Formulation of (18)F-FDG: pH adjustment of buffered solution

The steam-sterilized (18)F-FDG of our laboratory frequently has a pH of around 6.5. To avoid decomposition, we studied the possibility of adjusting the pH by adding a pharmaceutical compound but without modifying the usual production sequence and reagents.

Citric acid in 4 concentrations (0.01, 0.03, 0.05, and 0.06 M) was added to routine batches of (18)F-FDG. Established pharmacopeia quality controls at 0 and 12 h after synthesis were run, and the dilution effect was checked.

A 0.06 M concentration of 1:15 v/v citric acid brought about a pH range of 5.46-5.68; did not change significantly after 1/10 dilution; and did not interfere with quality control. The results of quality control 12 h after dispensing were in the desired range.

A 0.06 M concentration of 1:15 v/v citric acid modifies pH in a buffered (18)F-FDG solution without the need to change the synthesizer protocol or reagent composition. This new formulation allows pH adjustment; is an easy, reliable, and safe method with no technical difficulties; and does not interfere with the quality of the radiopharmaceutical.