last osis ▁and ▁is ▁commonly ▁seen ▁in ▁Vit amin ▁B 1 2 ▁def ic iency ▁and ▁fol ic ▁acid ▁def ic iency . ▁This ▁type ▁of ▁an emia ▁is ▁caused ▁by ▁imp a ired ▁DNA ▁synth esis ▁and ▁repair , ▁often ▁from ▁def ic ient ▁th ym id ine ▁production . ▁Th iam ine ▁respons ive ▁meg al ob last ic ▁an emia ▁synd rome ▁also ▁causes ▁meg al ob last ic ▁an emia . ▁ ▁The ▁red ▁blood ▁cells ▁grow ▁larger ▁because ▁they ▁cannot ▁produce ▁DNA ▁quickly ▁enough ▁to ▁divide ▁at ▁the ▁right ▁time ▁as ▁they ▁grow ▁and ▁thus ▁grow ▁too ▁large ▁before ▁division . ▁Add itional ▁causes ▁of ▁meg al ob last ic ▁an emia ▁include ▁medic ations ▁that ▁inter f ere ▁with ▁DNA ▁synth esis ▁or ▁with ▁the ▁absor ption ▁or ▁met abol ism ▁of ▁Vit amin ▁B 1 2 ▁or ▁fol ate ▁such ▁as ▁m eth ot re x ate , ▁sul fas al azine , ▁met form in , ▁ant icon v uls ant ▁medic ations ▁( e . g ., ▁val pro ic ▁acid ▁or ▁ph eny to in ), ▁certain ▁ant ib iot ics ▁( e . g ., ▁trim eth op rim / s ulf am eth ox az ole ), ▁ant ire t ro vir al ▁medic ations , ▁ch ol esty ram ine , ▁tri am ter ene , ▁ ▁and ▁nit r ous ▁ox ide . ▁ ▁Non - M eg al ob last ic ▁an em ias ▁ ▁Red ▁cell ▁memb