Amifampridine overdose leading to refractory status epilepticus.

3,4-Aminopyridine or Amifampridine belongs to the aminopyridine class of drugs which is used to treat multiple sclerosis and Lambert-Eaton Myasthenic Syndrome (LEMS). Aminopyridine pharmaceuticals inhibit presynaptic potassium channels. This increases available acetylcholine in the nerve cleft which leads to improved strength in this patient population. While overdoses have been reported of 4-Aminopyridine, no case reports of acute 3.4-Aminopyridine overdose are currently available. A 67 year old man presented to the emergency department 30 min after ingesting 100 mg of amifampridine in a suicide attempt. Within an hour of ingestion he experienced tachycardia, tachypnea, hypertension and tremor. The patient then started to experience seizures and had a cardiac arrest 3 h after the ingestion. The patient achieved return of spontaneous circulation but proceeded to have refractory seizures. Despite significant and escalating doses of anti-epileptic medications, the patient continued to have seizures until 18 h after ingestion. His anti-epileptic medications were weaned over the following days and he had no more seizures. This is a report of a novel overdose of 3,4-Aminopyridine, a medication that belongs to the aminopyridine class of pharmaceuticals that have been well used for many years. Aminopyridine overdoses are commonly thought to carry low morbidity and mortality; however, our patient had both a cardiac arrest and refractory status epilepticus. Ultimately, this case suggests that patients who overdose on 3,4-Aminopyridine could become critically ill and their presentation may be far more severe than that of other medications of the same class.

Safety, efficacy and steroid-sparing effect of amifampridine in Lambert-Eaton myasthenic syndrome patients - real world data.

INTRODUCTION: Lambert-Eaton myasthenic syndrome (LEMS) is an ultrarare neuromuscular disease with a triad of symptoms: muscle paresis, dysautonomy, and areflexia. Amifampridine is the symptomatic treatment of LEMS. AIM OF STUDY: To assess the effectiveness and safety of treatment in the real world. MATERIAL AND METHODS: 14 patients with non-neoplastic LEMS treated with amifampridine were enrolled in the study (female 42.9%, mean age 48.8 ± 11.4 years). The patients were assessed using the Quantitative Myasthenia Gravis (QMG) scale, QMG limb domain (LD) score, spirometry, Hand Grip Strength (GRIP) test, and repetitive nerve stimulation study (RNS) at baseline and at the end of follow-up. Diagnostic delay since first symptoms was from seven months up to 22 years. Treatment delay ranged from one to 26 years. The patients were treated and reevaluated after 21.1 ± 12.0 weeks (range 13-48). RESULTS: All of the patients improved in QMG score. Mean improvement was 5.1 ± 2.0 (range 1-8) points (p < 0.001) and this showed no correlation with the duration of the disease before treatment (p = 0.477). 85.7% of patients (N = 12) improved ≥ 3 points (clinically meaningful) in QMG. 78.6% of the patients improved in QMG LD (mean 2.2 ± 1.6 points (p < 0.001)). Also, forced vital capacity (FVC) improved after treatment (p = 0.031). Mean improvement in GRIP test was 7.0 ± 7.1 kg in the right hand and 5.2 ± 7.5 kg in the left hand (p < 0.001). In RNS before treatment, facilitation ( > 100%) was observed in 78.6% (N = 11) of patients, and was higher before treatment (p < 0.001). Compound muscle action potential (CMAP) amplitude was higher after treatment (p < 0.001). Mean increase of CMAP amplitude was 2.1 ± 1.6 times. In 64.3% (N = 9) of patients lowering of corticosteroid dose was achieved. CONCLUSIONS: Amifampridine is an effective treatment in non-neoplastic LEMS patients, regardless of disease duration. The treatment is well-tolerated and allows to reduce dose of corticosteroids in the majority of patients.

Clinical and Pathologic Features of Congenital Myasthenic Syndromes Caused by 35 Genes-A Comprehensive Review.

Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders characterized by impaired neuromuscular signal transmission due to germline pathogenic variants in genes expressed at the neuromuscular junction (NMJ). A total of 35 genes have been reported in CMS (AGRN, ALG14, ALG2, CHAT, CHD8, CHRNA1, CHRNB1, CHRND, CHRNE, CHRNG, COL13A1, COLQ, DOK7, DPAGT1, GFPT1, GMPPB, LAMA5, LAMB2, LRP4, MUSK, MYO9A, PLEC, PREPL, PURA, RAPSN, RPH3A, SCN4A, SLC18A3, SLC25A1, SLC5A7, SNAP25, SYT2, TOR1AIP1, UNC13A, VAMP1). The 35 genes can be classified into 14 groups according to the pathomechanical, clinical, and therapeutic features of CMS patients. Measurement of compound muscle action potentials elicited by repetitive nerve stimulation is required to diagnose CMS. Clinical and electrophysiological features are not sufficient to identify a defective molecule, and genetic studies are always required for accurate diagnosis. From a pharmacological point of view, cholinesterase inhibitors are effective in most groups of CMS, but are contraindicated in some groups of CMS. Similarly, ephedrine, salbutamol (albuterol), amifampridine are effective in most but not all groups of CMS. This review extensively covers pathomechanical and clinical features of CMS by citing 442 relevant articles.

New Charge Transfer Complexes of K+-Channel-Blocker Drug (Amifampridine; AMFP) for Sensitive Detection; Solution Investigations and DFT Studies.

UV-Vis spectroscopy was used to investigate two new charge transfer (CT) complexes formed between the K+-channel-blocker amifampridine (AMFP) drug and the two π-acceptors 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetracyanoethylene (TCNE) in different solvents. The molecular composition of the new CT complexes was estimated using the continuous variations method and found to be 1:1 for both complexes. The formed CT complexes' electronic spectra data were further employed for calculating the formation constants (KCT), molar extinction coefficients (εCT), and physical parameters at various temperatures, and the results demonstrated the high stability of both complexes. In addition, sensitive spectrophotometric methods for quantifying AMFP in its pure form were proposed and statistically validated. Furthermore, DFT calculations were used to predict the molecular structures of AMFP-DDQ and AMFP-TCNE complexes in CHCl3. TD-DFT calculations were also used to predict the electronic spectra of both complexes. A CT-based transition band (exp. 399 and 417 nm) for the AMFP-TCNE complex was calculated at 411.5 nm (f = 0.105, HOMO-1 → LUMO). The two absorption bands at 459 nm (calc. 426.9 nm, f = 0.054) and 584 nm (calc. 628.1 nm, f = 0.111) of the AMFP-DDQ complex were theoretically assigned to HOMO-1 → LUMO and HOMO → LUMO excitations, respectively.

Amifampridine for the Management of Lambert-Eaton Myasthenic Syndrome: A New Take on an Old Drug.

Objective: The purpose of this article is to review the literature for both 3,4-diaminopyridine (3,4-DAP) and amifampridine for the treatment of Lambert-Eaton myasthenic syndrome (LEMS). Amifampridine (Firdapse) is the salt form of 3,4-DAP and was approved by the Food and Drug Administration for the treatment of LEMS. Data Sources: PubMed, TRIP database, and EMBASE searches were conducted without a back date (current to June 2019) utilizing the following search terms: amifampridine, 3,4-diaminopyridine, and Lambert-Eaton myasthenic syndrome. Completed trials were also reviewed at clinicaltrials.gov. Study Selection and Data Extraction: Criteria for article inclusion consisted of human subjects, age ≥18 years, phase II or III clinical trials, and English language for both drugs. Observational and pharmacokinetic studies for amifampridine were also included. Data Synthesis: Prior to the approval of amifampridine, 3,4-DAP was first-line for the management of LEMS symptoms. Two phase III trials have evaluated amifampridine to confirm efficacy, both showing superiority over placebo in the management of LEMS symptoms, with minimal adverse effects. A significant improvement in both quantitative myasthenia gravis scores and Subjective Global Impression scores was established at days 4 and 14. Relevance to Patient Care and Clinical Practice: With an improved stability profile and decreased dose variability, amifampridine will likely assume the role of first-line management of LEMS. Conclusions: Amifampridine has been shown to improve symptoms of LEMS and is generally well tolerated.

