Quantitative assessment of sustained-release 4-aminopyridine for symptomatic treatment of multiple sclerosis

Pediatric multiple sclerosis

In the past 5 years, there has been an exponential growth in the knowledge about multiple sclerosis (MS) in children and adolescents. Recent publications have shed light on its diagnosis, pathogenesis, clinical course, and treatment. However, there remain several key areas that require further exploration. This article summarizes the current state of knowledge on pediatric MS and discusses future avenues of investigation.

Treatment of walking impairment in multiple sclerosis with dalfampridine

Potassium channel blockade has long been considered a potential therapeutic strategy for treatment of multiple sclerosis (MS) based on the pathophysiology of demyelinated axons. Dalfampridine, which is also known as fampridine or 4-aminopyridine (4-AP), is the potassium channel blocker that has been studied most extensively in MS and other demyelinating neurologic disorders. An extended-release formulation of dalfampridine was recently approved by the US Food and Drug Administration to improve walking in patients with MS. In randomized, double-blind, placebo-controlled trials, with dalfampridine extended release tablets 10 mg taken twice daily, about 12 h apart, walking speed was improved in approximately one-third of treated patients; in these patients, average walking speed on therapy was about 25% above baseline. This improvement was clinically meaningful as assessed by concurrent measurement of patient-reported severity of walking-related disability. Dalfampridine extended release tablets were generally well tolerated, with a range of adverse effects that appear to be related to increases in central nervous system excitation. There is a dose-dependent increase in the occurrence of seizures at doses higher than the recommended 10 mg twice daily.

Dalfampridine: a brief review of its mechanism of action and efficacy as a treatment to improve walking in patients with multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) can cause progressive walking impairment that contributes to disability, loss of independence, and reduced quality of life. Dalfampridine (4-aminopyridine), a voltage-dependent potassium channel blocker, has been shown to improve walking in patients with MS, as demonstrated by an increase in walking speed.

OBJECTIVE

To summarize knowledge about the mechanism of action of dalfampridine in the context of clinical evidence of walking improvement in MS patients.

METHODS

Although this was not a systematic review, which is the primary limitation of this study, searches of PubMed were performed using relevant search terms to identify studies that examined the mechanism of action related to MS and its effects in patients with MS in clinical trials.

RESULTS

Voltage-gated potassium channels represent a family of related proteins that span cell membranes, open and close in response to changes in the transmembrane potential, and help regulate ionic potassium currents. Action potential conduction deficits in demyelinated axons result in part from the exposure after demyelination of the paranodal and internodal potassium channels that are distributed in the axonal membrane. This exposure leads to abnormal currents across the axonal membrane that can slow action potential conduction, result in conduction failure, or affect the axon's capacity for repetitive discharge. While dalfampridine is a broad-spectrum blocker of voltage-dependent potassium channels at millimolar concentrations, studies have shown improvement in action potential conduction in demyelinated axons at concentrations as low as 1 μM, and therapeutic plasma concentrations (associated with improved walking) are in the range of 0.25 µM. However, no specific potassium channel subtype has yet been characterized with significant sensitivity to dalfampridine in this range, and the effects of the drug at this low concentration appear to be quite selective. Improved conduction translates into clinical benefit as measured by objectively and subjectively assessed walking relative to placebo. Such improvements were observed in approximately one third of patients treated with an extended-release formulation of dalfampridine in clinical trials. These patients who responded to dalfampridine had an average increase in walking speed of approximately 25%, and greater improvements than nonresponders on a self-reported subjective measure of walking.

CONCLUSIONS

The extended-release formulation of dalfampridine has been shown in clinical trials to improve walking speed in approximately one third of MS patients with ambulatory impairment. The putative mechanism of action of dalfampridine is restoration of action potential conduction via blockade of an as yet uncharacterized subset of potassium channels in demyelinated axons.

Treatment of walking impairment in multiple sclerosis: an unmet need for a disease-specific disability

INTRODUCTION

Walking impairment is a clinical hallmark of multiple sclerosis (MS), a chronic neurologic disease characterized by axonal demyelination and dysfunction that results in progressive disability. Until recently, there were no therapies that specifically targeted the axonal dysfunction associated with walking impairment in MS.

AREAS COVERED

The purpose of this review is to discuss the unmet need for the treatment of walking impairment in MS patients and to evaluate how a new class of pharmacologic therapies, neurofunctional modifiers, potentially addresses this unmet need. Discussion is based on clinical experience and opinions supported by publications identified in the PubMed literature using the search terms 'multiple sclerosis' and 'mobility OR walking'.

EXPERT OPINION

The development and approval of new treatments for MS show promise for improving adherence to therapy and increasing the potential for clinical effectiveness. Renewed emphasis on integrating strategies that target the underlying pathophysiology with those that address symptoms of concern to patients also has the potential to improve the lives of MS patients and their caregivers. The introduction of neurofunctional modifiers, such as dalfampridine for the improvement of walking impairment, may be of benefit by improving function, mobility and overall quality of life for MS patients.

Effects of 3-4 diaminopyridine (DAP) in motor neuron diseases

OBJECTIVE

To study the safety of 3-4 diaminopyridine (DAP) in patients with motor neuron diseases and to examine its efficacy in reducing muscle fatigue and weakness and in improving objective parameters of muscle function.

DESIGN

Assessments of safety included a questionnaire of symptoms, clinical examination, blood testing, and electrocardiography at each visit; efficacy was assessed by subjective scores of fatigue and weakness; an Amyotrophic Lateral Sclerosis Functional Rating Scale and functional ability scores, including timed verbal scores; manual muscle testing; grip dynamometry; pulmonary function tests; timed functional tests; and electrophysiological studies.

PARTICIPANTS

Thirteen subjects with amyotrophic lateral sclerosis and seven subjects with only a lower motor neuron syndrome.

MAIN OUTCOMES

Assess tolerability of DAP and determine if there was symptomatic improvement of muscle fatigue. SECONDARY OUTCOME: To determine the effects of DAP on objective parameters of muscle function.

