Concentration-independent plasma protein binding of benzodiazepines

In Vitro Hepatotoxicity of Routinely Used Opioids and Sedative Drugs

A hepatocyte cell line was used to determine the hepatotoxicity of sedatives and opioids, as the hepatotoxicity of these drugs has not yet been well characterized. This might pose a threat, especially to critically ill patients, as they often receive high cumulative doses for daily analgosedation and often already have impaired liver function due to an underlying disease or complications during treatment. A well-established biosensor based on HepG2/C3A cells was used for the determination of the hepatotoxicity of commonly used sedatives and opioids in the intensive care setting (midazolam, propofol, s-ketamin, thiopental, fentanyl, remifentanil, and sufentanil). The incubation time was 2 × 3 days with clinically relevant (Cmax) and higher concentrations (C5× and C10×) of each drug in cell culture medium or human plasma. Afterward, we measured the cell count, vitality, lactate dehydrogenase (LDH), mitochondrial dehydrogenase activity, cytochrome P 450 1A2 (CYP1A2), and albumin synthesis. All tested substances reduced the viability of hepatocyte cells, but sufentanil and remifentanil showed more pronounced effects. The cell count was diminished by sufentanil in both the medium and plasma and by remifentanil only in plasma. Sufentanil and remifentanil also led to higher values of LDH in the cell culture supernatant. A reduction of mitochondrial dehydrogenase activity was seen with the use of midazolam and s-ketamine. Microalbumin synthesis was reduced in plasma after its incubation with higher concentrations of sufentanil and remifentanil. Remifentanil and s-ketamine reduced CYP1A2 activity, while propofol and thiopental increased it. Our findings suggest that none of the tested sedatives and opioids have pronounced hepatotoxicity. Sufentanil, remifentanil, and s-ketamine showed moderate hepatotoxic effects in vitro. These drugs should be given with caution to patients vulnerable to hepatotoxic drugs, e.g., patients with pre-existing liver disease or liver impairment as part of their underlying disease (e.g., hypoxic hepatitis or cholestatic liver dysfunction in sepsis). Further studies are indicated for this topic, which may use more complex cell culture models and global pharmacovigilance reports, addressing the limitation of the used cell model: HepG2/C3A cells have a lower metabolic capacity due to their low levels of CYP enzymes compared to primary hepatocytes. However, while the test model is suitable for parental substances, it is not for toxicity testing of metabolites.

In Vitro Bioavailability of the Hydrocarbon Fractions of Dimethyl Sulfoxide Extracts of Petroleum Substances

Determining the in vitro bioavailable concentration is a critical, yet unmet need to refine in vitro-to-in vivo extrapolation for unknown or variable composition, complex reaction product or biological material (UVCB) substances. UVCBs such as petroleum substances are commonly subjected to dimethyl sulfoxide (DMSO) extraction in order to retrieve the bioactive polycyclic aromatic compound (PAC) portion for in vitro testing. In addition to DMSO extraction, protein binding in cell culture media and dilution can all influence in vitro bioavailable concentrations of aliphatic and aromatic compounds in petroleum substances. However, these in vitro factors have not been fully characterized. In this study, we aimed to fill in these data gaps by characterizing the effects of these processes using both a defined mixture of analytical standards containing aliphatic and aromatic hydrocarbons, as well as 4 refined petroleum products as prototypical examples of UVCBs. Each substance was extracted with DMSO, and the protein binding in cell culture media was measured by using solid-phase microextraction. Semiquantitative analysis for aliphatic and aromatic compounds was achieved via gas chromatography-mass spectrometry. Our results showed that DMSO selectively extracted PACs from test substances, and that chemical profiles of PACs across molecular classes remained consistent after extraction. With respect to protein binding, chemical profiles were retained at a lower dilution (higher concentration), but a greater dilution factor (ie, lower concentration) resulted in higher protein binding in cell medium, which in turn altered the ultimate chemical profile of bioavailable PACs. Overall, this case study demonstrates that extraction procedures, protein binding in cell culture media, and dilution factors prior to in vitro testing can all contribute to determining the final bioavailable concentrations of bioactive constituents of UVCBs in vitro. Thus, in vitro-to-in vivo extrapolation for UVCBs may require greater attention to the concentration-dependent and compound-specific differences in recovery and bioavailability.

Effect of lipophilicity on drug distribution and elimination: Influence of obesity

AIMS

For a given passively-distributed lipophilic drug, the extent of in vivo distribution (pharmacokinetic volume of distribution, V_d ) in obese individuals increases in relation to the degree of obesity. The present study had the objective of evaluating drug distribution in relation to in vitro lipophilicity, and the relative increase in V_d associated with obesity across a series of drugs.

METHODS

Cohorts of normal-weight control and obese subjects received single doses of drugs ranging from hydrophilic (acetaminophen, salicylate) to lipophilic (imipramine, verapamil). Lipid solubility was measured by the log-transformed values of the high-pressure liquid chromatographic (HPLC) retention index (Log₁₀ (HPLC)), and the octanol-water partition coefficient (LogP).

RESULTS

Among normal-weight controls, V_d normalized for protein binding was highly correlated with Log₁₀ (HPLC) (R² = .65) and with LogP (R² = .78). V_d of all drugs was increased in the obese cohort, but the relative increase (compared to controls) for individual drugs was disproportionately greater as lipid solubility increased. Since clearance was unrelated to lipophilicity, the increased V_d produced a parallel disproportionate increase in elimination half-life in the obese cohort that was associated with Log₁₀ (HPLC) (R² = .62).

CONCLUSION

Lipophilicity is a principal correlate of in vivo V_d , as well as the increased V_d of drugs in obese patients. The consequent prolongation of half-life in obesity has clinical safety implications in terms of delayed drug accumulation and washout during and after chronic dosage. The magnitude and importance of this effect for a given drug depends on the degree of obesity, as well as the lipid-solubility of the specific drug.

Experimental versus theoretical log D7.4 , pKa and plasma protein binding values for benzodiazepines appearing as new psychoactive substances

The misuse of benzodiazepines as new psychoactive substances is an increasing problem around the world. Basic physicochemical and pharmacokinetic data is required on these substances to interpret and predict their effects upon humans. Experimental log D7.4 , pKa and plasma protein binding values were determined for 11 benzodiazepines that have recently appeared as new psychoactive substances (3-hydroxyphenazepam, 4'-chlorodiazepam, desalkylflurazepam, deschloroetizolam, diclazepam, etizolam, flubromazepam, flubromazolam, meclonazepam, phenazepam, and pyrazolam) and compared with values generated by various software packages (ACD/I-lab, MarvinSketch, ADMET Predictor and PreADMET). ACD/I-LAB returned the most accurate values for log D7.4 and plasma protein binding while ADMET Predictor returned the most accurate values for pKa . Large variations in predictive errors were observed between compounds. Experimental values are currently preferable and desirable as they may aid with the future 'training' of predictive models for these new psychoactive substances.

