Use of drugs of abuse in less than 30-year-old drivers killed in a road crash in France: a spectacular increase for cannabis, cocaine and amphetamines

A collaborative study was conducted in France in order to determine the prevalence of cannabinoids, opiates, cocaine metabolites and amphetamines in blood samples from drivers killed in road accidents in 2003 and 2004 and to compare these values with those of a previous study performed during the period 2000-2001 involving 900 drivers. Blood samples were provided from 2003 under 30-year-old drivers, killed in a traffic accident. Drugs of abuse were determined by gas chromatography-mass spectrometry using the same analytical procedures in all the 12 laboratories. The most frequently observed compounds were by far cannabinoids, that tested positive in 39.6% of the total number of samples. Delta9 tetrahydrocannabinol (THC), the most active of the principle constituents in marijuana (cannabis sativa), was detected in the blood of 28.9% drivers and was the single drug of abuse in 80.2% of the positive cases. It was associated with amphetamines in 7.4% and with opiates and cocaine in 1.9 and 4.8%, respectively. Amphetamines were present in 3.1% of the total number of samples, cocaine metabolites in 3.0% and opiates in 3.5%. When comparing these results with those of a previous study performed 3 years before, a significant increase is observed for THC (28.9% versus 16.9%), cocaine metabolites (3.0% versus 0.2%) and amphetamines (3.1% versus 1.4%). This study demonstrates the critical necessity of implementing in France as soon as possible systematical roadside testing for drugs of abuse.

[An example of simulation for a better understanding of PK/PD relationship of antibiotics]

The interpretation of PK/PD indices is specific to each class of antibiotics. In order to illustrate this, we developed a multidisciplinary tutorial program based on simulation of clinical cases. Three drugs were included in this software: tobramycin, vancomycin and azithromycin. From the dosage regimen proposed by the user, the model simulates a plotting of antibiotic plasma concentrations vs. time (tobramycin, vancomycin and azithromycin) and tissue concentrations (azithromycin). Peak and trough concentrations are calculated at steady-state. A commentary is provided to evaluate the efficacy of treatment and to assist the user in improving his prescription of tobramycin or vancomycin. T(> MIC) (time the concentration remains above the MIC) and AUC(24) (area under the concentration-time curve) are calculated in plasma and tissues for azithromycin. In order to create a link between theoretical pharmacokinetics and clinical practice, we propose this model as a simulation of antibiotic monitoring. We put the emphasis on interactivity and simulation, leading to applied reasoning and decision making. It illustrates (i) the influence of pharmacokinetic parameters, location of infection and bactericidal kinetics on the use of three different classes of antibiotics, (ii) the role of route of administration, dosing and intervals between administrations on therapeutic response and (iii) the influence of erratic administrations on clinical efficacy.

Persistent bacteremia in rabbit fetuses despite maternal antibiotic therapy in a novel intrauterine-infection model

The effect of optimized maternal therapy by bactericidal agents was evaluated in a reproducible rabbit model of Escherichia coli maternofetal infection simulating human pharmacokinetics. Intravenous antibiotic therapy was begun in the pregnant rabbit 12 h after bacterial intrauterine inoculation, using a computer-controlled pump to simulate human pharmacokinetics of ceftriaxone (1 g/day) associated or not with gentamicin (3 mg/kg of body weight/day). Data were compared for fetal survival, quantitative blood cultures, fetal histology in treated versus untreated groups, and maternal and fetal antibiotic concentrations in plasma in treated animals. Antibiotic therapy led to dramatic improvement in maternal outcome (100% survival versus 100% death in the untreated group in association with maternal septicemia). Fetal survival also improved, with the two-drug combination providing a more potent effect. After 3 days of treatment, 32% of fetuses survived with one-drug therapy and 62% with two-drug therapy (Yates corrected chi(2), P < 0.05). In untreated animals, bacterial counts in blood cultures increased rapidly during the first 24 h up to 8.1 +/- 0.5 log CFU/ml, but remained relatively constant at all times with antibiotic treatment: 4.5 +/- 0.7 log CFU/ml at the start of treatment and 6.2 +/- 0.4 and 5.2 +/- 0.9 log CFU/ml after 72 h for one- and two-drug therapy, respectively (data are means +/- standard deviations). The failure of animals to be cured after 3 days of treatment was not due to an inadequate concentration of ceftriaxone, as the residual level in fetal serum at sacrifice was more than 1000 times the MIC of the microbe. Unexpectedly, inflammation in fetal lung decreased in the treated group after as little as 24 h of antibiotic therapy, despite persistent bacteremia. Although maternal outcome improved and drug concentrations were above the MIC, the treatment did not achieve sterilization of fetuses in utero for this rabbit E. coli maternofetal infection. However, fetal survival showed some improvement, and the histologic features of lung inflammation were reduced.

