Plasma Concentrations Of Diazepam Research Articles

Lack of clinically relevant differences in safety and pharmacokinetics after second‐dose administration of intranasal diazepam within 4 h for acute treatment of seizure clusters: A population analysis

ObjectiveCurrent diazepam nasal spray labeling requires waiting 4 h before administering a second dose. The objective of the current analyses was to examine safety and pharmacokinetic profiles of second doses of diazepam nasal spray given 0−4 h after the first dose.MethodsTwo datasets were analyzed. The first, a long‐term, repeat‐dose safety study of diazepam nasal spray, compared rates of treatment‐emergent adverse events (TEAEs), serious TEAEs, and treatment‐related TEAEs for patients receiving ≥1 second dose ≤4 h versus all second doses >4 h after the first. The second was a population pharmacokinetic analysis using data from three phase 1 studies to model drug exposure when a second dose of diazepam nasal spray was administered across multiple time points (1 min−4 h) following the first dose.ResultsIn the repeat‐dose safety study, a second dose of diazepam nasal spray was administered ≤24 h after the first to treat 485 seizure clusters in 79 patients. Rates of TEAEs were similar between patients receiving ≥1 second dose in ≤4 h (89.5%, n = 38) compared with >4–24 h only (80.5%, n = 41). The most common treatment‐related TEAEs were associated with nasal discomfort, which was mild or moderate and transient. There were no reports of respiratory or cardiac depression. The pharmacokinetic simulations of second doses predicted comparable elevations of plasma diazepam concentrations with administrations across a range of intervals after the first dose (1 min−4 h).SignificanceThese data indicate that the safety and pharmacokinetic profiles of a second dose of diazepam nasal spray administered within 4 h of the first dose are consistent with those associated with current labeling. This is potentially important for patients with seizure clusters who have a recurrent seizure within 4 h of first treatment and might benefit from immediate retreatment to reduce the risk of progression to status epilepticus.

Vaginal Diazepam for Nonrelaxing Pelvic Floor Dysfunction: The Pharmacokinetic Profile

BackgroundVaginal diazepam is frequently used to treat pelvic floor tension myalgia and pelvic pain despite limited knowledge of systemic absorption. AimTo determine the pharmacokinetic and adverse event profile of diazepam vaginal suppositories. MethodsWe used a prospective pharmacokinetic design with repeated assessments of diazepam levels. Eight healthy volunteers were administered a 10-mg compounded vaginal diazepam suppository in the outpatient gynecologic clinic. Serum samples were collected at 0, 45, 90, 120, and 180 minutes; 8, 24, and 72 hours; and 1 week following administration of a 10-mg vaginal suppository. The occurrence of adverse events was assessed using the alternate step and tandem walk tests, the Brief Confusion Assessment Method, and numerical ratings. Plasma concentrations of diazepam and active long-acting metabolites were measured. Pharmacokinetic parameters were calculated by standard noncompartmental methods. ResultsThe mean peak diazepam concentration (Cmax) of 31.0 ng/mL was detected at a mean time (Tmax) of 3.1 hours after suppository placement. The bioavailability was found to be 70.5%, and the mean terminal elimination half-life was 82 hours. The plasma levels of temazepam and nordiazepam peaked at 0.8 ng/mL at 29 hours and 6.4 ng/mL at 132 hours, respectively. Fatigue was reported by 3 of 8 participants. Clinical ImplicationsSerum plasma concentrations of vaginally administered diazepam are low; however the half-life is prolonged. Strengths & LimitationsStrengths include use of inclusion and exclusion criteria aimed at mitigating clinical factors that could adversely impact diazepam absorption and metabolism, and the use of an ultrasensitive LC-MS/MS assay. Limitations included the lack of addressing the efficacy of vaginal diazepam in lieu of performing a pure pharmacokinetic study with healthy participants. ConclusionVaginal administration of diazepam results in lower peak serum plasma concentration, longer time to peak concentration, and lower bioavailability than standard oral use. Providers should be aware that with diazepam’s long half-life, accumulating levels would occur with chronic daily doses, and steady-state levels would not be reached for up to 1 week. This profile would favor intermittent use to allow participation in physical therapy and intimacy.Larish AM, Dickson RR, Kudgus RA, et al. Vaginal Diazepam for Nonrelaxing Pelvic Floor Dysfunction: The Pharmacokinetic Profile. J Sex Med 2019;16;763–766.

