Monotherapy or polytherapy for epilepsy?

Although anticonvulsant polytherapy has been widely and traditionally used in the treatment of epilepsy, there is little evidence of its advantages over monotherapy. It does, however, lead to problems of chronic toxicity, drug interactions, failure to evaluate individual drugs, and sometimes exacerbation of seizures. There are many causes of polytherapy which could be avoided by more careful monitoring and supervision of therapy. Studies in new, previously untreated referrals suggest there is considerable potential for monotherapy. In the event of failure of optimum monotherapy, the value of polytherapy is not yet clear. In chronic patients on polytherapy there may be scope for careful rationalization to two or sometimes one drug, with reduction in chronic toxicity and sometimes improved seizure control. Reduction of therapy, however, may be impossible or hazardous due to withdrawal seizures. Even after successful reduction, seizure control is much less satisfactory than in new referrals. It is easier to avoid polytherapy than to reduce it. There is a need to define more carefully the limits of effective anticonvulsant therapy.

Topical clonazepam in stomatodynia: a randomised placebo-controlled study

Stomatodynia is characterised by a spontaneous burning pain in the oral mucosa without known cause or recognised treatment. The purpose of this double-blind, randomised, multicentre parallel group study was to evaluate the efficacy of the topical use of clonazepam. Forty-eight patients (4 men and 44 women, aged 65+/-2.1 years) were included, of whom 41 completed the study. The patients were instructed to suck a tablet of 1 mg of either clonazepam or placebo and hold their saliva near the pain sites in the mouth without swallowing for 3 min and then to spit. This protocol was repeated three times a day for 14 days. The intensity was evaluated by a 11-point numerical scale before the first administration and then after 14 days. Two weeks after the beginning of treatment, the decrease in pain scores was 2.4+/-0.6 and 0.6+/-0.4 in the clonazepam and placebo group, respectively (P = 0.014). Similar effects were obtained in an intent-to-treat analysis (P = 0.027). The blood concentration of clonazepam was similar whether it was measured 14 days after sucking a tablet three times a day or during the 5 h that followed sucking a single tablet (n = 5). It is hypothesised that clonazepam acts locally to disrupt the mechanism(s) underlying stomatodynia.

Significant dissociation of brain and plasma kinetics with antipsychotics

Current dosing regimens of psychotropic drugs are based on plasma kinetic considerations, although it is unclear whether plasma levels faithfully reflect brain kinetics of drugs.(1,2) To examine this, we compared the kinetics of plasma levels of two widely used antipsychotics, olanzapine and risperidone, vs the time course of their effects in the brain. We used positron emission tomography (PET) and [(11)C]-labeled ligands to quantify striatal and extra-striatal dopamine-2 (D(2)), and cortical serotonin-2A (5-HT(2A)) receptor occupancy in healthy subjects after a single dose, and in patients chronically treated for psychosis. We found a significant dissociation of brain and plasma kinetics. Mean plasma elimination half-lives of single doses of olanzapine and risperidone were 24.2 and 10.3 h, respectively, whereas it took on average 75.2 h with olanzapine, and 66.6 h with risperidone to decline to 50% of their peak striatal D(2) receptor occupancy. We found similar discrepancies between the time course of plasma levels and extra-striatal D(2) as well as 5-HT(2A) receptor occupancy. Our results question the current reliance on plasma kinetics as the main basis for dosing regimens of antipsychotics. Studies of brain kinetics may provide a sounder basis for determining dosing schedules of psychotropic medications.

Intranasal Mucoadhesive Microemulsions of Clonazepam: Preliminary Studies on Brain Targeting

