Distribution of Azithromycin in Plasma and Tonsil Tissue after Repeated Oral Administration of 10 or 20 Milligrams per Kilogram in Pediatric Patients

Abstract

Azithromycin concentrations in the tonsils of 56 pediatric patients, treated with 10 or 20 mg of the drug per kg of body weight for 3 days, were compared. Azithromycin levels in plasma and tonsil samples were determined up to 8.5 days after the last dose. The 20-mg/kg regimen resulted in an improved tonsillar distribution of azithromycin, suggesting the achievement of enhanced therapeutic concentrations at infective sites of the upper respiratory tract.Azithromycin, the prototype of azalides, possesses peculiar pharmacokinetics, consisting of high distribution into target tissues (4), and displays a broad antimicrobial spectrum (12). Guidelines for azithromycin MICs have established that breakpoints of Յ2, 4, and Ն8 mg/liter indicate susceptible, intermediately resistant, and resistant bacteria, respectively (7).Studies with adults have suggested that once-daily dosing with 500 mg for 3 days should maintain tonsillar azithromycin levels higher than 2 mg/kg of body weight for 10 days (3, 4). In pediatric patients, a 3-day treatment with 10 mg/kg allows a tonsillar azithromycin distribution similar to that of adults (15). Cure and improvement rates of 93 to 100% were obtained in children with bacterial pharyngitis and/or tonsillitis treated with 10 mg of azithromycin/kg for 3 days (7). However, lower success rates have also been reported (2, 11).After oral administration, azithromycin undergoes a rapid uptake from systemic circulation into phagocytes, which then release the drug at infection sites, exposing local extracellular compartments to azithromycin concentrations higher than plasma levels (5, 6). On this basis, azithromycin administration at doses higher than standard regimens might improve eradication rates in pharyngitis and tonsillitis. Accordingly, this study compared azithromycin concentrations in tonsils collected from pediatric patients treated with 10 or 20 mg/kg daily for 3 days.The study was performed with children scheduled to undergo surgical tonsil removal. The exclusion criteria were history of drug allergy; drug treatments, including antimicrobials, nonprescription drugs, or enzymatic inducers and/or inhibitors within the previous 2 weeks; conditions affecting drug absorption (vomiting, diarrhea, malabsorption); and major medical problems. Informed consent was obtained from parents or legal guardians. The investigation was approved by the local University Hospital Ethics Committee. Fifty-six patients (30 males, 26 females; age range, 4 to 12 years; mean age, 6.46 Ϯ 0.32 years [mean Ϯ standard deviation]) entered the study. They were assigned to two groups, balanced for sex and age, and were treated once daily with azithromycin in an oral suspension (Zitromax; Pfizer Italiana, Rome, Italy) at 10 or 20 mg/kg for 3 days. Patients underwent surgery from 0.5 to 8.5 days after the last dose. Standard anesthesiological procedures and perioperative medications were applied. All surgical procedures were performed by the same surgeon (P.B.). Plasma samples (2 ml) were collected before surgery. Specimen...

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