Lack of a clinically significant effect of zonisamide on phenytoin steady-state pharmacokinetics in patients with epilepsy

This study was designed to measure the effect of the addition of zonisamide on phenytoin pharmacokinetics under steady-state conditions in patients with epilepsy. Nineteen patients stabilized under phenytoin monotherapy were included in a 3-center, open-label, 1-way drug interaction trial. Zonisamide was gradually increased to 400 mg/day, taken twice daily. Three pharmacokinetic profiles were performed: on days -7 and -1, to assess pharmacokinetic parameters of oral phenytoin administered alone, and on day 35, after 14 days of zonisamide treatment, to evaluate the effect of zonisamide on phenytoin pharmacokinetics and to characterize zonisamide pharmacokinetics in the presence of phenytoin. Fourteen patients completed the study; the coadministration of zonisamide and phenytoin was safe and well tolerated. Zonisamide did not significantly affect the mean C(min), C(max), AUC(0-12), and CL/F of phenytoin measured before and after zonisamide administration. The pharmacokinetic measures of zonisamide in the presence of phenytoin were consistent with previous reports of induction of zonisamide metabolism by phenytoin.     

Single dose and steady state pharmacokinetics of valproic acid in adult epileptic patients.

The pharmacokinetics of valproic acid was studied in ten adult epileptic patients (five f + five m, 19-48 years; 28 +/- 12, mean +/- SD, and body mass 45 to 70 kg; 61 +/- 7, mean +/- SD) both after single dose and at the steady state. Sodium valproate was given in a 900 mg single oral dose on the first day of therapy, followed by 3 x 300 mg/day during the three subsequent days (at the intervals of 7, 8 and 9 h). During the first day, plasma was obtained just before the drug was given, and at 0.5, 1, 2, 3, 4, 5, 6, 8, 10 and 12 h after drug administration. On the fourth day of therapy (at steady state), plasma was obtained just before the next dose and 3 h after the drug administration. The plasma concentrations of valproic acid were measured by gas chromatography with flame ionization detection, after extraction with chloroform. The pharmacokinetic parameters, necessary to define the pharmacokinetics of valproic acid, were calculated both after single dose: Cmax, tmax, kel, t1/2, Vd, AUC and Cl, and at steady state: Cminss Cmaxss and Fl%. These parameters, as well as plasma levels of the drug, were used to describe the pharmacokinetic behaviour of valproic acid under these clinical conditions, and mainly were in agreement with the values published in the literature.     

Zonisamide: new drug. No advantage in refractory partial epilepsy

(1) The first-line treatment for patients with partial epilepsy is carbamazepine monotherapy. Second-line options include monotherapy with valproic acid, gabapentin, lamotrigine or oxcarbazepine. Other antiepileptics are also available for combination therapy of refractory partial epilepsy. (2) Zonisamide is a sulphonamide derivative that inhibits carbonic anhydrase; it resembles topiramate, a drug already approved for use for this indication in the European Union. (3) The main clinical trial, a double-blind study lasting 36 weeks, compared the addition of zonisamide or placebo to ongoing treatment in 351 patients with refractory partial epilepsy. The "response rate" (the proportion of patients with at least a 50% reduction in the frequency of seizures) was significantly higher with zonisamide plus the previous treatment than with placebo plus the previous treatment (46.6% versus 17.6%). An indirect comparison suggests that this is no better than treatment with a second-line antiepileptic drug. (4) Results of three other placebo-controlled trials of third-line combinations in a total of 499 patients treated for 12 weeks were similar. (5) The main adverse effects of zonisamide are those typically seen with topiramate: neuropsychological disorders and disorders due to carbonic anhydrase inhibition (kidney stones, reduced perspiration, and hyperthermia). There are various other adverse effects, including a risk of severe skin rash. (6) The profile of interactions is complex. There is a risk of pharmacokinetic interactions, and of pharmacodynamic interactions with other carbonic anhydrase inhibitors. (7) In France, treatment with zonisamide costs nearly 20 times more than treatment with carbamazepine or valproic acid. (8) Zonisamide has no therapeutic advantages over other antiepileptics available for combination therapy of partial epilepsy.     

