Topiramate Concentrations Research Articles

Topiramate concentration in saliva: an alternative to serum monitoring

This study examines the relationship between serum and saliva topiramate concentrations, and attempts to determine if saliva may be a useful alternative to serum for therapeutic monitoring. Saliva and blood specimens were collected from 31 epilepsy patients (mean age 10.5 ± 6.0 years; range 2.5 years to 24.8 years), and topiramate concentrations were determined by fluorescence polarization immunoassay. One patient’s results were omitted because the saliva concentration was below the limit of quantitation of the assay. A strong correlation exists between serum and saliva topiramate concentrations (adjusted r 2 = 0.97, n = 30, P < 0.0001). The mean fraction of saliva to serum concentration is 89.8% ± 12.1% (range 62.9% to 112.7%). The results of this study support the use of saliva as a viable alternative to serum for monitoring topiramate therapy. Topiramate concentration in saliva: an alternative to serum monitoring.

Clinical pharmacokinetics of oxcarbazepine.

Oxcarbazepine is an antiepileptic drug with a chemical structure similar to carbamazepine, but with different metabolism. Oxcarbazepine is rapidly reduced to 10,11-dihydro-10-hydroxy-carbazepine (monohydroxy derivative, MHD), the clinically relevant metabolite of oxcarbazepine. MHD has (S)-(+)- and the (R)-(-)-enantiomer, but the pharmacokinetics of the racemate are usually reported. The bioavailability of the oral formulation of oxcarbazepine is high (>95%). It is rapidly absorbed after oral administration, reaching peak concentrations within about 1-3 hours after a single dose, whereas the peak of MHD occurs within 4-12 hours. At steady state, the peak of MHD occurs about 2-4 hours after drug intake. The plasma protein binding of MHD is about 40%. Cerebrospinal fluid concentrations of MHD are in the same range as unbound plasma concentrations of MHD. Oxcarbazepine can be transferred significantly through the placenta in humans. Oxcarbazepine and MHD exhibit linear pharmaco-kinetics and no autoinduction occurs. Elimination half-lives in healthy volunteers are 1-5 hours for oxcarbazepine and 7-20 hours for MHD. Longer and shorter elimination half-lives have been reported in elderly volunteers and children, respectively. Mild to moderate hepatic impairment does not appear to affect MHD pharmacokinetics. Renal impairment affects the pharmacokinetics of oxcarbazepine and MHD. The interaction potential of oxcarbazepine is relatively low. However, enzyme-inducing antiepileptic drugs such as phenytoin, phenobarbital or carbamazepine can reduce slightly the concentrations of MHD. Verapamil may moderately decrease MHD concentrations, but this effect is probably without clinical relevance. The influence of oxcarbazepine on other antiepileptic drugs is not clinically relevant in most cases. However, oxcarbazepine appears to increase concentrations of phenytoin and to decrease trough concentrations of lamotrigine and topiramate. Oxcarbazepine lowers concentrations of ethinylestra-diol and levonorgestrel, and women treated with oxcarbazepine should consider additional contraceptive measures. Due to the absent or lower enzyme-inducing effect of oxcarbazepine, switching from carbamazepine to oxcarbazepine can result in increased serum concentrations of comedication, sometimes associated with adverse effects. The effect of oxcarbazepine appears to be related to dose and to serum concentrations of MHD. In general, daily fluctuations of MHD concentration are relatively slight, smaller than would be expected from the elimination half-life of MHD. However, relatively high fluctuations can be observed in individual patients. Therapeutic monitoring may help to decide whether adverse effects are dependent on MHD concentrations. A mean therapeutic range of 15-35 mg/L for MHD seems to be appropriate. However, more systematic studies exploring the concentration-effect relationship are required.

Topiramate kinetics during delivery, lactation, and in the neonate: preliminary observations.