The absorption kinetics of ketoconazole plays a major role in explaining the reported variability in the level of interaction with midazolam: Interplay between formulation and inhibition of gut wall and liver metabolism

The impact of different single oral doses of ketoconazole (KTZ) (100, 200 and 400 mg) and of staggering its dosage (400 mg at -12, -2, 0, 2 and 4 h), with respect to the administration of a single 5 mg oral dose of midazolam (MDZ) on the extent of inhibition of the metabolism of the latter, was evaluated in healthy subjects in two separate studies. Escalation of the ketoconazole dosage resulted in 2.3 (1.9), 2.7 (1.7) and 4.2 (2.5) -fold increases in the mean AUC_(0,12h) (and C_max ) values of midazolam. Dose-staggering was associated with 3.9 (2.5), 4.9 (2.9), 5.4 (2.8), 2.0 (1.3) and 1.2 (0.9) -fold increases in the mean AUC_(0,12h) (and C_max ) of midazolam. These findings could be predicted by physiologically based pharmacokinetic (PBPK) modelling using the ADAM (advanced dissolution absorption and metabolism) model within the Simcyp Simulator (Version 12 Release 2) to characterize the absorption kinetics of ketoconazole with respect to disintegration time, supersaturation ratio and precipitation rate. This study also emphasizes a need to account for inter-individual variability in the gut wall and systemic exposure of inhibitors with physicochemical properties similar to ketoconazole, in particular in their rate of oral absorption and when using different pharmaceutical formulations, in designing and evaluating the extent of drug-drug interactions. Copyright © 2016 John Wiley & Sons, Ltd.

Pharmacokinetic considerations and recommendations in palliative care, with focus on morphine, midazolam and haloperidol

INTRODUCTION

A variety of medications are used for symptom control in palliative care, such as morphine, midazolam and haloperidol. The pharmacokinetics of these drugs may be altered in these patients as a result of physiological changes that occur at the end stage of life.

AREAS COVERED

This review gives an overview of how the pharmacokinetics in terminally ill patients may differ from the average population and discusses the effect of terminal illness on each of the four pharmacokinetic processes absorption, distribution, metabolism, and elimination. Specific considerations are also given for three commonly prescribed drugs in palliative care: morphine, midazolam and haloperidol).

EXPERT OPINION

The pharmacokinetics of drugs in terminally ill patients can be complex and limited evidence exists on guided drug use in this population. To improve the quality of life of these patients, more knowledge and more pharmacokinetic/pharmacodynamics studies in terminally ill patients are needed to develop individualised dosing guidelines. Until then knowledge of pharmacokinetics and the physiological changes that occur in the final days of life can provide a base for dosing adjustments that will improve the quality of life of terminally ill patients. As the interaction of drugs with the physiology of dying is complex, pharmacological treatment is probably best assessed in a multi-disciplinary setting and the advice of a pharmacist, or clinical pharmacologist, is highly recommended.

Evaluation of hypothermia on the in vitro metabolism and binding and in vivo disposition of midazolam in rats

The effect of hypothermia on the in vivo pharmacokinetics of midazolam was evaluated, with a focus on altered metabolism in the liver and binding to serum proteins. Rat primary hepatocytes were incubated with midazolam (which is metabolized mainly by CYP3A2) at 37, 32 or 28 °C. The Michaelis-Menten constant (Km) and maximum velocity (Vmax) of midazolam were estimated using the Michaelis-Menten equation. The Km of CYP3A2 midazolam remained unchanged, but the Vmax decreased at 28 °C. In rats, whose temperature was maintained at 37, 32 or 28 °C by a heat lamp or ice pack, the plasma concentrations of midazolam were higher, whereas those in the brain and liver were unchanged at 28 °C. The tissue/plasma concentration ratios were, however, increased significantly. The unbound fraction of midazolam in serum at 28 °C was half that at 37 °C. These pharmacokinetic changes associated with hypothermic conditions were due to reductions in CYP3A2 activity and protein binding.

[Drugs for status epilepticus treatment]

The pharmacokinetics and pharmacodynamics of major antiepileptic agents are presented. The onset of action and the factors leading to extraction across the blood brain barrier are described as well as the mechanism and extent of metabolism, and the main interactions with other drugs. For each class, the dosing scheme and practical issues related to administration are described, based on evidence when available in the literature.

Adenosine and adenosine uptake inhibitors potentiate the neuromuscular blocking action of rocuronium mediated by adenosine A(1) receptors in isolated rat diaphragms

BACKGROUND

Adenosine, which pre-junctionally modulates neuromuscular transmission, and adenosine uptake inhibitors, which increase extracellular adenosine, have been used clinically. We investigated the effects of adenosine, dipyridamole and midazolam on the neuromuscular blocking action of rocuronium.

METHODS

Isometric twitch tensions of rat nerve-hemidiaphragm preparations elicited by indirect (phrenic nerve) supra-maximal stimulation at 0.1 Hz were evaluated (n=6 in all data).

RESULTS

Pre-treatments with adenosine (0.1 and 1 microM) and CCPA (1 microM, adenosine A(1) receptor agonist), but not that with CGS21680 (0.5 microM, A(2) receptor agonist), shifted the rocuronium concentration-twitch tension curves to the left and decreased the rocuronium concentration for 50% twitch depression (IC(50)) compared with the control (P<0.01). The leftward shift induced by 1 microM adenosine was inhibited by pre-treatments with theophylline (50 microM, non-selective adenosine receptor antagonist) and DPCPX (0.2 microM, A(1) receptor antagonist) but not by that with DPMA (5 microM, A(2) receptor antagonist). Pre-treatments with dipyridamole and midazolam, adenosine uptake inhibitors, shifted the curve to the left and decreased IC(50) at supra-therapeutic concentrations (10 and 2.5 microM, respectively) but not at clinical concentrations (2 and 0.5 microM, respectively), and the leftward shifts were inhibited by pre-treatment with DPCPX (0.2 microM).

CONCLUSION

The results indicate that adenosine potentiates the neuromuscular blocking action of rocuronium mediated by adenosine A(1) receptors and that supra-therapeutic concentrations of dipyridamole and midazolam also potentiate the action of rocuronium by increasing endogenous adenosine concentration.

Prevalence of alcohol and drugs among Norwegian motor vehicle drivers: a roadside survey

The objective of the study was to determine the prevalence of alcohol, psychoactive medicinal drugs and illegal drugs among drivers in Norwegian road traffic. Drivers of motor vehicles were selected from April 2005 to April 2006 in the south-eastern part of Norway, surrounding, but not including the capital, Oslo. A stratified two-stage cluster sampling procedure was used. In the first stage, random road sites and time intervals were selected, and in the second stage, drivers were stopped by random at those sites and time intervals. Altogether about 12,000 drivers were asked to provide a sample of oral fluid (saliva) and answer a few questions. Samples of oral fluid were obtained from 88% of the drivers, of whom 30% were females and 70% males. The prevalence of each drug was estimated by a weighted average using weights adjusted for under- or over-sampling compared to traffic statistics. Alcohol or drugs were found in oral fluid samples of 4.5% of the drivers; alcohol in 0.4%, psychoactive medicinal drugs in 3.4%, and illegal drugs in 1.0%. Illegal drugs were found more frequently in samples from younger drivers, while psychoactive medicinal drugs were more frequently found in samples from older drivers. Psychoactive medicinal drugs were more prevalent among females than males, among drivers stopped on working days rather than weekends, and among those who reported annual driving distances less than 16,000 km. The drugs found most frequently were zopiclone (1.4%), benzodiazepines (1.4%), codeine (0.8%), tetrahydrocannabinol (0.6%) and amphetamines (0.3%). Two or more drugs were found in 0.6% of the samples, corresponding to 15% of the drug-positive drivers.