Lack of clinically significant pharmacokinetic interactions between zonisamide and lamotrigine at steady state in patients with epilepsy

The present study was designed to assess the effect of the addition of zonisamide (ZNS) on lamotrigine (LTG) disposition and the safety of the combination under steady-state conditions in patients with epilepsy. A secondary objective was to characterize ZNS pharmacokinetics (PK) in the presence of LTG. Twenty subjects (male and female 18 to 55 years old) stabilized on LTG monotherapy (150-500 mg/d) took part in a 2-center, open-label, 1-way drug interaction study. ZNS was gradually increased to 200 mg twice daily over a 3-week period, and 3 PK profiles were performed: on days -7 and -1 to assess the PK of oral LTG administered alone and on day 35, after 14 days of ZNS at the maximal tolerated dose, to evaluate the effect of ZNS on LTG PK and to characterize ZNS PK in the presence of LTG. Eighteen subjects completed the study. Steady-state dosing of ZNS did not significantly affect the mean Cmin (mean +/- SD: 2.8 +/- 1.4 vs 3.5 +/- 2.4 microg/mL), Cmax (5.1 +/- 3.0 vs 5.1 +/- 3.0 microg/mL), AUC0-12 (45.5 +/- 22.6 vs 50.3 +/- 32.1 microg.h/mL), and CL/F (2778.5 +/- 1368.5 vs 3052.1 +/- 2744.9 mL/h) of LTG measured before (day -1) and after (day 35) ZNS administration, respectively. Further, 90% confidence intervals for the geometric mean ratios (day 35/day -1) fell within the no-effect range of 0.80-1.25. The fraction of dose of total and unconjugated LTG excreted in urine was not significantly different between baseline and ZNS treatment, but the renal clearance of LTG decreased significantly with ZNS dosing (P = 0.01). On the other hand, the PK parameters measured for ZNS in the presence of LTG were consistent with an absence of LTG effect on ZNS PK. The coadministration of ZNS and LTG was generally well tolerated. Steady-state safety and PK of LTG and ZNS are not affected significantly when these two drugs are coadministered at clinically relevant doses, indicating that no dosage adjustment of either drug should be required when they are used in combination.     

Pharmacokinetics and safety of extended-release divalproex sodium tablets: morning versus evening administration.

PURPOSE: The pharmacokinetics and safety of 1000-mg extended-release divalproex sodium given once daily either in the morning or evening were compared. METHODS: Healthy volunteers 19-55 years of age were enrolled in this open-label, parallel-design study. Subjects were randomized to receive extended-release divalproex either in the morning or in the evening. Blood samples were taken immediately before and at 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 121, 122, 123, 124.5, 126, 127.5, 129, 130.5, 132, 133, 134, 135, 136.5, 138, 139.5, 141, 142.5, and 144 hours after the first dose of each six-day regimen. Plasma samples were assayed for total valproic acid concentrations using gas chromatography. Valproic acid pharmacokinetic values were measured, and the safety of each regimen was evaluated. RESULTS: Mean steady-state valproic acid exposure, maximum concentration, and minimum concentration were 1771 mg x hr/L, 86.9 mg/L, and 55.5 mg/L for the morning dosing and 1728 mg x hr/L, 84.8 mg/L, and 57.4 mg/L for the evening dosing regimens, respectively. Adverse events reported by two or more subjects were abdominal pain and somnolence for the morning dosing regimen and asthenia, headache, and pain for the evening dosing regimen. All adverse events were mild or moderate; none caused subject withdrawal from the study. There were no significant differences in the pharmacokinetic parameters (p > 0.51) and safety between groups. Diurnal variation in plasma valproic acid concentrations was minimal with once-daily administration of extended-release divalproex. CONCLUSION: Evening once-daily administration of extended-release divalproex was not associated with substantial differences in pharmacokinetics or safety compared with morning once-daily administration.     

