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

Pharmacokinetics of oral clonazepam in growing commercial pigs (Sus scrofa domestica)

Clonazepam causes sedation and psychomotor impairment in people. Due to similarities between people and swine in response to benzodiazepines, clonazepam may represent a viable option to produce mild-to-moderate tranquillization in pigs. The objective of this study was to determine the pharmacokinetic profile of a single oral dose (0.5 mg/kg) of clonazepam in eight healthy, growing commercial cross pigs. Serial plasma samples were collected at baseline and up to 96 h after administration. Plasma concentrations were quantified using reverse-phase high-performance liquid chromatography, and compartment models were fit to time-concentration data. A one-compartment first-order model best fits the data. Maximum plasma concentration was 99.5 ng/mL, and time to maximum concentration was 3.4 h. Elimination half-life was 7.3 h, mean residence time 7.4 h, and apparent volume of distribution 5.7 L/kg. Achieved plasma concentrations exceeded those associated with psychomotor impairment in people although pharmacodynamic effects have not been investigated in pigs. A simulated oral regimen consisting of 0.35 mg/kg administered every 8 h to pigs would achieve plasma concentrations above 32 ng/mL which are shown to produce psychomotor impairment in people. Further studies to test the clinical efficacy of these dosages in commercial and miniature pigs are warranted.

Impact of using Sarcophaga (Liopygia) argyrostoma (Robineau-Desvoidy, 1830) as a toxicological sample in detecting clonazepam for forensic investigation

Background

Sarcophagidae along with Calliphoridae (superfamily Oestroidea) were known as important colonizers of cadavers and could be used to estimate the postmortem interval (PMI), through tracking the flies colonizing pattern and/or monitoring their growth rates on cadavers. Many previous researches discussed the impact of toxins in decomposing corpses, on the developmental stages of insects, which would affect the accuracy of PMI estimation. Clonazepam belongs to the benzodiazepines, and it is one of the most routinely used drugs to control humans’ seizures. The current study aimed to investigate the effect of clonazepam on the developmental stages of Sarcophaga argyrostoma, one of the most widespread Sarcophagidae in Giza Governorate. Also, we investigate the ability of these developmental stages to detect the drug.

Results

The current study used different concentrations of clonazepam (25, 50, and 100 mg/ml) as an in vitro application of the flesh fly S. argyrostoma. The drug has affected significantly the morphological measurements (weight, length, and width) of the different developmental stages, especially in the highest concentration (100 mg/ml). Quantitative and qualitative analyses were applied, by using high-performance liquid chromatography-mass spectrometry (HPLC–MS) and protein carbonyls amount respectively, to detect clonazepam in the second, early third, and late third larval instars and prepupa of S. argyrostoma. The results showed that the relationship between the concentration of the drug and its detection in the same developing instar is interdependent, using HPLC–MS. However, the drug faded from instar to the following one and transformed to its metabolite form. Measuring the protein carbonyls amount (OD/mg protein/min) revealed an elevation in the macromolecules damage, compared to the control groups, in almost all treated groups.

Conclusions

The current data suggested that clonazepam has oxidative damage in S. argyrostoma. While HPLC–MS was efficient in measuring the concentration of the drug in the insect, protein carbonyls analysis was a time- and cost-saving method and could be used to detect the drug in insects qualitatively.

Graphical abstract

Clonazepam: Indications, Side Effects, and Potential for Nonmedical Use

After participating in this activity, learners should be better able to:• Assess the misuse potential of clonazepam• Characterize the nonmedical use of clonazepam• Identify the health problems associated with long-term use of clonazepam ABSTRACT: Clonazepam, a benzodiazepine, is commonly used in treating various conditions, including anxiety disorders and epileptic seizures. Due to its low price and easy availability, however, it has become a commonly misused medication, both in medical and recreational contexts. In this review, we aim to highlight the behavioral and pharmacological aspects of clonazepam and its history following its approval for human use. We examine the circumstances commonly associated with the nonmedical use of clonazepam and raise points of particular concern. Clonazepam, alone or in combination with other psychoactive substances, can lead to unwanted effects on health, such as motor and cognitive impairment, sleep disorders, and aggravation of mood and anxiety disorders. Prolonged use of clonazepam may lead to physical dependence and tolerance. There is therefore a need to find safer therapeutic alternatives for treating seizures and anxiety disorders. Greater awareness of its frequent nonmedical use is also needed to achieve safer overall use of this medication.