Mycophenolate mofetil for the treatment of acute and chronic GVHD is effective and well tolerated but induces a high risk of infectious complications: a series of 21 BM or PBSC transplant patients

The use of mycophenolate mofetil (MMF) for prophylaxis of aGVHD and/or for treatment of acute or chronic GVHD is increasing. However, the benefit of MMF as an alternative to commonly used immunosuppressive agents still needs to be assessed. We ran a retrospective study on 21 consecutive patients (median age, 36 years; range, 20-63) with aGVHD or extensive cGVHD following related (17) or unrelated (4) matched donor SCT (BM, 16; PBSC, 5) who received MMF (2 g/day) because of intolerance to or failure of CsA-containing combinations. Four of the six patients with aGVHD responded, and the response rate was 69% in cGVHD patients. We observed neither significant differences in terms of response rate for skin, liver and bowel nor dissociated response in cases of multiple organ involvement (67% of the patients). Response was the same for lichenoid and sclerodermatous skin cGVHD subtypes. No adverse effects, except diarrhea (three patients), were observed. However, 22 opportunistic or serious viral or bacterial infections occurred in 10 patients. Analysis of trough plasma levels showed a trend for a higher mean MPA concentration in patients responding to MMF. Our study highlights the high risk of infectious complications induced by the administration of MMF, an otherwise efficient and well-tolerated treatment for GVHD.

Different aminoglycoside-resistant phenotypes in a rabbit Staphylococcus aureus endocarditis infection model

The impact of different types of enzymatic resistance on the in vivo antibacterial activity of aminoglycosides (amikacin, gentamicin, and netilmicin) was studied in the rabbit endocarditis model with four strains of Staphylococcus aureus. Animals were treated in a manner simulating the administration of a single daily human dose. Amikacin had no effect on the three kanamycin-resistant strains despite apparent susceptibility in the disk diffusion test. Gentamicin appears to be the preferable aminoglycoside for treatment of staphylococcal infections.

High-performance liquid chromatographic assay to determine the plasma levels of HIV-protease inhibitors (amprenavir, indinavir, nelfinavir, ritonavir and saquinavir) and the non-nucleoside reverse transcriptase inhibitor (nevirapine) after liquid-liquid extraction

A single HPLC assay was developed for therapeutic drug monitoring of 5 HIV protease inhibitors (indinavir, amprenavir, saquinavir, ritonavir, nelfinavir) and a non-nucleoside reverse transcriptase inhibitor (nevirapine) in human plasma. After liquid-liquid extraction in a mixture ethyl acetate-hexane, compounds are separated on a C18 column with a gradient elution of solvent A [acetonitrile and 0.025 M tetramethylammonium perchlorate in 0.2% aqueous trifluoroacetic acid (55:45 (v/v))] and solvent B [methanol and 0.025 M tetramethylammonium perchlorate in 0.2% aqueous trifluoroacetic acid (55:45 (v/v))]. The compounds are detected at various wavelengths: 320 nm (nevirapine), 259 nm (indinavir), 254 nm (amprenavir, nelfinavir, saquinavir) and 239 nm (ritonavir). The intra-day and inter-day precision and accuracy are lower than 15%. The limits of quantitation are 0.05 mg/l (amprenavir), 0.2 mg/l (indinavir, saquinavir, nelfinavir) and 0.4 mg/l (ritonavir, nevirapine). This method which allows to estimate simultaneously plasma levels of protease inhibitors and nevirapine can be used for therapeutic drug monitoring.

In vivo efficacy of continuous infusion versus intermittent dosing of ceftazidime alone or in combination with amikacin relative to human kinetic profiles in a Pseudomonas aeruginosa rabbit endocarditis model

