Gabapentin-induced sexual dysfunction

Predictors of sexual satisfaction among patients with chronic pain

Objectives

Sexual satisfaction is an important aspect of quality of life. Chronic pain, depression and anxiety, and relational problems correspond with higher risk for sexual difficulties. Less is known about how risk factors for sexual dysfunction and other problems-such as medical conditions, pain severity, and medication side effects-affect the sexual satisfaction of people with chronic pain. Using a biopsychosocial framework, this study explored factors related to sexual satisfaction among patients presenting for evaluation of chronic pain.

Methods

Researchers used a hierarchical multiple regression analysis to model potential predictors of sexual satisfaction. Variables analyzed were demographic features, medical history, average pain severity, depressed mood, anxiety, and perceived significant other support. Data collection involved administration of retrospective questionnaires and chart review. The sample included male and female participants (N = 134) presenting for evaluation at a multidisciplinary pain rehabilitation clinic.

Results

Medical history (i.e., medical conditions, surgical history, and medications) and clinical self-report variables (i.e., pain severity, depressed mood, anxiety, and perceived significant other support) were associated with sexual satisfaction. In this sample, antidepressant use and higher pain severity were unique predictors of lower sexual satisfaction. Married marital status and higher levels of perceived significant other support were predictive of greater sexual satisfaction.

Discussion

Findings highlight the importance of understanding the unique impact of biopsychosocial variables on the sexual satisfaction of patients presenting for evaluation at a multidisciplinary pain rehabilitation clinic. Further exploration of protective factors that account for sexual satisfaction among individuals with chronic pain may help inform screening, referrals, and treatment.

Impact of Occupational Therapy Interventions on Sexual Dysfunction in Epilepsy: A Case Report

Epilepsy is a chronic neurological disorder characterized by recurrent seizures, necessitating lifelong medication management. One common side effect of these medications is sexual dysfunction. In this case report, a 37-year-old male epilepsy patient who was an office clerk by occupation presented at the outpatient department (OPD) of occupational therapy with the chief complaints of anxiety, depression, and sexual dysfunction primarily reporting of anorgasmia, which required longer foreplay to reach an effective erection leading to delayed ejaculation. The patient reported a nine-year history of complicated, partial, and generalized seizures for which he consulted the physician who prescribed him AED (antiepileptic drug) carbamazepine twice a day; however, the symptoms persisted, and the medication was changed to pregabalin. In addition to this, the patient was advised for occupational therapy intervention by the physician. In the occupational therapy department, the patient was assessed for various parameters that involved sexual functioning using the Changes in Sexual Functioning Questionnaire-Male (CSFQ-M), for anxiety using the Generalised Anxiety Disorder-7 (GAD-7) questionnaire, for depression using the Patient Health Questionnaire-9 (PHQ-9), and quality of life (QOL) using the Quality of Life in Epilepsy Inventory - 31 (QOLIE-31) questionnaire. As part of the intervention, occupational therapy was provided to the patient for four months, which mainly focused on three major areas: health promotion, remediation, and modification. Each of these methods was used at all levels of the intervention, as outlined by the EX-Permission, Limited Information, Specific Suggestions, and Intensive Therapy model (P-LI-SS-IT), which reflected positive results, as there was enhanced sexual functioning, reduced symptoms of depression, and anxiety, and improved quality of life. In conclusion, occupational therapists along with doctors and other practitioners should focus on addressing intimacy and sexuality within their practice for epilepsy patients demonstrating symptoms of sexual dysfunction, which will consequently impact an individual's QOL. Additionally, screening and monitoring of sexual dysfunction should be included during the routine assessment of patients with epilepsy.