Different acute tolerance development to EEG, psychomotor performance and subjective assessment effects after two intermittent oral doses of alprazolam in healthy volunteers

BACKGROUND/AIMS

Benzodiazepines (BZDs) are the most effective of the psychotropic drugs in the treatment of anxiety disorders. Tolerance has been reported for the majority of BZDs after chronic administration. However, little attention has been paid to the possibility that tolerance might be present after the intermittent oral administration of BZDs. The objectives of the present study were to assess tolerance development after the administration of two intermittent single oral doses of alprazolam given 15 days apart in healthy volunteers, and to compare the results obtained using measures from different domains: neurophysiological, psychomotor and subjective.

METHODS

Twenty-four healthy volunteers received 2 mg of alprazolam orally on two experimental days, 15 days apart. Plasma concentrations and pharmacodynamics (PD) were assessed before drug intake and at different times in the following 24 h. PD was assessed through EEG (relative alpha and relative beta-1 activities), cancellation task (total and correct number of responses) and visual analogue scales (activity and drowsiness).

RESULTS

No differences were observed in the PKs of alprazolam between occasions. A proteresis was present in both administrations for impairments of psychomotor performance and relative beta-1 activity, whereas it was present only after the second administration for subjective assessments and relative alpha activity. The proteresis on the second occasion was higher than on the first one.

CONCLUSIONS

The administration of two single oral doses of alprazolam, 2 weeks apart in healthy volunteers, yielded the same PKs on both occasions, but significant changes were observed in the PD profile. Acute tolerance was observed after the second administration. Two patterns of acute tolerance development were obtained: (1) impairments of psychomotor performance and relative beta-1 activity, and (2) subjective assessments and relative alpha activity.

Prediction of in vivo drug clearance from in vitro data. I: impact of inter-individual variability

The Simcyp Population-Based ADME Simulator was used to predict median drug clearances and their associated variance from in vitro data. Fifteen drugs satisfied the entry criteria for the study and the relevant information (in vitro metabolism data and in vivo human clearance values) were collated from the literature. Predicted values of median clearances fell within 2-fold of observed values for 73% of the drugs (oral route) and 78% of the drugs (intravenous route) when microsomal binding was disregarded, and for 93% (oral) and 100% (intravenous) when it was considered. Irrespective of whether microsomal binding was considered, the predicted fold variability fell within 2-fold of the observed variability for 80% (oral) and 67% (intravenous) of the drugs.

Mechanisms involved in the relaxing effect of midazolam on coronary arteries

BACKGROUND AND OBJECTIVE

Hypotension, especially in elderly and hypovolaemic patients, is frequently associated with intravenous midazolam administration. The mechanisms are not completely understood. This study was designed to investigate the mechanisms involved in the relaxing effect of midazolam on coronary arteries.

METHODS

The substance was studied in isolated porcine coronary artery rings precontracted by either potassium chloride or prostaglandin F2alpha.

RESULTS

Midazolam caused vasodilatation in a concentration-dependent manner. Relaxation was more pronounced in prostaglandin F2alpha precontracted segments than in those treated with potassium chloride (P < 0.001). Vasodilatation was unaffected by Nomega-nitro-L-arginine, indomethacin and glibenclamide. Tetraethylammonium chloride, an inhibitor of the BK(Ca) K+ channel (a high conductance Ca(2+)-sensitive K+ channel), dose dependently attenuated the vasodilating effect of midazolam (P < 0.01).

CONCLUSIONS

Hyperpolarization of the smooth muscle cell in the vessel wall, elicited by the activation the BK(Ca) K+ channel, may contribute to the vasorelaxing effect of midazolam.

Intrathecal fentanyl added to intrathecal bupivacaine for day case surgery: a randomized study

BACKGROUND AND OBJECTIVE

The implication of intrathecal lidocaine in neurological toxicity has made intrathecal bupivacaine the commonly used drug for local anaesthesia in ambulatory surgery. However, in high doses intrathecal bupivacaine may produce a high level of sensory and motor block, and arterial hypotension; discharge from hospital may be delayed. Intrathecal opioids added to low-dose local anaesthetics produce a synergistic effect without increasing the sympathetic block or delaying discharge. The aim of our study was to identify the minimum effective dose of intrathecal fentanyl that in combination with low-dose intrathecal bupivacaine would provide adequate surgical conditions without prolonging recovery.

METHODS

A prospective, single, blind, randomized study was conducted in 45 adult males scheduled for minor urological procedures using intrathecal anaesthesia on a day care basis. Patients were randomly assigned to one of three groups (n = 15 each). They received bupivacaine 0.17% 5 mg--with either fentanyl 7.5 microg (fenta-7.5), 10 microg (fenta-10) or 12.5 microg (fenta-12.5) intrathecally in a total volume of 3 mL. The quality of anaesthesia, haemodynamic stability, time to two-segment and S2 regression, time to micturition, and time to discharge were assessed.

RESULTS

The time to two-segment regression and S2 regression with fenta-12.5 was significantly longer than with fenta-7.5 and fenta-10 (P < 0.01). Fenta-7.5 had a significantly higher number of failed blocks (four patients) compared with fenta-12.5 (P < 0.05). The time out of bed, time to micturition and time to discharge were significantly longer with fenta-10 and fenta-12.5 compared with fenta-7.5, and also with fenta-12.5 compared with fenta-10 (P < 0.01). Haemodynamic stability did not differ for all the drug combinations.

CONCLUSIONS

Fentanyl 12.5 microg added to low-dose bupivacaine (5 mg) intrathecally provides better surgical anaesthesia and increased reliability of block than intrathecal fentanyl 7.5 or 10 microg. Haemodynamic stability was the same for all dose combinations used.

Important physical principles in anaesthesiology

The aim of this Review is to introduce anaesthesiologists to the basic physical principles that are important for their work. A better understanding of the underlying processes during anaesthesia is required for greater safety and efficiency. Relevant physical quantities are presented along with the area of anaesthesiology where they are used. This approach provides better targeting to the needs of practising anaesthesiologists. This text has been a part of a specialist course in anaesthesiology at the University of Ljubljana for some years. Current results show that both the students and the specialist anaesthesiologists now show a better understanding of the underlying physical principles required for their work and are more successful in fulfilling the needs of their practical work.

High-dose midazolam and the attenuation of the contractile response to vasoconstrictors in coronary artery segments

BACKGROUND AND OBJECTIVE

Benzodiazepines may cause hypotension and are reported to interfere with smooth vascular muscle activity. The aim was to elucidate the influence of three different benzodiazepines on the vascular reactivity of coronary arteries.

