Buprederm™, a New Transdermal Delivery System of Buprenorphine: Pharmacokinetic, Efficacy and Skin Irritancy Studies

Evaluation of physical variables, thermal nociceptive threshold testing and pharmacokinetics during placement of transdermal buprenorphine matrix-type patch in healthy adult horses

Background

Matrix type transdermal buprenorphine patches have not been investigated in horses and may provide an effective means of providing continuous pain control for extended period and eliminating venous catheterization.

Objective

Assessment of the physiological variables (heart rate, respiratory rate, body temperature) and thermal nociceptive threshold testing, and describing the pharmacokinetic profile of transdermal buprenorphine matrix-type patch (20 μg h-1 and 40 μg h-1 dosing) in healthy adult horses.

Study design

Randomised experimental study with a Latin-square design.

Methods

Six adult healthy horses received each of the three treatments with a minimum 10 day washout period. BUP0 horses did not receive a patch (control). BUP20 horses received one patch (20 μg h-1) applied on the ventral aspect of the tail base resulting in a dose of 0.03-0.04 μg kg-1 h-1. BUP40 horses received two patches placed alongside each other (40 μg h-1) on the tail base resulting in a dose of 0.07-0.09 μg kg-1 h-1. Whole blood samples (for determination of buprenorphine concentration), physiological variables and thermal threshold testing were performed before (0 h) and at 2, 4, 8, 12, 16, 24, 32, 40, 48, 56, 64, 72, and 96 h after patch application. The patches were removed 72 h following placement and were analyzed for residual buprenorphine content.

Results

Between the three groups, there was no change in physiological variables across timepoints as compared to baseline (p > 0.1). With the higher dose, there was a significant increase in thermal thresholds from baseline values from 2 h until 48 h and these values were significantly higher than the group receiving the lower patch dose for multiple timepoints up to 40 h. 40 μg h-1 patch led to consistent measurable plasma concentrations starting at 2 h up to 96 h, with the mean plasma concentrations of > 0.1 ng/ml from 4 h to 40 h.

Conclusions

20 μg h-1 and 40 μg h-1 patch doses were well tolerated by all horses. At higher dose, plasma buprenorphine concentrations were more consistently measurable and blunted thermal thresholds for 48 h vs. 32 h with 20 μg h-1 dosing as compared to control.

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.

Sustained drug delivery strategies for treatment of common substance use disorders: Promises and challenges

Substance use disorders (SUDs) are a leading cause of death and other ill health effects in the United States and other countries in the world. Several approaches ranging from detoxification, behavioral therapy, and the use of antagonists or drugs with counter effects are currently being applied for its management. Amongst these, drug therapy is the mainstay for some drug abuse incidences, as is in place specifically for opioid abuse or alcohol dependence. The severity of the havocs observed with the SUDs has triggered constant interest in the discovery and development of novel medications as well as suitable or most appropriate methods for the delivery of these agents. The chronic need of such drugs in users warrants the need for their prolonged or sustained systemic availability. Further, the need to improve patient tolerance to medication, limit invasive drug use and overall treatment outcome are pertinent considerations for embracing sustained release designs for medications used in managing SUDs. This review aims to provide an overview on up-to-date advances made with regards to sustained delivery systems for the drugs for treatment of different types of SUDs such as opioid, alcohol, tobacco, cocaine, and cannabis use disorders. The clinical relevance, promises and the limitations of deployed sustained release approaches along with future opportunities are discussed.

Safety, Tolerability, and Pharmacokinetics of Ibuprofenamine Hydrochloride Spray (NSAIDs), a New Drug for Rheumatoid Arthritis and Osteoarthritis, in Healthy Chinese Subjects

Background

Ibuprofenamine hydrochloride spray is novel transdermal nonsteroidal anti-inflammatory drugs (NSAIDs), under clinical development for the treatment of Rheumatoid Arthritis and Osteoarthritis as a novel transdermal drug.

Methods

A single and multiple ascending dose study investigated the safety, tolerability and pharmacokinetics of ibuprofenamine hydrochloride in healthy Chinese subjects. A total of 34 subjects (single-dose study: 34 subjects and multiple-dose study: 20 subjects) were involved in the trial. In the single-dose study, subjects were assigned to one of the four groups received 35, 70, 140, 280 mg. In the 70 mg and 140 mg treatment groups, subjects received one dose on the first day and twice a day from day 6 to 12. The starting dose was determined considering the no observed adverse effect level based on preclinical studies, and the dose escalations in subsequent cohorts were decided based on safety, tolerability, and pharmacokinetic data from previous dose cohorts.