Dépendance aux benzodiazépines et syndrome de sevrage. Revue de la littérature

Ce travail rapporte les résultats d'une revue de la littérature mondiale (247 publications), concernant les syndromes de sevrage et la dépendance aux benzodiazépines, réalisant ainsi une mise à jour de l'tude eifectuée par Marks (1986) pour la période 1961-1984. Quatre-vingts cas publiés individuellement et 269 cas publiés par séries ont été recensés pour la période 1984-1988 (janvier), soit en ajoutant ces chiffres à ceux de Marks (1986): 928 cas individuels et 969 cas publiés par séries, soit encore au total: 1 897 cas publiés. L'analyse détaillée de ces cas, leur signification en termes de risque sont rapportées et discutées.

Au plan pratique, il apparaît que toutes les benzodiazépines peuvent être à l'origine de syndrome de sevrage, y compris celles à demi-vie courte. Le risque de dépendance est d'autant plus important que la durée de la prescription et les posologies employées sont élevées. Il est donc nécessaire de préconiser un sevragesystématiquementprogressif, quelles que soient la molécule et la durée de prescription, d'éviter l'administration aux sujets ayant des antécédents d'abus de toxiques ou de médicaments, de réserver l'usage à long terme aux pathologies anxieuses chroniques, en réévaluant régulièrement l'indication, de prescrire le moins longtemps possible et à la dose la plus faible possible dans tous les autres cas, en faisant varier la posologie selon l'évolution de l'intensité des symptômes.

A randomized, single-dose, two-sequence, two-period, crossover study to assess the bioequivalence between two formulations of clonazepam tablet in healthy subjects

Clonazepam is a benzodiazepine commonly prescribed to treat panic disorder, epilepsy, anxiety, depression and certain types of seizures. This study aimed to evaluate the bioequivalence between two formulations of clonazepam tablets in order to meet regulatory requirements for marketing in Colombia and other countries in Latin America. An open-label, randomized, single-dose, two-period, two-sequence, two-treatment crossover study was conducted in 36 healthy subjects of both genders. Subjects received a single dose of clonazepam 2 mg test tablet (Sanofi-Aventis de Colombia S.A.) and reference product (Rivotril®, Produtos Roche Químicos e Farmacêuticos S.A.) under fasting conditions according to a randomly assigned order with a 21-day washout period. Serial blood samples were collected up to 96 h post-dose. Plasma concentrations of clonazepam were obtained by a validated liquid chromatography-tandem mass spectrometry method. Pharmacokinetic parameters were calculated using non-compartmental methods. A total of 36 healthy subjects were enrolled and 31 of them completed the study. Twenty-nine adverse events were reported (11 events with test product versus 18 events with reference product). There were no serious adverse events during the study. Geometric mean ratios (90% confidence intervals) for C_max and AUC_0-96h were 103.28% (98.10-108.64) and 102.50% (99.87-105.19), respectively. The test formulation of clonazepam 2 mg tablet manufactured by Sanofi-Aventis de Colombia S.A. was considered bioequivalent to reference product Rivotril^® (Produtos Roche Químicos e Farmacêuticos S.A.) according to regulatory requirements. Both formulations were safe and well-tolerated during the study.

Prolonged clonazepam-induced withdrawal symptoms in an NAT2 ultraslow acetylator

Clonazepam undergoes nitroreduction to 7-amino-clonazepam via CYP3A4/5, followed by acetylation to 7-acetamido-clonazepam via NAT2 enzyme. While no pharmacological activity is attributed to the metabolites of clonazepam, 7-amino-clonazepam has some affinity for the benzodiazepine receptor as a partial agonist for the gamma aminobutyric acid-A receptor and can compete with clonazepam. Interindividual variability in the incidence of adverse events in patients may, in part, be attributable to differences in clonazepam metabolism. Here, we report on a case of a 70-year-old Caucasian female with insomnia and difficulty weaning off long-term use of clonazepam suggesting that a slow acetylator phenotype contributing to patient's presentation. This hypothesis was confirmed by NAT2 gene sequencing. NAT2 genotyping may play a role in guiding clonazepam therapy.

Optimization of Clonazepam Therapy Adjusted to Patient's CYP3A Status and NAT2 Genotype

BACKGROUND

The shortcomings of clonazepam therapy include tolerance, withdrawal symptoms, and adverse effects such as drowsiness, dizziness, and confusion leading to increased risk of falls. Inter-individual variability in the incidence of adverse events in patients partly originates from the differences in clonazepam metabolism due to genetic and nongenetic factors.