The aim of this investigation was to prepare clonazepam microemulsions (CME) for rapid drug delivery to the brain to treat acute status epileptic patients and to characterize and evaluate the performance of CME in vitro and in vivo in rats. The CME were prepared by the titration method and were characterized for globule size and size distribution, zeta potential, and drug content. CME was radiolabeled with (99m)Tc (technetium) and biodistribution of drug in the brain was studied in Swiss albino rats after intranasal and intravenous administrations. Brain scintigraphy imaging in rabbits was also performed to ascertain the uptake of the drug into the brain. Pre and postCME formulation treated human nasal mucosa was subjected to transmission electron microscopy to investigate the mechanism of drug uptake across the nasal mucosa. CME were transparent and stable with mean globule size of 15 +/- 10 nm and zeta potential of -30 mV to -40 mV. (99m)Tc-labeled clonazepam solution ((99m)Tc CS)/ clonazepam microemulsion (CME)/clonazepam mucoadhesive microemulsion (CMME) were found to be stable and suitable for in vivo studies. Brain/blood uptake ratios at 0.50 hour (h) following intranasal CMME, CME, clonazepam solution (CS), and intravenous CME administrations were found to be 0.67, 0.50, 0.48, and 0.13, respectively indicating more effective targeting with intranasal administration and best targeting of the brain with intranasal CMME. Brain/blood ratio at all sampling points up to 8 h following intranasal administration of CMME compared to intravenous was found to be twofold higher indicating larger extent of distribution of the drug in brain. Rabbit brain scintigraphy also showed higher intranasal uptake of the drug into the brain. Transmission electron microscopy revealed significant accretion of CMME within interstitial spaces and paracellular mode of transport due to stretching of the tight junctions present in the nasal mucosa. This investigation demonstrates a more rapid and larger extent of transport of clonazepam into the rat brain with intranasal CMME, which may prove useful in treating acute status epileptics.

Presence of peripheral-type benzodiazepine binding sites on human erythrocyte membranes

A nanomolar affinity peripheral-type benzodiazepine binding site is described in human erythrocyte membranes. [3H]PK 11195 is displaced from this binding site by unlabeled drugs with the rank order PK 11195 greater than Ro 5-4864 greater than flunitrazepam much greater than clonazepam. Neither GABA nor a non-hydrolyzable analog of GTP have an effect on binding parameters. These data provide evidence that a peripheral-type benzodiazepine binding site, pharmacologically similar to the intracellular binding site described in other tissues, is present in the plasma membrane of human erythrocytes.

Pharmacokinetics and side-effects of clonazepam and its 7-amino-metabolite in man

Clonazepam (CNP) and its principal metabolite in plasma, 7-amino-CNP (ACNP), have been investigated in a prospective study of 27 newly diagnosed epileptics and correlated with specified side-effects. At a daily dose of 6 mg, the average plasma levels of both substances were about 50ng/ml, and individual values ranged from 30 to about 80 ng/ml. There was a linear correlation between changes in dose and the resulting plasma levels, which indicates first order elimination kinetics. Side-effects were frequent, but neither their severity nor their occurrence could be related to plasma levels or to the rate of increase in plasma concentration of the drug. Three out of five patients who developed serious dysphoria had significantly high CNP levels. The concentration of ACNP was considerably increased in four patients who subsequently suffered from withdrawal symptoms. Drug interaction with diphenylhydantoin, i.e. decreased CNP level, was observed in all five patients who received both compounds. In general it is not yet possible to define an upper limit for the plasma levels of CNP and ACNP at which toxicity occurs. In patients treated with conventional doses of CNP, measurement of plasma concentration is not required, except in special circumstances, because of the lack of correlation between plasma level and side-effects.

Time-course of interaction between carbamazepine and clonazepam in normal man

The applicability of a pharmacokinetic model for drug interactions by enzyme induction was tested by chronic dosing situation using carbamazepine (Tegretol) as the inducer and clonazepam (Clonopin) as the drug affected. Seven healthy subjects received one 1.0 mg clonazepam tablet once a day for 29 days and one 200 mg carbamazepine tablet once a day from days 8 to 29. Plasma levels of clonazepam were measured by electron-capture gas-liquid chromatography and those of carbamazepine and its epoxide metabolite by gas chromatographic-chemical ionization-mass spectrometry. Clonazepam plasma levels reached an initial steady-state by day 7 and declined to a lower steady-state over 5 to 15 days after additions of carbamazepine. The decrease in clonazepam levels ranged between 19% and 37%. Autoinduction of carbamazepine metabolism was also evident. Urinary excretion of D-glucaric acid increased 2- to 4-fold following carbamazepine administration (p less than 0.005). This increase provided additional evidence that the present interaction was due to enzyme induction. Experimental clonazepam levels were fitted to an induction pharmacokinetic model for multiple dosing with an exponentially increasing clearance. Induced half-lives of clonazepam (mean = 22.5 +/- 11.5 hr) were shorter (p less than 0.005) than control values (32.1 +/- 16.6 hr). Apparent enzyme(s) turnover half-lives ranged between 1 and 6 days.