Reproductive health in patients with epilepsy

The aim of the present study was to review existing knowledge on the impact of epilepsy in reproductive health of both sexes. Extensive searches of relevant documentation published until February 2020 were retrieved from PubMed and Google Scholar literature in English or in other languages with an English abstract. In females, epilepsy may lead to estrogen and androgen level abnormalities. Women with epilepsy may develop Polycystic Ovaries Syndrome (PCOS), anovulatory cycles, and menstrual disorders. In men, epilepsy may cause sex hormone dysregulation and influence spermatogenesis. Males with epilepsy may also suffer from sexual dysfunction. Antiepileptic drugs (AEDs) have adverse effects on peripheral endocrine glands, influence hormones' biosynthesis and protein binding, diminish the bioactivity of serum sex hormones, and lead to secondary endocrine disorders related to changes concerning body weight and insulin sensitivity. Valproic acid (VPA) was the first recognized AED to cause disturbances potentially due to metabolic changes and increasing weight. Women taking VPA may develop PCOS, while men may have sperm abnormalities and/or sexual dysfunction. Liver enzyme inducing AEDs may also cause menstrual and sexual disorders in women and sexual dysfunction in men. Newer AEDs are much safer but studies still suggest reduced sexuality and erectile dysfunction.

Characterization of Sigma 1 Receptor Antagonist CM-304 and Its Analog, AZ-66: Novel Therapeutics Against Allodynia and Induced Pain

Sigma-1 receptors (S1R) and sigma-2 receptors (S2R) may modulate nociception without the liabilities of opioids, offering a promising therapeutic target to treat pain. The purpose of this study was to investigate the in vivo analgesic and anti-allodynic activity of two novel sigma receptor antagonists, the S1R-selective CM-304 and its analog the non-selective S1R/S2R antagonist AZ-66. Inhibition of thermal, induced chemical or inflammatory pain, as well as the allodynia resulting from chronic nerve constriction injury (CCI) and cisplatin exposure as models of neuropathic pain were assessed in male mice. Both sigma receptor antagonists dose-dependently (10–45 mg/kg, i.p.) reduced allodynia in the CCI and cisplatin neuropathic pain models, equivalent at the higher dose to the effect of the control analgesic gabapentin (50 mg/kg, i.p.), although AZ-66 demonstrated a much longer duration of action. Both CM-304 and AZ-66 produced antinociception in the writhing test [0.48 (0.09–1.82) and 2.31 (1.02–4.81) mg/kg, i.p., respectively] equivalent to morphine [1.75 (0.31–7.55) mg/kg, i.p.]. Likewise, pretreatment (i.p.) with either sigma-receptor antagonist dose-dependently produced antinociception in the formalin paw assay of inflammatory pain. However, CM-304 [17.5 (12.7–25.2) mg/kg, i.p.) and AZ-66 [11.6 (8.29–15.6) mg/kg, i.p.) were less efficacious than morphine [3.87 (2.85–5.18) mg/kg, i.p.] in the 55°C warm-water tail-withdrawal assay. While AZ-66 exhibited modest sedative effects in a rotarod assay and conditioned place aversion, CM-304 did not produce significant effects in the place conditioning assay. Overall, these results demonstrate the S1R selective antagonist CM-304 produces antinociception and anti-allodynia with fewer liabilities than established therapeutics, supporting the use of S1R antagonists as potential treatments for chronic pain.

Sexual dysfunction in men taking systemic dermatologic medication: A systematic review

BACKGROUND

Prescription medications are among the most common causes of sexual dysfunction, and patients are often hesitant to seek help when experiencing these symptoms.

OBJECTIVE

In this review, we identify the available evidence of sexual adverse effects in men using systemic dermatologic medications and suggest screening protocols and actions that may improve a patient's symptoms where possible.

METHODS

A systematic review was conducted of all articles in the PubMed database published from the time of inception to May 2018 to identify studies evaluating the use of systemic dermatologic medications in men with evidence of sexual adverse effects. Subsequently, a secondary in-depth literature review was performed for each individual medication.

RESULTS

There were 5497 articles reviewed in the primary systematic review, and 59 articles covering 11 systemic dermatologic medications met inclusion criteria. We identified level 1 evidence for sexual adverse effects as a primary outcome in patients taking finasteride.

LIMITATIONS

Many included studies were limited by sample size and methodology.

CONCLUSION

The information in this review may serve as a reference of adverse effects when deciding on a therapeutic agent and a guide to help identify patients to screen for sexual dysfunction.

