Chloramphenicol succinate, a competitive substrate and inhibitor of succinate dehydrogenase: possible reason for its toxicity.

From our previous study [Eur. J. Clin. Pharmacol. 56 (2000) 405] we hypothesized that chloramphenicol succinate (CAPS) may be a competitive substrate for succinate dehydrogenase (SDH). It may be oxidized by SDH to release chloramphenicol (CAP), which may inhibit SDH by feed back mechanism. The present ex-vivo/in vitro study was aimed to investigate this possibility by using human tissues (bone marrow and liver samples) and animal tissues (rat liver and kidney). The effect of different SDH activators and specific inhibitors was studied on CAPS metabolism by SDH. The metabolites and reduction products were detected by using HPLC. In marrow samples, CAPS was slowly oxidized to form CAP. The formation of CAP (oxidation product) was enhanced by FAD and low malonate and inhibited by high malonate and 3-NPA. Similar results were obtained with mitochondria from human and rat tissues. These studies suggest that CAPS could be a competitive oxidative substrate and the metabolite CAP could be an inhibitor at the reduction site. Therefore, SDH could be a target molecule responsible for CAPS induced toxicity.     

Pharmacokinetics of intravenous chloramphenicol sodium succinate in adult patients with normal renal and hepatic function

The pharmacokinetics of chloramphenicol (CAP) and total chloramphenicol succinate (CAPS) were studied in eight hospitalized adult patients with normal renal and hepatic function receiving intravenous chloramphenicol sodium succinate therapy. The steady-state peak concentrations of CAP (8.4–26.0 g/ml) occurred at an average of 18.0 min (range 5.4–40.2) after cessation of the chloramphenicol sodium succinate infusion. Unhydrolyzed CAPS prodrug, representing 26.0±7.0% of the dose, was recovered unchanged in the urine indicating that the bioavailability of CAP from a dose of intravenous chloramphenicol succinate is not complete. A pharmacokinetic model was developed for simultaneous fitting of CAP and CAPS plasma concentration data. Pharmacokinetic parameters determined by simultaneous fitting were: V, 0.81±0.18 liters/kg; t_1/2, 3.20 ±1.02 hr; CL_B, 3.21±1.27 ml/min/kg for chloramphenicol; and V, 0.38±0.13 liters/kg; t_1/2, 0.57±0.12hr; CL_B, 7.72±1.87 ml/min/kg for total chloramphenicol succinate.Supported in part by Faculty Research Council Grant VF648 from the University of North Carolina.     

CYP2E1-dependent benzene toxicity: the role of extrahepatic benzene metabolism

Benzene, a ubiquitous environmental pollutant, is haematotoxic and myelotoxic. As has been shown earlier, cytochrome P450 2E1 (CYP2E1)-dependent metabolism is a prerequisite for the cytotoxic and genotoxic effects of benzene, but which of the benzene metabolites produces toxicity is still unknown. The observed differences between the toxicity of benzene and that of phenol, a major metabolite of benzene, could be explained by alternative hypotheses. That is, whether (1) toxic benzene effects are caused by metabolites not derived from phenol (e.g. benzene epoxide, muconaldehyde), which are formed in the liver and are able to reach the target organ(s); or (2) benzene penetrates into the bone marrow, where local metabolism takes place, whereas phenol does not reach the target tissue because of its polarity. To further investigate hypothesis 2, we used various strains of mice (AKR, B6C3F1, CBA/Ca, CD-1 and C57Bl/6), for which different toxic responses have been reported in the haematopoietic system after chronic benzene exposure. In these strains, CYP2E1 expression in bone marrow was investigated and compared with CYP2E1 expression in liver by means of two independent methods. Quantification of CYP2E1-dependent hydroxylation of chlorzoxazone (CLX) by high-performance liquid chromatography (HPLC; functional analysis) was used to characterize specific enzymatic activities. Protein identification was performed by Western blotting using CYP2E1-specific antibodies. In liver microsomes of all strains investigated, considerable amounts of CYP2E1-specific protein and correspondingly high CYP2E1 hydroxylase activities could be detected. No significant differences in CYP2E1-dependent enzyme activities were found between the five strains (range of medians, 4.6–12.0 nmol 6-OH-CLX/[mg protein × min]) in hepatic tissue. In the bone marrow, CYP2E1 could also be detected in all strains investigated. However, chlorzoxazone hydroxylase activities were considerably lower (range of medians, 0.2–0.8 × 10⁻³ nmol 6-OH-CLX/[mg protein × min]) compared with those obtained from liver microsomes. No significant (P > 0.05) interstrain differences in CYP2E1 expression in liver and/or bone marrow could be observed in the mouse strains investigated. The data obtained thus far from our investigations suggest that strain-specific differences in the tumour response of the haematopoietic system of mice chronically exposed to benzene cannot be explained by differences in either hepatic or in myeloid CYP2E1-dependent metabolism of benzene. Received: 7 September 1998 / Accepted: 13 April 1999     