Results

After a single dose, both ibuprofenamine and ibuprofen plasma exposure showed a more than dose-proportional increase across a dose range of 35–280 mg. After multiple dosing, both ibuprofenamine and ibuprofen steady-state exposure increased obviously more than dose-proportional manner across the evaluated dose range (twice a day for 7 days) resulted in obvious accumulation. Single or multiple doses of ibuprofenamine hydrochloride were generally well tolerated and no obvious skin irritation was observed.

Conclusion

Ibuprofenamine hydrochloride exhibited a safety and pharmacokinetic profile that supports its future investigation as a potential therapeutic for Rheumatoid Arthritis and Osteoarthritis.

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.

Bioavailability of subcutaneous and intramuscular administrated buprenorphine in New Zealand White rabbits

Background

Buprenorphine is one of the most used analgesics for postoperative pain in rabbits. The recommended dose in rabbits (0.01–0.05 mg/kg) is the same for intravenous (IV), intramuscular (IM), and subcutaneous (SC) administration, despite lack of pharmacokinetic data. Five male and five female New Zealand White rabbits (mean ± SD body weight 3.1 ± 0.3 kg) were administered 0.05 mg/kg buprenorphine by the IV, IM and SC routes and 0.1 mg/kg by the SC route, in a cross-over design with two-week wash-out periods between treatments. Blood was collected before, and up to 8 h post buprenorphine injection, for determination of serum levels by UPHLC-MS/MS.

Results

The area under the time concentration curve (AUC_0-t) was lower after SC (398 ± 155 ng/mL/min) than IM (696 ± 168 ng/mL/min, p < 0.001) and IV (789 ± 189 ng/mL/min, p < 0.001) administration. The maximum serum concentration was lower after SC (2.2 ± 1.4 ng/mL) than after IM (11 ± 3.2 ng/mL) administration (p < 0.001). The bioavailability was lower after SC (50 ± 19%) than after IM (95 ± 21%) administration (p = 0.006). The elimination half-life was longer after SC (260 ± 120 min) than after IM (148 ± 26 min, p = 0.002) as well as IV (139 ± 33 min) injection (p < 0.001). An increase in the SC dose from 0.05 to 0.1 mg/kg resulted in an increase in the area under the time concentration curve of 50% in female (p = 0.022) and 165% in male rabbits (p < 0.001). The bioavailability did not change in the females (36 ± 14%, p = 0.6), whereas it increased in the males (71 ± 23%, p = 0.008).

Conclusions

The lower bioavailability of 0.05 mg/kg buprenorphine after SC administration could explain the lack of efficacy seen in clinical pain studies in rabbits, using this route. For immediate pain relief, IV or IM administration is therefore be recommended, whereas SC administration may be useful to sustain analgesic serum levels, once efficient pain relief has been achieved. The current data do not support an increase in dose to compensate for the lower SC bioavailability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-020-02618-7.

A Comparison of Buprenorphine, Sustained release Buprenorphine, and High concentration Buprenorphine in Male New Zealand White Rabbits

Pain management in rabbits can be difficult because they are adept at hiding pain and can be stressed by handling and restraint for injection. The use of opioid analgesics with prolonged durations of activity could alleviate pain, but associated adverse effects including gastrointestinal ileus, inappetence, and tissue reactions have been reported. In this study, we compared gross tissue reactions at the site of injection, food consumption, and fecal production after single injections of buprenorphine HCl (Bup; n = 7), sustained-release buprenorphine (BupSR; n = 8), and high-concentration buprenorphine (BupHC; n = 7) during the first 3 d after minor survival surgery. We also measured plasma concentrations of the parent drug, buprenorphine, and 3 metabolites (buprenorphine-3-glucuronide (B3G), norbuprenorphine-3β-glucuronide (N3G), and norbuprenorphine (NB)). Plasma levels of buprenorphine remained above the theoretical minimal analgesic concentration for 4 h for Bup and 42 h for BupHC. For BupSR, plasma levels of buprenorphine remained above the theoretical minimal analgesic concentration for approximately 77 h, starting 15 h after administration. For all 3 formulations, N3G was the most prominent metabolite in the blood. No injection site reactions were visible grossly in any rabbit. Relative to baseline measures and compared with controls (n = 8), food consumption was suppressed on days 1 through 3 in rabbits that received BupSR and on days 2 through 3 in those given BupHC. Feces production on day 3 was reduced to a greater extent in BupSR rabbits than control animals. Two rabbits in the BupHC group exhibited neurologic signs after drug administration. These adverse effects should be considered when choosing a long-lasting buprenorphine formulation to manage pain in rabbits.

