OBJECTIVES: To analyze clinical pharmacists’ interventions and determine classification types as well as clinical relevance. METHODS: This was a 5-month (January to May 2008) retrospective intervention study conducted at a 500-bed tertiary teaching hospital in Muscat, Oman. A standard manual documentation form was used to capture the interventions. Interventions were classified into five groups, namely; drug choice, drug regimen, monitoring, information, and prescribing issues. Clinical relevance was related to whether efficacy or toxicity was either improved or reduced. The outcome of each intervention was categorized as accepted, rejected or unknown according to the prescribing physician’s response. The pharmacists evaluated the clinical significance of the interventions based on their own clinical judgments. Analyses were performed using descriptive statistics.RESULTS: A total of 504 interventions were documented over the 5-month study period. On average each intervention took 15±14 (median, 10) minutes, ranging from 1 minute to 3 hours. The most common interventions performed were on drug regimen change (n=237; 47%), drug choice (n=128; 25%) and drug information issues (n=106; 21%). Dose change (n=153; 30%) and patient education (n=54; 11%) were the most frequent interventions performed in the drug regimen change and drug information categories, respectively. The most common indications for which interventions were made were infectious (n=100; 20%) and respiratory (n=77; 15%) diseases. Efficacy was improved and toxicity avoided in 38% (n=193) and 28% (n=140) of the interventions, respectively. Potential fatalities or end-organ damage was avoided in 1.6% (n=8) of the cases while interventions of major significance was recorded in 43% (n=215) of the interventions. CONCLUSIONS: The data show that clinical pharmacists play an important role in drug safety and efficacy to optimize pharmaceutical care as part of the multi-disciplinary team approach in the hospital.