3,4-Diaminopyridine

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3,4-Diaminopyridine
Diaminopyridine.png
3,4-diaminopyridine-3D-balls.png
Systematic (IUPAC) name
3,4-Diaminopyridine
Clinical data
Trade names Firdapse
AHFS/Drugs.com UK Drug Information
Pregnancy
category
  • No clinical data
Legal status
  • UK: POM (Prescription only)
Routes of
administration		 Oral
Pharmacokinetic data
Bioavailability 93–100%[1][2]
Metabolism Acetylation to 3-N-acetyl­amifampridine
Biological half-life 2.5 hrs (amifampridine)
4 hrs (3-N-acetyl­amifampridine)
Excretion Renal (19% unmetabolized, 74–81% 3-N-acetyl­amifampridine
Identifiers
CAS Number 54-96-6 N
ATC code N07XX05 (WHO)
PubChem CID: 5918
IUPHAR/BPS 8032
ChemSpider 5705 YesY
UNII RU4S6E2G0J YesY
KEGG D10228
ChEMBL CHEMBL354077 YesY
Chemical data
Formula C5H7N3
Molecular mass 109.13 g·mol−1
  • c1cncc(c1N)N
  • InChI=1S/C5H7N3/c6-4-1-2-8-3-5(4)7/h1-3H,7H2,(H2,6,8) YesY
  • Key:OYTKINVCDFNREN-UHFFFAOYSA-N YesY
Physical data
Melting point 218 to 220 °C (424 to 428 °F) decomposes
Solubility in water 24 mg/mL (20 °C)
 NYesY (what is this?)  (verify)

3,4-Diaminopyridine (or 3,4-DAP) is an organic compound with the formula C5H3N(NH2)2. It is formally derived from pyridine by substitution of the 3 and 4 positions with an amino group.

The compound 3,4-diaminopyridine has the International Nonproprietary Name amifampridine and is used as a drug, predominantly in the treatment of a number of rare muscle diseases. The phosphate salt of amifampridine is a more stable formulation that does not require refrigeration; it is marketed in the EU by BioMarin Pharmaceutical under the trade name Firdapse and designated as an orphan drug in the EU.[3] In the United States, amifampridine is under investigation for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) by Catalyst Pharmaceuticals,[4][5] and was granted a breakthrough therapy designation by the FDA in 2013.[6][7] In a Phase 3 clinical trial, it demonstrated superiority over placebo in both co-primary endpoints.[8][9][10] LEMS patients can receive amifampridine at no cost under an ongoing expanded access program.[11][12] A study to develop patient entry criteria for a clinical trial of the free base form of amifampridine has also been completed by Jacobus Pharmaceutical Company.[13] This form remains available at no cost to patients with Lambert-Eaton myasthenic syndrome and congenital myasthenic syndromes under a long-standing compassionate use program, with FDA oversight, from Jacobus Pharmaceutical Company (see also Medical uses and Economics, below).

Medical uses

A 2011 systematic review from the Cochrane Collaboration found data favoring its use in LEMS.[14] Although not approved for pharmaceutical use in the United States, amifampridine is available under compassionate use regulations for the treatment of LEMS.

Amifampridine is also used to treat many of the congenital myasthenic syndromes, particularly those with defects in choline acetyltransferase, downstream kinase 7, and those where any kind of defect causes "fast channel" behaviour of the acetylcholine receptor.[15] In the US, amifampridine is under development as an orphan drug for congenital myasthenic syndrome[16] and 3,4-diaminopyridine is available at no cost for patients with congenital myasthenic syndromes under a long-standing compassionate use program from Jacobus Pharmaceutical Co.

Amifampridine has also been proposed for the treatment of multiple sclerosis, but a 2002 systematic review found that there was little unbiased data to support its use in MS.[17]

Contraindications

As amifampridine prolongs QT time, it is contraindicated in patients with congenital long QT syndrome and in patients that already take one or more QT prolonging drugs such as sultopride, disopyramide, cisapride, domperidone, rifampicin or ketoconazol. It is also contraindicated in patients with epilepsy or badly controlled asthma.[2]

Adverse effects

Little is known about side effects because the drug is only used for rare diseases. Reported side effects include paraesthesia (tingling or prickling sensations) and hypoaesthesia (numbness), especially periorally (around the mouth), as well as gastrointestinal side effects such as nausea and diarrhoea.[2]

