providing adequate and prolonged pain relief to sheep undergoing invasive orthopedic surgery while keeping side effects and stress for the animals at a minimum is challenging. Transdermal patches continuously releasing the synthetic opioid fentanyl through the skin, are a frequently used method in veterinary and human medicine. To refine the current analgesia protocol, we compared the uptake of fentanyl from a transdermal fentanyl patch applied at two different skin locations in sheep. The fentanyl plasma levels were measured at different time points over five days. The patch applied on the foreleg resulted in a faster fentanyl uptake with higher peaks and a longer time within or above the target fentanyl plasma concentration when compared to the one on the thorax. Additionally, it was easier to apply the patch at the foreleg than at the thorax. Our findings suggest that the fentanyl patch should be applied to the foreleg 3–6 h before the painful insult and that its effect should last at least 48 h.

Abstract

When using animals in biomedical research, investigators have the responsibility to ensure adequate analgesia. Currently, transdermal fentanyl patches (TFP) are often used to provide postoperative analgesia in large laboratory animals. The aim of this study was to compare the fentanyl uptake resulting from TFP applied at two different locations, namely the foreleg and the thorax, in healthy adult sheep. Twelve sheep received a TFP with an intended dosage of 2 ug/kg/h. Blood samples were taken at different time points over a period of five days and the fentanyl plasma levels were measured. The TFP applied on the foreleg allowed a faster fentanyl uptake with higher peaks and a longer time within or above the target concentration of 0.6–1.5 ng/mL, shown to be analgesic in humans, when compared to the one on the thorax. Assuming that the effective plasma concentration described for humans is providing analgesia in sheep as well, the present findings suggest that it should be sufficient to apply the TFP 3–6 h before the painful insult and that its effect should last at least 48 h. Furthermore, when TFP are used to provide postoperative analgesia in sheep, they should be placed on the foreleg rather than on the thorax.

Comparison of analgesic efficacy and fetal effects between transdermal administration of fentanyl and intramuscular administration of buprenorphine in pregnant sheep

OBJECTIVE

To compare analgesic efficacy and fetal effects between transdermal administration of fentanyl and IM administration of buprenorphine in pregnant sheep.

ANIMALS

12 healthy pregnant ewes.

PROCEDURES

Before study initiation, each ewe was confirmed pregnant with a single fetus between 113 and 117 days of gestation. Ewes were randomly assigned to receive buprenorphine (0.01 mg/kg, IM, q 8 h for 48 hours beginning 1 hour before anesthesia induction; n = 6) or fentanyl (a combination of transdermal fentanyl patches sufficient to deliver a dose of 2 μg of fentanyl/kg/h applied between the dorsal borders of the scapulae 24 hours before anesthesia induction; 6). Ewes were anesthetized and underwent a surgical procedure to instrument the fetus with an arterial catheter and place a catheter in utero for collection of amniotic fluid samples. Physiologic variables and behavioral changes indicative of pain were assessed, and amniotic fluid and blood samples from ewes and fetuses were collected for determination of drug concentrations at predetermined times.

RESULTS

Both protocols provided acceptable postoperative analgesia with no adverse effects observed in the ewes or fetuses. Compared with the buprenorphine protocol, the fentanyl protocol induced more profound analgesia, decreased the requirement for isoflurane during surgery, and was associated with a shorter anesthesia recovery time. Fetal indices did not differ significantly between the 2 analgesic protocols.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that both protocols provided acceptable analgesia. However, the fentanyl protocol was superior in regard to the extent of analgesia induced, inhalant-sparing effects, and anesthesia recovery time.

Bone ongrowth and mechanical fixation of implants in cortical and cancellous bone

BACKGROUND

What is the right surface for an implant to achieve biological fixation? Surface technologies can play important roles in encouraging interactions between the implant surface and the host bone to achieve osseointegration. Preclinical animal models provide important insight into in vivo performance related to bone ongrowth and implant fixation.