Remedial dosing recommendations for valproic acid in nonadherence patients with epilepsy

OBJECTIVE To investigate the effect of delayed or missed doses on the pharmacokinetics(PK)of valproic acid(VPA) in patients with epilepsy and established remedial dosing recommendations for nonadherence patients. METHODS The Monte Carlo simulations based on all previous population pharmacokinetic models for pediatric, adult and elder patients with epilepsy receiving valproic acid. The following three remedial approaches were investigated for each delayed dose:(1) A partial dose was administered immediately, and the regular dose was administered at the next scheduled time.(2)The delayed dose was administered immediately, fol owed by a partial dose at the next scheduled time.(3)The delayed and partial doses were coadministered immediately, the next scheduled dose was skipped, and the regular dosing was resumed at the subsequent scheduled time. RESULTS The most appropriate remedial regimen was that with the shortest deviation time from the therapeutic window. The effect of nonadherence on PK was dependent on the delay duration and daily dose, and the recommended remedial dose was related to the delay duration and concomitant antiepileptic drugs. Remedial dosing strategies(1) and(2) were almost equivalent, whereas(3)showed a larger PK deviation time. If one dose was missed, double doses were not recommended for the next scheduled time. CONCLUTION Simulations provide quantitative insight into the remedial regimens for nonadherence patients and clinicians should select the optimal regimen based on the status of patients.     

Inhibitory effect of valproic acid on cytochrome P450 2C9 activity in epilepsy patients

Drug interactions constitute a major problem in the treatment of epilepsy because drug combinations are so common. Valproic acid is a widely used anticonvulsant drug with a broad therapeutic spectrum. Case reports suggest interaction between valproic acid and other drugs metabolized mainly by cytochrome P450 isoforms. The aim of this study was to evaluate the inhibitory effect of valproic acid on cytochrome P450 2C9 (CYP2C9) activity by using losartan oxidation as a probe in epilepsy patients. Patients were prescribed sodium valproate (mean 200 mg/day for the first week and 400 mg/day in the following period) according to their clinical need. A single oral dose of 25 mg losartan was given to patients before and after the first dose, first week and 4 weeks of valproic acid treatment. Losartan and E3174, the CYP2C9-derived carboxylic acid metabolite of losartan in 8 hr urine were assayed by using high pressure liquid chromatography. Urinary losartan/E3174 ratio did not change significantly on the first day (0.9, 0.3-3.5; median, range), and first week (0.6, 0.2-3.8; median, range), while a significant increase was observed after 4 weeks of valproic acid treatment (1.1, 0.3-5.7; median, range) as compared to that of measured before valproic acid administration (0.6, 0.1-2.1; median, range) (P = 0.039). The degree of inhibition was correlated with the steady-state plasma concentrations of valproic acid (r(2) = 0.70, P = 0.04). The results suggest an inhibitory effect of valproic acid on CYP2C9 enzyme activity in epilepsy patients at steady state. The risk of pharmacokinetic drug-drug interactions should be taken into account during concomitant use of valproic acid and CYP2C9 substrates.     