Effects of the anticonvulsant benzodiazepine clonazepam on event-related brain potentials in humans

The effects of the benzodiazepine clonazepam (a drug used as anticonvulsant) on event-related brain potentials were investigated in healthy human subjects. Thirty-six male student volunteers (mean age 30 years) received clonazepam or a placebo in a double-blind setting. VEPs (visual evoked potentials) were obtained from the standard checkerboard reversal procedure; AEPs (auditory evoked potentials) and slow cortical potentials (CNV) were measured during a 2-stimulus reaction time paradigm, in which the quality of the acoustic S1 signalled whether the acoustic S2 would follow after 2 sec or after 6 sec. Each S2 requested a speeded button press. Compared to placebo, clonazepam significantly reduced P100 amplitude of the VEP and the amplitudes of the AEP components N1 and P3. On the other hand, clonazepam boosted the development of a distinct N2 which was not apparent in placebo subjects. The CNV was significantly reduced and reaction time increased under clonazepam compared to placebo. Specific versus non-specific damping effects of the benzodiazepine are discussed, comparing the present result with the pattern of ERP effects of the anticonvulsant carbamazepine that had been obtained using the same experimental paradigms.

Pharmacokinetics of the anticonvulsant drug clonazepam evaluated from single oral and intravenous doses and by repeated oral administration

Eight healthy volunteers were given single i.v. and oral doses of clonazepam (2 mg). The disposition curves after i.v. administration showed a biexponential decline and the data were applied to a two-compartment open model. The volume of distribution ((Vd)beta) ranged between 1.5 and 4.4 l/kg and the plasma half-life (t1/2) between 19 and 60 hours. Absorption after oral administration was fast, with peak plasma concentrations within 4 hours in all subjects. Five of the subjects received repeated oral doses of clonazepam 0.5 mg bid for 15 days. The plasma level during steady state (estimated as Cmin within the dose interval) could be predicted from the constants A, B, alpha and beta obtained in the single dose study with a coefficient of variation of 6%. The plasma half-lives after cessation of the subchronic dosing were of the same magnitude as after single doses.

The effects of clonazepam and vigabatrin in hyperekplexia

Hyperekplexia is an autosomal dominant disorder caused by a point mutation in the alpha1 subunit of the glycine receptor, characterized by excessive startle responses followed by temporary generalized stiffness. Clonazepam, effective in open case studies, potentiates, through unknown mechanisms, the neurotransmitter gamma-aminobutyric acid (GABA). Vigabatrin increases GABA by inhibition of the GABA catabolic enzyme GABA-transaminase. Effects of clonazepam (1 mg for 1 day) and vigabatrin (1000 mg per day for 5 days) were investigated in a double-blind placebo-controlled cross-over study in 4 patients with hyperekplexia. The pharmacodynamic parameters were startle reflexes, studied 3 times during the day. At each time, 2 trains of 10 auditive stimuli (113 dB) were given at intervals of 10 and 60 s. Startle movements were quantified with summed areas of EMG-bursts of the orbicularis oculi, sternocleidomastoid, biceps and thenar muscles. The degrees of stiffness and drowsiness were quantified with visual analogue scores (VAS) 10 times during the day, by both the patient and the observer. Clonazepam, but not vigabatrin, reduced startle activity significantly in both paradigms. The degree of stiffness and drowsiness was not significantly influenced by either drug.

Assay of underivatized intrazepam and clonazepam in plasma by capillary gas chromatography applied to pharmacokinetic and bioavailability studies in humans

The assay procedure of underivatized, intact nitrazepam and clonazepam in human plasma is described, using gas chromatography with a support-coated open tubular column (OV-17), a solid injection system and electron-capture detection. Clonazepam is used as a internal standard in the assay of nitrazepam and vice versa. Linear calibration curves after a single extraction step were obtained in the concentration range 10--100 ng/ml plasma, with standard deviations less than 4.9%. The sensitivity limit of the method is about 1 ng/ml plasma for both drugs. The method was applied to pharmacokinetic and bioavailability studies of nitrazepam in humans. Seven healthy volunteers received two nitrazepam-containing tablet preparations (5 mg) and plasma concentrations were determined regularly from 15 min to 80 h following drug administration. The mean elimination half-life of nitrazepam was 27 h (range 13-34 h). Considerable intra-individual differences in peak level times between the two preparations were observed, whereas the extent of bioavailability was rather similar.

