Pharmakokinetics of Mistletoe Lectins after Intravenous Application of a Mistletoe Product in Healthy Subjects

Mistletoe lectins (ML) have cytotoxic and immunomodulating properties, and subcutaneously applied mistletoe products (MP) containing ML have approval for supportive cancer treatment. MP are also given off-label intravenously, but data about pharmacokinetics are widely lacking. Therefore, the aim of our phase I trial was to evaluate the pharmacokinetics and safety of intravenously applied natural ML. Initially, 12 healthy male volunteers were planned to receive a single infusion of 2000 mg Helixor^® P. We had to terminate the study prematurely after the inclusion of eight subjects due to elevation of all subjects' liver enzymes. ML was detected in all subjects after infusion. The mean half-life of serum ML was 7.02 ± 2.01 h. Mean alanine transaminase increased from 23 ± 6 to a maximum of 445 ± 260 U/L, and mean aspartate aminotransferase increased from 24 ± 3 to a maximum of 318 ± 33 U/L 72 h after infusion. Severity grading for drug-induced liver injury was mild. Participants did not suffer from any liver-specific symptoms and recovered completely. As a conclusion, the dose of 2000 mg Helixor^® P caused transient liver injury in healthy subjects and should, therefore, not be used for initial patient treatment. Liver enzymes should be monitored in patients receiving intravenous treatment with Helixor^® P.