Baclofen as an adjuvant analgesic

The effects of GABA(B) agonists and gabapentin on mechanical hyperalgesia in models of neuropathic and inflammatory pain in the rat

We have examined the effects of a novel GABA(B) agonist, CGP35024, in models of chronic neuropathic (partial sciatic ligation) and inflammatory (Freund's complete adjuvant) pain in the rat, and its inhibitory action on spinal transmission in vitro. The effects of CGP35024 were compared with L-baclofen and gabapentin. CGP35024 and L-baclofen reversed neuropathic mechanical hyperalgesia following single subcutaneous or intrathecal administration, but did not affect inflammatory mechanical hyperalgesia. Gabapentin only moderately affected neuropathic hyperalgesia following a single administration by either route, but produced significant reversal following daily administration for 5 days. It was only weakly active against inflammatory hyperalgesia following single or repeated administration. The antihyperalgesic effects of L-baclofen and CGP35024, but not gabapentin, were blocked by the selective GABA(B) receptor antagonist CGP56433A. CGP35024 was seven times more potent against neuropathic hyperalgesia than in the rotarod test for motor co-ordination, whilst L-baclofen was approximately equipotent in the two tests. In the isolated hemisected spinal cord from the rat, CGP35024, L-baclofen and gabapentin all inhibited capsaicin-evoked ventral root potentials (VRPs). CGP35024 and L-baclofen, but not gabapentin, also inhibited the polysynaptic and monosynaptic phases of electrically-evoked VRPs, as well as the 'wind-up' response to repetitive stimulation. These data indicate that CGP35024 and L-baclofen modulate nociceptive transmission in the spinal cord to inhibit neuropathic hyperalgesia, and that CGP35024 has a therapeutic window for antihyperalgesia over spasmolysis.

Symptom control in hospice--state of the art

There are a myriad of physical symptoms which can complicate the care of patients with advanced disease. Without knowledge of and attention to these distressing symptoms, the rest of the work of the interdisciplinary hospice team is greatly hampered. In this article, we review the management of ten prevalent symptoms in hospice care and to identify areas of clinical investigation underway and point of future areas ripe for investigation.

Trigeminal neuralgia: opportunities for research and treatment

Trigeminal neuralgia was the focus of a recent workshop convened by the National Institute of Neurological Disorders and Stroke (NINDS) and the National Institute of Dental and Craniofacial Research (NIDCR). The workshop brought together basic scientists, clinicians, epidemiologists, and patient advocates. New research directions for epidemiology, diagnosis and assessment, pain mechanisms, and treatment were identified. (The workshop was held in Rockville MD on September 14, 1999, with financial support from NINDS, NIDCR, the NIH Office of Rare Diseases, and the NIH Pain Research Consortium.)

Role of arginine in immunonutrition

Arginine plays an important role in many physiologic and biologic processes beyond its role as a protein-incorporated amino acid. Dietary supplementation of arginine can enhance wound healing, regulate endocrine activity and potentiate immune activity. Under normal unstressed conditions the arginine requirement of adult humans is fulfilled by endogenous sources, however this is compromised during times of stress, especially in critical illness. These finding have led to use of arginine supplementation as part of an immune-enhancing dietary regimen to help combat the immune suppression seen in such patients. Though the results from studies examining the use of this type of immunonutrition in critically ill patients are far from definitive, they are promising that this mode of therapy may be of some advantage. A better understanding of the in vivo biology of arginine and its metabolism is necessary to truly define a benefit from arginine supplementation.

Transplants of neuronal cells bioengineered to synthesize GABA alleviate chronic neuropathic pain

The use of cell lines utilized as biologic "minipumps" to provide antinociceptive molecules, such as GABA, in animal models of pain is a newly developing area in transplantation biology. The neuronal cell line, RN33B, derived from E13 brain stem raphe and immortalized with the SV40 temperature-sensitive allele of large T antigen (tsTag), was transfected with rat GAD67 cDNA (glutamate decarboxylase, the synthetic enzyme for GABA), and the GABAergic cell line, 33G10.17, was isolated. The 33G10.17 cells transfected with the GAD67 gene expressed GAD67 protein and synthesized low levels of GABA at permissive temperature (33 degrees C), when the cells were proliferating, and increased GAD67 and GABA during differentiation at nonpermissive temperature (39 degrees C) in vitro, because GAD67 protein expression was upregulated with differentiation. A control cell line, 33V1, transfected with the vector alone, contained no GAD67 or GABA at either temperature. These cell lines were used as grafts in a model of chronic neuropathic pain induced by unilateral chronic constriction injury (CCI) of the sciatic nerve. Pain-related behaviors, including cold and tactile allodynia and thermal and tactile hyperalgesia, were evaluated after CCI in the affected hind paw. When 33G10.17 and 33V1 cells were transplanted in the lumbar subarachnoid space of the spinal cord 1 week after CCI, they survived greater than 7 weeks on the pia mater around the spinal cord. Furthermore, the tactile and cold allodynia and tactile and thermal hyperalgesia induced by CCI was significantly reduced during the 2-7-week period after grafts of 33G10.17 cells. The maximal effect on chronic pain behaviors with the GABAergic grafts occurred 2-3 weeks after transplantation. Transplants of 33V1 control cells had no effect on the allodynia and hyperalgesia induced by CCI. These data suggest that a chronically applied, low local dose of GABA presumably supplied by transplanted cells near the spinal dorsal horn was able to reverse the development of chronic neuropathic pain following CCI. The use of neural cell lines that are able to deliver inhibitory neurotransmitters, such as GABA, in a model of chronic pain offers a novel approach to pain management.

