Plasma protein binding of diazepam and tolbutamide in chronic alcoholics

Benzodiazepines in the Management of Seizures and Status Epilepticus: A Review of Routes of Delivery, Pharmacokinetics, Efficacy, and Tolerability

Status epilepticus (SE) is an acute, life-threatening medical condition that requires immediate, effective therapy. Therefore, the acute care of prolonged seizures and SE is a constant challenge for healthcare professionals, in both the pre-hospital and the in-hospital settings. Benzodiazepines (BZDs) are the first-line treatment for SE worldwide due to their efficacy, tolerability, and rapid onset of action. Although all BZDs act as allosteric modulators at the inhibitory gamma-aminobutyric acid (GABA)_A receptor, the individual agents have different efficacy profiles and pharmacokinetic and pharmacodynamic properties, some of which differ significantly. The conventional BZDs clonazepam, diazepam, lorazepam and midazolam differ mainly in their durations of action and available routes of administration. In addition to the common intravenous, intramuscular and rectal administrations that have long been established in the acute treatment of SE, other administration routes for BZDs-such as intranasal administration-have been developed in recent years, with some preparations already commercially available. Most recently, the intrapulmonary administration of BZDs via an inhaler has been investigated. This narrative review provides an overview of the current knowledge on the efficacy and tolerability of different BZDs, with a focus on different routes of administration and therapeutic specificities for different patient groups, and offers an outlook on potential future drug developments for the treatment of prolonged seizures and SE.

Case Report: Enhanced Diazepam Elimination With the Molecular Adsorbents Recirculating System (MARS) in Severe Autointoxication: A Survival Case Report

Objective: Due to the extensive use of diazepam worldwide, self-induced intoxication is very common, yet rarely fatal. Nevertheless, the management of intoxication caused by extremely high doses of diazepam is not known, as well as the effectiveness of flumazenil, a specific benzodiazepine (BDZ) antagonist. Here we present the first report on the enhanced elimination (clearance) of diazepam using the Molecular Adsorbents Recirculating System (MARS) following autointoxication with an extremely high dose as part of a suicide attempt. Case: A 44-year-old male patient was admitted to the ICU because of impaired consciousness following the ingestion of 20 g of diazepam. Blood and urine samples revealed high benzodiazepine levels. Repeated doses of flumazenil were without effect on consciousness. Following deterioration of the patient's clinical condition, including unconsciousness, hypoventilation, and decreased SpO2 (88%), the patient was intubated and mechanically ventilated. On the fourth day after admission, the patient was unresponsive, with no attempt to breath spontaneously. The plasma level of benzodiazepines was 1,772 μg/l. The elimination of benzodiazepines by MARS was attempted, continuing for 5 days, with one session per day. Five sessions of MARS effectively enhanced benzodiazepine elimination. After the first MARS treatment, the plasma level of benzodiazepines dropped from 1,772 to 780 μg/l. After the final MARS treatment on the eighth day, the patient was weaned from mechanical ventilation and extubated. Two days later, the patient was discharged to the internal medicine department and subsequently to the psychiatry department. Conclusions: To the best of our knowledge, this is the first case reporting successful treatment of diazepam intoxication using MARS. In severe cases of diazepam intoxication, with prolonged unconsciousness and the necessity of mechanical ventilation, we suggest considering the use of MARS elimination therapy together with the monitoring of the BDZ plasma level.

Meeting the Challenge of Predicting Hepatic Clearance of Compounds Slowly Metabolized by Cytochrome P450 Using a Novel Hepatocyte Model, HepatoPac