RESULTS

The drug was well tolerated with only four subjects reporting tingling of lips and fingers during the active drug period. The subjective scores for fatigue and weakness showed a mild improvement after 4 weeks on DAP compared with placebo. A significant benefit of DAP was also demonstrated in the timed verbal scores.

CONCLUSION

3-4 DAP appeared to be safe and produced subjective benefit in motor neuron diseases. The drug could be added for symptomatic treatment in these diseases. Larger studies are necessary to demonstrate efficacy.

Community walking can be assessed using a 10-metre timed walk test

Background: A decline in mobility is a common feature of multiple sclerosis (MS). Community walking scales are used to categorize patients in their ability to move independently. The first purpose of this study was to determine which specific gait speed corresponded with the categories of the Modified Functional Walking Categories (MFWC). The second purpose was to determine the Minimally Important Change (MIC) in absolute gait speed using the MFWC and Expanded Disability Status Scale (EDSS) as external criteria.

Method: MS patients were measured six times in 6 years. Gait velocity was measured with the 10-metre timed walk test (10-m TWT), the severity of MS was determined with the EDSS, and community walking was assessed with the MFWC. For each category of the MFWC, Receiver Operating Characteristic (ROC) curves were used to find the best possible cut-off point on the 10-m TWT. The MIC in absolute gait speed was determined using a change of one category on the MFWC or one point on the EDSS.

Results: A strong relationship was found between gait speed and the MFWC; all areas under the ROC curves (AUCs) were between 0.74 and 0.86. The MIC in absolute gait speed could not be determined, because the AUCs were below the threshold of 0.70 and changes in gait speed were small.

Conclusions: Gait speed is related to community walking, but an MIC in absolute gait speed could not be determined using a minimally important change on the MFWC or the EDSS as external criteria.

Dalfampridine: review of its efficacy in improving gait in patients with multiple sclerosis

Multiple sclerosis (MS) is a progressive immune-mediated neurodegenerative disease of human central nervous system (CNS), which causes irreversible disability in young adults. The cause and cure for MS remain unknown. Pathophysiology of MS includes two arms: inflammatory demyelination and neurodegeneration. The inflammatory demyelination of MS which is mainly promoted by a massive activation of the immune system against putative CNS antigen(s) leads to loss of oligodendrocyte/myelin complex which slows down or halts impulse conduction in denuded axons. Practically, loss of myelin significantly reduces signal conduction along the demyelinated axons through alterations in the distribution of axonal ion channels. Dalfampridine (4-aminopyridine or 4-AP) is an oral potassium channel blocker, which was recently approved by FDA for symptomatic treatment of MS. Dalfampridine, which acts at the central and peripheral nervous systems, enhances conduction in demyelinated axons and improves walking ability of MS patients. A number of clinical trials have evaluated the safety and efficacy of fampridine in MS patients with the degree of gait improvement as the main outcome. The objective of this manuscript is to provide an overview of the pharmacology, pharmacokinetics, clinical trials, side effects and interactions of dalfampridine used in treatment of MS patients.

Pharmacological interventions for spinal cord injury: where do we stand? How might we step forward?

Despite numerous studies reporting some measures of efficacy in the animal literature, there are currently no effective therapies for the treatment of traumatic spinal cord injuries (SCI) in humans. The purpose of this review is to delineate key pathophysiological processes that contribute to neurological deficits after SCI, as well as to describe examples of pharmacological approaches that are currently being tested in clinical trials, or nearing clinical translation, for the therapeutic management of SCI. In particular, we will describe the mechanistic rationale to promote neuroprotection and/or functional recovery based on theoretical, yet targeted pathological events. Finally, we will consider the clinical relevancy for emerging evidence that pharmacologically targeting mitochondrial dysfunction following injury may hold the greatest potential for increasing tissue sparing and, consequently, the extent of functional recovery following traumatic SCI.

Impact of extended-release dalfampridine on walking ability in patients with multiple sclerosis

Dalfampridine extended release (ER) 10 mg is an oral tablet form of the potassium (K(+)) channel-blocking compounded dalfampridine, also known as fampridine, and chemically 4-aminopyridine or 4-AP, which received regulatory approval in the United States for the treatment of walking in patients with multiple sclerosis (MS) in January 2010. Two pivotal Phase 3 clinical trials demonstrated significant improvements in walking in patients with the four primary forms of MS following administration of dalfampridine ER tablets 10 mg twice daily. The drug is thought to act by restoring conduction in focally demyelinated axons and by enhancing neurotransmission, thereby leading to improved neurological function. This review describes how dalfampridine represents a new pharmacotherapeutic approach to the clinical management of mobility impairment. It describes the mechanism of action and chemistry of dalfampridine ER, its pharmacokinetics, tolerability, and side effects, and the outcomes of multicenter trials showing its efficacy in improving walking speed. Clinician and patient global assessments, as well as patient self-assessment of the impact of MS on their gait disability, confirm clinically relevant benefit from the therapy. Patients tolerate the drug well and their improvement in terms of household and community ambulation, inferred from analysis of pooled data from several studies, is likely to translate into benefits in the performance of instrumental activities of daily living and a reduction in the neuropsychiatric burden of disease.