Pharmacokinetics and pharmacodynamics of clevidipine in healthy volunteers after intravenous infusion

Objective: To determine the pharmacokinetics and pharmacodynamics of clevidipine, a new ultrashort-acting calcium antagonist, in healthy male volunteers following a constant rate infusion. Methods: Eight healthy male volunteers received 1030 nmol · min⁻¹ of clevidipine together with a tracer dose of ³[H]-clevidipine for 1 h as an i.v. infusion. Frequent venous blood samples and effect recordings were obtained during ongoing infusion and up to 32 h following termination of the infusion. The excretion of radioactivity in urine and faeces was followed for 7 days. Results: A two-compartment model gave the best fit to the individual clevidipine blood levels, resulting in a mean blood clearance of 0.14 (0.03) l · min⁻¹ · kg⁻¹ and a mean volume of distribution at steady state of 0.6 (0.1) l · kg⁻¹. The initial half-life was 1.6 (0.3) min, and the terminal half-life was 15 (5) min. The maximum concentration of the metabolite H 152/81 was reached 2.2 (1.3) min following termination of the infusion. The mean terminal half-life of the inactive primary metabolite was 9.5 (0.8) h and the mean recovery of the radioactive dose reached 83 (3)%. Following termination of the 1 h infusion, the effect on blood pressure (BP) and heart rate was back to pre-dose values within 15 min. Conclusion: Clevidipine is a high clearance drug, which is rapidly metabolized to the corresponding inactive acid. The t_max value of the primary metabolite, and a virtually identical value of the initial half-life and the half-life for elimination from the central compartment, indicate that the initial rapid decline of the post-infusion blood levels is mainly due to elimination rather than distribution. The duration of action of clevidipine is short. Received: 23 September 1998 / Accepted in revised form: 20 November 1998     

Distribution studies in CD-1 mice administered [14C]muconaldehyde

Trans,trans-muconaldehyde (muconaldehyde, MUC), a microsomal hematotoxic ring-opened metabolite of benzene, has been proposed to play a role in benzene hematotoxicity. In the present study, [¹⁴C]-muconaldehyde was administered to CD-1 mice and the distribution of [¹⁴C]muconaldehyde equivalents was investigated. The study was carried out to evaluate whether [¹⁴C]muconaldehyde equivalents could reach the bone marrow. [¹⁴C]Muconaldehyde at a dose of 2 mg/kg was administered intraperitoneally (3.4 μCi/mouse) and by intravenous injection (2.7 μCi/mouse). The amount of [¹⁴C]muconaldehyde equivalents was measured in the bone marrow, blood, liver, lung, kidney and spleen at 0.25, 0.5, 1, 2, 4, and 24 h after [¹⁴C]MUC administration. The results indicate that 0.044% or 0.018% of the total dose administered when given i.v. or i.p., respectively, reached the bone marrow. The elimination of the radioactivity in all organs had at least two phases. The bone marrow, kidney, and lung had a rapid first phase (t _1/2 0.5–1.2 h) and a slower second phase (t _1/2 2.8–15.7 h). In the liver, a slow first phase (t _1/2 3.7 h) was followed by a more rapid second phase (t _1/2 1.5 h). The level of radioactivity in blood and bone marrow was significantly higher when [¹⁴C]muconaldehyde was administered intravenously compared with intraperitoneally, demonstrating that the route of administration affects the distribution of [¹⁴C]muconaldehyde equivalents. Received: 26 March 1996 / Accepted: 17 June 1997     

Cerebrospinal fluid and plasma concentrations of dipyrone metabolites after a single oral dose of dipyrone

Objective: Dipyrone is a veteran analgesic and antipyretic drug. After oral administration it is rapidly converted by hydrolysis to 4-methylaminoantipyrine (MAA), which is further metabolized to 4-formylaminoantipyrine (FAA), 4-aminoantipyrine (AA) and 4-acetylaminoantipyrine (AAA). It is still debated whether the site of dipyrone action is in the central nervous system or in the periphery. The purpose of this study was to assess whether dipyrone metabolites cross the blood-brain barrier (BBB) when administered systemically. Methods: Twenty-eight patients undergoing diagnostic lumbar puncture (LP) were randomly assigned to receive two 0.5-g dipyrone tablets either 30 min, 1, 1.5, 2, 4, 6, 8 h or 12 h before the lumbar tap. A 5-ml blood sample was drawn concomitantly. Results: All four metabolites were found in the cerebrospinal fluid (CSF). Their appearance in the CSF lagged but followed that found in the plasma. Mean CSF/plasma ratios were 0.40 (for samples taken between 0.5–2 h) and 0.83 (for samples taken between 4–12 h) for MAA, 0.62 for AA, 0.55 for FAA and 0.40 for AAA (for all samples). Significant correlation was found between plasma and CSF concentrations for MAA, AA, FAA and AAA. Conclusion: The concentration-time course of dipyrone metabolite CSF concentrations are in agreement with that of their plasma concentrations and the analgesic effect of dipyrone. Received: 3 December 1997 / Accepted in revised form: 3 June 1998     