Determination of antiepileptic drugs

The present paper reviews gas and liquid chromatographic methods for the determination of the most commonly monitored antiepileptic drugs: phenobarbital, phenytoin, carbamazepine, primidone, ethosuximide, valproic acid and clonazepam along with a new compound, progabide. The individual classes of drugs are first treated separately to highlight specific aspects of their quantification, and this is followed by an overview of those methods permitting the concomitant analysis of two or more antiepileptic compounds. Sample preparation techniques as well as comparisons between chromatographic and other techniques are treated more fully in separate sections.

Simultaneous determination of twelve benzodiazepines in human serum using a new reversed-phase chromatographic column on a 2-microns porous microspherical silica gel

A high-performance liquid chromatographic method has been developed for the simultaneous analysis of twelve frequently used benzodiazepines (BZPs) (bromazepam, clonazepam, chlordiazepoxide, estazolam, etizolam, flutazoram, haloxazolam, lorazepam, nitrazepam, oxazolam, triazolam and diazepam, internal standard) by using commercially available 2 or 5 microns particle size reversed-phase columns and a microflow cell-equipped ultraviolet detector. The separation was achieved using a C18 reversed-phase column (condition 1: 100 x 4.6 mm I.D., particle size 2 microns, TSK gel Super-ODS: conditon 2: 100 x 4.6 mm I.D., particle size 5 microns, Hypersil ODS-C18). The mobile phase was composed of methanol-5 mM NaH2PO4 (pH 6) (45:55, v/v), and the flow-rate was 0.65 ml/min (condition 1 and 2). The absorbance of the eluent was monitored at 254 nm. Retention times under condition 1 were shorter than those of condition 2. When the twelve benzodiazepines were determined, sensitivity and limits of quantification were about four to ten times better under condition 1 than under condition 2. The rate of recovery and linearity in condition 1 were approximately the same as those in condition 2. These results show that a new ODS filler with a particle size of 2 microns was more sensitive, provided better separation and was more rapid than that with conventional ODS filler.

Stability of benzodiazepines in whole blood samples stored at varying temperatures

Study has been undertaken to determine the stability of four benzodiazepines: clonazepam, midazolam, flunitrazepam and oxazepam in whole blood samples. Spiked blood was stored at four different temperatures (room temperature, 4 degrees C, -20 degrees C and -80 degrees C) and analysed at selected times during one year. Determination was performed on the first, third and seventh day during the first week, then once a week for three weeks, once every two weeks for four weeks, then once a month for 4 months and finally, once every 2 months. Extraction was performed using liquid-liquid extraction with 1-chlorobutane, while quantification was carried out using high performance liquid chromatography equipped with a photodiode-array ultraviolet detector. At room temperature, the concentration of all benzodiazepines decreased over one year to 100 and 70% for low and high concentrations, respectively. At 4 degrees C, the decrease was between 90 and 100% for low concentrations and between 50 and 80% for high concentrations. At -20 degrees C, the measured decrease was between 10 and 20% for high and low concentrations, respectively. At -80 degrees C, the measured loss was not significant at high concentration except for midazolam. However, at low concentration the determined decrease was between 5 and 12%. The data collected suggests that quantitative results concerning long-term stored samples should be interpreted with caution in forensic cases. Further investigations concerning the stability of drugs in whole blood or other biological samples, additional methods of identification and determination as well as the establishment of optimal storage conditions should be undertaken in forensic cases.

Determination of clonazepam in human plasma by gas chromatography--negative ion chemical ionization mass spectrometry

Our previously reported gas chromatographic--mass spectrometric assay for clonazepam using positive ion chemical ionization has been modified to employ negative ion chemical ionization. The sensitivity using this technique (less than 0.1 ng/ml) is approximately twenty times better than the positive ion chemical ionization procedure with similar precision. The method was used to determine the clonazepam plasma concentration in one human for 96 h following a single 2-mg dose of clonazepam.

