N,N-dimethylpyridin-4-amine

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Review of scientifically valid study data by an authoritative body, the European Medicines Agency

Data source

Reference

Reference Type:

review article or handbook

Title:

Assessment Report, Fampyra (4-aminopyridine)

Author:

European Medicines Agency

Year:

2011

Bibliographic source:

http://www.ema.europa.eu/docs/en_GB/document_library/EPAR_-_Public_assessment_report/human/002097/WC500109957.pdf

Report date:

2011

Materials and methods

Objective of study:

toxicokinetics

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The pharmacokinetic studies, which were conducted over a course of several decades, were not generally conducted in compliance with GLP standards; however, they were considered adequate by design and their findings were supported by literature publications (EMEA, 2011).

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

4-pyridylamine

EC Number:

207-987-9

EC Name:

4-pyridylamine

Cas Number:

504-24-5

IUPAC Name:

pyridin-4-amine

Test material form:

not specified

Details on test material:

Pyridine-4-amine (fampridine) was described by the manufacturer as a white-to off-white non hygroscopic powder, practically soluble in water. Its pKa is 9.17 (protonated free base), its logP is 0.76 and the pH of its solution (50 mg/ml in water) is 11.

Radiolabelling:

yes

Test animals

Species:

rat

Administration / exposure

Route of administration:

other: as noted in text

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

4-Aminopyridine was shown to be readily and completely absorbed in the GI tract following oral administration of either a prolonged release tablet or an aqueous solution formulation to healthy adult volunteers in a clinical pharmacokinetics study. Oral bioavailability of fampridine was measured in rats and appeared to be moderate in both females (55%) and males (67%). Fampridine peak (Cmax) and total systemic exposure (AUC) increased with increasing dose in CD-1 mice, CD rats, NZW rabbits and Beagle dogs, but the increase was less than dose proportional. Sex differences were not observed in rats or dogs. No accumulation of fampridine was observed following repeated dose administration.

Details on distribution in tissues:

The volume of distribution of 4-aminopyridine at steady state was high in rats (3.4 L/kg in male, 3.3 L/kg in female), which suggests extensive tissue distribution4. One hour post-dose, highest concentrations were found in bladder, kidneys and liver. 4-Aminopyridine and 3, 4-diaminopyridine both have been shown to cross the blood-brain barrier. With radiolabelled 4-aminopyridine, radioactivity was observed in the cerebellum and cerebrum until 8 hours post-dose. Binding of 4-aminopyridine to plasma proteins was low with a high free fraction of >75% in rats and dogs and >90% in humans. Protein binding was dependent on the concentration, especially in rat and dog plasma (17% increase of the free drug at 500 ng/mL compared to 5 ng/mL).
The distribution of 4-aminopyridine across the placenta and into breast milk is not known as such studies were not identified in the literature4. The log P however favors distribution of 4-aminopyridine across the placenta and into breast milk.
No accumulation of 4-aminopyridine was demonstrated by the lack of increase in peak and total systemic exposure values following repeated dose administration at multiple doses for multiple days in CD-1 mice, Sprague-Dawley rats, New Zealand White rabbits, Beagle dogs and humans.

Details on excretion:

The low molecular weight and high water solubility of 4AP favors urinary excretion. In rats and dogs, as compared with humans, the clearance rate of 4-aminopyridine was higher and the elimination half-life (t1/2) was shorter; otherwise, the basic PK parameters of 4-aminopyridine were similar between species. Elimination of 4-aminopyridine was in a similar range between rats and dogs with a plasma half-life of 1-2 hours, but was slightly prolonged in humans. The predominant route of elimination of radioactivity in rat and dog following oral administration was via urine with a negligible contribution eliminated in feces.
Between 75 and 92% of the dose of 4-aminopyridine was detected in urine within the first 12 hours in rats and dogs, approximately 40% of which accounted for unchanged parent compound.

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

The genotoxic potential of 4-aminopyridine was tested in standard in vitro (Ames test, mouse lymphoma assay) and cytogenetic in vivo tests in mouse and rat. All in vitro tests were conducted with and without metabolic activation using S9 from both hamster and rat liver. No evidence of genotoxicity was seen in any of these studies which further supports that 4AP does not undergo metabolism to form genotoxic species,.

The specific enzymes involved in the metabolism of 4-aminopyridine were not identified in laboratory animals, but based on human microsome studies; it was suggested that CYP2E1 could be responsible for hydroxylation in man. In rat, approximately 36% of the parent drug was removed by hepatic first-pass metabolism. 4-Aminopyridine was metabolized primarily by hydroxylation, followed by sulfate conjugation. Two circulating metabolites were detected in mouse, rat, rabbit, dog and human plasma: 3-hydroxy-4-AP and 3-hydroxy-4-AP sulfate. Although these metabolites were identified in all species, more extensive metabolism was determined in rats and dogs than in humans4. In mouse and rat plasma, it was demonstrated that 4-AP-N-oxide was also a circulating metabolite. In human plasma, two unidentified metabolites were present; however, these metabolites accounted for <2% of radioactivity.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): low bioaccumulation potential based on study results
4-Aminopyridine is a relatively small molecular weight solid with high water solubility and slight lipophilicity which favors absorption by the oral, and likely dermal and inhalation, routes of administration. Absorption is likely > 75% by all three routes. The factors of significant absorption, low molecular weight, potential for tissue affinity and good water solubility favor wide distribution of any absorbed 4-aminopyridine in the body. The risk of bioaccumulation is low. DMAP is metabolized via hydroxylation however results of in vitro and in vivo genotoxicity studies on 4-aminopyridine indicate that resulting metabolites are not genotoxic. Urinary excretion of > 75% of the dose of 4-aminopyridine is demonstrated. The analogue approach for these two endpoints is adequate for the purposes of classification and labelling, and for risk assessment.