Determination of minimal steady-state plasma level of diazepam causing seizure threshold elevation in rats.

Diazepam, administered by the intravenous, oral, or rectal routes, is widely used for the management of acute seizures. Dosage forms for delivery of diazepam by other routes of administration, including intranasal, intramuscular, and transbuccal, are under investigation. In predicting what dosages are necessary to terminate seizures, the minimal exposure required to confer seizure protection must be known. Here we administered diazepam by continuous intravenous infusion to obtain near-steady-state levels, which allowed an assessment of the minimal levels that elevate seizure threshold. The thresholds for various behavioral seizure signs (myoclonic jerk, clonus, and tonus) were determined with the timed intravenous pentylenetetrazol seizure threshold test in rats. Diazepam was administered to freely moving animals by continuous intravenous infusion via an indwelling jugular vein cannula. Blood samples for assay of plasma levels of diazepam and metabolites were recovered via an indwelling cannula in the contralateral jugular vein. The pharmacokinetic parameters of diazepam following a single 80-μg/kg intravenous bolus injection were determined using a noncompartmental pharmacokinetic approach. The derived parameters Vd , CL, t1/2α (distribution half-life) and t1/2β (terminal half-life) for diazepam were, respectively, 608mL, 22.1mL/min, 13.7 minutes, and 76.8minutes, respectively. Various doses of diazepam were continuously infused without or with an initial loading dose. At the end of the infusions, the thresholds for various behavioral seizure signs were determined. The minimal plasma diazepam concentration associated with threshold elevations was estimated at approximately 70ng/mL. The active metabolites nordiazepam, oxazepam, and temazepam achieved levels that are expected to make only minor contributions to the threshold elevations. Diazepam elevates seizure threshold at steady-state plasma concentrations lower than previously recognized. The minimally effective plasma concentration provides a reference that may be considered when estimating the diazepam exposure required for acute seizure treatment.

Development of a simple and sensitive HPLC-MS/MS method for determination of diazepam in human plasma and its application to a bioequivalence study.

We developed a simple, sensitive, and effective ultra-performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) method with an electrospray ionization (ESI) interface in multiple reaction monitoring (MRM) and positive ion modes to determine diazepam concentrations in human plasma using voriconazole as an internal standard (IS). Diazepam and IS were detected at transition 285.2→193.1 and 350.2→127.1, respectively. After liquid-liquid extraction (LLE) using 1.2 ml of ethyl acetate:n-hexane (80:20, v/v), diazepam and IS were eluted on a Phenomenex Cadenza CD-C18 column (150 × 3.0 mm, 3 µm) with an isocratic mobile phase (10 mM ammonium acetate in water:methanol [5:95, v/v]) at a flow rate of 0.4 mL/min. The peak retention time was 2.32 min for diazepam and 2.01 min for IS, respectively. The lower limit of quantitation (LLOQ) was 0.5 ng/mL (S/N > 10) using 50 µL of plasma, and no interferences were observed in chromatograms. Our analytical method was fully validated and successfully applied to a bioequivalence study of two formulations of diazepam in healthy Korean volunteers.

Diabetes and hypertension increase the placental and transcellular permeation of the lipophilic drug diazepam in pregnant women