3,4-diaminopyridine base effectively treats the weakness of Lambert-Eaton myasthenia.

INTRODUCTION: 3,4-diaminopyridine has been used to treat Lambert-Eaton myasthenia (LEM) for 30 years despite the lack of conclusive evidence of efficacy. METHODS: We conducted a randomized double-blind placebo-controlled withdrawal study in patients with LEM who had been on stable regimens of 3,4-diaminopyridine base (3,4-DAP) for ≥ 3 months. The primary efficacy endpoint was >30% deterioration in triple timed up-and-go (3TUG) times during tapered drug withdrawal. The secondary endpoint was self-assessment of LEM-related weakness (W-SAS). RESULTS: Thirty-two participants were randomized to continuous 3,4-DAP or placebo groups. None of the 14 participants who received continuous 3,4-DAP had > 30% deterioration in 3TUG time versus 72% of the 18 who tapered to placebo (P < 0.0001). W-SAS similarly demonstrated an advantage for continuous treatment over placebo (P < 0.0001). Requirement for rescue and adverse events were more common in the placebo group. DISCUSSION: This trial provides significant evidence of efficacy of 3,4-DAP in the maintenance of strength in LEM. Muscle Nerve 57: 561-568, 2018.

Amifampridine phosphate (Firdapse(®)) is effective and safe in a phase 3 clinical trial in LEMS.

OBJECTIVE: We evaluated the efficacy and safety of amifampridine phosphate (Firdapse(®)) for symptomatic treatment in Lambert-Eaton myasthenic syndrome (LEMS). METHODS: Phase 3, randomized, double-blind, study. Patients were treated initially with amifampridine phosphate for 7-91 days, followed by randomization to continue amifampridine phosphate for 14 days or placebo (7-day taper, 7-day placebo). The primary efficacy endpoints were changes from baseline at day 14 in Quantitative Myasthenia Gravis and Subject Global Impression scores. RESULTS: The coprimary efficacy end points and 1 of the secondary efficacy end points were met, showing a significant benefit of aminfampridine phosphate over placebo at Day 14. All 5 primary, secondary, and tertiary endpoints achieved statistical significance at Day 8. Amifampridine phosphate was well tolerated; the most common adverse events were oral and digital paresthesias, nausea, and headache. CONCLUSIONS: This study provides Class I evidence of efficacy of amifampridine phosphate as a symptomatic treatment for LEMS.

Reduced Fatigue Symptoms in the Post-COVID Syndrome With Amifampridine: A Collective Casuistry With Double-Blind Discontinuation Trials.

After a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, approximately 10-20% of patients are affected by the post-COVID syndrome (PCS). This condition leads to a variety of functional complaints, including symptoms of fatigue. To date, there is still no adequate treatment option. Five patients are presented, including the self-observation of one of the authors, in whom the administration of amifampridine as an "off-label use" led to a normalization of the unphysiologically increased need for sleep with a simultaneous increase in the Bell score. This effect was confirmed in a double-blind discontinuation trial (the medication was discontinued on a trial basis) in two of the patients. The five patients, who were previously unable to lead a normal life due to their fatigue symptoms, were able to return to everyday life after treatment with amifampridine. This offers hope to millions of affected patients.

Investigation of N-Acetyltransferase 2-Mediated Drug Interactions of Amifampridine: In Vitro and In Vivo Evidence of Drug Interactions with Acetaminophen.

Amifampridine is a drug used for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) and was approved by the Food and Drug Administration (FDA) of the United States (US) in 2018. It is mainly metabolized by N-acetyltransferase 2 (NAT2); however, investigations of NAT2-mediated drug interactions with amifampridine have rarely been reported. In this study, we investigated the effects of acetaminophen, a NAT2 inhibitor, on the pharmacokinetics of amifampridine using in vitro and in vivo systems. Acetaminophen strongly inhibits the formation of 3-N-acetylamifmapridine from amifampridine in the rat liver S9 fraction in a mixed inhibitory manner. When rats were pretreated with acetaminophen (100 mg/kg), the systemic exposure to amifampridine significantly increased and the ratio of the area under the plasma concentration-time curve for 3-N-acetylamifampridine to amifampridine (AUCm/AUCp) decreased, likely due to the inhibition of NAT2 by acetaminophen. The urinary excretion and the amount of amifampridine distributed to the tissues also increased after acetaminophen administration, whereas the renal clearance and tissue partition coefficient (Kp) values in most tissues remained unchanged. Collectively, co-administration of acetaminophen with amifampridine may lead to relevant drug interactions; thus, care should be taken during co-administration.