Generating accurate in vitro intrinsic clearance data is an important aspect of predicting in vivo human clearance. Primary hepatocytes in suspension are routinely used to predict in vivo clearance; however, incubation times have typically been limited to 4-6 hours, which is not long enough to accurately evaluate the metabolic stability of slowly metabolized compounds. HepatoPac is a micropatterened hepatocyte-fibroblast coculture system that can be used for continuous incubations of up to 7 days. This study evaluated the ability of human HepatoPac to predict the in vivo clearance (CL) of 17 commercially available compounds with low to intermediate clearance (<12 ml/min/kg). In vitro half-life for disappearance of each compound was converted to hepatic clearance using the well stirred model, with and without correction for plasma protein binding. Hepatic CL, using three individual donors, was accurately predicted for 11 of 17 compounds (59%; predicted clearance within 2-fold of observed human in vivo clearance values). The accuracy of prediction increased to 82% (14 of 17 compounds) with an acceptance criterion defined as within 3-fold. When considering only low clearance compounds (<5 ml/min per kg), which represented 10 of the 17 compounds, the accuracy of prediction was 70% within 2-fold and 100% within 3-fold. In addition, the turnover of three slowly metabolized compounds (alprazolam, meloxicam, and tolbutamide) in HepatoPac was directly compared with turnover in suspended hepatocytes. The turnover of alprazolam and tolbutamide was approximately 2-fold greater using HepatoPac compared with suspended hepatocytes, which was roughly in line with the extrapolated values (correcting for the longer incubation time and lower cell number with HepatoPac). HepatoPac, but not suspended hepatocytes, demonstrated significant turnover of meloxicam. These results demonstrate the utility of HepatoPac for prediction of in vivo hepatic clearance, particularly with low clearance compounds.

Meeting the challenge of predicting hepatic clearance of compounds slowly metabolized by cytochrome P450 using a novel hepatocyte model, HepatoPac

Generating accurate in vitro intrinsic clearance data is an important aspect of predicting in vivo human clearance. Primary hepatocytes in suspension are routinely used to predict in vivo clearance; however, incubation times have typically been limited to 4-6 hours, which is not long enough to accurately evaluate the metabolic stability of slowly metabolized compounds. HepatoPac is a micropatterened hepatocyte-fibroblast coculture system that can be used for continuous incubations of up to 7 days. This study evaluated the ability of human HepatoPac to predict the in vivo clearance (CL) of 17 commercially available compounds with low to intermediate clearance (<12 ml/min per kg). In vitro half-life for disappearance of each compound was converted to hepatic clearance using the well stirred model, with and without correction for plasma protein binding. Hepatic CL, using three individual donors, was accurately predicted for 10 of 17 compounds (59%; predicted clearance within 2-fold of observed human in vivo clearance values). The accuracy of prediction increased to 76% (13 of 17 compounds) with an acceptance criterion defined as within 3-fold. When considering only low clearance compounds (<5 ml/min per kg), which represented 10 of the 17 compounds, the accuracy of prediction was 60% within 2-fold and 90% within 3-fold. In addition, the turnover of three slowly metabolized compounds (alprazolam, meloxicam, and tolbutamide) in HepatoPac was directly compared with turnover in suspended hepatocytes. The turnover of alprazolam and tolbutamide was approximately 2-fold greater using HepatoPac compared with suspended hepatocytes, which was roughly in line with the extrapolated values (correcting for the longer incubation time and lower cell number with HepatoPac). HepatoPac, but not suspended hepatocytes, demonstrated significant turnover of meloxicam. These results demonstrate the utility of HepatoPac for prediction of in vivo hepatic clearance, particularly with low clearance compounds.

Peritoneal Dialysis Alters Tolbutamide Pharmacokinetics in Rats with Experimental Acute Renal Failure

The plasma concentration profile of the antidiabetic agent tolbutamide was investigated in glycerol-induced acute renal failure (ARF) rats receiving or not receiving peritoneal dialysis (PD) to assess the impact of performing dialysis on tolbutamide pharmacokinetics. It was revealed that the plasma concentration of tolbutamide was decreased by 23.4% by performing PD in ARF rats, while it was not changed by PD in normal rats. The decrease in the plasma concentration of tolbutamide was nearly proportional to the increase in its volume of distribution. To clarify the mechanisms responsible for the decreased tolbutamide concentration caused by PD, the plasma protein binding of tolbutamide was examined in normal and ARF rats. The plasma unbound fraction of tolbutamide was higher in ARF rats than in normal rats, and the dissociation constants were 3.5+/-0.7 and 5.5+/-0.2 microg in normal and ARF rats, respectively. These results indicated that the unbound fraction of tolbutamide was increased in ARF rats because of its protein binding being suppressed. It is therefore likely that since a measurable amount of tolbutamide can distribute in peritoneal dialysate in ARF rats, but not in normal rats, the plasma concentration of tolbutamide was decreased by performing PD only in ARF rats. These findings suggest that diabetes medication with tolbutamide should be carefully performed in patients receiving dialysis treatment.

