In vitro and in vivo studies of subcutaneous hydromorphone implants designed for the treatment of cancer pain

Injectable peptide hydrogels for controlled-release of opioids

Peptide-based hydrogels as a drug carrier system for the subcutaneous administration of morphine.

Experimental Pharmacodynamics and Analgesic Efficacy of Liposome-Encapsulated Hydromorphone in Dogs

The purpose of this study was to determine the experimental side effects of liposome-encapsulated hydromorphone (LE-Hydro) in beagles and to evaluate LE-Hydro analgesia in dogs undergoing ovariohysterectomies (OVH). Beagles were injected subcutaneously with 1–3 mg/kg LE-Hydro or 0.1 mg/kg hydromorphone. Dogs were evaluated for sedation, temperature, respiratory rate, and heart rate. OVH dogs were injected with 2 mg/kg LE-Hydro subcutaneously or 0.2 mg/kg morphine and 0.05 mg/kg acepromazine intramuscularly. Side effects of LE-Hydro were within clinically acceptable limits. The analgesic efficacy was superior in dogs administered LE-Hydro at 12 hr postsurgically. LE-Hydro provided adequate, durable analgesia in dogs undergoing OVH.

A new extended release formulation (OROS) of hydromorphone in the management of pain

Opioid analgesics are essential in the treatment of moderate to severe cancer-related pain. Opioids are also recognized as important in the management of other severe, persistent refractory painful conditions, such as sickle cell disease and arthritis. In the clinical practice of pain management, stable opioid dosing generally depends on achieving maximal analgesia with tolerable side effects typical of opioid analgesics. There is a wide interindividual variability of responsiveness to exogenous opioids both in terms of analgesic efficacy and side effects. Optimizing pain management for the individual patient may require sequential trials of opioid medications until the regimen with the most favorable therapeutic ratio of efficacy to side effects is determined.

Polymer-based biodegradable drug delivery systems in pain management

Pain is an unpleasant sensory experience commonly produced by damage to bodily tissues and it is one of the most significant public health problems, because 21.5% of the world population is estimated to suffer from pain. It results in a total loss of more than 165 billion US dollars each year in the United States alone. Pain reflects a mixture of various pathophysiologic, psychologic, and genetic contributions. When undertreated, pain usually results in serious immune and metabolic upset. Therefore, it requires wide understanding and intensive effort for a better management. Currently, pain control is limited by the modest efficiency of the used drugs, the serious side effects of these drugs, and the inefficacy of conventional drug administration. By the introduction of the technology of biodegradable controlled-release devices into clinical practice, pain control not only benefits from these novel methods for a better delivery of various drugs, but the side effects of the drugs are reduced because use of the devices improves patient compliance. Biodegradable controlled-release devices are polymer-based devices that are designed to deliver drugs locally in a predesigned manner. Recently, there was a high interest in developing these devices for the delivery of different drugs used for pain control. This paper first highlights the dimensions and basics of the problem of pain. Then, it presents an overview of the biodegradable polymers that are used in drug delivery systems and summarizes the studies carried out on these systems in the field of pain management. We refer to our experience in developing a device for multimodal drug delivery, including the use of nanotechnology. Future perspectives are also presented.

Continuous dopaminergic stimulation reduces risk of motor complications in parkinsonian primates

Levodopa or short-acting dopamine (DA) agonist treatment of advanced parkinsonian patients exposes striatal DA receptors to non-physiologic intermittent stimulation that contributes to the development of dyskinesias and other motor complications. To determine whether continuous dopaminergic stimulation can delay or prevent onset of motor complications, four MPTP-lesioned, levodopa-naive cynomolgus monkeys were implanted subcutaneously with apomorphine containing ethylene vinyl acetate rods. Three other MPTP-lesioned monkeys received daily injections of apomorphine. Animals receiving apomorphine rods showed improved motor function ('ON' state) within 1 day of implantation, and remained continually 'ON' for the duration of treatment (up to 6 months) without developing dyskinesias. Injected animals also showed similar improvement in motor function after each apomorphine injection. However, these primates remained 'ON' for only 90 min and within 7-10 days all developed severe dyskinesias. Implanted monkeys evidenced local irritation, which was alleviated by steroid co-therapy.