METHODS

Since the prominent role in clonazepam nitro-reduction and acetylation of 7-amino-clonazepam is assigned to CYP3A and N-acetyl transferase 2 enzymes, respectively, the association between the patients' CYP3A status (CYP3A5 genotype, CYP3A4 expression) or N-acetyl transferase 2 acetylator phenotype and clonazepam metabolism (plasma concentrations of clonazepam and 7-amino-clonazepam) was evaluated in 98 psychiatric patients suffering from schizophrenia or bipolar disorders.

RESULTS

The patients' CYP3A4 expression was found to be the major determinant of clonazepam plasma concentrations normalized by the dose and bodyweight (1263.5±482.9 and 558.5±202.4ng/mL per mg/kg bodyweight in low and normal expressers, respectively, P<.0001). Consequently, the dose requirement for the therapeutic concentration of clonazepam was substantially lower in low-CYP3A4 expresser patients than in normal expressers (0.029±0.011 vs 0.058±0.024mg/kg bodyweight, P<.0001). Furthermore, significantly higher (about 2-fold) plasma concentration ratio of 7-amino-clonazepam and clonazepam was observed in the patients displaying normal CYP3A4 expression and slower N-acetylation than all the others.

CONCLUSION

Prospective assaying of CYP3A4 expression and N-acetyl transferase 2 acetylator phenotype can better identify the patients with higher risk of adverse reactions and can facilitate the improvement of personalized clonazepam therapy and withdrawal regimen.

Nutmeg poisonings: a retrospective review of 10 years experience from the Illinois Poison Center, 2001-2011

Nutmeg is a commonly consumed spice. The toxic effects of nutmeg have been purported to be due mainly to myristicin oil. Prior poison center series of nutmeg exposures show very few unintentional exposures of nutmeg to children younger than 13. Case series from these centers did not record drug exposures combined with nutmeg. This study is a review of Illinois Poison Center (IPC) data regarding nutmeg exposures from January of 2001 to December 2011. The goal of this study was to compare the Illinois data to the literature as well as look for current trends in nutmeg poisonings. The data were extracted using the code for hallucinogenic plants in the IPC database, and poisonings unrelated to nutmeg exposure were eliminated. Medical outcomes were noted as recorded. Thirty-two cases of nutmeg ingestion were reported. Of the 17 (53.1 %) unintentional exposures, 10 subjects (58.8 %) were under the age of 13. Four of the exposures in children under the age of 13 were ocular exposures. Fifteen exposures (46.9 %) were intentional exposures. Of these intentional exposures, five (33.3 %) were recorded to have combined drug intoxication. All of these were between the ages of 15 and 20. One patient with polypharmaceutical exposure required ventilatory support in the hospital. Our study shows an unexpected percentage of unintentional exposures in juveniles under the age of 13, out of the total exposures to nutmeg. Mixing of nutmeg with other drugs was seen and required more intervention in adolescents. More education about these two factors, i.e., nutmeg exposures as intentional polypharmacy in adolescents and unintentional exposures in young children, is advised.

Modern methods for analysis of antiepileptic drugs in the biological fluids for pharmacokinetics, bioequivalence and therapeutic drug monitoring

Epilepsy is a chronic disease occurring in approximately 1.0% of the world's population. About 30% of the epileptic patients treated with availably antiepileptic drugs (AEDs) continue to have seizures and are considered therapy-resistant or refractory patients. The ultimate goal for the use of AEDs is complete cessation of seizures without side effects. Because of a narrow therapeutic index of AEDs, a complete understanding of its clinical pharmacokinetics is essential for understanding of the pharmacodynamics of these drugs. These drug concentrations in biological fluids serve as surrogate markers and can be used to guide or target drug dosing. Because early studies demonstrated clinical and/or electroencephalographic correlations with serum concentrations of several AEDs, It has been almost 50 years since clinicians started using plasma concentrations of AEDs to optimize pharmacotherapy in patients with epilepsy. Therefore, validated analytical method for concentrations of AEDs in biological fluids is a necessity in order to explore pharmacokinetics, bioequivalence and TDM in various clinical situations. There are hundreds of published articles on the analysis of specific AEDs by a wide variety of analytical methods in biological samples have appears over the past decade. This review intends to provide an updated, concise overview on the modern method development for monitoring AEDs for pharmacokinetic studies, bioequivalence and therapeutic drug monitoring.

