Population pharmacokinetics and pharmacodynamics of dalfampridine-ER in healthy volunteers and in patients with multiple sclerosis

KCNA1 gain-of-function epileptic encephalopathy treated with 4-aminopyridine

Precision medicine for Mendelian epilepsy is rapidly developing. We describe an early infant with severely pharmacoresistant multifocal epilepsy. Exome sequencing revealed the de novo variant p.(Leu296Phe) in the gene KCNA1, encoding the voltage-gated K⁺ channel subunit K_V 1.1. So far, loss-of-function variants in KCNA1 have been associated with episodic ataxia type 1 or epilepsy. Functional studies of the mutated subunit in oocytes revealed a gain-of-function caused by a hyperpolarizing shift of voltage dependence. Leu296Phe channels are sensitive to block by 4-aminopyridine. Clinical use of 4-aminopyridine was associated with reduced seizure burden, enabled simplification of co-medication and prevented rehospitalization.

Treatment of internuclear ophthalmoparesis in multiple sclerosis with fampridine: A randomized double-blind, placebo-controlled cross-over trial

Aim

To examine whether the velocity of saccadic eye movements in internuclear ophthalmoparesis (INO) improves with fampridine treatment in patients with multiple sclerosis (MS).

Methods

Randomized, double‐blind, placebo‐controlled, cross‐over trial with fampridine in patients with MS and INO. Horizontal saccades were recorded at baseline and at multiple time points post‐dose. Main outcome measures were the change of peak velocity versional dysconjugacy index (PV‐VDI) and first‐pass amplitude VDI (FPA‐VDI). Both parameters were compared between fampridine and placebo using a mixed model analysis of variance taking patients as their own control. Pharmacokinetics was determined by serial blood sampling.

Results

Thirteen patients had a bilateral and 10 had a unilateral INO. One patient had an INO of abduction (posterior INO of Lutz) and was excluded. Fampridine significantly reduced both PV‐VDI (−17.4%, 95% CI: −22.4%, −12.1%; P < 0.0001) and FPA‐VDI (−12.5%, 95% CI: −18.9%, −5.5%; P < 0.01). Pharmacokinetics demonstrated that testing coincided with the average t_max at 2.08 hours (SD 45 minutes). The main adverse event reported after administration of fampridine was dizziness (61%).

Conclusion

Fampridine improves saccadic eye movements due to INO in MS. Treatment response to fampridine may gauge patient selection for inclusion to remyelination strategies in MS using saccadic eye movements as primary outcome measure.

Fampridine Prolonged Release: A Review in Multiple Sclerosis Patients with Walking Disability

Oral fampridine prolonged release (PR) [Fampyra^®] is a lipid-soluble selective potassium channel blocker that is approved in the EU for the improvement of walking in adult multiple sclerosis (MS) patients with walking disability (expanded disability status scale score of 4-7). In clinical trials (MS-F203 and MS-F204) using an objective measure of walking improvement [the timed 25-foot walk (T25FW)], more than one-third of patients receiving fampridine PR achieved a consistent on-treatment improvement in walking speed (i.e. became TW responders) over 9-14 weeks of treatment. Fampridine PR recipients who fulfilled the definition of TW responder had mean improvements of ≈25% from baseline in T25FW walking speed. In a clinical trial (ENHANCE) that used a patient-rated measure of walking improvement [12-item MS walking scale (MSWS-12)], a significantly greater proportion of fampridine PR recipients than placebo recipients achieved a ≥8-point improvement on the MSWS-12 with 24 weeks of treatment. Where reported, adverse events were mostly mild or moderate in severity, and generally consistent with the underlying disease or mechanism of action of fampridine PR. Fampridine PR is a useful treatment option to consider in adult MS patients with walking disability.

Clinically Relevant Levels of 4-Aminopyridine Strengthen Physiological Responses in Intact Motor Circuits in Rats, Especially After Pyramidal Tract Injury

BACKGROUND

4-Aminopyridine (4-AP) is a Food and Drug Administration-approved drug to improve motor function in people with multiple sclerosis. Preliminary results suggest the drug may act on intact neural circuits and not just on demyelinated ones.

OBJECTIVE

To determine if 4-AP at clinically relevant levels alters the excitability of intact motor circuits.

METHODS

In anesthetized rats, electrodes were placed over motor cortex and the dorsal cervical spinal cord for electrical stimulation, and electromyogram electrodes were inserted into biceps muscle to measure responses. The motor responses to brain and spinal cord stimulation were measured before and for 5 hours after 4-AP administration both in uninjured rats and rats with a cut lesion of the pyramidal tract. Blood was collected at the same time as electrophysiology to determine drug plasma concentration with a goal of 20 to 100 ng/mL.

RESULTS

We first determined that a bolus infusion of 0.32 mg/kg 4-AP was optimal: it produced on average 61.5 ± 1.8 ng/mL over the 5 hours after infusion. This dose of 4-AP increased responses to spinal cord stimulation by 1.3-fold in uninjured rats and 3-fold in rats with pyramidal tract lesion. Responses to cortical stimulation also increased by 2-fold in uninjured rats and up to 4-fold in the injured.

CONCLUSION

Clinically relevant levels of 4-AP strongly augment physiological responses in intact circuits, an effect that was more robust after partial injury, demonstrating its broad potential in treating central nervous system injuries.

Experience with fampridine in clinical practice: analysis of a possible marker of clinical response

PURPOSE OF THE STUDY

Approximately 85% of patients with multiple sclerosis experience reduced mobility, which negatively affects quality of life. Fampridine is the first symptomatic treatment aimed at improving gait. We analyzed effectiveness and tolerance in clinical practice. We also sought a prevalent gait pattern in responders as a potential clinical response marker.