Grapefruit juice increases the bioavailability of artemether

Objective: To evaluate the effect of grapefruit juice on the pharmacokinetics of artemether in plasma and saliva after a single oral dose and to detect concentration-dependent electrocardiographic changes (bradycardia and QT_c prolongation). Methods: Six healthy male subjects were given a standard breakfast followed by two tablets of 50-mg artemether administered with water; 1 week later, the tablets were administered with 350 ml double-strength fresh frozen grapefruit juice. For 8 h, 17 blood- and saliva samples were collected, and 17 electrocardiograms were recorded. Drug and metabolite concentrations were measured by means of high-performance liquid chromatography with electrochemical detection. The pharmacokinetic parameters were determined using a one-compartment model. Results: Grapefruit juice significantly (P = 0.001) increased the mean peak concentration (C_max) of artemether more then twofold from 42 (SD 17) ng/ml to 107 (28) ng/ml. The time to reach C_max (t_max) with grapefruit juice was 2.1 (0.6) h compared with 3.6 (17) h with water (P = 0.02). The area under the concentration–time curve (AUC) almost doubled with grapefruit juice from 177 ng · h/ml to 336 ng.h/ml (P = 0.003). The elimination half-life remained unchanged (1.0 h vs 1.3 h). No major changes in the kinetics of the metabolite dihydroartemisinin were detected. Low artemether levels and zero dihydroartemisinin levels were found in saliva. No influences of artemether were observed on 17 electrocardiograms during the 8 h after drug intake – in particular there were no signs of bradycardia or QT_c prolongation. Conclusion: Grapefruit juice significantly increases the oral bioavailability of artemether without an effect on the elimination half-life. It suggests a role for intestinal CYP3A4 in the presystemic metabolism of artemether. Received: 21 December 1998 / Accepted in revised form: 15 March 1999     

Food increases the bioavailability of mefloquine

Objectives: To assess the effect of food on the pharmacokinetics of the antimalarial mefloquine and its major plasma metabolite in healthy volunteers. Methods: In an open, two-way cross-over study, 20 healthy male volunteers who had fasted overnight were randomised to receive a single oral dose of 750 mg mefloquine in the absence or presence of a standardised, high-fat breakfast, administered 30 min before drug administration. Blood samples were taken at specific times over an 8-week period. Plasma concentrations of mefloquine and its carboxylic acid metabolite were determined by high-performance liquid chromatography for pharmacokinetic evaluation. Results: The parameters C_max and AUC of both mefloquine and its metabolite were significantly (P < 0.05) higher under post-prandial conditions than under fasting conditions (mefloquine: mean C_max 1500 vs 868 μg · l⁻¹, mean AUC 645 vs 461 mg l⁻¹ · h; metabolite: C_max 1662 vs 1231 μg · l⁻¹, AUC 1740 vs 1310 mg l⁻¹ · h). The intersubject variability in C_max and AUC of mefloquine was less than 30% (coefficient of variation). The time to peak plasma concentration of mefloquine was significantly shorter after food intake (17 vs 36 h). Compared with absorption in volunteers who had fasted, food did not alter t_1/2 (mefloquine and its metabolite) and t_max (metabolite). Conclusion: Under the conditions of this study, food increases the rate and the extent of mefloquine absorption. It is reasonable to recommend that mefloquine be administered with food in travellers receiving chemoprophylaxis and in patients on recovery receiving curative treatment. In acutely ill patients, mefloquine should be taken as soon as possible and administration with or shortly after meals should be attempted as soon as feasible. Received: 10 February 1997 / Accepted in revised form: 16 June 1997     

Absorption, metabolism and excretion of a single oral dose of 14C-repaglinide during repaglinide multiple dosing

