- Treatment with other medications known to potentiate guanfacine's hypotensive effects or cause arrhythmia (specifically antipsychotics (including sultopride, chlorpromazine, thioridazine, amisulpiride, sulpiride, haloperidol), and moxifloxacin, baclofen, verapamil, quinidine, hydroquinidine, dispyramide, amiodarone, dofetilide, ibutilide, sotalol, pimazide, bepridil, cisapride, diphemanil, erythromycin, halofantrine, pentamidine, sparfloxacin, vincamine, alfuzosin, prazosin, terazosin, tamsulosin, amifostine