METHODS

Using the model of isolated vessels, we studied the impact of midazolam (0.15, 1.5, 15 microg mL(-1)), diazepam (0.1, 1.0, 10 microg mL(-1)) and flunitrazepam (0.01, 0.1, 1.0 microg mL(-1)) on the contractile responses to histamine (2 x 10(-5) mol L(-1)) and serotonin (3 x 10(-5) mol L(-1)) in isolated intact and denuded coronary arteries.

RESULTS

Midazolam significantly attenuated the contractile response when administered in high concentrations (15 microg mL(-1)). This effect was more pronounced in intact than in denuded preparations (histamine: -22.7 versus -7.3%, P = 0.0079; serotonin: -47.1 versus -15.9%, P < 0.0001). Diazepam and flunitrazepam exerted no significant effects on the vascular tone of coronary arteries.

CONCLUSIONS

Midazolam, but not diazepam or flunitrazepam, attenuates the contractile responses to vasoconstrictors in concentrations beyond those used in clinical practice. This effect is in part mediated by endothelial factors.

Anaesthesia for day case surgery: a survey of adult clinical practice in the UK

BACKGROUND AND OBJECTIVE

In October 2000, we conducted a national postal survey of consultant day case anaesthetists in the UK to explore the range and variation in the practice of anaesthetizing a patient for day case surgery (paediatrics, urology and orthopaedics). The survey was carried out as part of a larger study that comprised a major two-centre randomized controlled trial designed to investigate the costs and outcome of several anaesthetic techniques during day care surgery in paediatric and adult patients (cost-effectiveness study of anaesthesia in day case surgery). We report the findings of this national survey of adult urology and orthopaedic day case anaesthetic practice in the UK.

METHODS

The survey used a structured postal questionnaire and collected data on the duration of the surgical procedure; the use of premedication; the anaesthetic agents used for induction and maintenance; the fresh gas flows used for anaesthesia; the use of antiemetics; and the administration of local anaesthesia and analgesia.

RESULTS

The overall response rate for the survey was 74% (63% for urology, 67% for orthopaedics). The survey indicated the following practice in adult urology and adult orthopaedic day case surgery: 6 and 12% used premedication; propofol was the preferred induction agent (96 and 97%) and isoflurane the preferred maintenance agent (56 and 58%); 32 and 41% used prophylactic antiemetics; 86 and 93% used a laryngeal mask.

CONCLUSIONS

This survey identifies the variation in current clinical practice in adult day surgery anaesthesia in the UK and discusses this variation in the context of current published evidence.

Effect of dexamethasone on motor brachial plexus block with bupivacaine and with bupivacaine-loaded microspheres in a sheep model

BACKGROUND AND OBJECTIVE

It has been suggested that dexamethasone potentiates the sensory block produced by bupivacaine when both drugs are loaded in microspheres. The aim of the study was to evaluate the effect of dexamethasone on the brachial plexus block obtained with plain bupivacaine and bupivacaine-loaded microspheres.

METHODS

Dexamethasone alone (Group 5) or added to plain bupivacaine (75 mg) with (Groups 3 and 4) and without pH correction (Group 2) was compared with plain bupivacaine (75 mg; Group 1). The effect of a small dose of dexamethasone (0.42 mg) was then evaluated on the brachial plexus block obtained with bupivacaine (750 mg) as bupivacaine-loaded microspheres (Group 6). Dexamethasone was added either in the suspending medium (Group 7) or incorporated with bupivacaine into microspheres (Group 8). The motor block was evaluated in a plexus brachial sheep model.

RESULTS

Dexamethasone alone did not produce any motor block. When added to plain bupivacaine without pH correction, complete motor block could not be obtained. When the pH was corrected, addition of dexamethasone to plain bupivacaine seemed to delay the onset of motor block and did not prolong its duration, and it had no effect on the pharmacokinetics of bupivacaine. With bupivacaine-loaded microspheres, the duration of complete motor block was reduced when a small dose of dexamethasone was added in the suspending medium. However, the duration of motor block was significantly prolonged when dexamethasone was incorporated with bupivacaine into microspheres.

CONCLUSIONS

Despite the delayed onset of motor block, the incorporation of dexamethasone in bupivacaine-loaded microspheres dramatically increases the duration of action (700 +/- 485-5160 +/- 2136 min), which could be clinically relevant when such a drug-delivery system will be available.

Haemodynamic response to a small intravenous bolus injection of epinephrine in cardiac surgical patients

BACKGROUND AND OBJECTIVE

The aim was to study the rapid changes in cardiac output and systemic vascular resistance produced by intravenous epinephrine (5 microg) on a beat-by-beat basis.

METHODS

Ten patients were studied during cardiac surgery. Radial or brachial arterial pressure was recorded continuously during intravenous administration of epinephrine (5 microg). Cardiac output and systemic vascular resistance were derived for each beat using arterial pulse contour analysis calibrated by lithium indicator dilution. In each patient a further dose of epinephrine (5 microg) was administered during cardiopulmonary bypass with the blood flow kept constant so that changes in arterial pressure corresponded to changes in systemic vascular resistance.

RESULTS

When the patients were not on cardiopulmonary bypass, the epinephrine produced an initial increase in systemic vascular resistance to 129 +/- 15% (mean +/- SD) of control, followed by a more prolonged reduction to 57 +/- 13% of control. Cardiac output showed a small initial reduction coincident with the increase in systemic vascular resistance, followed by an increase to 152 +/- 24% of control. During cardiopulmonary bypass, the changes produced by epinephrine on systemic vascular resistance were qualitatively similar but smaller in amplitude, probably because of a greater volume of dilution in the bypass circuit.

CONCLUSIONS

Small bolus doses of epinephrine produce an initial increase in systemic vascular resistance followed by a much greater reduction that may cause hypotension.

Anaesthesia for day case surgery: a survey of paediatric clinical practice in the UK

BACKGROUND AND OBJECTIVE

In October 2000, we conducted a national postal survey of day case consultant anaesthetists in the UK to explore the range and variation in practice of anaesthetizing a patient for day case surgery (paediatrics, urology and orthopaedics). This paper reports the findings of this national survey of paediatric day case anaesthetic practice carried out as part of a major two-centre randomized controlled trial designed to investigate the costs and outcome of several anaesthetic techniques during day care surgery in paediatric and adult patients (cost-effectiveness study of anaesthesia in day case surgery).

METHODS

The survey used a structured postal questionnaire and collected data on the duration of surgical procedure; the use of premedication; the anaesthetic agents used for induction and maintenance; the fresh gas flow rates used for general anaesthesia; the use of antiemetics; and the administration of local anaesthesia and analgesia.

RESULTS

The overall response rate for the survey was 74 and 63% for the paediatric section of the survey. Respondents indicated that 19% used premedication, 63% used propofol for induction, 54% used isoflurane for maintenance, 24% used prophylactic antiemetics and 85%, used a laryngeal mask. The findings of this national survey are discussed and compared with published evidence.

CONCLUSIONS

This survey identifies the variation in clinical practice in paediatric day surgery anaesthesia in the UK.

