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Althesin is an intravenous anaesthetic agent now withdrawn from the market due to severe drug reactions. It was popular because of its short duration of action. It is composed of a mixture of alphaxolone and alphadolone, two steroids. It provides rapid onset of action and recovery.

Cremophor EL was the solubilizing agent (excipient / additive) of Althesin.

Some authors have said "It should be emphasized that there is no evidence of any toxic action from Cremophor in man. The toxic effects or reactions to Propanidid and Althesin are due to the drugs themselves" [1].

However, more recent literature [2] state that Cremophor EL (aka Polyoxyl 35 Castor Oil, a surfactant and derivative of castor oil), when previously used as a solubilising agent in lipid emulsions (such as propofol, vitamin K, and Althesin), was responsible for severe anaphylactoid reactions. Propofol was reformulated as a Soya Bean Oil emulsion ("Diprivan"), and Vitamin K ("Konakion") is also free of Cremophor EL (see product descriptions).

Alphaxolone/Alphadolone has been re-branded as "Saffan" (Pitman-Moore Pharmaceuticals Ltd) and is available for use in veterinary anaesthesia. [3]


  1. "A new Steroid Anaesthetic - Althesin in Proc. roy. Soc. Med. Volume 66 October 1973" (pdf). PubMed. Retrieved 2007-01-07. See page 1/49
  2. Pharmaceutics for the Anaesthetist, MacPherson, Anaesthesia. 2001 Oct;56(10):965-79
  3. "Pharmacology - Intravenous Anaesthesia & Dissociatives" (pdf). Oklahoma State University.