Benzodiazepine poisoning. Clinical and pharmacological considerations and treatment

Benzodiazepines are among the most frequently prescribed drugs worldwide. This popularity is based not only on their efficacy but also on their remarkable safety. Pure benzodiazepine overdoses usually induce a mild to moderate central nervous system depression; deep coma requiring assisted ventilation is rare, and should prompt a search for other toxic substances. The severity of the CNS depression is influenced by the dose, the age of the patient and his or her clinical status prior to the ingestion, and the coingestion of other CNS depressants. In severe overdoses, benzodiazepines can occasionally induce cardiovascular and pulmonary toxicity, but deaths resulting from pure benzodiazepine overdoses are rare. Quantitative determinations of benzodiazepines are not useful in the clinical management of intoxicated patients since there is no correlation between serum concentrations and pharmacological and toxicological effects. Benzodiazepine overdoses occurring during pregnancy rarely induce serious morbidity in mothers or fetuses, although large doses administered near delivery can induce respiratory depression in neonates. The teratogenic potential of benzodiazepines remains controversial, but is probably small if it exists at all. There is clear evidence that the prolonged use of even therapeutic doses of benzodiazepines will lead to dependence. The risk of developing significant withdrawal symptoms is related to dosage and duration of treatment. Prevention of gastrointestinal absorption should be initiated in all intentional benzodiazepine overdoses. Forced diuresis and dialysis techniques are not indicated since they will not significantly accelerate the elimination of these agents. Intravenous administration of flumazenil, a pure benzodiazepine antagonist, effectively reverses benzodiazepine-induced CNS depression.

Pharmacokinetics of cefprozil in healthy subjects and patients with hepatic impairment

The pharmacokinetics of cefprozil were studied in 12 (9 men, 3 women) subjects with hepatic impairment and in 12 healthy subjects who were matched for age, sex, and weight. Each subject received a single 1000 mg oral dose of cefprozil, which consists of cis and trans isomers in approximately a 90:10 ratio. Serial blood and urine samples were collected and analyzed using validated HPLC/UV methods for the concentration of each isomer. The results of the plasma and urine analyses were subjected to noncompartmental pharmacokinetic analysis. The values for the peak plasma concentrations (Cmax), area under the plasma concentration versus time curve (AUC0-infinity), apparent total body clearance (Clt/F), renal clearance (Clr), and percent of drug excreted in urine (%UR) of each isomer were not significantly different in healthy subjects and patients with hepatic impairment. The only parameters that were significantly (P less than or equal to .05) longer in patients with hepatic impairment were mean residence time in the body (MRT) and half-life; the MRT for the cis isomer in healthy subjects and subjects with hepatic impairment were 3.33 hr and 3.88 hr, respectively, and for the trans isomer 3.17 hr and 3.68 hr; the half-life for the cis isomer was 1.62 hr and 2.22 hr, respectively, and for the trans isomer 1.21 hr and 1.54 hr. The pharmacokinetics of the cis and trans isomers of cefprozil were virtually identical in healthy subjects as well as those with hepatic impairment.

Tianeptine binding to human plasma proteins and plasma from patients with hepatic cirrhosis or renal failure