Ceftazidime and amikacin were administered in a Pseudomonas aeruginosa rabbit endocarditis model using computer-controlled intravenous (iv) infusion pumps to simulate human serum concentrations for the following regimens: continuous (constant rate) infusion of 4, 6 or 8 g of ceftazidime over 24 h or intermittent dosing of 2 g every 8 h either alone or in combination with amikacin (15 mg/kg once daily). The in vivo activities of these regimens were tested on four Pseudomonas aeruginosa strains. Animals were killed 24 h after the beginning of treatment. Efficacy was assessed by comparing the effects of the different groups on bacterial counts in vegetations for each strain tested. For a susceptible reference strain (ATCC 27853; MICs of ceftazidime and amikacin 1 and 2 mg/L, respectively), continuous infusion of 4 g alone or with amikacin was as effective as intermittent dosing with amikacin. For a clinical isolate producing an oxacillinase (MICs of ceftazidime and amikacin 8 and 32 mg/L, respectively), continuous infusion of 6 g was equivalent to intermittent dosing. For a clinical isolate producing a TEM-2 penicillinase (MIC of ceftazidime and amikacin 4 mg/L), continuous infusion of 6 g, but not intermittent dosing, had a significant in vivo effect. For a clinical isolate producing an inducible, chromosomally encoded cephalosporinase (MIC of ceftazidime and amikacin 8 and 4 mg/L, respectively), neither continuous infusion nor intermittent dosing proved effective. Determination of ceftazidime concentrations in vegetations showed that continuous infusion produced tissue concentrations at the infection site far greater than the MIC throughout the treatment. It is concluded that continuous infusion of the same total daily dose provides significant activity as compared with fractionated infusion. This study confirms that a concentration of 4-5 x MIC is a reasonable therapeutic target in most clinical settings of severe P. aeruginosa infection.

Thiopurine methyl transferase activity: new extraction conditions for high-performance liquid chromatographic assay

A new liquid-liquid extraction is described for thiopurine methyl transferase (TPMT, EC 2.1.1.67) activity determination: the use of a pH 9.5 NH4Cl buffer solution, before adding the solvent mixture, allows more rapid extraction, avoiding a centrifugation step, and reduces the global cost of analysis. After the extraction step, 6-methylmercaptopurine, synthesised during the enzymatic reaction, is determined by a liquid chromatographic assay. Analytical performance of the assay was tested on spiked erythrocyte lysates. The linear concentration range was 5-250 ng ml(-1) (r> or =0.997, slope=1.497, intercept=-0.367). The recoveries were 82.8, 89.9 and 82.2% for 75, 125 and 225 ng ml(-1), respectively. The coefficients of variation were < or =6.1% for within-day assay (n=6) and < or =9.5% for between-day assay precision (n=6; 14 days). TPMT activity was determined in a French adult Caucasian population (7 =70). The results ranged from 7.8 to 27.8 nmol h(-1) ml(-1) packed red blood cells and the frequency distribution histogram is similar to that previously published.

Constant rate infusion of vancomycin in premature neonates: a new dosage schedule

AIMS

Since vancomycin's bactericidal action has been shown to be time-dependent, a constant rate infusion over 24 h might result in a better bactericidal efficacy. The purpose of this study was to define a new dosage schedule in prematures.

METHODS

Two vancomycin 24 h constant rate infusion schedules were tested in two groups of neonates. Postconceptional age (PCA) was 27 to 41 weeks in group 1 (n=24) and 28 to 51.5 weeks in group 2 (n=29). Group 1 neonates received continuous infusion of 10 to 30 mgkg(-1) day(-1), adjusted for PCA and weight. Group 2 was designed to take into account the significant relationship observed in group 1 between vancomycin clearance standardized on weight and PCA and consisted of a constant loading dose of 7 mg kg(-1) followed by continuous infusion of 10 to 40 mg kg(-1) day(-1) adjusted for PCA and weight.

RESULTS

Mean vancomycin serum concentration at steady state was 11+/-3.1 mg1(-1) in group 1 and 15.4+/-6.2 mg1(-1) in group 2. Fifty-six percent of group 1 values vs 88% of group 2 values were between 10 and 30 mg at steady state (P<0.01). Both regimens were well tolerated.

CONCLUSIONS

A loading dose of vancomycin followed by constant rate infusion of the appropriate dose adjusted for PCA and weight might improve vancomycin concentrations in neonates.

Quantitation of amphotericin B in plasma by second-derivative spectrophotometry

A method is described for determining amphotericin B in plasma using second-derivative spectrophotometry after deproteinization. The assay was based on the absorbance at 407.5 nm. The second-derivative spectrum recorded between 350 and 450 nm allowed identification of the analyte and showed absence of drug interference. Only bilirubin interfered at high concentration (> or = 50 mumol l-1. The linear concentration ranges were 0.05 -5.0 mg l-1 (r = 0.999, slope = 2.731, intercept = 0.008). Between-day CV < or = 9.7%, within-day CV < or = 5.5%, analytical recovery close to 100% were suitable for clinical investigations. This method provides better specificity than direct absorbance, is simpler and faster than a high performance liquid chromatography assay and can be used routinely by any laboratory possessing a spectrophotometer with a derivative accessory.

