Dosage Form: injection, powder, lyophilized, for solution
Amifostine for Injection
 Amifostine Description
Amifostine for injection is an organic thiophosphate cytoprotective agent known chemically as 2-[(3-aminopropyl) amino] ethanethiol dihydrogen phosphate (ester) and has the following structural formula:
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Amifostine is a white crystalline powder, which is freely soluble in water. Its molecular formula is C5H15N2O3PS and it has a molecular weight of 214.22.
Amifostine for Injection is the trihydrate form of Amifostine and is supplied as a sterile powder requiring reconstitution for intravenous infusion. Each single-use 10 mL vial contains 500 mg of Amifostine on the anhydrous basis.
Amifostine - Clinical Pharmacology
Amifostine is a prodrug that is dephosphorylated by alkaline phosphatase in tissues to a pharmacologically active free thiol metabolite. This metabolite is believed to be responsible for the reduction of the cumulative renal toxicity of cisplatin. The ability of Amifostine to differentially protect normal tissues is attributed to the higher capillary alkaline phosphatase activity, higher pH and better vascularity of normal tissues relative to tumor tissue, which results in a more rapid generation of the active thiol metabolite as well as a higher rate constant for uptake into cells. The higher concentration of the thiol metabolite in normal tissues is available to bind to, and thereby detoxify, reactive metabolites of cisplatin. This thiol metabolite can also scavenge reactive oxygen species generated by exposure to cisplatin.
Pharmacokinetics:
Clinical pharmacokinetic studies show that Amifostine is rapidly cleared from the plasma with a distribution half-life of <1 minute and an elimination half-life of approximately 8 minutes. Less than 10% of Amifostine remains in the plasma 6 minutes after drug administration. Amifostine is rapidly metabolized to an active free thiol metabolite. A disulfide metabolite is produced subsequently and is less active than the free thiol. After a 10-second bolus dose of 150 mg/m2 of Amifostine, renal excretion of the parent drug and its two metabolites was low during the hour following drug administration, averaging 0.69%, 2.64% and 2.22% of the administered dose for the parent, thiol and disulfide, respectively. Measurable levels of the free thiol metabolite have been found in bone marrow cells 5 to 8 minutes after intravenous infusion of Amifostine. Pretreatment with dexamethasone or metoclopramide has no effect on Amifostine pharmacokinetics.
Clinical Studies
Chemotherapy for Ovarian Cancer.
A randomized controlled trial compared six cycles of cyclophosphamide 1000 mg/m2, and cisplatin 100 mg/m2 with or without Amifostine pretreatment at 910 mg/m2, in two successive cohorts of 121 patients with advanced ovarian cancer. In both cohorts, after multiple cycles of chemotherapy, pretreatment with
Amifostine significantly reduced the cumulative renal toxicity associated with cisplatin as assessed by the proportion of patients who had ≥ 40% decrease in creatinine clearance from pretreatment values, protracted elevations in serum creatinine (>1.5 mg/dL), or severe hypomagnesemia. Subgroup analyses suggested that the effect of Amifostine was present in patients who had received nephrotoxic antibiotics, or who had preexisting diabetes or hypertension (and thus may have bee