METHODS

A large animal model was used to compare the in vivo response of HA and plasma-sprayed titanium coatings in a well-reported adult ovine model to evaluate bone ongrowth in terms of mechanical properties in cortical sites, and histology and histomorphometry in cortical and cancellous sites at 4 and 12 weeks.

RESULTS

Titanium plasma-sprayed surfaces outperformed the HA-coated samples in push-out testing in cortical sites while both surfaces supported new bone ongrowth and remodeling in cortical and cancellous sites.

CONCLUSIONS

While both HA and Ti plasma provided an osteoconductive surface for bone ongrowth, the Ti plasma provided a more robust bone-implant interface that ideally would be required for load transfer and implant stability in the longer term.

A preclinical large-animal model for the assessment of critical-size load-bearing bone defect reconstruction

Critical-size bone defects, which require large-volume tissue reconstruction, remain a clinical challenge. Bone engineering has the potential to provide new treatment concepts, yet clinical translation requires anatomically and physiologically relevant preclinical models. The ovine critical-size long-bone defect model has been validated in numerous studies as a preclinical tool for evaluating both conventional and novel bone-engineering concepts. With sufficient training and experience in large-animal studies, it is a technically feasible procedure with a high level of reproducibility when appropriate preoperative and postoperative management protocols are followed. The model can be established by following a procedure that includes the following stages: (i) preoperative planning and preparation, (ii) the surgical approach, (iii) postoperative management, and (iv) postmortem analysis. Using this model, full results for peer-reviewed publication can be attained within 2 years. In this protocol, we comprehensively describe how to establish proficiency using the preclinical model for the evaluation of a range of bone defect reconstruction options.

Does implantation site influence bone ingrowth into 3D-printed porous implants?

BACKGROUND CONTEXT

The potential for osseointegration to provide biological fixation for implants may be related to anatomical site and loading conditions.

PURPOSE

To evaluate the influence of anatomical site on osseointegration of 3D-printed implants.

STUDY DESIGN

A comparative preclinical study was performed evaluating bone ingrowth in cortical and cancellous sites in long bones as well as lumbar interbody fusion with posterior pedicle screw stabilization using the same 3D-printed titanium alloy design.

METHODS

3D-printed dowels were implanted in cortical bone and cancellous bone in adult sheep and evaluated at 4 and 12 weeks for bone ingrowth using radiography, mechanical testing, and histology/histomorphometry. In addition, a single-level lumbar interbody fusion using cages based on the same 3D-printed design was performed. The aperture was filled with autograft or ovine allograft processed with supercritical carbon dioxide. Interbody fusions were assessed at 12 weeks via radiography, mechanical testing, and histology/histomorphometry.

RESULTS

Bone ingrowth in long bone cortical and cancellous sites did not translate directly to interbody fusion cages. While bone ingrowth was robust and improved with time in cortical sites with a line-to-line implantation condition, the same response was not found in cancellous sites even when the implants were placed in a press fit manner. Osseointegration into the porous walls with 3D porous interbody cages was similar to the cancellous implantation sites rather than the cortical sites. The porous domains of the 3D-printed device, in general, were filled with fibrovascular tissue while some bone integration into the porous cages was found at 12 weeks when fusion within the aperture was present.

CONCLUSION

Anatomical site, surgical preparation, biomechanical loading, and graft material play an important role in in vivo response. Bone ingrowth in long bone cortical and cancellous sites does not translate directly to interbody fusions.

Effect of three opioid-based analgesic protocols on the perioperative autonomic-mediated cardiovascular response in sheep

