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