BackgroundPrevious studies carried out in our laboratories have demonstrated impaired drug permeation in diabetic animals. In this study the permeation of diazepam (after a single dose of 5 mg/day, administered intramuscularly) will be investigated in diabetic and hypertensive pregnant women.MethodsA total 75 pregnant women were divided into three groups: group 1 (healthy control, n = 31), group 2 (diabetic, n = 14) and group 3 (hypertensive, n = 30). Two sets of diazepam plasma concentrations were collected and measured (after the administration of the same dose of diazepam), before, during and after delivery. The first set of blood samples was taken from the mother (maternal venous plasma). The second set of samples was taken from the fetus (fetal umbilical venous and arterial plasma). In order to assess the effect of diabetes and hypertension on diazepam placental-permeation, the ratios of fetal to maternal blood concentrations were determined. Differences were considered statistically significant if p ≤ 0.05.ResultsThe diabetes and hypertension groups have 2-fold increase in the fetal umbilical-venous concentrations, compared to the maternal venous concentrations. Feto: maternal plasma-concentrations ratios were higher in diabetes (2.01 ± 1.10) and hypertension (2.26 ± 1.23) groups compared with control (1.30 ± 0.48) while, there was no difference in ratios between the diabetes and hypertension groups. Umbilical-cord arterial: venous ratios (within each group) were similar among all groups (control: 0.97 ± 0.32; hypertension: 1.08 ± 0.60 and diabetes: 1.02 ± 0.77).ConclusionsOn line with our previous findings which demonstrate disturbed transcellular trafficking of lipophilic drugs in diabetes, this study shows significant increase in diazepam placental-permeation in diabetic and hypertensive pregnant women suggesting poor transcellular control of drug permeation and flux, and bigger exposure of the fetus to drug-placental transport.

Effect of Pluronic F68 on plasma and brain diazepam concentrations in mice

Effect of Pluronic F68 on plasma and brain diazepam concentrations in mice

Evaluation of plasma diazepam and nordiazepam concentrations following administration of diazepam intravenously or via suppository per rectum in dogs

To evaluate the pharmacokinetics of diazepam administered per rectum via compounded (ie, not commercially available) suppositories and determine whether a dose of 2 mg/kg in this formulation would result in plasma concentrations shown to be effective for control of status epilepticus or cluster seizures (ie, 150 to 300 ng/mL) in dogs within a clinically useful interval (10 to 15 minutes). 6 healthy mixed-breed dogs. Dogs were randomly assigned to 2 groups of 3 dogs each in a crossover-design study. Diazepam (2 mg/kg) was administered IV or via suppository per rectum, and blood samples were collected at predetermined time points. Following a 6- or 7-day washout period, each group received the alternate treatment. Plasma concentrations of diazepam and nordiazepam were analyzed via reversed phase high-performance liquid chromatography. Plasma concentrations of diazepam and nordiazepam exceeded the targeted range ≤ 3 minutes after IV administration in all dogs. After suppository administration, targeted concentrations of diazepam were not detected in any dogs, and targeted concentrations of nordiazepam were detected after 90 minutes (n = 2 dogs) or 120 minutes (3) or were not achieved (1). On the basis of these results, administration of 2 mg of diazepam/kg via the compounded suppositories used in the present study cannot be recommended for emergency treatment of seizures in dogs.

Bioavailability of Intranasal vs. Rectal Diazepam

There remains an unmet medical need in the out-of-hospital management of seizure emergencies because older children and adults often refuse treatment with diazepam rectal gel due to social objections. We have previously reported that intranasal diazepam (DZP) administration is feasible, with maximum plasma concentrations (C(max)) and time to maximum concentration (T(max)) that are comparable to rectal DZP; but tolerability was poor. In the present study, the tolerability and pharmacokinetics of two investigational nasal formulations were compared with DZP rectal gel. Twelve healthy volunteers were enrolled into an active-control, double-blind, four-period, crossover pharmacokinetic and tolerability study. Three intranasal treatments (Nas-A 10mg, Nas-B 10mg and Nas-B 13.4 mg) were compared to a 10mg dose of the rectal gel. A single dose of each formulation was administered followed by at least a 14 day washout period. Blood samples for plasma DZP concentration-time characterization were collected pre-dose and at regular intervals to 240 h post-dose. Tolerability and sedation were assessed using visual analog scales. Mean DZP C(max) (±SD) was 181.8 ± 84.16, 151.3 ± 108.1 and 180.7 ± 82.1 ng/mL for Nas-A 10mg, Nas-B 10 and Nas-B 13.4 mg respectively; in comparison the C(max) for the rectal gel was 160.9 ± 109.4 ng/mL. Median T(max) was 0.75 h for all treatments. Both intranasal formulations were well tolerated and exhibited relatively rapid, but variable, absorption with bioavailability of 70-90% relative to DZP rectal gel. This study shows that the development of a well-tolerated nasal formulation is possible and that the rate and extent of absorption approximates that of DZP rectal gel. We conclude that intranasal DZP offers a viable alternative to rectal administration, but enhancement of formulations is needed to improve the extent and consistency of absorption.