Few reports evaluate the clinical effects of opioids in sheep during experimental surgical procedures. Catecholamine-mediated haemodynamic changes resulting from surgical noxious stimulation are blunted by opioids. The aim of this study was to evaluate the efficacy of three opioid-based analgesic protocols in avoiding a 20% increase in heart rate (HR) and/or mean arterial blood pressure (MAP) during experimental intervertebral disk nucleotomy in sheep. Eighteen female Brogna sheep were anaesthetized with propofol and maintained with a fixed end-tidal isoflurane concentration of 1.5 ± 0.1%. Sheep were assigned to one of three groups that intravenously received methadone 0.3 mg/kg (group M), fentanyl 2 µg/kg followed by 10 µg/kg/h (group F), or buprenorphine 10 µg/kg and 30 minutes later ketamine 1 mg/kg followed by 5 mg/kg/h (group BK). Intravenous fentanyl at 2 µg/kg would have been used for rescue analgesia in case HR and/or MAP had increased. During surgery, HR and MAP values did not increase over 20% in all groups. All animals maintained the percentage change between -4 and 7% for both variables; only one sheep in group BK had an increase in MAP superior to 20% after ketamine administration before surgical stimulation. In group M, HR decreased over time and in group BK, MAP tended to increase during surgery. All the opioid-based protocols tested were able to control the cardiovascular response to noxious stimulation in sheep undergoing spinal surgery, although ketamine may have represented a confounding factor.

MAC-Sparing Effect of Transdermal Fentanyl in Sevoflurane-Anesthetized Sheep

Transdermal fentanyl allows for consistent plasma concentrations of a potent synthetic μ-opioid receptor agonist and can provide constant post-operative analgesia for up to 72 h. The aim of this study was to determine the reduction of the minimum alveolar concentration of sevoflurane (MACSEVO) by transdermal fentanyl in nonpregnant ewes. Nine sheep were mask induced with sevoflurane (SEVO in oxygen). MACSEVO determinations involved electrical current applied to the lateral metacarpus as a supramaximal stimulus and measurements in duplicate. Seven days later, a fentanyl patch (75 μg/h) was applied to each sheep and 15.1 ± 1.8 h later the MAC re-determined (MACSF). MACSF was 1.99 ± 0.32 %, corresponding to 25.6 ± 8.1 % reduction from MACSEVO (P < 0.001). Transdermal fentanyl produces a significant MACSEVO-sparing effect with minimal effect on cardiovascular parameters.

A review of factors affecting analgesic selection in large animals undergoing translational research

The widespread physiological effects of pain in experimental animals are likely to reduce the validity of data except when pain itself is studied. Appropriately prescribed analgesics will limit pain and improve the welfare of animals undergoing noxious experimental procedures. However, their injudicious use may also introduce variability in data and limit study reproducibility. Optimizing both animal welfare and the value of scientific data from experimental studies requires the ability to identify, quantify and treat animal pain by applying a knowledge of analgesic pharmacology that is sympathetic to study objectives. This review first examines the reasons for promoting analgesic use in translational animal research and, in focussing on pigs and small ruminants, then identifies factors that should be considered when devising analgesic plans.

Adverse reactions to fentanyl transdermal patches in calves: a preliminary clinical and pharmacokinetic study

OBJECTIVE

To describe adverse reactions and measure plasma fentanyl concentrations in calves following administration of a fentanyl transdermal patch (FTP).

STUDY DESIGN

Prospective, experimental clinical study.

ANIMALS

Six female Holstein calves and one male Angus calf. Four calves were healthy experimental animals and three calves were clinical patients.

METHODS

Plasma fentanyl concentrations were measured in blood collected from a jugular vein. FTP 2 μg kg^-1 hour^-1 and 1 μg kg^-1 hour^-1 was applied to four and three calves, respectively. Heart rate, respiratory rate, temperature and ataxia were recorded at the same times as blood collection (0, 2, 4, 6, 12, 24, 36, 48, 60, 72, 84 and 96 hours). Substance P concentrations were determined via radioimmunoassay for two calves.

RESULTS

After the FTP (2 μg kg^-1 hour^-1) application, two calves developed tachycardia, hyperthermia, excitement and ataxia within 6 hours; no adverse effect was observed in the other two calves. The three calves administered FTP (1 μg kg^-1 hour^-1) exhibited tachycardia and excitement, and the FTP were removed at 4 hours. Naloxone was administered to two calves before the adverse clinical signs ceased, while adverse events in the other three calves resolved within 2 hours of FTP removal. Variables returned to previous baseline values by 2-4 hours after FTP removal. Maximum plasma fentanyl concentrations were variable among calves (0.726-6.923 ng mL^-1). Substance P concentrations measured in two calves were not consistently depressed during FTP application. Fentanyl concentrations at 4 and 6 hours were significantly associated with the appearance of adverse effects.

