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Pharmacokinetics of oral acyclovir in neonates and in infants: a population analysis
1Pharmacie and Centre de Recherche en Pathologie Infectieuse et Tropicale, Hopital Avicenne, Bobigny 93009, France. michel.tod@avc.ap-hop-paris.fr
Insights
This study determined acyclovir pharmacokinetics in children under 2 years old. The proposed dosing regimen is effective for herpes simplex virus (HSV) but may need doubling for varicella-zoster virus (VZV) in infants over 3 months.
Area of Science:
- Pharmacology
- Pediatric Infectious Diseases
Background:
- Acyclovir is approved for herpes simplex virus (HSV) and varicella-zoster virus (VZV) in children.
- Oral acyclovir use in children under 2 years is limited by insufficient pharmacokinetic data.
Purpose of the Study:
- To determine acyclovir pharmacokinetics and interindividual variability in children younger than 2 years.
- To support a proposed dosing regimen for oral acyclovir suspension.
Main Methods:
- A multicenter study involving 79 children (under 2 years) treated with oral acyclovir suspension for HSV or VZV.
- Plasma acyclovir concentrations were measured by radioimmunoassay and analyzed using a population approach.
Main Results:
- Acyclovir clearance correlated with estimated glomerular filtration rate, body surface area, and serum creatinine.
- Elimination half-life decreased significantly in the first month of life; bioavailability was 0.12.
- Simulations indicated the proposed dose is adequate for HSV but may require doubling for VZV in infants over 3 months.
Conclusions:
- Dosage adjustment by body weight is recommended for pediatric patients.
- The proposed acyclovir dosing regimen appears adequate for HSV treatment.
- A twofold increase in acyclovir dosage may be necessary for VZV treatment in children older than 3 months.
Abstract:
Acyclovir is approved for the treatment of herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections in children by the intravenous and oral routes. However, its use by the oral route in children younger than 2 years of age is limited due to a lack of pharmacokinetic data. The objectives of the present study were to determine the typical pharmacokinetics of an oral suspension of acyclovir given to children younger than 2 years of age and the interindividual variabilities in the values of the pharmacokinetic parameters in order to support the proposed dosing regimen (24 mg/kg of body weight three times a day for patients younger than 1 month of age or four times a day otherwise). Children younger than age 2 years with HSV or VZV infections were enrolled in a multicenter study. Children were treated for at least 5 days with an acyclovir oral suspension. Plasma samples were obtained at steady state, before acyclovir administration, and at 2, 3, 5, and 8 h after acyclovir administration. Acyclovir concentrations were measured by radioimmunoassay. The data were analyzed by a population approach. Data for 79 children were considered in the pharmacokinetic study (212 samples, 1 to 5 samples per patient). Acyclovir clearance was related to the estimated glomerular filtration rate, body surface area, and serum creatinine level. The volume of distribution was related to body weight. The elimination half-life decreased sharply during the first month after birth, from 10 to 15 h to 2.5 h. Bioavailability was 0.12. The interindividual variability was less pronounced when the parameters were normalized with respect to body weight. Hence, dosage adjustment by body weight is recommended for this population. Simulations showed that the length of time that acyclovir remains above the 50% inhibitory concentration during a 24-h period was more than 12 h for HSV but not for VZV. The proposed dosing regimen seems adequate for the treatment of HSV infections, while for the treatment of VZV infections, a twofold increase in the dose seems necessary for children older than age 3 months.