Objective: The present study was designed to assess the disposition of ¹⁴C-repaglinide in whole blood, plasma, urine and faeces, and to measure the total recovery of drug-related material in urine and faeces after a single 2-mg oral dose of ¹⁴C-repaglinide during multiple dosing. Methods: In this single-centre, open-label, phase-I trial, six healthy male volunteers received 2 mg of the prandial glucose regulator, repaglinide, four times daily for 13 days, 15 min before meals. On the morning of day 7, breakfast was omitted and the dose was given as an oral solution containing 2 mg of ¹⁴C-repaglinide. Results: After oral dosing, a mean peak plasma concentration of repaglinide of 27.74 ng · ml⁻¹ (range: 16.84–36.65 ng · ml⁻¹) was observed with a time to peak concentration of 0.5 h. Approximately 20% of repaglinide and its associated metabolites were distributed into red blood cells. No measurable ¹⁴C-radioactivity was present in whole blood samples 6 h after dosing. Within 96 h of dosing with ¹⁴C-repaglinide, 90% of the administered dose appeared in the faeces and 8% was excreted in urine. In the plasma, the major compound was repaglinide (61%). In the urine, the major metabolites were unidentified polar compounds, the aromatic amine (M₁) (24%), and the dicarboxylic acid (M₂) (22%). In the faeces, the major metabolite was M₂ (66% of administered dose). Therefore, repaglinide was excreted predominantly as metabolites and the major in vivo metabolite of repaglinide in humans was M₂. During regular dosing for 6 days, the morning plasma trough levels of repaglinide were, with very few exceptions, almost always too low to measure, indicating the absence of accumulation at this dose of 2 mg four times daily. Repaglinide was well tolerated, and there were no episodes of hypoglycaemia. Conclusion: After oral dosing with repaglinide, the mean peak plasma concentration was rapidly attained and, thereafter, plasma concentrations decreased promptly. The major route of excretion was via the faeces. These properties make repaglinide a suitable insulin secretagogue for all patients with type-2 diabetes who retain sufficient β-cell function. Received: 13 January 1999 / Accepted in revised form: 15 June 1999     

Effect of erythromycin and itraconazole on the pharmacokinetics of intravenous lignocaine

Objective: We have studied the possible interaction of erythromycin and itraconazole, both inhibitors of cytochrome P450 3A4 isoenzyme (CYP3A4), with intravenous lignocaine in nine healthy volunteers using a randomized cross-over study design. Methods: The subjects were given oral placebo, erythromycin (500 mg three times a day) or itraconazole (200 mg once a day) for 4 days. Intravenous lignocaine 1.5 mg · kg⁻¹ was given with an infusion for 60 min on the fourth day of pretreatment with placebo, erythromycin or itraconazole. Timed plasma samples were collected until 11 h. The concentrations of lignocaine and its metabolite monoethylglycinexylidide (MEGX) were measured by gas chromatography. Results: The area under the lignocaine concentration-time curve was similar during all three phases but erythromycin significantly increased the elimination half-life of lignocaine from 2.5 to 2.9 (0.7) h compared with placebo. Following itraconazole administration, t_1/2 was 2.6 h. The values for plasma clearance and volume of distribution at steady state were similar during all the phases. Compared with placebo and itraconazole, erythromycin significantly increased MEGX peak concentrations by approximately 40% and AUC_(0–11 h) by 45–60%. Conclusion: The plasma decay of lignocaine administered intravenously is virtually unaffected by the concomitant administration of erythromycin and itraconazole. However, erythromycin increases the concentrations of MEGX, which indicates that erythromycin either increases the relative amount of lignocaine metabolized via N-de-ethylation or decreases the further metabolism of MEGX. Further studies are necessary to elucidate the clinical significance of the erythromycin-induced elevated concentrations of MEGX during prolonged intravenous infusions of lignocaine. Received: 8 January 1998 / Accepted in revised form: 8 June 1998     

Effect of orlistat on blood cyclosporin concentration in an obese heart transplant patient

Objective: We detected markedly decreased cyclosporin blood levels in a heart-transplanted patient after the gastrointestinal lipase inhibitor orlistat was accidentally added to the treatment program to control for his obesity. Therefore, we determined cyclosporin plasma concentration time kinetics with and without orlistat reexposition in this patient. Methods: Plasma concentration time kinetics of whole blood cyclosporin levels in an obese heart-transplant patient were measured using a standard monoclonal fluorescence polarisation immunoassay. Results were obtained in hourly intervals up to 12 h without and with co-therapy of 3 × 120 mg orlistat (Xenical, Roche Ltd., Switzerland). The orlistat re-exposition was started the day before taking blood samples. Results: Cyclosporin trough levels (98 ng/ml vs 52 ng/ml), maximum concentrations (532 ng/ml vs 74 ng/ml) and the area under the blood drug concentration-time curve (2832 ng h ml⁻¹ vs 700 ng h ml⁻¹) were greatly reduced with orlistat. Conclusions: Orlistat markedly decreased blood cyclosporin concentrations, possibly due to an interference with its absorption in the small intestine. To avoid potential dangerous under-immunosuppression, orlistat should not be used in patients taking cyclosporin. Received: 12 April 1999 / Accepted in revised form: 20 August 1999     