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.

Evaluation of buprenorphine hydrochloride Pluronic(®) gel formulation in male C57BL/6NCrl mice

Providing adequate analgesia while minimizing handling and stress post-surgery can be challenging. Recently, there have been commercial products made available for providing long acting analgesia in rodents. However, we find there are limitations for use in mice due to the viscosity of the product and the small dosing volumes needed. This project evaluated an in-house compounded formulation of buprenorphine easily made in the laboratory using pharmaceutical grade products. The release of buprenorphine was evaluated when compounded with two types of hydrogels (Pluronic(®) F-127 and F-68). Mice given buprenorphine in hydrogel (BP) demonstrated higher serum levels of buprenorphine for a longer period of time compared to mice given standard buprenorphine (Bup). However, the rate of decline in serum levels between the groups was similar; thus, it is more likely that the higher buprenorphine concentration seen in the BP group is due to the higher dose of buprenorphine given, rather than a slower release of product. Feed consumption was decreased in both groups one day after dosing; however, there was no difference in body weights. Increased activity in the open field was observed with both buprenorphine formulations, and lipemia was observed in mice given BP which persisted to at least 96 h. Based on our results, we conclude that this formulation did not sustain the release of buprenorphine or eliminate the increased activity commonly seen in mice given buprenorphine. In addition, the lipemia may confound research parameters, especially in cardiac studies and lipid metabolism studies. Therefore, we cannot recommend this formulation for use.

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.

Advances in exotic mammal clinical therapeutics

It is important that veterinarians treating exotic companion mammals stay abreast of the latest developments relating to medications and drug delivery approaches for safety, efficacy and welfare issues. Sustained release formulations of commonly used drugs as well as newer routes for administration of therapeutic agents allow the veterinarian treating exotic companion mammals to reduce the stress associated with drug administration. Interactions can occur between vehicle and drugs when formulations are compounded, therefore research studies are warranted regarding potential problems associated with these formulations.

Subcutaneous Implants of Buprenorphine-Cholesterol-Triglyceride Powder in Mice

Subcutaneous drug implants are convenient systems for the long-term delivery of drugs in animals. Lipid carriers are logical tools because they generally allow for higher doses and low toxicity. The present study used an US Food and Drug Administration Target Animal Safety test system to evaluate the safety of a subcutaneous implant of a cholesterol-triglyceride-buprenorphine powder in 120 BALB/c mice. Mice were evaluated in 4- and 12-day trials with 1- and 5-fold doses of the intended 3 mg/kg dose of drug. One male mouse treated with three 3 mg/kg doses and surgery on days 0, 4, and 8 died on day 9. The cause of death was not determined. In the surviving 119 mice there was no evidence of skin reaction at the site of the implant. Compared to control animals treated with saline, weight measurements, clinical pathology, histopathology, and clinical observations were unremarkable. These results demonstrate that the lipid carrier is substantially safe. Cholesterol-triglyceride-drug powders may provide a valuable research tool for studies of analgesic and inflammatory drug implants in veterinary medicine.