The European Lambert-Eaton Myasthenic Syndrome Registry: Long-Term Outcomes Following Symptomatic Treatment.

INTRODUCTION: Lambert-Eaton myasthenic syndrome (LEMS) is characterized by autoantibodies against voltage-gated calcium channels (VGCC) at the neuromuscular junction causing proximal muscle weakness, decreased tendon reflexes, and autonomic changes. The European LEMS registry aimed to collate observational safety data for 3,4-diaminopyridine phosphate (3,4-DAPP) and examine long-term outcomes for patients with LEMS. METHODS: Thirty centers across four countries participated in the non-interventional European LEMS registry. Any patients diagnosed with LEMS by means of clinical assessment and abnormal neurophysiological testing, or clinical assessment and positive for VGCC antibodies were eligible to participate. Patients were monitored using standard assessments for LEMS-related clinical manifestations. RESULTS: Among 96 evaluable participants, 50 (52.1%) were being treated with 3,4-DAPP, 21 (21.9%) with 3,4-diaminopyridine (3,4-DAP), and 25 (26.0%) with other treatments (e.g., pyridostigmine, corticosteroids, immunoglobulins, and azathioprine); 74 participants (77.1%) were exposed to 3,4-DAPP at any time. Quantitative myasthenia gravis scores were similar across treatment groups. Muscle strength was generally good and maintained during follow-up. Cerebellar ataxia, defined as a negative Romberg's test and at least one other positive ataxia test, was observed in 30 (56.6%) patients. Most participants had reduced reflex tone and limited functioning. Sustained or improved functioning was observed in participants administered 3,4-DAPP. Inconsistent and sporadic functional improvement and regression was observed with 3,4-DAP and other treatments. Fifty-five treatment-related adverse events (AEs) were reported by 32 (33.3%) participants. Eight (8.3%) participants reported nine treatment-related serious AEs. No new safety signals were identified. CONCLUSION: No new safety signals were observed following long-term management of LEMS with 3,4-DAPP.

Amifampridine safety and efficacy in spinal muscular atrophy ambulatory patients: a randomized, placebo-controlled, crossover phase 2 trial.

BACKGROUND: Spinal muscular atrophy (SMA) is an autosomal recessive disease where a deficient amount of SMN protein leads to progressive lower motor neuron degeneration. SMN-enhancing therapies are now available. Yet, fatigue and signs of impaired neuromuscular junction (NMJ) transmission could contribute to SMA phenotype. Amifampridine prolongs presynaptic NMJ terminal depolarization, enhancing neuromuscular transmission. METHODS: SMA-001 was a phase 2, 1:1 randomized, double-blind, placebo-controlled crossover study. Ambulatory (walking unaided at least 30 m) SMA Type 3 patients, untreated with SMN-enhancing medications, entered a run-in phase where amifampridine was titrated up to an optimized stable dose. Patients achieving at least three points improvement in Hammersmith Functional Motor Score Expanded (HFMSE) were randomized to amifampridine or placebo, alternatively, in the 28-day double-blind crossover phase. Safety was evaluated by adverse events (AE) collection. Primary efficacy measure was the HFMSE change from randomization. Secondary outcomes included timed tests and quality of life assessment. Descriptive analyses and a mixed effects linear model were used for statistics. RESULTS: From 14 January 2019, 13 patients, mean age 34.5 years (range 18-53), with 5/13 (38.5%) females, were included. No serious AE were reported. Transient paresthesia (33.3%) was the only amifampridine-related AE. Six patients for each treatment sequence were randomized. Amifampridine treatment led to a statistically significant improvement in HFMSE (mean difference 0.792; 95% CI from 0.22 to 1.37; p = 0.0083), compared to placebo, but not in secondary outcomes. DISCUSSION: SMA-001 study provided Class II evidence that amifampridine was safe and effective in treating ambulatory SMA type 3 patients. CLINICAL TRIAL REGISTRATION: NCT03781479; EUDRACT 2017-004,600-22.