S-p -Toluylmercapturic acid in the urine of workers exposed to toluene: a new biomarker for toluene exposure

A mercapturic acid attached to the aromatic ring of toluene was for the first time detected in human urine as a metabolite of toluene. Since the metabolism of toluene is usually considered to take place at the side-chain, this gives, besides the biosynthesis of cresols, a further hint of a metabolic conversion of the aromatic system. We examined a group of 33 workers occupationally exposed to toluene, determining the concentrations of toluene in ambient air and in whole blood, o-cresol and hippuric acid in urine and p-toluylmercapturic acid (p-TMA) in urine. All blood and urine samples were collected post-shift. The renal excretion of S-p-toluylmercapturic acid showed highly significant correlations with established parameters of a biological monitoring of toluene. The median ambient air concentration was 63 ppm, ranging from 13 to 151 ppm, the median concentration of toluene in whole blood was 804 μg/l, corresponding to median urinary concentrations for o-cresol of 2.3 mg/l, hippuric acid of 2.3 g/l and p-TMA of 20.4 μg/l. p-TMA was not detectable in urine samples of a control group of 10 non-exposed persons. Both the German Biological Tolerance Values (BAT-values) for toluene in blood (1000 μg/l) and o-cresol in urine (3 mg/l) correspond to a mean p-TMA elimination of ∼50 g/l, and thus are in agreement with each other. According to our results p-TMA reflects internal toluene exposure diagnostically sensitive and specifical. With the developed analytical procedure we determined a median benzylmercapturic acid (BMA) concentration of 190 μg/l in the urine samples of the toluene exposed persons. We also determined a median BMA concentration of 30 μg/l in the control samples of non-exposed persons. However, these results are preliminary and require further confirmation as the reliability of the method was determined only for p-TMA. Received: 15 July 1997 / Accepted: 24 September 1997     

Modulation of nonprotein sulphydryl compounds rhythm with buthionine sulphoximine: relationship with oxaliplatin toxicity in mice

The relationship between the rhythm in tissue nonprotein sulphydryl groups (NPSH) and that in 1,2-diamine (trans-I)-cyclohexane oxalatoplatinum (l-OHP) toxicity was investigated in a total of 266 male B₆D₂F1 mice, using buthionine sulphoximine (BSO), an inhibitor of γ-glutamylcysteine synthetase. Mice were synchronized with an alternation of 12 h light (L) and 12 h darkness (D; LD 12:12), and circadian time was expressed in hours after light onset (HALO). NPSH was measured in liver, jejunum and bone marrow at 0, 8 and 16 HALO. Dosing l-OHP at these times achieved intermediate, high or low toxicity respectively. The physiological circadian rhythm in NPSH content was statistically significant in all tissues studied, with a maximum at the transition from D to L (0 HALO). BSO administration (450 mg/kg i.p., 4 h before sampling) induced a large depletion in liver and jejunum NPSH at their physiological peak (0 HALO), but exerted no significant effect at their trough (8 HALO). As a result, 24 h rhythm was suppressed in liver and jejunum, but remained similar to the physiological one in bone marrow. BSO enhanced l-OHP-induced mortality and jejunal toxicity, but exerted no significant effect upon bone marrow toxicity. Despite these differences, l-OHP remained least toxic at 16 HALO, near the middle of the dark span, which corresponds to maximum activity in the circadian rest/activity cycle. Our results show that mean NPSH levels in liver seem to account for the mean level of l-OHP toxicity, while jejunal NPSH rhythm plays an important role in the intestinal toxicity rhythm of this drug. Received: 19 January 1998 / Accepted: 18 June 1998     

CYP2E1 expression in bone marrow and its intra- and interspecies variability: approaches for a more reliable extrapolation from one species to another in the risk assessment of chemicals

When characterizing the health risks for man by exposure to chemicals, species-specific differences have to be taken into consideration, otherwise extrapolation from animal data to the human situation would be inadequate. The site-specific toxicity of chemicals may be explained by the following alternatives: (1) reactive metabolites are generated in the liver and subsequently transported to the target tissue(s); (2) metabolism of the parent compound occurs in the target tissue, a pathway by which the enzymes necessary for activation must be expressed in the target tissue. Cytochrome P450 2E1 (CYP2E1) is an important phase-I enzyme activating several chemicals. In the study described in this paper, myeloid intra- and interspecies variability in the expression of CYP2E1 has been investigated in rats, rabbits and man, because the bone marrow represents an important target organ for toxic effects of several chemicals, e.g. benzene. CYP2E1 at the protein level was detected by Western blotting and enzyme activities were determined by CYP2E1-dependent hydroxylation of chlorzoxazone (CLX). In the bone marrow of Wistar rats, the CLX hydroxylase activities were within the same order of magnitude (range: 0.1–0.4 pmol/mg protein per min) as previously described for mice (range 0.2–0.8 pmol/mg protein per min), whereas the CYP2E1 activities in two strains of rabbits were significantly higher (range: 1.7–4.7 pmol/mg protein per min) than in the rodents (P < 0.05). In human CD34⁺ bone marrow stem cells, CYP2E1 could also be detected on the protein level by Western blotting. The data demonstrate a presence of CYP2E1 in the bone marrow of all species investigated, thus supporting the hypothesis of CYP2E1-dependent local metabolism of several chemicals as a factor possibly contributing to their myelotoxicity and haematotoxicity. The data show that intraspecies/intrastrain variability of CYP2E1 activity in rodents is small. However, CYP2E1 activity between rodents and a non-rodent species was quite different indicating considerable interspecies variability. Received: 5 August 1999 / Accepted: 5 November 1999     