To study the pharmacokinetics of topiramate (TPM) during delivery, lactation, and in the neonate. TPM concentrations in plasma and breast milk were measured with fluorescence polarization immunoassay (FPIA) in five women with epilepsy treated with TPM during pregnancy and lactation. Blood samples were obtained at delivery from mothers, from the umbilical cord, and from the newborns on three occasions (24, 48, and 72 h) after delivery. Blood and breast milk also were collected from mothers 2 weeks, and 1 and 3 months postpartum. Blood samples also were drawn from the infants during breast-feeding. Three of the mother-infant pairs were studied both at delivery and during lactation; two contributed with data from delivery only. The umbilical cord plasma/maternal plasma ratios were close to unity, suggesting extensive transplacental transfer of TPM. The mean milk/maternal plasma concentration ratio was 0.86 (range, 0.67-1.1) at 2-3 weeks after delivery. The milk/maternal plasma concentration ratios at sampling 1 and 3 months after delivery were similar (0.86 and 0.69, respectively). Two to 3 weeks after delivery, two of the breast-fed infants had detectable (>0.9 microM) concentrations of TPM, although below the limit of quantification (2.8 microM), and one had an undetectable concentration. Our limited data suggest free passage of TPM over the placenta and an extensive transfer into breast milk. Breast-fed infants had very low TPM concentrations, and no adverse effects were observed in the infants.

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.

Topiramate Therapeutic Monitoring in Patients With Epilepsy: Effect of Concomitant Antiepileptic Drugs

The authors assessed the effect of concomitant antiepileptic therapy on steady-state plasma concentrations of the new antiepileptic drug (AED) topiramate and the potential relation between topiramate plasma levels and side effects in a cohort of 116 patients with epilepsy. On the basis of concomitant AEDs, patients were divided into two subgroups, otherwise comparable for age and weight-adjusted daily dose of topiramate. Group A (n = 73) received topiramate plus AED inducers of cytochrome P450 (CYP) metabolism, such as carbamazepine, phenobarbital, and phenytoin. Group B (n = 43) received topiramate plus AEDs without inducing properties of CYP metabolism (namely valproic acid and lamotrigine). Weight-normalized topiramate clearance values, calculated as dosing rate/steady-state plasma drug concentration, were about 1.5-fold in patients receiving AED inducers compared with patients receiving AED noninducers. Topiramate plasma concentrations were linearly related to daily drug doses, regardless of concomitant AED therapy, over a dose range from 25 to 800 mg/d, although, at a given daily dose, a large interpatient variability was observed in matched plasma drug concentrations within each group of patients. Thirty-nine patients (34%) reported side effects associated with topiramate, mostly central nervous system effects. No consistent relation was observed between topiramate plasma concentrations and adverse effects, either in the cohort of patients as a whole or within each subgroup. From a clinical point of view, patients receiving concurrent treatment with enzyme-inducing AEDs can show twofold lower topiramate plasma concentrations compared with patients receiving valproic acid or lamotrigine, and appropriate topiramate dosage adjustments may be required when concomitant AED inducers are either added or withdrawn. Due to the observed variability in topiramate metabolic variables and the complex spectrum of possible pharmacokinetic and pharmacodynamic interactions with the most commonly coprescribed AEDs, monitoring of plasma topiramate concentrations may help the physician in the pharmacokinetic optimization of the drug dosage schedule in individual patients.

Modulation of high-voltage-activated calcium channels in dentate granule cells by topiramate.

In this study, we assessed the effects of topiramate (TPM) on high-voltage-activated calcium channel (HVACC) currents in vitro. HVACC currents were recorded from rat dentate gyrus granule cells by using whole-cell patch-clamp techniques. The biophysical properties of HVACCs were used to separate voltage-activated Ca2+ currents into different subtypes. Three concentrations of TPM were tested: 1, 10, and 50 microM. TPM inhibited L-type currents and was more effective at 10 microM than at 50 microM, suggesting that there may be an optimal concentration at which TPM decreases L-type currents. Non-L-type currents were transiently increased by TPM at a high concentration (50 microM). Because the location of L-type calcium channels on soma and proximal dendrites gives these channels a crucial role in controlling dendritic excitability and in providing calcium for intracellular effectors, the decrease in the L-type HVA Ca2+ currents may be an important anticonvulsant mechanism of TPM.