Changes in GAD- and GABA- immunoreactivity in the spinal dorsal horn after peripheral nerve injury and promotion of recovery by lumbar transplant of immortalized serotonergic precursors

We have utilized RN46A cells, an immortalized neuronal cell line derived from E13 brainstem raphe, as a model for transplant of bioengineered serotonergic cells. RN46A cells require brain-derived neurotrophic factor (BDNF) for increased survival and serotonin (5HT) synthesis in vitro and in vivo. RN46A cells were transfected with the rat BDNF gene, and the 46A-B14 cell line was subcloned. These cells survive longer than 7 weeks after transplantation into the subarachnoid space of the lumbar spinal cord and synthesize 5HT and BDNF. Chronic constriction injury (CCI) of the sciatic nerve was used to induce chronic neuropathic pain in the affected hindpaw in rats. Transplants of 46A-B14 cells placed 1 week after CCI alleviated chronic neuropathic pain, while transplants of 46A-V1 control cells, negative for 5HT and without the BDNF gene, had no effect on the induction of thermal and tactile nociception. When endogenous cells of the dorsal horn which contain the neurotransmitter gamma-aminobutyric acid (GABA) and its synthetic enzyme glutamate decarboxylase (GAD) were immunohistochemically quantified in the lumbar spinal cord 3 days and 1-8 weeks after CCI, the number of GABA- and GAD-immunoreactive (ir) cells decreased bilateral to the nerve injury as soon as 3 days after CCI. At 1 week after CCI, the number of GABA-ir cells continued to significantly decline bilaterally, returning to near normal numbers on the side contralateral to the nerve injury by 8 weeks after the nerve injury. The number of GAD-ir cells began to increase bilaterally to the nerve injury at 1 week after CCI and continued to significantly increase in numbers over normal values by 8 weeks after the nerve injury. When examined 2 and 8 weeks after CCI plus cell transplants, the transplants of 46A-B14 cells reversed the increase in GAD-ir cell numbers and the decrease in GABA-ir cells by 1 week after transplantation, while 46A-V1 control cell transplants after CCI had no effect on the changes in numbers of GAD-ir or GABA-ir cells. Collectively, these data suggest that altered 5HT levels, and perhaps BDNF secretion, related to the transplants ameliorate chronic pain and reverse the induction and maintenance of an endogenous pain mechanism in the dorsal horn. This induction mechanism is likely dependent on altered GAD regulation and GABA synthesis, initiated by CCI.

Trigeminal neuralgia : a guide to drug choice

Trigeminal neuralgia, also known as tic douloureux, is an idiopathic condition of severe, unilateral, paroxysmal facial pain. The abrupt nature of the painful attacks (a temporal profile that is similar to that of seizures) led to the discovery that some anticonvulsant drugs are effective against neuralgia.Carbamazepine is the drug of choice, and treatment requires careful dosage titration. Baclofen, phenytoin and sodium valproate are also effective. Transient relief is sometimes possible with local anaesthetics. Limited data suggest that topical capsaicin, and tizanidine, lamotrigine, oxcarbazepine, pyridostigmine and enalapril have helped some patients. While effective, other drugs are limited by their adverse effects; for example, clonazepam is too sedating, pimozide induces extrapyramidal adverse effects, and tocainide and felbamate can cause aplastic anaemia. Phenobarbital (phenobarbitone), opioids, mexiletine, tricyclic antidepressants, corticosteroids, nonsteroidal anti-inflammatory drugs and sympatholytics are ineffective.The antineuralgic effect of any drug may eventually wear off. If this occurs, combination therapy can restore pain relief, as can the reintroduction of a previously effective drug following a drug-free interval.Similar pharmacological strategies potentially apply to other paroxysmal pain syndromes such as vagoglossopharyngeal neuralgia. Clinical overlap with multiple sclerosis or cluster headache suggests additional drugs that may be useful in specific patients. Effective neurosurgical procedures exist for patients with trigeminal neuralgia that is refractory to medications.