Probing the Strength and Mechanism of Binding Between Amifampridine and Calf Thymus DNA.

In this work, we have investigated the strength and mechanism of amifampridine (3,4-Diaminopyridine/3,4-DAP) interaction with calf thymus DNA (ct-DNA). The existence and the strength of interaction are evaluated using circular dichroism (CD), UV-vis absorption, and differential pulse voltammogram studies. Results from UV-vis absorption technique indicate that amifampridine can significantly interact with DNA through a binding constant of Kb = 1.66 × 105 M-1 at 298 K. The mechanism of the interaction between amifampridine and DNA is also studied using ionic effect investigations, competitive fluorescence experiments, viscosity measurements, and molecular docking studies. The viscosity results indicate that amifampridine can bind to DNA via intercalation binding mode. Competitive fluorescence experiments using Acridine Orange (AO) and Hoechst 33258 (HO) probes also reveal that amifampridine binds to DNA via an intercalation mode of binding. Finally, the molecular docking studies also suggest that amifampridine tends to bind with the G-C rich region of DNA.

Amifampridine to treat Lambert-Eaton myasthenic syndrome.

Lambert-Eaton myasthenic syndrome (LEMS) is a presynaptic autoimmune disabling neuromuscular disease caused by antibodies against presynaptic voltage-gated calcium channels. It reduces the quantal release of acetylcholine (Ach), causing muscle weakness, reduced or absent reflex and dysautonomia. About half of LEMS patients have associated small cell lung cancer. For symptomatic treatment, amifampridine (3,4-diaminopyridine [3,4-DAP]) is ideal because it increases the release of Ach at the presynaptic membrane. Since the first use of 3,4-DAP in LEMS patients in the 1980s, 136 LEMS patients were treated with amifampridines in the open-label studies and 208 patients in the eight randomized studies. These studies showed that amifampridine is the most effective drug for symptomatic treatment in LEMS. Now, 3,4-DAPP (3,4-DAP phosphate) is approved for adult LEMS patients and 3,4-DAP for pediatric patients. The recommended dose is 80 mg a day, divided 3 or 4 times a day. Side effects are usually mild, and the most frequently reported are paresthesia.

Amifampridine tablets for the treatment of Lambert-Eaton myasthenic syndrome.

Introduction: Lambert-Eaton myasthenic syndrome is an autoimmune disease of the neuromuscular junction characterized by a presynaptic defect of neuromuscular transmission resulting in muscle weakness and fatigability. Diagnostic features are specific neurophysiological alterations and autoantibody detection. The present review is focused on the use of Amifampridine Phosphate to treat LEMS patients.Areas covered: Medline search from 1990 to 2019 was examined using the free subject terms: Lambert-Eaton myasthenic syndrome, LEMS, Amifampridine, 3,4-diaminopyridine, which were then combined with Treatment, Therapy, Clinical Trial, Controlled Clinical Trial, Randomized Clinical Trial and Cochrane Review. The author has done a supervised analysis of the retrieved articles and focused on those subjectively evaluated as most relevant.Expert commentary: Data from randomized clinical trials and case series have demonstrated that Lambert-Eaton myasthenic syndrome symptoms were successfully treated by Amifampridine Phosphate. Hence, the drug represents a substantial step forward in the symptomatic treatment of the disease due to its efficacy, safety and reliable GMP formulation. As Amifampridine Phosphate works by enhancing the release of acetylcholine at the neuromuscular junction by blocking K+ efflux at the pre-synaptic membrane, it is also conceivable to use it for other diseases of the neuromuscular junction in which such an effect is searched for.

Amifampridine for the treatment of Lambert-Eaton myasthenic syndrome.