Safety studies of post-surgical buprenorphine therapy for mice

The use of appropriate analgesia in laboratory mice may be suboptimal because of concerns about adverse events (AE). Target Animal Safety trials were conducted to determine the safety of an extended-release suspension of buprenorphine. Drug or control suspensions were injected subcutaneously in surgically-treated BALB/c mice anesthetized with ketamine-xylazine to mimic post-operative conditions in which the compound might commonly be administered. Single and repeat five-fold (5×) excesses of the 3.25 mg/kg intended dose were used to provoke potential AE. Trials included prospective measurements of weight changes, blood chemistry, hematology, and histopathology. Clinical and histopathology findings were similar in drug-treated and control mice in a four-day trial using a single 16.25 mg/kg, 5× overdose of the drug. In a 12-day trial, which used a total buprenorphine dose of 48.75 mg/kg, clinical and histopathology values were also similar in control and drug-treated female mice. In the male arm of the repeat-overdose trial, two of eight mice died on the morning of day 12, three days following the third 16.25 mg/kg overdose administration. Histopathology did not reveal a cause of death. In a 14-month trial using a single 3.25 mg/kg dose of the drug, no significant findings identified potential AE. These findings indicate a high tolerance to an extended-release buprenorphine suspension administered post-operatively in mice with appropriate husbandry.

The applicability of a gel delivery system for self-administration of buprenorphine to laboratory mice

Oral administration of perioperative analgesia to laboratory mice is beneficial compared with administration by injection. The mice become less stressed when allowed to voluntarily ingest the drug in a palatable feed item and it results in high and long-lasting serum concentrations of the drug. We have previously demonstrated sticky nut and chocolate paste to be well-liked by mice and readily ingested in most cases. However, a disadvantage with nut and chocolate paste is its high content of fat and sugar, which may have undesirable effects in some experimental models. Alternatively, a delivery system using an aqueous gel may serve as a supplementary source of fluid post-operatively and as a vehicle for analgesic drugs. In the present study, we investigated the willingness of the mice to ingest a commercially available gel, by measuring the duration from introduction of the gel to first ingestion, as well as the amount ingested overnight. Furthermore, buprenorphine in two different concentrations (5 and 15 µg/mL) was mixed in the gel and the resulting serum concentrations of buprenorphine were investigated. The aqueous gel was ingested by the mice, but their willingness was low and did not increase over time. The serum concentrations of buprenorphine were similar to, or higher than, those following a subcutaneous injection (0.1 mg/kg body weight), but the variation was considerably higher. In conclusion, aqueous gel may serve as a relevant vehicle for the voluntary ingestion of buprenorphine in mice, but the willingness of the mice to ingest the gel needs to be improved.

Safety and efficacy of buprenorphine for analgesia in laboratory mice and rats

Buprenorphine is a long-acting opiate with a high therapeutic index. The authors review the pharmacology, toxicity, analgesic effects and delivery of buprenorphine for use in laboratory mice and rats. Buprenorphine-based analgesic therapy has a substantial record of safety, and there is growing evidence of its effectiveness for treating post-operative pain. Nonetheless, more research is needed to determine optimal delivery systems and analgesic regimens for pain therapy in laboratory animals.

New developments and opportunities in oral mucosal drug delivery for local and systemic disease

The oral mucosa's accessibility, excellent blood supply, by-pass of hepatic first-pass metabolism, rapid repair and permeability profile make it an attractive site for local and systemic drug delivery. Technological advances in mucoadhesives, sustained drug release, permeability enhancers and drug delivery vectors are increasing the efficient delivery of drugs to treat oral and systemic diseases. When treating oral diseases, these advances result in enhanced therapeutic efficacy, reduced drug wastage and the prospect of using biological agents such as genes, peptides and antibodies. These technologies are also increasing the repertoire of drugs that can be delivered across the oral mucosa to treat systemic diseases. Trans-mucosal delivery is now a favoured route for non-parenteral administration of emergency drugs and agents where a rapid onset of action is required. Furthermore, advances in drug delivery technology are bringing forward the likelihood of transmucosal systemic delivery of biological agents.

Modulation of CNS pain circuitry by intravenous and sublingual doses of buprenorphine

