The effect of isoniazid on BCG-induced toxicity in patients with superficial bladder cancer

The use of bacillus Calmette-Guérin in the treatment of transitional cell cancer of the bladder has caused concern because of its associated adverse effects. We conducted a randomized prospective, double-blind, multicentre study to determine whether isoniazid prophylaxis could reduce BCG-induced toxicity without compromising its immunotherapeutic effects. Patients (n = 160) with histologically documented urothelial cancer (pTa-T1, pTis, G1-3) were treated with 6 weekly instillations of BCG Connaught strain, 81 mg, administered concomitantly with a 3-day course of isoniazid (300 mg o.d.) or placebo. Side-effects were recorded with each treatment and at follow-up. Of the patients treated with isoniazid, 19% remained free from side-effects, compared with 16% of the placebo group. Local side-effects confined to the bladder were significantly lower among those receiving isoniazid (35% vs. 48%, p < 0.01). Local side-effects together with systemic adverse effects such as fever, nausea or skin rash were experienced by 30% of patients in each arm. There were no differences in tumour recurrence between the two patient groups. Concomitant isoniazid reduces the local, but not the systemic side-effects of topically applied BCG without compromising the antitumour effect on superficial, transitional cell cancer of the bladder during a follow-up period that now exceeds 2 years.