CONCLUSIONS AND CLINICAL RELEVANCE

FTP (1-2 μg kg^-1 hour^-1) administered to calves may result in adverse behavioral and cardiovascular effects. Patch removal and treatment with an opioid antagonist may resolve these adverse effects. Additional research is needed to determine optimal FTP dosing for cattle.

Pharmacokinetics of fentanyl citrate and norfentanyl in Holstein calves and effect of analytical performances on fentanyl parameter estimation

This study describes the pharmacokinetics of intravenously administered (i.v.) fentanyl citrate, and its primary metabolite norfentanyl in Holstein calves. Eight calves (58.6 ± 2.2 kg), aged 3-4 weeks, were administered fentanyl citrate at a single dose of 5.0 μg/kg i.v. Blood samples were collected from 0 to 24 hr. Plasma (nor)fentanyl concentrations were determined using liquid chromatography with mass spectrometry and a lower limit of quantification (LLOQ) of 0.03 ng/ml. To explore the effect of analytical performance on fentanyl parameter estimation, the noncompartmental pharmacokinetic analysis was then repeated with a hypothetical LLOQ value of 0.05 ng/ml. Terminal elimination half-life was estimated at 12.7 and 3.6 hr for fentanyl and norfentanyl, respectively. For fentanyl, systemic clearance was estimated at 2.0 L hr^-1  kg^-1 , volume of distribution at steady-state was 24.8 L/kg and extraction ratio was 0.42. At a hypothetical LLOQ of 0.05 ng/ml fentanyl half-life, volume of distribution at steady-state and clearance were, respectively, of 3.0 hr, 8.8 L/kg and 3.4 L kg^-1  hr^-1 . Fentanyl citrate administered i.v. at 5.0 μg/kg can reach levels associated with analgesia in other species. Pharmacokinetic parameters should be interpreted with respect to LLOQ, as lower limits can influence estimated parameters, such as elimination half-life or systemic clearance and have significant impact on dosage regimen selection in clinical practice.

Sedation of sheep following the administration of acepromazine with buprenorphine or morphine is similar

The aim of this study was to compare sedation of sheep with acepromazine and buprenorphine or morphine. Twenty merino sheep received acepromazine (0.03mg/kg) with buprenorphine (0.02mg/kg, AB, n=10) or morphine (0.3mg/kg, AM, n=10) by intramuscular injection. Sedation was scored (SS) on a scale from 0 (no sedation) to 10 (heavy sedation). Response to restraint was scored (RS) on a scale from 0 (agitated) to 4 (relaxed). Three independent blinded observers and a single blinded observer determined the SS and RS, respectively. The SSs were summed (maximum 30). Data were compared using a t-test. Data is mean±SD (95% confidence interval). Each group comprised 2 wethers and 8 ewes. There was no difference between the AB and AM groups: weight 44±3.1kg and 44.7±3kg (p=0.58); SS 4.6±3.2 (2.4-6.9) and 6.6±3.5 (4.1-9.1) (p=0.21); and RS 1.6±1.3 (0.5-2.7) and 2±1.5 (0.7-3.3) (p=0.6). No adverse effects of the drugs were observed. Sedation with AB or AM at these doses is similar in sheep without observed adverse effects.

A novel method of suspending sheep for clinical research

The slinging of sheep is a commonly reported, yet poorly described procedure, which is useful for the advancement of veterinary and medical preclinical research. We have described a novel, flexible and repeatable method of suspending sheep to varying degrees while not affecting mobility and thereby improving animal husbandry and welfare.

