what were the four most commonly prescribed drugs for patients that had previously received packed cell transfusion within 2 months, until 2 years ago?
select t3.drug from ( select t2.drug, dense_rank() over ( order by count(*) desc ) as c1 from ( select admissions.subject_id, procedures_icd.charttime from procedures_icd join admissions on procedures_icd.hadm_id = admissions.hadm_id where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'packed cell transfusion' ) and datetime(procedures_icd.charttime) <= datetime(current_time,'-2 year') ) as t1 join ( select admissions.subject_id, prescriptions.drug, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where datetime(prescriptions.startdate) <= datetime(current_time,'-2 year') ) as t2 on t1.subject_id = t2.subject_id where t1.charttime < t2.startdate and datetime(t2.startdate) between datetime(t1.charttime) and datetime(t1.charttime,'+2 month') group by t2.drug ) as t3 where t3.c1 <= 4