Relationship between cerebral pharmacokinetics and anxiolytic activity of diazepam and its active metabolites after a single intra-peritoneal administration of diazepam in mice

The relationship between the cerebral pharmacokinetics of diazepam and its active metabolites (desmethyldiazepam, oxazepam) and the anxiolytic effect evaluated by the four-plates test and the light/dark test were investigated after a single intra-peritoneal injection of diazepam (1 mg/kg or 1.5 mg/kg). For up to 30 min after administration, the sedative effect interfered with the anxiolytic effect, thus the results of the anxiolytic effect were not interpretable. From 30 min to 60 min after administration, this interference disappeared, the cerebral level of benzodiazepines was stable (the brain elimination of diazepam was compensated for by the appearance of desmethyldiazepam followed by oxazepam) but the anxiolytic effect decreased dramatically in all the tests with diazepam 1 mg/kg or 1.5 mg/kg. The acute tolerance to benzodiazepines and the difference of affinity for subtypes of GABA(A) receptors between diazepam, desmethyldiazepam, oxazepam could explain this result.     

Pharmacokinetic model for diazepam and its major metabolite desmethyldiazepam following diazepam administration

A five-compartment open model was used to simulate the blood concentration profiles of diazepam and its metabolite, desmethyldiazepam, following single- and multiple-dose administrations of diazepam. The parameter estimates for diazepam were previously reported literature values. The parameters estimates for the metabolite were calculated from literature values of blood concentrations of desmethyldiazepam following the administration of clorazepate. The five-compartment open model suggests that approximately 50% of the administered diazepam is biotransformed to desmethyldiazepam, and that the elimination profile of the metabolite is not altered by the presence of the drug. The model may also be readily adapted to predict the concentrations of diazepam and desmethyldiazepam in cerebrospinal fluid following the administration of diazepam by simply correcting the blood or plasma concentrations of the drug and metabolite for the degree of plasma protein binding.     

Influence of cimetidine on the pharmacokinetics of desmethyldiazepam and oxazepam

Summary The pharmacokinetics of single oral doses of desmethyldiazepam 20 mg or oxazepam 50 mg were studied in 5 healthy volunteers under controlled conditions, before and following a 24 h pretreatment with cimetidine 200 mg×5. Cimetidine significantly impaired (p=0.03) the elimination of desmethyldiazepam, as shown prolongation of its elimination half-life from 51.7±21.9 h to 72.6±39.4 h (mean ± SD), and a decrease in total plasma clearance from 12.0±2.7 ml/min to 8.6±3.3 ml/min. The disposition of oxazepam was not affected. From these results, and recently published data on diazepam and chlordiazepoxide, it is concluded that cimetidine impairs the hepatic elimination of those benzodiazepines which are metabolized by phase I reactions.     

The elimination of diazepam in Chinese subjects is dependent on the mephenytoin oxidation phenotype

1 The disposition of diazepam and desmethyldiazepam was studied in 21 healthy male Chinese subjects who were phenotyped with mephenytoin. Four poor metabolizers (PM) were identified by phenotyping with mephenytoin and by genotyping for CYP2C19 .
2 Serum diazepam and desmethyldiazepam concentrations were measured by high performance liquid chromatography in samples drawn up to 24 days after administration.
3 The plasma elimination half-lives of diazepam (100.8±32.3  h) and desmethyldiazepam (219.9±62.7  h) in PMs were significantly longer than those (34.7±23.0  h for diazepam, 103.1±25.9  h for desmethyldiazepam) of the 17 phenotyped extensive metabolizers (EM), and those (30.8±24.9  h for diazepam, 103.1±27.5  h for desmethyldiazepam) of the five genotyped EMs.
4 The mephenytoin S/R ratios were significantly correlated with the plasma half-lives of diazepam ( r =0.543, P <0.05) and desmethyldiazepam ( r =0.522, P <0.05), and with the clearance ( r =−0.524, P <0.05) of diazepam in 21 subjects.
5 These results are compatible with the conclusion that both diazepam and desmethyldiazepam are metabolized by cytochrome P450 CYP2C19 in the Chinese population.
6 The mephenytoin S/R ratios in nine EMs who drank alcohol frequently were significantly higher than those of seven EMs who were non-drinkers, but the plasma kinetics of diazepam and desmethyldiazepam were not significantly different between the two groups. The explanation for these finding is not clear.     

