Unchanged acetylation of isoniazid by alcohol intake.

SETTING: In 10 healthy subjects, the influence of acute alcohol intake on the pharmacokinetics of isoniazid (INH) was studied. OBJECTIVE: To test the hypothesis that alcohol increases the conversion of INH by acetylation into its metabolite acetylisoniazid. DESIGN: In a crossover design, an oral dose of 300 mg INH was administered on 2 separate days, 14 days apart, with or without alcohol to a serum alcohol of about 21 mmol/l (1 g/l) maintained for 12 h. RESULTS: Neither the metabolism of INH nor that of acetylisoniazid was changed by acute alcohol intake. CONCLUSION: Acute alcohol intake has no impact on the conversion of INH to its metabolite acetylisoniazid, which is catalysed by the enzyme N-acetyltranferase. Accordingly, a metabolic effect of acute alcohol intake on INH metabolism probably contributes little to the therapeutic failure of anti-tuberculosis treatment among alcoholics.

Activated charcoal alone or after gastric lavage: a simulated large paracetamol intoxication.

AIMS: Activated charcoal is now being recommended for patients who have ingested potentially toxic amounts of a poison, where the ingested substance adsorbs to charcoal. Combination therapy with gastric lavage and activated charcoal is widely used, although clinical studies to date have not provided evidence of additional efficacy compared with the use of activated charcoal alone. There are also doubts regarding the efficacy of activated charcoal, when administered more than 1 h after the overdose. The aim of this study was to examine if there was a difference in the effect of the two interventions 1 h post ingestion, and to determine if activated charcoal was effective in reducing the systemic absorption of a drug, when administered 2 h post ingestion. METHODS: We performed a four-limbed randomized cross-over study in 12 volunteers, who 1 h after a standard meal ingested paracetamol 50 mg kg(-1) in 125 mg tablets to mimic real-life, where several factors, such as food, interfere with gastric emptying and thus treatment. The interventions were activated charcoal after 1 h, combination therapy of gastric lavage followed by activated charcoal after 1 h, or activated charcoal after 2 h. Serum paracetamol concentrations were determined by h.p.l.c. Percentage reductions in the area under the curve (AUC) were used to estimate the efficacy of each intervention (paired observations). RESULTS: There was a significant (P<0.005) reduction in the paracetamol AUC with activated charcoal at 1 h (median reduction 66%, 95% confidence intervals 49, 76) compared with controls, and a significant (P<0.01) reduction for gastric lavage followed by activated charcoal at 1 h (median reduction 48.2%, 95% confidence interval 32.4, 63.7) compared with controls. There was no significant difference between the two interventions (95% confidence interval for the difference -3.8, 34.0). Furthermore, we found a significant (P<0.01) reduction in the paracetamol AUC when activated charcoal was administered 2 h after tablet ingestion when compared with controls (median 22.7%, 95% confidence intervals 13.6--34.4). CONCLUSIONS: These results suggest that combination treatment may be no better than activated charcoal alone in patients presenting early after large overdoses. The effect of activated charcoal given 2 h post ingestion is substantially less than at 1 h, emphasizing the importance of early intervention.

Therapeutic drug monitoring of haloperidol, perphenazine, and zuclopenthixol in serum by a fully automated sequential solid phase extraction followed by high-performance liquid chromatography.

In Denmark, haloperidol, perphenazine, and zuclopenthixol are among the most frequently requested antipsychotics for therapeutic drug monitoring. With the number of requests made at the authors' laboratory, the only rational analysis is one that can measure all three drugs simultaneously. The authors therefore decided to develop an automated high-performance liquid chromatography (HPLC) method. Two milliliters serum, 2.0 mL 10 mmol/L sodium phosphate buffer (pH 5.5), and 150 microL internal standard (trifluoperazine) solution were pipetted into HPLC vials and extracted on an ASPEC XL equipped with 1 mL (50 mg) Isolute C2 (EC) extraction columns and acetonitrile-methanol-ammonium acetate buffer (60:34:6) as extracting solution. Three hundred fifty microliters was analyzed by HPLC; a 150 x 4.6-mm S5CN Spherisorb column with a mobile phase of 10 mmol/L ammonium acetate buffer-methanol (1:9), a flow rate of 0.6-1.7 mL/min, and ultraviolet detection at 256 and 245 nm were used. Reproducibility was 5-12% and the lower limit of quantitation was 10, 1, and 5 nmol/L (4, 0.4, and 2 ng/mL) for haloperidol, perphenazine, and zuclopenthixol, respectively. The method was found to be sufficiently selective and robust for routine analysis.