Population Pharmacokinetics of Levetiracetam in Japanese and Western Adults

OBJECTIVE: To assess the population pharmacokinetics of levetiracetam, a second-generation antiepileptic drug, in adult Japanese and Western populations. METHODS: Data were pooled from ten matched clinical trials conducted in Japan and in Europe and the USA, in which levetiracetam was administered orally to healthy subjects and subjects with epilepsy. Overall, 5408 plasma concentrations were available from 524 subjects in six clinical pharmacology studies and two confirmatory and two long-term safety studies of add-on treatment for partial epilepsy. A one-compartment open model with first-order absorption and elimination was fitted to the plasma concentrations using nonlinear mixed-effects modelling with first-order estimation. RESULTS: Ethnicity had no statistically significant effect on the pharmacokinetics of levetiracetam in the presence of the other covariates. Bodyweight, sex, creatinine clearance and concomitant intake of enzyme inducers or valproic acid had a statistically significant effect on apparent plasma clearance of levetiracetam. Bodyweight, disease and valproic acid had a statistically significant effect on the volume of distribution. Levetiracetam exposure (the area under the plasma concentration-time curve over the 12-hour dosing interval at steady state) was 12% higher in females than in males. Decreasing bodyweight from 70 kg to 40 kg was predicted to increase exposure by 16%, while halving creatinine clearance was predicted to increase exposure by 10%. Enzyme inducers reduced exposure by 8%, while valproic acid resulted in a 23% increase in exposure. The latter effect was assumed to arise from the known association between valproic acid and increased body fat, since levetiracetam is negligibly metabolised by cytochrome P450 enzymes. CONCLUSIONS: Population pharmacokinetic analysis points to the absence of ethnic differences in the pharmacokinetics of levetiracetam between Japanese and Western populations, other than those arising from bodyweight differences. Small, clinically non-relevant differences between individual demographic characteristics suggest that dose adjustment is usually not necessary.     

Pharmacokinetics of valproic acid in patients with bipolar disorder

The pharmacokinetics of valproic acid (VPA) were studied in nine patients with bipolar disorder who were receiving VPA as prophylactic therapy, following the full daily dose (400-1500 mg), on which the patients had been maintained for at least the past 3 months. The data from our study showed that the pharmacokinetics of valproate followed a two compartment open model. A time lag of 1-2 h was observed in each patient, followed by rapid absorption, with the peak concentrations being recorded approximately 4 h after drug administration. The average 12 h trough concentration was found to be 54.73+/-11.96 microg/ml. The plasma level decline was biphasic with a terminal half-life of 14.2+/-6.39 h. Total plasma clearance was 0.095+/-0.035 ml/min/kg. The steady-state apparent volume of distribution was found to be 0.11+/-0.05 l/kg. A positive correlation (r = 0.69) was found between the dose (mg/kg) and steady-state serum concentration (Css) of VPA and all patients, except one, had their Css above 50 microg/ml. Most of the pharmacokinetic parameters in this study involving euthymic bipolar patients on long-term VPA monotherapy were found to be in agreement with those reported in literature on seizure disorder patients on similar regime; however, the plasma elimination half-life appears to be prolonged in bipolar patients.     

Pharmacologic management of epilepsy in the elderly

OBJECTIVE: To review the epidemiology and pharmacologic management of epilepsy in elderly patients. DATA SOURCES: Controlled trials, case studies, and review articles identified via MEDLINE using the search terms epilepsy, seizures, elderly, phenobarbital, primidone, phenytoin, carbamazepine, valproic acid, felbamate, gabapentin, lamotrigine, topiramate, tiagabine, levetiracetam, oxcarbazepine, and zonisamide. Recently published standard textbooks on epilepsy were also consulted. DATA SYNTHESIS: Epilepsy is a common neurologic disorder in the elderly. Cerebrovascular and neurodegenerative diseases are the most common causes of new-onset seizures in these patients. Alterations in protein binding, distribution, elimination, and increased sensitivity to the pharmacodynamic effects of antiepileptic drugs (AEDs) are relatively frequent, and these factors should be assessed at the initiation, and during adjustment, of treatment. Drug-drug interactions are also an important issue in elderly patients, because multiple drug use is common and AEDs are susceptible to many interactions. In addition to understanding age-related changes in the pharmacokinetics and pharmacodynamics of AEDs, clinicians should know the common seizure types in the elderly and the spectrum of AED activity for these seizure types. AEDs with activity against both partial-onset and generalized seizures include felbamate, lamotrigine, levetiracetam, topiramate, valproic acid, and zonisamide. Other AEDs discussed in this review (carbamazepine, gabapentin, phenobarbital, phenytoin, primidone, and tiagabine) are most useful for partial-onset seizures. CONCLUSION: The provision of safe and effective drug therapy to elderly patients requires an understanding of the unique age-related changes' in the pharmacokinetics and pharmacodynamics of AEDs as well as an appreciation of common seizure types and the drugs that are effective for the specific types seen in the elderly.     