Symptomatic relief of botulinum neurotoxin/a intoxication with aminopyridines: a new twist on an old molecule

Botulinum neurotoxins (BoNT) are the etiological agents responsible for botulism, a disease characterized by peripheral neuromuscular blockade and a characteristic flaccid paralysis of humans. BoNT/A is the most toxic protein known to man and has been classified by the Centers of Disease Control (CDC) as one of the six highest-risk threat agents for bioterrorism. Of particular concern is the apparent lack of clinical interventions that can reverse cellular intoxication. Efforts to uncover molecules that can act within an intoxicated cell so as to provide symptomatic relief to BoNT/A are paramount. Aminopyridines have shown clinical efficacy for multiple sclerosis treatment as well as BoNT/A intoxication; yet, aminopyridines for BoNT/A treatment has been abandoned because of blood brain barrier (BBB) penetration producing undesired neurotoxic side effects. Two aminopyridines (5 and 11) exhibited inhibitory activity toward Shaker-IR voltage-gated potassium (K(V)1.x) channels with potencies similar to that of the previous "gold-standard", 3,4-diaminopyridine (3,4-DAP), including reversal of symptoms from BoNT-induced paralysis in phrenic nerve-hemidiaphragm preparations. Importantly, pharmacokinetic experiments revealed a lack of BBB penetration of 5, which is a significant advancement toward resolving the neurotoxicity issues associated with prolonged 3,4-DAP treatments. Finally, 5 was found to be as effective as 3,4-DAP in rescuing BoNT-poisoned mice in the mouse lethality assay, signifying an optimized balance between the undesired permeability across the BBB and the required permeability across lipid cellular membranes. The results demonstrate that 5 is the most promising small molecule K(+) channel inhibitor discovered to date for the treatment of BoNT/A intoxication.

Dalfampridine sustained-release for symptomatic improvement of walking speed in patients with multiple sclerosis

Dalfampridine sustained-release (SR) is a time-release formulation of 4-aminopyridine, recently approved by the Food and Drug Administration to improve walking in patients with multiple sclerosis (MS). In Phase II trials, walking speed and lower extremity muscle strength was increased in patients with MS, but the increase in walking speed did not reach statistical significance. A responder analysis revealed that approximately 35% of treated patients had a statistically significant and clinically meaningful increase in walking speed. When treated responders were compared with treated nonresponders, walking speed significantly increased in the responder group, but not in the nonresponder or placebo groups. This result was duplicated in two larger Phase III trials. The optimal dose to maximize the risk-benefit ratio was 10 mg twice daily. Higher doses were associated with a greater risk of seizure, but no further improvement in walking speed or in the proportion of responders. Dalfampridine SR is eliminated by renal clearance and undergoes only limited metabolism (<10%). It is contraindicated in patients with moderate or severe renal insufficiency and in those with a history of seizures or epileptiform activity on electroencephalography. The development of time-released 4-aminopyridine represents a major advance in symptomatic therapy for MS.

New approaches in the management of multiple sclerosis

Multiple sclerosis (MS) is a central nervous system chronic inflammatory disease that is characterized by an extensive and complex immune response. Scientific advances have occurred in immunology, pathophysiology, and diagnostic and clinical assessment tools, and recent discovery of unique therapeutic targets has spurred numerous Phase II and Phase III clinical trials. Reductions in MS relapse rates and improvements in T₂ or gadolinium-enhancing lesion burdens have been reported from Phase III trials that include fingolimod, alemtuzumab, cladribine, and rituximab. Promising Phase II trial data exist for teriflunomide, daclizumab, laquinimod, and fumarate. The optimism created by these favorable findings must be tempered with evaluation of the adverse effect profile produced by these new agents. Given the discovery of progressive multifocal leukoencephalopathy with the use of natalizumab, ongoing vigilance for rare and life-threatening reactions due to new agents should be paramount. Patients with MS often experience difficulty with ambulation, spasticity, and cognition. Recent clinical trial data from two Phase III dalfampridine-SR trials indicate certain patients receive benefits in ambulation. This article provides an overview of data from clinical trials of newer agents of potential benefit in MS.

Walking impairment in patients with multiple sclerosis: exercise training as a treatment option

Multiple sclerosis (MS) is a chronic disease of the central nervous system that culminates in the progression of physical and cognitive disability over time. Walking impairment is a ubiquitous feature of MS and a sentinel characteristic of the later or advanced stages of the disease. This paper presents a conceptual rationale along with empirical evidence for exercise training as a rehabilitation approach for managing walking impairment and improving walking function in persons with MS. Conceptually, MS is associated with a decrease in physical activity, which, in turn, can result in deconditioning across multiple domains of physiological functioning. The resulting deconditioning feeds back and further drives physical inactivity until a threshold is reached that likely initiates the progression of walking impairment in MS. Empirically, physical activity and exercise training have been associated with beneficial effects on walking function in persons with MS. This is based on cross-sectional, longitudinal, and experimental research that included diversity in the breadth of measures of walking, persons with MS, and exercise/physical activity characteristics. Of particular importance, future researchers might consider examining the combinatory effects of exercise training plus pharmacological agents on walking mobility in MS. Collectively, exercise training and physical activity might hold significant potential for the management of progressive mobility disability in MS.

Dalfampridine extended release: in multiple sclerosis

Dalfampridine extended release (ER) is an orally administered formulation of dalfampridine (fampridine, 4-aminopyridine), a potassium channel antagonist indicated for the improvement in walking ability in patients with multiple sclerosis (MS). Oral dalfampridine ER improved walking ability in patients with MS in three randomized, double-blind trials of up to 15 weeks' duration. In a phase II trial, percentage improvements in walking speed on the Timed 25-Foot Walk (T25FW) test (primary endpoint) were not significant versus baseline or placebo during treatment with dalfampridine ER 10, 15 or 20 mg twice daily. However, according to a post hoc analysis, response rates were significantly higher with dalfampridine ER than placebo, with a consistent mean improvement in walking speed of 25-29% seen in the pooled results from dalfampridine ER responders during the double-blind treatment period. In two phase III trials, the proportion of timed walk responders (primary endpoint) was significantly greater with dalfampridine ER 10 mg twice daily than with placebo, with improvements in walking speed of approximately 25% seen during dalfampridine ER treatment amongst timed walk responders. Interim results of noncomparative extensions of the two phase III trials showed that consistent improvements in walking speed were sustained above baseline for up to 2.5 years of dalfampridine ER treatment. Oral dalfampridine ER 10 mg twice daily was generally well tolerated in patients with MS, according to the results of the three randomized, double-blind, placebo-controlled trials.