In vivo measurement of haloperidol affinity to dopamine D2/D3 receptors by [123I]IBZM and single photon emission computed tomography.

This study examines the feasibility of a steady-state bolus-integration method with the dopamine D2/D3 receptor single photon emission computer tomography (SPECT) tracer, [123I]IBZM, for determination of in vivo affinity of haloperidol. The nonspecific binding of [123I]IBZM was examined in the rat brain by infusion of haloperidol to plasma levels approximately 100 times the Kd level in man. In humans, Kd for haloperidol binding was measured in four healthy volunteers that were examined twice: once with partial dopamine D2/D3 receptor blockade obtained by a scheduled infusion of unlabeled haloperidol (0.7 mg total dosage), and once in an unblocked state. Blood sampling and SPECT were performed intermittently during 6 hours after intravenous [123I]IBZM bolus injection. Plasma [123I]IBZM was determined by octane extraction. Plasma haloperidol was determined by a radioimmunoassay, and plasma protein binding was determined by equilibrium dialysis. In humans, the striatal D2/D3 receptor occupancy was 0.27+/-0.085 and the in vivo Kd for haloperidol was 0.25+/-0.1 nmol/L, which is comparable to Kd values as obtained from in vitro studies. The authors conclude that steady-state [123I]IBZM SPECT studies allow for determination of dopamine D2/D3 receptor occupancy in striatum and in vivo measurement of drug affinity to striatal dopamine D2 and D3 receptors.

Bioavailability and pharmacokinetics of isradipine after oral and intravenous administration: half-life shorter than expected?

Isradipine is a calcium channel-blocking agent of the dihydropyridine type, used in the treatment of hypertension. A terminal half-life of 8-9 hr has been reported, in several pharmacokinetic studies after oral administration of isradipine. In a yet unpublished study a much shorter half-life was observed, and the present trial was therefore conducted in order to estimate the half-life after intravenous administration of isradipine. The bioavailability was estimated as well. In a randomised cross-over design ten healthy young volunteers were given either isradipine orally or an intravenous infusion. The two study periods were separated by at least 3 days. Blood samples for measurement of isradipine concentration were collected for 10-12 hr after administration and half-life and bioavailability were estimated. Mean terminal half-life after intravenous administration was calculated to be 2.8 hr, and the bioavailability to be 0.28. None of the 10 subjects suffered from side effects. In the present intravenous study the half-life of isradipine seems to be of much shorter than demonstrated in previous oral studies.

A reversed-phase high-performance liquid chromatography method for the determination of cotrimoxazole (trimethoprim/ sulphamethoxazole) in children treated for malaria.

A high-performance liquid chromatography (HPLC) method was developed for the simultaneous analysis of trimethoprim (TMP), sulphamethoxazole (SMX), and acetylsulphamethoxazole (AcSMX) in small amounts of blood. The method involved precipitation with 50 microL trichloracetic acid (1M) to 125 microL plasma or serum sample. 60 microL supernatant was added to 60 microL mobile phase, modified with 50microL 1 M sodium hydroxide/mL. The mobile phase consisted of 20% acetonitrile and 80% phosphate buffer adjusted to pH 6.15. Using 125 microL of the sample, limits of quantitation were 0.1 microg/mL for TMP, 1.0 microg/mL for SMX, and 1.0 microg/mL for AcSMX. The precision of the method was 2% to 11% over the range of concentrations tested, 0.5-30 microg/mL for TMP, 5-300 microg/mL for SMX, and 2.5-150 microg/mL for AcSMX, respectively. No interference with other commonly used drugs was observed. The method is rapid, simple, specific, and sensitive enough for pharmacokinetic studies. The small amount of blood required makes it suitable for pediatric patients. The method was used to analyze samples from Tanzanian children aged 6-59 months participating in a cotrimoxazole (TMP/SMX)/chloroquine randomized trial for the treatment of uncomplicated malaria. Venous blood samples from 68 children were collected 2 hours after the first dose of TMP/SMX (4 mg/kg TMP/20 mg/kg SMX at two divided doses for 5 days) and again at treatment day 4. Individual variations in plasma concentrations of TMP, SMX, and AcSMX were considerable. The mean and SEM plasma concentrations (g/mL) of TMP, SMX, and AcSMX 2 hours after the first treatment dose were 2.0 +/- 1.0 (range 0.5-6), 53 +/- 22 (range 24-146), and 13.5 +/- 12 (range 0-65), respectively. On the fourth day the attained plasma concentrations were not significantly different from samples collected after the first dose.