Serial free and plasma valproic acid and phenytoin monitoring and drug interactions

In 12 institutionalized epilepsy patients who had been treated 19 months (SD +/- 5) with valproic acid, 27.0 mg/kg (SD +/- 11.9), phenytoin, 6.33 mg/kg (SD +/- 1.36), and co-anticonvulsants, the mean percentage of daily free valproic acid was 11.72 (SD +/- 2.10) and of phenytoin 20.39 (SD +/- 3.32). By serial within-day blood samplings for a.m., noon, and p.m. periods, the diurnal variation of percentage free valproic acid and phenytoin was determined for each patient. For morning and noon periods the variations in the percentages of free valproic acid and phenytoin were independent of each other, correlation coefficients (r) being zero for each period. In contrast, for early p.m. the correlation coefficient was highly significant at r = 0.894 (p less than 0.01). It is apparent that diurnal variations in the percentages of free valproic acid and phenytoin occur even in patients who have been treated with these compounds for more than a year.     

Population pharmacokinetics of free carbamazepine in adult Omani epileptic patients

OBJECTIVE: The aim of this study was to define the pharmacokinetic profile of free carbamazepine (F-CBZ) in adult Omani epileptic patients in order to improve on dosing schedules through population pharmacokinetic analysis using the NONMEM program. METHOD: Steady-state trough F-CBZ serum concentrations, carbamazepine (CBZ) dosing history and associated information were collected prospectively. RESULTS: Forty-eight patients with two or more available F-CBZ serum concentrations (total of 149 dose/serum concentration pairs) met our inclusion criteria. Patients were taking CBZ (200-1200 mg/day) in monotherapy. The analysis assumed a one-compartmental open model with first-order absorption and elimination. The apparent clearance (CL/F) and apparent volume of distribution (V/F) and their interindividual variabilities were estimated using the program. The population estimates for clearance (CL; modelled independently of dose) and volume of distribution were 13.2 +/- 0.6 l/h and 525 +/- 44 1, respectively. However, CL increased as a function of dosing rate and consequently was modelled as a linear function of steady-state concentration. In order to validate these results, the predictions of the population model were tested against data from 13 further patients subjected to the same inclusion criteria but who were not included in the original analysis. The predictions were good, being unbiased (P=0.31), and had an average deviation from the observed values of 18%. CONCLUSION: In order to establish steady-state dosage regimens, a population pharmacokinetic model is proposed, based on the patient's dose, to estimate the individual CL for an Omani epileptic patient receiving CBZ in monotherapy.     