MATERIAL AND METHODS

Six-month prospective study of fampridine in patients with multiple sclerosis. Response was evaluated using the Timed 25-Foot Walk Test (T25FW) and the 12-Item Multiple Sclerosis Walking Scale (MSWS-12). Response was defined as increased gait speed (≥20%) and decreased MSWS-12 score (≥4 points).

RESULTS

Fifty-five patients (67.3% women; mean age, 51.7 [11.1] years) with a baseline Expanded Disability Status Scale (EDSS) score of 5.8. Gait pattern was paraparetic (40%), hemiparetic (21.8%) and ataxic (38.2%). Of all patients, 70.9% demonstrated clinical benefit based on response criteria established, at the 14-d follow-up, 61.8% at 3 months and 45.5% at 6 months. A similar response pattern was observed in the MSWS-12. A significant decrease in the mean (SD) EDSS score was observed in responders at 6 months (6.1 [0.9] vs. 5.64 [0.1], p < 0.05). Adverse effects were recorded in 50.9%, although most were mild-moderate and resolved completely. We did not identify a prevalent gait pattern among responders. After a washout period, some patients received fampridine a second time obtaining response recovery.

CONCLUSIONS

In our patients' cohort, fampridine proved clinical benefit, being safe and well tolerated in most cases. We did not identify a gait pattern that was predictive of clinical response.

Pharmacokinetic profile of dalfampridine extended release: clinical relevance in patients with multiple sclerosis

BACKGROUND

In January 2010, dalfampridine extended release tablets (dalfampridine-ER [Ampyra *]; prolonged-, modified- or sustained-release fampridine [Fampyra †] in some countries), 10 mg to be administered twice daily approximately 12 hours apart, were approved by the US Food and Drug Administration. This was the first drug indicated to improve walking in patients with MS.

SCOPE

Publications describing the pharmacokinetics of dalfampridine-ER or the immediate release formulation were identified from a search of PubMed through June 2012 using the search terms 'dalfampridine OR fampridine OR 4-aminopyridine' AND 'pharmacokinetics' and were supplemented with unpublished studies made available by Acorda Therapeutics Inc.

FINDINGS

Pharmacokinetic studies show dose proportionality, with dalfampridine-ER having a more favorable profile than immediate-release dalfampridine. With twice-daily dosing of dalfampridine-ER, time to peak plasma concentration (3.2-3.9 hours) and apparent terminal plasma half-life (5.6-6.4 hours) are approximately twice those of immediate-release formulations, with comparable overall exposure and peak plasma concentrations (21.6 ng/mL) that were maintained at levels approximately 50% lower than immediate release. Steady state is achieved within 39 hours; pharmacokinetics are predictable based on single dosing. Trough plasma concentrations of 13-15 ng/mL are required to maintain efficacy. Renal excretion is predominantly as unchanged compound, and renal clearance in healthy individuals exceeds the glomerular filtration rate. Since dalfampridine-ER exposure increases with renal impairment, it is contraindicated in patients with moderate or severe impairment in the US, and in patients with any renal impairment in the European Union.

CONCLUSIONS

Dalfampridine-ER has low protein binding, is not a substrate for p-glycoprotein and does not affect CYP450 enzymes, suggesting a low potential for drug-drug interactions. Because of the narrow therapeutic range and risk of adverse events, including seizure, with increasing plasma concentrations, the recommended dose and regimen of dalfampridine-ER should not be exceeded and not be used with other dalfampridine formulations. A limitation of this review is that it includes some data that have not yet been published.

Identification of metabolites of dalfampridine (4-aminopyridine) in dog and rat

Background

Dalfampridine (4-aminopyridine; 4-AP) is a potassium channel blocker available in the United States to improve walking in patients with multiple sclerosis as demonstrated by an increase in walking speed. Its pharmacokinetics have been evaluated in human studies but its metabolites are not well characterized. This study characterizes the metabolic profile of dalfampridine in two animal species that were used to support nonclinical toxicology evaluation.

Methods

Metabolic profiling of single oral ¹⁴C-4-AP doses was performed in 12 adult male Sprague–Dawley rats. Similarly, metabolic profiling was performed in beagle dogs in two studies that administered ¹⁴C-4-AP by gastric intubation; the first study included six animals (three males, three females), and the second study included two animals (one male, one female). Blood and urine samples were evaluated using high performance liquid chromatography, thin layer chromatography, and radioanalysis (liquid scintillation counting), with further identification of components by gas chromatography/mass spectrometry.

Results

Five radioactive components, M1–M5, were detected in rat plasma, although most of the radioactivity corresponded with unchanged 4-AP. Based on R_f values, M1 and M2 coseparated with reference standards of 3-hydroxy-4-AP and 4-AP, respectively. Additionally, components M1, M2, and M3 coseparated with the same components isolated from the urine of a dog dosed with ¹⁴C-4-AP and identified as 3-hydroxy-4-AP, 4-AP, and 3-hydroxy-4-AP sulfate, respectively; M4 and M5 could not be identified because of low concentrations. In dogs, most of the radioactivity was excreted within the first 24 hours as unchanged compound.

Conclusions

Following oral dosing, 4-AP was rapidly absorbed in rats and dogs, with rapid excretion and almost complete urinary recovery in dogs. The primary metabolites in both animal models were 3-hydroxy-4-AP and 3-hydroxy-4-AP sulfate. Systemic clearance not accounted for by renal excretion of 4-AP may occur by liver metabolism by hydroxylation of 4-AP to 3-hydroxy-4-AP followed by sulfate conjugation to 3-hydroxy-4-AP sulfate.