In vivo simulation of human pharmacokinetics in the rabbit

The evaluation of drugs in vivo is often based on experimental models using small animals such as mice, rats and rabbits. However, these models could be improved to correspond more closely to the human situation if the pharmacokinetics of the drugs tested in animals were similar to that observed in humans. The use of a computer-controlled pump allowing an adequate flow of tobramycin and amikacin to be infused into rabbits enabled us to simulate the human pharmacokinetics of these antibiotics in vivo in this study. The function defining the rate of infusion required to perform the simulation of an intravenous bolus was first determined generally and symbolically for linear pharmacokinetic models independently from the number of compartments involved. The practical simulation of a decreasing monoexponential serum profile with a half-life of 2 h (one-compartment model for the human pharmacokinetics of aminoglycosides) was then studied for tobramycin and amikacin on the basis of a two-compartment model in the animal. The kinetics obtained had an apparent elimination half-life of 1.97 and 1.86 h, respectively. Linearity of the semilogarithmic regressions of the profiles obtained was quite sound. Finally, an a posteriori analysis of the pharmacokinetic model and its parameters is proposed on the basis of the results obtained after simulation.

Bactericidal effect of pefloxacin and fosfomycin against Pseudomonas aeruginosa in a rabbit endocarditis model with pharmacokinetics of pefloxacin in humans simulated in vivo

The bactericidal activity of pefloxacin and fosfomycin alone and in combination against Pseudomonas aeruginosa was evaluated in an experimental rabbit endocarditis model after 24 h of treatment. Two strains with intermediate susceptibility to pefloxacin and good susceptibility to fosfomycin were tested. The serum kinetics obtained during administration of 400 mg every 12 h in humans were simulated in the animals using computer-controlled variable-flow infusion. Fosfomycin was administered as a continuous infusion at a constant flow, allowing a steady-state concentration of 47.4 +/- 11.9 mg/ml to be reached in serum. In valvular vegetations, pefloxacin was less bactericidal than fosfomycin, and in combination treatment, it reduced (but did not abolish) the bactericidal effect of fosfomycin. The duration of the pretreatment interval (12-48 h) had a negative effect on the bactericidal activity of both drugs, especially that of fosfomycin.

Adaptive resistance of Pseudomonas aeruginosa induced by aminoglycosides and killing kinetics in a rabbit endocarditis model

Adaptive resistance following the first exposure to aminoglycosides is a recently described in vitro phenomenon in Pseudomonas aeruginosa and other aerobic gram-negative bacilli. We investigated the in vivo relevance of adaptive resistance in P. aeruginosa following a single dose of amikacin in the experimental rabbit endocarditis model. Rabbits with P. aeruginosa endocarditis received either no therapy (control) or a single intravenous (i.v.) dose of amikacin (80 mg/kg of body weight) at 24 h postinfection, after which they were sacrificed at 5, 8, 12, 16, or 24 h postdose. Excised aortic vegetations were subsequently exposed ex vivo to amikacin at 2.5, 5, 10 or 20 times the MIC for 90 min. In vivo adaptive resistance was identified when amikacin-induced pseudomonal killing within excised aortic vegetations was less in animals receiving single-dose amikacin in vivo than in vegetations from control animals not receiving amikacin in vivo. Maximal adaptive resistance occurred between 8 and 16 h after the in vivo amikacin dose, with complete refractoriness to ex vivo killing by amikacin seen at 12 h postdose. By 24 h postdose, bacteria within excised vegetations had partially recovered their initial amikacin susceptibility. In a parallel treatment study, we demonstrated that amikacin given once daily (but not twice daily) at a total dose of 80 mg/kg i.v. for 1-day treatment significantly reduced pseudomonal densities within aortic vegetations versus those in untreated controls. When therapy was continued for 3 days with the same total daily dose (80 mg/kg/day), amikacin given once or twice daily significantly reduced intravegetation pseudomonal densities versus those in controls. However, amikacin given once daily was still more effective than the twice-daily regimen. These data confirm the induction of aminoglycoside adaptive resistance in vivo and further support the advantages of once-daily aminoglycoside dosing regimens in the treatment of serious pseudomonal infections.