Detection of benzodiazepine receptor occupancy in the human brain by positron emission tomography

Benzodiazepine receptor occupancy in the brain following oral administration of clonazepam (CZP) with a dose of 30 micrograms/kg in six healthy young men and a further dose of 50 micrograms/kg in one of the subjects was estimated by carbon-11 labeled Ro15-1788 and positron emission tomography (PET). The effects of CZP on the latency of auditory event-related potentials (P300) were also studied. Overall brain 11C uptake was depressed and the % inhibition of 11C uptake in the gray matter of the brain at 30 min after [11C]Ro15-1788 injection was 15.3-23.5% (mean, n = 6) following 30 micrograms/kg CZP when compared with that in the control experiment without any previous treatment. The 11C uptake in the cerebral cortex in the subject who received both doses decreased in a dose-related manner after 30 micrograms/kg and 50 micrograms/kg CZP. The P300 latency was prolonged significantly by 30 micrograms/kg CZP [31.6 +/- 16.3 ms (mean +/- SD, n = 6), P less than 0.05]. The P300 latency in the same subject was prolonged in a dose-related manner by 30 micrograms/kg and 50 micrograms/kg CZP. The technique using [11C]Ro15-1788 and PET permits comparison of the pharmacological effects with the percentage of receptor sites which benzodiazepines occupy in the human brain. P300 also seems to be useful to investigate the pharmacological effects of benzodiazepines.

Heterogeneity of cerebral capillary flow in man and its consequences for estimation of blood-brain barrier permeability

Blood-brain barrier permeability studies made in man using the indicator dilution method revealed that the extraction of the test substance increases during the upslope of the venous (outflow) dilution curve. The present study aimed to obviate the possibility that this could result from intravascular phenomena, such as interlaminar diffusion (the result of differences in molecular size) and erythrocyte carriage. Several reference substances were employed for the determination of the extraction in order that careful correction could be made for differences in intravascular behavior of the test and reference substance. The test substances studied were D-glucose, L-phenylalanine, water, propranolol, and benzodiazepines, representing both carrier-transported and lipophilic substances. In-diethylenetriamine pentaacetic acid, Na+, Cl-, L-glucose, and L-lysine were employed as reference substances. For all the substances tested, and after correction for intravascular phenomena, the extractions were found to increase during the initial part of the dilution curve. This increasing extraction can be ascribed to heterogeneity of the cerebral circulation; the higher extraction corresponds to longer contact with the blood-brain barrier and indicates a longer transit time. Signs of heterogeneity were also present when blood flow was elevated above normal. Any influence that heterogeneity might have on the mean extraction value can be minimized by using an appropriate calculation of the extraction of the test substance.

Intravenous clonazepam in the treatment of status epilepticus in children

Seventeen children (age range 2 weeks to 15 years) who developed status epilepticus were treated with intravenous clonazepam (Rivotril). Status was promptly stopped in each instance with between 0.25 to 0.75 mg clonazepam. In 6 children who had a further episode of status epilepticus, diazepam 0.25 to 0.75 mg/kg was given. A comparison of their relative efficacy showed that in each case clonazepam had a more prolonged action. No serious side effects occurred and it was felt that i.v. clonazepam, because of its more prolonged action, could be the drug of choice in controlling status epilepticus.

Respiratory and sedative effects of clobazam and clonazepam in volunteers

1. The respiratory and psychomotor effects of two benzodiazepines used mainly as anticonvulsants were compared in healthy volunteers, using a double-blind placebo controlled design. 2. Clobazam (10 and 20 mg) produced significantly fewer psychomotor side effects than clonazepam (0.5 and 1 mg). Neither drug at either dose affected the ventilatory response to CO2. 3. Although clonazepam produced significant effects on psychomotor performance, these did not correlate with plasma drug concentration. 4. Our studies provide further evidence that at the doses chosen clobazam is considerably less sedating than clonazepam. Further investigation is required into the tolerance profile of both drugs in patients.

