Plasma gabapentin concentrations in children with epilepsy: influence of age,relationship with dosage,and preliminary observations on correlation with clinical response

The influence of age and administered daily dosage on the plasma concentrations of gabapentin (GBP) at steady state was evaluated in a group of 41 children and young adults (aged 3-30 years) receiving long-term adjunctive treatment with GBP for the management of refractory partial-onset seizures. For each patient, peak and trough concentrations were determined by a specific high-performance liquid chromatography (HPLC) method in samples obtained before the morning dose and 2.5 hours later, respectively. To assess within-subject relationship between plasma concentration and dosage, 30 patients were evaluated at more than one dosage level. Within the assessed dose range, plasma GBP concentrations were linearly related to dose. Apparent oral clearance values (mean +/- SD) in children aged 6 years or less (4.8 +/- 0.9 mL/kg/min) were comparable with those observed in children aged 7 to 15 years (4.6 + 1.5 mL/kg/min) and moderately higher than those found in young adults (3.9 + 0.9 mL/kg/min), even though differences among groups failed to reach statistical significance. There was, however, a significant difference in CL/F between children aged 10 years or less and older children (5.1 +/- 1.1 vs. 3.8 +/- 1.2 mL/kg/min, P < 0.005). Of the 41 patients who entered the study, 22 discontinued treatment, mostly due to insufficient efficacy. No significant difference in plasma GBP concentration was detected between patients showing a greater than 50% reduction in seizure frequency (4.1 +/- 1.9 microg/mL, n = 11, mean +/- SD) and those having no significant clinical improvement (4.4 +/- 1.7 microg/mL, n = 30). These results indicate that in children given dosages up to 50 mg/kg/d (mean, 25 mg/kg/d), GBP pharmacokinetic analyses show no important deviation from linearity. The data also suggest that, on average, children may need moderately higher dosages to reach plasma GBP concentrations comparable with those found in adults. There seems to be a large variation in the plasma concentrations of the drug associated with a favorable therapeutic response.     

Serum concentrations of topiramate in patients with epilepsy: influence of dose,age, and comedication

Topiramate is a new antiepileptic drug (AED) approved as add-on therapy. Previous studies have shown that topiramate has only a limited effect on other AEDs, but its own metabolism can be induced by enzyme-inducing drugs. The aim of this study was to investigate the influence of topiramate dose, age, and comedication, especially of carbamazepine, phenytoin, phenobarbital, oxcarbazepine, lamotrigine, and valproic acid (VPA) on topiramate serum concentrations in patients with epilepsy. In total, 480 samples of 344 inpatients who fulfilled the inclusion criteria (e.g., trough concentration, body weight available) were investigated. The topiramate serum concentration in relation to topiramate dose per body weight (level-to-dose ratio) was calculated and compared for patients receiving topiramate monotherapy and for patients receiving topiramate plus one other AED. Analysis of covariance (using age as covariate) showed that comedication had a highly significant influence on the topiramate serum concentrations. Regression analysis including all 480 samples confirmed that in combinations with phenytoin, carbamazepine, phenobarbital, and oxcarbazepine, the topiramate concentrations were significantly lower compared with topiramate monotherapy, whereas VPA and lamotrigine had no significant influence. Moreover, regression analysis indicated that primidone and methsuximide lowered topiramate concentrations, whereas gabapentin, bromide, and sulthiame did not. In addition to comedication, the patient's age was significantly correlated with topiramate clearance. In accordance with the results of previous studies, these results indicated that infants and children had lower topiramate concentrations than adults receiving the same topiramate dose per body weight. Comedication and age should be considered in adjusting topiramate dosage. Determination of topiramate serum concentrations may be useful, especially when enzyme-inducing drugs are withdrawn or added.     

