Comparison of the therapeutic effectiveness of aprindine, procainamide and quinidine in chronic ventricular dysrhythmias

1 A cross-over study with aprindine (100 mg daily after a loading dose of 200 mg), procainamide (4 × 1000 mg daily) and quinidine bisulphate (2 × 750 mg daily), all given orally, was performed in seventeen patients with stable chronic premature ventricular contractions following healed myocardial infarction. 2 The effectiveness of the treatment was evaluated during three consecutive weeks by continuous ambulatory tape recording of the electrocardiogram and repeated determinations of plasma levels were done. 3 The results showed that aprindine was more effective than procainamide and quinidine. 4 For the three drugs the therapeutic plasma levels varied markedly from patient to patient, but for each patient taken individually, the therapeutic activity could be correlated with the plasma levels.

Liquid chromatographic determination of the plasma concentrations of cefotaxime and desacetylcefotaxime in plasma of critically ill patients

A method for the simultaneous determination of cefotaxime (CTX) and desacetylcefotaxime (DES) in plasma was developed, using acetonitrile protein precipitation and high-performance liquid chromatography (HPLC) with UV-detection at 285 nm. Desacetylcefotaxime was also analysed after conversion in highly acidic medium to its lactone form (DES-lactone). The chromatographic separation was performed on a C18 Aqua column. The lower limit of quantitation was 1 microg/ml for CTX and 0.5 microg/ml for DES and DES-lactone, using 25 microl of plasma samples. The linearity of the calibration curves was satisfactory as indicated by correlation coefficients of > or =0.990. The within-day and between-day precisions were <12% (n = 18) for the two products and the accuracy was between 88 and 101%. The developed HPLC method was applied for CTX and DES determination in plasma samples of critically ill patients after continuous intravenous infusion of CTX.

Relationship between gamma-hydroxybutyrate plasma concentrations and its electroencephalographic effects in the rat

In view of the potential interest in an objective parameter for the depth of coma in intoxications with the recreational drug gamma-hydroxybutyrate (GHB), we have studied the relationship between the plasma concentrations and the electroencephalographic (EEG) changes induced by GHB in the rat. Fifteen rats randomly received either 150 (n = 3), 200 (n = 6) or 300 mg kg(-1) (n = 6) GHB over 5 min, followed by a supramaximal dose of 450 mg kg(-1) over 5 min at the end of the experiment. Plasma concentrations were determined with HPLC. The EEG was continuously recorded and the amplitude in the 15.5-30 Hz frequency band was quantified using aperiodic analysis. The plasma concentration-time profiles were fitted to a two-compartment model with Michaelis-Menten elimination. The pharmacokinetic parameters Vmax, Km and the apparent volume of distribution (Vd) proved to be independent of the dose and the mean pooled values were Vmax 2068 +/- 140 microg min(-1) kg(-1), Km 58 +/- 16 microg mL(-1) and Vd 476 +/- 12 mL kg(-1). The EEG amplitude in the 15.5-30 Hz frequency band displayed a monophasic inhibition and the effect-plasma concentration curve showed hysteresis. This hysteresis between EEG effect and plasma concentrations was minimized by simultaneous calculation of hypothetical effect-site concentrations and fitting the effect vs effect-site concentration curve to a sigmoid inhibitory Emax model. The descriptors of this Emax model (Emax, EC50, k(e,0), gamma and E0) were independent of the dose with an equilibration half-life t1/2k(e,0) of 5.6 +/- 0.3 min (mean value of the pooled results of the 5-min treatment groups). To investigate the origin of this hysteresis, a dose of 600 mg kg(-1) GHB was infused over either 45 or 60 min each in three animals. The hysteresis was much less pronounced with 45 min than with 5 min and was absent with 60-min infusions. This indicated that the hysteresis was due to a distribution delay between the central compartment and the effect site. This study showed that the concentration-effect relationship of GHB could be characterized in individual rats using aperiodic analysis in the 15.5-30 Hz frequency band.

Development and validation of a high-performance liquid chromatographic method for the determination of gamma-hydroxybutyric acid in rat plasma

A method for the determination of gamma-hydroxybutyric acid (GHB) in rat plasma was developed using solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with UV detection. GHB was isolated from plasma using strong anion-exchange SPE columns. The chromatographic separation was performed on a C18 Aqua column. The lower limit of quantification was 10 microg/ml using 60 microl of plasma. The linearity of the calibration curves was satisfactory as indicated by correlation coefficients of >0.990. The within-day and between-day precision were <10% (n=24), the accuracy was nearly 101%. Plasma concentrations in rats after GHB infusion determined by HPLC-UV were compared with the corresponding concentrations determined with a validated gas chromatographic-mass spectrometric method by orthogonal distance regression. A good correlation was observed and a t-test indicated no significant differences from 0 and 1 for the intercept and slope, respectively.

Influence of hypovolemia on the pharmacokinetics and the electroencephalographic effect of propofol in the rat

BACKGROUND

Hypovolemia decreases the dose requirement for anesthetics, but no data are available for propofol. As it is impossible to study this in patients, a rat model was used in which the influence of hypovolemia on the pharmacokinetics and pharmacodynamics of propofol was investigated.

METHODS

Animals were randomly allocated to either a control (n = 9) or a hypovolemia (n = 9) group, and propofol was infused (150 mg x kg(-1) x h(-1)) until isoelectric periods of 5 s or longer were observed in the electroencephalogram. The changes observed in the electroencephalogram were quantified using aperiodic analysis and used as a surrogate measure of hypnosis. The righting reflex served as a clinical measure of hypnosis.

