Preclinical Pharmacology

The mechanism of action of ZADAXIN is not completely understood but is thought to be related to its immunomodulating activities, centered primarily around augmentation of T-cell function. In various in vitro assays, thymosin alpha 1 has been shown to promote T-cell differentiation and maturation; for example, CD4+, CD8+, and CD3+ cells have all been shown to be increased. Thymosin alpha 1 has also been shown to increase production of IFN-g, IL-2, IL-3, and expression of IL-2 receptor following activation by mitogens or antigens, increase NK cell activity, increase production of migratory inhibitory factor (MIF), and increase antibody response to T-cell dependent antigens. Thymosin alpha 1 has also been shown to antagonize dexamethasone-induced apoptosis of thymocytes in vitro. In vivo administration of thymosin alpha 1 to animals immunosuppressed by chemotherapy, tumor burden, or irradiation showed that thymosin alpha 1 protects against cytotoxic damage to bone marrow, tumor progression and opportunistic infections, thereby increasing survival time and number of survivors. Many of the in vitro and in vivo effects of thymosin alpha 1 have been interpreted as influences on either differentiation of pluripotent stem cells to thymocytes or activation of thymocytes into activated T-cells.

Pharmacokinetics

The pharmacokinetics of thymosin alpha 1 were studied in adult volunteers at single subcutaneous doses ranging from 0.8 to 6.4 mg and in multiple dose studies of 5 to 7 days duration atsub-cutaneous subcutaneous doses ranging from 1.6 to 16 mg. Thymosin alpha 1 was rapidly absorbed with peak serum levels achieved at approximately 2 hours. A dose proportional increase was seen in serum levels for C_max and AUC, and serum levels returned to basal levels by 24 hours after administration. The serum half-life was approximately 2 hours and there was no evidence of accumulation following multiple subcutaneous doses. Urine excretion ranged from 31% to 60% of the administered dose following single and multiple doses.

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