Tissue distribution of diazepam and its metabolite desmethyldiazepam: a human autopsy study

Concentrations of diazepam (DZ) and desmethyldiazepam (DMDZ) were determined quantitatively in the brain, skeletal muscle, heart, liver, lung, fat, adrenal gland, and kidney in 14 autopsied patients who had been treated with DZ or clorazepate (a DMDZ prodrug) during their hospital course. To facilitate interpatient comparisons, all tissue concentrations from the same patient were normalized as ratios to the concentration of DZ or DMDZ found in that patient's skeletal muscle. Tissue uptake ratios were not influenced by gender or chronicity of dosage. Distribution equilibrium was reached in at least two hours. Tissue uptake ratios differed considerably among tissues for DZ and DMDZ. Mean (+/- SE) DZ uptake ratio was highest for adrenal gland (12.1 +/- 5.9), liver (5.9 +/- 1.9), heart (4.3 +/- 1.0), and kidney (4.0 +/- 1.0), with lower values for lung (2.1 +/- 0.5), fat (2.2 +/- 0.4), and brain (1.9 +/- 0.4). Similar patterns were observed for DMDZ, except for significantly lower fat uptake. Extrapolating to an average body composition for a 70 kg man with 16% body fat, the largest fractions of total body stores of DZ would be found in muscle (42%), fat (35%), and liver (12%), with smaller stores in brain (4.3%), lung (3.3%), heart (1.7%), kidney (2.0%), and adrenal gland (0.24%).     

Comparison of the pharmacokinetics of diazepam after single and subchronic doses

Summary In seven healthy male volunteers the effects of the pattern of dosing on the pharmacokinetics of diazepam have been studied. A cross-over design was employed that consisted of three parts: a single intravenous dose (0.1 mg/kg), and oral dosing (10 mg/day) for six days followed by an intravenous bolus (0.1 mg/kg) on the seventh day, followed by re-examination of a single intravenous dose after diazepam (D) and its major metabolite desmethyldiazepam (DD) had been completely eliminated. Plasma levels of D and DD were monitored by a specific, sensitive GLC-method. In younger patients (n=5, age 29 – 35 years) the elimination half-life, T_{1/2 ()}, of D was 33.9±10.6 h (mean±S.D.) after the single dose. The control study gave an almost identical result (35.7±12.1). After subchronic dosage in all patients T_{1/2 ()} showed a modest but significant prolongation (paired t-test p<0.01) to 52.9±17.4 h. It was caused by a significant decrease (p=0.016) in total plasma clearance ( ), from 26.0±10.8 ml/min to 18.2±7.0 ml/min. Older patients (age 43–60 years) showed the same phenomenon. Blood/plasma ratios remained constant indicating no change in protein binding. Biliary excretion of D was measured in five patients with a T-tube. Only negligible amounts (0.3–0.4%) of administered D were excreted within 3 days after subchronic dosage, which demonstrates a lack of enterohepatic cycling of D. After multiple administration of D, there was accumulation of DD to levels approximately five times higher than after a single dose. The possibility that the slower elimination of D after subchronic treatment might be caused by DD was also supported by experiments in dogs and rabbits. After pretreating rabbits with DD and maintaining a high DD plasma level, there was prolongation of T_{1/2 ()} from 2.7 h to 5.2 h, with a corresponding decrease of from 101.6 ml/min to 23.4 ml/min. Similar results were obtained in dogs. It is concluded that the disposition of D is altered by subchronic use and may be regulated by the plasma DD concentration.The results were presented in part at the 6th International Congress of Pharmacology, Helsinki, 1975     

