technetium tc 99m exametazime - Medications

The Ceretec kit is supplied as a pack of 5 vials for use in the preparation of a technetium Tc99m exametazime intravenous injection as a diagnostic radiopharmaceutical for use as an adjunct in the detection of altered regional cerebral perfusion and for the radiolabeling of autologous leukocytes. Each vial of Ceretec contains a pre-dispensed sterile, non-pyrogenic, lyophilized mixture of 0.5 mg exametazime [(RR,SS)-4.8-diaza-3,6,6,9-tetramethylundecane-2, 10-dione bisoxime], 7.6 µg stannous chloride dihydrate (minimum stannous tin 0.6 µg; maximum total stannous and stannic tin 4.0 µg per vial) and 4.5 mg sodium chloride, sealed under nitrogen atmosphere with a rubber closure. The product contains no antimicrobial preservative. Prior to publication of the USAN, exametazime was formerly known as hexamethylpropylene amine oxime (HM-PAO). The name HM-PAO appears in many publications. The structural formula of exametazime is: When sterile pyrogen-free sodium pertechnetate Tc99m in isotonic saline is added to the vial of Ceretec, a Tc99m complex of exametazime is formed. Administration is by intravenous injection for diagnostic use. Physical Characteristics Technetium Tc99m decays by isomeric transition with a physical half-life of 6.03 hours. (1) Photons that are useful for imaging studies are listed in Table 1. Table 1. Principal Radiation Emission Data-technetium Tc99m Radiation Mean %/ Disintegration Mean Energy (keV) (1) Dillman, L.T. and Von der Lage, F.C. Radionuclide decay schemes and nuclear parameters for use in radiation-dose estimation. MIRD Phamphlet No. 10, p. 62, 1975. Gamma 2 87.87 140.5 External Radiation The specific gamma ray constant for technetium Tc99m is 206 microCoulomb kg-1/37 MBq-h, (0.8 R/millicurie-h) at 1 cm. The first half-value thickness of lead (Pb) for technetium Tc99m is 0.2 mm. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from interposition of various thicknesses of Pb is shown in Table 2. For example, the use of a 2.7 mm thickness of Pb will decrease the external radiation exposure by a factor of 1,000. Table 2. Radiation Attenuation by Lead Shielding Shield Thickness (Pb) mm Coefficient of Attenuation 0.2 0.5 0.95 10 –1 1.8 10 –2 2.7 10 –3 3.6 10 –4 4.5 10 –5 To correct for physical decay of this radionuclide, the fractions that remain at selected intervals relative to the time of calibration are shown in Table 3. Table 3. Physical Decay Chart: Tc99m half-life 6.03 hours Hours Fraction Remaining Hours Fraction Remaining 0 Calibration time (time of preparation) 1.000 7 0.447 1 0.891 8 0.399 2 0.795 9 0.355 3 0.708 10 0.317 4 0.631 11 0.282 5 0.563 12 0.252 6 0.502 24 0.063 Chemical Structure

11.1 Chemical Characteristics Drax Exametazime (kit for the preparation of technetium Tc 99m exametazime for leukocyte labeling) prepares a radioactive diagnostic agent. Each single-dose vial contains a sterile, non-pyrogenic, lyophilized mixture of 0.5 mg exametazime, 7.6 mcg stannous chloride dihydrate (minimum stannous tin 0.6 mcg; maximum total stannous and stannic tin 4 mcg per vial) and 4.5 mg sodium chloride, sealed under nitrogen atmosphere with a rubber closure. The product contains no antimicrobial preservative. The chemical formula of exametazime is C 13 H 28 N 4 O 2 , with the following structural formula: Prior to publication of the USAN, exametazime [also known as (RR,SS)-4.8-diaza-3,6,6,9-tetramethylundecane-2, 10-dione bisoxime] was known as hexamethylpropylene amine oxime (HM-PAO). The name HM-PAO appears in many publications. When Tc 99m pertechnetate in Sodium Chloride Injection, USP (0.9%) is added to Drax Exametazime vial, a Tc 99m complex of exametazime is formed. chemical formula 11.2 Physical Characteristics Tc 99m decays by isomeric transition with a physical half-life of 6 hours. Photons that are useful for imaging studies are listed in Table 2. Table 2 Principal Radiation Emission Data - Tc 99m Radiation Mean %/Disintegration Mean Energy (keV) Gamma 2 88.5 140.5 11.3 External Radiation The air-kerma-rate (exposure-rate) constant for technetium Tc 99m is 5.23 m 2 ·pGy·(MBq) -1 ·s -1 [0.795 cm 2 ·R·(mCi) -1 ·h -1 ]. The first half-value thickness of lead (Pb) for Tc 99m is 0.25 mm. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from interposition of various thicknesses of Pb is shown in Table 3. For example, the use of a 3 mm thickness of Pb will decrease the external radiation exposure by a factor of approximately 1,000. Table 3 Radiation Attenuation by Lead Shielding Shield Thickness (Pb) mm Coefficient of Attenuation 0.25 0.5 1 10 -1 2 10 -2 3 10 -3 4 10 -4 5 10 -5 To correct for physical decay of this radionuclide, the fractions that remain at selected intervals relative to the time of calibration are shown in Table 4. Table 4 Physical Decay Chart - Tc 99m half-life 6 hours Hours Fraction Remaining Hours Fraction Remaining 0 Calibration time (time of preparation) 1.00 7 0.45 1 0.89 8 0.4 2 0.79 9 0.35 3 0.71 10 0.32 4 0.63 11 0.28 5 0.56 12 0.25 6 0.50 24 0.063