Buprenorphine (BUP) is a partial agonist at μ-, δ- and ORL1 (opioid receptor-like)/nociceptin receptors and antagonist at the κ-opioid receptor site. BUP is known to have both analgesic as well as antihyperalgesic effects via its central activity, and is used in the treatment of moderate to severe chronic pain conditions. Recently, it was shown that intravenous (IV) administration of 0.2mg/70 kg BUP modulates the blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) response to acute noxious stimuli in healthy human subjects. The present study extends these observations by investigating the effects of BUP dose and route of administration on central nervous system (CNS) pain circuitry. Specifically, the modulation of evoked pain BOLD responses and resting state functional connectivity was measured following IV (0.1 and 0.2mg/70 kg) and sublingual (SL) (2mg) BUP administration in healthy human subjects. While 0.1mg/70 kg IV BUP is sub-analgesic, both 0.2mg/70 kg IV BUP and 2.0mg SL BUP are analgesic doses of the drug. Evoked BOLD responses were clearly modulated in a dose-dependent manner. The analgesic doses of BUP by both routes of administration yielded a potentiation in limbic/mesolimbic circuitry and attenuation in sensorimotor/sensory-discriminative circuitry. In addition, robust decreases in functional connectivity between the putamen and the sensorimotor/sensory-discriminative structures were observed at the two analgesic doses subsequent to measuring the maximum plasma BUP concentrations (C(max)). The decreases in functional connectivity within the sensorimotor/sensory-discriminative circuitry were also observed to be dose-dependent in the IV administration cohorts. These reproducible and consistent functional CNS measures at clinically effective doses of BUP demonstrate the potential of evoked pain fMRI and resting-state functional connectivity as objective tools that can inform the process of dose selection. Such methods may be useful during early clinical phase evaluation of potential analgesics in drug development.

Skin permeation of buprenorphine and its ester prodrugs from lipid nanoparticles: lipid emulsion, nanostructured lipid carriers and solid lipid nanoparticles

The aim of this study was to develop and characterize lipid nanoparticle systems for the transdermal delivery of buprenorphine and its prodrugs. A panel of three buprenorphine prodrugs with ester chains of various lengths was synthesized and characterized by solubility, capacity factor (log K'), partitioning between lipids and water and the ability to penetrate nude mouse skin. Colloidal systems made of squalene (lipid emulsion, LE), squalene + Precirol (nanostructured lipid carriers, NLC) and Precirol (solid lipid nanoparticles, SLN) as the lipid core material were prepared. Differential scanning calorimetry showed that the SLN had a more-ordered crystalline lattice in the inner matrix compared to the NLC. The particle size ranged from 220-300 nm, with NLC showing the smallest size. All prodrugs were highly lipophilic and chemically stable, but enzymatically unstable in skin homogenate and plasma. The in vitro permeation results exhibited a lower skin delivery of drug/prodrug with an increase in the alkyl chain length. SLN produced the highest drug/prodrug permeation, followed by the NLC and LE. A small inter-subject variation was also observed with SLN carriers. SLN with soybean phosphatidylcholine (SLN-PC) as the lipophilic emulsifier showed a higher drug/prodrug delivery across the skin compared to SLN with Myverol, a palmitinic acid monoglyceride. The in vitro permeation of the prodrugs occurred in a sustained manner for SLN-PC. The skin permeation of buprenorphine could be adjusted within a wide range by combining a prodrug strategy and lipid nanoparticles.

Transdermal buprenorphine - a critical appraisal of its role in pain management

This paper reviews the current clinical data for the role of transdermal buprenorphine (BUP TDS) in the treatment of diverse acute and chronic pain syndromes. Literature searches were carried out using PubMed (1988 to June 2009). The published findings seem to support hypotheses regarding the rather unique analgesic mechanisms of buprenorphine as compared with pure μ-opioids like morphine and fentanyl. However, the exact mechanism of this analgesic efficacy still remains largely unknown despite recent advances in preclinical pharmacological studies. Such assessments have demonstrated the sustained antihyperalgesic effect of buprenorphine in diverse animal pain models. These findings are supported in a growing number of clinical studies of oral, intrathecal, intravenous, and Bup TDS. This review paper focuses almost entirely on the clinical experience concerning the transdermal administration of buprenorphine, although preclinical aspects are also addressed in order to provide a complete picture of the unique pharmacological properties of this analgesic drug. Mounting evidence indicates the appropriateness of Bup TDS in the treatment of diverse acute and chronic pain syndromes which have been less or not responsive to other opioids. Additionally, BUP TDS seems to hold great promise for other difficult-to-treat (pain) conditions, such as patients in the intensive care setting. However, its use is somewhat tempered by the occurrence of local skin reactions which have been shown to be often therapy resistant. Further studies are certainly warranted to identify even more precisely the clinical syndromes that are most sensitive to buprenorphine treatment, and to compare buprenorphine to other opioids in head-to-head trials of acute and chronic pain conditions.