Interim analysis showed positive results, it was difficult to include patients and also the fact that the grant for this project has ended, we have decided to complete the study before we had included the total number of 16 patients.

Valacyclovir has replaced acyclovir in many clinical scenarios. Pharmacokinetic data support the use of oral valacyclovir in children, but practical problems exist in children having to take adult-dose tablets. A formulation with acceptable palatability, good pharmaceutical quality and possibility of flexible dosing is developed. Pharmacokinetic data of this formulation is missing.

The present study investigates the pharmacokinetics of valacyclovir oral solution in children by determine the area under the curve (AUC0-12), time above critical concentration (Ccrit), Cmax and Tmax of acyclovir.

Secondary, the safety profile of a single dose of valacyclovir oral solution will be determined.

Inclusion Criteria:

• Subject is in the age of 2-12 years.
• Subject has an indication for (val)acyclovir prophylaxis and are planned to receive valacyclovir oral solution.
• Subject is managed with a central venous catheter (CVC/Port-a-Cath).
• Subject's parents have signed the Informed Consent Form prior to screening evaluations.
• Subject is willing to participate after study procedures are explained in comprehensible language for the child.

Exclusion Criteria:

• Severe anemia (<6.0 mmol/L).
• Full dose has not been taken.