Dalfampridine for the treatment of ambulatory impairment in multiple sclerosis

Dalfampridine is a potassium-channel blocker that is approved by the US FDA as 10 mg extended-release tablets to improve walking in patients with multiple sclerosis. Approval is currently pending in Europe. This is the first pharmacological symptomatic treatment approved for multiple sclerosis patients of any type with walking difficulties. Relative to an immediate-release formulation, the extended-release formulation of dalfampridine lowers peak serum concentrations that contribute to toxicity while maintaining a comparable amount of total drug exposure. Several studies show the efficacy and tolerability of dalfampridine. The pivotal published clinical trial demonstrated a treatment–responder rate of 35% compared with an 8% placebo–responder rate (p < 0.0001). The subjects who responded to treatment had an average improvement in their 25-foot walking test time of 25.2% (95% CI: 21.5–28.8) compared with an average improvement of 4.7% (95% CI: 1.0–8.4) in subjects who responded to placebo. Seizures are the most serious adverse effect of dalfampridine with a probable dose-dependent likelihood of occurrence.

4-Aminopyridinium 4-carboxybutanoate

The asymmetric unit of the title salt, C₅H₇N₂⁺·C₅H₇O₄⁻, contains two 4-amino­pyridinium cations and two 4-carb­oxy­butano­ate anions. Each 4-amino­pyridinium cation is planar, with a maximum deviation of 0.005 (2) Å. Both 4-carb­oxy­butano­ate anions adopt an extended conformation. In the crystal structure, the cations and anions are linked via N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds, forming a two-dimensional network parallel to the bc plane.

Bis(4-amino-pyridinium) sulfate monohydrate

The asymmetric unit of the title compound, 2C₅H₇N₂⁺·SO₄²⁻·H₂O, contains two 4-amino­pyridinium cations (A and B), a sulfate dianion and a water mol­ecule. One of the 4-amino­pyridinium cations (B) is disordered over two orientations with refined site occupancies of 0.568 (4) and 0.432 (4). The non-H atoms of the 4-amino­pyridinium cations are essentially coplanar, with a maximum deviation of 0.055 (1) Å (in cation A), 0.022 (3) Å (for the major component in cation B) and 0.009 (3) Å (for the minor component in cation B). In the crystal, the sulfate O atoms link the 4-amino­pyridinium cations and water mol­ecules into a three-dimensional network via inter­molecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds. The crystal structure is further consolidated by N—H⋯O(water) and C—H⋯O(water) hydrogen bonds.

4-Amino-pyridinium 2-hy-droxy-benzoate

In the salicylate anion of the title salt, C₅H₇N₂⁺·C₇H₅O₃⁻, an intra­molecular O—H⋯O hydrogen bond generating an S(6) ring motif is observed. In the crystal structure, the cations and anions are linked into a two-dimensional network parallel to the ab plane by N—H⋯O and C—H⋯O hydrogen bonds. The network contains R₂²(7) and R₁²(4) ring motifs. Weak π–π inter­actions between the benzene and pyridinium rings [centroid–centroid distance = 3.688 (1) Å] are also observed.

RNA editing modulates the binding of drugs and highly unsaturated fatty acids to the open pore of Kv potassium channels

The time course of inactivation of voltage-activated potassium (Kv) channels is an important determinant of the firing rate of neurons. In many Kv channels highly unsaturated lipids as arachidonic acid, docosahexaenoic acid and anandamide can induce fast inactivation. We found that these lipids interact with hydrophobic residues lining the inner cavity of the pore. We analysed the effects of these lipids on Kv1.1 current kinetics and their competition with intracellular tetraethylammonium and Kvbeta subunits. Our data suggest that inactivation most likely represents occlusion of the permeation pathway, similar to drugs that produce 'open-channel block'. Open-channel block by drugs and lipids was strongly reduced in Kv1.1 channels whose amino acid sequence was altered by RNA editing in the pore cavity, and in Kv1.x heteromeric channels containing edited Kv1.1 subunits. We show that differential editing of Kv1.1 channels in different regions of the brain can profoundly alter the pharmacology of Kv1.x channels. Our findings provide a mechanistic understanding of lipid-induced inactivation and establish RNA editing as a mechanism to induce drug and lipid resistance in Kv channels.

Effect of 4-Aminopyridine on Action Potential Parameters in Isolated Dog Purkinje Fibers

Introduction

4-Aminopyridine (fampridine), a potassium channel blocker, has demonstrated efficacy in improving lower extremity strength and walking speed in patients with multiple sclerosis. Since in vitro electrophysiologic studies are recommended for evaluating a drug's potential to prolong the QT interval and induce such cardiac arrhythmias as Torsades de Pointes, we examined the electrophysiologic effects of 4-aminopyridine (0.5, 5.0, 50, and 500 µM) on isolated canine Purkinje fibers.

Methods

Microelectrodes monitored the resting membrane potential, overshoot, amplitude of action potential (AP), and maximal rate of depolarization of the AP upstroke in Purkinje fibers stimulated at 0.5 and 1.0 Hz.

Results

None of the above variables were altered in the presence of 4-aminopyridine. The AP duration at 30%, 50%, and 90% repolarization was also monitored, with only the 500-µM concentration at the 1.0-Hz frequency significantly increasing these values with respect to baseline (P < 0.05). However, the small sample size (N = 4) was small. The proportional increases, and their 95% confidence intervals, were 90.8% (−36.4%, 218.0%), 25.8% (11.9%, 39.7%), and 22.0% (14.9%, 29.1%) for APD 30%, 50%, and 90% repolarization, respectively. Reverse rate dependence was not observed, suggesting inhibition of ion channels other than those contributing to QT interval prolongation.

Assessment of the cardiac safety of fampridine-SR sustained-release tablets in a thorough QT/QTc evaluation at therapeutic and supratherapeutic doses in healthy individuals

OBJECTIVE

To characterize the effects of a sustained-release formulation of fampridine (fampridine-SR) on QT interval in healthy subjects.