Four benzodiazepine radioimmunoassays are described, the most sensitive of which can detect sub-therapeutic levels of bromazepam, chlordiazepoxide, clobazam, demoxepam, desalkylflurazepam, desmethyldiazepam, diazepam, flunitrazepam, lorazepam, medazepam, nitrazepam, oxazepam, prazepam, temazepam and triazolam. The standard curve for diazepam has a concentration range of 0–2·5 ng ml The assay is particularly applicable to blood samples of forensic interest that may be haemolysed or decomposing. A 75 μI sample is required. The antiserum and [3 H]flunitrazepam used are commercially available

Four benzodiazepine radioimmunoassays are described, the most sensitive of which can detect sub-therapeutic levels of bromazepam, chlordiazepoxide, clobazam, demoxepam, desalkylflurazepam, desmethyldiazepam, diazepam, flunitrazepam, lorazepam, medazepam, nitrazepam, oxazepam, prazepam, temazepam and triazolam. The standard curve for diazepam has a concentration range of 0–2·5 ng ml The assay is particularly applicable to blood samples of forensic interest that may be haemolysed or decomposing. A 75 μI sample is required. The antiserum and [3 H]flunitrazepam used are commercially available.

[Therapeutic drug monitoring of clonazepam]

Clonazepam is a 1-4 benzodiazepine mainly used to treat epilepsy and epileptiform convulsion state. Rapidly absorbed after oral administration, it is widely distributed in the organism and is extensively converted in metabolites, poorly or not active, eliminated mainly in urine (70%) and feces. Elimination half-life is long, around 40 h. In adult and child, several studies showed a concentration-effect relation. Meanwhile, a large inter-individual variability in the dose-concentration relation was observed. A 15-50 microg/L range of clonazepam blood concentrations appears to be retained as an acceptable target to control a majority of epileptic seizures. The Therapeutic Drug Monitoring (TDM) of clonazepam can be considered as possibly useful in case of association with CYP450 inducers or inhibitors, suspicion of poor observance, or toxicity signs.

Pharmacoepidemiologic investigation of clonazepam relative clearance by mixed-effect modeling using routine clinical pharmacokinetic data in Japanese patients

The effects of drug-drug interactions on clonazepam clearance were examined through a retrospective analysis of serum concentration data from pediatric and adult epileptic patients. Patients received clonazepam as monotherapy or in combination with other antiepileptic drugs. A total of 259 serum clonazepam concentrations gathered from 137 patients were used in a population analysis of drug-drug interactions on clonazepam clearance. Data were analyzed using a nonlinear mixed-effects modeling (NONMEM) technique. The final model describing clonazepam clearance was CL = 152 x TBW(-0.181) x DIF, where CL is clearance (ml/kg/h), TBWis total body weight (kg), and DIF (drug interaction factor) is a scaling factor for concomitant medication with a value of 1 for patients on clonazepam monotherapy, 1.18 for those patients receiving concomitant administration of clonazepam and one antiepileptic drug (carbamazepine or valproic acid), and 2.12 x TBW(-0.119) for those patients receiving concomitant administration of clonazepam and more than two antiepileptic drugs. Clonazepam clearance decreased in a weight-related fashion in children, with minimal changes observed in adults. Concomitant administration of clonazepam and carbamazepine resulted in a 22% increase in clonazepam clearance. Concomitant administration of clonazepam and valproic acid resulted in a 12% increase in clonazepam clearance. Concomitant administration of clonazepam with two or more antiepileptic drugs resulted in a 23% to 75% increase in clonazepam clearance.

Influence of age and comedication on steady-state clonazepam serum level-dose ratios in Japanese epileptic patients

BACKGROUND

In antiepileptic drugs, the marked inter- and intrapatient variability of the level-dose ratio makes it difficult to predict serum concentrations from the administered per kg dose. It is therefore important to identify factors, such as age and comedication, that could contribute to this observed variability.

OBJECTIVE

To investigate the effect of age and comedication on clonazepam (CZP) level-dose (L/D) ratios.

METHOD

A retrospective evaluation of data from 137 epileptic patients who had received clonazepam.

RESULTS

The CZP L/D ratio increased slowly with age up to 15 years in patients on monotherapy. Associated antiepileptic therapy affected the CZP L/D ratio, which was significantly reduced in patients on polytherapy as compared to patients on monotherapy.

