In this study, an optimized procedure of sample preparation for quantitative determination of the antiviral agent camphecene in dried rat blood spots was developed. It has been shown that when using methanol containing 0.1% HCOOH as an extractant, the recovery of the substance increases in comparison with the previously developed method. In addition to this, there is no need to dilute the obtained solutions with water for the analysis of the sample by high-performance liquid chromatography (HPLC) on a column with a reversed-phase sorbent. By using the developed method, the stability of samples of dried rat blood spots containing camphecene in different concentrations at different temperatures was studied. It was found that while the samples were stored at room temperature, apparently, desorption of the substance occurs leading to a loss of more than 15% of its initial amount after 5–10 days. Lowering the temperature increases the stability of samples and their storage at −70°C is possible for 4 weeks.