Therapeutic monitoring of topiramate: evaluation of the saturable distribution between erythrocytes and plasma of whole blood using an optimized high-pressure liquid chromatography method.

Topiramate (TPM) reportedly binds in a saturable manner to erythrocytes but minimally to plasma proteins. Two studies were performed to evaluate this distribution phenomenon. In all studies, TPM was measured with a newly developed, optimized procedure that uses octyldecyl (C-18) solid phase sorbents disks/packed cartridges and a DB-1 methylsilicone capillary gas chromatography (GC) column. Between-run precision coefficients of variation (CVs) (n = 16) ranged from 3.6%-5.6% at concentrations from 3.0 to 15 microg/mL, with low limit of detection of 0.2 to 0.3 microg/mL. For the distribution studies, drug-free whole-blood specimens from five healthy adult volunteers were supplemented with TPM and used to test the influence of TPM concentration and HCT differences on the plasma/blood (P/B) distribution ratio of TPM. In study A, TPM concentration was varied (1-15 microg/mL) and HCT remained constant (40% +/- 5%). In study B, TPM (3 microg/mL) was added to blood specimens comprising a range of HCT values (20%-40%). Study A results were: mean TPM P/B ratios: 0%, 14.2% +/- 5%, 44.2% +/- 4%, 76% +/- 5.5% at 1, 3, 5, 15 microg/mL, respectively. Data between each group were statistically different (p < 0.001). Study B results were: mean TPM P/B ratio: 17.3% +/- 7.3%, 27.5% +/- 10.1%, 39.8% +/- 8% and 56.1% +/- 8.8% at HCT values of 40%, 32%, 26.5%, 20%, respectively. The TPM P/B ratio was significantly inversely correlated to HCT (r = -905, p < 0.001). TPM P/B partitioning was not temperature-dependent. Researchers concluded that the saturable binding of TPM to RBC is significant and is correlated to HCT. As a result, TPM in the plasma fraction of whole blood will increase when HCT decreases and as total TPM concentration in whole blood increases.

A study of topiramate pharmacokinetics and tolerability in children with epilepsy

The pharmacokinetic and safety profile of topiramate as adjunctive therapy was assessed in pediatric patients with epilepsy in an open-label, 4-week, single-center study. Six children from each of the following age groups were enrolled: 4-7 years, 8-11 years, and 12-17 years. Patients received topiramate 1 mg/kg/day for 1 week, with subsequent progressive weekly increases in dosage to 3, 6, and then 9 mg/kg/day or 800 mg/day, whichever was less. Topiramate oral plasma clearance (CL/F) was independent of dose, and steady-state plasma concentrations increased in proportion to dose. Weight-normalized topiramate CL/F was higher ( P = 0.003) in pediatric patients receiving enzyme-inducing concomitant antiepileptic drugs (AEDs) (mean = 70.1 mL/minute/70 kg) than in those not receiving enzyme-inducing AEDs (mean = 33.1 mL/minute/kg). Topiramate CL/F in children was approximately 50% greater than that observed in adults regardless of the type of concomitant AED therapy. Thus steady-state plasma topiramate concentrations for the same mg/kg dose will be approximately 33% lower in pediatric patients than in adult patients. The most frequently reported treatment-emergent adverse events considered related to topiramate therapy included anorexia, fatigue, and nervousness, and no patient discontinued therapy. This study indicates that, in children 4-17 years of age, topiramate has linear pharmacokinetics, 50% higher clearance than in adults, and is generally well tolerated.

In vivo microdialysis and liquid chromatography/thermospray mass spectrometry of the novel anticonvulsant 2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate (topiramate) in rat brain fluid.

