Total Carbamazepine Concentrations Research Articles

Anticonvulsant Effectiveness and Neurotoxicity Profile of 4-butyl-5-[(4-chloro-2-methylphenoxy)methyl]-2,4-dihydro-3H-1,2,4-triazole-3-thione (TPL-16) in Mice

Protective (antiseizure) effects of 4-butyl-5-[(4-chloro-2-methylphenoxy)-methyl]-2,4-dihydro-3H-1,2,4-triazole-3-thione (TPL-16) and acute neurotoxic effects were determined in the tonic-clonic seizure model and rotarod test in mice. The interaction profile of four classic antiepileptic drugs (carbamazepine, phenobarbital, phenytoin and valproate) with TPL-16 was also determined in the tonic-clonic seizure model in mice. The protective effects of TPL-16 from tonic-clonic seizures (as ED50 values) and acute neurotoxic effects of TPL-16 (as TD50 values) were determined in 4 pretreatment times (15, 30, 60 and 120 min after its i.p. administration), in adult male albino Swiss mice. The interaction profile of TPL-16 with carbamazepine, phenobarbital, phenytoin and valproate in the tonic-clonic seizure model was determined with isobolographic analysis. Total concentrations of carbamazepine, phenobarbital, phenytoin and valproate were measured in the mouse brain homogenates. The candidate for novel antiepileptic drug (TPL-16) administered separately 15 min before experiments, has a beneficial profile with protective index (as ratio of TD50 and ED50 values) amounting to 5.58. The combination of TPL-16 with valproate produced synergistic interaction in the tonic-clonic seizure model in mice. The combinations of TPL-16 with carbamazepine, phenobarbital and phenytoin produced additive interaction in terms of protection from tonic-clonic seizures in mice. None of the total brain concentrations of classic AEDs were changed significantly after TPL-16 administration in mice. Synergistic interaction for TPL-16 with valproate and the additive interaction for TPL-16 with carbamazepine, phenobarbital and phenytoin in the tonic-clonic seizures in mice allows for recommending TPL-16 as the promising drug for further experimental and clinical testing.

Variability of carbamazepine and valproate concentrations in elderly nursing home residents

Measuring antiepileptic drug (AED) concentrations is common practice in nursing homes. Phenytoin (PHT) concentrations fluctuate substantially in many nursing home residents under constant dose conditions; however, the stability of other AED concentrations has not been studied. We investigated the variability of carbamazepine (CBZ) and valproate (VPA) concentrations under constant dose conditions in US nursing home residents. A database of elderly persons (≥65 years) in 119 nursing homes throughout the US was reviewed for residents with at least one measurement of total PHT, CBZ or VPA. Inclusion criteria for this study were three or more serum concentration measurements while on the same dose of CBZ or VPA, a two-month minimum stay, and no interfering co-medications (inducers or inhibitors). Enrollment occurred over a 2-year period. Data were collected on residents for a minimum of 6 months. Of the 593 residents identified, 245 had CBZ or VPA concentrations measured and 44 (18%) met inclusion criteria (22 on CBZ and 22 VPA). Some subjects had little variability in AED concentrations, others had large fluctuations. Total CBZ concentrations within individuals varied as little as 0mg/L to as much as 6.3mg/L and total VPA concentrations as little as 10.0mg/L to as much as 77.6mg/L. The variability of PHT, CBZ, and VPA concentrations in many but not all nursing home residents implies that a re-evaluation of the role of AED concentration measurements in the management of patients is needed. Strategies for use and interpretation of AED concentration measurements need to be reevaluated.

Effect of heating human sera at a temperature necessary to deactivate human immunodeficiency virus on measurement of free phenytoin, free valproic acid, and free carbamazepine concentrations.

