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Sunday, 30 January 2011

New Drug Approvals 2011 - Pt. III Ioflupane 123I (DaTSCANTM)

ATC code : V09AB03

On January 14th 2011, the FDA approved Ioflupane 123I (USAN: Ioflupane I123 USAN date: 2009 tradename: DaTSCAN, NDA 022454)) for the imaging of dopamine transporters in the brain of adult patients with potential Parkinsonian Syndromes. Ioflupane is a radiopharmaceutical agent intended for use with single photon emission computed tomography (SPECT) imaging, to help physicians differentiate essential tremor, from tremor due to Parkinsonian Syndromes.

Ioflupane 123I binds to, and allows imaging of, the Dopamine Transporter (DaT) (Ki = 0.62 nM IC50 = 0.71 nM). Synonym:SLC6A3 UniProt:Q01959 Pfam:PF00209). Variation or malfunction of the Dopamine Transporter is linked to many neurological and psychiatric disorders.
The chemical structure of Ioflupane (IUPAC: methyl(1S,3S,4S,5R)-8-(3-fluoropropyl)-3-(4-iodanylphenyl)-8-azabicyclo[3.2.1]octane-4-carboxylate PubChem: CID3086674) is a tropane derivative; tropanes are a class of natural product alkaloids found in a large number of plant species, notable members of this chemical class include cocaine and atropine (a.k.a. hyoscyamine). Therefore Ioflupane is a natural product derivative. The molecular weight is 427.3 Da, with a relatively large fraction of that coming from the single iodine atom (126.9 Da for 'normal' iodine). The calculated logP is 4.0 and Ioflupane contains no hydrogen bond donors and six hydrogen bond acceptors. Ioflupane is therefore fully compliant with Lipinski's rule of five. Other relevant molecular descriptors include a polar surface area of 29.5 Å2 and the molecule contains 6 rotatable bonds. The iodine in DaTSCAN is the radioactive isotope 123I, which has a half-life of 13.2 hr, and decays with emission of gamma rays, it is these gamma rays that are imaged, showing the location of the DaTs in the brain.

Ioflupane 123I is dosed intravenously, with a total recommended dose in the range 111 to 185 MBq.

Ioflupane (123I) is cleared from the blood after intravenous (iv) injection, with only 5% of the administered activity remaining in whole blood  5 minutes post-administration. Uptake in the brain is rapid, reaching about 7% of injected activity 10 minutes post-administration, then decreasing to ~3% after 5 hours. By 48 hours post-injection, ~60% of the injected radioactivity is excreted in the urine, with faecal excretion calculated at ~14%.

The license holder for DaTSCAN is GE Healthcare, the product website is here, and the full prescribing information can be found here (DaTSCAN was approved in the EU in 2007, the European SPC can be found here).

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