Ioflupane (123I)

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Introduction

Ioflupane (¹²³I) is the International Nonproprietary Name of a neuro-imaging radiopharmaceutical used for the differentiation of Parkinson’s disease from other disorders presenting similar symptoms. It is injected into a patient and viewed with a gamma camera in order to acquire SPECT images of the brain with particular respect to the striatum, a subcortical region of the basal ganglia^[1]. Ioflupane (¹²³I) is sold under the tradename DaTSCAN and is manufactured by GE Healthcare, formerly Amersham plc.

Technical Details

DaTSCAN is a solution of I-123 Ioflupane for injection into a living test subject. It is a cocaine analogue with the chemical name [I-123] N-ω-fluoropropyl-2β- carbomethoxy-3β-(4-iodophenyl) nortropane

The iodine introduced during manufacture is a radioactive isotope, I-123, and it is the properties of this isotope that makes the solution visible to a gamma camera. I-123 has a half life of approximately 13 hours and a gamma photon energy of 159 keV making it an appropriate radionuclide for medical imaging. The solution also contains 5% ethanol to aid solubility and is supplied sterile since it is intended for intravenous use.

Ioflupane has a high binding affinity for dopamine transporters (DaT) in the brains of mammals, in particular the striatal region of the brain. A feature of Parkinson's disease is a marked reduction in dopaminergic neurones in the striatal region. By introducing an agent that binds to the dopamine transporters a quantitative measure and spatial distribution of the transporters can be obtained.

Method of Administration

The DaTSCAN solution is supplied ready to inject with a certificate stating the calibration activity and time. The nominal injection activity is 185MBq^[2] and a scan should not be performed with less than 111MBq. The radiopharmaceutical can only be prescribed by a current ARSAC license holder and patients should only be referred by a physician specialising in neurology or the management of movement disorders.

Thyroid blocking via oral administration of 120mg Potassium iodide is recommended to minimise unnecessary excessive uptake of radioiodine. One dose is given 2 hours before the injection and a further dose 24 hours later.

The most convenient way to administer the IV dose is via a peripheral intravenous cannula. The scan is carried out 3-6 hours post injection.

Risks

Extensive pharmacological and toxicological studies have been performed on DaTSCAN, as with any other pharmaceutical for human use. In nuclear medicine, it is invariably the aim of a diagnostic test to gain functional information without having a biological effect on the body, adverse or otherwise. DaTSCAN is reported pharmacologically as a very low risk drug and the rarely occurring side effects are listed as mild headache, vertigo and loss of appetite.

The radiation risks are also reported as minimal. The committed effective dose for a single investigation on a 70kg individual is 4.35mSv^[3]. Pregnant patients should not undergo the test and breast feeding patients must cease since I-123 is secreted in breast milk.

References

1. ^ http://www.datscan.com/referring_physicians/spc.shtml.
2. ^ http://www.datscan.com/referring_physicians/spc.shtml
3. ^ http://www.arsac.org.uk/notes_for_guidence/documents/ARSACNFG2006Corrected06-11-07.pdf