Serum concentrations of rufinamide in children and adults with epilepsy: the influence of dose, age, and comedication

Rufinamide (RUF) is an orphan drug for adjunctive treatment of seizures associated with Lennox-Gastaut syndrome in persons aged 4 years and older. Several studies have investigated the pharmaconkinetics of RUF, but information about interactions is still limited and the results are in part inconsistent. The aim of our study was to analyze the effect of age, gender, daily RUF dose per body weight (mg/kg), valproic acid (VPA), and enzyme-inducing antiepileptic drugs (EIAEDs) on RUF concentration-to-dose ratio (RUF serum concentration/RUF dose per body weight), RUF clearance (RUF dose/RUF serum concentration), and RUF trough concentrations. Different statistical methods were used to evaluate 292 blood samples from 119 patients who fulfilled the inclusion criteria. In summary, the results using generalized estimating equation regression models confirm a moderate but statistically significant nonlinear RUF concentration-dose relationship. At steady state, the trough concentrations of RUF increase in a less than dose proportional manner. Children (younger than 12 years) had significantly lower RUF concentrations (19.0%, P < 0.001) than adults (18 years or older) on comparable RUF doses per body weight. VPA was the most frequent comedication (51%) in our patient group. Mean RUF concentrations were 86.6% higher when VPA concentrations were greater than 90 μg/mL (P < 0.001) and 45.4% higher when VPA concentrations were between 50 and 90 μg/mL (P < 0.001) but not significantly different at VPA concentrations less than 50 μg/mL (4.4%, P > 0.1) compared with combinations without VPA. In combination with EIAEDs, mean RUF concentrations were 21.8% lower (P = 0.002) compared with combinations without EIAEDs. However, the group of AEDs classified as EIAEDs was heterogeneous and the number of patients, especially of children with EIAEDs, was relatively small. Our data indicate that oxcarbazepine and, especially, methsuximide decrease RUF concentrations as well. Therapeutic drug monitoring might be helpful because RUF concentrations differ markedly in patients on comparable RUF doses.     

Influence of age and gender on risperidone plasma concentrations

There is limited information on gender- and age-specific effects on plasma concentrations of risperidone and its active metabolite, 9-hydroxyrisperidone. The present study investigated dose- and weight-adjusted plasma concentrations of risperidone and its metabolite in three age groups (45 years, 45-60 years, over 60 years). Gender-specific differences were examined in the whole sample and for the premenopausal subgroup. One hundred and twenty-nine patients (18-93 years) were included in the study, 52 (40%) male and 77 (60%) female. Concentrations of risperidone and 9-hydroxyrisperidone were measured at steady-state by high-performance liquid chromatography with electrochemical detection (HPLC-ED). When total plasma concentrations (risperidone plus 9-hydroxyrisperidone) were adjusted for daily maintenance dose (ng/mL/mg C/D ratio), significant differences between all age groups were found. We found a mean increase of the C/D ratio by 34.8% per decade in patients older than 42 years. No significant sex-related differences in the average plasma concentrations were observed for the whole sample and for the premenopausal subgroup. This study shows clear evidence of higher risperidone total plasma concentrations for patients over 40 years of age. This linear increase (over 30% per decade) may then lead to an increased incidence of adverse effects in elderly patients.     

Plasma concentrations of the enantiomers of fluoxetine and norfluoxetine: sources of variability and preliminary observations on relations with clinical response

Factors affecting the plasma concentrations of the R- and S-enantiomers of fluoxetine and norfluoxetine were investigated in 131 adult patients receiving long-term fluoxetine, of 10 to 60 mg/d (mean, 24 +/- 10 mg/d). Plasma concentration values (geometric means, CI 95%) in these patients were 186 (156, 223) nmol/L for S-fluoxetine, 67 (58, 77) nmol/L for R-fluoxetine, 247 (212, 287) nmol/L for S-norfluoxetine, and 118 (102, 137) nmol/L for R-norfluoxetine. The difference between the concentrations of the respective R- and S-enantiomers was statistically significant ( P< 0.0001) for both the parent drug and the demethylated metabolite. A significant correlation was found between the concentrations of each enantiomer and the prescribed daily dosage (r = 0.44, P< 0.0001 for S-fluoxetine; r = 0.48, P < 0.0001 for R-fluoxetine; r = 0.36, < 0.0001 for S-norfluoxetine; r = 0.32, P = 0.0003 for R-norfluoxetine), but the variability in concentration at any given dosage was considerable. When an iterative model based on multiple polynomial regressions was applied to determine the potential contributions of dosage, age, gender, body weight, and concomitant medication to the variability in the plasma concentration of the enantiomers, dosage was consistently found to provide the greatest predictive value. The predictive value of the model could be consistently improved when concentrations of other enantiomers were included as covariates. Of 58 patients with depressive symptoms for whom evaluation of clinical response (CGI scale) was available, 33 (57%) responded favorably to treatment. The plasma levels of individual enantiomers and of the active moiety (ActM, sum of the concentrations of R-fluoxetine, S-fluoxetine, and S-norfluoxetine) in these patients did not differ significantly from those found in patients with unsatisfactory therapeutic response. Likewise, the concentrations of individual enantiomers and of the ActM were similar in patients with or without adverse effects. Overall, these results demonstrate that the pharmacokinetics of fluoxetine and norfluoxetine exhibit marked stereoselectivity and considerable interpatient variability, which could not be explained by differences in gender, age, or comedication. In addition, a considerable variability was found in the enantiomers' concentrations associated with a favorable therapeutic response.     