In vivo pain relief effectiveness of an analgesic-anesthetic carrying biodegradable controlled release rod systems

Pain is the most common and feared symptom for patients, especially those with cancer. Treatment of chronic pain with conventional ways of medication usually fails with increasing severity of the pain. New approaches enabling the prolonged provision of pain relievers are required. We designed a controlled release system of pain relievers, mainly for opioids (morphine, M, codeine, C, and hydromorphone, HM), and a local anesthetic (bupivacaine, BP) in the form of poly(L-lactide-co-glycolide) (PLGA) rods. The efficacy of these rods implanted alone or in combination in relieving chronic pain in rats caused by the ligation of the sciatic nerve of their right hind limbs was studied. The two most common tests for measuring analgesia, i.e. tail-flick tests, that show analgesia at sites other than the site of injury, were used to study the degree of systemic distribution of the drugs and paw-withdrawal tests were used to study the analgesia at the site of injury. Alleviation of this chronic and severe neuropathic pain could be obtained for about 3-4 days when rods for two drugs, 'dual drug' (analgesic-anesthetic), were used. This duration is decreased by half (2 days) with the single-drug rods. Also the dual-drug rods, though at half the dose of each single drug application, enhanced the degree of analgesia of the first day. These in vivo results are also consistent with the previous in vitro results as in the case with codeine which had a higher first-day analgesia than morphine, despite a lower potency due to the faster in vitro release rate. Similarly, slower release of hydromorphone from PLGA (85:15) rods resulted in less systemic analgesia than the more rapidly eroding PLGA (50:50) rods of the same drug.

Effects of cocaine in rats exposed to heroin

We investigated whether chronic exposure to heroin alters responses to cocaine in ways that might explain the use of cocaine by opioid addicts. To this end, the effects of cocaine (5 and 20 mg/kg) were assessed on locomotor activity of rats chronically exposed to heroin (0.0, 3.5, 7.0, and 14.0 mg/kg/day, over 14 days, via osmotic mini-pumps), or withdrawn from heroin (1 day, acute withdrawal, and 14 days, protracted withdrawal). Chronic heroin exposure, in itself, dose dependently increased locomotion and acute cocaine administration further elevated locomotor activity in a dose-dependent and additive manner. During acute withdrawal, there was a dose-dependent decrease in locomotion that was reversed by cocaine in a dose-dependent manner. During protracted withdrawal, spontaneous locomotion normalized, but rats previously exposed to heroin displayed cross-sensitization to cocaine as indicated by small, but significant, enhanced locomotor response to 5 mg/kg of cocaine, and enhanced intravenous self-administration of low doses of cocaine (0.13 mg/kg/infusion). In a separate study, we measured extracellular dopamine (DA) in the nucleus accumbens (Acb) using in vivo microdialysis before and after acute withdrawal from heroin. During chronic exposure to heroin, basal extracellular DA was elevated dose dependently, whereas in acute withdrawal, levels were not different from those in vehicle-treated rats. In response to cocaine, however, DA activity in the Acb was significantly lower in rats withdrawn from the highest dose of heroin.

Antihyperalgesic effect of simultaneously released hydromorphone and bupivacaine from polymer fibers in the rat chronic constriction injury model

We aimed to evaluate the antihyperalgesic efficacy of a combination of hydromorphone (HM) and bupivacaine (BP) delivered via controlled release from a biodegradable cylindrical rod. In vivo studies were performed using a rat model of thermal hyperalgesia induced by chronic constriction injury (CCI) of the sciatic nerve with loose ligatures. Poly(lactic-co-glycolic acid) (PLGA) rods (10 mm length, 1 mm diameter) loaded with HM (5 mg per rod), BP (5 mg per rod) or no drug (placebo) were implanted subcutaneously, in single or dual pairs, adjacent to the constriction injury, immediately after nerve ligation. We evaluated the efficacy of two dose levels for each drug, alone or in combination, in attenuating thermal hyperesthesia over a period of 12 days according to a prevention protocol. Plasma levels of drugs released from the rods and also released in an in vitro simulation were evaluated. In vitro studies demonstrated that drug release is maintained for at least 10 days. HM (5 mg) alone and BP (5 mg) alone did not attenuate hyperalgesia. Their combination provided a significant increase in the paw withdrawal latency as compared to single agents or placebo. When the dose in each group was doubled, implanting four rods, significant attenuation of hyperalgesia was observed. Analyses of rods retrieved after termination of experiments (after 12 days) revealed 30% residual HM and 70% residual BP content. Prolonged delivery of HM and BP alone or in combination via locally applied PLGA rods may offer a feasible alternative to provide long-lasting analgesia.