Pharmacokinetics of liposomal amphotericin B in neutropenic cancer patients

This study was conducted to characterise the pharmacokinetics of a liposomal pharmaceutical product of amphotericin B (LAB) in three neutropenic cancer patients complicated by suspected fungal infections. LAB was administered at a constant dose of 50 mg/day over 1--6 h by intravenous infusion, and blood samples were obtained between two infusion intervals without complicating the systemic therapy of the patients. Quantitative analysis of amphotericin B (AB) in plasma was established by a validated reversed-phase high-performance liquid chromatographic (HPLC) assay. Model independent pharmacokinetic parameters were estimated using area and moment analysis. Administration of LAB to the first patient (day 1) diagnosed as malignant melanoma resulted in a mean maximum concentration (C(max)) of 679+/-6 ng/ml and a mean minimum concentration (C(min)) of 139+/-9 ng/ml of AB. Pre-dose, C(max) and C(min) values of AB, after multiple LAB dosing to the other two patients both having acute myeloblastic leukemia were found to be 440+/-6, 1140+/-10, 409+/-11 ng/ml (day 19) and 408+/-3, 1180+/-10, and 283+/-1 ng/ml (day 9), respectively. The area under the plasma concentration-time curve (AUC) and the mean residence time (MRT) calculated between the two infusion intervals were 6180 ngh/ml, 7.79 h (day 1) for the first patient; 13,700 ng.h/ml, 10.5 h (day 19) and 14,000 ng.h/ml, 9.93 h (day 9) for the other two patients, respectively. The pharmacokinetic profiles and non-compartmental parameters calculated were comparable for both patients diagnosed with acute myeloblastic leukemia after multiple dosing at steady state, which also demonstrated a twofold increase in their AUC values compared with the AUC of the first patient. Although C(min) values supported the assumption that there was AB accumulation in plasma and this accumulation could be increased at high doses, LAB was administered safely to these patients and well tolerated at the doses given.     

Open-label steady-state pharmacokinetic drug interaction study on co-administered quetiapine fumarate and divalproex sodium in patients with schizophrenia, schizoaffective disorder, or bipolar disorder

OBJECTIVE: To determine whether there is a pharmacokinetic drug interaction between quetiapine fumarate and divalproex sodium. METHODS: The pharmacokinetics and short-term tolerability and safety of coadministered quetiapine and divalproex were examined in adults with schizophrenia/schizoaffective disorder (Cohort A) or bipolar disorder (Cohort B) in an open-label, parallel, 2-cohort drug-interaction study conducted at three centers in the United States. Cohort A was administered quetiapine (150 mg bid) prospectively for 13 days, with divalproex (500 mg bid) added on days 6-13. Cohort B was administered divalproex (500 mg bid) for 16 days, with quetiapine (150 mg bid) added on days 9-16. Quetiapine and valproic acid plasma concentration-time data over a 12-h steady-state dosing interval were used to determine C(max), T(max), C(min), area under the plasma concentration-time curve (AUC(tau)), and oral clearance (CL/F). RESULTS: In Cohort A (n = 18), addition of divalproex did increase the C(max) of quetiapine by 17% but did not change AUC(tau). In Cohort B (n = 15), addition of quetiapine decreased both total valproic acid C(max) and AUC(tau) by 11%. No differences were observed in adverse events (AEs) with either quetiapine or divalproex monotherapy or their combination. CONCLUSION: Combination therapy with quetiapine (150 mg bid) and divalproex (500 mg bid) resulted in small and statistically non-significant pharmacokinetic changes.     

Single-dose pharmacokinetics of levetiracetam in healthy Chinese male subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: * Levetiracetam has been evaluated for epilepsy since 1992. * Pharmacokinetic studies of levetiracetam have been conducted in healthy volunteers, in adults, children and elderly patients with epilepsy, and in patients with renal and hepatic impairment. * Although this antiepileptic has been well studied in Western countries, this paper describes the first such trial of the drug in a Chinese population. WHAT THIS STUDY ADDS: * Information is given on the pharmacokinetics, dose proportionality, safety and tolerability profile of levetiracetam in healthy male Chinese volunteers, and the results are compared with published data obtained in White subjects. * The pharmacokinetics and the pattern of adverse events of levetiracetam in Chinese subjects are similar to the data reported in White subjects. AIMS: The main aims of this study were to evaluate the pharmacokinetics of levetiracetam in healthy male Chinese volunteers and to assess the dose proportionality between the 500-mg and 1500-mg single doses. METHODS: This was a randomized, single-centre, single-dose, two-way crossover study. Twenty-six healthy male Chinese subjects were enrolled. All subjects received a single dose of 500 mg or 1500 mg levetiracetam tablet(s) on the dosing day, and the wash-out period was 7 days. Blood was obtained for a 36-h pharmacokinetic evaluation. RESULTS: Following single-dose administration of 500 mg and 1500 mg of levetiracetam, the median t(max) was 0.5 and 0.5 h; t(1/2) was 7.3 +/- 0.8 and 7.3 +/- 0.7 h; C(max) was 13.6 +/- 3.2 and 47.1 +/- 12.1 microg ml(-1); AUC(0-infinity) was 109.3 +/- 14.1 and 340.4 +/- 50.6 microg h(-1) ml(-1); and AUC(0-t) was 105.7 +/- 13.3 and 329.0 +/- 47.9 microg h(-1) ml(-1), respectively. CONCLUSIONS: Both C(max) and AUCs were dose-proportional over the range of 500-1500 mg. The pharmacokinetic data obtained in these Chinese subjects were similar to the historical data from a matched group of White subjects.     