Recollection of dreams after short general anaesthesia: influence on patient anxiety and satisfaction

BACKGROUND AND OBJECTIVE

We ascertained whether dreams during short general anaesthesia influence subsequent patient satisfaction and anxiety.

METHODS

Fifty female patients were randomized into two groups to test for a difference between intravenous and inhalational anaesthesias. In Group Propo, anaesthesia was induced and maintained with propofol; in Group Metho-Iso, anaesthesia was induced with methohexital and maintained with isoflurane. Satisfaction and anxiety with anaesthesia were evaluated using a visual analogue scale from 0 to 100. Dream incidence rate, satisfaction and anxiety were assessed from immediately after waking until 3 months later.

RESULTS

Seventeen patients (34%) dreamed during anaesthesia. There were no significant differences in satisfaction or anxiety after anaesthesia between the dreaming and non-dreaming patients (satisfaction, 92.3 +/- 21.6 versus 92.1 +/- 21.6; anxiety, 21.1 +/- 21.1 versus 30.3 +/- 32.1), or between Group Propo and Group Metho-Iso (satisfaction, 94.4 +/- 19.3 versus 90.0 +/- 23.4; anxiety, 26.0 +/- 27.6 versus 28.4 +/- 30.7). There was no significant difference in the incidence rate of dreaming with the type of anaesthesia used (Group Propo, 11 patients; Group Metho-Iso, 6 patients).

CONCLUSIONS

Dreaming during general anaesthesia is common but does not influence satisfaction or anxiety after anaesthesia.

In vitro, pharmacokinetic, and pharmacodynamic interactions of ketoconazole and midazolam in the rat

Interactions of midazolam and ketoconazole were studied in vivo and in vitro in rats. Ketoconazole (total dose of 15 mg/kg intraperitoneally) reduced clearance of intravenous midazolam (5 mg/kg) from 79 to 55 ml/min/kg (p < 0.05) and clearance of intragastric midazolam (15 mg/kg) from 1051 to 237 ml/min/kg (p < 0.05), increasing absolute bioavailability from 0.11 to 0.36 (p < 0.05). Presystemic extraction occurred mainly across the liver as opposed to the gastrointestinal tract mucosa. Midazolam increased electroencephalographic (EEG) amplitude in the beta-frequency range. Ketoconazole shifted the concentration-EEG effect relationship rightward (increase in EC(50)), probably because ketoconazole is a neutral benzodiazepine receptor ligand. Ketoconazole competitively inhibited midazolam hydroxylation by rat liver and intestinal microsomes in vitro, with nanomolar K(i) values. At a total serum ketoconazole of 2 microg/ml (3.76 microM) in vivo, the predicted reduction in clearance of intragastric midazolam by ketoconazole (to 6% of control) was slightly greater than the observed reduction in vivo (to 15% of control). However, unbound serum ketoconazole greatly underpredicted the observed clearance reduction. Although the in vitro and in vivo characteristics of midazolam in rats incompletely parallel those in humans, the experimental model can be used to assess aspects of drug interactions having potential clinical importance.

Effect of 7-day exposure to midazolam on electroencephalogram pharmacodynamics in rats: a model to study multiple pharmacokinetic-pharmacodynamic relationships in individual animals

The objective of this study was to determine the concentration-electroencephalogram (EEG) relationships for midazolam, a full-agonist benzodiazepine ligand, on multiple occasions in individual rats, and to examine the effect of chronic midazolam exposure on that relationship. Rats were chronically instrumented with venous and arterial cannulas, and cortical EEG electrodes. The rats received either: 7 days of midazolam 10 mg kg(-1) intravenously once a day (midazolam group); or midazolam on days 1 and 7 and vehicle on days 2-6 (vehicle group). Concentration-effect relationships were determined on days 1, 4 and 7 from multiple blood and EEG samples before and after the administration of the midazolam dose. The concentration-EEG effect relationships were consistent with a sigmoidal Emax (maximal effect) model. No differences in pharmacokinetic or pharmacodynamic parameters were found between day 1 and day 7 in either group. However, in the midazolam group, both the fraction unbound of midazolam in serum and the EC50 (concentration at half-maximal effect) for free midazolam increased from days 1-7 by 35 +/- 3% and 54 +/- 25%, respectively (means +/- s.d., P< 0.05). This may be related to decreased serum albumin levels in the midazolam group (-19+5%, P < 0.05) which, in turn, could be explained by the sedation associated with daily midazolam treatment. We concluded that concentration-EEG effect relationships can be studied on multiple occasions in individual animals, reducing animal use and variability. A modest degree of tolerance to midazolam was found with this paradigm, the effect only being evident after correction for the fraction unbound of midazolam.

Prediction of the disposition of midazolam in surgical patients by a physiologically based pharmacokinetic model

The aim of this study was to predict the disposition of midazolam in individual surgical patients by physiologically based pharmacokinetic (PBPK) modeling and explore the causes of interindividual variability. Tissue-plasma partition coefficients (k(p)) were scaled from rat to human values by a physiologically realistic four-compartment model for each tissue, incorporating the measured unbound fraction (f(u)) of midazolam in the plasma of each patient. Body composition (lean body mass versus adipose tissue) was then estimated in each patient, and the volume of distribution at steady state (V(dss)) of midazolam was calculated. Total clearance (CL) was calculated from unbound intrinsic CL, f(u), and estimated hepatic blood flow. Curves of midazolam plasma concentration versus time were finally predicted by means of a perfusion-limited PBPK model and compared with measured data. In a first study on 14 young patients undergoing surgery with modest blood loss, V(dss) was predicted with an only 3.4% mean error (range -24-+39%) and a correlation between predicted and measured values of 0.818 (p < 0.001). Scaling of k(p) values by the four-compartment model gave better predictions of V(dss) than scaling using unbound k(p). In the PBPK modeling, the mean +/- standard deviation (SD) prediction error for all data was 9.7 +/- 33%. In a second study with 10 elderly patients undergoing orthopedic surgery, hemodilution and blood loss led to a higher f(u) of midazolam. The PBPK modeling correctly predicted a marked increase in V(dss), a smaller increase in CL, and a prolonged terminal half-life of midazolam, as compared with findings in the first study. Interindividual variation in the disposition of midazolam could thus in part be related to the physiological characteristics of the patients and the f(u) of the drug in their plasma.

Comparative pharmacokinetics of alprazolam and lorazepam in humans and in African Green Monkeys

The comparative pharmacokinetics of alprazolam and lorazepam were evaluated in African Green Monkeys and in healthy male human volunteers. Six monkeys received a single 250 micrograms/kg oral dose of alprazolam and of lorazepam on two separate occasions. Mean kinetic values for the two drugs, respectively, were: elimination half-life, 5.7 and 1.7 h; oral clearance, 5.5 and 40.2 ml/min/kg. Healthy male volunteers (n = 22) received a single 1 mg oral dose of alprazolam; another group (n = 24) received a single 2 mg oral dose of lorazepam. Mean values of elimination half-life in humans (11.5 and 12.4 h, for alprazolam and lorazepam, respectively) were substantially longer than corresponding values in the primate animal model, and human values of clearance (0.85 and 1.40 ml/min/kg) likewise were much lower. However, in humans, kinetic differences between the two drugs were much smaller than in the primate animals. Thus comparative studies of the behavioral effects of these two drugs in African Green Monkeys should utilize relative dosages that reflect the pharmacokinetic properties of the drugs in that species. Use of dosage ratios analogous to those used in humans may lead to results that cannot be extrapolated to humans.

