kit for the preparation of technetium tc 99m exametazime for leukocyte labeling - Generic Medications

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