CONCLUSION

The study therefore suggests that routine monitoring of CZP serum levels is extremely useful, especially in the paediatric age group, and in patients who require associated antiepileptic medication.

Clonazepam disposition in pediatric patients

Plasma clonazepam (CZP) and its metabolite [7-aminoclonazepam (7ACZP) and 7-acetamidoclonazepam (7AACZP)] concentrations were measured during a single dosing interval in 10 pediatric epilepsy patients (2-18 years, 11-102 kg) who had been receiving CZP therapeutically from 2 weeks to 4 years. These concentrations were used to determine CZP and metabolite pharmacokinetics. With controlled dosing and postdose sample collection times, large variations were observed in calculated CZP nitroreduction rates [clearance (CL/F) ranged from 7 to 64 ml/h/kg] as well as 7ACZP acetylation rates (CL/F from 10 to 85 ml/h/kg). No 7AACZP (i.e., < 5 ng/ml) was detected by the methods used. Acetylation rates are known to be under genetic control. Further studies are needed to determine whether nitroreduction rates are also under genetic control and whether differences in either of these metabolic rates can explain intraindividual differences in clinical responses observed in CZP-treated patients.

Seizures with clonazepam: discontinuation and suggestions for safe discontinuation rates in children

Clinical characteristics of clonazepam (CZP) discontinuation seizures were clarified from 17 patients who developed seizure exacerbation after rapid discontinuation, including abrupt discontinuation, reduction, or replacement with nitrazepam (NZP). Safe discontinuation rates of CZP were estimated by comparing these patients with 23 patients without CZP discontinuation seizures. The seizures consisted of status epilepticus or frequent attacks of generalized tonic-clonic seizures (GTC) or non-GTC, and the first attack of GTC. Incidence did not differ significantly between CZP-effective cases and CZP-ineffective cases at discontinuation. The reasons for abrupt discontinuation included adverse effects, insufficient efficacy, difficulty in taking CZP owing to pneumonia, or carelessness of the doctors or the families. Seizure exacerbation occurred 1-6 days after CZP discontinuation. Most of the problems improved with readministration of the original or smaller dosages of CZP or of NZP in an amount threefold or more greater than the original CZP dose. Safe discontinuation rates were estimated to be < or = 0.04 mg/kg for abrupt discontinuation, < or = 0.04 mg/kg/week for reduction, and replacement with NZP of 2.5 or more times the original amount of CZP. These safe discontinuation rates were prospectively confirmed by 84 cases of CZP discontinuation in 54 other patients, and no seizure exacerbation occurred with these discontinuation rates.

Discontinuation of clonazepam after long-term treatment

Frequent unwanted side effects and development of tolerance are the main disadvantages of clonazepam (CZP) in long-term treatment of epileptic patients. A review of the literature shows that CZP tolerance more often appears in severe forms of childhood epilepsy (West and Lennox-Gastaut syndromes) than in other epileptic syndromes. We prospectively studied the consequences of CZP discontinuation in 40 consecutive children with difficult-to-treat epilepsies and multiple-drug therapy. The CZP was reduced stepwise in a variable daily reduction rate (0.003-0.16 mg/kg), while serum levels of the comedication were kept unchanged. In only three children (7.5%), CZP was believed to have had some antiepileptic effect; in 30 (75%) it had been ineffective, whereas in six (15%), a decrease in seizure frequency after CZP discontinuation even suggested a negative therapeutic effect. Discontinuation symptoms, mostly in the form of a transitory exacerbation of seizure frequency, occurred in 19 children (47.5%). These children had a significantly higher CZP dose and longer duration of treatment than did children without discontinuation symptoms, but there was no difference between the two groups related to the rate of CZP discontinuance.

Benzodiazepine-induced epileptiform activity in vitro

Drug naive rat hippocampal slices were incubated in artificial cerebrospinal fluid (ACSF) containing 20 nM clonazepam, a concentration approximating those measured in the cerebrospinal fluid (CSF) of rats treated with high doses of clonazepam which resulted in behavioral hyperexcitability and convulsions upon withdrawal. In the slice, epileptiform activity began within 2 h of incubation in clonazepam. This activity was enhanced upon drug withdrawal. Measured intracellularly, the long-lasting post-spike train afterhyperpolarization was reduced in duration in drug-treated cells whereas just subthreshold antidromic or orthodromic IPSPs were not changed. As some of the hyperexcitability phenomena noted here were similar to those observed in slices taken from rats chronically administered with clonazepam, the technique of long-term in vitro exposure to substances which cause tolerance and dependence may be a useful model of drug withdrawal epilepsy.