METHODS

In a double-blind, double-dummy trial, healthy subjects were randomized to 5 days treatment with fampridine-SR at therapeutic (10 mg twice daily) or supratherapeutic (30 mg twice daily) doses, placebo or moxifloxacin (400 mg on treatment day 5). Digital 12-lead electrocardiograms were recorded before treatment and on day 5; blood samples determined fampridine concentrations. Central tendency analysis determined whether the upper limit of the CI for the QT (individual-corrected QT; QTcI) interval change exceeded 10 ms. Outlier analysis determined new-onset QT (corrected QT; QTc) intervals; maximum change in QTc from baseline of 30 - 60 ms and maximum change from baseline >or= 60 ms. The relationship between pharmacokinetic parameters and QTcI values is explored.

RESULTS

Moxifloxacin was associated with a QTcI interval increase > 5 ms at 7 time points; no increase was observed with either dose of fampridine-SR; there were no fampridine outliers. Pharmacokinetic evaluation failed to find dose-dependent cardiac effects. Fampridine was well tolerated, with a higher frequency of adverse events at the supratherapeutic dose.

CONCLUSION

This study showed that fampridine-SR at therapeutic and supratherapeutic doses was not associated with QT prolongation in healthy subjects.

[4-Aminopyridine (Fampridine). A new attempt for the symptomatic treatment of multiple sclerosis]

Mobility limitation is a frequent clinical symptom of multiple sclerosis (MS) that poses a therapeutic challenge. For years results of animal experiments and clinical experience have indicated that the potassium channel blocker 4-aminopyridine improves axonal excitatory circuits and thus muscular strength in demyelinating diseases. A recently conducted randomized, placebo-controlled, multicenter phase 3 clinical trial in MS patients was able to show that an oral sustained-release formulation of 4-aminopyridine (Fampridine-SR) represents a suitable agent for treatment of walking disability in MS patients.This overview presents the study data and discusses the value of 4-aminopyridine for the symptomatic treatment of MS as a neurofunctional modifier of this disabling disease.

Steady-state pharmacokinetics and tolerability of orally administered fampridine sustained-release 10-mg tablets in patients with multiple sclerosis: a 2-week, open-label, follow-up study

BACKGROUND

Fampridine sustained release (SR) has generally been well tolerated in clinical studies in patients with multiple sclerosis (MS) at doses < or = 20 mg/d. The pharmacokinetics of single escalating doses of fampridine SR (5, 10, 15, and 20 mg) were evaluated in a companion study.

OBJECTIVES

The primary objective of this study, which followed on from the single-dose pharmacokinetic study, was to assess the steady-state pharmacokinetics of fampridine in patients with MS over 2 weeks of oral administration of open-label fampridine SR 20 mg BID. Tolerability was also evaluated.

METHODS

The dose of fampridine SR was titrated upward to twice-daily administration over days 1 and 2, with 20 mg given in the morning and 10 mg in the evening. From days 3 to 14, patients received fampridine SR 20 mg BID (total daily dose, 40 mg). Fampridine pharmacokinetic parameters were determined on days 1, 8, and 15. The parameters of interest included C(max), T(max), C(min), AUC, and apparent t((1/2)) These parameters were compared with those from the single-dose study. Tolerability was assessed based on adverse events, physical examinations, vital signs, laboratory tests, and ECGs.

RESULTS

Twenty-one white patients who participated in the single-dose study were enrolled in the steady-state study (52.4% female; mean [SD] age, 45.1 [7.4] years; weight range, 54-87 kg). Fampridine pharmacokinetic parameters on day 1 were consistent with those obtained in the single-dose study. The T(max) did not differ significantly between day 1, day 8, day 15, and the single-dose study (range, 3.25-3.78 hours). C(max) values on days 8 and 15 (66.7 and 62.6 ng/mL, respectively) were significantly higher than those on day 1 (48.6 ng/mL) and in the single-dose study (50.5 ng/mL) (all, P < 0.001), reflecting accumulation of fampridine with multiple dosing. Values for C(max)/C(min) did not differ significantly between day 1 and the single-dose study (2.44 and 2.43, respectively) or between days 8 and 15 (2.90 and 2.88, respectively); however, the single-dose and day-1 values differed significantly from the day-8 and day-15 values (P < or = 0.001). There were no significant differences with respect to any other pharmacokinetic parameters. One hundred adverse events were reported by 21 patients. With the exception of 1 case of severe nausea, all adverse events were of mild to moderate severity. Thirty-five events reported by 14 subjects were considered treatment related. Dizziness was the most common treatment-related adverse event, with 11 episodes reported by 8 patients. No clinically significant changes were found in clinical laboratory values, vital signs, or physical examination findings from baseline to the last visit, and there were no clinically significant changes in QTc intervals (Bazett's correction).

CONCLUSIONS

In these patients with MS, the steady-state pharmacokinetic profile of fampridine SR 20 mg BID administered for 2 weeks appeared to support the use of twice-daily dosing in this population. This dosage was generally well tolerated.

Pharmacokinetics and tolerability of single escalating doses of fampridine sustained-release tablets in patients with multiple sclerosis: a Phase I-II, open-label trial

BACKGROUND

Fampridine (4-aminopyridine) is a potassium channel-blocking agent that has been reported to have therapeutic potential for improving walking and mobility in patients with multiple sclerosis (MS). A sustained-release (SR) formulation of fampridine was developed to improve the agent's pharmacokinetic profile by extending its t((1/2)) relative to that of immediate-release fampridine.

OBJECTIVES

The primary study objective was to examine the pharmacokinetics of fampridine SR tablets after single escalating doses in patients with MS. Tolerability was evaluated as a secondary end point.

