3771
For patients with prior zidovudine therapy , the mean change in CD4 cells in the combination and zidovudine groups was 63 . 7 cells / mm3 and 4 . 9 cells / mm3 at week 8 and 6 . 8 cells / mm3 and - 45 . 1 cells / mm3 at week 16 , respectively .
 Chemical: zidovudine; Chemical: zidovudine
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 Chemical: zidovudine; Chemical: zidovudine