Minimizing the risk for infection to laboratory staff from a contaminated blood sample is a major safety goal in the clinical laboratory. One dangerous pathogen, the human immunodeficiency virus (HIV), can be deactivated by heating sera at 56 degrees C for 30 minutes. The authors previously reported that if serum was subjected to those conditions, the concentrations of the nine most commonly monitored drugs were not altered, whereas phenytoin and carbamazepine concentrations were reduced slightly. Monitoring free phenytoin, free valproic acid, and free carbamazepine concentrations is strongly recommended for patients with uremia, liver disease, and hypoalbuminemia. Because drug protein binding can be affected by temperature, the authors investigated the effect on free drug concentrations of sera heated to levels necessary for deactivation of the HIV virus. They measured total and free drug concentrations in serum pools prepared from patients receiving phenytoin, valproic acid, and carbamazepine. Serum pools were heated at 56 degrees C for 30 minutes and then brought to room temperature. The total and free drug concentrations were measured immediately after heating and then at 20- and 45-minute intervals. The concentrations of free phenytoin and free valproic acid were significantly higher after heat treatment. However, after equilibration of sera at room temperature for 20 minutes, the free concentrations of phenytoin were comparable to preheating values, although total phenytoin concentrations (Serum Separator Tubes) were reduced slightly. In contrast, free valproic acid concentrations did not return to the original levels even after 45 minutes. Free carbamazepine concentrations did not change even immediately after heating. However, total carbamazepine concentrations were reduced slightly when sera were heated in serum separator tubes (SST Tubes).

Epilepsy and pregnancy: a prospective study of seizure control in relation to free and total plasma concentrations of carbamazepine and phenytoin.

Seizure control and plasma concentrations of antiepileptic drugs (AEDs) were determined in a prospective, population-based study of 93 pregnancies (cases) of 70 patients with epilepsy. Seventy-seven cases were treated with monotherapy, which in 70 cases consisted of carbamazepine (CBZ) or phenytoin (PHT). Dosage was kept constant unless poor seizure control prompted an increase. Plasma concentrations were determined at monthly intervals throughout pregnancy and compared with baseline levels obtained at least 10 weeks postpartum. Both free and total CBZ and PHT concentrations were analyzed. Seizure frequency during pregnancy for the group as a whole was not different as compared with the 9 pregestational months and was unaltered or improved in 85% of cases. Total CBZ concentration was slightly lower during the third trimester as compared with baseline, whereas free concentration was unchanged. In contrast, PHT levels decreased steadily as pregnancy progressed. Total plasma concentration was 39% of baseline during the third trimester, whereas free PHT concentration decreased far less, being 82% of baseline level during the third trimester. No clear-cut relation could be demonstrated between seizure control and plasma concentrations, which may be explained by the limited changes in free AED concentrations and the small number of cases with an increased seizure frequency. Our results indicate that total plasma concentrations may be misleading and that monitoring of free concentrations, in particular of PHT concentrations, may be advantageous during pregnancy.

Micro High-Performance Frontal Analysis for Simultaneous Determination of Unbound and Total Carbamazepine Concentrations in Protein Binding Equilibrium

Micro high-performance frontal analysis (MHPFA) method has been developed for the simultaneous determination of unbound and total carbamazepine (CBZ) concentrations in protein binding equilibrium. When a 300-μl portion of 4-12μg/ml CBZ and 593μM human serum albumin (HSA) mixed solution was directly injected into a small bore ISRP column (10cm×2.0mm i.d.), CBZ gave a trapezoidal peak with a plateau separated from HSA. The CBZ concentration calculated from the plateau height agreed well with the unbound concentration determined by the conventional ultrafiltration-HPLC method, while the CBZ concentration calculated from the peak area coincided with the total (bound plus unbound) concentration. The within-run and day-to-day reproducibilities were satisfactory (relative standard deviation, <1.27%, n=5). Compared with the injection volume (1.4ml) required for the HPFA using a conventional size (15cm×4.6mm i.d.) ISRP column, MHPFA could reduce the sample size to about one-fifth (300μl).

Effect of Serum Separator Tubes on Free and Total Phenytoin and Carbamazepine Serum Concentrations

The effect of serum separator tubes (SSTs) on free and total serum phenytoin and carbamazepine concentrations was determined by comparing standard no-additive tubes with SSTs (Becton Dickinson SST and Terumo Autosep). The influence of time prior to centrifugation, sample volume, and initial drug concentration on the effects were also studied. Results were analyzed using repeated measures two-way analysis of variance with tube type and either time, sample volume, or concentration as main effects. The most significant reductions noted were with Becton Dickinson SSTs in free and total serum phenytoin and total carbamazepine concentrations, where all reductions were less than 10%. The only factor to significantly influence extent of reduction was the effect of time on total serum phenytoin concentration in Becton Dickinson SSTs. Terumo Autosep tubes caused no major reductions in free or total phenytoin or carbamazepine serum concentrations. Autosep tubes should provide accurate measurements of total and free serum phenytoin and carbamazepine concentrations. With Becton Dickinson SSTs, the reductions noted in free and total phenytoin and total carbamazepine concentrations were not large enough to preclude their clinical use. Becton Dickinson SSTs should not be used for determining free or total phenytoin or total carbamazepine concentrations for purposes of research.

