Development of a standard, freeze‐dried serum containing the drugs assayed most often in French hospitals

A quality control program for the therapeutic drug monitoring methodology used to determine serum levels of the fourteen drugs assayed most frequently by French hospital laboratories is described. The program has been adopted by the Societe Francaise de Biologie Clinique (SFBC), which provides participating laboratories with a statistical analysis of the performance data. The control samples developed for the program are prepared by spiking calf serum with, in one case, phenobarbital, phenytoin, carbamazepine, sodium valproate, amikacin, lithium carbonate, digitoxin and hydroquinidine, and, in the other case, caffeine, quinidine, digoxin, isoniazid and gentamycin. After freeze-drying the spiked serum, the drugs were shown to be stable for at least a year when stored at −20°, +4° and +22°; at the end of this time, the samples were pathogen free. For checking therapeutic drug monitoring methods, the freeze-dried serum is diluted with distilled water (10 ml); these solutions are chemically stable, and remain pathogen-free, when stored in stoppered glass tubes at −20° or +4° for 4 weeks.