Bioavailability of rectally administered valproic acid syrup

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Abstract
The bioavailability of commercially available valproic acid (VPA) syrup was studied following rectal administration in both dogs and children. Six dogs were studied following both oral (PO) and rectal (PR) administration of a dilute VPA syrup given in a dose of 40 mg/kg. There was no significant difference in the area under the serum concentration-time curve between the oral (201.1 mg l-1 h) and rectal (219.6 mg l-1 h) routes of administration. Four children were given VPA syrup by the rectal route. In 3 patients on maintenance VPA therapy, absorption following rectal administration was similar to that following oral administration. In a 4th child, VPA serum levels following an initial rectal dose of 20 mg/kg reached a maximum of 42 mg/l 2 h after the drug was given. Bioavailability of a diluted VPA syrup given rectally is comparable to that following oral administration. Rectal administration of VPA syrup appears to be a satisfactory alternative when the oral route is unavailable.