For the 12-hour QTcF analysis , the largest 1-sided 95 % UCB was 10.34 ms ( 12 hours post-supratherapeutic dose ) , representing the only 1-sided 95 % UCB > 10 ms. Following the supra-therapeutic dose , maximum guanfacine plasma concentration was attained at 5.0 hours ( median ) post-dose .