Effect of antiepileptic drug (Topiramate) and cold pressed ginger oil on testicular genes expression, sexual hormones and histopathological alterations in mice

Sexual dysfunction in the epileptic patient is difficult to confirm whether it is ailment or therapy related. Antiepileptic drugs often use in reproductive age, through reproductive progress and maturation. On the other side, cold-pressed oils are rich in bioactive phytochemicals with health-promoting traits. The target of this work was to appraise the sexual dysfunction of antiepileptic Topiramate (TPM) and cold pressed ginger oil (CPGO) as antiepileptic alternative medicine in male mice. Fifty-four adult male albino mice were divided into nine groups (n = 6 mice). One group given saline and used as negative control; another one was given corn oil as vehicle. Six groups administered orally with TPM or CPGO at 100, 200 and 400 mg/kg. Moreover, group of animals co-administrated orally CPGO with TPM (400 mg/kg) to study their interaction. Fatty acid profile and tocols composition of CPGO were determined. in vitro assays were undertaken to evaluate radical scavenging traits of CPGO utilizing sable 1,1-diphenyl-2-picrylhydrazyl (DPPH·) and galvinoxyl radicals. The study investigated antioxidant and oxidative stress markers, sexual hormones levels, mRNA levels of vascular endothelial growth factor (Vegfa), synaptonemal complex protein (Sycp3), Wilms tumor gene (Wt1) as well as histopathological and immunohistochemical examination. Strong radical scavenging potential of CPGO against stable DPPH· and galvinoxyl radicals was recorded. The results revealed that TPM caused a dose-dependent reduction in the antioxidant activities and testosterone content, while, malonaldehyde (MDA) and nitric oxide (NO) as oxidative stress markers were elevated. Vegfa and Sycp3 mRNA expression down-regulated at all Topiramate tested doses, but Wt1 up-regulated at 400 mg/kg. TPM (400 mg/kg) revealed histological alterations associated with strong positive Bax immune reactive spermatogoneal and Leydig cells. Ginger oil elevated the CAT and SOD (antioxidant enzymes), serum testosterone and diminished the oxidative stress, up regulated the expression of Vegfa and Sycp3 and down-regulated the Wt1 expression. Meanwhile, CPGO revealed no histopathological alterations and no Bax immune-reactive cells. CPGO co-administration with TPM (400 mg/kg) attenuated the TPM toxicity. High doses of TPM may exhibit sexual dysfunction but CPGO is safe and has androgenic property. CPGO co-administration could protect the antiepileptic patient from the TPM sexual dysfunction.

Alprazolam-induced dose-dependent anorgasmia: case analysis

BACKGROUND

Sexual dysfunctions are associated with multiple medical and psychiatric disorders, as well as pharmacotherapies used to treat these disorders. Although sexual dysfunctions negatively affect both quality of life and treatment adherence, patients infrequently volunteer these symptoms and clinicians do not pose directed questions to determine their presence or severity. This issue is especially important in psychiatric patients, for whom most common psychotropics may cause sexual dysfunctions (antidepressants, antipsychotics, anxiolytics and mood-stabilising agents). There is limited literature addressing benzodiazepines, and alprazolam in particular.

AIMS

To report dose-dependent alprazolam anorgasmia.

METHOD

Case analysis with PubMed literature review.

RESULTS

A 30-year-old male psychiatric patient presented with new-onset anorgasmia in the context of asymptomatic generalised anxiety disorder, social anxiety, panic disorder with agoraphobia, obsessive-compulsive disorder, major depression in remission, and attention-deficit hyperactivity disorder treated with escitalopram 10 mg q.a.m., gabapentin 1000 mg total daily dose, lisdexamfetamine dimesylate 70 mg q.a.m., nortriptyline 60 mg q.h.s. and alprazolam extended-release 2.5 mg total daily dose. All psychotropic doses had been constant for >6 months excluding alprazolam, which was titrated from 1 mg to 2.5 mg total daily dose. The patient denied any sexual dysfunction with alprazolam at 1 mg q.d. and 1 mg b.i.d. Within 1 week of increasing alprazolam to 2.5 mg total daily dose, the patient reported anorgasmia. Anorgasmia was alprazolam dose-dependent, as anorgasmia resolved with reduced weekend dosing (1 mg b.i.d. Saturday/1.5 mg total daily dose Sunday).