Mechanism-based modeling of functional adaptation upon chronic treatment with midazolam

PURPOSE

A mechanism-based model is applied to analyse adaptive changes in the pharmacodynamics of benzodiazepines upon chronic treatment in rats.

METHODS

The pharmacodynamics of midazolam was studied in rats which received a constant rate infusion of the drug for 14 days, resulting in a steady-state concentration of 102 +/- 8 ng x ml(-1). Vehicle treated rats were used as controls. Concentration-EEG effect data were analysed on basis of the operational model of agonism. The results were compared to data obtained in vitro in a brain synaptoneurosomal preparation.

RESULTS

The relationship between midazolam concentration and EEG effect was non-linear. In midazolam pre-treated rats the maximum EEG effect was reduced by 51 +/- 23 microV from the original value of 109 +/-15 microV in vehicle treated group. Analysis of this change on basis of the operational model of agonism showed that it can be explained by a change in the parameter tissue maximum (Em) rather than efficacy (tau). In the in vitro studies no changes in density, affinity or functionality of the benzodiazepine receptor were observed.

CONCLUSIONS

It is concluded that the observed changes in the concentration-EEG effect relationship of midazolam upon chronic treatment are unrelated to changes in benzodiazepine receptor function.

Rate of change of blood concentrations is a major determinant of the pharmacodynamics of midazolam in rats

The objective of this investigation was to characterize quantitatively the influence of the rate of increase in blood concentrations on the pharmacodynamics of midazolam in rats. The pharmacodynamics of midazolam were quantified by an integrated pharmacokinetic-pharmacodynamic modelling approach. Using a computer controlled infusion technique, a linear increase in blood concentrations up to 80 ng ml(-1) was obtained over different time intervals of 16 h, resulting in rates of rise of the blood concentrations of respectively, 1.25, 1.00, 0.87, 0.46, 0.34 and 0.20 ng ml(-1) min(-1). In one group of rats the midazolam concentration was immediately brought to 80 ng ml(-1) and maintained at that level for 4 h. Immediately after the pretreatment an intravenous bolus dose was given to determine the time course of the EEG effect in conjunction with the decline of midazolam concentrations. The increase in beta activity (11.5-30 Hz) of the EEG was used as pharmacodynamic endpoint. For each individual animal the relationship between blood concentration and the EEG effect could be described by the sigmoidal Emax model. After placebo, the values of the pharmacodynamic parameter estimates were Emax = 82+/-5 microV, EC50,u = 6.4+/-0.8 ng ml(-1) and Hill factor = 1.4+/-0.1. A bell-shaped relationship between the rate of change of midazolam concentration and the value of EC50,u was observed with a maximum of 21+/-5.0 ng ml(-1) at a rate of change of 0.46 ng ml(-1) min(-1); lower values of EC50,u were observed at both higher and lower rates. The findings of this study show that the rate of change in plasma concentrations is an important determinant of the pharmacodynamics of midazolam in rats.

The effects of cardiopulmonary bypass on total and unbound plasma concentrations of propofol and midazolam

OBJECTIVE

To examine the effects of cardiopulmonary bypass (CPB) on total and unbound plasma concentrations of propofol and midazolam when administered by continuous infusion during cardiac surgery.

DESIGN

Prospective clinical study.

SETTING

University hospital.

PARTICIPANTS

Twenty-four adult patients undergoing cardiac surgery.

INTERVENTIONS

Patients received either propofol or midazolam to supplement fentanyl anesthesia. Twelve patients received a propofol bolus (1 mg/kg) followed by an infusion of 3 mg/kg/hr. A second group received midazolam, 0.2 mg/kg bolus, followed by an infusion of 0.07 mg/kg/hr.

MEASUREMENTS AND MAIN RESULTS

Blood sample were collected from the radial artery cannula at 0, 2, 4, 8, 8, 10, 15, 20 minutes and then every 10 minutes before CPB, at 1, 2, 3, 4, 6, 10, 15, 20 minutes and then each 10 minutes during CPB. On weaning from CPB samples were collected at 0, 5, 10 and 20 minutes. Plasma binding, total and unbound propofol and midazolam concentrations were determined by ultrafiltration and high-pressure liquid chromatography (HPLC). CPB resulted in a fall in total propofol and midazolam plasma concentrations, but the unbound concentrations remained stable. The propofol unbound fraction increased from 0.22 +/- 0.06% to 0.41 +/- 0.17%. The midazolam unbound fraction increased from 5.6 +/- 1.0% to 11.2 +/- 2.1%.

CONCLUSIONS

Unbound concentrations of propofol and midazolam are not affected by cardiopulmonary bypass. Total intravenous anesthesia algorithms do not need to be changed to achieve stable unbound plasma concentrations when initiating CPB.

Pharmacokinetics of midazolam in Vietnamese subjects

In order to examine the investigators' clinical suspicion that Vietnamese patients were more sensitive to the sedative effects of midazolam than were Caucasians, the pharmacokinetics of a single, weight-adjusted intravenous dose of midazolam (0.05 mg/kg) were compared in a group of healthy Caucasian and Vietnamese male volunteers. The Vietnamese group (n = 8) had a significantly lower height, lean body mass and mean weight (59.8 +/- 5.5 vs 72.1 +/- 8.1 kg, respectively) compared with the Caucasian group (n = 8). No significant differences were found between the Vietnamese and Caucasian groups with regard to distribution half-life of midazolam (8.38 +/- 13.1 vs 1.49 +/- 0.63 min, respectively), elimination half-life (2.49 +/- 1.80 vs 1.48 +/- 0.66 h, respectively), clearance (4.93 +/- 1.31 vs 5.90 +/- 2.12 mL/min per kg, respectively), steady state volume of distribution (0.863 +/- 0.497 vs 0.530 +/- 0.132 L/kg, respectively) or percentage of unbound drug in plasma (4.89 +/- 0.74 vs 4.11 +/- 1.08, respectively). This suggests that dosage of midazolam in Vietnamese should be based on total bodyweight. Two Vietnamese subjects who were brothers had marked elevation of distribution half-life and initial volume of distribution and lesser elevations in elimination half-life and volume of distribution at steady state. This suggests that the known subgroup of subjects who demonstrate dyshomogeneity in midazolam volume of distribution may be genetically determined.