METHODS

This multicenter, Phase I-II, open-label trial evaluated the dose proportionality and tolerability of 4 single doses of fampridine SR (5, 10, 15, and 20 mg) in patients with MS. There was a 4-day washout between doses. Blood samples were collected immediately before drug administration, hourly for the first 8 hours after administration, and at 10, 12, 14, 18, and 24 hours after administration. The pharmacokinetic parameters evaluated included C(max), T(max), AUC, elimination rate constant, apparent elimination t((1/2)), and apparent CL/F. Twelve-lead ECGs were obtained at baseline (0.5 hour before dosing) and at 1, 4, 12, and 24 hours after drug administration to evaluate potential effects on the QTc interval. All adverse events, abnormal laboratory values, and ECG abnormalities were recorded and evaluated for clinical relevance. Adverse-event data were monitored for 24 hours after the last dose, and patients were instructed to report any adverse events for 14 days after the conclusion of the study.

RESULTS

Twenty-four white patients were enrolled (58% female; mean [SD] age, 45.4 [7.3] years; weight range, 47.8-87.1 kg), and 23 completed the study. Mean plasma concentrations and AUC values were dose proportional. T(max) occurred at 3.36 to 3.92 hours after dosing; the apparent elimination t((1/2)) was 5.47 hours. Both sex and weight affected the pharmacokinetic parameters of fampridine SR. Eleven treament-related adverse events were reported in 10 patients, with dizziness being the most common (7 incidents reported by 6 patients [1 at 10 mg, 3 at 15 mg, and 3 at 20 mg]). Other adverse events included amblyopia, asthenia, headache, and ataxia. All treatment-related adverse events were mild to moderate in severity, with the exception of 1 case of dizziness (20 mg) that was considered severe. No serious adverse events were reported, and no clinically significant changes in corrected QT intervals were observed. No patients with-drew due to treatment-related adverse events.

CONCLUSION

In these patients with MS, fampridine SR (5-20 mg) had a potentially advantageous pharmacokinetic profile relative to that associated with immediate-release fampridine and was generally well tolerated.

Crystal structure and spectroscopic elucidation of 3-phenylpyridinium hydrogensquarate

The novel 3-phenylpyridinium hydrogensquarate (1) has been synthesized and its structure and properties are elucidated spectroscopically, thermally and structurally, using single crystal X-ray diffraction, linear-polarized solid-state IR-spectroscopy, UV-spectroscopy, TGA, DSC, DTA and ESI MS. Quantum chemical calculations were used to obtain the electronic structure, vibrational data and electronic spectrum. 3-Phenylpyridinium hydrogensquarate, crystallizes in the space group P-1 and the ions in the unit cell are joined into layers by intermolecular NH...O=C((Sq)) bonds with bond lengths of 2.625 and 2.626 A, respectively. Hydrogentartarates form dimers by strong O=COH...OCO interactions (2.499 A).

Single-Dose pharmacokinetics of sustained-release fampridine (Fampridine-SR) in healthy volunteers and adults with renal impairment

Fampridine-SR is a sustained-release formulation of fampridine (4-aminopyridine), a potassium channel blocker demonstrated to improve walking ability in patients with multiple sclerosis. This study evaluated the pharmacokinetics of fampridine and its metabolites after administration of fampridine-SR 10 mg in healthy volunteers and in subjects with mild, moderate, or severe renal impairment (5 per group). Analysis of variance was used to calculate 90% confidence intervals (CIs) for the ratios (impaired/healthy) of least squares mean in maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC). Clearance was primarily through urinary excretion. In renally impaired subjects, fampridine plasma concentrations were consistently higher than in healthy individuals: ratios for C(max) ranged from 166.5% to 199.9% for mild and severe renal impairment, respectively. AUC(0-infinity) ratios ranged from 175.3% to 398.7%, respectively, for mild and severe renal impairment. Mean terminal disposition half-life was 6.4 hours in healthy individuals, compared with 7.4, 8.1, and 14.3 hours in patients with mild, moderate, and severe renal impairment, respectively. Regression analysis confirmed the significant relationship between creatinine clearance and extent of exposure as quantified by AUC for fampridine and its metabolites, suggesting cautious use in patients with mild renal impairment and avoidance in cases of moderate or severe renal impairment.

Quantification of 4-aminopyridine in plasma by capillary electrophoresis with electrokinetic injection

A rapid and sensitive CE method for the determination of 4-aminopyridine in human plasma using 3,4-diaminopyridine as an internal standard was developed and validated. The analytes were extracted from 0.5-mL aliquots of human plasma by liquid-liquid extraction, using 8 mL of ethyl ether, and injected electrokinetically into capillary electrophoresis equipment. The instrumental conditions were obtained and optimized by Design of Experiments (DOE--factorial and response surface model), having as factors: separation voltage, ionic strength (buffer concentration), pH and temperature. The response variables were migration time, resolution, tailing factor and drug peak area. After obtaining mathematically predicted values for the response variables with best factors combinations, these were reproduced experimentally in good agreement with predicted values. In addition to optimal separation conditions obtained by Design of Experiments, sensitivity was improved using electrokinetic injection at 10 kV for 10 s, and a capillary with 50 cm effective length and 100 microm I.D. The final instrumental conditions were voltage at 19 kV, capillary temperature at 15 degrees C, wavelength at 254 nm, and phosphate buffer 100 mM, pH 2.5 as the background electrolyte. This assay was linear over a concentration range of 2.5-80 ng/mL with a lower limit of quantification of 2.5 ng/mL. The relative standard deviation for the assay precision was <7% and the accuracy was >95%. This method was successfully applied to the quantification of 4-aminopyridine (4-AP) in plasma samples from patients with spinal cord injury.

