when was the last time when patient 46422 had the minimum value of pt in 07/2103?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 46422 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'pt' ) and strftime('%y-%m',labevents.charttime) = '2103-07' order by labevents.valuenum asc, labevents.charttime desc limit 1