Diazepam autoinjector intramuscular delivery system versus diazepam rectal gel: A pharmacokinetic comparison

Rectal administration of diazepam (DZ) has been used effectively in patients with epilepsy who experience acute repetitive seizures, but rectal gel may be difficult to administer during a seizure and is subject to variable drug absorption. An intramuscular (IM) autoinjector DZ formulation may offer a practical alternative to rectal DZ. This single-center, open-label, 3-treatment, 3-period crossover study compared the pharmacokinetic and safety profiles of 10mg DZ administered rectally in 24 healthy, fasted and fed subjects versus IM autoinjector delivery in fasted subjects. Blood samples were collected at baseline and for up to 24h postdose and plasma DZ concentrations were determined by liquid chromatography and tandem mass spectrometry. There were no significant differences between plasma concentrations for rectal administration of DZ in fasted and fed subjects at any time point. Intramuscular DZ administration resulted in more rapid and less variable drug absorption than rectal delivery. At 30min postdose and at all subsequent evaluations, IM administration resulted in significantly higher areas under the curve versus rectal administration in fasted subjects (p<0.05). This significant difference was sustained throughout the remainder of the 24-h study period (p<0.05). All reported adverse events were considered mild, and none required treatment.

Effect of diazepam and desmethyldiazepam in spasticity and rigidity. A quantitative study of reflexes and plasma concentrations.

Benzodiazepines are known to reduce increased muscle stretch reflexes. To investigate the relationship between the necessary plasma concentrations of diazepam and its major metabolite desmethyldiazepam on the one hand and the phasic and tonic ankle reflex activity on the other, 10 mg diazepam was given intravenously to nine patients, seven with spasticity due to multiple sclerosis and two with parkinsonian rigidity. Diazepam and desmethyldiazepam both had a normalizing effect on the increased phasic ankle reflex seen in spasticity. No effect was observed on the increased tonic reflexes in rigidity. The concentrations of diazepam necessary to reduce spasticity ranged between 300-2,200 mg/l and were so high that drowsiness did occur. However, the study may indicate that desmethyldiazepam has a higher potency and a more long lasting effect on the increased phasic reflexes than diazepam.

Bioavailability and Dose Proportionality of Intramuscular Diazepam Administered by Autoinjector

A diazepam 10-mg autoinjector was evaluated in bioequivalence and dose proportionality studies; both involved 24 young, healthy subjects and used randomized, open-label, 2-treatment, 2-period crossover designs with a 3-week washout period between treatments. The bioequivalence study compared a single diazepam 10-mg autoinjector with a conventional needle and syringe containing 10 mg of diazepam injectable. The dose proportionality study compared the pharmacokinetics of a single diazepam 10-mg autoinjector with that of 2 diazepam 10-mg autoinjectors given simultaneously (20 mg). Injections were intramuscular in the midanterolateral thigh in both studies. The studies showed that the diazepam autoinjector produced consistent plasma diazepam levels, with a rapid onset of absorption. The diazepam 10-mg autoinjector given intramuscularly was bioequivalent to a conventional syringe containing diazepam 10 mg. A single (10-mg) autoinjector and 2 (20-mg) diazepam autoinjectors administered simultaneously produced plasma diazepam concentrations that were essentially dose proportional.

