Initiate therapy with drastically reduced starting doses. Reduce starting dose by 10-fold and reduce frequency to thrice weekly instead of daily. During therapy, adjust thioguanine doses based on degree of myelosuppression and disease-specific guidelines. It usually takes at least 4-6 weeks of stable dosing to reach steady state after each dose adjustment. If myelosuppression occurs, emphasis should be on reducing thioguanine over other agents.