indication

For reduction in the cumulative renal toxicity in patients with ovarian cancer (using cisplatin) and moderate to severe xerostomia in patients undergoing post-operative radiation treatment for head and neck cancer.

pharmacology

Amifostine is an organic thiophosphate cytoprotective agent indicated to reduce the cumulative renal toxicity associated with repeated administration of cisplatin in patients with advanced ovarian cancer or non-small cell lung cancer and also to reduce the incidence of moderate to severe xerostomia in patients undergoing post-operative radiation treatment for head and neck cancer. Amifostine is a prodrug that is dephosphorylated by alkaline phosphatase in tissues to a pharmacologically active free thiol metabolite, 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. Healthy cells are preferentially protected because amifostine and metabolites are present in healthy cells at 100-fold greater concentrations than in tumour cells.

mechanism of action

The thiol metabolite is responsible for most of the cytoprotective and radioprotective properties of amifostine. It is readily taken up by cells where it binds to and detoxifies reactive metabolites of platinum and alkylating agents as well as scavenges free radicals. Other possible effects include inhibition of apoptosis, alteration of gene expression and modification of enzyme activity.

toxicity

Rat LD₅₀: 826 mg/kg

biotransformation

Amifostine is rapidly dephosphorylated by alkaline phosphatase in tissues primarily to the active free thiol metabolite and, subsequently, to a less active disulfide metabolite.

half life

8 minutes

route of elimination

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.

drug interactions

Chlorothiazide: Antihypertensives may enhance the hypotensive effect of amifostine. When amifostine is used at doses recommended for chemotherapy, antihypertensive medications should be withheld for 24 hours prior to amifostine administration to avoid excessive hypotension during or immediately after infusion. If antihypertensive therapy can not be withheld, then that patient should not receive amifostine. Caution is recommended when using amifostine at the lower doses recommended for radiotherapy, but routine interruption of antihypertensive therapy is not recommended in these patients.

Telmisartan: Telmisartan may increase the hypotensive effect of Amifostine. At chemotherapeutic doses of Amifostine, Telmisartan should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Terazosin: Terazosin may increase the hypotensive effect of Amifostine. At chemotherapeutic doses of Amifostine, Terazosin should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Tolazamide: Additive hypotensive effects may occur. At chemotherapeutic doses of Amifostine, Tolazamide should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Torasemide: Torasemide may increase the hypotensive effect of Amifostine. At chemotherapeutic doses of Amifostine, Torasemide should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Trandolapril: Trandolapril may increase the hypotensive effect of Amifostine. At chemotherapeutic doses of Amifostine, Trandolapril should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Trichlormethiazide: Trichlormethiazide may increase the hypotensive effect of Amifostine. At chemotherapeutic doses of Amifostine, Trichlomethiazide should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Valsartan: Additive hypotensive effects may occur. At chemotherapeutic doses of Amifostine, Valsartan should be withheld for 24 hours prior to Amifostine administration. Use caution at lower doses of Amifostine.

Verapamil: Verapamil may enhance the hypotensive effect of Amifostine. At chemotherapeutic doses of Amifostine, Verapamil should be withheld for 24 hours prior to Amifostine administration. Caution should be used at lower Amifostine doses used during radiotherapy, but routine interruption of Verapamil therapy is not recommended.