CONCLUSIONS

Sexual dysfunction is an important adverse effect negatively influencing therapeutic outcome. This case reports alprazolam-induced dose-dependent anorgasmia. Clinicians/patients should be aware of this adverse effect. Routine sexual histories are indicated.

DECLARATION OF INTEREST

None.

Sexual concerns after Spinal Cord Injury: An update on management

BACKGROUND

Spinal Cord Injury (SCI) causes neurological impairment with resultant neurogenic sexual dysfunction which can compound preexisting psychological and medical sexual concerns. Understanding these concerns is important in managing the lifelong needs of persons with SCIs.

OBJECTIVES

To provide an overview of the impact of SCI on sexuality along with a framework for treatment of sexual concerns. To briefly review male infertility and its treatments and pregnancy in females after SCI.

METHODS

Interdisciplinary literature review and synthesis of information.

RESULTS

The average age at SCI is increased, thus persons with SCIs may have preexisting sexual concerns. Sexual activity and satisfaction are decreased after SCI. Psychogenic sexual arousal is related to remaining sensation in the T11-L2 dermatomes. Orgasm occurs in approximately 50% of persons with SCIs with all injuries except subjects with complete lower motor neuron (LMN) injuries affecting the lowest sacral segments A structured approach to treatment including assessing preinjury function, determining the impact of injury, education, assessing and treating iatrogenic sexual dysfunction and treatment of concomitant problems is recommended. Basic and advanced methods to improve sexual arousal and orgasm are discussed and treatment of anejaculation and issues associated with pregnancy and SCI are reviewed.

CONCLUSIONS

Sexual satisfaction is impaired after SCI; however, education and new therapies can improve responsiveness. Future research is warranted to improve sexual function and fertility potential in persons with SCIs.

Adverse cognitive effect of gabapentin in individuals with spinal cord injury: preliminary findings

Study design

Prospective observational cohort study.

Objectives

To assess the effects of gabapentin on neuropsychological variables including memory, attention, and executive function in individuals with spinal cord injury.

Setting

Santa Clara Valley Medical Center inpatient spinal cord injury unit.

Methods

Ten patients (three females, seven males) with traumatic spinal cord injury underwent testing, with a mean age of 35.6 years (range 19-59, SD ±15.74). There were five patients with tetraplegia and five with paraplegia. Nine tests to assess neuropsychological function and two tests to assess pain were performed at 1 week post initiation of therapy, and at 4 weeks post initiation of therapy. The neuropsychological tests assessed aspects of memory, attention, and executive function.

Results

The average score for six out of the nine neuropsychological items administered at 1 week post initiation of gabapentin displayed a decrease in cognitive function when compared to baseline. The average score for five out of nine neuropsychological items improved from 1 week post initiation of treatment to 4 weeks post initiation of treatment.

Conclusions

Gabapentin therapy is associated with a tangible decline in memory, executive function, and attention in individuals with spinal cord injury. However, owing to small sample size, loss of patient follow-up at the 4 week post-treatment assessment, and lack of a control group, we cannot definitively state that any decreases in cognition are solely attributable to treatment with gabapentin.

Lamotrigine-induced sexual dysfunction and non-adherence: case analysis with literature review

BACKGROUND

Optimal anti-epileptic drug (AED) treatment maximises therapeutic response and minimises adverse effects (AEs). Key to therapeutic AED treatment is adherence. Non-adherence is often related to severity of AEs. Frequently, patients do not spontaneously report, and clinicians do not specifically query, critical AEs that lead to non-adherence, including sexual dysfunction. Sexual dysfunction prevalence in patients with epilepsy ranges from 40 to 70%, often related to AEDs, epilepsy or mood states. This case reports lamotrigine-induced sexual dysfunction leading to periodic non-adherence.