High thiamine diphosphate concentrations in erythrocytes can be achieved in dialysis patients by oral administration of benfotiamine

Objective: The influence of either orally administered S-benzoylthiamine-O-monophosphate (benfotiamine) or thiamine nitrate on the thiamine status was tested in a randomised, two-group comparison study in 20 end-stage renal disease (ESRD) patients. Main outcome measures were the pharmacokinetics of thiamine diphosphate (TDP) in blood, the in vitro erythrocyte transketolase activity, its activation coefficient (α-ETK) and the TDP concentration in erythrocytes. Methods: After ingestion of a single dose of either 100 mg thiamine nitrate (corresponding to 305 μmol thiamine) or 100 mg benfotiamine (corresponding to 214 μmol thiamine), the blood levels of thiamine phosphate esters were analysed by means of high-performance liquid chromatography for a 24-h period. The TDP concentration in erythrocytes was calculated using the haematocrit and TDP concentration in blood. Erythrocyte transketolase activity and α-ETK were measured before and 10 h after administration. The pharmacokinetics of TDP in blood were compared with healthy subjects of other studies retrieved from database query. Results: Regarding the blood concentrations of TDP, the patients with ESRD had a 4.3 times higher area under the concentration–time curve after benfotiamine administration than after thiamine nitrate. After benfotiamine administration, the peak plasma concentration of TDP exceeded that in healthy subjects by 51%. In the ESRD patients, after 24 h, the mean TDP concentration in erythrocytes increased from 158.7 ± 30.9 ng/ml initially to 325.8 ± 50.9 ng/ml after administration of benfotiamine and from 166.2 ± 51.9 ng/ml to 200.5 ± 50.0 ng/ml after thiamine nitrate administration. The ratio between the maximum erythrocyte TDP concentration and basal concentration was 2.66 ± 0.6 in the benfotiamine group and 1.44 ± 0.2 in the group receiving thiamine nitrate (P < 0.001). After 24 h, it was 2.11 ± 0.4 and 1.23 ± 0.2, respectively. The transketolase activity increased from 3.54 ± 0.7 μkat/l initially to 3.84 ± 0.6 μkat/l after benfotiamine intake (P=0.02) and from 3.71 ± 0.8 μkat/l to 4.02 ± 0.7 μkat/l after thiamine nitrate intake (P=0.08). Likewise, α-ETK decreased from initially 1.10 ± 0.07 to 1.04 ± 0.04 (P=0.04) and from 1.12 ± 0.05 to 1.08 ± 0.06 (P=0.09). After 24 h, the phosphorylation ratio in whole blood decreased from 12.9 ± 6.9 initially to 5.6 ± 3.2 after benfotiamine administration (P=0.02) and from 13.5 ± 7.3 to 9.0 ± 4.8 (P=0.03) after administration of thiamine nitrate. No correlation between erythrocyte TDP concentration and transketolase activity and/or α-ETK was observed in ESRD patients, either before or 10 h after administration. Conclusion: Compared with thiamine nitrate, the oral administration of benfotiamine leads to higher TDP concentrations in erythrocytes accompanied with a significant improvement of the erythrocyte transketolase activity in ESRD patients. Received: 4 October 1999 / Accepted: 15 March 2000     

Effects and pharmacokinetics of high dose metoprolol on chest pain in patients with suspected or definite acute myocardial infarction