RESULTS

The propofol dose needed to reach the electroencephalographic end point in the hypovolemic rats was reduced by 60% (P < 0.01). This could be attributed to a decrease in propofol clearance and in distribution volume. Protein binding was similar in both groups. To investigate changes in end organ sensitivity during hypovolemia, the electroencephalographic effect versus effect-site concentration relation was studied. The effect-blood concentration relation was biphasic, exhibiting profound hysteresis in both hypovolemic and control animals. Semiparametric minimization of this hysteresis revealed similar equilibration half-lives in both groups. The biphasic effect-concentration relation was characterized by descriptors showing an increased potency of propofol during hemorrhage. The effect-site concentration at the return of righting reflex was 23% (P < 0.01) lower in the hypovolemic animals, also suggesting an increased end organ sensitivity.

CONCLUSIONS

An increased hypnotic effect of propofol occurs during hypovolemia in the rat and can be attributed to changes in both pharmacokinetics and end organ sensitivity.

Trovafloxacin concentrations in airway fluids of patients with severe community-acquired pneumonia

The penetration of trovafloxacin (TVA), 200 mg once daily, into the airways of 17 patients with severe pneumonia was studied. The mean (standard deviations are given in parentheses) steady-state TVA concentrations, 2 h after the last intake, were 3.1 (0.3) mg/liter in induced sputum (n = 8), 3.2 (1.1) mg/liter in bronchial secretions (n = 9), 3.2 (0.9) mg/liter in bronchoalveolar lavage fluid (n = 10), and 4.9 (1.4) mg/liter in epithelial lining fluid (n = 11).

Effects of smoking, CYP2D6 genotype, and concomitant drug intake on the steady state plasma concentrations of haloperidol and reduced haloperidol in schizophrenic inpatients

The effects of smoking, CYP2D6 genotype, and concomitant use of enzyme inducers or inhibitors on the steady state plasma concentrations of haloperidol (HAL) and reduced haloperidol (RHAL) were evaluated in 92 schizophrenic inpatients. All but three of these patients received concomitant medication, in many cases with drugs potentially interacting with HAL. Of the 92 patients, 63 were treated orally with HAL in a daily dose of 0.4 to 50 mg; 29 patients were treated intramuscularly with a daily equivalent dose of HAL decanoate (expressed as HAL) of 1.8 to 17.9 mg. A wide interindividual variation in HAL dose and in steady state plasma concentrations of HAL and RHAL was observed. In the patients treated orally, the daily oral dose was about 4 times higher and the dose-normalized HAL (but not RHAL) plasma concentrations were significantly lower in smokers (n = 40) than in nonsmokers (n = 23) (p < 0.01). The dose-normalized RHAL (but not HAL) plasma concentrations and the RHAL/HAL ratio were significantly higher in poor metabolizers (PMs) than in extensive metabolizers (EMs). There was a trend toward an effect of potentially interacting drugs (inducers or inhibitors) on dose, dose-normalized HAL and RHAL plasma concentrations, and the RHAL/HAL ratio. In the patients treated intramuscularly, the dose-normalized HAL (but not RHAL) plasma concentrations were significantly lower in smokers than in nonsmokers, but no differences in doses were observed. This naturalistic study of modest sample size in a polymedicated population shows an effect of smoking and CYP2D6 genotype (and to a lesser extent, of interacting drugs) on the kinetics of HAL.

Relationship between etomidate plasma concentration and EEG effect in the rat

PURPOSE

The effect-plasma concentration relationship of etomidate was studied in the rat using electroencephalographic changes as a pharmacodynamic parameter.

METHODS

Etomidate was infused (50 mg/kg/h) in chronically instrumented rats (n=6) until isoelectric periods of 5 s or longer were observed in the electroencephalogram (EEG). The EEG was continuously recorded during the experiment and frequent arterial blood samples were taken for determination of etomidate plasma concentrations. The changes observed in the raw EEG signal were quantified using aperiodic analysis in the 2.5-7.5 Hz frequency band. The return of the righting reflex was used as another parameter of anesthesia.

RESULTS

A mean dose of 8.58+/-0.41 mg/kg needed to be infused to reach the end point of 5 s isoelectric EEG. The plasma concentration time profiles were most adequately fitted using a three-exponential model. Systemic clearance, volume of distribution at steady-state and elimination half-life averaged 93+/-6 ml/min/kg, 4.03+/-0.24 l/kg and 59.4+/-10.7 min respectively. The EEG effect-plasma concentration relationship was biphasic exhibiting profound hysteresis. Semi-parametric minimization of this hysteresis revealed an equilibration half-life of 2.65+/-0.15 min, and the biphasic effect-concentration relationship was characterized nonparametrically by descriptors. The effect-site concentration at the return of the righting reflex was 0.44+/-0.03 microg/ml.

CONCLUSIONS

The results of the present study show that the concentration-effect relationship of etomidate can be characterized in individual rats using aperiodic analysis in the 2.5-7.5 Hz frequency band of the EEG. This characterization can be very useful for studying the influence of diseases on the pharmacodynamics of etomidate in vivo.

The influence of hemorrhagic shock on the pharmacokinetics and the analgesic effect of morphine in the rat

The influence of hemorrhagic shock (removal of 30% of the blood volume) on the pharmacokinetics and the analgesic effect of morphine was investigated in conscious rats. Plasma concentrations of morphine after a bolus injection (5 mg/kg) are higher in the shock animals, which is attributed to a small decrease in clearance (-22%; P > 0.05) and a significant decrease in distribution volume (-33%; P < 0.05) of the drug. The areas under the plasma concentration-time curve of the metabolite morphine-3-glucuronide (M3G) are significantly higher (+237%; P < 0.01) in the shock rats, which is probably explained by a decreased distribution and renal excretion. The analgesic effect of morphine was evaluated using the tail-flick test during a continuous infusion (10 mg/kg/h) with measurement of the plasma concentrations of morphine and M3G. Data from these experiments show higher plasma concentrations of morphine (+33%; P < 0.05) and M3G (+66%; P > 0.05) during shock, and a significantly increased analgesic effect (+43%; P < 0.05). Our data suggest that the increased analgesic effect of morphine during hemorrhagic shock can most likely be explained by pharmacokinetic changes resulting in higher morphine concentrations.