Alprazolam, caffeine and their interaction: relating DRL performance to pharmacokinetics

Three-hour sessions of differential reinforcement of low-rate behavior (DRL 45-s) in rats were used to investigate alprazolam, caffeine, and their interactions at the onset, peak and disappearance of serum alprazolam, while caffeine level remained constant. The dose-response curve (DRC) method of Pöch permitted an extensive evaluation of the kind (additivity or independence) of interactions occurring in combined drug effects. The alprazolam and caffeine DRCs were used to derive theoretical additive and independent relations, and the observed combined effects compared to these functions. Behavior-time profiles of the combined effects were similarly compared. Serum alprazolam and caffeine concentrations correlated with their respective behavior-time profiles. No acute tolerance was observed either for the individual drugs or their combinations. Alprazolam was more potent than caffeine in disrupting DRL behavior. Because alprazolam is much shorter-lived (t1/2 = 32 min) than caffeine (t1/2 = 3 h) in rats, potency ratios between alprazolam and caffeine changed across session time (from 123 to 4), which determined the expression of the combined effects. Although the combined effects were not distinguishable in terms of additivity or independence in both the DRCs and in the behavior-time profiles, they showed neither synergism nor antagonism. The pharmacokinetics of alprazolam were not altered by caffeine, but those of caffeine were affected by alprazolam.

Brain-plasma distribution of free and total benzodiazepines in dogs physically dependent on different doses of diazepam

Steady-state levels of oxazepam (OX), nordiazepam (ND), and diazepam (DZ) in plasma, brain tissue, cerebrospinal fluid (CSF), and intracranial microdialysis perfusate were determined in dogs dependent on 0.56, 4.5, 9, and 36 mg/kg per day of DZ. There was a linear relationship between the total plasma and brain levels of DZ, ND, and OX and the chronic dose of DZ. Levels of free benzodiazepines in plasma and CSF and levels in microdialysis perfusates from plasma and brain were significantly correlated. With increasing dependence on DZ there was progressively more free ND and OX and less free DZ in plasma, CSF, and brain. There was a correlation between several signs of precipitated abstinence and free ND in the brain interstitial fluid, whereas convulsions emerged only when free metabolites exceeded free DZ. The changes in contribution of free DZ, ND, and OX to the overall levels of benzodiazepines present in the CNS may explain differences in signs of abstinence for different levels of dependence on DZ.

Pharmacokinetics and pharmacodynamics of triazolam after two intermittent doses in obese and normal-weight men

This study was designed to determine whether differences in alpha-1 acid glycoprotein and free drug concentrations result in an altered response to triazolam. Twelve normal-weight and 12 obese adult male subjects received intravenous doses of triazolam, 0.5 mg, on two occasions separated by 1 week. There was a small difference in the alpha-1 acid glycoprotein concentrations between groups but no difference in free fraction of triazolam. There was a longer terminal half-life (t1/2 beta) in the obese subjects (3.16 +/- 0.87 vs. 3.83 +/- 1.24, p = 0.0098). Overall, week 1 data revealed no difference in effect between normal and obese subjects. However, response data reveal a pattern of increased sensitivity with the second exposure to triazolam. For example, area under the effect curve (AUEC) on all tests was significantly greater in week 2 for both groups of subjects. For a memory test and sedation from 0 to 12 hours, AUEC/free AUC ratios were significantly greater in week 2 for all subjects. The obese had a higher ratio on week 2 than on week 1 for all psychomotor tests and sedation (0 to 4.5 hours; p < 0.05). The results of modeling psychomotor impairment-concentration data pooled by group for each week continue the pattern: week 1 data are similar between the obese and normal-weight subjects. Although EC50 values are up to 15% lower in week 2 for the normal-weight subjects, EC50 values are as much as 66% lower in week 2 for the obese, where a lower EC50 indicates greater sensitivity. Logistic regression of the recognition data is consistent with these results.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of midazolam administered concurrently with ketamine after intravenous bolus or infusion in dogs

Midazolam, a water-soluble benzodiazepine tranquilizer, has been considered by some veterinary anaesthesiologists to be suitable as a combination anaesthetic agent when administered concurrently with ketamine because of its water solubility and miscibility with ketamine. However, the pharmacokinetics of midazolam have not been extensively described in the dog. Twelve clinically healthy mixed breed dogs (22.2-33.4 kg) were divided into two groups at random and were administered ketamine (10 mg/kg) and midazolam (0.5 mg/kg) either as an intravenous bolus over 30 s (group 1) or as an i.v. infusion in 0.9% NaCl (2 ml/kg) over 15 min. Blood samples were obtained immediately before the drugs were injected and periodically for 6 h afterwards. Serum concentrations were determined using gas chromatography with electron-capture detection. Serum concentrations were best described using a two-compartment open model and indicated a t1/2-alpha of 1.8 min and t1/2-beta of 27.8 min after i.v. bolus, and t1/2-alpha of 1.35 min and t1/2-beta of 31.6 min after i.v. infusion. The calculated pharmacokinetic coefficient B was significantly smaller after i.v. infusion (429 +/- 244 ng/ml) than after i.v. bolus (888 +/- 130 ng/ml, P = 0.004). Furthermore, AUC was significantly smaller after i.v. infusion (29,800 +/- 6120 ng/h/ml) than after i.v. bolus (42,500 +/- 8460 ng/h/ml, P < 0.05), resulting in a larger ClB after i.v. infusion (17.4 +/- 4.00 ml/min/kg than after i.v. bolus (12.1 +/- 2.24 ml/min/kg, P < 0.05). No other pharmacokinetic value was significantly affected by rate of intravenous administration.

Pharmacokinetics of nordiazepam in physical dependence and precipitated abstinence in dogs

Previous studies suggested that the extensive accumulation of benzodiazepines is an important factor in the induction of physical dependence. The mechanistic basis for accumulation of nordiazepam (ND) and its metabolite, oxazepam (OX), have been examined in crossover studies in drug-naive and in ND-dependent dogs that exhibited a flumazenil-precipitated abstinence syndrome. ND and parent OX have similar pharmacokinetic profiles. Steady-state plasma levels of ND and OX cannot be predicted from single-dose pharmacokinetics. Reduced plasma clearance of ND and altered plasma protein binding were observed in dogs physically dependent upon ND. The benzodiazepine antagonist, flumazenil, significantly reduces steady-state plasma levels of total and free ND.

Classification of benzodiazepine hypnotics in humans based on receptor occupancy theory

Benzodiazepine (BZP) hypnotics are now classified into four groups according to their plasma elimination rates: ultrashort-, short-, intermediate-, and long-acting drugs. Since the specific binding affinities for the BZP receptor vary widely among the BZPs and their active metabolites, it may be more reasonable to correlate their pharmacological activities with the BZP receptor occupancy rather than with their plasma concentrations. The time courses of total plasma concentrations of BZPs and their active metabolites after a single oral administration were obtained from the literature, and their unbound concentrations (Cu) were calculated from the reported values of their plasma unbound fractions. The data of the receptor binding affinities of the BZPs, reported as dissociation constants (Kd) determined by in vitro binding experiments, were also obtained from the literature. Using these values, the time courses of receptor occupancies [Cu/(Kd + Cu) x 100%] were calculated for the various BZPs. A mutual competitive inhibition was considered in the case of the drugs that had active metabolites. Although plasma total and unbound concentration time profiles of the BZPs showed a wide variation, similar patterns were obtained for the time courses of the receptor occupancy among the BZPs in each group, indicating that the BZP hypnotics can be classified more conveniently based on receptor occupancy theory.

