OBJECTIVES To determine workflow variables associated with medication administration process conducted by nurses in intensive and acute care units of a hospital. METHODS A time-and-motion study was conducted in intensive and acute care units of a hospital. Each medication administration was operationalised as a combination of five activities namely direct patient care (five tasks), indirect patient care (four tasks), administration (four tasks), miscellaneous (three tasks) and other. Time devoted to each medication administration and each task were evaluated by means of two pre-calibrated stop-watches. Perception of nurses regarding workflow burden during each medication administration was determined on a five point Likert scale as strongly disagree (1)—Strongly agree (5). Furthermore patient features (age, gender, number of co-morbidities, length of stay) and complexity of medication administration (frequency of each task, number of assistants involved, number of drugs administered through different routes) were used to predict medication administration time. Descriptive statistics were reported. Stepwise regression analysis was performed to examine predictors of medication administration time. RESULTS Mean medication administration time in intensive (N=101) and acute (N=100) care units were 5.2±3.7 minutes and 5.3±3.5 minutes respectively. Overall nurses had positive perception regarding the supportive workflow structure of intensive (4.4±0.08) and acute care (4.6±0.5) units. Stepwise regression analysis indicated that significant (p<0.05) predictors of medication administration time in intensive care unit were time devoted to administration (β=0.57), direct patient care (β=0.30), and miscellaneous (β=0.14) activities. Likewise significant (p<0.05) predictors of medication administration time in acute care unit were time devoted to administration activity (β=0.67), gender of patient (β=0.21) and number of inhaled drugs administered (β=0.16). CONCLUSIONS Administration activity played a predominant role during medication administration in both units. Measures taken by hospital pharmacy to optimize such an activity may result in reduction of workflow burden encountered by nurses in the units.