Population pharmacokinetic meta-analysis of trabectedin (ET-743, Yondelis) in cancer patients

OBJECTIVE: To characterise the population pharmacokinetics of trabectedin (ET-743, Yondelis(R)) in cancer patients. METHODS: A total of 603 patients (945 cycles) receiving intravenous trabectedin as monotherapy at doses ranging from 0.024 to 1.8 mg/m(2) and given as a 1-, 3- or 24-hour infusion every 21 days; a 1- or 3-hour infusion on days 1, 8 and 15 of a 28-day cycle; or a 1-hour infusion daily for 5 consecutive days every 21 days were included in the analysis. An open four-compartment pharmacokinetic model with linear elimination, linear and nonlinear distribution to the deep and shallow peripheral compartments, respectively, and a catenary compartment off the shallow compartment was developed to best describe the index dataset using NONMEM V software. The effect of selected patient covariates on trabectedin pharmacokinetics was investigated. Model evaluation was performed using goodness-of-fit plots and relative error measurements for the test dataset. Simulations were undertaken to evaluate covariate effects on trabectedin pharmacokinetics. RESULTS: The mean (SD) trabectedin elimination half-life was approximately 180 (61.4) hours. Plasma accumulation was limited when trabectedin was given every 3 weeks. Systemic clearance (31.5 L/h, coefficient of variation 51%) was 19.2% higher in patients receiving concomitant dexamethasone. The typical values of the volume of distribution at steady state for male and female patients were 6070L and 5240L, respectively. Within the range studied, age, body size variables, AST, ALT, alkaline phosphatase, lactate dehydrogenase, total bilirubin, creatinine clearance, albumin, total protein, Eastern Cooperative Oncology Group performance status and presence of liver metastases were not statistically related to trabectedin pharmacokinetic parameters. The pharmacokinetic parameters of trabectedin were consistent across the infusion durations and dose regimens evaluated. CONCLUSIONS: The integration of trabectedin pharmacokinetic data demonstrated linear elimination, dose-proportionality up to 1.8 mg/m(2) and time-independent pharmacokinetics. The pharmacokinetic impact of dexamethasone and sex covariates is probably limited given the moderate to large interindividual pharmacokinetic variability of trabectedin. The antiemetic and hepatoprotective effects are still a valid rationale to recommend dexamethasone as a supportive treatment for trabectedin.     

Pharmacokinetics of primaquine in man. II. Comparison of acute vs chronic dosage in Thai subjects.

We have investigated the pharmacokinetics of primaquine after acute and chronic administration of the drug to five healthy Thai volunteers. After acute dosage (15 mg p.o.) mean (+/- s.d.) peak plasma concentrations of 65.0 +/- 34.7 ng ml-1 were achieved within 2 +/- 1h. Thereafter plasma drug concentrations declined monoexponentially with a mean elimination half life of 4.4 +/- 1.4 h. The mean (+/- s.d.) oral clearance was 37.6 +/- 15.5 1 h-1. These values are in broad agreement with values obtained in healthy Caucasians after administration of an equivalent dose of primaquine. Repeated dosing with primaquine had no effect on the mean pharmacokinetic parameters calculated for this drug. In contrast, individual pharmacokinetic parameters for some subjects exhibited gross and unpredictable changes after chronic dosage. The carboxylic acid metabolite of primaquine accumulated in plasma after repeated dosing such that by day 14 of chronic dosing the mean AUC (0,24) for this metabolite was 74% greater than that obtained after acute administration of primaquine.     