Comparison of two high-performance liquid chromatographic methods for monitoring plasma concentrations of haloperidol and reduced haloperidol

Two high-performance liquid chromatographic methods for monitoring haloperidol (HAL) and reduced haloperidol (RHAL) plasma concentrations were compared. In one method ultraviolet detection and a C18 column were used (UV method); in the other method electrochemical detection and a CN-column were used (EC method). Both methods are accurate and precise. For plasma samples spiked with HAL or RHAL, an excellent correlation was observed between the concentrations of HAL and RHAL found with both methods (r < or = 0.99, p < 0.01). However, for plasma obtained from patients treated with HAL the correlation between the two methods was poor (r > or = 0.71, p < 0.01). The main reason for the discrepancy between the two methods is probably interference of comedications or their metabolites, mostly in the EC method. Although the quantitation limit of the UV method (2 ng/ml for HAL and RHAL) is higher than that of the EC method (0.5 ng/ml for HAL and RHAL), the UV method is to be preferred for monitoring plasma levels in psychiatric patients because there is less interference from comedication.

Variability of morphine disposition during long-term subcutaneous infusion in terminally ill cancer patients

OBJECTIVE

To study the plasma concentrations of morphine and its glucuronides to assess the intra- and interindividual variability of the disposition of morphine administered by subcutaneous infusion in cancer patients.

METHODS

Blood samples were taken repeatedly in eight patients with severe cancer pain who were being treated with morphine (60-3000 mg per day) via chronic (8-160 days) subcutaneous infusion. Venous blood samples were collected at least weekly and, when possible, on 3 consecutive days after dose adaptation or any other major change in the patients' treatment. Concentrations of morphine and its glucuronides in plasma were measured after solid-phase extraction using a validated high-performance liquid chromatography assay. The stability of the morphine solutions was determined by repeated measurement of the concentrations of morphine and its degradation products in the solutions.

RESULTS

The morphine concentration in the infusion solutions remained unchanged during storage and infusion. The plasma concentrations of morphine and its glucuronides were within the ranges reported in the literature. There was, as expected, a large interindividual variability: from patient to patient, the mean of the normalised plasma concentrations ranged from 0.3 ng.ml(-1).mg(-1) to 0.8 ng.ml(-1).mg(-1) for morphine, from 1.0 ng.ml(-1).mg(-1) to 3.1 ng.ml(-1).mg(-1) for morphine-6-glucuronide and from 6.8 ng.ml(-1).mg(-1) to 24.3 ng.ml(-1).mg(-1) for morphine-3-glucuronide. Intraindividual variability was also important. The residual standard deviation of the mean normalised plasma concentrations calculated for each patient ranged from 26% to 56% for morphine, from 20% to 51% for morphine-6-glucuronide and from 20% to 49% for morphine-3-glucuronide. The normalised plasma concentrations of morphine and its glucuronides did not increase with dose or time, and no explanation for the pronounced pharmacokinetic intraindividual variability was found.

CONCLUSION

During subcutaneous infusion of morphine, there is a large intra- and interindividual variability of the morphine disposition which could be of clinical relevance.

Characterization of the cytochrome P450 isoenzymes involved in the in vitro N-dealkylation of haloperidol

AIMS

The present study was carried out to identify the cytochrome P450 isoenzyme(s) involved in the N-dealkylation of haloperidol (HAL).

METHODS

In vitro studies were performed using human liver microsomes and c-DNA-expressed human P450 isoforms. N-dealkylation of HAL was assessed by measuring the formation of 4-(4-chlorophenyl)-4-hydroxypiperidine (CPHP).

RESULTS

There was a tenfold variation in the extent of CPHP formation amongst the nine human liver microsomal preparations. The CPHP formation rates as a function of substrate concentration, measured in three livers, followed monophasic enzyme kinetics. Km and Vmax values ranged respectively from 50 to 78 microM and from 180 to 412 pmol mg-1 min-1 CPHP formation rates in the nine liver preparations were significantly correlated with dextromethorphan N-demethylase activity (a marker of CYP3A4 activity), but not with the activity of dextromethorphan O-demethylase (CYP2D6), phenacetin O-deethylase (CYP1A2) or tolbutamide hydroxylase (CYP2C9). Ketoconazole, an inhibitor of CYP3A4, inhibited competitively CPHP formation (Ki=0.1 microM), whereas sulphaphenazole (CYP2C9), furafylline (CYP1A2) and quinidine (CYP2D6) gave only little inhibition (IC50 > 100 microM). CPHP formation was, moreover, enhanced by apha-naphtoflavone, an effect common to CYP3A4 mediated reactions. Anti-CYP3A4 antibodies strongly inhibited CPHP formation, whereas no inhibition was observed in the presence of CYP2D6 antibodies. Among the recombinant human CYP isoforms tested, CYP3A4 exhibited the highest activity with respect to CPHP formation rate, with no detectable effect of other CYP isoforms (CYP1A2, CYP2D6 and CYP2C9). HAL inhibited dextromethorphan O-demethylase (CYP2D6) with IC50 values between 2.7 and 8.5 microM, but not (IC50 > 100 microM) dextromethorphan N-demethylase (CYP3A4), phenacetin O-deethylase (CYP1A2) or tolbutamide hydroxylase (CYP2C9).

CONCLUSIONS

These results strongly suggest that the N-dealkylation of HAL in human liver microsomal preparations is mediated by CYP3A4.