Introduction: The present status of amifampridine (AFP) for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) is reviewed. Areas covered: All relevant literature identified through a PubMed search under treatment of LEMS, aminopyridine, and amifampridine are reviewed. An expert opinion on AFP was formulated. Expert opinion: AFPs, 3,4-DAP and 3,4-DAPP, are the most studied drugs in neuromuscular diseases. Randomized and non-randomized studies showed the most effective drug as symptomatic medication for LEMS. AFPs are safe and tolerable. Thus, AFPs should be the drug of choice for the symptomatic treatment in LEMS. As long as the daily dose is less than 80 mg a day, there is no concern for the serious side-reaction, seizure. Because of short-acting drug effects, it should be given three or four times a day. Peri-oral and finger paresthesia, the most common side-reaction, is accepted as a sign of drug-intake by many patients. Gastro-intestinal side reactions, the next common side-reaction of AFPs, are tolerable. AFPs are also the drug of choice and life-saving for LEMS crisis. For the long-term usage, it is proven to be safe and AFPs can be supplemented with liberal amount of pyridostigmine to sustain a symptomatic improvement without any undue side-reaction.

Amifampridine phosphate in the treatment of muscle-specific kinase myasthenia gravis: a phase IIb, randomized, double-blind, placebo-controlled, double crossover study.

OBJECTIVE: The aim of this study is to determine the safety and the efficacy of amifampridine phosphate in muscle-specific kinase antibody-positive myasthenia gravis, in a 1:1 randomized, double-blind, placebo-controlled, switchback, double crossover study. METHODS: Eligible patients had muscle-specific kinase myasthenia gravis, >18 years of age, and Myasthenia Gravis Foundation of America class II-IV with a score of ⩾9 on Myasthenia Gravis Composite scale. After the run-in phase, during which amifampridine phosphate was titrated to a tolerable and effective dosage, patients were randomized to receive placebo-amifampridine-placebo sequence or amifampridine-placebo-amifampridine sequence daily for 7 days. Then, patients switched treatment arms twice, for a total of 21 days of double-blind treatment. Safety was determined by serial assessments of adverse events/serious adverse events, physical examinations, and clinical and laboratory tests. The co-primary outcome measures included changes from baseline of Quantitative Myasthenia Gravis score and Myasthenia Gravis-specific Activities of Daily Living Profile score. The secondary outcome measures comprised changes from baseline of Myasthenia Gravis Composite score, Myasthenia Gravis Quality of Life scale-15 questions, Fatigue Severity Scale, and Carlo Besta Neurological Institute-Myasthenia Gravis scale. Statistical analyses were assessed using a switchback model for three-period, two-treatment crossover design. RESULTS: A total of 10 patients were screened, enrolled, and treated. Transient paresthesias (60%) were the only amifampridine phosphate-related adverse events reported. Four patients were randomized to receive placebo-amifampridine-placebo sequence and three patients to receive amifampridine-placebo-amifampridine sequence. The co-primary objectives were statistically met (Quantitative Myasthenia Gravis score: p = 0.0003 and Myasthenia Gravis-specific Activities of Daily Living Profile score: p = 0.0006), as well as all the secondary endpoints (Myasthenia Gravis Composite score: p < 0.0001, Myasthenia Gravis Quality of Life scale-15 questions: p = 0.0025, Fatigue Severity Scale: p = 0.0061, and Carlo Besta Neurological Institute-Myasthenia Gravis scale: p = 0.0014). CONCLUSION: Despite the low number of patients, MuSK-001 study provided evidence that amifampridine phosphate, in the range of 30-60 mg daily dose, was safe and effective in treating muscle-specific kinase myasthenia gravis, suggesting the need for a large multi-center trial to confirm these results.

Acetylator Status Impacts Amifampridine Phosphate (Firdapse™) Pharmacokinetics and Exposure to a Greater Extent Than Renal Function.