妥泰治疗小儿癫痫时体重变化的临床观察

目的：观察妥泰治疗小儿癫痫时体重的变化情况。方法：将94例患儿随机分为3组，分别用妥泰、丙戊酸钠和卡马西平，比较观察前后每组体重的变化。结果：A组51例中体重下降10例，体重无变化12例，体重增加29例；B组和C组患儿体重均较观察前增加。结论：使用妥泰治疗小儿癫痫时有体重下降的现象，较胖的患儿更明显。     

Therapeutic drug monitoring of levetiracetam by high-performance liquid chromatography with photodiode array ultraviolet detection: preliminary observations on correlation between plasma concentration and clinical response in patients with refractory epilepsy

Levetiracetam is a new antiepileptic drug prescribed for the treatment of patients with refractory partial seizures with or without secondary generalization as well as for the treatment of juvenile myoclonic epilepsy. A rapid and specific method by high-performance liquid chromatography diode array detection was developed to measure the concentration of levetiracetam in human plasma. The trough plasma concentrations measured in 69 epileptic patients treated with 500 to 3000 mg/d of levetiracetam ranged from 1.1 to 33.5 microg/mL. The mean (range) levetiracetam plasma concentrations in responders and nonresponders were 12.9 microg/mL (4.6-21 microg/mL) and 9.5 microg/mL (1.1-20.9 microg/mL), respectively. A wide variability in concentration-response relationships was observed in patients. Using a receiver operating characteristic curve, the threshold levetiracetam concentration for a therapeutic response was 11 microg/mL. The sensitivity and specificity for this threshold levetiracetam concentration were 73% and 71%, respectively. According to chi analysis, this finding was not significant probably because of the small number of patients and because of their refractory seizure type. Nevertheless, the levetiracetam plasma concentration could be used to help clinicians detect severe intoxication or to verify compliance by repeating the measurement in patients.     

探讨丙戊酸钠联合托吡酯在小儿癫痫治疗中的疗效分析

目的 探讨应用丙戊酸钠联合托吡酯治疗小儿癫痫的临床疗效,进一步为临床治疗提供参考依据.方法 选取2012年2月至2014年2月我院收治的小儿癫痫患者70例,随机分为A、B、C三组,A组患儿应用托吡酯进行治疗,B组患儿应用丙戊酸钠,C组患儿应用丙戊酸钠联合托吡酯联合治疗,比较三组患儿临床总有效率.结果 经过治疗,A组托吡酯总有效率为83.3％,B组丙戊酸钠总有效率为79.2％,C组联合治疗总有效率为91.3％,C组与A、B组比较,P＜0.05,差异有统计学意义,A组与B组间比较差异无统计学意义.三组患儿均存在一定程度的不良反应,包括恶心、感觉异常、嗜睡以及体制变化等,但组间差异小(P＞ 0.05).结论 应用丙戊酸钠联合托吡酯治疗小儿癫痫临床疗效突出,明显优于两者单独应用,且不良反应无增加,患儿耐受良好,值得临床进一步推广和应用.     