Measurement of cefuroxime in human bronchoalveolar lavage fluid by high-performance liquid chromatography after solid-phase extraction

A sensitive and selective method for the determination of cefuroxime in bronchoalveolar lavage (BAL) fluid using high-performance liquid chromatography (HPLC) with UV detection at 280 nm after solid-phase extraction with C18 cartridges was developed. A Waters symmetry C18 column was used and the mobile phase was acetonitrile-0.05 M ammonium phosphate buffer (pH 3.2) (15:85, v/v). The method enabled the determination of cefuroxime at concentrations below 100 ng/ml, with a linear calibration curve at concentrations of 5-100 ng/ml for 400 microliters of BAL. The intra- and inter-assay coefficient of variations for 10, 40 and 80 ng/ml were between 5.3 and 8.9%. Analytical recoveries were between 92.7 and 106.2%. The detection limit was 1 ng/ml at a signal-to-noise ratio of 3:1 using 400 microliters of BAL. The method was successfully used for the analysis of BAL fluid from patients after oral administration of 500 mg cefuroxime axetil twice daily.

High performance liquid chromatography determination of dextromethorphan and its metabolites in urine using solid-phase extraction

A high performance liquid chromatography assay coupled with fluorescence detection was developed for the determination of dextromethorphan and its metabolites in urine. The products and the internal standard, pholcodine, were separated on an Alltima C18, 5 microns column (250 x 4.6 mm), using a mobile phase containing sodium dodecyl sulphate (1 mM) in a mixture of acetonitrile-sodium dihydrogen phosphate (0.01 M) 40.5:59.5, v/v) (pH* = 2.5). A novel solid-phase extraction procedure with strong cation exchange, non end-capped, Isolute SCX cartridges allows good recovery of the products (mean 85% or more). For all analytes, the assay is sensitive (LOQ 25 ng ml-1, using 200 microliters urine), reproducible (RSD < 15%) and accurate (< 15% deviation of the nominal value) over the range evaluated. This method can be used to measure dextromethorphan and its metabolites to phenotype individuals as poor or extensive metabolizers of drugs metabolized by CYP2D6.

Severe diltiazem poisoning with intestinal pseudo-obstruction: case report and toxicological data

This case report concerns a 30-year-old man who survived a 4.2 g diltiazem overdose. He sustained vasoplegic shock with a junctional escape rhythm which required high doses of norepinephrine and epinephrine. Among other complications, ileus with paralytic intestinal pseudo-obstruction developed on day three. Cecal distention was demonstrated by abdomen computed tomodensitometry. The ileus resolved on day seven following the poisoning. Diltiazem plasma concentrations were determined during the first three days. The possible role of other medications, activated charcoal and sufentanil, is noted.

Capillary gas chromatographic determination with nitrogen-phosphorus detection of the calcium antagonist nicardipine and its pyridine metabolite M-5 in plasma

A capillary gas chromatographic method with nitrogen-phosphorus detection for the simultaneous determination of nicardipine and its pyridine metabolite M-5 was developed. The method involves extraction of the plasma with hexane-methylene chloride (1:1, v/v), followed by evaporation of the organic phase. The extract is injected into a fused-silica capillary column coated with cross-linked 5% phenyl-methylsilicone. A temperature gradient (85-285 degrees C) is applied and the two products and the internal standard can be separated within 22 min. The limit of detection is 0.5 ng/ml for both products. The method is suitable for pharmacokinetic studies in humans.

Metabolism and hepatotoxicity of N,N-dimethylformamide, N-hydroxymethyl-N-methylformamide, and N-methylformamide in the rat

The metabolism and hepatotoxicity of N,N-dimethylformamide (DMF) and two of its metabolites, N-hydroxymethyl-N-methylformamide (HMMF) and N-methylformamide (NMF) were evaluated over a 4-day period in rats. DMF toxicity was dose dependent and delayed toxicity after the administration of a high DMF dose (13.7 mmol/kg) in comparison to a lower dose (4.1 mmol/kg) was observed. Treatment of rats with 13.7 mmol/kg DMF, HMMF, or NMF showed i) that DMF is more toxic than HMMF or NMF, and ii) that hepatotoxicity occurs later for DMF than for HMMF or NMF. Analysis of serum and urine samples demonstrated that DMF is first metabolized to HMMF, which is then partially converted to NMF. After HMMF administration, NMF was found both in serum and in urine. The time course of DMF and HMMF toxicity in relation to NMF formation fitted the hypothesis that the hepatotoxicity of DMF and HMMF is mediated via NMF. The degree of hepatotoxicity after HMMF and NMF treatment is similar. However, the degree of DMF hepatotoxicity is much higher than in the case of NMF or HMMF. The role of NMF as an obligatory intermediate in DMF and HMMF hepatotoxicity is discussed.

Influence of endotoxin on the stereoselective pharmacokinetics of oxprenolol, propranolol, and verapamil in the rat

The influence of endotoxin-induced inflammation on the enantioselective pharmacokinetics of propranolol, oxprenolol, and verapamil, which bind to alpha 1-acid glycoprotein, was studied in the rat. The racemic mixtures were given orally. In the control animals, for propranolol and oxprenolol, the plasma concentrations of the (R)-enantiomer were higher than those of the (S)-enantiomer, while for verapamil the reverse was true. Protein binding and intrinsic clearance are the main factors responsible for this enantioselectivity. After endotoxin treatment, for the three drugs tested the plasma concentrations and the plasma binding of both enantiomers were significantly increased. This effect was more pronounced for (R)-propranolol, (R)-oxprenolol, and (S)-verapamil than for their respective antipodes. The enantioselective effect of endotoxin on the plasma concentrations of the drugs studied seems mainly due to the enantioselective increase in binding to alpha 1-acid glycoprotein.

Chiral high-performance liquid chromatographic determination of oxprenolol in plasma

A sensitive, stereospecific high-performance liquid chromatographic assay for oxprenolol enantiomers in rat plasma was developed, using a chiral derivatization agent. Racemic oxprenolol and the internal standard (racemic propranolol) are extracted with dichloromethane after alkalinization of the plasma. Quantitation of R(+)- and S(-)-oxprenolol is based on derivatization with the chiral agent S(-)-1-(1-naphthyl)-ethyl isocyanate, followed by chromatographic separation on a C18 reversed-phase column, with fluorometric detection (excitation at 226 nm, emission at 333 nm). The assay is reproducible as judged by a coefficient of variation of less than 17.5% for both enantiomers at all concentrations used. Preliminary experiments in the rat demonstrate that the method is sufficiently sensitive for pharmacokinetic studies in that species.