地西泮亚微乳注射液大鼠体内药动学

目的:研究地西泮亚微乳注射液在大鼠体内药动学特征.方法:大鼠股静脉注射地西泮亚微乳注射液(4 mg·kg-1),采用HPLC法测定不同时间点大鼠血浆中的药物浓度,并用3P87药动学程序对血药浓度进行处理.结果:地西泮可与血浆中的其他成分较好地分离,在0.05～5 mg·L-1的血药浓度范围内呈良好的线性关系.地西泮亚微乳注射液和地西泮注射液2种制剂大鼠静脉给药后体内药动学符合三室模型,主要药动学参数t1/2β,AUC0～∞,MRT和Vc分别为:(10.97±1.89)和(5.72±1.24)h,(6.10±1.25)和(6.24±1.80)mg·L-1·h,(15.67±1.48)和(9.98±1.31)h,(0.34±0.03)和(0.10±0.01)L·kg-1;2种制剂的t1/2β,MRT和Vc均存在统计学差异(P＜0.01).结论:地西泮亚微乳注射液可在一定程度上延长药物体内循环时间.     

Entry of diazepam and its major metabolite into cerebrospinal fluid

Five dogs received a single 1.0 mg/kg dose of diazepam (DZ) IV. Concentrations of DZ and its major metabolite desmethyldiazepam (DMDZ) were simultaneously measured in plasma and cisternal cerebrospinal fluid (CSF) for up to 8 h after the dose by electron-capture gas-liquid chromatography. DZ was rapidly eliminated from plasma (half-life 0.3–1.3 h); DZ disappearance was mirrored by formation of DMDZ, which in turn was eliminated slowly. Both DZ and DMDZ rapidly penetrated CSF and concentrations in CSF declined parallel with those in plasma. Despite rapid uptake, the extent of CSF transfer of DZ and DMDZ was limited by plasma protein binding. Mean CSF: plasma concentration ratios for DZ (range 0.023–0.137) and DMDZ (range 0.047–0.119) were highly correlated with the unbound fraction in plasma (r=0.95 and 0.80, respectively). Thus DZ and DMDZ concentrations in CSF, presumed to reflect concentrations at the site of action, are determined by unbound plasma concentrations. The intensity of pharmacologic action is more likely to correlate with unbound than with total plasma concentrations.     

Pharmacokinetics of diazepam following multiple-dose oral administration to healthy human subjects

Six healthy subjects between the ages of 21 and 31 years received diazepam tablets orally at a dose of 5 mg t.i.d. atO, 5, and 10hr on days 1–13. On day 14, the dose was 5 mg at 0 and 5 hr and 15 mg at 10 hr. Subsequently, the dose was 15 mg once daily on days 15–24. Numerous plasma samples were obtained during the multiple-dose regimen, and appropriate equations were fitted to all the multiple-dose data. Diazepam absorption was satisfactorily described by a first-order process, with disposition characterized by a linear two-compartment open model. The harmonic mean absorption half-life was 32 min, and the harmonic mean terminal exponential half-life was 57hr. The mean apparent oral total drug plasma clearance was 22.7ml/hr/kg. Steady-state plasma levels of the primary metabolite, desmethyldiazepam, were reached after 5–8 days of dosing. Steady-state diazepam plasma concentration-time profiles suggested that once daily administration of the total daily dose at bedtime might be a satisfactory dosing regimen.     

