Antibiotic line locks
NHS Borders clinical guidelines
This guideline has been adapted with permission from University College London Hospitals NHS Foundation Trust Guideline December 2021
Prior to starting, discuss with Infection Specialist.
Antibiotic Locks
Antibiotic locks may be used as an adjunctive to systemic treatment for associated bacteraemias.
The antibiotic solution is instilled or “locked” into each catheter lumen during periods when the catheter is not being used.
Rapidly decreasing antibiotic concentrations may occur over time in the distal lumen of catheters instilled with an antibiotic lock, especially among ambulatory patients with femoral catheters. Thus, the antibiotic concentration used for locking should be at least 1000 times higher than the minimal inhibitory concentration of antibiotic for the bacterium (the MIC is the lowest concentration that will inhibit the growth of the bacterium). So a catheter infection caused by a coagulase negative staphylococcus (typically with a teicoplanin MIC of 1mg/L) can be locked using teicoplanin (concentration of 10mg/mL = 10 000mg/L).
Antibiotic lock concentrations to be used
The most commonly used antibiotic concentrations are shown below. Any remaining antibiotic in the vial should be discarded.
| Drug | How to make up the antibiotic lock | Final concentration |
| Vancomycin | Reconstitute a 500mg vial with 9.8mL water for injections. Draw up 2mL of this solution and further dilute it to 10mL with sodium chloride 0.9% |
10mg/mL |
| Teicoplanin | Reconstitute the 200mg vial with the ampoule of water for injections provided. Draw up 1mL of this solution and dilute to 6.7mL with sodium chloride 0.9% |
10mg/mL |
| Gentamycin | Draw up the contents of one 80mg/2mL vial and further dilute to 16mL with sodium chloride 0.9% | 5mg/mL |
| Amikacin | Draw up the contents of a 100mg/2mL vial and dilute to 20mL with sodium chloride 0.9% |
5mg/mL |
| Ciprofloxacin | Ready diluted. Do not further dilute. | 2mg/mL |
Antibiotic lock volumes
If the fill (luminal) volume is clearly marked on the lumen, use that volume for the antibiotic lock even if the catheter is known to have been trimmed.
Where the fill (luminal) volume is not printed on the lumen, use the guide below for antibiotic lock volume.
When using lumens for antibiotic locks, it is important to ensure the “locked” lumen iseasy to identify e.g. attach a label to the locked catheter.
| Type of CVC catheter | Lumen volume (if not marked on lumen)7 |
| PICC | 1mL per lumen |
| Hickman catheter | 2mL per lumen |
| Portacaths | 2mL per lumen |
| Vascath | 2mL per lumen |
| Temporary CVC (eg. jugular/femoral) | 0.5mL per lumen |
Addition of heparin to catheter lock
Addition of heparin is not generally recommended. There is poor evidence of the role of heparin in reducing central venous catheter thrombosis.
In addition, precipitation occurs when some antibiotics are mixed with heparin, especially with increasing antibiotic concentrations.
Antibiotic lock dwell time
Ideally the antibiotic lock should be left in place for 24 hours and generally should not exceed 48 hours before re-instillation. If necessary the catheter may be used between
antibiotic locks unless this gives rise to rigors or fever.
For in-patients, the antibiotic lock should be aspirated and replaced every 24 hours. For patients on thrice-weekly dialysis, the antibiotic lock solution can be changed after every
dialysis session.
Re-instillation of the antibiotic locks
The antibiotic lock should be aspirated before infusion of the next dose of the antibiotic lock, other intravenous medication or solution.
Where it is difficult to aspirate the lock due to bleed back, the lock may be flushed through systemically.
Duration of antibiotic lock therapy1
Although the duration of antibiotic lock therapy has varied substantially among different studies (3– 30 days), most studies have used 2-week duration.
If antibiotic lock therapy is used in conjunction with systemic antimicrobial therapy for catheter-associated infection, treat for 7–14 days.
For patients with multiple positive catheter-drawn blood cultures that grow coagulase-negative staphylococci or gram negative bacilli and concurrent negative peripheral blood cultures, a trial of antibiotic lock therapy may be used without systemic therapy for 10–14 days.