AIMS

To report lamotrigine-induced sexual dysfunction leading to periodic lamotrigine non-adherence in the context of multiple comorbidities and concurrent antidepressant and antihypertensive pharmacotherapy.

METHOD

Case analysis with PubMed literature review.

RESULTS

A 56-year-old male patient with major depression, panic disorder without agoraphobia and post-traumatic stress disorder was well-controlled with escitalopram 20 mg bid, mirtazapine 22.5 mg qhs and alprazolam 1 mg tid prn. Comorbid conditions included complex partial seizures, psychogenic non-epileptic seizures (PNES), hypertension, gastroesophageal reflux disease and hydrocephalus with patent ventriculoperitoneal shunt that were effectively treated with lamotrigine 100 mg tid, enalapril 20 mg qam and lansoprazole 30 mg qam. He acknowledged non-adherence with lamotrigine secondary to sexual dysfunction. With lamotrigine 300 mg total daily dose, he described no libido with impotence/anejaculation/anorgasmia. When off lamotrigine for 48 h, he described becoming libidinous with decreased erectile dysfunction but persistent anejaculation/anorgasmia. When off lamotrigine for 72 h to maximise sexual functioning, he developed auras. Family confirmed patient's consistent monthly non-adherence for 2-3 days during the past year.

CONCLUSIONS

Sexual dysfunction is a key AE leading to AED non-adherence. This case describes dose-dependent lamotrigine-induced sexual dysfunction with episodic non-adherence for 12 months. Patient/clinician education regarding AED-induced sexual dysfunction is warranted as are routine sexual histories to ensure adherence.

DECLARATION OF INTEREST

No financial interests. K.R.K. is Editor of BJPsych Open; he took no part in the peer-review of this work.

COPYRIGHT AND USAGE

© The Royal College of Psychiatrists 2017. This is an open access article distributed under the terms of the Creative Commons Non-Commercial, No Derivatives (CC BY-NC-ND) license.

The impact of drugs on male fertility: a review

Beside cytotoxic drugs, other drugs can impact men's fertility through various mechanisms. Via the modification of the hypothalamic-pituitary-gonadal axis hormones or by non-hormonal mechanisms, drugs may directly and indirectly induce sexual dysfunction and spermatogenesis impairment and alteration of epididymal maturation. This systematic literature review summarizes existing data about the negative impact and associations of pharmacological treatments on male fertility (excluding cytotoxic drugs), with a view to making these data more readily available for medical staff. In most cases, these effects on spermatogenesis/sperm maturation/sexual function are reversible after the discontinuation of the drug. When a reprotoxic treatment cannot be stopped and/or when the impact on semen parameters/sperm DNA is potentially irreversible (Sulfasalazine Azathioprine, Mycophenolate mofetil and Methotrexate), the cryopreservation of spermatozoa before treatment must be proposed. Deleterious impacts on fertility of drugs with very good or good level of evidence (Testosterone, Sulfasalazine, Anabolic steroids, Cyproterone acetate, Opioids, Tramadol, GhRH analogues and Sartan) are developed.

Corino de Andrade disease: mechanisms and impact on reproduction

Familial amyloid polyneuropathy was first described by Corino de Andrade in 1952 in Northern Portugal. It is a fatal autosomal dominant neurodegenerative disorder characterized by a progression of neurologic symptoms, beginning early in the reproductive life. The Transthyretin gene mutation originates a mutated protein that precipitates in the connective tissue as amyloid deposits. This disease is presently named Transthyretin-related hereditary amyloidosis. We performed an extensive review on this disease based on searches in Medical databases and in paper references. In this review, we briefly summarize the epidemiology and the mechanisms involved on amyloid deposition; we detailed how to evaluate the mechanisms implicated on the development of the major signs and symptoms associated with reproductive dysfunction; and we discuss the mechanisms involved in secondary sexual dysfunction after psychological treatments. Treatment of the disease is directed towards relieving specific symptoms in association with liver transplant, and molecular and genetic therapeutics. Although the current clinical trials indicate symptoms relief, no data on the reproductive function was reported. Thus, preimplantation genetic diagnosis is presently the only available technique that eradicates the disease as it avoids the birth of new patients.