The concentration of a novel anticonvulsant, 2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate (topiramate), was determined in the extracellular fluid of rat brain by in vivo microdialysis combined off-line with liquid chromatography/thermospray mass spectrometry. A microdialysis probe was stereotaxically implanted in the nucleus accumbens region of the rat brain. The maximum concentration of topiramate in the brain dialysate for a dose of 50 mg kg-1 i.v. was approximately 10 microM and occurred 45 min post-injection. The detection limit of topiramate in the extracellular fluid of rat brain was in the 0.1 microM range using selected ion monitoring techniques. The base peak, which was the ammonium adduct ion [M + NH4]+, was used for detection. An internal standard of d12-labeled topiramate was utilized for quantitation by isotope dilution analysis.

Topiramate: a new antiepileptic drug.

To review proposed mechanisms of action, clinical pharmacology, efficacy, safety, and tolerability of the antiepileptic drug (AED) topiramate. All available data from the clinical development program--published and unpublished data (provided by investigators or the RW Johnson Pharmaceutical Research Institute)--were analyzed, with emphasis on the results of double-blind, placebo-controlled trials. Data from open-label studies provided information about long-term efficacy and tolerability. Topiramate is highly effective in the control of previously therapy-resistant partial seizures, with or without secondary generalization. In the refractory adult patient population enrolled in controlled clinical trials, seizures were reduced by 50% or more in 27-47% of patients compared with 0-18% in placebo-treated patients and by 75% or more in 9-36% of the patients compared with 0-9% of those receiving placebo. The most common adverse effects involve the central nervous system and are mild to moderate in nature. Adverse effects include somnolence, fatigue, psychomotor slowing, and concentration problems. The currently recommended dosing is lower and titration slower than schedules used in the clinical trials; this may improve the tolerability of topiramate. Topiramate has few interactions with currently available AEDs, but phenytoin concentrations increased in some patients. Topiramate can be used initially as adjunctive therapy. Plasma topiramate concentrations are reduced substantially when used with enzyme-inducing AEDs. Open-label data and a single double-blind trial suggest that topiramate monotherapy may be effective. Open-label data also indicate that topiramate may be effective in generalized seizures of nonfocal origin, including those associated with Lennox-Gastaut syndrome. The robust clinical effects of topiramate expand the therapeutic options for patients with epilepsy. Controlled clinical trials are needed to verify initial observations that topiramate may be effective against a broad spectrum of seizure types and to directly compare efficacy and tolerability with other new and standard AEDs.

Topiramate

Clinical evidence is emerging that topiramate (TPM) may be effective in pediatric epilepsies. Topiramate pharmacokinetics appear to be linear in children when administered in dosages up to 9 mg/kg/d. Mean oral clearance is 44% to 54% higher in children when compared with historical data from adults; steady-state plasma TPM concentrations for the same mg/kg dose are expected to be 33% lower in children. While double-blind, placebo-controlled trials of adjunctive TPM therapy in Lennox-Gastaut syndrome, primary generalized tonic-clonic seizures, and refractory partial-onset seizures in children are ongoing, preliminary results of pilot studies and the open-label extension phases of these double-blind studies suggest TPM may be effective as adjunctive therapy in a broad range of seizure disorders. In the open-label extension phase of a double-blind trial, the proportion of patients with Lennox-Gastaut syndrome experiencing 50% or greater reduction in seizures was 47%. Likewise, seizures were reduced 50% or more with TPM adjunctive therapy in 64% of children with partial-onset seizures and in 67% of patients with primary generalized tonic-clonic seizures treated with open-label during the extension phase of two separate double-blind studies. Preliminary experience suggests that TPM monotherapy can be successfully substituted for another antiepileptic drug in some children. The results of the well-controlled trials are needed to confirm these preliminary observations of TPM effectiveness in pediatric epilepsies.

Epidemiology and Prevention of Injuries

Injuries are the leading cause of death for ages 1 to 44 and are responsible for more years of productive life lost than any other disease. The common perception of injuries as random, unpredictable events has impeded the application of existing knowledge and technology fully capable of preventing many injuries or lessening their severity. This article explores the concept of injury control, the application of standard epidemiologic methods of investigation, the identification of high-risk groups, and the development and implementation of strategies for trauma prevention.