Simultaneous determination of N,N-dimethylformamide, N-monomethylformamide and N-hydroxymethyl-N-methylformamide in rat plasma by capillary gas chromatography

A capillary gas chromatographic method with nitrogen-phosphorus detection for the simultaneous quantitative determination of N,N-dimethylformamide, and its two metabolites, N-monomethylformamide and N-hydroxymethyl-N-methylformamide, in rat plasma has been developed. The method involves a single extraction step with ethyl acetate-acetone (4:1, v/v). The extract is injected into a fused-silica capillary column coated with Carbowax 20M. A temperature gradient (65-110 degrees C) is applied, and the three products can be separated within 10 min. The quantitation limits, using 25 microliters of rat plasma, for N,N-dimethylformamide, N-monomethylformamide and N-hydroxymethyl-N-methylformamide are 0.4, 0.4 and 2 micrograms/ml, respectively. This method is suitable for toxicokinetic studies in rats.

Intrapleural quinacrine instillation for recurrent pneumothorax or persistent air leak

From 1982 to 1990, 27 patients with recurrent pneumothorax or persistent air leak (28 episodes) underwent pleurodesis with intrapleural administration of quinacrine, according to a standardized scheme. A first evaluation was done about 1 month after the intervention. In August 1990, all patients were invited for a second check-up. In 4 patients quinacrine plasma concentrations were determined. There was one early failure. No late recurrences were observed. Neither serious nor late complications were seen with our low-dose regimen. Transient fever was the only constant side effect. In contrast to other chemicals proposed for pleurodesis, quinacrine did not cause major pain. Only very low quinacrine plasma concentrations (peak, < 10 ng/mL) were found. In conclusion, chemical pleurodesis with quinacrine can be considered a safe and effective treatment. The number of administrations as well as the dosage are important to prevent morbidity and recurrence.

Stereoselective pharmacokinetics of atenolol in the rat: influence of aging and of renal failure

The pharmacokinetics of R- and S-atenolol after intravenous administration of racemic atenolol were studied in 3-, 12- and 24-month-old rats and in 3-month-old rats with renal failure induced by uranyl nitrate. In all age groups, the area under the plasma concentration-time curves is higher for R- than for S-atenolol; volume of distribution, total clearance and renal clearance are lower for R-atenolol than for S-atenolol, but the differences are small. In function of age there is for both enantiomers a significant increase in AUC, due, at least in part, to a decreased renal clearance; the effect of aging is not stereoselective. In rats with renal failure, the AUC of both enantiomers increases, due mainly to a decrease in renal clearance, but to a lesser degree also to a decrease in nonrenal clearance. For both enantiomers, the volume of distribution decreases and the half-life increases in the uraemic rats. The total amount of both enantiomers excreted in the urine is decreased in the rats with renal failure. There are no stereoselective effects of treatment of the rats with uranyl nitrate.

Propofol anaesthesia for ultrasound guided oocyte retrieval: accumulation of the anaesthetic agent in follicular fluid

Propofol (2,6-diisopropylphenol, Diprivan, ICI-Pharmaceuticals, Manchester, UK) is widely used either as an adjunct in general anaesthesia or as sole anaesthetic agent by the continuous intravenous route and intermittent bolus injections for minor surgical interventions. For several years, we have been using this kind of anaesthesia in transvaginal oocyte retrieval for in-vitro fertilization (IVF), allowing a completely painless puncture on an out-patient basis. From in-vitro studies on mouse oocytes, it appeared that propofol could be deleterious for fertilization in a dose- and time-dependent manner. We therefore investigated the concentrations of propofol in follicular fluid during oocyte retrieval in women. We measured propofol levels in serum and follicular fluid of nine patients at fixed intervals during ultrasound guided oocyte retrieval. Serum levels fluctuated randomly, due to interference from top-off doses of propofol. In follicular fluid, however, we found a steady increase of propofol levels, which was proportional to the total dose of propofol administered. These data indicate that propofol accumulates in follicular fluid. Although it seems unlikely that propofol as used in the present protocol exerts a clinically significant unfavourable effect on IVF, we suggest that the oocyte retrieval procedure should be kept as short as possible, in order to limit the accumulation of the anaesthetic in follicular fluid.

Influence of age on stereoselective pharmacokinetics and metabolism of hexobarbital in the rat

The influence of age on stereoselective pharmacokinetics and in vitro metabolism of R- and S-hexobarbital was studied in the rat. After intravenous administration of the racemate, the plasma concentrations of S-hexobarbital are markedly lower than those of R-hexobarbital. For S-hexobarbital the half-life is somewhat shorter and the volume of distribution and plasma clearance is higher than for its antipode. For both enantiomers an increase in AUC and half-life, and a decrease in clearance are observed with aging. These changes occur mainly between the 3rd and the 12th month and are slightly more pronounced for R- than for S-hexobarbital, as appears from the S/R ratios. The volume of distribution shows no changes with aging. In vitro disappearance rate in 3-month-old rats is significantly higher for S- than for R-hexobarbital. There is for both enantiomers an increase in disappearance rate in 12-month-old rats as compared to younger or older rats, but this is significant only for the R-enantiomer. There are pronounced differences in the kinetics and metabolism of both hexobarbital enantiomers; changes with aging occur, but are only slightly and not always significantly more important for R- than for S-hexobarbital.