Pharmacokinetic and pharmacodynamic interactions of bretazenil and diazepam with alcohol

1 Interaction between alcohol and bretazenil (a benzodiazepine partial agonist in animals) was studied with diazepam as a comparator in a randomized, double-blind, placebo controlled six-way cross over experiment in 12 healthy volunteers, aged 19−26 years.
2 Bretazenil (0.5  mg), diazepam (10  mg) and matching placebos were given as single oral doses after intravenous infusion of alcohol to a steady target-blood concentration of 0.5  g l⁻¹ or a control infusion of 5% w/v glucose at 1 week intervals.
3 CNS effects were evaluated between 0 and 3.5  h after drug administration by smooth pursuit and saccadic eye movements, adaptive tracking, body sway, digit symbol substitution test and visual analogue scales.
4 Compared with placebo all treatments caused significant decrements in performance. Overall, the following sequence was found for the magnitude of treatment effects: bretazenil+alcohol>diazepam+alcohol≥bretazenil> diazepam>alcohol>placebo.
5 There were no consistent indications for synergistic, supra-additive pharmacodynamic interactions between alcohol and bretazenil or diazepam.
6 Bretazenil with or without alcohol, and diazepam+alcohol had marked effects. Because subjects were often too sedated to perform the adaptive tracking test and the eye movement tests adequately, ceiling effects may have affected the outcome of these tests.
7 No significant pharmacokinetic interactions were found.
8 Contrary to the results in animals, there were no indications for a dissociation of the sedative and anxiolytic effects of bretazenil in man.     

Competitive Inhibition of Zidovudine Clearance by Probenecid During Continuous Coadministration

The pharmacokinetics of zidovudine in the rabbit were studied during coadministration of probenecid at two infusion rates. Each animal (n = 6) served as its own control during an initial 8-hr infusion of zidovudine. In the second 8-hr infusion period, probenecid was coadministered with zidovudine. Urine samples were collected by bladder flush hourly for 19 hr. Plasma samples were taken at the midpoint of the urine collection interval and at predetermined intervals for 3 hr postinfusion. Plasma concentrations of zidovudine reached steady state during control periods but showed incomplete attainment of steady state during the infusions of probenecid at the higher rate. Total and renal clearance of zidovudine were reduced by 24.0 ± 4.0 and 20.7 ± 15%, respectively, during low-dose probenecid treatment and 48.9 ± 7.4 and 55.7 ± 3.4%, respectively, with high-dose probenecid treatment. Plasma probenecid concentrations during low-dose and high-dose infusion were 56.9 ± 12 and 248 ± 42 µg/ml. Postinfusion data showed that the zidovudine terminal half-life during high-dose probenecid treatment was longer than that with low-dose probenecid treatment (58.2 ± 4.6 vs 39.0 ± 9.1 min). The volume of distribution of zidovudine also decreased (1.76 ± 0.27 vs 1.10 ± 0.095 L/kg) as a result of probenecid coadministration. The results are consistent with competitive inhibition of renal and nonrenal clearances. A drug interaction model relating zidovudine clearances to plasma probenecid concentrations was derived. Michaelis-type constants for probenecid inhibition of zidovudine renal and nonrenal clearances were 73 and 55 µg/ml, respectively. The maximum proportion of AZT's renal clearance subject to inhibition is significantly greater (72%) than that of the nonrenal clearance (54%) and agrees closely with the fraction not filtered.     

甲状腺功能对地西泮及其代谢产物在大鼠体内代谢的影响

目的：研究甲状腺功能对地西泮及其代谢物的药代动力学影响。方法：采用HPLC技术，测定不同甲状腺功能状态时，大鼠血液中地西泮及其体内主要代谢产物去甲基地西泮的浓度。结果：甲亢组大鼠地西泮在体内消除加速，峰浓度下降，AUC减少，消除T1/2缩短。甲减组大鼠则消除减慢，峰浓度增高，AUC增大，消除孔。延长。而其主要代谢产物去甲地西泮的药动学参数则相反。结论：甲状腺功能提高时，大鼠对地西泮的代谢能力明显增加，消除加速；而甲腺功能降低则相反。     