Teratogenicity of carbamazepine in rats

The teratogenicity of carbamazepine (CBZ) was investigated in Sprague-Dawley CD rats at doses of 0, 200, 400, and 600 mg/kg administered by gavage in corn oil on days 7-18 of gestation in a dosage volume of 2 ml/kg. The CBZ-600 dose was maternally toxic in that dams in this group weighed 30.6% less than controls by E20. This group had significantly increased resorptions, reduced live fetal weight (51.6% less than controls), and increased skeletal and visceral abnormalities. The CBZ-400 dose also significantly reduced maternal weight gain during gestation to 26.6% less than controls by E20. No significant increase in resorptions occurred in this group; live fetuses weighted 42.9% less than controls and showed an increase in visceral, but not skeletal, abnormalities. The CBZ-200 dose did not significantly affect maternal weight gain or increase resorptions or fetal abnormalities but did reduce fetal body weight (20.3% less than controls). Maternal serum total CBZ concentrations 1 hr after the final dose were 22.9, 27.9, and 34.4 micrograms/ml for the 200, 400, and 600 mg/kg groups, respectively. These levels were little changed 6 h post-treatment. CBZ was 65-70% serum protein bound across dose groups. Human therapeutic levels of CBZ are 4-12 micrograms/ml and the drug is typically 80% serum protein bound. This suggests that abnormalities in rats occur at concentrations well above the human therapeutic range. However, a no-effect level was not found for fetal body weight. Further experiments will be required to determine how much lower doses will need to be in order to find a no-effect level for fetal body weight. Nevertheless, the present data suggest that CBZ is not potent at inducing malformations in rats.

Simultaneous determination of the free and total carbamazepine concentrations in human plasma by high-performance frontal analysis using an internal-surface reversed-phase silica support.

High-performance frontal analysis (HPFA) was applied to simultaneous determinations of the free and total carbamazepine (CBZ) concentrations in human plasma. When 1.5ml of human plasma containing CBZ at a clinical therapeutic level (free fraction, about 30%) was directly injected into an internal-surface reversed-phase silica column, the CBZ was separated from the plasma blank and was eluted as a zonal peak with a plateau height corresponding to the free CBZ concentration in protein binding equilibrium. Slow and continuous introduction of the plasma sample and the use of titanium filters permitted us to inject the sample repeatedly while avoiding a rapid increase in column pressure. The free and total CBZ concentrations were determined simultaneously from the peak height at the plateau region and the area of the CBZ peak, respectively. The within-run and day-to-day reproducibilities were satisfactory (C.V. less than or equal to 1.63%, n = 5).

Determination of free drug in protein binding equilibrium by high-performance frontal analysis using internal-surface reversed-phase silica support.

An internal-surface reversed-phase silica column was employed in the frontal analysis method to determine free drug concentration in warfarin (Wf)-bovine serum albumin (BSA) mixed solution and in indomethacin(Im)-BSA mixed solution. When a 4-ml portion of aqueous solution containing 2-30 microM Im and 28 microM BSA and a 10-ml portion of aqueous solution containing 0.5-175 microM Wf and 28 microM BSA were applied, the elution curves reached a plateau level corresponding to both free drug and drug-BSA complex (beta-plateau), followed by another plateau due to free drug alone (gamma-plateau). The drug concentration at the gamma-plateau agreed well with the free drug concentration determined after ultrafiltration of the same solution. The gamma-plateau was observed even when the applied volume was reduced to a level which was insufficient to produce the beta-plateau. The injection of a 400-microliters portion of the 0.5-100 microM Im and 28 microM BSA mixed solution and a 90-microliters portion of 50 microM Im and 550 microM BSA mixed solution onto the ISRP silica column gave a clear gamma-plateau. Compared to the conventional frontal analysis, the present method can determine a wide range of drug levels with much smaller injection volume. This method is applicable to plasma. By a single frontal analysis, both free and total concentrations of carbamazepine in plasma were determined simultaneously.

