The Food and Drug Administration has approved paclitaxel for the treatment of ovarian and breast cancer but has not yet approved it for the treatment of lung cancer. Because supplies of paclitaxel from bark are limited, the drug is being extracted from yew twigs and needles, which are renewable sources. After extraction of the precursor of paclitaxel, 10-deacetylbaccatin III, a side chain is added in the laboratory to form paclitaxel. Yew bark harvests ended in August 1993. The dose-limiting toxicity with paclitaxel is granulocytopenia.
Hypersensitivity reactions require premedication with dexamethasone and diphenhydramine.
The optimal dose and schedule of paclitaxel are under investigation. A three-hour infusion, which can be administered on an outpatient basis, appears to be effective. Side effects differ slightly from those of paclitaxel and include fluid retention, which can be reduced with administration of corticosteroids. I inhibitors are structurally related to the parent compound camptothecin, a natural product isolated from the abundant Chinese shrub Camptotheca acuminata . These drugs are very active in animal tumor systems.