A pilot study of 220 mg/m2 melphalan followed by autologous stem cell transplantation in patients with advanced haematological malignancies: pharmacokinetics and toxicity

We studied the pharmacokinetics and toxicity of 220 mg/m2 melphalan (HDM 220) followed by autologous stem cell transplantation in 16 patients with advanced haematological malignancies. Pharmacokinetic parameters (mean values of steady-state volume of distribution 14.6 l/m2, total body clearance 313 ml/min/m2, elimination half-life 46 min) were the same as those of 140 or 200 mg/m2 melphalan in previous reports. HDM 220 was feasible. Extramedullary toxicity was mainly W.H.O. grade 4 mucositis (13/16 patients). The median duration of 41 d (10, not reached) of thrombocytopenia < 25 x 10(9)/l was long. In multiple myeloma the response rate was 89% in heavily pretreated patients, suggesting that HDM 220 could be considered earlier in the course of the disease as an alternative consolidation therapy.

In vivo antibacterial effects of simulated human serum profiles of once-daily versus thrice-daily dosing of amikacin in a Serratia marcescens endocarditis experimental model

Once-daily dosage of aminoglycosides is currently under consideration. The lower toxicity of this regimen has been clearly established, but there are conflicting experimental and clinical data concerning its efficacy. It is inadvisable to optimize human therapy by extrapolation from experimental studies since animal and human pharmacokinetics differ. The simulation of human pharmacokinetics in experimental infectious models would seem to offer a more rational approach. We used computer-controlled infusion of amikacin at a variable flow rate to simulate human pharmacokinetics in a Serratia marcescens rabbit endocarditis model and to compare two therapeutic regimens (once-daily versus thrice-daily doses). The doses corresponded to simulations of 15 and 30 mg/kg of body weight per day in humans, and antibacterial activity was measured in vegetations (Veg) after 24 h of treatment. The results show that the dose corresponding to 15 mg/kg/day failed to produce a significant reduction of CFU (6.8 +/- 0.9 and 6.4 +/- 0.8 log10 CFU/g of Veg, respectively, for once-daily and thrice-daily doses versus 7.6 +/- 1.0 for controls). A significant reduction was observed only for the dose corresponding to 30 mg/kg/day in humans (5.2 +/- 1.5 and 5.4 +/- 1.1 log10 CFU/g of Veg, respectively, for the two regimens). With this model, the efficacy of amikacin was similar for both regimens after 24 h of treatment simulating human pharmacokinetics.

Hemodiafiltration in pentobarbital poisoning

We report the use of continuous venovenous hemodiafiltration (CVVHD) in a case of massive intentional ingestion of pentobarbital associated with severe coma and hypotension. Despite a poor hemodynamic state, toxic epuration (15% of drug ingested) was obtained. However, death occurred 7 hr after the end of treatment. This report suggests that CVVHD can be effective in the treatment of massive pentobarbital intoxication.

Pharmacokinetics of high-dose melphalan in adults: influence of renal function

BACKGROUND

The pharmacokinetics of melphalan were studied in 20 patients with multiple myeloma, primary amyloidosis or lymphoma after IV dose of 140 mg/m2 infused over 30 minutes (two patients were treated with a higher dose).

MATERIALS AND METHODS

Six patients received melphalan alone, 8 received melphalan combined with total body irradiation, 2 received busulphan plus melphalan and 4 received the BEAM association (BCNU + etoposide + high dose aracytine + high dose melphalan). Creatinine clearance was measured immediately before the infusion of melphalan, and 9 blood samples were taken to monitor elimination kinetics.

RESULTS

Pharmacokinetic parameters (CIT, Vdss, t1/2) and areas under the curve (AUC) were comparable to those obtained by Ardiet et al after rapid IV injection. For all patients, AUC, CIT, Vdss, t1/2 beta and MRT were significantly correlated with creatinine clearance; the different pharmacokinetic parameters calculated showed great interindividual variations.

CONCLUSIONS

Renal insufficiency did not lead to a large decrease in melphalan clearance compared to interindividual variations in systemic clearance.

Application of USC*PACK clinical programs to vancomycin in neutropenic patients

The pharmacokinetics of vancomycin were studied in 10 neutropenic patients (4 male, 6 female) using the USC*PACK Clinical Programs. The experimental data was determined after the first administration of 1000 mg injected as a 1-h infusion. Eight blood samples were collected between 15 min and 11 h after the end of the infusion. Plasma vancomycin concentrations were measured by immunoassay procedure. Creatinine clearance and urine flow were also measured. Pharmacokinetic parameters were computed using a two-compartment model: Vc = 0.270665 +/- 0.161033 (l.kg-1); Kcp = 0.732927 +/- 0.464449 (h-1); Ks = 0.004952 +/- 0.00272 (min.ml-1.h-1); Kpc = 0.470243 +/- 0.194677 (h-1); Ki = 0.011675 +/- 0.004086 (h-1); Ke = 0.644415 +/- 0.239376 (h-1). When we compared this population to the general population of the program, Ke was increased. Elimination constant Ke was not correlated to either creatinine clearance or urine flow. Evaluation of the predictive performance of the Bayesian PC Program for adaptive control of vancomycin therapy in neutropenic patients is the next step of this study.

