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The action mechanism of these products is different: they provoke bundles of microtubules and the stabilisation of cellular microtubules which are normally in equilibrium with soluble tubuline. Thus a great number of vital cell functions are disturbed: mitosis, maintenance of cell morphology, morphologic changes, neurone formation. The dividing cells are stopped at interphase G2-M.

Comparison of the action mechanisms of spindle poisons (such as periwinkle alkaloids) and taxanes. The former prevent the normal formation of ttubulin by adding tubulin through phospho-kinase. The latter prevent the liberation of the various tubuline elements which require the action of phosphatase.

Two drugs are now available:

• paclitaxel (Taxol™ or Paxene™ )

• docetaxel (Taxotère™)

Whereas their activities present great similarities, the toxicities of paclitaxel and docitaxel are somewhat different.

Both have a severe haematological toxicity essentially in the form of leukopenia. They both provoke complete hair loss.

Paclitaxel has slowly progressing neurological toxicity with allergic phenomena which can be prevented by pre-medication.

Docletaxel provokes the progressive, dose related appearance of persisting oedema (first limited to lower limbs). Pre-medication by corticosteroids reduces the incidence of this complication.