Investigation of a possible pharmacokinetic interaction between ibopamine and isosorbide-5-mononitrate

The possibility of a pharmacokinetic interaction between isosorbide-5-mononitrate (5-ISMN) and epinine, the active metabolite of ibopamine, has been investigated in 8 healthy male subjects given single doses of 200 mg ibopamine and 20 mg 5-ISMN, separately and together. The plasma 5-ISMN concentration-time profile was the same whether 5-ISMN was administered concomitantly with ibopamine or alone [AUC(o-t): 2.24 micrograms.ml-1.h after 5-ISMN alone, 2.16 micrograms.ml-1.h after 5-ISMN+ibopamine]. The plasma concentrations of total and free epinine and the urinary recovery of total epinine, homovanillic acid and dihydroxyphenylacetic acid, too, were not different when ibopamine was administered alone or concomitantly with 5-ISMN. The intake of ibopamine did not change the blood pressure and heart rate. The decrease in diastolic blood pressure induced by 5-ISMN was not influenced by concomitant intake of ibopamine. The observations suggest that in healthy volunteers there is no pharmacokinetic interaction between 5-ISMN and ibopamine.

Reversed-phase high-performance liquid chromatographic analysis of atenolol enantiomers in plasma after chiral derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate

A sensitive high-performance liquid chromatographic method for the determination of the enantiomers of atenolol in rat plasma has been developed. Racemic atenolol and practolol (internal standard) were extracted from alkalinized plasma (pH 12) into dichloromethane containing 3% (v/v) heptafluoro-1-butanol, and the organic layer was evaporated. The samples were derivatized with (+)-1-(9-fluorenyl)ethyl chloroformate at pH 8.5 for 30 min. After removal of excess reagent, the diastereomers were extracted into dichloromethane. The diastereomers were separated on a Microspher C18 column (3 microns) with a mobile phase of acetonitrile-sodium acetate buffer (0.01 M, pH 7) (50:50, v/v) at a flow-rate of 0.8 ml/min. Fluorescence detection (lambda ex = 227 nm, lambda em = 310 nm) was used. When 100 microliters of plasma were used, the quantitation limit was 10 ng/ml for the atenolol enantiomers. The assay was applied to measure concentrations of atenolol enantiomers in plasma after intravenous administration of racemic atenolol to rats.

High-performance liquid chromatographic method for the simultaneous determination of R-(-)- and S-(+)-hexobarbital in rat plasma

The enantiospecific determination of R- and S-hexobarbital in rat plasma is described. The method involves liquid-liquid extraction of racemic hexobarbital from plasma, separation of the underivatized enantiomers by high-performance liquid chromatography on an alpha 1-acid glycoprotein column and ultraviolet detection. The mobile phase consists of a phosphate buffer (pH 5.4) containing 0.4% 2-propanol as organic modifier. An alpha 1-acid glycoprotein guard column is used to increase the lifetime of the analytical column. Heptabarbital is the achiral internal standard. With detection limits of ca. 0.05 microgram/ml for both R- and S-hexobarbital, the assay is suitable for pharmacokinetic studies of the enantiomers in rats.

Determination of cetirizine in human urine by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of the histamine H1-receptor antagonist cetirizine in human urine was developed. Cetirizine and the internal standard are extracted from acidified (pH 5) urine (0.5 ml) into chloroform and the organic layer is evaporated to dryness. The residue is chromatographed on a Spherisorb 5ODS-2 column using Pic A (5 mM aqueous tetrabutylammonium phosphate)-methanol-tetrahydrofuran (33:65:2, v/v) as the mobile phase with ultraviolet detection (230 nm). The calibration graph is linear from 0.1 to 10 micrograms/ml and using 0.5 ml of urine the detection limit is 20 ng/ml. The within-run relative standard deviation is less than 6% and the accuracy is within 10% of the theoretical value at concentrations between 0.1 and 10 micrograms/ml in urine. There is a good correlation (r = 0.99606) with a previously described capillary gas chromatographic assay.

Effect of aging on the pharmcokinetics of atenolol, metoprolol and propranolol in the rat

The pharmacokinetics of three beta adrenoceptor blocking drugs atenolol, metoprolol, propranolol and of the model drug antipyrine were studied in 3-, 12- and 24-month-old rats. Alpha-1-acid glycoprotein in plasma was slightly increased and the free fraction of propranolol was slightly decreased in the 24-month-old rats. For the four drugs studied, the volume of distribution and the clearance were decreased in the older rats. For propranolol, metoprolol and antipyrine these decreases were already observed in 12-month-old rats, for atenolol only in the 24-month-old rats. There was no change in half-life as a function of age for the three beta blockers; for antipyrine a significant increase in half-life was seen. The decreased volume of distribution suggests a lower tissue binding or a decrease in total body fluid. The change in clearance in function of age can probably be explained for metoprolol and propranolol by a decrease in hepatic blood flow as no change in metabolism or protein binding occurs, for atenolol by a decrease in renal function and for antipyrine by a decrease in metabolism. After p.o. administration of the beta blockers, no significant increase in area under the plasma drug concentration-time curve was observed for propranolol and metoprolol as a function of age, but for atenolol, a significant increase in area under the plasma drug concentration-time curve was seen in the 24-month-old rats, due to a decrease in renal function, as bioavailability of atenolol did not change in function of age.

Penetration of ampicillin and sulbactam in the lower airways during respiratory infections

We studied the penetration of ampicillin-sulbactam in the alveolar lining fluid (ALF) of eight patients after intravenous administration of 2,000 mg of ampicillin and 1,000 mg of sulbactam three times daily over 30 min. Bronchoalveolar lavage was performed on day 3, 30 min after the end of the morning drug administration. The mean penetration ratios (i.e., the ratios of the concentrations in ALF versus those in serum) were 53% (standard error, 12%) and 61% (standard error 31%) for ampicillin and sulbactam, respectively. The concentration ratio of ampicillin versus sulbactam in serum was not significantly different from that in ALF. From a pharmacokinetic point of view, ampicillin-sulbactam is a good choice for treatment of infectious exacerbation of chronic obstructive pulmonary disease and community-acquired bacterial pneumonia, since the concentrations of both drugs in ALF exceed the MICs for the respiratory pathogens responsible.