1. The binding of tianeptine to human plasma, isolated plasma proteins, red blood cells and to plasma from patients with cirrhosis or renal failure was studied in vitro by equilibrium dialysis. 2. Tianeptine is highly bound to plasma (95%) at therapeutic concentrations (0.3-1 microM). No saturation of the binding sites was seen. 3. Human serum albumin (HSA) was shown to be mainly responsible for this binding (94%) with a saturable process characterized by one binding site with a moderate affinity (Ka = 4.2 x 10(4) M-1) and a non-saturable process with a low total affinity (nKa = 1.2 x 10(4) M-1). 4. Like many basic and amphoteric drugs, tianeptine showed a saturable binding to alpha 1-acid glycoprotein (AAG) with one site and a moderate affinity (Ka = 3.7 x 10(4) M-1). Its binding to lipoproteins and red blood cells (RBC) was weak and non-saturable. Over the range of therapeutic drug concentrations (0.3-1 microM), the unbound fraction in blood remains constant (4.5%). 5. Interactions were studied using non-esterified fatty acids (NEFA) at pathological concentrations; they altered tianeptine binding to plasma and to isolated HSA. Tianeptine seems to bind to a HSA site different from sites I (warfarin) and II (diazepam), but close to site II. It also shares the only basic-site on AAG. However, at therapeutic drug concentrations (0.3-1 microM), not all of these interactions occur. 6. The binding of tianeptine varied according to HSA, AAG and NEFA concentrations both in patients and healthy subjects. In patients with chronic renal failure having high NEFA concentrations the unbound fraction of tianeptine (fu) increased from 0.045 to 0.153 compared with normal (P less than 0.001). In cirrhotic patients, with relatively low HSA concentrations, the fu of tianeptine increased from 0.045 to 0.088 compared with normal (P less than 0.01). 7. Multiple regression analysis of all of the data indicated that the fu of tianeptine was related significantly to HSA, NEFA and AAG concentrations, with a particularly strong correlation with NEFA concentrations. Therefore, variation of HSA and NEFA concentrations in patients on maintenance therapy may cause an increase of tianeptine fu.

Plasma protein binding of frusemide in liver disease: effect of hypoalbuminaemia and hyperbilirubinaemia

The binding of frusemide was studied in the plasma of 20 healthy subjects and 45 patients with liver disease. The unbound percentage (mean +/- s.d.) of frusemide was 1.64 +/- 0.21 healthy subjects) and 2.24 +/- 0.79 (patients) (P less than 0.01). By grouping the patients on the basis of plasma albuminaemia and bilirubinaemia four clusters namely: 'normal concentrations of albumin and bilirubin' (A), 'hyperbilirubinaemia and normal albumin concentration' (B), 'hypoalbuminaemia and normal bilirubin concentration' (C) and 'hypoalbuminaemia and hyperbilirubinaemia' (D) were defined. The unbound percentage of frusemide was 1.80 +/- 0.36 in (A); 2.44 +/- 1.05 in (B); 2.23 +/- 0.38 in (C); 2.76 +/- 0.77 in (D). The figure for healthy volunteers was not different from A, whereas it was significantly lower than those for B and D (P less than 0.01) and for C (P less than 0.05). A lowered binding of frusemide was associated with hypoalbuminaemia or hyperbilirubinaemia.

Determinants of low serum concentrations of salicylates in patients with Kawasaki disease

The mechanisms leading to the previously reported difficulties in achieving therapeutic serum concentrations of salicylates in Kawasaki disease were studied in eight children, once during the acute (febrile) phase and again during the nonfebrile (subacute) phase of the disease. Salicylate bioavailability was impaired during the acute phase of the disease (47.7% +/- 6.6%), and increased significantly thereafter to 75.1% +/- 9.3%. During the febrile phase there was a significant correlation between salicylate bioavailability and steady-state serum concentrations. Salicylate renal clearance was significantly higher during the febrile phase (14.45 +/- 2.5 mL/kg.h), compared with the nonfebrile phase (7 +/- 1.6 mL/kg.h, P less than 0.05). The change in salicylate clearance could be explained by decreased protein binding in the acute phase (82.5% +/- 1.9%) with substantially more free salicylates caused by significantly lower serum albumin concentrations. Changes in urine metabolites during the acute and subacute phases were consistent with the changes in dose administered (100 mg/kg in the acute phase vs 10 mg/kg in the subacute phase). The pattern of metabolites excreted in the urine of children with Kawasaki disease receiving 100 mg/kg was similar to that in children with juvenile rheumatoid arthritis receiving the same dose.