Teaching individualized antibiotic dosage regimens by means of two computer-assisted learning programs

We developed two multidisciplinary tutorial programs (TOBRA-DIDACT and VANCO-DIDACT) for teaching the basic principles of antibiotic drug monitoring by simulation of repeated administrations to fictitious patients whose physio-pathologic characteristics were pre-defined in the programs. To illustrate the two types of bactericidal kinetics, we have chosen one time-dependent (vancomycin) and one concentration-dependent (tobramycin) antibiotic. These computer-assisted programs operate on an interactive mode. In each of them, three main steps are connected: (1) Various types of clinical cases are submitted to the student: for each of them, case report includes clinical characteristics, location of infection, bacterial strain and minimal bactericidal concentration. These data must be taken into account during the following steps. (2) The student has to establish the treatment schedule: route of administration, dose for each injection, intervals between injections and duration of infusion. (3) The result of the dosage scheme proposed by the student is represented by a simulation of plotting antibiotic plasma concentrations vs. time during the first 4 days of treatment. These curves are obtained by a monoexponential (TOBRA-DIDACT) or biexponential (VANCO-DIDACT) pharmacokinetic model. Peak and trough concentrations are calculated at steady-state. An expert system provides a commentary with each result to evaluate the efficacy of the treatment and to assist the student in improving his prescription. TOBRA-DIDACT and VANCO-DIDACT illustrate the influence of age, obesity, renal impairment, location of infection and bacterial strain on antibiotic therapy. They also show the role of route of administration, dosing and intervals between injections on therapeutic response.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetic parameters of vancomycin for therapeutic regimens in neutropenic adult patients

Vancomycin (V) is widely used in neutropenic patients, though its kinetics are known in this type of patient. In the present study, ten patients were included: all of them received an intensive therapy for non-Hodgkin malignant lymphoma, Hodgkin disease, myeloma, acute leukemia, followed by an autologous bone marrow transplantation in 6 cases. All patients were neutropenic (100/mm3). The pharmacokinetic study was done at the first V administration: 1000 mg V were injected as a 1-h infusion. Plasma V concentrations were measured by an enzyme immunoassay (EMIT, Syva, France). V maximal and minimal concentrations were 61.3 +/- 38.6 micrograms/ml and 1.69 +/- 0.77 microgram/ml, respectively. Total V clearance was 158 +/- 51 ml/min, with a creatinine clearance of 141.2 +/- 36.2 ml/min on test day. V plasma kinetics can be described by a biexponential model, with the following parameters: [table: see text] These data show a 3-fold increase of initial volume of distribution and a shortened (3-fold) T1/2 beta, if compared to values obtained in normal subjects. Because the bactericidal effect is time dependent, there can be a risk of insufficient antibiotic effect throughout the day. Our data suggest that new therapeutic regimens are needed for these patients.

Effects of administration route on pharmacokinetics of viloxazine in the rabbit

The absorption of viloxazine chlorhydrate was investigated in ten rabbits. Each animal received the drug (15 mg/kg) by three routes: intravenous, gastric and duodenal. Viloxazine plasma concentrations were low when administered by gastric and duodenal routes compared to those after intravenous injection. Concentrations to peak were 1-2 times higher after duodenal than gastric administration. Times to peak were 23.0 +/- 4.7 min after gastric administration and 9.5 +/- 5.4 min after duodenal administration. A better absorption of viloxazine after administration occurred in the duodenum than in the stomach; these results agree with viloxazine pKa = 8.13. The other pharmacokinetic parameters such as half-life, clearance and volume of distribution where the same irregardless of the administration route.

Effects of administration route on valproate pharmacokinetics in the rabbit

The absorption of sodium valproate was studied in 5 rabbits. Each animal received the drug (70 mg/kg) via 3 routes: intravenous, gastric and duodenal. For the 2 extravascular routes, the absolute bioavailability F, maximal plasma concentrations Cmax, times to peak Tmax and absorption coefficients Kabs were the same. Absolute bioavailability was always close to unity. This indicated that valproic acid was absorbed from the intestine as well as from the whole gastrointestinal tract. The other pharmacokinetic parameters such as terminal plasma half-life, total clearance and volume of distribution remained unchanged whatever the route of administration.

