Source: FDA, National Drug Code (US) Revision Year: 2020
Following intravenous administration for brain and renal imaging, Technetium Tc 99m pentetate is distributed in the vascular compartment. It is cleared by the kidneys, which results in the ability to image the kidney.
Following inhalation of the aerosol, Technetium Tc 99m pentetate deposits on the epithelium of ventilated alveoli.
Technetium Tc 99m pentetate with intravenous administration tends to accumulate in intra-cranial lesions with excessive neovascularity or an altered blood brain barrier. Technetium Tc 99m pentetate accumulation in the brain is prevented by an intact blood brain barrier. It does not accumulate in the choroid plexus.
The first few minutes after intravenous administration, Technetium Tc 99m pentetate is present in the vascular compartment within the renal system.
In patients with normal lungs, the deposition of Technetium Tc 99m pentetate is homogeneous throughout the lungs. In patients with airway disease, the deposition patterns become inhomogeneous with irregular deposition of Technetium Tc 99m pentetate in the airways and alveolar regions of the lung.
After an intravenous administration, the pharmacokinetics of Technetium Tc 99m pentetate were studied by monitoring radioactivity in serial venous blood samples for 7 hours post-administration. The mean plasma clearance rate was 6.8 (L/h) and the mean plasma elimination half-life (t½) was 2.1 hours. The mean volume of distribution at steady state conditions calculated with clearance and mean residence time was 17 L. This relatively low volume of distribution after intravenous administration suggests that Technetium Tc 99m pentetate distributes to the extracellular fluid only. The rate of elimination of Technetium Tc 99m pentetate from the systemic circulation appears to be constant over an approximately 20-fold intravenous dose range.
Following inhalation Technetium Tc 99m pentetate was absorbed (Tmax <2 hours after inhalation) and distributed across the lung epithelium (bioavailability approximately 70%) and into the systemic circulation.
Following intravenous administration, Technetium Tc 99m pentetate is distributed throughout the extracellular fluid space and is cleared from the body by the kidney.
The steady-state volume of distribution (Vss) was 17 L following an intravenous administration. Technetium Tc 99m pentetate distribution appears to be limited to the extravascular compartment.
A variable percentage of the Technetium Tc 99m pentetate binds to the serum proteins; this ranges from 3.7% following a single injection to approximately 10% if the material is continuously infused. Although the chelate gives useful information on the glomerular filtration rate, the variable percent which is protein bound leads to a measured renal clearance rate which is lower than that determined by inulin clearance.
Technetium Tc 99m pentetate is not metabolized.
After either intravenous administration or inhalation, excretion is by glomerular filtration. The mean fraction of intravenously administered Technetium Tc 99m pentetate excreted in urine over 24 hours was 102%.
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