The relationship between epilepsy and sexual dysfunction: a review of the literature

Background and objectives

Regardless of the disease states that people suffer from, maintaining sexual function is an important indicator of quality of life. The objective of this review was to figure out the relationship between epilepsy, antiepileptic drugs (AEDs) and sexual dysfunction.

Results

In various epidemiological and clinical studies, epilepsy has been correlated with a reduction in sexual function. This sexual dysfunction is not always detected in epileptic patients until systematic efforts are put in place, as part of the assessment and treatment process. Therefore, precise evaluations of the incidence of treatment related sexual dysfunction in epileptic patients is still lacking.

Conclusions

This literature review concluded that sexual function is influenced by the pathophysiology of epilepsy, as well as through the use of AEDs. To maximize quality of care in patients with epilepsy and those patients with other disease states who receive AEDs, it is important to address the status of the patient’s sexual function as part of the initial routine assessment and with any treatment related follow-up. Minimizing the effects of AED related sexual dysfunction can be achieved by raising awareness among patients, providing education and training for physicians regarding sexual dysfunction and obtaining a baseline sexual history from the patient so are important recommendations. In addition, systematic studies are needed to explore the risk and mechanism of such treatment related side effects on sexual function.

Sexual dysfunction related to antiepileptic drugs in patients with epilepsy

INTRODUCTION

Epilepsy is a common disease that is mostly treated with antiepileptic drugs (AEDs). However, the sexual dysfunction (SD) side effects related to the use of AEDs have not received sufficient attention.

AREAS COVERED

The purpose of this review is to examine the current evidence on SD-related side effects of AEDs. The incidence, clinical features and major types of SD are summarized. Furthermore, various AEDs that may cause SDs are addressed in detail. Finally, we briefly summarize the treatments for SD related to AEDs.

EXPERT OPINION

SD related to AEDs is common. Symptoms include erectile dysfunction (ED), hyposexuality, hypersexuality and ejaculatory dysfunction. Traditional AEDs such as valproate and enzyme-inducing AEDs (EIAEDs) may produce high incidences of decreased libido. Recently, sexual function changes related to new AEDs have been reported. Topiramate, pregabalin and gabapentin may cause SD, whereas oxcarbazepine, lamotrigine and levetiracetam may improve sexual function. Although the treatment for SD related to AEDs remains unclear, switching to another AED may be an option. Further studies are necessary to better understand and treat SD related to AEDs.

Epilepsy and AED-induced decreased libido - The unasked psychosocial comorbidity

Therapeutic treatment for persons with epilepsy (PWE) should address seizure control and the broad spectrum of associated comorbidities. Since both epilepsy and antiepileptic drugs (AEDs) can induce decreased libido, sexual health assessment is an important aspect of quality care in PWE as well as other patients receiving AEDs. This paper presents findings from a pilot quality initiative conducted in the ambulatory care epilepsy, pain management, and psychiatric services (N=15 clinicians) which addressed two themes: 1) whether libido is routinely questioned with/without the electronic medical record (EMR) and 2) clinicians' knowledge that both epilepsy and AEDs can induce decreased libido. All clinicians used the EMR, 40% used the GU-ROS section, but only 1 clinician (6.67%) questioned patients regarding libido. Of the clinicians, 26.7% demonstrated knowledge that both AEDs and epilepsy can cause decreased libido. Our results suggest that a treatment gap for epilepsy-induced and AED-induced decreased libido may be related to systems issues (duration of clinical visit, billing codes, EMR template) and physician barriers including decreased knowledge. Further research in this field and replication of this pilot quality initiative are indicated.

