Clinical progress with a new antiandrogen, Casodex (bicalutamide)

Casodex (bicalutamide, Zeneca Limited) is a nonsteroidal competitive inhibitor of androgens at the androgen receptor. The drug was developed to fulfil a number of needs for the treatment of prostate cancer. The specific aim was to demonstrate pharmacological activity, which would translate into clinical efficacy, good tolerability in the context of its use, oral availability, a convenient and forgiving dosing regimen, and clinical acceptability. Casodex has been shown to be orally bioavailable and well absorbed, with a plasma half-life of around 1 week. Although steady-state levels are not reached for 1 month, there is evidence that the androgen receptor blockade achieved with Casodex is equivalent to that of flutamide by the end of the first day. The dose of Casodex was established in a series of dose-ranging studies using the surrogate endpoints of prostatic acid phosphatase (PAP) and prostate-specific antigen (PSA). Initial studies suggested that a dose of 50 mg daily gave a fall in PAP equivalent to that seen with castration. This dose was, therefore, evaluated as monotherapy and subsequently as a component of combined androgen blockade. Higher doses were evaluated using PSA as a surrogate endpoint and, although doses up to 450 mg have been given to man, 150 mg daily is well tolerated with demonstrable evidence of activity. Although trials of the drug at 150 mg in monotherapy have, to date, not shown survival equivalence with castration, Casodex has been well tolerated with evidence of good symptomatic response and quality-of-life benefits including the potential of retaining libido. In combination treatment, Casodex is associated with significantly less gastrointestinal effects (diarrhoea) than the nonsteroidal antiandrogen flutamide (Eulexin, Schering-Plough International). Casodex is not associated with alcohol intolerance, pneumonitis and ocular defects which have been seen with the antiandrogen nilutamide (Anandron, Roussel). Moreover, since Casodex is a nonsteroidal antiandrogen, no steroidal effects have been seen.