PK data from individuals who vomited after drug ingestion

Dear NM-users, I have a question regarding NONMEM modeling of PK data from individuals who vomited after drug ingestion. Basically, I have a set of data from about 150 subjects (about 5 measurements per subject) who orally ingested alcohol at time = 0 h. However, about 15% of this group vomited more than 1 h post-dose. Based on NONMEM modeling of PK data from subjects who did not vomit during the study, the mean elimination half-life is about 30 min. May I ask if I should model vomiting incidence (a "yes" or a "no") as a categorical covariate for analysis of all the data? I have demographic covariate information at hand. Or, should I introduce a mixture model during NONMEM modeling? I would expect the vomiting subgroup to display different values for Vd, Ka etc as compared to the non-vomiting subgroup. Thank you very much for your time and kind advice. Best wishes, Kok-Yong Seng, PhD DSO National Laboratories Republic of Singapore