what's the yearly maximum dose of pe 20 fs po for patient 4718 until 48 months ago?
select max(inputevents_cv.amount) from inputevents_cv where inputevents_cv.icustay_id in ( select icustays.icustay_id from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 4718 ) ) and inputevents_cv.itemid in ( select d_items.itemid from d_items where d_items.label = 'pe 20 fs po' and d_items.linksto = 'inputevents_cv' ) and datetime(inputevents_cv.charttime) <= datetime(current_time,'-48 month') group by strftime('%y',inputevents_cv.charttime)