Intradose and circadian variation in circulating carbamazepine and its epoxide in epileptic patients: a consequence of autoinduction of metabolism.

Total and free carbamazepine (CBZ), and CBZ 10,11 epoxide (CBZ-E) concentrations were measured over 24 h in 19 patients receiving CBZ 400 mg b.i.d. either as monotherapy (n = 13) or combined with another anticonvulsant (n = 6). Differences in CBZ and CBZ-E disposition between day and night dosing were minor. Mean plasma CBZ concentrations were higher and CBZ-E/CBZ ratios were lower in the monotherapy patients. Variations in total and free plasma CBZ levels were comparable in the monotherapy and polypharmacy groups. Peak free and total CBZ concentrations coincided at approximately 4 h postdose. Free CBZ levels correlated significantly with total in each patient. The extent of variation in total plasma CBZ concentration during 24 h correlated significantly with antipyrine clearance in the monotherapy group. Circadian rhythms are unlikely to influence CBZ disposition to a clinically relevant extent. Measurement of peak and trough CBZ concentrations should improve the value of therapeutic drug monitoring. The diurnal variation in CBZ concentration appears related to the degree of autoinduction of metabolism and is substantial enough to warrant the development of a slow-release preparation of the drug.

Total and free serum concentrations of carbamazepine and carbamazepine-10,11-epoxide in children with epilepsy.

Simultaneous steady-state serum total and free (non-protein-bound) concentrations of carbamazepine and carbamazepine-10,11-epoxide were measured in 68 patients under the age of 21 years with epilepsy (44 males, 24 females; mean age, 11.8 +/- 4.5 years). Thirty patients were maintained on monotherapy with carbamazepine. Mean serum total carbamazepine and carbamazepine-10,11-epoxide concentrations obtained were 7.0 +/- 2.4 mg/L (29.5 +/- 10.0 mumol/L) and 1.5 +/- 0.6 mg/L (5.9 +/- 2.6 mumol/L), respectively. Mean serum-free carbamazepine and carbamazepine-10,11-epoxide concentrations obtained were 1.3 +/- 0.5 mg/L (5.7 +/- 2.1 mumol/L) and 0.5 +/- 0.3 mg/L (2.2 +/- 1.1 mumol/L), respectively. Binding of carbamazepine and carbamazepine-10,11-epoxide was 81% +/- 3% and 62% +/- 10%, respectively. There was no significant difference in binding between male and female patients or those maintained on monotherapy and polytherapy. Age correlated significantly with carbamazepine binding but not with carbamazepine-10,11-epoxide binding. Free concentrations of carbamazepine and carbamazepine-10,11-epoxide correlated significantly with total carbamazepine and total carbamazepine-10,11-epoxide concentrations, respectively, indicating that the binding capacities of both carbamazepine and carbamazepine-10,11-epoxide are constant at serum total carbamazepine concentrations within the quoted therapeutic range.

Utilisation of Free Valproic Acid Determinations

with phenobarbital. Carbamazepine was given in 3 or 4 daily doses immediately after meals and blood samples were collected at 2-hour intervals during the day. Carbamazepine was analysed by EMIT® on whole plasma (total concentration) and in plasma ultrafiltrates (free concentration) obtained by using EMIT FreeLevelTM filters as recommended by the manufacturer (Syva Co., Palo Alto). At each time, a brief neurological examination aimed at documenting the presence of adverse effects was performed. Results: In all patients, both total and free carbamazepine concentrations fluctuated considerably (mean ± SD of the fluctuation around the mean of the plasma concentrations, 40 ± 15% for total and 45 ± 16% for free). Side effects (particularly nystagmus and/or diplopia) were observed in 5 patients (intermittent in 4). Side effects were apparent when total carbamazepine concentrations exceeded 9 ~g/ml but were never found at total concentrations under 8 ~g/ml.