Use of microencapsulation technology in combination with absorption enhancers eliminated epithelium irritation and necrosis commonly associated with nasal delivery of cytotoxic therapeutic agents. Phenothiazines, such as ethopropazine (ETZ), promethazine, trimeprazine and propiomazine have been used for the treatment of allergenic conditions, motion sickness, nausea, Parkinson's disease, Prion disease and as a sedative for psychiatric disorders. The enantiomers of commercially available racemic phenothiazines were isolated and purified using classical diastereomeric salt techniques. The racemate and the enantiomers of ETZ were tested in vitro for their cellular toxicity using lung fibroblast cells. Each enantiomer was shown to be cytotoxic at concentrations greater than 10(-5) molar. The ETZ enantiomers were encapsulated using spinning disk atomization to prepare a nasal delivery dosage form that does not produce an irritation response. Release rates for the ETZ microcapsules were determined in vitro and an animal study was conducted to determine the irritation response of rat nasal mucosa when dosed with encapsulated vs. non-encapsulated ETZ.