Case Report of Novel Genetic Variant in KCNT1 Channel and Pharmacological Treatment With Quinidine. Precision Medicine in Refractory Epilepsy.

Case introduction: In this work we present a female infant patient with epilepsy of infancy with migrating focal seizures (EIMFS). Although many pharmacological schemes were attempted, she developed an encephalopathy with poor response to antiepileptic drugs and progressive cerebral dysfunction. Aim: To present the pharmacological response and therapeutic drug monitoring of a paediatric patient with a severe encephalopathy carrying a genetic variant in KCNT1 gene, whose identification led to include quinidine (QND) in the treatment regimen as an antiepileptic drug. Case report: Patient showed slow rhythmic activity (theta range) over left occipital areas with temporal propagation and oculo-clonic focal seizures and without tonic spasms three months after birth. At the age of 18 months showed severe impairments of motor and intellectual function with poor eye contact. When the patient was 4 years old, a genetic variant in the exon 24 of the KCNT1 gene was found. This led to the diagnosis of EIMFS. Due to antiepileptic treatment failed to control seizures, QND a KCNT1 blocker, was introduced as a therapeutic alternative besides topiramate (200 mg/day) and nitrazepam (2 mg/day). Therapeutic drug monitoring (TDM) of QND plasma levels needed to be implemented to establish individual therapeutic range and avoid toxicity. TDM for dose adjustment was performed to establish the individual therapeutic range of the patient. Seizures were under control with QND levels above 1.5 mcg/ml (65-70 mg/kg q. i.d). In addition, QND levels higher than 4.0 mcg/ml, were related to higher risk of suffering arrhythmia due to prolongation of QT segment. Despite initial intention to withdrawal topiramate completely, QND was no longer effective by itself and failed to maintain seizures control. Due to this necessary interaction between quinidine and topiramate, topiramate was stablished in a maintenance dose of 40 mg/day. Conclusion: The implementation of Precision Medicine by using tools such as Next Generation Sequencing and TDM led to diagnose and select a targeted therapy for the treatment of a KCNT1-related epilepsy in a patient presented with EIMFS in early infancy and poor response to antiepileptic drugs. QND an old antiarrhythmic drug, due to its activity as KCNT1 channel blocker, associated to topiramate resulted in seizures control. Due to high variability observed in QND levels, TDM and pharmacokinetic characterization allowed to optimize drug regimen to maintain QND concentration between the individual therapeutic range and diminish toxicity.

[Pharmacokinetic variability of oxcarbazepine in epileptic patients]. / Variabilidad farmacocinética de oxcarbazepina en pacientes epilépticos.

The aim of this study was to analyze the population pharmacokinetics of oxcarbazepine (OCBZ) measuring the serum level of its active metabolite, monohydroxylated oxcarbazepine (MHD). We studied a group of patients with symptomatic and cryptogenic epilepsy treated with OCBZ monotherapy orally, at least for 3 weeks. The mean doses, age and weight of the patients were 17.9 +/- 7.8 mg/kg/day, 35.6 +/- 16.4 years and 70.3 +/- 19.2 kg, respectively. Blood samples were taken before the first morning dose of OCBZ and MHD levels were determined by HPLC. A linear relationship was found between OCBZ dose and MHD serum level (r = 0.844, p < 0.001). The MHD serum concentration (mg/l) can be predicted as 0.85 x OCBZ dose (mg/kg). There was a significant correlation between observed and predicted MHD concentrations for each patient. The mean MHD clearance (Cl/F) calculated was 4.05 +/- 1.69 l/h, with a coefficient variation of 41%. It was independent of dose, age and weight and followed a non normal distribution. The half-life of MHD was 10.50 +/- 3.17 hours. The influence of other antiepileptic drugs on MHD pharmacokinetics was analyzed by comparing the Cl/F medians from groups of patients receiving concomitant drugs with OCBZ monotherapy group where no significant differences were found. The results can be used to estimate a priori OCBZ doses, in order to individualize the treatment.

Variabilidad farmacocinética de oxcarbazepina en pacientes epilépticos. / [Pharmacokinetic variability of oxcarbazepine in epileptic patients]

The aim of this study was to analyze the population pharmacokinetics of oxcarbazepine (OCBZ) measuring the serum level of its active metabolite, monohydroxylated oxcarbazepine (MHD). We studied a group of patients with symptomatic and cryptogenic epilepsy treated with OCBZ monotherapy orally, at least for 3 weeks. The mean doses, age and weight of the patients were 17.9 +/- 7.8 mg/kg/day, 35.6 +/- 16.4 years and 70.3 +/- 19.2 kg, respectively. Blood samples were taken before the first morning dose of OCBZ and MHD levels were determined by HPLC. A linear relationship was found between OCBZ dose and MHD serum level (r = 0.844, p < 0.001). The MHD serum concentration (mg/l) can be predicted as 0.85 x OCBZ dose (mg/kg). There was a significant correlation between observed and predicted MHD concentrations for each patient. The mean MHD clearance (Cl/F) calculated was 4.05 +/- 1.69 l/h, with a coefficient variation of 41

. It was independent of dose, age and weight and followed a non normal distribution. The half-life of MHD was 10.50 +/- 3.17 hours. The influence of other antiepileptic drugs on MHD pharmacokinetics was analyzed by comparing the Cl/F medians from groups of patients receiving concomitant drugs with OCBZ monotherapy group where no significant differences were found. The results can be used to estimate a priori OCBZ doses, in order to individualize the treatment.

