Preparation of Radiopharmaceuticals: Precautions

There are many precautions one must take during the preparation and use of radiopharmaceuticals, in general, and Tc-99m radiopharmaceuticals, in particular. Since most radiopharmaceuticals are intended to be administered intravenously, it is imperative to use aseptic technique in order to maintain sterility of the product. The vial septum must be wiped with 70% isopropanol prior to puncturing the septum with a needle. This is really a cleansing step rather than a true sterilizing step since the alcohol doesn't remain on the septum long enough to kill all pathogens that might be present.

Air must NEVER be injected into any radiopharmaceutical vial, especially one containing a Tc-99m product. The oxygen contained in only 0.1 ml of air is enough to completely destroy the stannous ion used in many commercially available cold kits as a reducing agent. In addition, room air is not sterile so it is possible to introduce pathogens into the vial by using a preliminary injection of air to increase internal pressure in the vial and ease the removal of the contents.

Prior to reconstituting a cold kit with Tc-99m pertechnetate, oxidant-free pertechnetate must be diluted to the required final volume with 0.9% NaCl solution. Ideally, oxidant-free saline (Low Dissolved Oxygen Saline) should be used for the dilution step. Reconstitution of a cold kit with a small volume of pertechnetate followed a few minutes later by dilution with saline solution can cause dissociation of certain weak chelates, resulting in the formation of significant amounts of Free Tc. This is not a problem with sulfur colloid or other insoluble Tc-99m compounds.