Acetaldehyde adducts with serum proteins are not responsible for decreased drug binding in alcoholic patients

Decreased plasma binding of phenytoin and diazepam has previously been described in patients with alcoholic liver diseases. It has been attributed to hypoalbuminemia, endogenous displacers and/or qualitative changes in albumin such as formation of adducts with acetaldehyde, a highly reactive metabolite of ethanol. In the present report this hypothesis was tested. After treating the sera with activated charcoal to remove the endogenous displacers and adjusting albumin concentration to a constant level, the binding parameters of both drugs, phenytoin and diazepam, were determined in 14 healthy men and 16 alcoholic patients by equilibrium dialysis. In these conditions, no significant difference in the number of binding sites nor in the affinity constant was observed, which suggests that acetaldehyde adducts with proteins do not contribute, to a major extent, to the defect of drug binding observed in alcoholic patients.

Binding properties of glycosylated albumin and acetaldehyde albumin

Glucose and acetaldehyde react covalently with albumin to form the post-translationally modified group of proteins, the glycosylated albumins and the acetaldehyde albumins, respectively. This study contrasts the binding ability of a major acetaldehyde albumin fraction synthesized in vitro with glycosylated albumin. A microdialysis rate method, using either [14C]monoacetyldiaminodiphenyl sulfone (MADDS), a deputy ligand for bilirubin, or [14C]diazepam, was employed to evaluate binding at these two sites. Our results indicate that prolonged exposure of purified human serum albumin to acetaldehyde results in a major acetaldehyde albumin fraction that lacks the ability to bind MADDS and diazepam. This fraction migrates identically to albumin on SDS polyacrylamide gel electrophoresis, but exhibits microheterogeneity with a more acidic pI band as seen on analytical isoelectric focusing. We suggest that altered drug binding in alcoholics may be partially explained by altered binding ability of acetaldehyde albumins.

Effects of ethanol on drug and metabolite pharmacokinetics

Pharmacokinetic interactions of ethanol with other drugs, including its effects upon drug metabolite disposition, are reviewed in terms of clearance concepts. This approach is particularly useful in understanding the mechanisms of ethanol-drug interactions, i.e. in separating the effects of ethanol upon drug clearance, volume of distribution and plasma protein binding. The application of clearance concepts provides the basis for understanding the qualitative differences in ethanol interactions with low and high hepatic extraction ratio drugs. The effects of short and long term ethanol consumption upon different types of drug metabolism (oxidative, acetylation and glucuronidation) have been considered. Long term ethanol consumption may increase the clearance of a drug by induction of oxidative metabolism whereas short term consumption may decrease the clearance of such a drug. Clearance by N-acetylation appears to be increased in the presence of ethanol, and clearance by conjugation to glucuronic acid is decreased for some drugs by single-dose consumption of ethanol.

Valproic acid and diazepam interaction in vivo

1 The effect of oral administration of sodium valproate (1500 mg daily) on the distribution and elimination kinetics of intravenously administered diazepam in six healthy volunteers has been studied. 2 During valproate administration the unbound fraction of diazepam in serum increased approximately two fold. This was accompanied by a significant increase in apparent volume of distribution and plasma clearance of diazepam. 3 There was a positive correlation between the change in free fraction and the increase in both apparent volume of distribution and plasma clearance of the drug. 4 The concentration of unbound diazepam in serum (calculated from the percent free diazepam and total serum concentration) was significantly higher during valproate administration. Both the intrinsic clearance and volume of distribution of unbound drug were significantly reduced. 5 Mean serum N-desmethyldiazepam levels were significantly lower during valproate coadministration. 6 These results suggest that valproic acid displaces diazepam from plasma protein binding sites and inhibits its metabolism.