Interactions

No systematic interaction studies have been conducted. Based on theoretic reasoning, other QT prolonging drugs may increase the risk of long QT syndrome and torsades de pointes (see contraindications above). Other drugs that lower the seizure threshold may increase the risk of seizures. Interactions via the liver's cytochrome P450 enzyme system are considered unlikely.[2]

Pharmacology

Mechanism of action

In Lambert-Eaton syndrome, acetylcholine release is inhibited as antibodies meant to target certain cancers target Ca2+ channels on the prejunctional membrane instead. Amifampridine works by blocking potassium channel efflux in nerve terminals so that action potential duration is increased.[18] Ca2+ channels can then be open for a longer time and allow greater acetylcholine release to stimulate muscle at the end plate.

Pharmacokinetics

N-(4-Amino-3-pyridinyl)acetamide or 3-N-acetylamifampridine, the metabolite

Amifampridine is quickly and almost completely (93–100%) absorbed from the gut. In a study with 91 healthy subjects, maximum amifampridine concentrations in blood plasma were reached after 0.6 (±0.25) hours when taken without food, or after 1.3 (±0.9) hours after a fatty meal, meaning that the speed of absorption varies widely. Biological half-life (2.5±0.7 hrs) and the area under the curve (AUC = 117±77 ng∙h/ml) also vary widely between subjects, but are nearly independent of food intake.[2]

The substance is deactivated by acetylation via N-acetyltransferases to the single metabolite 3-N-acetylamifampridine. Activity of these enzymes (primarily N-acetyltransferase 2) in different individuals seems to be primarily responsible for the mentioned differences in half-life and AUC: the latter is increased up to 9-fold in slow metabolizers as compared to fast metabolizers.[2]

Amifampridine is eliminated via the kidneys and urine to 74–81% as N-acetylamifampridine and to 19% in unchanged form.[2]

Physical and chemical properties

3,4-Diaminopyridine is a pale yellow to pale brown crystalline powder that melts at about 218–220 °C (424–428 °F) under decomposition. It is readily soluble in methanol, ethanol and hot water, but only slightly in diethyl ether.[19][20] Solubility in water at 20 °C (68 °F) is 25 g/L.

The drug formulation contains the phosphate salt, more specifically 4-aminopyridine-3-ylammonium dihydrogen phosphate.[20] This salt forms prismatic, monoclinic crystals (space group C2/c)[21] and is readily soluble in water.[22]

Society and culture

Economics

The licensing of Firdapse in 2010 led to a sharp increase in price for the drug. In some cases, this has led to hospitals using an unlicensed form rather than the licensed agent, as the price difference proved prohibitive. BioMarin has been criticized for licensing the drug on the basis of previously conducted research, and yet charging exorbitantly for it.[23] A group of UK neurologists and pediatricians have petitioned to prime minister David Cameron in an open letter to review the situation.[24] The company responded that it submitted the licensing request at the suggestion of the French government, and points out that the increased cost of a licensed drug also means that it is monitored by regulatory authorities (e.g. for uncommon side effects), a process that was previously not present in Europe.[25]

Availability

In the United States, both the phosphate and the free base have completed clinical trials to treat LEMS.[26][27][28] Both formulations are available to LEMS patients in the U.S.: the free base is available to patients with LEMS and congenital myasthenic syndromes under a compassionate distribution program by Jacobus Pharmaceutical Company, and the phosphate salt is available to LEMS patients under an expanded access program by Catalyst Pharmaceuticals. Patients must be diagnosed with LEMS or congenital myasthenic syndrome and meet appropriate inclusion criteria.[11]

Compounding pharmacies may also be a source of amifampridine in the U.S. In Europe, the phosphate is sold by BioMarin, and the free base is compounded, usually by hospital pharmacies.

See also

References

  1. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Clinical trial number NCT00265148 for "A Phase 3 Study of Amifampridine Phosphate in Patients With Lambert Eaton Myasthenic Syndrome (LEMS)" at ClinicalTrials.gov
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ American Neurological Association 2013 Meeting Poster ID: S737WIP
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Muscular Dystrophy Association Press Release
  11. ↑ 11.0 11.1 Clinical trial number NCT02189720 for "Expanded Access Study of Amifampridine Phosphate in LEMS, Congenital Myasthenic Syndrome, or Downbeat Nystagmus Patients (EAP-001)" at ClinicalTrials.gov
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ [1][dead link]
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ 20.0 20.1 Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  24. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  25. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  26. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  27. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  28. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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