Clinical pharmacology of valpromide

Valpromide has been used as an antiepileptic and antipsychotic drug for the past 25 years in several European countries. Unlike its corresponding acid, valproic acid, whose pharmacokinetics have been quite extensively reviewed, and despite years of clinical use, it appears that no reviews have been written on the pharmacokinetics of valpromide. This article summarises and analyses its pharmacokinetics from various aspects, with a special emphasis on the differences between valpromide and valproic acid. In humans, valpromide is a prodrug of valproic acid. Despite their chemical similarity, the pharmacokinetics of the 2 drugs in humans are quite distinct. Compared with valproic acid. valpromide has a very short half-life (mean +/- SD: 0.84 +/- 0.33h; n = 6), a high clearance value (70 +/- 31 L/h) and a large volume of distribution (75 +/- 13L). Despite its rapid biotransformation to valproic acid, valpromide has some special characteristics, such as its inhibition of the enzyme epoxide hydrolase which is responsible for the metabolism of carbamazepine-10, 11-epoxide. This review discusses the pharmacokinetics of valpromide, the interactions between it and other drugs such as carbamazepine and amitriptyline, and its antiepileptic and antipsychotic activities.     

Valproic acid in dementia: does an optimal dose exist?

Valproic acid is widely used in the treatment of behavioral disturbances in patients with dementia; however, there is uncertainty about its dosing and studies have reported mixed findings. The current article examines published trials of valproic acid in the treatment of patients with dementia to identify whether an optimal dosing strategy exists. Secondarily, valproic acid dosing from published studies is compared with a real-world 5-year sample of valproic acid prescribing. Twenty studies met selection criteria and were included in the review. Based primarily on uncontrolled trials and the current retrospective study, valproic acid serum levels between 40 and 60 mcg/mL and relatively low doses (ie, 7-12 mg/kg per d) are associated with improvements in agitation in some patients with dementia. At the same time, similar valproic acid levels produced no significant behavioral improvements in most placebo-controlled studies and led to substantial side effects in some patients. Considerable trial design differences exist between controlled and uncontrolled trials. Overall, valproic acid appears to have limited efficacy as monotherapy in many patients with dementia. Its optimal role may be in combination with other psychotropics as a treatment of agitation associated with dementia.     

Unbound plasma phenytoin concentrations measured using enzyme immunoassay technique on the cobas MIRA analyser--in vivo effect of valproic acid.

This communication describes a modification of the total plasma phenytoin enzyme immunoassay technique (EMIT) run on the Cobas MIRA analyser that allows quantitation of unbound phenytoin concentrations in human plasma for routine therapeutic drug monitoring (TDM) purposes. An application of this method is also presented to consider the previously described protein binding drug interaction with concomitantly administered valproic acid in patients with epilepsy. The coefficients of variation for the unbound phenytoin assay ranged from 7.5 to 9.6% and the assay had a reproducibility and accuracy similar to the total phenytoin assay, acceptable for routine TDM. Phenytoin protein binding was linear over a range of total plasma concentrations of 3-65 mg/L. Patients also receiving valproic acid (nine patients, 105 specimens) had a significantly (p less than 0.0001) greater mean +/- SD unbound phenytoin fraction (13.3 +/- 3.1%) compared to nine patients (110 specimens) not receiving valproic acid (8.3 +/- 1.6%). There was also a significant correlation (p less than 0.001) between plasma valproic acid concentration and unbound phenytoin fraction, which resulted in greater intrasubject variability in phenytoin protein binding.