High-performance liquid chromatographic determination of propylthiouracil in plasma

A high-performance liquid chromatographic method for the determination of the antithyroid drug propylthiouracil in dog plasma has been developed. Propylthiouracil and the internal standard, methylthiouracil, are extracted from plasma with methylene chloride at pH 6 and the organic layer is evaporated to dryness. The residue is chromatographed on a Chromspher C18 reversed-phase column using Pic B-7 (0.005 M 1-heptanesulphonic acid in water)-1% acetic acid-methanol (40:45:15, v/v/v) as the mobile phase. Quantification is achieved by monitoring the UV absorbance at 300 nm. The response is linear (0.1-15 micrograms/ml) and using 100 microliters of plasma the detection limit is 50 ng/ml. The within-run coefficient of variation is less than or equal to 5% and the accuracy is within 10% of the theoretical value at concentrations between 0.1 and 15 micrograms/ml plasma.

Influence of lignocaine on plasma protein binding and pharmacokinetics of verapamil in dogs

The effect of lignocaine (lidocaine) on the plasma protein binding of verapamil has been studied in-vitro and in-vivo in dogs. The binding of verapamil was ca 85%. In-vitro addition of lignocaine at therapeutic concentrations displaced verapamil from its plasma binding sites. Lignocaine in this regard was equipotent with tris(2-butoxyethyl)phosphate, suggesting an interaction at the level of alpha 1-acid glycoprotein binding sites. On in-vivo administration of 4 mg kg-1 in a bolus to dogs in which steady state concentrations of verapamil were present, the free fraction of verapamil increased transiently. During the lignocaine maintenance infusion, it then decreased to a level higher than that before administration of the local anaesthetic. The free verapamil concentrations increased suddenly upon the administration of the lignocaine loading dose, and then returned to values slightly higher than those before lignocaine. After a bolus injection of verapamil during a lignocaine infusion, the verapamil total plasma concentrations were lower than during a saline infusion, but the free concentrations were not different. The volume of distribution of verapamil was increased, whereas the blood clearance had not changed; the lignocaine infusion did not change the hepatic blood flow, as measured by indocyanine green clearance. These results show that lignocaine displaces verapamil in-vitro and in-vivo from its plasma protein binding sites, but the ensuing pharmacokinetic changes do not lead to significant changes in free verapamil concentrations.

Plasma concentrations and haemodynamic effects of nimodipine in patients resuscitated after cardiac arrest

As the pharmacokinetics of a drug may be altered in haemodynamically compromised patients, the plasma concentrations and haemodynamic effects of the calcium entry blocker nimodipine have been examined in patients resuscitated after out-of-hospital cardiac arrest. In 7 patients nimodipine was infused at increasing rates up to 30 micrograms.kg-1.h-1. The plasma concentrations increased with increasing dose; at the highest dose a mean steady-state plasma concentration of 22.1 ng.ml-1 was obtained, and the mean plasma clearance was 1.41.kg-1.h-1. There were no marked changes in mean arterial blood pressure or heart rate. In 9 other patients nimodipine was given as a bolus infusion of 10 micrograms.kg-1 over 3 min, followed by a continuous infusion of 30 micrograms.kg-1.h-1. A mean steady-state plasma concentration of 17.6 ng.ml-1 was obtained and the mean plasma clearance was 1.91.kg-1.h-1. Heart rate did not change significantly, but the mean arterial blood pressure fell. The data indicate that in patients resuscitated after cardiac arrest, the pharmacokinetics of nimodipine are not markedly different from patients with other conditions, e.g. subarachnoid haemorrhage. However, if a loading dose is given to obtain a steady-state concentration sooner, there will be a fall in arterial blood pressure.

Influence of exercise on plasma concentrations of isosorbide dinitrate

As the fall in hepatic blood flow caused by exercise is expected to decrease the elimination of high extraction drugs, the influence of exercise on the fate of the anti-anginal drug isosorbide dinitrate has been assessed. Isosorbide dinitrate 10 mg was given orally, after an overnight fast, on 2 different days to 7 healthy volunteers and the plasma concentrations of the parent compound and its mononitrate metabolites were measured. Heavy bicycle exercise from the 45th to the 105th min after intake of the drug on one of the experimental days did not change the plasma isosorbide dinitrate concentrations as compared to those on the rest day. The concentrations of both mononitrates were lower on the exercise day, but the difference was already present before the exercise started.

Influence of cardiopulmonary resuscitation on plasma concentrations of nimodipine in the dog

The influence of cardiopulmonary resuscitation on the plasma concentrations of nimodipine in the anaesthetized dog has been examined. Nimodipine was given as a bolus injection followed by a maintenance infusion. When, during the maintenance infusion, the dogs were subjected to cardiac arrest followed by external cardiac massage combined with artificial ventilation (basic life support), a fast and almost threefold increase in the steady-state plasma concentrations of nimodipine was observed. When the maintenance infusion of nimodipine was stopped immediately before cardiac arrest and basic life support, the nimodipine concentrations decreased. These results indicate that during basic life support, there is a decreased transfer of infused nimodipine from plasma to the tissues. This is also supported by the fact that for antipyrine, a drug with a smaller volume of distribution than nimodipine, the increase in plasma concentrations when infused during cardiac arrest and basic life support, was much smaller. When nimodipine was started after restoration of the spontaneous circulation (advanced life support) in dogs that had been subjected to cardiac arrest and basic life support, the plasma concentrations were not significantly higher than in control dogs. It can be concluded that the fate of nimodipine is markedly altered during basic life support but not in the period following restoration of spontaneous circulation.