Influence of age, gender, body weight and valproate comedication on quetiapine plasma concentrations

Quetiapine is a second-generation antipsychotic with a favourable risk/benefit profile that is increasingly used in psychiatric patients. Similar to other antipsychotics, the efficacy and adverse effects of quetiapine depend much more on the actual plasma concentration of the active drug than on the prescribed dose. The present study investigated whether age, gender, body weight or certain comedications influence quetiapine plasma concentration by determining quetiapine plasma levels by tandem mass spectrometry in 94 (36 male and 58 female) patients aged 42.2 +/- 20.0 years. Older age was a significant predictor of a higher quetiapine plasma concentration, with a mean increase of weight-corrected concentration/dose ratio of 11% per 10 years of age (P = 0.003). In females, the concentration/dose (C/D) ratio was 35.4% higher than in males (adjusted mean 0.144 ng/ml/mg for males versus 0.195 ng/ml/mg for females, respectively; P = 0.035). However, after correction for weight, the gender difference in C/D ratio dropped to 22% and significance was lost (P = 0.133). Valproate comedication was associated with a 77% increase in quetiapine plasma levels (P = 0.016). In conclusion, older age, body weight and comedication with valproate have to be considered when prescribing quetiapine. Higher plasma levels in female patients need to be replicated in larger samples.     

Carbamazepine clearance in paediatric epilepsy patients. Influence of body mass, dose, sex and co-medication

Carbamazepine clearance was studied in Black paediatric epilepsy patients, 90 receiving monotherapy and 17 on combination therapy. For patients on monotherapy the following relationship are shown: clearance decreases with increasing body mass (r= 0.87); clearance increases with increasing dose (r = 0.70); and mean clearance for male are higher than those for females throughout the mass ranges, though the difference is not statistically significant. In the case of patients on carbamazepine plus another anticonvulsant, clearance also decreases with increasing body mass, and increases with increasing dose. Furthermore, in the mass groups which corresponded with those on monotherapy, mean carbamazepine clearance higher by a factor varying from 1.3 to 1.7; in the corresponding dosage groups, it is higher by a factor of between 1.4 and 1.7.     

托吡酯与卡马西平对照治疗成人癫痫133例

目的:比较托吡酯(TPM)及卡马西平(CBZ)单药治疗新诊断的部分性发作成人癫痫患者的疗效及耐受性.方法:133例患者入组,自愿选择进入TPM组58例和CBZ组75例.起始剂量TPM 25mg·d-1,nd,CBZ100mg·d-1,bid.根据患者的发作情况及是否发生不良反应调整剂量,并充分观察该剂量下的疗效及耐受性,以达最佳或最终剂量.通过比较两组患者治疗前后的月平均发作次数变化和因不良反应退出试验的病例比例评价药物的总体疗效.结果:观察时间TPM组(8.10±6.35)个月,CBZ组(15.69±10.23)个月.最佳或最终剂量范围TPM组50～300mg·d-1,CBZ组100～600mg·d.按照发作频率减少≥50%、无效或发作增加、因不良反应退出试验分级,两组比较差异有显著性,两组总有效率分别为75.9%及68.0%(P=0.033 6),因不良反应退出比例TPM组明显低于CBZ组(1.7%vs 14.7%).结论:TPM单药治疗成年新诊断部分性发作癫痫患者的疗效与CBZ相当,安全性和耐受性明显优于CBZ.     

An inter-ethnic comparison study of clozapine dosage, clinical response and plasma levels

The present study investigated clozapine dosage, plasma clozapine and metabolite levels, clinical and side-effect profiles in Asian versus Caucasian patients with chronic schizophrenia who were on stable maintenance treatment. Twenty Asian patients from Singapore and 20 Caucasian patients from Australia were systematically evaluated with the following rating scales: Positive and Negative Syndrome Scale for Schizophrenia, drug attitude scale (DAI-10), drug adverse reaction profile (Liverpool University Neuroleptic Side-effect Rating Scale), extrapyramidal side-effects scales (Abnormal Involuntary Movement Scale, Simpson and Angus Scale). Cigarette and caffeine consumption were recorded and steady-state plasma clozapine and metabolites levels were measured. Although Asian patients received a significantly lower mean clozapine dose (176 mg/day) than the Caucasian group (433 mg/day, P<0.001), plasma clozapine levels were similar between the groups. As a result, Asian patients had more than twice the effective clozapine concentration to dose ratio (P<0.001). The findings remained significant even after controlling for gender, body mass index, cigarette, alcohol and caffeine use. Conversely, the plasma metabolites (desmethylclozapine and clozapine N-oxide) to clozapine ratios were higher in the Caucasian patients (P<0.01). Compared to Caucasian patients, Asian patients appeared to have a lower dosage requirement for clinical efficacy. Hence, appropriate dose adjustment should be considered in Asian patients receiving maintenance clozapine therapy in clinical practice.     

