Once-daily tobramycin in cystic fibrosis: better for clinical outcome than thrice-daily tobramycin but more resistance development?
OBJECTIVE
Once-daily administration of aminoglycosides in cystic fibrosis (CF) patients is considered equally efficacious and potentially less nephrotoxic than dosing three times a day. However, the choice of the most suitable PK/PD index (C(max)/MIC versus AUC(24)/MIC) to ensure optimum clinical outcome in this patient population is not clear.


METHODS
In a single-centre, open, randomized, controlled, non-blinded study 33 adult CF patients (20 females, 19-37 years) were treated with intravenous tobramycin (10 mg/kg/day) for 14 days given either as single dose once a day (Q24; 17 patients) or divided into three equal doses every 8 h (Q8; 16 patients). Tobramycin serum concentrations and MICs for Pseudomonas aeruginosa were determined on days 1 and 14. The clinical outcome parameter, correlated to PK/PD indices, was the percentage predicted forced expiratory volume in 1 s (FEV(1)% pred.).


RESULTS
FEV(1)% pred. improved significantly for both treatments. There was a log-linear relationship between C(max)/MIC and FEV(1)% pred. and AUC/MIC and FEV(1)% pred. for both treatments. For equal values of AUC24/MIC, however, Q24 treatment provided better improvement in lung function than Q8 dosing, whereas C(max)/MIC did not show any dosing interval dependence. A statistically significant increase was observed for MIC (day 1) versus MIC (day 14) for Q24 treatment, however, no such difference was observed for Q8 treatment.


CONCLUSIONS
The most important PK/PD parameter for clinical outcome in CF patients was C(max)/MIC. Outcome prediction of AUC(24)/MIC was dependent on the regimen. The increase of P. aeruginosa resistance after once-daily administration is linked to a long dosing interval. More and larger studies are needed to optimize the dosing regimen for maximum clinical outcome with minimum resistance development.
Burkhardt
Olaf
O
Department of Pulmonary Medicine, Medical School Hannover, Hannover, Germany. burkhardt.olaf@mh-hannover.de
Lehmann
Christine
C
Madabushi
Rajanikanth
R
Kumar
Vipul
V
Derendorf
Hartmut
H
Welte
Tobias
T
D000328:Adult; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D003550:Cystic Fibrosis / Q000188:drug therapy* / Q000382:microbiology; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D011552:Pseudomonas Infections / Q000188:drug therapy / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D012129:Respiratory Function Tests; D014031:Tobramycin / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents; D014031:Tobramycin