Therapeutic monitoring of treatment with antidepressants

The present status of the relationship between blood plasma concentrations of tricyclic antidepressants and clinical outcome is reviewed. Plasma levels of imipramine, desmethylimipramine and nortriptyline are generally accepted as useful clinically but it is more difficult to establish a well-defined relationship between clomipramine and amitriptyline blood levels and clinical outcome. These assays are clinically relevant, particularly in cases of treatment failure, but also in the treatment of the elderly and of overdosage. The technical problems of the assay have practically been solved with the development of new analytic methods.

Comparative pharmacokinetic study of conventional and sustained-release viloxazine in normal volunteers

Animal and human studies have indicated that viloxazine hydrochloride, an antidepressant drug with a half-life of 3-4 h in most subjects at low dosage, is rapidly and almost completely absorbed after oral administration. A sustained-release form might be useful to decrease the frequency of administration. In our study, the pharmacokinetics of sustained-release form containing 300 mg viloxazine were compared with 300 mg conventional viloxazine in 11 normal volunteers (6 women, 5 men). Wide interindividual variations were observed with respect to plasma levels, but there was no significant statistical correlation between weight and blood concentration (conventional form: Cmax = 3,599 +/- 579 ng/ml, tmax = 86 +/- 26 min; sustained-release form: Cmax = 1,917 +/- 922 ng/ml, tmax = 215 +/- 77 min). Twelve hours after administration, plasma levels ranged between 540 and 1,600 ng/ml for the conventional form and between 660 and 2,120 ng/ml for the sustained-release form. Despite the great interindividual variation this new viloxazine form appears to be of interest for one daily administration.

Quantitative analysis of serum methohexital by GLC using capillary column and nitrogen-selective detection

A gas chromatographic method for routine quantitation of methohexital in plasma samples is reported. One-step extraction in organic phase, the use of a fused silica capillary column, and nitrogen-selective detection permit simple, precise, and sensitive determination of methohexital in plasma. A linear relationship is described between peak height ratio and methohexital concentrations ranging from 0.125 to 50.0 micrograms/ml (r = 0.998). The sensitivity limit of the assay was 6 ng/ml in plasma. No interfering peak was observed with numerous other drugs. The procedure was successfully applied to the determination of pharmacokinetic parameters of methohexital after IV administration or continuous infusion in a child and an adult.

[Blood concentrations of maprotiline in depressive patients]

Blood levels of Maprotiline were analysed and their relationship to the clinical response was examined in 89 depressed inpatients, according DSM III criteria for Major Depressive Episode, given the drug treatment for 3 weeks. Maprotiline produced marked decreases in mean MADRS and COVI scale scores by the end of treatment. On day 21, no correlation between blood levels of Maprotiline and MADRS or COVI scores were found when all patients were considered. Nevertheless, significant correlations were observed on day 14 (r = .22; p less than .05 for MADRS and r = .23; p less than .05 for COVI scale). In addition, a significant correlation between MADRS or COVI scale scores and Maprotiline blood levels were observed on days 14 and 21 in subgroups of young patients, severe depression (high scores to clinical global investigations), during of at least 3 months, treated without other drug than Maprotiline and good responders.

Effects of administration route on pharmacokinetics of aspirin in the rabbit

The absorption of aspirin used in the form of lysine acetylsalicylate was studied in the rabbit. Each animal received the drug by three routes: intravenous, gastric and duodenal. Plasma concentrations of acetylsalicylic acid (ASA) and salicylic acid (SA) were compared. ASA plasma concentrations obtained after gastric or duodenal administration were low compared to those after intravenous injection. Concentrations were 2 to 5 times higher after gastric than duodenal administration. SA plasma concentrations were lower at the beginning of the experiment for gastric than for duodenal administration; after 90 min the concentrations were similar. A better absorption of aspirin (as lysine acetylsalicylate) after administration occurred in the stomach than in the duodenum, but the amount of ASA which reached the central compartment was quite poor.

Rapid gas-chromatographic assay of bupivacaine in plasma

A method for estimating bupivacaine concentration in human plasma by capillary gas-chromatography using solid injection and nitrogen-specific detection is described. Etidocaine, another anilidetype local anesthetic was used as internal standard and added to the sample before single-step extraction with diethylether. This method demonstrates high sensitivity (6 ng/ml plasma) and combines selectivity, rapidity, and simplicity. Results of this procedure correlate well with those obtained by an HPLC method.

