DESCRIPTION

ETHYOL (amifostine) is an organic thiophosphate cytoprotective agent known chemically as 2-[(3-aminopropyl)amino]ethanethiol dihydrogen phosphate (ester) and has the following structural formula:

H2N(CH2)3NH(CH2)2S-PO3H2

Amifostine is a white crystalline powder which is freely soluble in water. Its empirical formula is C5H15N2O3PS and it has a molecular weight of 214.22.

ETHYOL is the trihydrate form of amifostine and is supplied as a sterile lyophilized powder requiring reconstitution for intravenous infusion. Each single-use 10 mL vial contains 500 mg of amifostine on the anhydrous basis.

CLINICAL PHARMACOLOGY

ETHYOL 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 and for the reduction of the toxic effects of radiation on normal oral tissues. The ability of  ETHYOL 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 either cisplatin or radiation.

Pharmacokinetics

Clinical pharmacokinetic studies show that ETHYOL 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 ETHYOL remains in the plasma 6 minutes after drug administration. ETHYOL 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 ETHYOL, 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 5-8 minutes after intravenous infusion of  ETHYOL.  Pretreatment with dexamethasone or metoclopramide has no effect on ETHYOL 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 ETHYOL 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 ETHYOL 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 ETHYOL was present in patients who had received nephrotoxic antibiotics, or who had preexisting diabetes or hypertension (and thus may have been at increased risk for significant nephrotoxicity), as well as in patients who lacked these risks. Selected analyses of the effects of ETHYOL in reducing the cumulative renal toxicity of cisplatin in the randomized ovarian cancer study are provided in TABLES 1 and 2, below.

In the randomized ovarian cancer study, ETHYOL had no detectable effect on the antitumor efficacy of cisplatin-cyclophosphamide chemotherapy. Objective response rates (including pathologically confirmed complete remission rates), time to progression, and survival duration were all similar in the ETHYOL and control study groups. The table below summarizes the principal efficacy findings of the randomized ovarian cancer study.

Radiotherapy for Head and Neck Cancer. A randomized controlled trial of standard fractionated radiation (1.8 Gy - 2.0 Gy/day for 5 days/week for 5-7 weeks) with or without ETHYOL, administered at 200 mg/m2 as a 3 minute i.v. infusion 15-30 minutes prior to each fraction of radiation, was conducted in 315 patients with head and neck cancer.  Patients were required to have at least 75% of both parotid glands in the radiation field. The incidence of Grade 2 or higher acute (90 days or less from start of radiation) and late xerostomia (9-12 months following radiation) as assessed by RTOG Acute and Late Morbidity Scoring Criteria, was significantly reduced in patients receiving ETHYOL (TABLE 4).

At one year following radiation, whole saliva collection following radiation showed that more patients given ETHYOL produced >0.1 gm of saliva (72% vs. 49%). In addition, the median saliva production at one year was higher in those patients who received ETHYOL (0.26 gm vs. 0.1 gm). Stimulated saliva collections did not show a difference between treatment arms.  These improvements in saliva production were supported by the patients' subjective responses to a questionnaire regarding oral dryness.

In the randomized head and neck cancer study, locoregional control, disease-free survival and overall survival were all comparable in the two treatment groups after one year of follow-up (see TABLE 5).

INDICATIONS AND USAGE

ETHYOL (amifostine) is indicated to reduce the cumulative renal toxicity associated with repeated administration of cisplatin in patients with advanced ovarian cancer. 

ETHYOL is indicated to reduce the incidence of moderate to severe xerostomia in patients undergoing post-operative radiation treatment for head and neck cancer, where the radiation port includes a substantial portion of the parotid glands (see Clinical Studies).

For the approved indications, the clinical data do not suggest that the effectiveness of cisplatin based chemotherapy regimens or radiation therapy is altered by ETHYOL. There are at present only limited data on the effects of ETHYOL on the efficacy of chemotherapy or radiotherapy in other settings. ETHYOL should not be administered to patients in other settings where chemotherapy can produce a significant survival benefit or cure, or in patients receiving definitive radiotherapy, except in the context of a clinical study (see WARNINGS).

CONTRAINDICATIONS

ETHYOL is contraindicated in patients with known hypersensitivity to aminothiol compounds.

WARNINGS

1. Effectiveness of the Cytotoxic Regimen

Limited data are currently available regarding the preservation of antitumor efficacy when ETHYOL is administered prior to cisplatin therapy in settings other than advanced ovarian cancer. Although some animal data suggest interference is possible, in most tumor models the antitumor effects of chemotherapy are not altered by amifostine. ETHYOL should not be used in patients receiving chemotherapy for other malignancies in which chemotherapy can produce a significant survival benefit or cure (e.g., certain malignancies of germ cell origin), except in the context of a clinical study.

2. Effectiveness of Radiotherapy

ETHYOL should not be administered in patients receiving definitive radiotherapy, except in the context of a clinical trial, since there are at present insufficient data to exclude a tumor-protective effect in this setting. ETHYOL was studied only with standard fractionated radiotherapy and only when ≥75% of both parotid glands were exposed to radiation. The effects of ETHYOL on the incidence of xerostomia and on toxicity in the setting of combined chemotherapy and radiotherapy and in the setting of accelerated and hyperfractionated therapy have not been systematically studied.

3. Hypotension

Patients who are hypotensive or in a state of dehydration should not receive ETHYOL. Patients receiving ETHYOL at doses recommended for chemotherapy should have antihypertensive therapy interrupted 24 hours preceding administration of ETHYOL. Patients receiving ETHYOL at doses recommended for chemotherapy who are taking antihypertensive therapy that cannot be stopped for 24 hours preceding ETHYOL treatment, should not receive ETHYOL.

Prior to ETHYOL infusion patients should be adequately hydrated. During ETHYOL infusion patients should be kept in a supine position. Blood pressure should be monitored every