Innovations in pharmacologic therapies

OBJECTIVES

To describe the mechanism of action of four new neurotransmitters that may play a role in pain modulation and to review the clinical implications of these new classes of analgesics.

DATA SOURCES

Research studies, proceedings, abstracts, and book chapters pertaining to new pharmacologic therapies for pain relief.

CONCLUSIONS

Recent advances in our understanding of neurotransmitter and receptor physiology have provided new directions for the development and testing of analgesic compounds. NMDA antagonists and calcium channel blockers warrant investigations in humans. Additional human studies are needed of alpha 2 adrenergic agonists and GABA agonists.

IMPLICATIONS FOR NURSING PRACTICE

Knowledge of new novel classes of analgesics is important as further investigative studies will take place to determine which types of pain problems are most effectively treated by these classes of drugs.

[Review of current pharmacologic treatment of pain]

Pain is the main reason prompting patients to consult their physicians. In acute conditions, pain has a very particular significance as a warning sign, enabling the physician to attempt a diagnosis. Nevertheless, its detrimental effect upon the individual (even in the case of acute pain) and its cost to society are now widely acknowledged. There can be no doubt about the physical component of pain, but the psychological and social aspects should not be ignored, particularly in the case of chronic pain. There is no single therapeutic approach to pain and, more often than not, successful treatment comprises a combination of several. Pharmacological treatments are undeniably the most common approach. In clinical practice, recent advances have been based upon an improved understanding of 'old' substances such as morphine and, at the same time, research continues in the hope of finding the 'ideal' analgesic-effective in most situations but without adverse effects: this appears to be a somewhat utopian arm at present, considering the number of different causes of pain. An improved understanding of the physiological mechanisms of pain has led, within the field of clinical practice, to several methods of differentiating pain. These depend on whether or not pain responds to morphine, or on the type of pain: pain due to an excess of nociception, pain resulting from deafferentation (caused by damage to nerve pathways) in the central or peripheral nervous system and psychogenic (idiopathic) pain. Likewise, there are several different ways of classifying analgesic treatments: according to the intensity of pain, as with use of the WHO ladder (which is based on the notion of steps) for the treatment of cancer pain; according to the presumed physiopathological mechanism and, in particular, the response to morphine, and according to the presumed central or peripheral mechanism of the drugs. In reality, peripherally acting drugs can also have a central mechanism of action, just as drugs known to have a central mechanism of action can also have peripheral activity. As a result, several therapeutic classes have been identified. Firstly NSAIDs, which act by inhibiting the enzymes that synthesise prostaglandins, cyclooxygenases (COX-1, COX-2), but which also act upon lipo-oxygenases: Their efficacy is interesting, although somewhat limited by both their ceiling effect and the frequent adverse gastrointestinal reactions they produce. Specific inhibitors of COX-2 could well reduce the risk of adverse effects. Opioids constitute the first-line treatment for pain, particularly severe pain. There are several classifications for these drugs. Firstly, weak opioids (such as codeine) and strong opioids (such as morphine) are differentiated. Secondly, a distinction is made between pure agonists (such as morphine), partial agonists (such as buprenorphine), agonist-antagonists (such as nalbuphine) and antagonists (such as naloxone). Finally, agents are distinguished on the basis of their chemical structure (synthetic, semi-synthetic or natural derivatives). These molecules act upon different receptors (mu, delta, kappa, sigma) and, although peripheral mechanisms have been described, their activity occurs mainly at spinal and supraspinal levels. They provide a potent analgesic effect but are also responsible for various adverse effects-nausea, vomiting, sedation, constipation and respiratory depression-which seriously limit their use. As long as the indication is appropriate, these drugs should not be withheld because of fear of dependence or abuse. It has been observed that other adjuvant therapeutic approaches, generally used to treat conditions other than pain, provide pain relief in certain situations. These include corticosteroids, which are-widely used in rheumatology and oncology, and antidepressants, which are frequently used to treat chronic pain, especially that with a neuropathic component. Anti-epileptics are also used, particularly for excrutiating

Intrathecal clonidine and baclofen in the management of spasticity and neuropathic pain following spinal cord injury: a case study

Spasticity and pain are common disabling sequelae following spinal cord injury (SCI) and are often difficult to manage. The two problems are also not infrequently related. A variety of pharmacological and other approaches have been described for management of these problems in SCI. This case study reports a 32-year-old woman with an established incomplete C5 tetraplegia (anterior cord syndrome) who developed severe, intractable anal spasm following a hemorrhoidectomy, which persisted despite very good healing. This prevented evacuation of her bowels and resulted in severe rectal pain and episodes of autonomic dysreflexia. Attempts to modify the rate and mode of delivery of intrathecal baclofen through an existing programmable infusion pump failed to reduce anal sphincter spasm or improve symptoms. A right-sided pudendal block with lignocaine provided some relief. Clonidine was added to baclofen in the pump reservoir and both drugs were administered intrathecally in combination. This resulted in an immediate improvement in anal sphincter spasm and pain relief, allowing rapid reestablishment of her normal bowel pattern without need for any supplemental analgesia. It appears that intrathecal clonidine may have an important role in the treatment of spasticity, either as a single or an adjuvant agent, when intrathecal baclofen alone is ineffective or there is increasing tolerance to baclofen. Intrathecal clonidine may also prove useful in the management of intractable neuropathic pain.