Pharmacokinetics and preliminary observations of behavioral changes following administration of midazolam to dogs

The pharmacokinetics of midazolam were investigated following intravenous and intramuscular administration of 0.5 mg of midazolam hydrochloride/kg of body weight to five healthy mixed-breed dogs. One dog also received the same dose of midazolam by oral and rectal routes. The disposition of midazolam following intravenous administration was characterized by very rapid and relatively extensive distribution followed by rapid elimination. Mean (+/- SD) apparent volume of distribution was 3.0 +/- 0.9 l/kg, mean elimination half-life was 77 +/- 18 min, and clearance was 27 +/- 3 ml/kg/min. Following intramuscular administration, absorption was rapid and complete. A mean peak midazolam concentration of 549 +/- 121 ng/ml was reached within 15 min, and systemic availability was over 90% in each dog. Oral administration to one dog resulted in peak midazolam concentrations within 10 min and a systemic availability of 69%. Rectal administration to the same dog yielded very low systemic availability. Midazolam was extensively bound to canine plasma proteins, with the unbound fraction representing less than 4% of the total plasma midazolam concentration. Plasma samples were also assayed for the presence of the major metabolites, 1-OH and 4-OH midazolam. Neither metabolite were detected, probably as a result of rapid elimination of these compounds by hepatic glucuronidation. Behavioral responses to administration of midazolam included initial signs of profound weakness, ataxia and transient agitation followed by a period of quiesence. A normal behavior pattern returned within 2 h of midazolam administration.

Differences in intrinsic efficacy of benzodiazepines are reflected in their concentration-EEG effect relationship

1. The relevance of EEG effect parameters as a measure of the central nervous system effects of benzodiazepines was evaluated. The concentration-EEG effect relationships of the benzodiazepine agonist midazolam, partial agonist bretazenil, antagonist flumazenil and inverse agonist Ro 19-4603 were quantified and compared with the intrinsic efficacy and affinity of these compounds at the gamma-aminobutyric acid (GABA)-benzodiazepine receptor complex. 2. The pharmacokinetics and pharmacodynamics of the compounds were determined after a single intravenous bolus administration of 5 mg kg-1 midazolam, 2.5 mg kg-1 bretazenil, 10 mg kg-1 flumazenil or 2.5 mg kg-1 Ro 19-4603 to male Wistar derived rats. In a separate experiment the distribution between blood, cerebrospinal fluid and brain concentrations of these compounds was determined. A sensitive assay was developed to measure bretazenil and Ro 19-4603 concentrations in small samples of biological fluids. 3. The benzodiazepine-induced changes in amplitudes in the 11.5-30 Hz frequency band, as determined by aperiodic analysis, was used as EEG effect measure. Concentration-EEG effect relationships were derived by a pharmacokinetic-pharmacodynamic modelling procedure and in the case of midazolam, bretazenil and Ro 19-4603 successfully quantified by the sigmoidal Emax model. Large differences in maximal effect of midazolam (Emax = 73 +/- 2 microVs-1), bretazenil (Emax = 19 +/- 1 microVs-1) and Ro 19-4603 (Emax = -6.5 +/- 0.4 microVs-1) were observed, reflecting their differences in intrinsic efficacy. A close correlation was found between the EC50 values based on free drug concentration and receptor affinity as determined by displacement of [3H]-flumazenil in a washed brain homogenate at 37 degrees C. In the concentration range of receptor saturation flumazenil did not produce any changes in the EEG effect measure.4. The study demonstrated that the change in amplitudes in the 11.5-30 Hz frequency band of the EEG is a relevant measure of the pharmacological effect intensity of benzodiazepines, because it seems to reflect their affinity and intrinsic efficacy at the central GABA-benzodiazepine receptor complex.

Biopharmacological data and high-performance liquid chromatographic analysis of 1,4-benzodiazepines in biological fluids: A review

A review with 123 references on the analysis of 1,4-benzodiazepines in biological samples using HPLC is presented. Some important physico-chemical and biopharmacological data for the development of analytical methods are collected. Different methods of sample pretreatment, chromatographic conditions and detection systems are discussed.

Decreased systemic clearance of lorazepam in humans with spinal cord injury

Serum concentration-time course profiles, serum protein binding, and disposition parameters of lorazepam (LRZ), a benzodiazepine with sedative-hypnotic, anxiolytic, and anti-seizure properties, were studied as part of a systematic effort to define population-specific pharmacokinetic behavior in humans with chronic spinal cord injury (SCI). Twenty-four healthy subjects (nine tetraplegic, six paraplegic, nine able-bodied) were given an IV bolus of 2.0 mg of LRZ. Noncompartmental estimation of pharmacokinetic parameters disclosed a 37% decrease in the total systemic clearance (CL) of LRZ in tetraplegic patients. Altered LRZ clearance was observed independently of significant changes in volume of distribution or serum protein binding. The early elimination of LRZ (0-10 hr) was characterized by wide fluctuations in serum concentration suggestive of impaired enterohepatic circulation and could be distinguished from LRZ elimination observed in able-bodied subjects. We conclude that decreased systemic CL and the altered terminal elimination profile of LRZ are attributable to the pathophysiology of SCI.

Sensitivity to triazolam in the elderly

BACKGROUND

Elderly persons frequently appear to be sensitive to the effects of many drugs that depress the central nervous system. We studied the effect of age on the pharmacokinetics and pharmacodynamics of the benzodiazepine hypnotic agent triazolam, now the most frequently prescribed hypnotic drug in the United States.

METHODS

Twenty-six healthy young subjects (mean age, 30 years) and 21 healthy elderly subjects (mean age, 69 years) participated in a four-way crossover study. After a single-blind adaptation trial with placebo, each subject received, in random order and in double-blind fashion, single doses of placebo, 0.125 mg of triazolam, and 0.25 mg of triazolam. For 24 hours after the administration of each of the three study medications, plasma triazolam levels were determined and psychomotor performance, memory, and degree of sedation were assessed.

RESULTS

Plasma triazolam concentrations increased in proportion to the dose, but the elderly subjects had higher plasma concentrations due to reduced clearance of the drug. The degree of sedation as rated by an observer and the reduction in the subjects' performance on the digit-symbol substitution test were both greater in the elderly than in the young subjects after they were given the same doses. The relation of the plasma triazolam concentration to the degree of impairment was similar for the two groups. As part of the study, information was presented 1 1/2 hours after the administration of the drugs; the subjects' ability to recall the information 24 hours later was impaired by both doses of triazolam, and the percent decrease was similar in the young and elderly groups.

CONCLUSIONS

Triazolam caused a greater degree of sedation and greater impairment of psychomotor performance in healthy elderly persons than in young persons who received the same dose. These effects resulted from reduced clearance and higher plasma concentrations of triazolam rather than from an increased intrinsic sensitivity to the drug. On the basis of these results, the dosage of triazolam for elderly persons should be reduced on average by 50 percent.