OCTREOSCAN

OCTREOSCAN- indium in -111 pentetreotide
Mallinckrodt Inc.

Diagnostic — For Intravenous Use.
Rx Only.

DESCRIPTION

OctreoScan® is a kit for the preparation of Indium In-111 pentetreotide, a diagnostic radiopharmaceutical. It is a kit consisting of two components:

1. A 10-mL OctreoScan® Reaction Vial which contains a lyophilized mixture of:

(i) 10 μg pentetreotide [N-(diethylenetriamine-N,N,N',N”-tetraacetic acid-N”-acetyl)-D-phenylalanyl-L-hemicystyl-L-phenylalanyl-D-tryptophyl-L-lysyl-L-threonyl-L-hemicystyl-L-threoninol cyclic (2→7) disulfide], (also known as octreotide DTPA),
(ii) 2.0 mg gentisic acid [2, 5-dihydroxybenzoic acid],
(iii) 4.9 mg trisodium citrate, anhydrous,
(iv) 0.37 mg citric acid, anhydrous, and(v) 10.0 mg inositol.

Pentetreotide has the following structural formula:

Chemical Structure

Prior to lyophilization, sodium hydroxide or hydrochloric acid may have been added for pH adjustment. The vial contents are sterile and nonpyrogenic. No bacteriostatic preservative is present.

2. A 10-mL vial of Indium In-111 Chloride Sterile Solution, which contains: 1.1 mL or 111 MBq/mL (3.0 mCi/mL) indium In-111 chloride in 0.02N HCl at time of calibration. The vial also contains ferric chloride at a concentration of 3.5 μg/mL (ferric ion, 1.2 μg/mL). The vial contents are sterile and nonpyrogenic. No bacteriostatic preservative is present.

Indium In-111 pentetreotide is prepared by combining the two kit components (see INSTRUCTIONS FOR THE PREPARATION OF INDIUM In-111 PENTETREOTIDE). Indium In-111 reacts with the diethylenetriaminetetraacetic acid portion of the pentetreotide molecule to form indium In-111 pentetreotide. The pH of the resultant indium In-111 pentetreotide solution is between 3.8 and 4.3. No bacteriostatic preservative is present.

The indium In-111 pentetreotide solution is suitable for intravenous administration as is, or it may be diluted to a maximum volume of 3.0 mL with 0.9% Sodium Chloride Injection, U.S.P., immediately before intravenous administration. In either case, the labeling yield of indium In-111 pentetreotide should be determined before administration to the patient. A method recommended for determining the labeling yield is presented at the end of this package insert.

Physical Characteristics

Indium In-111 decays by electron capture to cadmium-111 (stable) and has a physical half-life of 2.805 days (67.32 hours) (see Table 2).1 The principal photons that are useful for detection and imaging are listed in Table 1.

Table 1. Principal Radiation Emission Data *
*
Kocher, David C., ”Radioactive Decay Data Tables,” DOE/TIC-11026, 115 (1981).
Radiation Mean Percent Per Disintegration Energy (keV)
Gamma-2 90.2 171.3
Gamma-3 94.0 245.4

The specific gamma ray constant for In-111 is 3.21 R/hr-mCi at 1 cm 1. The first half-value thickness of lead (Pb) for In-111 is 0.023 cm. Selected coefficients of attenuation are listed in Table 2 as a function of lead shield thickness. For example, the use of 0.834 cm of lead will attenuate the external radiation by a factor of about 1000.

Table 2. Radiation Attenuation by Lead Shielding
Shield Thickness (Pb) cm Coefficient of Attenuation
0.023 0.5
0.203 0.1
0.513 0.01
0.834 0.001
1.12 0.0001

Table 3 lists fractions remaining at selected time intervals before and after calibration. This information may be used to correct for physical decay of the radionuclide.

Table 3. Physical Decay Chart: Indium In-111, Half-life 2.805 Days (67.32 hours)
*
Calibration time
Hours Fraction Remaining Hours Fraction Remaining
-72 2.100 0* 1.000
-60 1.854 3 0.970
-48 1.639 6 0.940
-36 1.448 12 0.885
-24 1.280 24 0.781
-12 1.131 36 0.690
-6 1.064 48 0.610

1
From Radiopharmaceutical Internal Dosimetry Information Center, Oak Ridge Associated Universities, Oak Ridge, TN 37831-0117, February 1985.

CLINICAL PHARMACOLOGY

General

Pentetreotide is a DTPA conjugate of octreotide, which is a long-acting analog of the human hormone, somatostatin. Indium In-111 pentetreotide binds to somatostatin receptors on cell surfaces throughout the body. Within an hour of injection, most of the dose of indium In-111 pentetreotide distributes from plasma to extravascular body tissues and concentrates in tumors containing a high density of somatostatin receptors. After background clearance, visualization of somatostatin receptor-rich tissue is achieved. In addition to somatostatin receptor-rich tumors, the normal pituitary gland, thyroid gland, liver, spleen and urinary bladder also are visualized in most patients, as is the bowel, to a lesser extent. Excretion is almost exclusively via the kidneys.

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