The long-term safety of antiepileptic drugs

Antiepileptic drugs (AEDs) are used by millions of people worldwide for the treatment of epilepsy, as well as in many other neurological and psychiatric conditions. They are frequently associated with adverse effects (AEs), which have an impact on the tolerability and success of treatment. Half the people who develop intolerable AEs discontinue treatment early on after initiation, while the majority of people will continue to be exposed to their effects for long periods of time. The long-term safety of AEDs reflects their potential for chronic, cumulative dose effects; rare, but potentially serious late idiosyncratic effects; late, dose-related effects; and delayed, teratogenic or neurodevelopmental effects. These AEs can affect every body system and are usually insidious. With the exception of delayed effects, most other late or chronic AEs are reversible. To date, there is no clear evidence of a carcinogenic effect of AEDs in humans. While physicians are aware of the long-term AEs of old AEDs (the traditional liver enzyme-inducing AEDs and valproate), information about AEs of new AEDs (such as lamotrigine, levetiracetam, oxcarbazepine, topiramate or zonisamide), particularly of their teratogenic effects, has emerged over the years. Sporadic publications have raised issues about AEs of the newer AEDs eslicarbazepine, retigabine, rufinamide, lacosamide and perampanel but their long-term safety profiles may take years to be fully appreciated. Physicians should not only be aware of the late and chronic AEs of AEDs but should systematically enquire and screen for these according to the individual AED AE profile. Care should be taken for individuals with comorbid conditions that may render them more susceptible to specific AEs. Prevention and appropriate management of long-term AED AEs is expected to improve adherence to treatment, quality of life and control of epilepsy.

Implications and mechanism of action of gabapentin in neuropathic pain

Gabapentin is an anti-epileptic agent but now it is also recommended as first line agent in neuropathic pain, particularly in diabetic neuropathy and post herpetic neuralgia. α2δ-1, an auxillary subunit of voltage gated calcium channels, has been documented as its main target and its specific binding to this subunit is described to produce different actions responsible for pain attenuation. The binding to α2δ-1 subunits inhibits nerve injury-induced trafficking of α1 pore forming units of calcium channels (particularly N-type) from cytoplasm to plasma membrane (membrane trafficking) of pre-synaptic terminals of dorsal root ganglion (DRG) neurons and dorsal horn neurons. Furthermore, the axoplasmic transport of α2δ-1 subunits from DRG to dorsal horns neurons in the form of anterograde trafficking is also inhibited in response to gabapentin administration. Gabapentin has also been shown to induce modulate other targets including transient receptor potential channels, NMDA receptors, protein kinase C and inflammatory cytokines. It may also act on supra-spinal region to stimulate noradrenaline mediated descending inhibition, which contributes to its anti-hypersensitivity action in neuropathic pain.

Sildenafil influences the anticonvulsant activity of vigabatrin and gabapentin in the timed pentylenetetrazole infusion test in mice

Sildenafil, a selective phosphodiesterase 5 (PDE5) inhibitor, has recently been reported to affect convulsant activity in some animal models of seizures and epilepsy. Moreover, its influence on the protective activity of some antiepileptic drugs (AEDs) was also noted. The aim of the present study was to investigate the effect of sildenafil on the anticonvulsant potential of gabapentin (GBP) and vigabatrin (VGB) in the timed intravenous (i.v.) pentylenetetrazole (PTZ) test in mice. The chimney test, the passive avoidance task and the grip strength test were used to estimate some possible side effects caused by the studied AEDs and their combinations with sildenafil. Total brain and free plasma concentrations of GBP and VGB were determined to evaluate the characteristics of interactions. Our studies revealed that GBP (25-100 mg/kg) increases the threshold for the forelimb tonic extension, whereas VGB raises thresholds both, for myoclonic (200-600 mg/kg) and generalized clonic (400-600 mg/kg) seizures in the used model of seizures. GBP at sub-effective dose of 12.5 mg/kg co-administered with sildenafil at doses of 10 and 20 mg/kg significantly increases the threshold for tonic seizures in the i.v. PTZ test in mice. Combination of sub-effective dose of VGB (200 mg/kg) with sildenafil at a dose of 5mg/kg also showed significant anticonvulsant activity against clonic seizures. The studied AEDs and their combinations with sildenafil did not produce any changes in the motor coordination, long-term memory and muscular strength in mice. Sildenafil did not influence total brain and free plasma concentrations of GBP and VGB. Interactions between the studied AEDs and sildenafil were pharmacodynamic in nature and for that reason they are worthy of consideration in the clinical practice.