The uptake of transdermal fentanyl in a pregnant sheep model

OBJECTIVE

To evaluate the maternal and foetal uptake of transdermal fentanyl patch applied to the groin of pregnant sheep following surgery.

STUDY DESIGN

Prospective series.

ANIMALS

A group of 16 singleton pregnant sheep underwent anaesthesia for laparotomy, hysterotomy and instrumentation of the foetus. Of these ewes 10 (101 ± 12 days of gestation) were used to evaluate the maternal uptake of transdermal fentanyl, and the efficacy of the drug in the postoperative period (n = 10). To determine the extent of transplacental transfer of fentanyl, six ewes from the group of 10, and six other ewes (92 ± 1 days' gestation) were studied.

METHODS

A 75 μg hour^-1 fentanyl patch was placed onto the woolless skin of the medial thigh close to the groin at the end of surgery. Maternal blood samples were collected from the cephalic or jugular vein, and pain and sedation scores were determined, prior to application of the patch (time 0) and at 3, 6, 12, 24, 36 and 48 hours after. A commercial Fentanyl ELISA kit was used to determine the concentration of fentanyl. Paired maternal and foetal blood samples were collected 48 hours after surgery. Animals were euthanized at the end of the study. Data were tested for normality and compared with Student t test or one-way anova and are expressed as mean ± standard deviation or median (range).

RESULTS

Recovery from anaesthesia and surgery was uneventful in all ewes. The dose of fentanyl was 1.4 ± 0.2 μg kg^-1 hour^-1. The maximum maternal plasma concentration of fentanyl was 0.547 ng mL^-1 (range, 0.349-0.738 ng mL^-1) at 12 hours. After 48 hours, the concentration of fentanyl was 0.381 ng mL^-1 (range, 0.211-0.487 ng mL^-1; maternal) and 0.295 ng mL^-1 (range, 0.185-0.377 ng mL^-1; foetal; p = 0.175). The placental transfer rate of fentanyl was 77%.

CONCLUSIONS AND CLINICAL RELEVANCE

The uptake of fentanyl varied between animals. The placental transfer rate of fentanyl was 77%.

Does PEEK/HA Enhance Bone Formation Compared With PEEK in a Sheep Cervical Fusion Model?

BACKGROUND

Polyetheretherketone (PEEK) has a wide range of clinical applications but does not directly bond to bone. Bulk incorporation of osteoconductive materials including hydroxyapatite (HA) into the PEEK matrix is a potential solution to address the formation of a fibrous tissue layer between PEEK and bone and has not been tested.

QUESTIONS/PURPOSES

Using in vivo ovine animal models, we asked: (1) Does PEEK-HA improve cortical and cancellous bone ongrowth compared with PEEK? (2) Does PEEK-HA improve bone ongrowth and fusion outcome in a more challenging functional ovine cervical fusion model?

METHODS

The in vivo responses of PEEK-HA Enhanced and PEEK-OPTIMA^® Natural were evaluated for bone ongrowth in the form of dowels implanted in the cancellous and cortical bone of adult sheep and examined at 4 and 12 weeks as well as interbody cervical fusion at 6, 12, and 26 weeks. The bone-implant interface was evaluated with radiographic and histologic endpoints for a qualitative assessment of direct bone contact of an intervening fibrous tissue later. Gamma-irradiated cortical allograft cages were evaluated as well.

RESULTS

Incorporating HA into the PEEK matrix resulted in more direct bone apposition as opposed to the fibrous tissue interface with PEEK alone in the bone ongrowth as well as interbody cervical fusions. No adverse reactions were found at the implant-bone interface for either material. Radiography and histology revealed resorption and fracture of the allograft devices in vivo.

CONCLUSIONS

Incorporating HA into PEEK provides a more favorable environment than PEEK alone for bone ongrowth. Cervical fusion was improved with PEEK-HA compared with PEEK alone as well as allograft bone interbody devices.

CLINICAL RELEVANCE

Improving the bone-implant interface with a PEEK device by incorporating HA may improve interbody fusion results and requires further clinical studies.