[Reconsidering fatigue at the onset of multiple sclerosis]

Fatigue is a frequent symptom of multiple sclerosis (MS). It has been reported to varying degrees at all stages of the disease by 50 to 90% of all MS patients. Fatigue is now recognised as a disabling symptom which negatively impacts daily living. This symptom was underrated until recently but has now been included in clinical practice. Most fatigue scales have been developed in the English language and are culturally specific to their country of origin. The Fatigue Severity Scale is a one-dimensional nine-item scale which briefly assesses the impact of fatigue on the daily lives of MS patients. It has been widely used in different studies, even though it appears to be less relevant than the multi-dimensional 40-item Fatigue Impact Scale which was developed in Canada by Fisk et al (1994). The Fatigue Impact Scale is useful because it assesses different aspects of MS-related fatigue, such as the effects of fatigue on cognitive and physical activities and can include daily living. The Multiple Sclerosis Council for Clinical Practice Guidelines recommends the use of a 21-item Modified Fatigue Impact Scale which is a shortened version of the 40-item Fatigue Impact Scale. Using word-for-word translations of these scales into French would fail because the results would not be interpretable. We first translated and culturally adapted the Fatigue Impact Scale to French-speaking patients. We then evaluated the psychometric properties of this French version (EMIF-SEP). We used the EMIF-SEP scale to study fatigue in French MS patients. We found a significant correlation between higher EMIF-SEP total scores and higher EDSS scores; likewise physical dimension of the EMIF-SEP were linked to disability. But no correlations were found between the cognitive aspects of fatigue and disability. Other studies have failed to show any correlation between fatigue and disability. We suggest that this may be due to differences in sample size, or to the type of instrument used to quantify fatigue. As seen above, some tools do not allow for multi-dimensional assessment of fatigue. The EMIF-SEP scale is useful in that it allows for qualitative and quantitative assessment of fatigue.

Effects of 4-Aminopyridine on Cloned hERG Channels Expressed in Mammalian Cells

INTRODUCTION: Non-clinical evaluation of a medication's potential to induce cardiac toxicity is recommended by regulatory agencies. 4-Aminopyridine (fampridine) is a potassium channel blocker with the demonstrated ability to improve walking ability in patients with multiple sclerosis. We evaluated the in vitro effects of 4-aminopyridine on the human ether-à-go-go-related gene (hERG) channel current, since hERG current inhibition is associated with QT interval prolongation-a precursor to torsade de pointes (TdP). METHODS: 4-Aminopyridine was evaluated in concentrations ranging from 0.1 mM to 30 mM in human embryonic kidney 293 cells stably transfected with the hERG gene; terfenadine 60 nM was used as a positive control. RESULTS AND DISCUSSION: We observed concentration-dependent inhibition of hERG current with 4-aminopyridine doses between 0.3 and 30 mM. The concentration of 3.8 mM resulting in 50% inhibition (IC(50)) is approximately three orders of magnitude higher than expected therapeutic plasma concentrations, suggesting 4-aminopyridine has low potential for prolonging QT interval or inducing TdP.

Treatment of acute demyelinating optic neuritis

Patients with typical acute monosymptomatic demyelinating optic neuritis should receive gadolinium-enhanced magnetic resonance imaging (MRI) of the brain and orbits to determine if they are at high risk for the subsequent development of clinically definite multiple sclerosis (CDMS). The presence of >or=2 white matter lesions (>or=3 mm in diameter, at least 1 lesion periventricular or ovoid) indicates high risk for CDMS; the following treatment should be considered for such patients: 1. Intravenous methylprednisolone sodium succinate (1 gram IV/day for 3 days) followed by oral prednisone (1 mg/kg/day for 11 days) with 4-day taper (20 mg on day 1, 10 mg on days 2 and 4); 2. Interferon beta 1-a (Avonex 30microg intramuscularly [IM] weekly, or Rebif 22 microg subcutaneously [SQ] weekly). These two drugs have been shown to reduce the short-term risk of CDMS in high risk monosymptomatic patients. In monosymptomatic patients with <2 white matter lesions, and in patients for whom CDMS has been established, IV methylprednisolone treatment followed by oral prednisone should be considered on an individual basis. Treatment in these patients may hasten visual recovery, but does not affect long-term visual outcome. Oral prednisone alone, without prior treatment with IV methylprednisolone, may increase the risk for recurrent optic neuritis and should be avoided.

Pharmacokinetics of 14C-radioactivity after oral intake of a single dose of 14C-labeled fampridine (4-aminopyridine) in healthy volunteers

BACKGROUND

Fampridine (4-aminopyridine) is a potassium channel blocker that has been evaluated as a treatment for patients with spinal cord injury and multiple sclerosis.

OBJECTIVE

The purpose of this study was to determine the pharmacokinetics of a single dose of an orally administered solution of (14)C-labeled fampridine in healthy volunteers.

METHODS

In this open-label, single-dose study conducted in an inpatient setting, healthy adult men were administered an oral solution containing 15 mg of (14)C-labeled fampridine (100 microCi) in a fasted state. In addition to blood sampling for analysis of plasma (14)C-radioactivity at prescribed intervals over 7 days, all urine and feces were collected for analysis of drug recovery and disposition. Urine samples were also analyzed for metabolic profiling. Plasma pharmacokinetic parameters of the (14)C-radiolabeled drug were determined using standard liquid-scintillation techniques. Recovery was calculated to provide the total amount of radioactivity excreted as a proportion of the original dose. Nonhydrolyzed and hydrolyzed urine extracts were analyzed for radioactivity and metabolites using reverse-phase, isocratic high-performance liquid chromatography with spectrophotometric and radioactive detection. Tolerability was assessed through evaluation of vital signs, hematologic and other laboratory parameters, and electrocardiography.

RESULTS

The 4 white male subjects had a mean (SD) age of 21 (2) years. No clinically significant abnormalities in vital signs, clinical chemistry, hematology, urinalysis, or electrocardiography were observed either before or during the study. Peak plasma radioactivity was reached at 1 hour after dosing, with a median concentration of 72.9 ng x mL(-1). There was complete disappearance of radioactivity by 24 hours (limit of quantitation, 400 disintegrations/min per peak), and the calculated median t(1/2) was 3.14 hours. Total cumulative recovery of (14)C-radioactivity was 96.36%, with only 0.51% of drug recovered in feces. On chromatography, 2 metabolites accounted for a low proportion of total urinary radioactivity (3% and 6% of total radioactivity in the interval from 0 to 4 hours after dosing; 17% and 9% in the interval from 8 to 12 hours after dosing). Three subjects reported mild and transient dizziness occurring 1 half-hour after dosing; this was considered possibly related to the study drug.