HPLC法同时测定血浆地西泮及其代谢物浓度

目的 :建立同时测定血浆中地西泮及其代谢物浓度的方法。方法 :选用ZORBAXRP C18柱 (15 0mm× 4 6mm ,5 μm) ;甲醇 - 2 5mmol·L-1醋酸铵溶液 (6 0∶4 0 ,V/V)作流动相 ;流速 0 8mL·min-1;检测波长 2 30nm。取血浆样品 0 5mL ,在碱性条件下用二氯甲烷 -正己烷提取 ,HPLC检测。结果 :本法对替马西泮、去甲地西泮和地西泮 3种物质的最低检测限均为 2 μg·L-1,线性范围为 10～ 15 0 0 μg·L-1;奥沙西泮的最低检测限为 5 μg·L-1,线性范围为 2 0～ 15 0 0 μg·L-1。回收率均接近 10 0 % ,日内、日间RSD <5 %。结论 :本法能同时测定血浆中地西泮及其代谢物浓度 ,具有重现性好 ,灵敏、可靠 ,可用于地西泮中毒的监测     

Pharmacokinetics and anticonvulsant effects of diazepam in children with severe falciparum malaria and convulsions

AIMS: Convulsions are a common complication of severe malaria in children and are associated with poor outcome. Diazepam is used to terminate convulsions but its pharmacokinetics and pharmacodynamics have not been studied in this group. Accordingly, we carried out a comparative study of the pharmacokinetics of intravenous (i.v.) and rectal (p.r.) diazepam. METHODS: Twenty-five children with severe malaria and a convulsion lasting >5 min were studied. Sixteen children received diazepam intravenously (i.v.; 0.3 mg kg(-1)) and nine rectally (p.r.; 0.5 mg kg(-1)). Plasma diazepam concentrations were measured by reversed phase high-performance liquid chromatography. The duration of convulsions, depth of coma, respiratory and cardiovascular parameters were monitored. RESULTS: Median maximum plasma diazepam concentrations of 634 (range 402-1507) ng ml(-1) and 423 (range 112-1953) ng ml(-1) were achieved at 5 and 25 min following i.v. and p.r. administration, respectively. All patients except three (one i.v. and two p.r.) achieved plasma diazepam concentration >200 ng ml(-1) within 5 min. Following p.r. administration, plasma diazepam concentrations were more variable than i.v. administration. A single dose of i.v. diazepam terminated convulsions in all children but in only 6/9 after p.r. administration. However, nine children treated with i.v. and all those treated with p.r. diazepam had a recurrence of convulsions occurring at median plasma diazepam concentrations of 157 (range: 67-169) and 172 (range: 74-393) ng ml(-1) , respectively. All the children in the i.v. and four in the PR diazepam group who had recurrence of convulsions required treatment. None of the children developed respiratory depression or hypotension. CONCLUSIONS: Administration of diazepam i.v. or p.r. resulted in achievement of therapeutic concentrations of diazepam rapidly, without significant cardio-respiratory adverse effects. However, following p.r. administration, diazepam did not terminate all convulsions and plasma drug concentrations were more variable.     

高效液相色谱法测定血清中地西泮的浓度

目的建立血清中地西泮的高效液相色谱测定方法。方法以甲醇-水（70：30）为流动相;Kromasil C18（250mm×4．6mm5μm）柱为层析柱,以卡马西平为内标物,检测波长216nm。结果地西泮在0．1～20．0mg·L^-1浓度范围内具有良好的线性关系,平均回收率为97、67％,日内、日间RSD小于4．8％,最低检测浓度为20μg·L^-1。结论本方法简便可行,适合于地西泮的血药浓度测定。     

Disposition of diazepam in young and elderly subjects after acute and chronic dosing