Objective: Pain intensity and the plasma concentrations of metoprolol and its major metabolite α-hydroxymetoprolol as well as noradrenaline (NA), adrenaline (A) and neuropeptide Y (NPY) were determined in patients with pain due to definite or suspected acute myocardial infarction (AMI) after graded metoprolol infusion. Pain intensity and metoprolol kinetics were assessed over 8 h. Methods: Twenty-seven patients of either sex, aged 48–84 years with ongoing chest pain upon arrival to the Coronary Care Unit (CCU) were subdivided into two groups: (1) patients with ECG signs of threatening transmural myocardial damage (n=15); and (2) patients without such ECG signs (n=12). Pain intensity was assessed by a numerical rating scale (NRS) and venous blood was obtained for determination of plasma catecholamine and NPY concentrations. A continuous infusion of metoprolol (3 mg · min⁻¹ i.v) was started and serial blood samples for plasma catecholamines, NPY as well as metoprolol and its major metabolite α-hydroxymetoprolol were obtained from the contralateral arm. Results: Initial pain intensity was 5.9 (arbitrary units) and 5.4 in the groups with and without signs of transmural myocardial damage, respectively. One third of the patients with ST changes reported full pain relief (NRS=0) within 70 min after starting metoprolol infusion (accumulated dose, 15–180 mg). Among the patients without ST changes upon arrival, full pain relief was obtained in 70% (accumulated dose, 30–120 mg). There was a dose-dependent relation between accumulated metoprolol dose and pain relief. The diagnosis of acute myocardial infarction (AMI) was confirmed in all 15 patients with ECG signs on arrival of transmural myocardial damage. The mean metoprolol dose in this group was 91(12) mg. The mean metoprolol dose in the 12 patients without ST changes was 64(8) mg. In all, seven of these patients developed definite AMI. The terminal half-life of unchanged metoprolol ranged from 2.5 to 8.5 h in group 1 and from 2.2 to 5.2 h in group 2. In group 1, metoprolol half-life was 4.5 h and total plasma clearance (CL) 54.1 l · h⁻¹. In group 2, the metoprolol half-life was 3.7 h and total plasma clearance 75.4 l · h⁻¹. There was a significant difference in clearance between the groups. After the intravenous metoprolol infusion, α-hydroxymetoprolol concentrations increased gradually. In groups 1 and 2, maximal concentrations in plasma (C_max) were 143 and 135 nmol · l⁻¹ for α-hydroxymetoprolol and 2830 and 1653 nmol · l⁻¹ for metoprolol, respectively. Plasma NA or NPY did not differ between the groups. In contrast, plasma A was significantly higher during the initial 90 min of observation in patients with ECG signs of transmural myocardial damage. Conclusion: High-dose intravenous metoprolol was well tolerated in patients with suspected AMI. There was a more rapid and almost complete pain relief in patients without signs of transmural ischaemia compared with the patients with ECG signs of transmural AMI at arrival. In the later group of patients, plasma clearance of metoprolol was significantly reduced. Received: 23 August 1996 / Accepted in revised form: 6 March 1997     

The pharmacokinetics of caffeine in Nigerian children suffering from malaria and kwashiorkor

Objectives: Caffeine-containing beverages are generally consumed by Nigerians suffering from malaria and kwashiorkor in the belief that caffeine aids early recovery from these illnesses, which are common in the tropics. However, there are no studies on the influence of these diseases on the absorption and pharmacokinetics of caffeine in Africans. Materials and methods: A single oral dose of caffeine was given to five healthy children and to five and seven children suffering from malaria and kwashiorkor, respectively. Caffeine and its dimethylxanthine metabolites were measured in plasma using high-performance liquid chromatography. Results: The maximum plasma concentration (C_max) of caffeine and the time of C_max were similar (P > 0.05) in the three groups. However, the elimination half-life of caffeine was significantly longer in children with malaria (9.2 ± 3.5 h) (P < 0.01) and kwashiorkor (13.1 ± 7.9 h) (P < 0.05) than in the healthy controls (3.7 ± 1.8 h). The total plasma oral clearance of caffeine of 4.4 ± 1.9 ml/min/kg in healthy children was significantly higher (P < 0.01) than in those with kwashiorkor (2.0 ± 0.9 ml/min/kg) and malaria (1.6 ± 1.0 ml/min/kg) (P < 0.05). Paraxanthine was the principal metabolite in all the three groups with C_max significantly higher in healthy children (1.3 ± 0.3 μg/ml) than in children with malaria (0.8 ± 0.4 μg/ml) (P < 0.05) and kwashiorkor (0.3 ± 0.1 μg/ml) (P < 0.0001). CYP1A2 activity, measured by the plasma ratios of paraxanthine: caffeine, was significantly lower in kwashiorkor and malaria. Conclusions: This study showed that the plasma kinetics of caffeine are significantly altered in malaria and kwashiorkor, and CYP1A2 activity was lower in these two disease groups. Received: 12 April 1999 / Accepted in revised form: 30 November 1999     

