Bioavailability of sodium valproate suppositories during repeated administration at steady state in epileptic children

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Abstract
Oral administration of antiepileptic drugs can temporarily be impossible under certain conditions, such as altered states of consciousness, spike-wave stupour, gastrointestinal disturbances with nausea and vomiting, prior to or during surgery or certain diagnostic procedures, and because of drug refusal in patients with mental retardation or psychiatric problems. Although rectal administration of sodium valproate (NaVPA) has been shown to be a possible alternative route, little is known about the bioavailability and local effects during repeated administration of NaVPA suppositories. These aspects were investigated in 13 epileptic children and adolescents on chronic NaVPA therapy. Eight patients were treated with the oral solution (Group A, mean age 10.6 years) and five patients with enteric coated tablets (Group B, mean age 16.4 years). In every patient five serum levels of VPA over a 24 h period were measured under steady-state conditions. Thereafter, suppositories were administered for 2–7 days and serum levels were again determined (identical dosing and sampling times). Bioavailability of NaVPA was calculated on the basis of the area under the concentration vs. time curve over 24 h. The average bioavailability for suppositories compared with the oral form was 112.4% in Group A and 99.5% in Group B. Fluctuations of serum VPA levels were very similar with suppositories and oral solution, and more pronounced than with the enteric coated tablets. Stool frequency was not increased by repeated administration of suppositories, except for a three-fold increase in one patient. There was no objective or subjective evidence of local irritation from the suppositories. In conclusion, NaVPA suppositories have the same bioavailability under steady-state conditions as oral preparations and they are well tolerated. NaVPA suppositories thus represent a useful alternative when oral administration is temporarily impossible, and no adjustment in dose is necessary.