Aim Intravenous gentamicin is given as a 5 day course to paediatric patients who have undergone abdominal surgery. There was an impression that the multiple daily dosing regimen in use at the time (2.5 mg/kg three times a day) did not provide therapeutic levels in this patient cohort therefore the aim was to develop a dosing regimen that did.

Method A retrospective audit of pre- and post-dose gentamicin levels in patients on a multiple daily dose regimen was undertaken. Data was gathered using a microbiology database and children aged between 1 month and 16 years who had gentamicin prophylaxis following abdominal surgery between January 2005 and January 2010 were included. Following on from the initial audit a once daily gentamicin dosing regimen was introduced for all patients who met the inclusion criteria: child aged over 1 month of age without ascites, cystic fibrosis, endocarditis, major burns or significant renal impairment and not pregnant. The once daily dose chosen was based on BNF-c guidance and an administration guideline was incorporated into a prescription chart. A survey of 7 hospitals and a literature review was conducted to determine when gentamicin levels were monitored. Once the regimen had been in place for 12 months a prospective audit of trough levels was undertaken.

Results Multiple day dosing.

336 children were reviewed, of these 35 had incomplete data and were excluded. Data was analysed from 301 children, 207 (68.7%) had a post dose below the recommended therapeutic range (5–10 mg/L) and the dose was increased by 10%. 132/207 of this subset had a second post dose measured and 99/132 (75%) were still below the therapeutic range. Overall, only 31.2% of children had gentamicin levels within the therapeutic range during the course of treatment.

The Hartford nomogram has not been validated for use in children therefore it cannot it be applied to this patient cohort. The literature review and survey of practice revealed that with once daily dosing a peak gentamicin level does not need to be measured, as it is assumed that with a 7 mg/kg dose the pharmacodynamic goal of achieving a peak to minimum inhibitory concentration ratio greater than 104 will be achieved.1 ,2 Therefore, it is routine practice to only measure the trough level 1.

Once daily dosing

Thirty patients were audited after the introduction of the once daily regimen and 100% of patients had a trough level of ≤1 mg/L.

Conclusion A once daily gentamicin regimen of 7 mg/kg was found to achieve therapeutic levels in paediatric surgery patients who met the inclusion criteria when administered in accordance with the local prescription chart. A further audit is planned to determine if the new dosage regimen affects the clinical outcome.