Comparative protein binding of diazepam and desmethyldiazepam

The extent of plasma protein binding of diazepam (DZ) and its major metabolite, desmethyldiazepam (DMDZ), was determined by equilibrium dialysis in plasma samples drawn from 62 nonfasting unheparinized volunteers aged 20 to 85 years. The free fraction for diazepam averaged 1.48 per cent (range 0.85 to 2.30 per cent) and increased with age (r = 0.33). Desmethyldiazepam also was extensively bound. The mean free fraction was 2.97 per cent (range 1.78 to 5.28 per cent) and increased with age (r = 0.27). Free fractions for both diazepam and desmethyldiazepam were negatively correlated with plasma albumin concentration (r = --0.17 and --0.39). However, age, sex, and albumin explained only a small proportion of variability in free fraction for either compound. Free fraction for desmethyldiazepam always exceeded that for diazepam, and the two were correlated (r = 0.32). Thus, at any given total plasma concentration, the unbound concentration of desmethyldiazepam will exceed that of diazepam.

Comparison of plasma and saliva levels of diazepam

1. Salivary, unbound and total plasma levels of diazepam have been compared in nineteen subjects. 2. Salivary diazepam levels were significantly higher (P < 0.001) than, but closely related to the corresponding unbound levels (r = 0.97) at 2.5-3 h after administration of the drug. 3. The results presented suggest that saliva levels can be used to predict the corresponding plasma levels at a given time, but there is no 1:1 relation between the unbound diazepam concentration in plasma and the saliva level of the drug.

Disease-induced changes in the plasma binding of basic drugs

The plasma binding of basic (cationic) drugs differs from that of the more completely studied acidic drugs. Basic drugs associate with a number of plasma constituents. alpha 1-Acid glycoprotein, lipoprotein, and albumin all appear to play an important role in the binding of most of these drugs. Acidic drugs bind largely to albumin. The variation in plasma albumin is relatively narrow and is almost always in the direction of decreased concentrations. alpha 1-Acid glycoprotein and lipoproteins show large fluctuations due both to physiological and pathological conditions. Decreases and increases in concentration have been observed. Associated with these changes in binding proteins, both decreases and increases in plasma binding of basic drugs have been recorded. Increased binding with disease appears to be virtually unique to basic drugs. The implications of these newly described disease-induced increases in plasma binding have yet to be explored. With the limited information in hand the following consequences are predicted. Increased binding will tend to decrease the volume of distribution of total (bound plus free) drug. The clearance will be unchanged or decreased depending upon the initial clearance of the drug and the avidity of the protein binding. As the half-life depends upon both clearance and volume of distribution, changes in it will be variable, depending upon changes in these two parameters. It is predicted that the area under the free drug plasma concentration-time curve will decrease with increasing binding after an intravenous dose while it will be unchanged after an oral dose. The relationship of total drug plasma concentration to free drug concentration will change with changes in binding. Thus plasma concentration monitoring of drug therapy by use of total drug concentrations will be inaccurate in situations in which large variations in binding occur. Misinterpretations of both therapeutic monitoring and pharmacokinetics studies in disease states with altered binding are likely unless these changes are appreciated.

Diurnal variations in plasma diazepam concentrations associated with reciprocal changes in free fraction

1 The characteristics and mechanism of fluctuations in diazepam and N-desmethyldiazepam concentrations and diazepam free fraction were studied in six volunteers, who received diazepam (10 mg, i.v. over 20 min) and in five chronic diazepam users. 2 Within a day total diazepam and N-desmethyldiazepam concentrations varied significantly (P less than 0.001) and were lower than predicted between 23.00 and 08.00 h and higher by 09.00 h. In contrast, diazepam free fraction also varied significantly (P less than 0.001) and was highest between 23.00 and 08.00 h and lower by 09.00 h. Coincident increases in total diazepam concentrations (P less than 0.005) and decreases in diazepam free fraction were associated with food intake (P less than 0.05). 3 The coincident diurnal variations in diazepam and N-desmethyldiazepam concentrations and the negative correlation between total diazepam concentration and diazepam free fraction (r = 0.73, P less than 0.001) suggest that the mechanism of the fluctuations is intravascular and tissue redistribution rather than effect on drug biotransformation. 4 These variations may introduce large between and within investigator experimental differences in the determination of kinetic parameters. Free drug concentration varies over the day, and within day variations in clinical effect may be observed.