PURPOSE: The purpose of this study is to evaluate safety, tolerability, and pharmacokinetic (PK) properties of amifampridine phosphate (Firdapse™) and its major inactive 3-N-acetyl metabolite in renally impaired and healthy individuals with slow acetylator (SA) and rapid acetylator (RA) phenotypes. METHODS: This was a Phase I, multicenter, open-label study of the PK properties and safety profile of amifampridine phosphate in individuals with normal, mild, moderate, or severely impaired renal function. Amifampridine phosphate was given as a single 10 mg (base equivalent) dose, and the plasma and urine PK properties of amifampridine and its 3-N-acetyl metabolite were determined. The safety profile was evaluated by monitoring adverse events (AEs), clinical laboratory tests, and physical examinations. FINDINGS: Amifampridine clearance was predominantly metabolic through N-acetylation, regardless of renal function in both acetylator phenotypes. In individuals with normal renal function, mean renal clearance represented approximately 3% and 18% of the total clearance of amifampridine in RA and SA, respectively. Large differences in amifampridine exposure were observed between acetylation phenotypes across renal function levels. Mean amifampridine exposure values of AUC0-∞ and Cmax were up to 8.8-fold higher in the SA group compared with the RA group across renal function levels. By comparison, mean AUC0-∞ was less affected by renal function within an acetylator group, only 2- to 3-fold higher in individuals with severe renal impairment (RI) compared with those with normal renal function. Exposure to amifampridine in the SA group with normal renal function was higher (AUC0-∞, approximately 1.8-fold; Cmax, approximately 4.1-fold) than the RA group with severe RI. Exposure to the inactive 3-N-acetyl metabolite was higher than amifampridine in both acetylator groups, independent of renal function level. The metabolite is cleared by renal excretion, and exposure was clearly dependent on renal function with 4.0- to 6.8-fold increases in AUC0-∞ from normal to severe RI. No new tolerability findings were observed. IMPLICATIONS: A single dose of 10 mg of amifampridine phosphate was well tolerated, independent of renal function and acetylator status. The results indicate that the PK profile of amifampridine is affected by metabolic acetylator phenotype to a greater extent than by renal function level, supporting Firdapse™ administration in individuals with RI in line with current labeling recommendations. Amifampridine should be dosed to effect per the individual patient need, altering administration frequency and dose in normal through severe RI. The therapeutic dose of amifampridine phosphate should be tailored to the individual patient needs by gradual dose titration up to the present maximum recommended dose (60-80 mg/day) or until dose-limiting AEs intervene to avoid overdosing and underdosing. EudraCT identifier: 2013-005349-35.

The European LEMS Registry: Baseline Demographics and Treatment Approaches.

INTRODUCTION: Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder affecting the neuromuscular junction, clinically characterized by proximal muscle weakness and autonomic changes. LEMS is often associated with an underlying tumor (paraneoplastic form) but also occurs in the absence of cancer (idiopathic form). Treatment consists of immunomodulation (immunosuppression), anticancer treatment when carcinoma is present, and symptomatic treatment [acetylcholinesterase inhibitors and potassium channel blockers, e.g., amifampridine (3,4-diaminopyridine, i.e., 3,4-DAP), to improve neurotransmission]. Although there has long been information from case reports, several randomized controlled trials, and treatment guidelines, population data are still scarce. METHODS: The LEMS patient registry was launched in the European community in mid-2010 as a voluntary, multinational, observational, non-interventional program to collect structured empirical data on clinical course, treatment utilization, and safety and efficacy from the use of LEMS-specific treatments. RESULTS: Sixty-nine patients have been enrolled [36 males, 32 females, 1 gender not reported; mean age 61.5 (27-84) years]. Eighteen patients (26%) were diagnosed with an associated carcinoma. At the time of enrollment, the majority of patients (65%) were receiving amifampridine [either compounded 3,4-DAP (22%) or 3,4-DAP phosphate, Firdapse(®) (43%)]. At enrollment, most patients demonstrate a profile of mild-to-moderate deficits in daily functioning but generally have good muscle strength, albeit with reduced deep tendon reflexes, frequent ataxia during walking, and signs of autonomic dysfunction including dry mouth, bladder dysfunction, and constipation. CONCLUSION: The LEMS European Union registry will continue to enroll patients and periodically report the accrued longitudinal data obtained on clinical assessments and laboratory findings, treatment practices, the safety and efficacy of treatment approaches, and long-term clinical outcomes. FUNDING: BioMarin Pharmaceutical Inc., Novato, CA, USA.