Clinical effects and plasma concentrations of long-term clonazepam monotherapy in previously untreated epileptics

Ninety-three, previously untreated epileptics were subjected to clonazepam monotherapy. The plasma clonazepam concentrations were monitored to achieve optimal therapeutic effects of the drug. Within a mean duration of follow-up of 32 months, 57 (61.3%) of the 93 cases became seizure-free. The drug showed a high efficacy for complete seizure control of more than 80% for both simple partial seizures and primary generalized tonic clonic ones. The mean plasma level of clonazepam giving complete seizure control was 14.7 ng/ml (range: 3.0-34.6 ng/ml) in cases of generalized epilepsy, and 15.6 ng/ml (range: 4.5-42.3 ng/ml) in cases of partial epilepsy. There was a high correlation between the plasma level and the dose, but no correlation between the plasma level and the clinical effect of the drug. The variable therapeutic range and great interindividual differences in the optimal plasma clonazepam level imply that individually tailored regimens are necessary to achieve optimal therapeutic effects of the drug.

Differences between the tolerance characteristics of two anticonvulsant benzodiazepines

Clobazam (10 mg/kg) and clonazepam (0.25 mg/kg) were administered to mice twice daily by the intraperitoneal route. The development of tolerance to their anticonvulsant effect was compared using a slow intravenous infusion of pentylenetetrazole as the convulsant stimulus. Tolerance to clonazepam developed gradually throughout a 72 h study and did not become significant until the fifth dose. In contrast, tolerance to clobazam occurred extremely rapidly, after only one dose; it was manifested as a single step and no further significant change in protection was observed. Recovery from benzodiazepine tolerance was also studied and seen to occur rapidly with both these compounds; following cessation of dosing, protection was restored to initial levels within 36-48 h.

Pharmacokinetic interactions of antiepileptic drugs

The problem of antiepileptic drug interactions is significant in that many epileptic patients are treated with multiple drug therapy. Moreover, patients may also be receiving additional medication for other concurrent disorders. Most drug interactions are pharmacokinetic, involving changes in absorption, protein binding, metabolism, or excretion. As a result, plasma levels of the antiepileptic drug may decrease leading to exacerbation of seizures. Alternatively, plasma levels may rise resulting in toxic side effects. Similar changes may also occur with drugs given for other disorders. In this paper, possible mechanisms of drug interactions are discussed. This is followed by a description of clinically significant interactions involving phenytoin, carbamazepine, barbiturates, valproic acid, benzodiazepines, and succinimides. Potentially serious drug interactions may be minimized by using as few medications as possible and by regularly monitoring plasma levels of antiepileptic drugs.

Quantitation of clonazepam and its 7-amino and 7-acetamido metabolites in plasma by high-performance liquid chromatography

A high-performance liquid chromatographic method is reported for the determination of clonazepam and its metabolites 7-amino- and 7-acetamidoclonazepam. Extraction from buffered plasma is carried out at pH 9.5 with hexane-ethyl acetate (7:3) for clonazepam and with chloroform for the metabolites. Flunitrazepam, 7-aminodemethylflunitrazepam and 7-acetamidoflunitrazepam are used as the internal standards for clonazepam and its 7-amino and 7-acetamido metabolites, respectively. To prevent decomposition of 7-aminoclonazepam a high concentration of 7-aminomethylclonazepam is added to the plasma. Chromatography is carried out on a reversed-phase column with detection at 254 nm for clonazepam and 240 nm for the metabolites. Using the method it was possible to determine 5 ng/ml clonazepam, 7-aminoclonazepam and 7-acetamidoclonazepam in plasma with coefficients of variation of 9.5%, 5.9% and 8.9%, respectively. This method can be used to measure clonazepam in plasma from patients treated with other antiepileptics. It may also be utilized for in vitro studies on the metabolism of clonazepam in subcellular fractions from the liver.