Voriconazole and fluconazole increase the exposure to oral diazepam

We assessed the effect of voriconazole and fluconazole on the pharmacokinetics and pharmacodynamics of diazepam. Twelve healthy volunteers took 5 mg of oral diazepam in a randomised order on three study sessions: without pretreatment, after oral voriconazole 400 mg twice daily on the first day and 200 mg twice daily on the second day, or after oral fluconazole 400 mg on the first day and 200 mg on the second day. Plasma concentrations of diazepam and N-desmethyldiazepam were determined for up to 48 h. Pharmacodynamic variables were measured for 12 h. In the voriconazole phase, the area under the plasma concentration time curve (AUC 0-infinity) of diazepam was increased (geometric mean ratio) 2.2-fold (p < 0.05; 90% confidence interval [CI] 1.56 to 2.82). This was associated with the prolongation of the mean elimination half-life (t(1/2)) from 31 h to 61 h (p < 0.01) after voriconazole. In the fluconazole phase, the AUC 0-infinity of diazepam was increased 2.5-fold (p < 0.01; 90% CI 1.94 to 3.40), and the t(1/2) was prolonged from 31 h to 73 h (p < 0.001). The peak plasma concentration of diazepam was practically unchanged by voriconazole and fluconazole. The pharmacodynamics of diazepam were changed only modestly. Both voriconazole and fluconazole considerably increase the exposure to diazepam. Recurrent administration of diazepam increases the risk of clinically significant interactions during voriconazole or fluconazole treatment, because the elimination of diazepam is impaired significantly.

Changes in plasma diazepan concentration and its anticonvulsant effect after discharge of a diazepam suppository from the rectum in rats

One of the clinical problems regarding the use of suppositories for patients is the discharge of the medication itself after the insertion of the suppository. The effects of the discharge of diazepam (DZP) suppositories from the rectum on the plasma DZP concentration and its anticonvulsant action were investigated in rats. The plasma DZP concentration reached a maximum at approx. 30 min after the rectal administration of a 5 mg/kg DZP suppository. The discharge of the DZP suppository from the rectum at 5 or 10 min after rectal administration significantly reduced the plasma DZP concentration and the anticonvulsant action of the DZP suppository against pentylenetetrazol-induced seizures. However, when the suppository was discharged from the rectum after 20 min, the plasma DZP concentration and the anticonvulsant action were only slightly but not significantly decreased. These results suggest that the discharge of the DZP suppository in the early phase, within 20 min, decreases the plasma concentration and the anticonvulsant action of the DZP suppository in rats. Therefore, when the suppository is discharged from the rectum immediately, sufficient observation and proper treatment are necessary.

Effect of Simultaneous Insertion of Oleaginous Base on the Absorption and on the Anticonvulsant Effect of Diazepam Suppository

To clarify the drug-base interaction between diazepam (DZP) suppository and oleaginous base, we investigated the effect of simultaneous combination of oleaginous base on the absorption and on the anticonvulsant effect of DZP Suppository in rats. Simultaneous insertion of DZP suppository and oleaginous base significantly decreased maximum concentration (C(max)) and area under the blood concentration-time curve (AUC) of plasma DZP concentrations. Administration of DZP suppositories (2.5, 5 mg/kg) dose-dependently suppressed the pentylenetetrazol (PTZ)-induced seizures, and the anticonvulsant effect of DZP suppository (5 mg/kg) was reduced by simultaneous insertion of oleaginous base. In an in vitro study using a suppository release apparatus, simultaneous combination of DZP suppository and oleaginous base (1.5-98 mg) significantly decreased the accumulative release of DZP in a dose-dependent manner. These results suggested that when DZP suppository and oleaginous base are inserted simultaneously, the released DZP distributes partially to the oleaginous base, and this phenomenon is related to the decreases in the plasma concentration and the anticonvulsant effect of DZP.

Impairment State of Cognitive Performance and the Affecting Factors in Outpatients Following Gastrointestinal Endoscopy after Single-dose Diazepam

Diazepam is commonly used as premedicant for endoscopic procedures. Wide interindividual differences have been observed in the residual cognitive effects of the drug after gastrointestinal endoscopy. Our aim was to clarify the major factors, including pharmacokinetic factors, contributing to this wide variation in residual cognitive effect after gastrointestinal endoscopy in the study. Sixty-one outpatients undergoing gastrointestinal endoscopy participated in the study. Cognitive effects were evaluated in the diazepam group (n=52) by the digit symbol substitution test (DSST) twice before and 30 min after an intravenous administration of 5 mg diazepam; in the intervening time gastrointestinal endoscopy was performed. Plasma concentrations of diazepam were determined by HPLC. The control group (n=9) was tested by DSST in the same manner. The cognitive effects according to the change in DSST score was significantly decline in the diazepam group compared with the control group (by 0.2 versus -4.6; P=0.014). This prospective study confirmed that cognition was significantly impaired after gastrointestinal endoscopy by premedication to subjects with 5 mg diazepam. There were very wide variations in change in DSST score. However we could not identify the independent variables that best predicted DSST score difference in a multiple regression analysis for age, plasma albumin level, and plasma diazepam concentration 30 min after intravenous administration. We should pay attention to patients' individual states in cognitive performance following gastrointestinal endoscopy after single-dose diazepam.

