Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1.   Pharmacodynamic properties
Pharmacotherapeutic group: Diagnostic radiopharmaceuticals, ATC code: V09 No pharmacological activity has been observed in the range of doses administered for diagnostic purposes.

Pharmacokinetic Properties

5.2.   Pharmacokinetic properties
Distribution
The pertechnetate ion has similar biological distribution to iodide and perchlorate ions, concentrating temporarily in salivary glands, choroid plexus, stomach (gastric mucosa) and in the thyroid gland, from which it is eliminated, unchanged. The pertechnetate ion also tends to concentrate in areas with hypervascularisation or with abnormal vascular permeability, particularly when pre-treatment with blocking agents inhibits uptake in glandular structures.
With intact blood brain barrier pertechnetate (99mTc) does not penetrate into the brain tissue.
Organ uptake
In the blood 70-80% of the intravenously injected pertechnetate (99mTc) is bound to proteins, primarily in an unspecific way to albumin. The unbound fraction (20-30%) accumulates temporarily in thyroid and salivary glands, stomach and nasal mucous membranes as well as in the plexus chorioideus.
Pertechnetate (99mTc) in contrast to iodine, nevertheless, is neither used thyreoidal in thyroid hormone synthesis (organification), nor absorbed in the small intestine. In the thyroid the maximum accumulation, depending on functional state and iodine saturation (in euthyreosis approx. 0.3-3%, in hyperthyreosis and iodine depletion up to 25%) is reached about 20 min after injection and then decreases quickly again. This also applies for the stomach mucous membrane parietal cells and the salivary glands acinar cells.
The thyroid gland releases pertechnetate (99mTc) into the bloodstream and it is also secreted in the saliva and gastric juices. Maximum accumulation in the salivary gland of approximately f 0.5% of the applied activity occurs within approximately 20 minutes. One hour after injection the concentration in the saliva is about 10-30 fold higher than in the plasma. The excretion can be accelerated by lemon juice or by stimulation of the parasympathetic nerve system, the absorption is reduced by perchlorate.
Elimination
Plasma clearance takes approximately 3 hours. pertechnetate (99mTc) is not metabolised in the organism. A fraction is eliminated very quickly renally, the rest more slowly via faeces, salivary and lacrimal fluid. Excretion during the first 24 hours following administration is mainly urinary (approximately 25%) with faecal excretion occurring over the next 48 hours.
Approximately 50% of the administered activity is excreted within the first 50 hours. When selective uptake of pertechnetate (99mTc) in glandular structures is inhibited by the preadministration of blocking agents, excretion follows the same pathways but there is a higher rate of renal clearance.
When sodium pertechnetate (99mTc) solution for injection is used for the production of technetium-99m-complexes pharmacologic as well as the toxicological qualities may change, depending on the kind of the respective technetium ligands.