BACKGROUND: Primary care clinical pharmacy specialists (PCCPSs) are positioned to promote effective, safe, and affordable medication use. Documentation of performed interventions is difficult because the diversity of performed interventions in a variety of disease states in some practice settings. Validation of cost-avoidance projections is also difficult because traditional projection methods have several limitations.OBJECTIVE: To (1) compare projected medication cost avoidance (MCA) to actual MCA for medication conversions related to hyperlipidemia, hypertension, depression, and chronic pain initiated by PCCPS, and (2) estimate medication discontinuation that might be attributable to serious adverse drug events (ADEs) possibly associated with medication conversions.METHODS: This was a retrospective, longitudinal study conducted in a not-for-profit, integrated health system comprising approximately 470,000 members. Using a portable documentation tool, PCCPSs recorded projected annual MCA for medication conversions in 4 disease conditions (i.e., hyper tension, dyslipidemia, depression, and chronic pain) in the 6-month period from December 1, 2003, through May 31, 2004. Actual annual MCA for these interventions for a 1-year follow-up period was calculated using integrated, electronic data from an administrative pharmacy database. Comparisons were made between projected MCA and actual MCA. Cost was defined as actual drug acquisition cost. In addition, an assessment of serious ADEs potentially related to the conversions was undertaken by reviewing electronic medical records of converted, nonpersistent patients.