Background As treatment out of hospital with outpatient parenteral antimicrobial therapy (OPAT) increases, so too does the risk for patients of being less visible, with potential for suboptimal care.

Objectives We aimed to compare pre-expansion and post-expansion (1) successful completion, complications and (2) the impact of an OPAT-specific antimicrobial stewardship (AMS) intervention to mitigate inappropriate antibiotic prescribing.

Design A prospective longitudinal study during two consecutive 12-month periods: period A (1 August 2012 to 31 July 2013) and period B (1 August 2013 to 31 July 2014).

Setting The Hospital-in-the-Home (HITH) programme at The Royal Children’s Hospital Melbourne.

Participants All patients who received OPAT during the study period.

Interventions Between the two periods, the programme expanded from 16 to 32 patients/day. To coincide with this, a combined AMS intervention was introduced: (1) OPAT-specific guidelines and (2) active review of OPAT prescriptions and input by Paediatric Infectious Diseases.

Main outcomes Successful completion of OPAT, OPAT-related complications, readmission, length of stay and antibiotic appropriateness.

Results Over 2 years, 646 patients (47% female, median age 7 years) were treated via OPAT for 754 episodes. Patient episodes increased from 254 in period A to 500 in period B, with proportional increases in infants under 1 month and immunocompromised patients. OPAT was successfully completed in 245/251 (98%) versus 473/482 (98%) (OR 1.8, 95% CI 0.7 to 4.5, p=0.3). OPAT-related complications remained low: intravenous catheter-associated complications 16/138 (12%) versus 41/414 (10%), and antibiotic-associated complications 0/254 (0%) versus 2/500 (0.4%). Despite the increase in activity, with the AMS intervention, overall appropriate antibiotic prescribing remained high: 71% versus 76%. Inappropriately long durations reduced from 30/312 (10%) to 37/617 (6%) (OR 0.6, 95% CI 0.4 to 0.99, p=0.04), and median number of days on broad-spectrum antibiotics from 11 (IQR 8–24.5) to 8 (IQR 5–11).

Conclusion During a period of substantial expansion, we maintained clinical outcomes. A modest AMS intervention reduced some but not all aspects of inappropriate antibiotic prescribing.