Effect of carbamazepine and gabapentin on excitability in the trigeminal subnucleus caudalis of neonatal rats using a voltage-sensitive dye imaging technique

Oral Gabapentinoids and Nerve Blocks for the Treatment of Chronic Ocular Pain

PURPOSE

There is a recognition that nerve dysfunction can contribute to chronic ocular pain in some individuals. However, limited data are available on how to treat individuals with a presumed neuropathic component to their ocular pain. As such, the purpose of this study was to examine the efficacy of our treatment approaches to this entity.

METHODS

A retrospective review of treatments and outcomes in individuals with chronic ocular pain that failed traditional therapies.

RESULTS

We started eight patients on an oral gabapentinoid (gabapentin and/or pregabalin) as part of their pain regimen (mean age 46 years, 50% women). Two individuals reported complete ocular pain relief with a gabapentinoid, in conjunction with their topical and oral medication regimen. Three individuals noted significant improvements, one slight improvement, and two others no improvement in ocular pain with gabapentin or pregabalin. We performed periocular nerve blocks (4 mL of 0.5% bupivacaine mixed with 1 mL of 80 mg/mL methylprednisolone acetate) targeting the periocular nerves (supraorbital, supratrochlear, infratrochlear, and infraorbital) in 11 individuals (mean age 54 years, 36% women), 10 of whom had previously used a gabapentinoid without ocular pain improvement. Seven individuals experienced pain relief after nerve blocks that lasted from hours to months and four failed to benefit. Five of the individuals who experienced pain relief underwent repeat nerve blocks, weeks to months later.

CONCLUSIONS

Approaches used to treat chronic pain outside the eye can be applied to ocular pain that is not responsive to traditional therapies.

Psychotropic Drugs for the Management of Chronic Pain and Itch

Clinical observations have shown that patients with chronic neuropathic pain or itch exhibit symptoms of increased anxiety, depression and cognitive impairment. Such patients need corrective therapy with antidepressants, antipsychotics or anticonvulsants. It is known that some psychotropic drugs are also effective for the treatment of neuropathic pain and pruritus syndromes due to interaction with the secondary molecular targets. Our own clinical studies have identified antipruritic and/or analgesic efficacy of the following compounds: tianeptine (atypical tricyclic antidepressant), citalopram (selective serotonin reuptake inhibitor), mianserin (tetracyclic antidepressant), carbamazepine (anticonvulsant), trazodone (serotonin antagonist and reuptake inhibitor), and chlorprothixene (antipsychotic). Venlafaxine (serotonin-norepinephrine reuptake inhibitor) is known to have an analgesic effect too. The mechanism of such effect of these drugs is not fully understood. Herein we review and correlate the literature data on analgesic/antipruritic activity with pharmacological profile of these compounds.

Gabapentin completely neutralized the acute morphine activation in the rat hypothalamus: a c-Fos study

Aim: The molecular mechanism of gabapentin (GBP)–morphine combinational function and its neuro-anatomical sites of action to prevent, to neutralize morphine side effects and also the enhancement its analgesic effect of morphine is unknown. Methods: Morphine (10 mg/kg), saline, co-injection: GBP (150 mg/kg) with morphine (10 mg/kg) were injected by intraperitoneal injection in rats under deep anaesthesia. C-Fos immunohistochemistry technique was used to locate c-Fos expression in rat hypothalamus. Results: Gabapentin in combination with morphine significantly (p < 0.01) attenuated the acute morphine induced c-Fos immunoreactive neuron in hypothalamus. Conclusion: GBP neutralized the morphine sensitization in rat hypothalamus. GBP might neuromodulate and or antagonize the receptor regulatory machinery of morphine sensitization circuit which might work for drug discovery of morphine abuse.

Opiate-Free Pain Therapy Using Carbamazepine-Loaded Microparticles Provides Up to 2 Weeks of Pain Relief in a Neuropathic Pain Model

INTRODUCTION

Opioids remain a mainstay in the treatment of acute and chronic pain, despite numerous and potentially dangerous side effects. There is a great unmet medical need for alternative treatments for patients suffering from pain that do not result in addiction or adverse side effects. Anticonvulsants have been shown to be effective in managing pain, though high systemic levels and subsequent side effects limit their widespread usage. Our goal was to determine if the incorporation of an anticonvulsant, carbamazepine, into a biodegradable microparticle for local sustained perineural release would be an efficacious analgesic following a peripheral injury.

METHODS

Following induction of the chronic constriction injury model in Sprague-Dawley rats, mechanical allodynia testing was performed using von Frey filaments and thermal allodynia was evaluated using the Hargreaves method. Histology and blood work were performed to evaluate toxicity as well as to monitor drug and metabolite presence over time.

RESULTS

A 2-fold increase in hindpaw withdrawal thresholds in animals receiving carbamazepine-loaded microparticles relative to controls was observed for up to 14 days after treatment. Drug and metabolite had a peak blood concentration of 54.7 ng/mL and dropped off exponentially to < 5 ng/mL over a few days.

CONCLUSION

This formulation reduced systemic exposure to carbamazepine over 1,000-fold relative to traditional analgesic dosing regimens. This 2-component drug delivery system has been specifically engineered to release a controlled amount of carbamazepine over a 14-day period, providing significant pain relief with no toxicological or observable adverse events via behavioral or histochemical analysis.

[Complex regional pain syndrome: A review]

BACKGROUND

Complex regional pain syndrome is characterized by spontaneous or induced pain disproportionate in relation to the initial event and is accompanied by a variety of regional and motor disturbances, leading to a variety of clinical presentations. It is often associated with surgery and minor trauma.

PATHOPHYSIOLOGY

Three mechanisms are postulated: changes secondary to post traumatic inflammation, peripheral vasomotor dysfunction and structural and functional changes of the central nervous system as a result of maladaptation.

DIAGNOSIS

made based on the criteria of Budapest. The patient must have one symptom and sign of each criterion at diagnosis: Continuing pain, disproportionate to any inciting event. A sensory, vasomotor, oedema and motor/trophic change sign and symptoms that are not explained by another diagnosis or cause.

TREATMENT

Multimodal treatment is suggested. There is no gold standard. In early stage NSAIDs or steroids can be used. Drugs used for neuropathic pain treatment have been suggested, but there is not enough evidence for any of these. There is low evidence that bisphosphonates, calcitonin, ketamine and mirror therapy are effective compared to placebo. Interventional treatment should be stepped from epidural block, neurostimulation, intrathecal pump to experimental therapies in case of intractable pain.

DISCUSSION

Although complex regional pain syndrome has been a recognized entity for over 100 years, no clear evidence exists for first-line treatments; however, new technologies that are applicable in complex regional pain syndrome treatment have been developed.