Kinetics of clonazepam in relation to electroencephalographic and clinical effects

The aim of this study was to see if the immediate EEG and clinical response to an intravenous dose of clonazepam was predictive for the effect of oral clonazepam maintenance therapy. Four children with petit mal epilepsy were given clonazepam intravenously during continuous EEG recording. Clonazepam plasma concentrations were determined repeatedly with a high performance liquid chromatographic method using a reversed phase system. The day after the intravenous dose the patients were given oral therapy with clonazepam. Repeated long-term EEG recordings were made and plasma concentrations of clonazepam were determined. There was no clinically satisfactory effect of clonazepam during oral maintenance treatment in three of the children who responded well to the intravenous dose of clonazepam. Thus, the immediate response to intravenous clonazepam was not a good predictor of the long-term effects in our patients.

Serum concentration of clonazepam and the therapeutic effect of the drug

The effect of other anticonvulsants (phenytoin, phenobarbitone and primidone) on serum clonazepam concentrations has been studied. Serum clonazepam concentrations were measured in 47 epileptic patients in whom a dose of clonazepam (3 mg or 6 mg) was added to existing therapy. 44 patients were receiving other anticonvulsants; 3 were not receiving any other medication. Patients on low doses of other anticonvulsants showed high clonazepam concentrations. Patients on multiple therapy with high doses of other anticonvulsants showed excessive side-effects on clonazepam and low serum clonazepam concentrations. We conclude that other anticonvulsants may reduce serum clonazepam concentrations and therefore that clonazepam is best given alone.

Pharmacokinetic interactions with antiepileptic drugs

A large number of pharmacokinetic interactions with antiepileptic drugs have been reported in recent years. Among the interactions affecting the disposition of anticonvulsants, the most important are probably those resulting in inhibition of the metabolism of phenytoin, phenobarbitone and carbamazepine. Drugs which have been shown to inhibit the metabolism of these anticonvulsants and to precipitate clinical signs of intoxication in epileptic patients include sulthiame, valproic acid, chloramphenicol, certain sulphonamides, phenylbutazone, isoniazid and propoxyphene. Interactions affecting the plasma protein binding of antiepileptic drugs are less likely to cause long-lasting alterations in response, but they are important because they change the relationship between serum drug concentrations and clinical effect. Anticonvulsant agents may induce important alterations in the pharmacokinetics of other drugs. Phenytoin and phenobarbitone may decrease the gastrointestinal absorption of frusemide and griseofulvin, respectively. Many of the drugs used in the treatment of the adult epilepsies, including phenytoin, phenobarbitone, primidone and carbamazepine, are potent inducers of the hepatic microsomal enzymes. This results in an increased rate of metabolism and decreased clinical efficacy of a number of drugs, including dicoumarol, steroid oral contraceptives, metyrapone, glucocorticoid agents, doxycycline, quinidine and vitamin D.

Clonazepam (Rivotril) and carbamazepine (Tegretol) in psychomotor epilepsy: a randomized multicenter trial

The antiepileptic properties of carbamazepine (Tegretol) and clonazepam (Rivotril) were compared in a double-blind randomized study comprising 36 patients with newly diagnosed, untreated psychomotor epilepsy (partial seizures with complex symptomatology). No significant differences were found between the two drugs during the 6 months of treatment. Measurements of concentrations in plasma confirmed that the patients exceeded the accepted lower limit for therapeutic range of the drugs.

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.

Interictal acute psychoses in temporal lobe epilepsy during withdrawal of anticonvulsant therapy

Acute interictal psychotic attacks during withdrawal of medication are described in two patients with temporal lobe epilepsy submitted to depth EEG study with a view to surgical treatment. The patients were on chronic treatment with clonazepam associated in one with phenobarbitone and in the other with phenobarbitone plus carbamazepine. Our observations suggest that the acute withdrawal of clonazepam, the plasma levels of which were monitored may play a part in producing psychotic attacks characterised by dysphoric manifestations, irritability, aggressiveness, anxiety, and hallucinations. These symptoms could be interpreted as a withdrawal syndrome.

Determination of nitrazepam and its main metabolites in urine by gas--liquid chromatography: use of electron capture and nitrogen-selective detectors

Nitrazepam and its main urinary metabolites, 7-aminonitrazepam and 7-acetamidonitrazepam, free and conjugared, were determined from 24-h fractions of human urine after a single oral dose of 5 mg of nitrazepam. Nitrazepam and the metabolites were extracted before and after glusulase hydrolysis with benzene--dichloromethane (90:10) from a 1.0 ml sample. Methylnitrazepam and methylbromazepam served as internal standards. Recoveries were better than 90%. GLC analysis of nitrazepam was performed using a 63Ni electron-capture detector. The metabolites were measured by a dual flameless nitrogen selective detector. The detection limits were about 0.2 ng/ml for nitrazepam and 50 ng/ml for the metabolites. The nitrogen-selective detector responds similarly to all three compounds. The 63Ni electron-capture detector gives very poor response to 7-amino-nitrazepam but allows very sensitive detection of nitrazepam. Combined use of the two detectors gives valuable information about the metabolic profile of nitrazepam.

