Background Most of the pharmacist's work is performed in the morning shift, but little is known about the volume and nature of the work done during the afternoon shift.

Purpose The aim is to quantify, analyse and compare the pharmacist's work pattern during the afternoon shift with that of the morning shift.

Materials and methods Retrospective study at a tertiary university hospital from January 2010 to March 2011. During the morning, 10 pharmacists and six residents review and approve medical orders (MOs) of inpatient treatments. In the afternoon this activity is undertaken by one pharmacist and one resident. A search for starts and changes on drug treatments (SAC) (electronic prescribing and transcription of MOs), approved MOs (AMOs), pharmacist's interventions (PIs) and medication errors (MEs) was performed electronically. Then, results recorded between 8:00 a.m and 2:59 p.m were compared with those between 3:00 p.m and 8:59 p.m using descriptive statistics.

Results Total SACs: 822 440 (29.5% in the afternoon) and total AMOs: 551 011 (26.3% in the afternoon), with a mean of 2.4 (SD 0.15) more SACs and a mean of 2.8 (SD 0.22) more MOs approved per month during the morning.

Conclusions During the period studied, nearly one third of the total work done was during the afternoon shift, while the staff was reduced to approximately 10%. Notification of MEs accounted for nearly half of the total. Type of PIs and MEs were similar between the two shifts.