Tramadol encapsulated into polyhydroxybutyrate microspheres: in vitro release and epidural analgesic effect in rats

BACKGROUND

Controlled release techniques are used to increase the duration of action and decrease the toxicity of drugs. Any controlled release form of tramadol in spinal or epidural blocks has not been studied previously. Tramadol was encapsulated into polyhydroxybutyrate (PHB) microspheres and release kinetics was studied. The epidural analgesic effect of this solution in rats was also compared with free tramadol.

METHODS

Controlled release of tramadol from PHB microspheres into 10 ml of phosphate buffer solution at pH 7.4 and 37 degrees C was studied in vitro. In vivo studies were performed in 40 rats. Epidural catheters were placed during general anaesthesia. Rats were randomly allocated into one of the four study groups to receive normal saline, 4 mg of tramadol, PHB microspheres without tramadol, or 4 mg of tramadol encapsulated into PHB microspheres. Analgesia was evaluated with tail flick tests performed at 52.5 +/- 0.5 degrees C before injection and at intervals up to 30 h after injection. Catalepsy and loss of corneal reflexes were considered as signs of supraspinal toxicity.

RESULTS

In vitro drug release was observed for more than 6 days. Epidural analgesic effects of tramadol released from PHB microspheres were observed for 21 h, whereas an equal dose of free tramadol was effective for less than 5 h. No signs of toxicity were observed.

CONCLUSION

Controlled release of tramadol from PHB microspheres is possible, and pain relief during epidural analgesia is prolonged by this drug formulation compared with free tramadol.

Antinociceptive effects of hydromorphone, bupivacaine and biphalin released from PLGA polymer after intrathecal implantation in rats

Intraspinal drug delivery, based on the concept of controlling pain by delivering drug to a nociceptive target rich in opioid and other relevant receptors is increasingly used clinically. The therapeutic ratio for opioids or other centrally acting agents is potentially greater if they are administered intrathecally (i.t.) than outside the central nervous system (CNS). The present study was designed with the ultimate goal of formulating a controlled release system for intrathecal analgesia characterized by effectiveness, rapid onset and few side effects for chronic pain control. A biodegradable copolymer poly(L-lactide-co-glycolide) (PLGA) was used to prepare a rod-shaped drug delivery system containing hydromorphone (HM), bupivacaine (BP), both HM and BP, or biphalin (BI). In vitro drug release kinetics of these systems showed a zero-order release rate for HM and BP from PLGA (85:15) rods. Drug-loaded rods were implanted i.t. Control groups received only placebo implants. Measurement of analgesic efficacy was carried out with tail flick and paw-withdrawal tests. In vivo studies showed potent, prolonged analgesia in comparison to controls for all active treatments. Analgesic synergy was observed with HM and BP. With further refinements of drug release rate, these rods may offer a clinically relevant alternative for intrathecal analgesia.

Managing chronic arthritis

Many compounds are being investigated for the control of symptoms of osteoarthritis in people and animals. Ideally, treatment should include analgesia, inflammation control, and chondroprotection. With further progress in this area, combination therapies tailored to the needs of the individual animal should enable us to maximize efficacy and minimize side effects. Only a few of the newer therapies and pharmaceutic agents have been investigated in the horse, however. With more rigorous investigation, they may be determined to be ineffective or unsafe. Meanwhile, as much information should be gathered from manufacturers as possible so as to ensure that appropriate recommendations are made.

Developing Techniques and Strategies for the Management of Cancer Pain

The past 20 years have seen a great surge of interest in understanding and treating pain. The introduction of sustained-release opioid delivery systems has tremendously advanced our ability to provide improved pain control. Parenteral opioid delivery systems, although available in many developed nations, remain expensive and cumbersome. New advances in parenteral sustained-release systems are currently in development. These advances include liposomal opioid preparations for intrathecal use, transcutaneous patient-controlled delivery, and implantable diffusion reservoirs. Even more exciting are new developments in tissue engineering that may allow the transplantation of human or animal cells, capable of producing natural analgesic substances, into the vicinity of the spinal cord.

