Many recombinant proteins and peptides have short half-lives of elimination in vivo. After a single injection, the plasma concentration of protein rises to a peak and may then decline rapidly until the compound is eliminated. The duration of activity following a single injection can be limited to several minutes or hours, hence biological effects either fail to develop or develop poorly.
When testing a novel recombinant protein in vivo, rapid elimination following injection can result in a mistaken assessment of potential activity. If no effect is observed, it is difficult to determine whether the protein is inactive, or if it simply was not present in adequate concentration and for a sufficient duration to elicit an effect.
Prolonging exposure to recombinant proteins by multiple daily injections results in repeated fluctuations in the level of protein in plasma and tissues, and corresponding variations in protein effects over time. Because the protein concentration is constantly changing during the time course of the experiment, the resulting data can be misleading as to the nature of protein effects and the dose required to elicit them. Additionally, repeated injections are stressful to the animal and difficult to maintain around-the-clock.