Sixty years ago Geyelin found that many patients with epilepsy remained free of seizures while fasting and for several months after return to a normal diet.' Wilder in the same year suggested that the ketonaemia induced by fasting was responsible for this effect and proposed that a 'ketogenic diet', high in fat and low in carbohydrate, should be used in the treatment of epilepsy.2 This was undertaken in children by Peterman3 and Helmholtz,4 and the best results seemed to occur in the younger age groups. Livingston reported over a period of 41 years that he had controlled myoclonic epilepsy in 54% of 975 cases using the ketogenic diet.5 In spite of these good results, however, the traditional ketogenic diet (87% of dietary energy being provided by fat) has been limited by its unpalatability and nutritional inadequacy in young children. It is also difficult to prepare and has not gained wide acceptance.Recently, there has been a resurgence of interest in ketogenic diets as many children with seizuresfor example, tonic-clonic and astatic myoclonic-are not controlled by anticonvulsants used singly or in combination.6 After reports that medium chain triglyceride (MCT) was more ketogenic than fat Huttenlocher et al introduced MCT as an alternative to fat in their ketogenic diet.7 They showed that a ketogenic diet using MCT to provide 60% of dietary energy was at least as effective as a 3:1 ketogenic diet (75% of energy provided by fat) in producing ketosis and controlling seizures. As less carbohydrate restriction was involved such a diet became easier to prepare, was more palatable, and was less

SUMMARY Octanoic and decanoic acid, the major constituents of the Medium Chain Triglyceride (MCT) Emulsion diet, have been detected in appreciable quantities in the peripheral blood of children with intractable seizures treated with the MCT diet. Serum concentrations of these acids as well as ,1 hydroxybutyrate and acetoacetate rose as the diet was introduced and on full diet showed pronounced diurnal variation and low concentrations in the morning. No correlation between octanoic and decanoic acid concentrations and control of seizures was established, but further studies with octanoic and decanoic acid using animal models are necessary to assess the role of these acids and of control of seizures.

We describe a procedure for gas-chromatographic determination of n-octanoic and n-decanoic acids in 100 microL of plasma from children with intractable epilepsy treated with medium-chain triglyceride (MCT) diet. With n-nonanoic acid as the internal standard, the extraction efficiencies for octanoic and decanoic acids were 98 and 105%, respectively. Within-run CVs for octanoic acid at 0.5, 1.0, 2.5, 5.0, 7.5, and 10.0 micrograms/0.1 mL were 8.8, 7.9, 8.5, 6.5, 4.3, and 5.7%, respectively. For decanoic acid at identical concentrations, the CVs were 10.0, 7.4, 4.9, 4.0, 2.6, and 3.5%, respectively. For 10 children on MCT diet (45.9% of calories supplied as MCT) the mean concentrations of octanoic and decanoic acids were 44.2 and 27.0 mg/L, respectively. Presence of relatively "high" quantities of these acids in plasma may contribute to seizure control when MCT diet is prescribed for intractable childhood epilepsy.

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