Adjunctive analgesic therapy

Adjuvant analgesics are drugs that have weak or nonexistent analgesic action when administered alone but can enhance analgesic actions when coadministered with known analgesic agents. Such agents are often administered in cases of refractory pain. For some chronic pain syndromes, however, they may constitute a first-line approach. Because pain is such an individual experience, analgesic regimens may require several drugs at varying dosages to confer a comfortable state. Adjunctive therapies such as the tricyclic antidepressants, anticonvulsants, N-methyl-D-aspartic acid receptor antagonists and low-dose intravenous local anesthetics, to name a few, have proved to be efficacious in relieving certain types of pain, especially neuropathic and cancer pain. Their use in animals is increasing, with anecdotal reports of some success.

Novel Drug Delivery Systems

Interest in pain management is growing, with the emerging demand by our patients and colleagues, for pain relief. To meet that need, pharmaceutical and medical technology companies have provided the medical field with a variety of choices and options to deliver medication for pain control. Examination and review of the present systemic options are introduced. A more detailed look at the intrathecal route is necessary because of the tremendous potential for receptor-targeted drug delivery. The ability to treat nociceptive and neuropathic pain with drug-specific therapy makes this system all the more exciting. Because of this future, a wealth of new and old drugs are being found or reexamined for their use.

Therapeutic applications of implantable drug delivery systems

In the past, drugs were frequently administered orally, as liquids or in powder forms. To avoid problems incurred through the utilization of the oral route of drug administration, new dosage forms containing the drug(s) were introduced. As time progressed, there was a need for delivery systems that could maintain a steady release of drug to the specific site of action. Therefore, drug delivery systems were developed to optimize the therapeutic properties of drug products and render them more safe, effective, and reliable. Implantable drug delivery systems (IDDS) are an example of such systems available for therapeutic use. The application of currently available implantable drug delivery systems is the main focus of this review. IDDS can be classified into three major categories: biodegradable or nonbiodegradable implants, implantable pump systems, and the newest atypical class of implants. Biodegradable and nonbiodegradable implants are available as monolithic systems or reservoir systems. The release kinetics of drugs from such systems depend on both the solubility and diffusion coefficient of the drug in the polymer, the drug load, as well as the in vivo degradation rate of the polymer, especially, in the case of the biodegradable systems. Controlled release of drug from the implantable pump is generally achieved utilizing the microtechnology of electronic systems and remote-controlled flow rate manipulation through the maintenance of a constant pressure difference. The third atypical class includes those which have been recently developed such as ceramic hydroxyapatite antibiotic systems used in the treatment of bone infections, intraocular implants for the treatment of glaucoma, and transurethral implants utilized in the treatment of impotence. The major advantages of these systems include targeted local delivery of drugs at a constant rate, less drug required to treat the disease state, minimization of possible side effects, and enhanced efficacy of treatment. Also, these forms of delivery systems are capable of protecting drugs which are unstable in vivo and that would normally require a frequent dosing intervals. Due to the development of such sustained release formulations, it is now possible to administer unstable drugs once a week to once a year that in the past required frequent daily dosing. Preliminary studies using these systems have shown superior effectiveness over conventional methods of treatment. However, one limitation of these newly developed drug delivery systems is the fact that their cost-to-benefit ratio (cost/benefit) is too high which restricts their use over conventional dosage forms. Hopefully, in the future, new implantable systems can be developed at a lower cost, thereby minimizing the cost-to-benefit ratio and therefore, be used extensively in standard therapeutic practice. Some of the most recently discovered implants are in the early developmental stages and more rigorous clinical testing is required prior to their use in standard practice.

Hydromorphone polymer implant. A potential alternative to methadone maintenance

Although methadone maintenance remains the best available treatment for opioid addiction, the need for daily oral dosing limits the effectiveness of methadone as opioid substitution therapy. Limitations of methadone maintenance include the administrative costs and burdensome time commitment associated with daily clinic visits, the danger of illicit diversion and accidental overdose associated with oral dosing, the low rate of treatment retention, and inadequate treatment capacity. A new opioid delivery device awaiting approval for clinical use may overcome some of these limitations. The device, a button-size polymer containing hydromorphone, releases near constant levels of opioid when implanted subcutaneously. Because of its location and duration of effect, the polymer may eliminate the need for daily clinic visits, reduce the costs and time constraints of treatment, reduce the risk of illicit diversion, provide an incentive for compliance with initial methadone maintenance treatment, and increase treatment capacity and retention.