Pulmotech MAA (Page 3 of 4)

8.4 Pediatric Use

Technetium Tc 99m Albumin Aggregated Injection is indicated for lung scintigraphy as an adjunct in the evaluation of pulmonary perfusion in pediatric patients [see Dosage and Administration ( 2)]. The safety profile of Technetium Tc99m Albumin Aggregated Injection is similar to the one in adults.

11 DESCRIPTION

Pulmotech MAA (kit for the preparation of technetium Tc 99m albumin aggregated injection), when prepared with sodium pertechnetate Tc 99m injection, provides Technetium Tc 99m Albumin Aggregated Injection. Pulmotech MAA contains macroaggregates of U.S.-licensed human serum albumin (non- reactive when tested for hepatitis B antigen (HBs Ag) by enzyme immunoassay). The macroaggregated albumin (MAA) is obtained by heat denaturation of stannous chloride treated human serum albumin under controlled conditions.

Upon radiolabeling with sodium pertechnetate Tc 99m injection solution, the stannous reduced Tc99m binds to the aggregated albumin to provide technetium Tc 99m albumin aggregated. The particle size distribution of the aggregated albumin is such that not less than 90 percent are 10 to 90 microns in size. There are no aggregated albumin particles greater than 150 microns in size as determined by circular equivalents.

Pulmotech MAA is provided as a 15 mL multiple-dose glass vial containing white lyophilized powder. The contents of the vial are under nitrogen. Each vial contains 2 mg of albumin aggregated, 7.1 mg of albumin human (soluble), 0.22 mg of maximum total tin (as SnCl2 ยท 2H2 O), 0.1 mg (minimum) stannous chloride, and 9 mg of sodium chloride. Hydrochloric acid is added for pH adjustment and the pH of the reconstituted solution is between 5 and 7. The kit does not contain any bacteriostatic agent.

11.1 Physical Characteristics

Technetium Tc 99m decays by isomeric transition with a physical half-life of 6.02 hours.The principal photon that is useful for detection and imaging is listed in Table 5.

Table 5 โ€“ Principal Radiation Emission Data
Radiation Mean % per Disintegration Energy (keV)
Gamma-2 89.07 140.5

11.2 External Radiation

The specific gamma ray constant for Technetium Tc 99m is 0.78 R/mCi-hr at 1 cm. The first half-value thickness of lead (Pb) for Technetium Tc 99m is 0.017 cm. 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 6. For example, the use of 0.25 cm of Pb will decrease the external radiation exposure by a factor of about 1000.

Table 6 โ€“ Radiation Attenuation by Lead Shielding
Shield Thickness(Pb) cm Coefficient of Attenuation
0.017 0.5
0.08 10-1
0.16 10-2
0.25 10-3
0.33 10-4

To correct for physical decay of this radionuclide, the fractions that remain at selected time intervals after the time of calibration are shown in Table 7.

Table 7 โ€“ Physical Decay Chart: Technetium Tc 99m Half-Life 6.02 Hours
Hours Fraction Remaining Hours Fraction Remaining
0* 1.000 7 0.447
1 0.891 8 0.398
2 0.794 9 0.355
3 0.708 10 0.316
4 0.631 11 0.282
5 0.562 12 0.251
6 0.501

*Calibration Time

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Within 1 to 5 minutes of intravenous injection, over 90 percent of the technetium Tc 99m albumin aggregated particles are trapped in the arterioles and capillaries of the lung.

Following intraperitoneal administration of Technetium Tc 99m Albumin Aggregated Injection, the radiopharmaceutical mixes with the peritoneal fluid. Clearance from the peritoneal cavity varies from insignificant, which may occur with complete shunt blockage, to very rapid clearance with subsequent transfer into the systemic circulation when the shunt is patent.

12.3 Pharmacokinetics

Distribution

Organ selectivity is a direct result of particle size. At 10 microns and below, the albumin aggregates are taken up by the reticuloendothelial system. Above 10 to 15 microns, the aggregates become lodged in the lung capillaries by a purely mechanical process. Distribution of aggregated albumin in the lungs is a function of regional pulmonary blood flow.

The albumin aggregated is sufficiently fragile for the capillary micro-occlusion to be temporary. Erosion and fragmentation reduce the particle size, allowing passage of the aggregates through the pulmonary alveolar capillary bed. The fragments then accumulate in the reticuloendothelial system.

Elimination

Elimination of the Technetium Tc 99m Albumin Aggregates from the normal and abnormal human lungs occurs with a biological half-life of 10.8 hours (range 6.9 to 19 hours, n=5).

13 NONCLINICAL TOXICOLOGY

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