Diazepam and N-desmethyldiazepam in saliva of hospital inpatients

Saliva samples were obtained from 25 hospital inpatients (14 males, 11 females, aged 19 to 79 years) taking diazepam (6 to 45 mg) daily. Despite interindividual variations in pharmacokinetics, a correlation was found between both dose and salivary diazepam concentration (r = 0.54, P less than 0.01) and dose and salivary N-desmethyldiazepam concentration (r = 0.78, P = 0.01). The correlation between the salivary concentration of diazepam and that of its metabolite is good (r = 0.76, P less than 0.01). The slope of this linear regression, 1.58, reflects the relative clearances of the metabolite and parent drug and agrees with the theoretical value, 1.60, obtained by calculation using known plasma pharmacokinetic and protein-binding parameters. There is a weak linear correlation of steady-state salivary benzodiazepine (drug and metabolite) concentration per milligram dose and age (r = 0.37, P less than 0.01).

[Clinical pharmacokinetics of diazepam and its biologically active metabolites (author's transl)]

The pharmacokinetics of diazepam and its biologically active metabolites desmethyldiazepam and oxazepam is critically evaluated from a clinically relevant point of view. The slow elimination of diazepam is dependent on the degree of plasma protein binding, the duration of the medication, the age and the liver function of the patient. While the normal half-life (T1/2(beta)) varies between 1 and 2 days, it can be increased to up to 80--100 h in subjects over 60 years of age. In patients with liver disease T1/2(beta) is about doubled, which is caused by a reduction (factor 2) of the normal hepatic clearance of 26 ml/min. After subchronic treatment with diazepam the elimination rate is reduced about 20--70% in healthy subjects, but liver patients exhibit only a slightly further prolongation in T1/2(beta). The major metabolite desmethyldiazepam has a T1/2(beta) of 51 h and a Cl of 11 ml/min and accumulates after multiple doses of diazepam since its elimination is much slower than that of its parent compound. The elimination of this drug is also impaired (factor 2) in patients with liver disease. In contrast to these findings oxazepam is excreted as glucuronide in the urine relatively fast and independently of the liver function with a T1/2(beta) of 5.5 h and a Cl of 130 ml/min.

Transfer of nitrazepam across the human placenta

Six women from 14 to 17 weeks pregnant, and 12 woman from 36 to 40 weeks pregnant, were given nitrazepam 5 mg orally about 12 h before legal abortion by hysterotomy in the former group and elective caesarean section in the latter group. The concentration of nitrazepam was determined by gas-liquid chromatography. Binding to plasma proteins was evaluated by separation of the protein-free fraction by ultracentrifugation. In the first group (early pregnancy) the level of nitrazepam was found to be lower in the fetal than in the maternal circulation. The concentration in amniotic fluid was still lower. In the latter group (late pregnancy) the concentration both of unbound and total nitrazepam in maternal and fetal plasma were in equilibrium, which indicated an increase in transplancental transfer in late pregnancy. The percentage of unbound nitrazepam in both cases was 12%.

Protein binding and kinetics of drugs in liver diseases

Although the liver is the major site for drug biotransformation, the effect of hepatic dysfunction on drug disposition has not been consistent or predictable. Most early studies of drug kinetics in liver disease measured only half-life. Only in the past few years has it been realised that liver diseases can affect drug absorption, hepatic metabolism, tissue distribution, and protein binding, which complicate interpretation of any change, or lack of change in drug half-life. Furthermore, it is now apparent that the efficiency with which a drug is metabolised by the liver, the extent of binding to blood constituents, and the aetiology and stage of the hepatic disorder are each important in determining whether significant alterations in drug disposition will occur. A pharmacokinetic perfusion model which takes into account many of the above factors has been proposed, and appears to be useful for predicting changes in the disposition of rapidly metabolised compounds. Nevertheless, the state of knowledge about those factors which limit the rate of metabolism of individual drugs or classes of drugs in inadequate, and no general model or guidelines which are useful clinically have been developed. Patients with hepatic disorders may show increases or decreases in sensitivity independent of alterations in drug disposition. The clinician caring for such patients must be cautious about the use of any drugs, and rely heavily on careful patient observation to determine efficacy or toxicity.