Pharmacokinetics of Terbinafine in Young Children Treated for Tinea Capitis

Background: Dermatophytes are the most common cause of human fungal infections. Response rates to existing therapy are lower than optimal, but newer agents like terbinafine hold promise for improved management of such infections. This investigation was designed to evaluate the single dose and steady state pharmacokinetics of terbinafine in young children with tinea capitis. Methods: Twenty-two otherwise healthy children (4–8 years) with tinea capitis were eligible for enrollment. Children were treated with terbinafine once daily according to body weight (<25 kg, 125 mg; 25–35 kg, 187.5 mg), and pharmacokinetic sampling was conducted after the first dose, at the midpoint of treatment and at steady state. Plasma terbinafine concentrations were quantitated, and the pharmacokinetic indices compared with adult data. Results: Absolute estimates of Cmax and area under the concentration curve (AUC)0–24 were comparable between children and adults for the administered dose; however, children demonstrated significantly lower estimates of exposure when dose was corrected for weight (Cmax SS 200 ± 104 versus 454 ± 185 ng/mL per mg/kg dose, P < 0.01; AUCSS: 1110 ± 640 versus 2756 ± 1775 ng*h/mL per mg/kg dose, P < 0.01). When examined along a continuum, age accounted for ∼50% of the variability observed in dose-normalized Cmax and AUC (P < 0.01). A slight but significant reduction in apparent oral clearance was observed with increasing age (0.02 L/h/kg per yr) that likely accounts for the lesser degree of accumulation observed in children at steady state (accumulation ratio, 1.5 ± 0.8 versus 2.3 ± 0.6, P < 0.01). Adverse events consisted principally of headache (n = 3) and gastrointestinal complaints (altered eating habits n = 3, loss of appetite n = 3, stomachache n = 4, diarrhea n = 2). A reduction in neutrophil count was observed in 5 children and thought to be related to study drug in 2. Conclusions: Children require significantly larger weight-normalized doses to approximate the exposure estimates observed in adults. The dosing scheme used in this investigation results in absolute exposure estimates at steady state and a safety profile that are not appreciably different from adults.