OBJECTIVE: To compare the use of in-line filtration with the addition of heparin/hydrocortisone (hep/hc) to the infusate for both phlebitis prevention and intravenous(iv) line survival in peripheral iv catheters. This study was specific for a patient group receiving prolonged courses of iv antibiotics. Analysis of the two endpoints for conventional short iv catheters (short lines) versus long (30 cm) iv catheters (long lines) was also performed. METHODS: Patients with cystic fibrosis receiving intermittent iv antibiotics were randomly allocated to receive their drugs either through an in-line filter using a drug-free infusate or with no filter and an infusate containing heparin 500 units and hydrocortisone 10 mg/L. Infusion sites were assessed daily. RESULTS: Both the hep/hc and filter groups were similar in terms of phlebitis incidence and iv line survival when analyzed separately for both short and long lines. Long lines displayed markedly prolonged survival times and reduced phlebitis compared with short lines. CONCLUSIONS: The effectiveness of iv filters in excluding the large particle load introduced by iv antibiotics and hence in reducing the subsequent phlebitis makes them a useful alternative to the use of hep/hc. The use of filters in this patient group may offer advantages in terms of ease of use and a possible decrease in hep/hc-related problems. Long lines offer practical advantages over short lines for patients requiring longer term iv access.