Amifampridine, or 3,4-diaminopyridine (3,4-DAP), is a quaternary ammonium compound that blocks presynaptic potassium channels, and subsequently prolongs the action potential and increases presynaptic calcium concentrations. It was first discovered in Scotland in the 1970s and its clinical effectiveness for neuromuscular disorders, including Lambert–Eaton myasthenic syndrome (LEMS), has been investigated in the 1980s. Amifampridine phosphate is a more stable salt that serves as an active ingredient of EMA-approved Firdapse, which was previously marketed as Zenas. It is currently used as the first-line symptomatic treatment for LEMS in adult patients and is ideally given as oral tablets in divided doses, three or four times a day. Firdapse (amifampridine) was formally approved by the US FDA for the treatment of adults with LEMS as recently as November of 2018. LEMS is a rare auto-immune disorder of the neuromuscular junction that is characterized by proximal muscle weakness, depressed tendon reflexes, and posttetanic potentiation in addition to autonomic dysfunction. About 50-60% of the patients develop more rapidly progressive LEMS and small cell lung cancer, which influences the prognosis. Patients with LEMS develop serum antibodies against presynaptic P/Q-type voltage-gated calcium channels, leading to decreased presynaptic calcium levels and reduced quantal release of acetylcholine, which is mainly responsible for causing symptoms of LEMS. Reduced acetylcholine release at the neuromuscular junction leads to decreased frequency of miniature endplate potentials of normal amplitude, and insufficient acetylcholine levels for the activation of postsynaptic muscle fibers following a single nerve impulse. This leads to the reduction of the compound muscle action potential (CMAP). Treatment for LEMS include immunotherapy such as conventional immunosuppression or intravenous immunoglobulins, however such treatments are recommended in patients in whom symptomatic treatment would not suffice. Amifampridine is the nonimmune treatment options for LEMS. In phase III clinical trials of adult patients with LEMS, treatment of amifampridine significantly improved symptoms of LEMS compared to placebo with good tolerance. It was demonstrated in clinical studies involving healthy volunteers that the pharmacokinetics and systemic exposure to amifampridine is affected by the genetic differences in N-acetyl-transferase (NAT) enzymes (acetylator phenotype) and NAT2 genotype, which is subject to genetic variation. Slow acetylators were at higher risk for experiencing drug-associated adverse reactions, such as paresthesias, nausea, and headache.
Science-backed PDE/ADE, OEL & OEB derivation by certified toxicologists with ex-agency experts -
Amifampridine
Drug Overview
What is Amifampridine?
To derive PDE/ADE, OEL, and OEB values, Masuu Global follows a scientifically justified, risk-based toxicological assessment approach in accordance with internationally recognized guidelines and industry best practices that are widely accepted by regulatory authorities, including European Medicines Agency (EMA), Pharmaceutical Inspection Co-operation Scheme (PIC/S), and Agência Nacional de Vigilância Sanitária (ANVISA).
Request Your Assessment
Add this compound to your inquiry list and our team will follow up with full documentation, pricing, and licensing terms.
View Inquiry List →Full OEL derivation · ADE/PDE value · Control band assignment · All cited references · EMA / ICH Q9 compliance
Regulatory Framework
Assessment Methodology
Masuu Global follows a scientifically justified, risk-based toxicological approach aligned with internationally recognized guidelines accepted by EMA, PIC/S, and ANVISA.
EMA – Guideline on Setting Health-Based Exposure Limits (HBELs)
Provides the framework for establishing scientifically justified PDE/ADE values for use in shared manufacturing facilities.
PIC/S – Shared Facilities and Contamination Control Guidance
Supports the application of HBEL-based approaches for cross-contamination prevention and cleaning validation.
ICH Q9 – Quality Risk Management
Provides a structured methodology for risk identification, assessment, control, communication, and review.
ICH M7 – Assessment and Control of DNA-Reactive (Mutagenic) Impurities (where applicable)
Applied for compounds with potential mutagenic or genotoxic concerns.
Risk-Based Toxicological Assessment
Comprehensive evaluation of available toxicological and pharmacological data, including NOAEL, LOAEL, BMDL, pharmacological potency, carcinogenicity, reproductive and developmental toxicity, sensitization potential, and target organ toxicity.
Weight-of-Evidence (WoE) Approach
Integration and critical review of all relevant data sources, including non-clinical studies, clinical studies, human exposure data, pharmacological information, post-marketing safety data, and structure–activity relationship (SAR/QSAR) assessments.
How We Work
Report Preparation Process
Every assessment moves through a rigorous five-stage workflow — from data gathering to regulatory-ready delivery.
Comprehensive Data Review
Assessment of pharmacology, toxicology, clinical data, literature, and available regulatory information.
Scientific Evaluation
Identification of critical endpoints and selection of appropriate exposure limits.
PDE / HBEL Derivation
Transparent and scientifically justified calculations aligned with global toxicological principles.
Ex-Agency Expert Review (Our Differentiator)
Reports are reviewed with an ex-agency perspective, bringing regulatory expectations, inspection readiness, and practical implementation into every assessment.
Final Report Delivery
Regulatory-ready reports with scientific rationale, calculations, and clear recommendations by certified toxicologists (ERT, UKRT and DABT).
Ex-Agency Advantage
Why Masuu Global?
Our ex-agency toxicologists bring a practical regulatory perspective that transforms how assessments are built, reviewed, and defended.
Regulatory expectation–driven assessments aligned with how authorities actually evaluate submissions.
Inspection-ready reports — scientifically defensible and audit-prepared from day one.
Faster review cycles with direct decision support from certified toxicologists (ERT, UKRT, DABT).
Practical implementation recommendations that translate science into actionable contamination control.
Reduced internal effort — offload complex assessments without sacrificing quality or defensibility.
Global reach across PDE/ADE, HBEL, OEL, OEB, cleaning validation, and impurity assessments.
Ready to request your assessment?
Add this compound to your inquiry list, or browse our full database of 3,000+ molecules.