Desipramine modulates 3H-ouabain binding in rat hypothalamus.

We have previously shown that Na+, K(+)-ATPase activity in hypothalamus is increased after administration of an acute dose of desipramine, a noradrenaline uptake inhibitor (Viola et al., Cell Molec Neurobiol 9:263-271, 1989). In this report the same treatment (10 mg per kg) was applied to evaluate 3H-ouabain binding in rat brain sections by quantitative autoradiography. Results disclosed an increase in the number of ouabain binding sites in hypothalamus but not in cerebral cortex. Concomitantly, such acute DMI treatment enhanced K(+)-stimulated-p-nitrophenylphosphatase activity in hypothalamus membranes whereas it failed to modify cerebral cortex membranes. A direct interaction of DMI with the enzyme was ruled out since in vitro DMI is known to inhibit the enzyme. It may be speculated that DMI indirectly stimulates Na+, K(+)-ATPase through the increase in noradrenaline which acts in turn on the external phosphorylated site of the enzyme.

Na+,K(+)-ATPase activity in CNS and noradrenergic neurotransmission: time course of differential desipramine (DMI) effects.

ATPase activities in CNS membranes were studied after administration of desipramine (DMI), a noradrenaline (NA) uptake inhibitor. In a previous paper we reported that Na+,K(+)-ATPase activity significantly increased 3 h after DMI administration (10 mg/kg) in hypothalamus and mesencephalus but not in cerebral cortex and pons-medulla oblongata membranes (Viola et al., Cell. molec. Neurobiol. 1989, 9, 263-271). Here it was observed that Na+,K(+)-ATPase increase induced by acute DMI disappeared at 24 h in hypothalamus but remained during 21 days in mesencephalus. Na+,K(+)-ATPase increase by acute DMI was inhibited when endogenous NA was depleted by the noradrenergic neurotoxin DSP-4 or the NA synthesis inhibitor alpha-methyl-p-tyrosine. On the whole, Mg(2+)-ATPase activity was not modified by treatment. 5'-nucleotidase, another membrane-bound enzyme, was unchanged by acute DMI. The addition of DMI in vitro (50 ng/mg tissue) during Na+,K(+)-ATPase assay failed to affect ATPase activities. Acute DMI effects on Na+,K(+)-ATPase are thus attributable to noradrenergic neurotransmission rather than to non-specific drug-CNS membrane interaction. Furthermore, DMI produces differential effects on membrane Na+,K(+)-ATPase, depending on treatment conditions and CNS area studied.

Stimulation of Na+,K+-ATPase activity in certain membranes of the rat central nervous system (CNS) by acute administration of desipramine (DMI).

1. The activities of ATPase in rat CNS were studied 3 hr after administration of the noradrenaline uptake inhibitor, desipramine (DMI: 10 mg.kg-1, i.p.). Na+K+-ATPase activity significantly increased after DMI in the whole particulate from hypothalamus and mesencephalus but no changes in frontal cortex or in pons-medulla oblongata areas were found. This increase was prevented when the animals were pretreated with the noradrenergic neurotoxic N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4). 2. Purified membrane fractions from hypothalamus were obtained by differential and sucrose gradient centrifugation (0.8-1.2 M sucrose). It was observed that after DMI, Na+,K+-ATPase activity increased only in the membranous fraction lying at 0.9 M sucrose. 3. Mg2+- or Ca2+-ATPase activities were not modified by DMI treatment. 4. Citalopram, a specific serotonergic uptake inhibitor, did not affect ATPase activities. 5. The results obtained could indicate that DMI acute administration selectively stimulates Na+,K+-ATPase activity of certain membranes of the CNS after an increase in the concentration of the noradrenergic neurotransmitter in the synaptic gap.

Increase of alpha 2-presynaptic adrenoceptor response after neuronal uptake inhibition in vivo.

alpha 2-adrenoceptor antagonists, yohimbine or idazoxan (1 mg kg-1 i.p.), administered alone, did not change noradrenaline content in the central and peripheral tissues of the rat (hypothalamus, brain stem, frontal cortex and heart). The inhibition of neuronal uptake by desipramine (DMI) administered alone or prior to alpha 2-adrenoceptor antagonists did not affect the neurotransmitter content either. alpha-methyl-p-tyrosine (alpha-MT) 6 hr before sacrifice, induced a marked disappearance of the noradrenaline content, greater in central nervous tissues than in heart. When the catecholamine synthesis was inhibited by alpha-MT, neither alpha 2-adrenoceptor antagonists nor DMI at the dose used, significantly changed the disappearance rate of noradrenaline in any of the tissues studied. Under these experimental conditions, however, the combination of DMI plus alpha 2-adrenoceptor antagonists significantly decreased the neurotransmitter content in all tissues when the values were compared with the control or DMI-treated groups. The present results might suggest evidence in favour of a functional coupling between presynaptic alpha 2-autoreceptors and noradrenaline uptake mechanism.