托吡酯与丙戊酸钠对照治疗成人癫痫124例

目的:观察托吡酯及丙戊酸钠单药对照治疗新诊断的成人癫痫患者的疗效及耐受性。方法:入组患者124例,其中试验组60例,起始剂量25 mg·d-1,qd,对照组64例,起始剂量丙戊酸钠200 mg·d-1,bid。根据患者发作情况及药物不良反应调整剂量,观察药物的疗效及耐受性,以达最佳或最终剂量。通过比较2组患者治疗前后的月平均发作次数和退出试验的病例比例评价药物的总体疗效。结果:观察时间试验组(8．10±6．44)个月,对照组(14．16±11．75)个月。最佳或最终剂量范围试验组50～300 mg·d-1。对照组200～1500 mg·d-1。两组总有效率分别为78．33％及59．38％,两组比较差异有显著性(P=0．0383)。试验组和对照组分别有2例和1例因不良反应退出或换药。结论:托吡酯单药治疗成年新诊断癫痫患者的疗效好于丙戊酸钠,具有较好的安全性和耐受性。     

丙戊酸托吡酯治疗儿童特发性全身性癫痫疗效比较研究

目的：评价丙戊酸和托吡酯治疗儿童特发性全身性癫痫的疗效及耐受性。方法：对1999年10月至2003年4月来我院的152例首诊特发性全身性癫痫并接受丙戊酸或/和托吡酯治疗的病人进行随访。并对结果进行分析。结果：丙戊酸单药治疗完全控制率为63．41％。托吡酯单药治疗完全控制率40．00％,二者有显著差异;丙戊酸部分控制者添加托吡酯治疗31．25％完全控制,托吡酯治疗部分控制者添加丙戊酸后36．84％发作停止。无显著差异。两种药物的不良反应均较轻且耐受性较好。结论：丙戊酸是治疗儿童特发性全身性癫痫的最有效药物之一。如丙戊酸未能完全控制发作。添加托吡酯治疗疗效好。     

托吡酯对0～8岁癫痫病儿血清瘦素水平及体重指数的影响

目的:探讨托吡酯对0～8a癫痫病儿血清瘦素水平及体重指数(BMI)的影响。方法:对43例服用托吡酯单药治疗的0～8a癫痫病儿随访6mo,采用放射免疫法分别对其用药前及用药后1,3,6mo的血清瘦素水平的进行测定,同时测量身高与体重,以BMI评定体脂情况。结果:托吡酯治疗前病儿血清瘦素水平为(6.5±s2.5)μg·L-1,服用托吡酯1mo后为(7.1±2.6)μg·L-1,3mo后为(9±3)μg·L-1,6mo后为(11±3)μg·L-1。治疗后3mo血清瘦素的水平变化有非常显著差异(P<0.01);BMI的下降在用药后6mo明显降低(P<0.01)。结论:托吡酯能提高癫痫病儿血清瘦素水平,降低BMI。     

Methylphenidate oral dose plasma concentrations and behavioral response in children

The relationship between methylphenidate (MP) oral dose and plasma concentration to social and cognitive behaviors was studied in 25 boys diagnosed as having attention deficit disorder with hyperactivity. Children were administered successive 1-week treatment conditions under the following schedule of fixed oral doses given twice daily: placebo; 0.25 mg/kg; 0.50 mg/kg; 1.0 mg/kg; placebo. Teacher and parent ratings showed increased improvement in social behavior as a function of MP dose. No drug effects were obtained on cognitive performance. MP plasma concentrations were significantly associated with oral dose and with measures of social behavior. No relationship was found with cognitive behavior. Side effects at the largest dose were severe enough to require discontinuation of treatment for five children, but were relatively mild for the remaining children.     