CONCLUSION

Fampridine administered as an oral solution was rapidly absorbed and was nearly completely and rapidly eliminated as unchanged drug via urinary excretion, suggesting that it is unlikely to undergo substantial metabolic transformation.

Bis(4-amino-pyridinium) tetra-chlorido-cobaltate(II)

In the title compound, (C₅H₇N₂)₂[CoCl₄], the cobalt(II) ion is coordinated by four chloride ions in a slightly distorted tetra­hedral geometry. The crystal packing is stabilized by inter­molecular N—H⋯Cl hydrogen bonding, forming a three-dimensional network. The crystal was a non-merohedral twin emulating tetra­gonal symmetry, but being in fact ortho­rhom­bic.

Bis(4-amino-pyridinium) bis(hydrogen oxalate) monohydrate

In the title compound, 2C₅H₇N₂⁺·2C₂HO₄⁻·H₂O, the asymmetric unit consists of an amino­pyridinium cation, an oxalic actetate anion and a half-molecule of water, which lies on a two-fold rotation axis. The crystal packing is consolidated by inter­molecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds. The mol­ecules are linked into an infinite one dimensional chain along [010].

4-Amino-pyridinium hydrogen succinate

In the title salt, C₅H₇N₂⁺·C₄H₅O₄⁻, the asymmetric unit comprises an amino­pyridinium cation and a hydrogen succinate anion as protonation of the aromatic N atom of the 4-amino­pyridine mol­ecule has occurred. The crystal packing is stabilized by inter­molecular O—H⋯O and N—H⋯O hydrogen bonds that lead to a two-dimensional array. Short C—H⋯O contacts are also present.

Sustained-release oral fampridine in multiple sclerosis: a randomised, double-blind, controlled trial

BACKGROUND

Clinical studies suggested that fampridine (4-aminopyridine) improves motor function in people with multiple sclerosis. This phase III study assessed efficacy and safety of oral, sustained-release fampridine in people with ambulatory deficits due to multiple sclerosis.

METHODS

We undertook a randomised, multicentre, double-blind, controlled phase III trial. We randomly assigned 301 patients with any type of multiple sclerosis to 14 weeks of treatment with either fampridine (10 mg twice daily; n=229) or placebo (n=72), using a computer-generated sequence stratified by centre. We used consistent improvement on timed 25-foot walk to define response, with proportion of timed walk responders in each treatment group as the primary outcome. We used the 12-item multiple sclerosis walking scale to validate the clinical significance of the response criterion. Efficacy analyses were based on a modified intention-to-treat population (n=296), which included all patients with any post-treatment efficacy data. The study is registered with ClinicalTrials.gov, number NCT00127530.

FINDINGS

The proportion of timed walk responders was higher in the fampridine group (78/224 or 35%) than in the placebo group (6/72 or 8%; p<0.0001). Improvement in walking speed in fampridine-treated timed walk responders, which was maintained throughout the treatment period, was 25.2% (95% CI 21.5% to 28.8%) and 4.7% (1.0% to 8.4%) in the placebo group. Timed walk responders showed greater improvement in 12-item multiple sclerosis walking scale scores (-6.84, 95% CI -9.65 to -4.02) than timed walk non-responders (0.05, -1.48 to 1.57; p=0.0002). Safety data were consistent with previous studies.

INTERPRETATION

Fampridine improved walking ability in some people with multiple sclerosis. This improvement was associated with a reduction of patients' reported ambulatory disability, and is a clinically meaningful therapeutic benefit.

Octa-akis(4-amino-pyridine)-1κN,2κN-aqua-2κO-μ-carbonato-1:2κO,O':O''-dinickel(II) dichloride penta-hydrate

In the title compound, [Ni(2)(CO(3))(C(5)H(6)N(2))(8)(H(2)O)]Cl(2)·5H(2)O, one of the the Ni(II) ions is six-coordinated in a distorted octa-hedral geometry, with the equatorial plane defined by four pyridine N atoms from four amino-pyridine ligands, the axial positions being occupied by one water O and a carbonate O atom. The other Ni(II) ion is also six-coordinated, by four other pyridine N atoms from four other amino-pyridine ligands and two carbonate O atoms to complete a distorted octa-hedral geometry. In the crystal structure, mol-ecules are linked into an infinite three-dimensional network by O-H⋯O, N-H⋯Cl, N-H⋯O, O-H⋯N, C-H⋯O, C-H⋯N and C/N-H⋯π inter-actions involving the pyridine rings.

Sustained-release fampridine for symptomatic treatment of multiple sclerosis

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical trials, and adverse effects of sustained-release (SR) fampridine in patients with multiple sclerosis (MS).

DATA SOURCES

An English-language human data search was done using PubMed/MEDLINE (1966-August 2008) to retrieve relevant material using the search terms fampridine-SR, 4-aminopyridine, and multiple sclerosis. References of selected articles and information from the drug developer were used to further identify pertinent trials.

STUDY SELECTION AND DATA EXTRACTION

Article selection was based primarily on studies that evaluated the pharmacokinetics, safety, and efficacy of fampridine-SR in patients with MS. Relevant meeting abstracts were also included as part of the analysis.

DATA SYNTHESIS

Fampridine-SR is a sustained-release, orally administered potassium-channel blocker acting in the central nervous system to enhance conduction in demyelinated axons. Several small trials have evaluated the safety and efficacy of fampridine-SR in patients with MS to improve their walking ability. Data from a recent large Phase 3 trial indicated that walking speed improved in 42.9% of patients with MS who were treated with fampridine-SR compared with 9.3% of those who received placebo (p < 0.001). Treatment-related adverse events associated with the use of fampridine-SR include dizziness, insomnia, nausea, and paresthesia. More severe adverse events, such as seizure, have occurred in patients receiving doses higher than those currently recommended.

CONCLUSIONS

Positive results from 2 Phase 3 clinical trials have put fampridine-SR on the path toward approval as a medication for improving walking speed and lower extremity strength in patients with MS.