Psychomotor effects of zaleplon and thioridazine coadministration

Objective: To assess the potential pharmacokinetic and pharmacodynamic interaction of zaleplon and thioridazine administered concomitantly in healthy volunteers. Methods: A three-period, double-blind, randomized crossover study of the psychomotor effects of single oral doses of zaleplon 20 mg alone, thioridazine 50 mg alone, or the two drugs administered concomitantly was performed in 12 healthy subjects. Pharmacodynamic testing was performed before, and at 1, 2, 4, and 8 h after drug administration. Critical flicker fusion (CFF), tapping rate (TR), reaction time (RT) with dominant and nondominant hands, and digit symbol substitution test (DSST) were used to assess psychomotor performance. Results: Pharmacokinetic results showed that coadministration of zaleplon and thioridazine did not alter the pharmacokinetic profile of either drug. In both CFF and TR tests, values for change from baseline with combined treatment were not significantly different from those with thioridazine at any time point, indicating no pharmacodynamic interaction. RT test values with coadministered treatment were significantly different from those with thioridazine alone at 1 h after administration, indicating additivity. Supra-additivity was observed in DSST results at 1, 2, and 4 h. There was no interaction at 8 h. Conclusion: The results of single-dose administration showed an additive pharmacodynamic interaction between zaleplon and thioridazine at 1 h in one of four tests and supra-additivity for 4 h in another test. This interaction is relatively short in duration due to the short half-life of zaleplon. Received: 26 April 1999 / Accepted: 14 March 2000     

In vivo and in vitro pharmacokinetics of 4,6-benzylidene-D-glucose (BG) in rats

Summary In vivo pharmacokinetics of 4,6-benzylidene-D-glucose (BG) was investigated in rats following an i.v. bolus injection of 85 mg BG/kg body weight. High performance liquid chromatography (HPLC) was used to characterize and quantitate BG in whole blood or serum samples. It was found that BG rapidly disappeared with a half-life (t_1/2)on the order of 10 min. At the same time a metabolite appeared which eluted before the double isomer peaks of BG. It increased in concentration from 0 to 30 min after initial i.v. injection of BG. Thereafter the metabolite was slowly removed or cleared from the animals. The t_1/2 of the metabolite calculated from the time of maximum concentration was found to be about 1 h. BG was also metabolized by whole rat blood at 37°C, but on a different time scale in vitro. The t_1/2 of BG in the in vitro assays was now about 4 h, as compared to 10 min in vivo. BG was not metabolized in rat plasma or rat serum. In contrast to in vivo data, the metabolite of BG was not reduced upon further incubation, but remained in blood samples with no reduction for at least 24 h. In addition, we found that protein synthesis was inhibited by approximately 50% when isolated rat hepatocytes were incubated with 3.2 mM BG. BG was slowly metabolized by hepatocytes to produce a metabolite indistinguishable (by HPLC) from that found in blood samples. Analysis of the metabolite by combined gas chromatography-mass spectrometric (GC-MS) methods identified it as being 1,3-benzylidene-D-glucitol. An intracellular reduction of BG by aldose reductase is proposed to occur.Fellow of the Norwegian Cancer Society     

Lack of a pharmacokinetic interaction between atovaquone and proguanil

Objective: To assess the magnitude of the putative effect of atovaquone on the pharmacokinetics of proguanil and to determine whether the pharmacokinetics of atovaquone are affected by concomitant administration of proguanil, with both drugs administered for 3 days to healthy adult volunteers. Methods: This was an open-label, randomized, three-way cross-over study, in which 18 healthy volunteers received 400 mg proguanil, 1000 mg atovaquone and 1000 mg atovaquone + 400 mg proguanil. Each treatment was given once daily for 3 days with a 3-week wash-out period between each occasion. For the assay of proguanil, cycloguanil and atovaquone, blood was sampled before dosing and at regular intervals over 8 days when proguanil was given, and over 17 days when atovaquone was given. Results: The geometric mean of the area under the atovaquone plasma concentration-time curve calculated from 0 to 24 h after the last dose (AUC_0→24h) was 180 μg · ml⁻¹ · h following administration of atovaquone alone and 193 μg · ml⁻¹ · h following atovaquone with proguanil. The geometric mean AUC_0→24h for proguanil was 6296 ng · ml⁻¹ · h after proguanil alone and 5819 ng · ml⁻¹ · h following proguanil with atovaquone. The corresponding values for the metabolite cycloguanil were 1297 ng · ml⁻¹ · h and 1187 ng · ml⁻¹ · h, respectively. The geometric mean elimination half-life (t_1/2) of atovaquone was 57.1 h when given alone and 59.0 h when administered together with proguanil. The corresponding geometric mean values of t_1/2 for proguanil were 13.7 h and 14.5 h. Exploratory statistical analysis showed no important gender effects on the pharmacokinetics of atovaquone, proguanil, or cycloguanil. Conclusion: The pharmacokinetics of atovaquone and proguanil and its metabolite, cycloguanil, were not different when atovaquone and proguanil were given alone or in combination. Received: 14 October 1998 / Accepted in revised form: 8 February 1999