Determination of tobramycin in saliva is not suitable for therapeutic drug monitoring of patients with cystic fibrosis.
BACKGROUND
Tobramycin, used in the treatment of infections caused by Gram-negative bacteria, requires therapeutic drug monitoring (TDM) due to its narrow therapeutic index. The collection of blood for these assays may cause pain and trauma to the child and/or be difficult because of limited access to appropriate blood vessels. We undertook an evaluation of the role of saliva concentrations in the TDM of once-daily tobramycin therapy in patients with cystic fibrosis.


METHODS
Fourteen patients (mean age 15 years) with cystic fibrosis were enrolled at Women's and Children's Hospital, Adelaide (WCH). All patients received once-daily dose of intravenous tobramycin for 2-3 weeks and had plasma levels measured once a week. At the same time of blood sampling at 1 and 6 h after initiation of tobramycin infusion, the patients also provided saliva samples. For collection of saliva, the Salivette (Sarstedt Laboratories) system was used which was developed specifically for saliva sampling. Concentrations in blood and saliva were measured by the Beckman Synchron CX system, which is utilized for routine assays of plasma tobramycin.


CONCLUSIONS
Tobramycin could not be detected in saliva within the first 6 h after a once-daily dosing. Therefore, plasma cannot be substituted with saliva for the TDM of tobramycin using the clinical routines at WCH.
Madsen
Vibeke
V
Department of Pharmaceutics, The Danish University of Pharmaceutical Sciences, Copenhagen, Denmark.
Lind
Aileen
A
Rasmussen
Mette
M
Coulthard
Kingsley
K
D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics*; D002648:Child; D003550:Cystic Fibrosis / Q000150:complications / Q000188:drug therapy / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D016903:Drug Monitoring / Q000379:methods*; D005260:Female; D006801:Humans; D007275:Injections, Intravenous; D008171:Lung Diseases / Q000150:complications / Q000188:drug therapy / Q000378:metabolism; D008297:Male; D009391:Nephelometry and Turbidimetry; D011552:Pseudomonas Infections / Q000150:complications / Q000188:drug therapy / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000302:isolation & purification; D012463:Saliva / Q000378:metabolism*; D014031:Tobramycin / Q000493:pharmacokinetics*
D000900:Anti-Bacterial Agents; D014031:Tobramycin