Enhanced Heat Loss and Age-Related Hypersensitivity to Diazepam

Whether elderly people suffer from age-related changes in pharmacokinetics and/or pharmacodynamics with administration of benzodiazepines is still a matter of controversy. We investigated the course of brain function and thermoregulation after oral administration of a standard benzodiazepine, diazepam (DZP), in 8 healthy young men (mean age, 19.8 years; range, 18 to 23 years) and 8 healthy middle-aged and older men (mean age, 60.9 years; range, 53 to 71 years). Placebo or DZP was administered in a single-blind crossover manner to the young men (placebo, 5-mg, 10-mg DZP) and to the older men (placebo, 5-mg DZP), and plasma DZP concentration, choice reaction time, proximal body temperature, and distal body temperature were monitored with high time resolution under a modified constant routine condition to exclude masking effects. Whereas there was no evidence of age-related alterations in pharmacokinetics between the 2 groups, the older subjects, in comparison to the young subjects, showed a more delayed choice reaction time in response to the same plasma DZP level, suggesting that hypersensitivity is related to increased age. DZP at 5 mg in the older subjects induced acute and transient hypothermia to the same degree as that induced by DZP at 10 mg in the young subjects. The distal-proximal body temperature gradient (difference between distal body temperature and proximal body temperature), an indicator of blood flow in distal skin regions, showed strong positive correlation with the delay in choice reaction time in both groups. These findings suggest that hypersensitivity to benzodiazepine in older persons may be due, at least in part, to age-related changes in thermoregulation, especially in the heat loss process.

Vitreous humour as a complementary sample to blood for the detection/confirmation of diazepam: ante-mortem and post-mortem studies in an animal model

The quantification of medical or toxic substances in vitreous humour (VH) could be very useful in forensic toxicology when blood sample determinations are impossible due to absence or deterioration. However, few studies have been made in this area and even fewer have tried to find a relationship between drug levels in both samples. To determine a correlation ratio between blood and VH diazepam (DZ) levels, we performed an experimental study using rabbits administered with a sub-toxic dose of DZ under known and controlled conditions. Blood and VH samples were collected 0.5, 1, 2, 3 and 6 hours after the drug administration in order to determine DZ and its main active metabolite, desmethyldiazepam (DMD). In addition, we have studied an animal group sacrificed 2 hours after intramuscular (i.m.) drug administration with blood and VH collection 24 hours later, to evaluate the existence of possible post-mortem changes. After DZ administration, a fast absorption phase was observed with a plasma Cmax value 1 hour after, followed by a rapid concentration decrease, with a half-life of 1 hour, indicating that, besides elimination, a fast distribution to other organs and tissues and/or hepatic metabolism occurred. Diazepam Cmax value in VH was achieved between 1 and 2 hours, when plasma concentrations had already decreased to half the value. The plasma/VH DZ ratio calculated at this time was 10. In the post-mortem study, while plasma DZ concentration at 24 hours was smaller, DMD levels were higher than those at the time of death. In the VH, both DZ and DMD concentrations at 24 hours were higher than those obtained at the time of death. That is, in both fluids DZ and DMD concentrations were different from those at the time of death and post-mortem distribution and redistribution phenomena occurred. The combination of ante-mortem and post-mortem studies has allowed the determination of a correlation ratio for DZ in the rabbit of 6 x, comparing the concentrations in VH collected 24 hours after death with the concentrations detected in plasma at the time of death. This study opens new perspectives for the use of VH as a complementary sample to blood for DZ detection and confirmation. The putative relevance of the correlation ratio obtained, for forensic toxicology practice with medical substances, namely benzodiazepines, recommends further studies in humans.

Intramuscular diazepam pharmacokinetics in soman-exposed guinea pigs.

