Pharmaceutical stability of methemoglobin-albumin cluster as an antidote for hydrogen sulfide poisoning after one-year storage in freeze-dried form.

Long-term stability during storage is an important requirement for pharmaceutical preparations. The methemoglobin (metHb)-albumin cluster, in which bovine metHb is covalently enveloped with an average of three human albumin molecules, is a promising antidote for hydrogen sulfide (H2S) poisoning. In this study, we investigated the pharmaceutical stability of metHb-albumin cluster after storage for one year in solution and as freeze-dried powder. The lyophilized powder of metHb-albumin cluster stored for one year was readily reconstituted in sterile water for injection, yielding a homogeneous brown solution. Physicochemical measurements revealed that the overall structure of the metHb-albumin cluster was still maintained after preservation. Results of the pharmacological study showed that 100 % of the H2S-poisoned mice survived after treatment with the reconstituted solution of metHb-albumin cluster powder. Furthermore, the solution did not cause any toxic reactions. The antidotal efficacy of metHb-albumin cluster for H2S poisoning was preserved in freeze-dried powder form for at least one year.