Exposure–Response Analysis of Micafungin in Neonatal Candidiasis: Pooled Analysis of Two Clinical Trials

BACKGROUND: Neonatal candidiasis causes significant morbidity and mortality in high risk infants. The micafungin dosage regimen of 10 mg/kg established for the treatment of neonatal candidiasis is based on a laboratory animal model of neonatal hematogenous Candida meningoencephalitis and pharmacokinetic (PK)–pharmacodynamic (PD) bridging studies. However, little is known about the how these PK–PD data translate clinically. METHODS: Micafungin plasma concentrations from infants were used to construct a population PK model using Pmetrics software. Bayesian posterior estimates for infants with invasive candidiasis were used to evaluate the relationship between drug exposure and mycologic response using logistic regression. RESULTS: Sixty-four infants 3–119 days of age were included, of which 29 (45%) infants had invasive candidiasis. A 2-compartment PK model fits the data well. Allometric scaling was applied to clearance and volume normalized to the mean population weight (kg). The mean (standard deviation) estimates for clearance and volume in the central compartment were 0.07 (0.05) L/h/1.8 kg and 0.61 (0.53) L/1.8 kg, respectively. No relationship between average daily area under concentration–time curve or average daily area under concentration–time curve:minimum inhibitory concentration ratio and mycologic response was demonstrated (P > 0.05). Although not statistically significant, mycologic response was numerically higher when area under concentration–time curves were at or above the PD target. CONCLUSIONS: While a significant exposure–response relationship was not found, PK–PD experiments support higher exposures of micafungin in infants with invasive candidiasis. More patients would clarify this relationship; however, low incidence deters the feasibility of these studies.