Intramuscular (i.m.) diazepam is included by the US military as an anticonvulsant in the standard therapeutic regimen for organophosphorus nerve agent intoxication. In this study we investigated the pharmacokinetics of diazepam after i.m. administration while monitoring pharmacodynamic (electroencephalogram, EEG) data in soman-exposed guinea pigs. Prior to experiments the animals were surgically implanted with EEG leads to monitor seizure activity. For the study, animals were administered pyridostigmine (0.026 mg x kg(-1) i.m.) 30 min prior to soman (56 microg x kg(-1), 2 x LD50; subcutaneously, s.c.), which was followed in 1 min by atropine sulfate (2 mg x kg(-1) i.m.) and pralidoxime chloride (25 mg x kg(-1) i.m.). All animals receiving this regimen developed seizure activity. Diazepam (10 mg x kg(-1) i.m.) was administered 5 min after onset of seizure activity. Based on EEG data, animals were categorized as either seizure terminated or not terminated at 30 min after diazepam. Serial blood samples were obtained from each animal. Diazepam (10 mg x kg(-1) i.m.) terminated seizure activity in 52% of the animals within 30 min. The pharmacokinetics were characterized by a one-compartment model with first-order absorption and elimination. The maximum plasma concentrations (Cmax) were 991 and 839 ng x ml(-1) for seizure terminated and not terminated, respectively. Mean plasma concentrations of diazepam were significantly different (P < 0.05) for seizure terminated vs not terminated groups at 30 min. The plasma Cmax in seizure-terminated animals in this study is similar to the minimum range of plasma diazepam (200-800 ng x ml(-1)) reported to suppress seizure activity in humans. It has been reported in an earlier study that the minimum effective i.m. dose (0.1 mg x kg(-1)) required to prevent soman-induced convulsions in Rhesus monkeys produces a mean Cmax of 50 ng x ml(-1) for diazepam. The data from our current study suggest that a higher dose (and corresponding Cmax) is necessary to terminate ongoing seizure activity.

Different effects of diazepam in Fischer rats and two stocks of Wistar rats in tests of anxiety

The behaviour of animals in tests of anxiety varies between strains, even in identical tests and surroundings. To evaluate the results obtained, a more detailed knowledge of the behaviour of different rat strains is indispensable. Identically raised Fischer 344 rats and two stocks of Wistar rats were examined in two animal tests of anxiety: the X-maze and a modified open-field test following diazepam treatment (0.5–4.0 mg/kg). Harlan–Wistar rats were the least ‘anxious’ when the behaviour of vehicle treated controls was compared. The largest effect of the anxiolytic diazepam, however, was observed in Harlan–Fischer rats. To determine possible reasons for strain and stock differences, plasma concentrations of diazepam and metabolites and concentrations of serotonin (5-HT) in the CNS were measured. Plasma concentrations of diazepam and metabolites differed between the strains with the Harlan–Fischer rats showing higher diazepam concentrations. 5-HT levels in discrete brain regions varied with Harlan–Fischer rats having higher 5-HT concentrations. Strain differences influence the anxiety-associated behaviour of untreated animals and the effect of anxiolytics.

High-performance liquid chromatographic determination of diazepam in plasma of children with severe malaria

A sensitive, selective and reproducible reversed-phase HPLC method with ultraviolet detection was developed for the quantification of diazepam in small plasma samples from children with severe malaria. The method involves plasma deproteinization with acetonitrile, followed by liquid–liquid extraction with ethyl acetate– n-hexane. Diazepam was eluted at ambient temperatures from a reversed-phase C 18 column with an acidic (pH 3.5) aqueous mobile phase (10 m M KH 2PO 4–acetonitrile, 69:31, v/v). Calibration curves in spiked plasma were linear from 10 to 200 ng ( r 2≥0.99). The limit of detection was 5.0 ng/ml, and relative recoveries at 25 and 180 ng were >87%. Intra- and inter-assay relative standard deviations were <15%. There was no interference from drugs commonly administered to children with severe malaria (phenobarbitone, phenytoin, chloroquine, quinine, sulfadoxine, pyrimethamine, halofantrine, cycloguanil, chlorcycloguanil, acetaminophen and salicylate). This method has been used for monitoring plasma diazepam concentrations in children with seizures associated with severe malaria.