基于群体药动学的奥卡西平儿童个体化给药模式的建立

目的基于群体药动学(PPK)和贝叶斯原理,建立奥卡西平的癫痫患儿个体化给药工作模式,促进临床合理用药。方法利用已发表的中国癫痫患儿口服奥卡西平后的PPK模型和JPKD-Bayesian软件建立奥卡西平个体化给药的预测模型。运用该模型对100例癫痫患儿进行个体化给药方案设计。患儿按设计方案规律服药2~4周后测定10-羟基卡马西平的稳态血清谷浓度并与模型预测值相比较,计算平均预测误差、平均绝对预测误差、平均相对预测误差、相对预测误差在±20%和±30%内的比例来验证模型的预测性能。结果个体化给药预测模型的平均预测误差为(0.54±2.00)mg·L~(-1),平均绝对预测误差为(1.75±1.09)mg·L~(-1),平均相对预测误差为(3.86±14.56)%,其中分别有78%和96%的血药浓度数据相对预测误差在±20%和±30%以内。血药浓度预测值对实测值的决定系数R2=87.8%。上述验证结果说明模型的预测准确度和精密度均较高。结论本研究成功建立了可用于儿科患者实施奥卡西平个体化给药的预测模型和完整的工作模式,有助于临床合理用药。     

Comparison of topiramate concentrations in plasma and serum by fluorescence polarization immunoassay

Topiramate has been recently licensed as an antiepileptic drug. A fluorescence polarization immunoassay (FPIA), the Innofluor, has been developed to determine topiramate in heparinized plasma. Since therapeutic drug monitoring laboratories may not have control over collection of the samples submitted to them, it is important for analytical methods to be robust and able to cope with any specimen. The effect of different anticoagulants on the topiramate FPIA assay was investigated by collecting blood from 50 patients with epilepsy being maintained on a range of topiramate doses as part of their therapy. After venesection the blood was divided among four tubes: plain, heparinized, EDTA, and fluoride/oxalate. Erythrocytes were separated by centrifugation and supernatant fluid frozen to await duplicate assay by FPIA. Results were compared by means of Altman and Bland difference plots which indicated that there was no significant difference between values obtained with heparinized plasma and the other fluids. It was concluded that the Innofluor assay is robust and gives similar results when blood samples are collected into any of the specified anticoagulants.     

High plasma concentrations of paroxetine impede clinical response in patients with panic disorder

Selective serotonin reuptake inhibitors are thought to interact with serotonergic neurons and be effective for treatment of panic disorder. In the present study, the authors investigated an association between plasma concentrations of paroxetine in patients with panic disorder and clinical response to initial treatment with paroxetine. Subjects were 21 unrelated Japanese patients who fulfilled DSM-IV-TR criteria for a diagnosis of panic disorder (6 males, 15 females, mean age 35.9 +/- 11.3 years). Subjects were administered 10 mg/day of paroxetine for 2 weeks as initial treatment. Improvement of the symptoms of the disorder was assessed with the Panic and Agoraphobia Scale (PAS). In the range of plasma levels >20 ng/mL, none of the subjects showed the reduction ratio in PAS score >0.2. The subjects whose plasma concentrations of paroxetine were less than 20 ng/mL had a significantly higher mean reduction ratio in PAS score than the subjects whose plasma concentrations of paroxetine were >20 ng/mL. Multiple regression analysis showed that the plasma concentration of paroxetine was the only significant factor and accounted for 28.0% of the variability in the reduction ratio of PAS score of the subjects. The final model of correlation was: reduction ratio in PAS score = 0.423 - 0.009 x (plasma concentrations of paroxetine) (R = 0.529, P = 0.014, coefficient of determination (R2) = 0.280). Assuming that the reduction ratio in PAS score was 0.2 in the equation above, plasma concentration of paroxetine is calculated to be about 25 ng/mL, which is suggested to be the upper end of the therapeutic window for the initial phase of the treatment with paroxetine for panic disorder.