Statistical interpretations in a bioequivalence trial are considered and studied when the missing observations occurred in $2;{ imes};2$ crossover experiment. Patel (1985) suggested the approximate test procedures for carryover effect and drug effect in $2;{ imes};2$ crossover design when some of data are missing in the second period. A modified Patel method is newly proposed to the bioequivalence trial and it is compared with the current method through the simulation study.