16672
The presence of ritonavir , a known P - gp inhibitor , increased the intestinal permeation of indinavir by 2 - fold in FaHIF , while there was no increase when using FeHIF .
 ritonavir, indinavir
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 ritonavir, indinavir