Kinetics of biotransformation of clonazepam to its 7-amino metabolite in the monkey

The pharmacokinetic behavior of the 7-amino metabolite of clonazepam administered exogenously and formed endogenously from the parent drug was studied in a group of rhesus monkeys using constant rate intravenous infusions. Plasma levels of the 7-amino metabolite and/or clonazepam were determined with a GC-CI-MS method. The biological half-life of the 7-amino metabolite (2.2 +/- 1.0 hr) was shorter than that of clonazepam (4.9 +/- 0.2 hr). Total body clearance of the metabolite (0.83 +/- 0.16 liters/hr/kg) was larger than that of the parent drug (0.55 +/- 0.09 liters/hr/kg). The kinetics of in vivo biotransformation were described by a two-compartment model in which formation and disposition of the metabolite follow first-order processes. The fraction of a dose of clonazepam appearing in the systemic circulation as 7-amino metabolite was 0.70 +/- 0.30. This value may underestimate the actual fraction formed, if the metabolite is susceptible to first-pass metabolism following in situ formation.

Comparison of two gas-liquid chromatographic methods for the determination of nitrazepam in plasma

Nitrazepam in plasma was determined by gas-liquid chromatography with a nickel-63 electron-capture detector, unchanged by a direct method and also by a hydrolysis method. The extraction in the direct method was carried out with benzenedichloromethane (90:10) and in the hydrolysis method with diethyl ether. The hydrolysis was performed with 6 N sulphuric acid. The hydrolysis product was extracted with toluene-n-heptane-ethyl acetate (80:20:5) directly from acid. Thus the commonly used change in pH was omitted. Nitrazepam concentrations in plasma were determined in 10 healthy volunteers after two oral doses (5 and 10 mg); 0.5 ml of plasma was used for each determination and clonazepam, methylbromazepam and methylnitrazepam were used as internal standards. The recoveries of the methods are almost quantitative (greater than 96%). The two methods are clinically comparable. The high sensitivity and specificity make these methods useful in clinical determinations of nitrazepam in plasma. Advantages and disadvantages of both methods are discussed.

Lack of effect of clonazepam on serum levels of diphenylhydantoin, phenobarbital and carbamazepine

The influence of clonazepam on steady-state serum levels of diphenylhydantoin, phenobarbital and carbamazepine was studied in 22 patients with epilepsy receiving one or two of these drugs. Clonazepam was given in slowly increasing doses for 2 weeks until a maximum dose of 4-6 mg per day was reached; thereafter the dose was kept constant. The serum levels of diphenylhydantoin, phenobarbital and carbamazepine were determined once a week for at least 6 weeks. During clonazepam medication in ordinary doses the serum levels of the drugs in question were unaltered. Thus, it is unlikely that the antiepileptic effect of clonazepam in these patients even partly may be due to increased serum levels of these other drugs mentioned.

Radioimmunoassay of the anticonvulsant agent clonazepam

A simple and specific radioimmunoassay was developed for the determination of the anticonvulsant agent clonazepam directly in plasma without extraction. Antibodies to clonazepam were produced in rabbits after immunization with an immunogen prepared by covalently linking the 3-hemisuccinyloxy derivative of clonazepam to bovine serum albumin. When employing 3H-clonazepam as the tracer, the radioimmunoassay has a limit of sensitivity of 5 ng/ml using a 0.1-ml sample of plasma. The antibodies exhibited a high degree of specificity for clonazepam; no cross-reactivity was observed with its 7-amino and 7-acetylamino metabolites nor with a number of other widely prescribed anticonvulsant agents that might be administered in conjuction with clonazepam. Satisfactory agreement was obtained for the plasma levels of clonazepam in humans when samples were assayed by the radioimmunoassay and an established electron-capture GC technique. By virtue ot its simplicity, the radioimmunoassay offers a distinct advantage to the clinician for monitoring plasma clonazepam levels and the compliance of patients undergoing anticonvulsant therapy with the drug.