High-performance liquid chromatographic procedure for the measurement of nitrobenzodiazepines and their 7-amino metabolites in blood

A simple and sensitive HPLC method is described for the determination of the nitrobenzodiazepines, nitrazepam, flunitrazepam and clonazepam and their respective 7-amino metabolites in post-mortem blood. Using a single-step extraction the nitrobenzodiazepines were recovered from 0.5 ml of blood using butyl chloride. The solvent was evaporated to dryness and the reconstituted residue injected onto an HPLC system. Separation was achieved using a phenyl-bonded reversed-phase column with an acetonitrile-phosphate buffer mobile phase. Ultraviolet detection (240 nm) was used for quantitation. A linear response was observed between 0.01 and 0.60 mg/l. Assay precision between and within assays was less than 20% for all analytes. The limits of detection ranged from 0.001 to 0.008 mg/l with a limit of quantitation of 0.01 mg/l for all analytes.

Quantitative determination of clonazepam in plasma by gas chromatography-negative ion chemical ionization mass spectrometry

A gas chromatographic-negative ion chemical ionization mass spectrometric (GC-NCI-MS) method for the quantitative analysis of clonazepam in human plasma is described. Clonazepam (M(r) = 315) was derivatized by N,O-bis-(trimethylsilyl)trifluoroacetamide with 1% trimethylchlorosilane. A pre-conditioning procedure involving injection of a silyl-8 and ethyl acetate extraction solution from plasma reduces the interaction between clonazepam-TMS and the analytical system. The routine limit of quantification was set to be 0.25 ng/ml with an injection volume of 2 microliters and a sample volume of 1 ml. The signal-to-noise ratio was greater than five. The detection limit for clonazepam can reach 0.1 ng/ml. The isotope clonazepam-d5 was used as the internal standard.

2-Chloroadenosine, a preferential agonist of adenosine A1 receptors, enhances the anticonvulsant activity of carbamazepine and clonazepam in mice

2-Chloroadenosine (0.25-1 mg/kg) significantly raised the threshold for electroconvulsions in mice. This preferential adenosine A(1) receptor agonist (at 0.125 mg/kg) significantly potentiated the protective activity of carbamazepine against maximal electroshock-induced seizures in mice. 2-Chloroadenosine (1 mg/kg) showed also anticonvulsive efficacy against pentylenetetrazol-evoked seizures, raising the CD(50) value for pentylenetetrazol from 77.2 to 93.7 mg/kg. The drug (at 0.5 mg/kg) significantly enhanced the protective action of clonazepam in this test, decreasing its ED(50) value from 0.033 to 0.011 mg/kg. Moreover, aminophylline, a non-selective adenosine receptor antagonist (5 mg/kg), and 8-cyclopentyl-1,3-dimethylxanthine (8-CPX), a selective A(1) adenosine receptor antagonist (5 mg/kg) reversed the 2-chloroadenosine (0.125 mg/kg)-induced enhancement of the protective activity of carbamazepine and clonazepam. 2-Chloroadenosine administered alone or combined with antiepileptic drugs, caused neither motor nor long-term memory impairment. Finally, the adenosine A(1) agonist did not change the free plasma concentration of antiepileptics, so a pharmacokinetic factor is not probable. Summing up, 2-chloroadenosine potentiated the protective activity of both carbamazepine and clonazepam, which seems to be associated with the enhancement of purinergic transmission mediated through adenosine A(1) receptors.

Development of a rapid RP–HPLC method for the determination of clonazepam in human plasma

A rapid and sensitive high-performance liquid chromatography method with UV detection was developed for the determination of clonazepam in human plasma using 3-methylclonazepam, as internal standard. A one-step extraction of both compounds was performed with a mixture of hexane/ethyl acetate (90:10, v/v). The HPLC analysis was carried out on a Nova Pak((R)) C(18) reversed-phase column with a mobile phase of acetonitrile-0.01 M sodium acetate adjusted to pH 7 with dilute acetic acid (40:60, v/v). A linear response was observed over the concentration range 5-100 ng/mL. Intra- and inter-day assay precision and accuracy fulfilled the international requirements. The lower limit of quantification was 5 ng/mL without interference of endogenous components. For analytical purpose, the stability of clonazepam in bidistilled water and plasma has been studied. A rapid degradation was noticed when clonazepam was stored in bidistilled water at the daylight following a first-order kinetic rate with a 87 min half life whereas no significant degradation was observed in plasma. This method was applied to measure plasma concentrations of clonazepam either in patients receiving therapeutic doses or in poisoning cases.