Pharmacokinetics of isoniazid: influence of age

The distribution of the acetylator phenotype of isoniazid was studied in 458 patients of different ages, and the influence of age on its apparent distribution volume, clearance and half-life was investigated in slow and rapid acetylators. The doses of isoniazid for the patients were determined according to the inactivation index method, as described by Vivien. Apparent distribution volume showed no difference between slow and rapid acetylators but it did decrease significantly with age. Clearance and half-life varied significantly in slow acetylators, and these variations led to a decrease in the necessary dose of isoniazid.

A monitoring study of cardiotonic treatment by immunoenzymologic measurement of digoxinemia (emit)

We performed a study on 96 patients to compare monitoring by immunoenzymologic measurement (EMIT) of digoxinemia. In doing so, we uniquely relied on clinical and electrocardiographic results. Compliance was good because only 9 patients had a digoxinemia equal or below 0.8 ng/ml, but we emphasize that our patients were hospitalized. Correlation between intoxications and plasmatic levels shows that 5 patients presented clinical or electrocardiographic signs indicative of digitalis intoxication with a digoxinemia less than 2.5 ng/ml and 14 patients without intoxication with a digoxinemia higher than 2.5 ng/ml. We point out in this study that for EMIT immunoassay it is better to take 2.5 ng/ml as the concentration limit to be sure to avoid intoxication.

Pharmacokinetics of intravenous and intramuscular methohexitone in dogs

Twenty-four dogs received methohexitone, either intravenously injected (2 mg kg-1 of a 1% solution) or intramuscularly (10 mg kg-1 of a 2% solution). Plasma methohexitone concentrations were measured by gas/liquid chromatography and pharmacokinetics were obtained from the general equations of a multicompartment model. Peak blood concentrations were equivalent following i.v. (18.2 +/- 9.9 mg 1(-1); at 30 s) and i.m. (19.1 +/- 5.6 mg 1(-1); at 3 min) injections. After i.v. injection a rapid distribution phase (half-life t 1/2 lambda 1; 1.3 +/- 0.5 min) was followed by an elimination phase (elimination half-life t 1/2 lambda z; 26.4 +/- 7.8 min). After i.m. injection the distribution phase was followed by two further phases (half-lives: 10.1 +/- 3.6 min and 75.6 +/- 22.6 min). The authors conclude that an i.m. dose five times as great as the i.v. dose produces equivalent peak blood concentration 30 s after i.v. injection and 3 min after i.m. injection. In addition, after i.m. injection of 10 mg kg-1 an additional compartment was apparent, indication substantial drug uptake by poorly perfused tissues.

[Isoniazid and rifampicin in the rabbit. Effect on hepatic microsomal enzyme activity]

1. Enzymatic induction or inhibition induced by isoniazid (10 mg/kg) and/or rifampicin (13 mg/kg) oral treatment of 13 days in the rabbit, is evaluated with the following parameters: --variation of antipyrine half-life measured before treatment and 24 h after the end of treatment, --cytochrome P450 content, aniline hydroxylase and aminopyrine N-demethylase activities in hepatic microsomes. Isoniazid half-life is evaluated before treatment, in order to obtain an homogeneous repartition of animals in each group: isoniazid, rifampicin, isoniazid + rifampicin and control. 2. Rifampicin treatment gives a variable enzyme induction of antipyrine metabolism, cytochrome P450 and aniline hydroxylase activity; aminopyrine N-demethylase activity is significantly inhibited. Isoniazid treatment inhibits antipyrine metabolism and increases the cytochrome P450 content.

Tuberculosis therapy and enzyme induction in man

The enzymatic inducing effect of an antituberculous treatment (Rifampicin, Isoniazid and Ethambutol) is tested by recording variations in the urinary D-glucaric acid elimination and in the antipyrine half-life test, measured before starting treatment and after two weeks of treatment. This study concerns 21 patients: 14 are slow acetylators and 7 are rapid acetylators of isoniazid. After two weeks of treatment an increase of the urinary glucaric acid elimination is observed but variations in the antipyrine half-life test are not univocal and allow us to separate two categories of patients: 10 have a significant decrease of antipyrine half-life, 11 have not. A link seems to exist between the rapid acetylator phenotype and this enzyme induction which is revealed by the antipyrine test. An interpretation of these two enzyme induction tests, the nature of the rifampicin inducing action and its relation to the acetylator phenotype are discussed.