1. The pharmacokinetics of diazepam were examined in seven young (20–30 years) and six elderly (60–75 years) males prior to and also after chronic oral dosing of diazepam.
2. Following intravenous administration, the half-life and volume of distribution of ¹⁴C-labelled diazepam in the elderly were approximately twofold greater than corresponding estimates in younger subjects (mean ±s.d., 71.5±27.6 vs 44.5±16.5 h and 1.39±0.32 vs 0.88±0.30 1 kg⁻¹, respectively). Clearance did not differ between the two groups (0.26±0.09 vs 0.29±0.09 ml min⁻¹ kg⁻¹).
3. The accumulation of diazepam and its major metabolite, desmethyldiazepam, were extensive during chronic administration. A radioreceptor assay that measured total benzodiazepine activity, including diazepam and its active metabolites, indicated that the accumulation of ‘benzodiazepine equivalents’ was similar to the sum of the accumulated diazepam and desmethyldiazepam concentration levels. However, the level of ‘benzodiazepine equivalents’ on multiple-dosing was about double that of the predicted steady-state ‘equivalent’ concentration from single-dose studies. This was due to the insensitivity of the radioreceptor assay for desmethyldiazepam following single-dose diazepam administration.
4. There were no age- or dosing-related differences in diazepam clearance (0.37±0.22 vs 0.32±0.18 ml min⁻¹ kg⁻¹, young vs elderly, single-dose; 0.37± 0.11 vs 0.27±0.12 ml min⁻¹ kg⁻¹, young vs elderly, multiple-dose) and no age-related differences in the levels of accumulated ‘benzodiazepine equivalents’ (243.7±60.1 vs 288.0±125.8 ng ml⁻¹, young vs elderly).

     

The action of cisapride on gastric emptying and the pharmacodynamics and pharmacokinetics of oral diazepam

Summary The effects of the benzamide cisapride (C) (8 mg) i.v. have been compared to placebo (P) in a double blind randomised study. The effects on gastric emptying, the absorption and effects of oral diazepam, and BP and pulse were observed.Cisapride increased the rate of gastric emptying of 500 ml liquid containing diazepam 10 mg (t_1/2 C: 7.4 min, P: 14.9 min). The initial rate of absorption of diazepam contained in the drink was increased by C (AUC 0–1 h C: 328 µg h 1^–1, P: 253 µg h 1^–1, but there was no change in overall bioavailability. This change in diazepam kinetics was associated with a significantly greater impairment in reaction time in the first 45 min after drinking but not in self rated sedation. Cisapride produced a significant tachycardia (e.g. after 10 min C: 82 beats/min, P: 69 beats/min) which probably reflects a peripheral vasodilator action. Cisapride may therefore alter the pharmacokinetics and dynamics of concurrently administered drugs.     

HPLC法测定地西泮和艾司唑仑的血药浓度

建立ＨＰＬＣ法同时测定地西泮和艾司唑仑血药浓度。方法：以Ｕｌｔｒａｓｐｈｅｒｅ－ＯＤＳ５μｍ４．６ｍｍ＊２５ｃｍ色谱柱为分离柱,流动相：甲醇－乙腈－水（４０：２０：４０）;检测波长为２５４ｎｍ,以外标法峰面积定量。结论本法可用于血药浓度测定。     

Antagonism of diazepam hyperphagia by propranolol in rats

The effects of adrenergic beta-receptor blockers on the hyperphagia produced by diazepam were studied in free-feeding rats. The hyperphagia produced by 1.0 mg/kg subcutaneous (s.c.) diazepam, was antagonised by dl-propranolol (6.0 mg/kg s.c.) and 1-propranolol (6.0 mg/kg s.c.), but not by d-propranolol (6.0 mg/kg s.c.). Intracerebroventricular administration of dl-propranolol (50, 100, and 200 μg) failed to antagonise this hyperphagia. Other specific β₁ and β₂ blockers, metoprolol (10.0 mg/kg s.c.), and butoxamine (10.0 mg/kg s.c.) also did not antagonise this hyperphagia. It is suggested that some intrinsic property other than β-blockade, tranquilising, or local anesthetic activity is responsible for this antagonism caused by s.c. administration of dl- or l-propranolol.