Management of painful paraneoplastic syndromes

The majority of patients with advanced malignant disease experience pain, so pain is commonly present in patients with paraneoplastic syndromes. It is rare, however, that the pain itself is a paraneoplastic manifestation of cancer. Usually, the pain in this context is associated with a paraneoplastic syndrome but is not a direct result of that syndrome. Three syndromes in which pain is part of the syndrome and a paraneoplastic manifestation of malignant disease--neuropathy, ganglionitis, and monolitis--have been described in the literature. These syndromes and their management are discussed in this article.

The contribution of GABAB receptor-mediated events to inflammatory pain processing: carrageenan oedema and associated spinal c-Fos expression in the rat

In this pharmacological study we have assessed the effect of baclofen, a selective GABAB receptor agonist, on spinal expression of the immediate early gene c-Fos and the peripheral oedema evoked by a prolonged peripheral inflammation due to intraplantar carrageenan. Baclofen was administered intravenously 30 min before intraplantar injection of carrageenan in freely moving rats. Three hours after carrageenan the number of spinal c-Fos protein-like immunoreactive neurons and peripheral (ankle and paw) oedema were assessed. For the two series of experiments the total number of control carrageenan-evoked c-Fos protein-like immunoreactive neurons in segments L4-L5 of the spinal cord was 176 +/- 6 and 177 +/- 9 c-Fos protein-like immunoreactive neurons per section, for carrageenan control with intravenous and intraplantar saline, respectively. c-Fos protein-like immunoreactive neurons were predominantly located in laminae I-II and V-VI of the dorsal horn of the spinal cord in carrageenan controls receiving intravenous (68 +/- 3 and 69 +/- 2 c-Fos protein-like immunoreactive neurons, respectively) and intraplantar (62 +/- 4 and 71 +/- 5 c-Fos protein-like immunoreactive neurons, respectively) saline. Pre-administered systemic baclofen (0.05, 1.5 and 3 mg/kg i.v.) dose dependently reduced the total number of c-Fos protein-like immunoreactive neurons (81 +/- 3, 66 +/- 4 and 49 +/- 4% of control total number of c-Fos protein-like immunoreactive neurons, respectively), with strongest effects on the number of deep (74 +/- 3, 60 +/- 3 and 43 +/- 4% of control, respectively) as compared with superficial (90 +/- 4, 77 +/- 5 and 59 +/- 5% of control, respectively) c-Fos protein-like immunoreactive neurons. The effects of systemic baclofen on the carrageenan-induced spinal c-Fos expression and both the paw and ankle oedema were positively correlated (r = 0.479, P < 0.05 and r = 0.733, P < 0.001, respectively). Intraplantar baclofen (50 and 100 micrograms in 50 microliters of saline), simultaneously injected with intraplantar carrageenan, did not significantly influence carrageenan-evoked spinal c-Fos expression or ankle oedema. Despite the fact that the highest dose of intraplantar baclofen significantly reduced paw oedema (23 +/- 3% reduction of control paw oedema), our results are clearly in favour of a spinal site of action of systemic baclofen.

Management of chronic pain. Part I

Chronic pain is associated with substantial psychosocial and economic stress, coupled with functional loss and various levels of vocational dysfunction. The role of a pain center is to focus on chronic pain in a multidisciplinary, comprehensive manner, providing the patient with the most effective opportunity to manage his or her chronic disease syndrome. This article focuses on methods to manage many types of chronic pain and describes a broad range of pharmacologic and nonpharmacologic interventions and options available to the patient. Part I of this two-part monograph describes pharmacotherapeutic interventions and regional nerve blocks. Part II focuses on psychologic assessment and treatment and physical therapy. A multimodal management strategy offers patients the greatest improvement potential for specific chronic pain syndromes. Cognitive and behavioral therapies and physical therapies are described. This combination of therapies may provide patients with the skills and knowledge needed to increase their sense of control over pain. The integration of appropriate pharmacotherapeutic regimens, neural blockades, physical therapy, and psychologic techniques maximizes a patient's effectiveness in dealing with chronic pain. Three case studies are presented in Part II.