Effects of Food Intake on the Relative Bioavailability of Amifampridine Phosphate Salt in Healthy Adults.

PURPOSE: Amifampridine (3,4-diaminopyridine) has been approved in the European Union for the treatment of Lambert-Eaton myasthenic syndrome. Amifampridine has a narrow therapeutic index, and supratherapeutic exposure has been associated with dose-dependent adverse events, including an increased risk for seizure. This study assessed the effect of food on the relative bioavailability of amifampridine in healthy subjects and informed on conditions that can alter exposure. METHODS: This randomized, open-labeled, 2-treatment, 2-period crossover study enrolled 47 healthy male and female subjects. Subjects were randomly assigned to receive 2 single oral doses of amifampridine phosphate salt (20 mg base equivalents per dose) under fed or fasted conditions separated by a washout period. Blood and urine samples for pharmacokinetic analyses were taken before and after dosing. Plasma concentrations of amifampridine and an inactive 3-N-acetyl metabolite were determined. The relative bioavailability values of amifampridine and metabolite were assessed based on the plasma PK parameters AUC0-∞, AUC0-t, and Cmax in the fed and fasted states using noncompartmental pharmacokinetic analysis. Parent drug and metabolite excretion were calculated from urinary concentrations. A food effect on bioavailability would be established if the 90% CI of the ratio of population geometric mean value of AUC0-∞, AUC0-t, or Cmax between fed and fasted administration was not within the bioequivalence range of 80% to 125%. Tolerability was assessed based on adverse-event reporting, clinical laboratory assessments, physical examination including vital sign measurements, 12-lead ECG, and concurrent medication use. FINDINGS: Food slowed and somewhat decreased the absorption of amifampridine. There was a decrease in exposure (Cmax, 44%; AUC, 20%) after oral administration of amifampridine phosphate salt in the presence of food, and mean Tmax was 2-fold longer in the fed state. The extent of exposure and plasma elimination half-life of the major metabolite was greater than those of amifampridine in the fed and fasted conditions. Mean AUCs in the fed and fasted states were slightly greater in women than men, with no difference in mean Cmax. Orally administered amifampridine was renally eliminated (>93%) as the parent compound and metabolite within 24 hours. Single oral doses of 20 mg of amifampridine phosphate salt were considered well tolerated in both the fed and fasted conditions. High intersubject variability (%CVs, >30%) in amifampridine pharmacokinetic parameter values was observed. IMPLICATIONS: At the intended dose under fasting conditions, amifampridine exposure may be increased. European Union Drug Regulating Authorities Clinical Trials identifier: 2011-000596-13.

Update on treatment options for Lambert-Eaton myasthenic syndrome: focus on use of amifampridine.

In Lambert-Eaton myasthenic syndrome (LEMS), antibodies against presynaptic voltage-gated calcium channels reduce the quantal release of acetylcholine, causing muscle weakness and autonomic dysfunction. More than half of the affected patients have associated small cell lung cancer, and thorough screening for an underlying malignancy is crucial. The mainstay of treatment for LEMS is symptomatic but immunotherapy is needed in more severely affected patients. Symptomatic therapies aim at increasing the concentration of acetylcholine at the muscle endplate. While acetylcholinesterase inhibitors were the first drugs to be used for the amelioration of symptoms, 3,4-diaminopyridine (3,4-DAP, amifampridine) has been shown to be more effective. 3,4-DAP blocks presynaptic potassium channels, thereby prolonging the action potential and increasing presynaptic calcium concentrations. This then results in increased quantal release of acetylcholine. The efficacy of 3,4-DAP for increasing muscle strength and resting compound muscle action potentials has been demonstrated by four placebo-controlled trials. Side effects are usually mild, and the most frequently reported are paresthesias. The most common serious adverse events are epileptic seizures. 3,4-DAP is currently the treatment of choice in patients with Lambert-Eaton myasthenic syndrome.