Propofol combined with nitrous oxide-oxygen for induction and maintenance of anaesthesia

After a bolus of 2 mg/kg, propofol was given by continuous infusion (150 micrograms/kg/minute for 30 minutes and then 100 micrograms/kg/minute) supplemented with nitrous oxide for anaesthesia during ear surgery in 12 patients. Cardiovascular changes were not significant except for a decrease in heart rate after 60 minutes. Acid-base balance was unaffected by the amount of fatty emulsion. Cortisol levels showed a nonsignificant decrease during the prolonged administration of propofol but had recovered completely by one hour following anaesthesia. Mean blood concentrations of propofol were 10.5 micrograms/ml (SEM 1.2) at the onset of unconsciousness, between 3.4 and 4.5 micrograms/ml during continuous infusion and 2.9 micrograms/ml (SEM 0.3) on awakening. Patients opened their eyes 6 minutes (SEM 1) after discontinuation of the infusion, and were responsive at 7.5 minutes (SEM 0.5), which suggests that propofol infusion can be used safely for surgery of 2 hours' duration.

Binding to serum alpha 1-acid glycoprotein and effect of beta-adrenoceptor antagonists in rats with inflammation

The beta-blocking effect of 4 beta-adrenoceptor antagonists with different pharmacokinetic properties was studied after intravenous and intraportal administration to control rats and to rats with experimental inflammation. In rats with inflammation the effects of propranolol and oxprenolol, which are mainly bound to alpha 1-acid glycoprotein (alpha 1-AGP), were significantly less after intravenous administration, but not after intraportal administration. In contrast, for metoprolol and atenolol, which are only negligibly serum bound, no difference was observed between control rats and rats with inflammation for either route of administration. Total and unbound serum concentrations of propranolol were measured 20 min after intravenous and intraportal administration. After intravenous administration, in the rats with inflammation total concentrations of propranolol were more than twice, and unbound concentrations less than half those of control rats. After intraportal administration the total concentrations were 8 times, and the unbound concentrations 3 times higher in the rats with inflammation. There was a significant correlation between the beta-blocking effect and the unbound concentrations of propranolol after intravenous administration, but not after intraportal administration. The latter finding is probably because the unbound concentrations were supramaximal.

The pharmacokinetics of ciprofloxacin in patients with impaired renal function

Pharmacokinetics of ciprofloxacin after single oral administration of 250 mg were studied in patients with and without renal failure. Ciprofloxacin concentrations were measured by HPLC. The elimination half-life was 8.7 +/- 0.9 h (mean +/- S.E.M.) in six renal failure patients not on haemodialysis, as compared to 4.4 +/- 0.2 h in six patients with normal renal function. The urinary recovery of unchanged ciprofloxacin was 5.3 +/- 1.7% of dose over 24 h in the renal failure patients, as compared to 37.0 +/- 3.7% in the patients with normal renal function. In haemodialysis patients, the half-life was 5.8 +/- 0.9 h on an interdialysis day, and 3.2 +/- 0.4 h during haemodialysis.

Fate of orally given isosorbide dinitrate in cirrhotic patients

In 5 out of 7 patients with cirrhosis and extensive shunting, plasma concentrations of isosorbide dinitrate after oral administration of 10 mg of the substance were markedly higher than those found in subjects without hepatic disease. The explanation could be a higher bioavailability and/or a lower systemic clearance, due to shunting and hepatic cell dysfunction. The difference was confirmed by the calculation of the areas under the concentration-time curves.

Preliminary pharmacokinetics of intravenous ciramadol in humans

Plasma concentrations of ciramadol were measured after intravenous administration of 30 mg in 8 healthy volunteers. A high-performance liquid chromatographic method with U.V.-detection for simultaneous determination of the substance and of its desmethyl metabolite was developed. The disposition of the drug in these volunteers could be described by a two-compartment open model. Distribution volume was on average 561, elimination half-life 3.85 hours and mean body clearance 154 ml/min. Desmethylciramadol was not detected in the plasma.

Determination of nifedipine in human plasma by capillary gas chromatography with nitrogen detection

A gas chromatographic method for the determination of nifedipine in human plasma is presented. Nifedipine was extracted from plasma at basic pH with toluene, and nitrendipine was used as the internal standard. Chromatography was performed on a cross-linked methylsilicone fused-silica column by on-column injection and with a nitrogen-phosphorus ionization detector. The minimal detectable concentration was approximately equal to 0.5 ng/ml of plasma. The standard curve was linear in the range evaluated, 2-300 ng/ml plasma. The within-analysis coefficient of variation was 3.9-10.4%, and the day-to-day coefficient of variation was 3.8%. A peak with the same retention time as the nitropyridine derivative of nifedipine was detected in the plasma of patients who had taken 10 mg nifedipine orally.

High-performance liquid chromatographic determination of metoprolol in plasma

A high-performance liquid chromatographic method is presented for the determination of metoprolol in human plasma. Metoprolol was extracted from plasma by a single extraction procedure with 4-methylpropranolol as the internal standard. Chromatography was done on a reversed-phase column with fluorescence detection. The minimum detectable concentration was 5.0 ng/ml of plasma. The standard curve was linear in the range evaluated, 10-300 ng/ml. The within-run coefficient of variation was 2.3-6.0%, and the day-to-day variation was 6.8%. The method is free from interference by major metoprolol metabolites.

Analysis of methoxsalen in plasma by reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of methoxsalen in plasma was developed. The method includes extraction from plasma of the drug and the internal standard (5-methoxypsoralen) into methylene chloride. Chromatography was performed on a reversed-phase C8 column connected with a UV detector set at 254 nm. The mobile phase was methanol-acetonitrile-water (2:30:68). For a plasma sample of 0.25 ml, the maximal sensitivity was approximately 10 ng/ml. Accuracy was within 7.5% for therapeutic plasma levels, and the coefficient of variation varied between 4.3 and 0.9% for 28 and 300 ng/ml of plasma, respectively.