Enantioselective high-performance liquid chromatographic method for the determination of methadone and its main metabolite in urine using an AGP and a C8 column coupled serially.

A simple and sensitive method for the enantioselective high-performance liquid chromatographic determination of methadone and its main metabolite, EDDP, in human urine is described. (-)-(R)-Methadone, (+)-(S)-methadone, (+)-(R)-EDDP, (-)-(S)-EDDP and imipramine as an internal standard are detected by ultraviolet detection at 200 nm. The enantiomers of methadone and EDDP were extracted from human urine by a simple liquid-liquid extraction procedure. The extracted sample was reconstructed in mobile phase and the enantiomers of methadone and EDDP were quantitatively separated by HPLC on a short analytical LiChrospher RP8 column coupled in series with a chiral AGP column. Determination of all four enantiomers was possible in the range of 0.03 to 2.5 microM. The recoveries of methadone enantiomers and EDDP enantiomers added to human urine were about 90% and 80%, respectively. The method was applicable for determination of methadone enantiomers and the enantiomers of its main metabolite in urine samples from methadone maintenance patients and patients suffering from severe chronic pain.

Enantioselective determination of isradipine in human serum using chiral stationary phase liquid chromatography and gas chromatography with nitrogen selective detection.

rac-Isradipine is a dihydropyridine type calcium antagonist. Its calcium entry blocking effect is due primarily to the (+)-(S)-enantiomer. This study describes a sensitive enantioselective method for the determination of isradipine in human serum. Following alkaline extraction into hexane, the enantiomers of isradipine are separated quantitatively by high-performance liquid chromatography on a Chiralcel OJ column at 39 degrees C. The collected fractions were evaporated and assayed using capillary gas chromatography on a HP 50+ column with nitrogen selective detection. Using 2.0 ml of serum, 0.7 nmol/1 (0.26 ng/ml) of each enantiomer could be determined with acceptable precision. The method has successfully been used to measure (+)-(S)- and (-)-(R)-isradipine concentrations in samples from volunteers after intravenous and oral administration of isradipine.

Serum concentrations of lignocaine and its metabolite monoethylglycinexylidide during fibre-optic bronchoscopy in local anaesthesia.

Fibre-optic bronchoscopy was performed in local anaesthesia using lignocaine. Serum concentrations of lignocaine and its active metabolite monoethylglycinexylidide (MEGX) were measured in 16 patients at regular intervals up to 120 min after administration. Lignocaine was administered as an aerosol in the upper respiratory tract and as a solution in the bronchial tree. The total dose of lignocaine ranged from 243 to 608 mg (2.4-8.0 mg kg-1 body weight). The dose of lignocaine given as an aerosol ranged from 163 to 508 mg (1.6-6.6 mg kg-1) and the dose given as a solution ranged from 60 to 180 mg (0.8-2.5 mg kg-1). The highest median serum lignocaine concentration, 10.5 mumol l-1, was measured 20 min after administration. None of the patients had toxic serum lignocaine levels (> 26 mumol l-1) or adverse effects. The highest median serum MEGX concentration, 1.7 mumol l-1, was measured 120 min after administration. The dose of lignocaine, expressed in mg per kg body weight correlated with serum lignocaine and serum MEGX (rs = 0.47 and rs = 0.39, respectively). Lignocaine is a clinically safe, local anaesthetic agent provided the total dose does not exceed 6-7 mg kg-1 body weight.

Dose-finding study of oral metopimazine.

A few studies indicate a dose-response effect of the antiemetic metopimazine. The aim of this study was therefore to investigate the tolerability of increasing doses of metopimazine given orally every 4 h for eleven doses. The dose levels 20 mg, 30 mg, 40 mg, 50 mg and 60 mg were studied in 36 patients completing 46 cycles of chemotherapy. Serum concentrations of metopimazine and the acid metabolite AMPZ were measured by HPLC in 13 patients (15 cycles). The dose-limiting toxicity was moderate to severe dizziness caused by orthostatic hypotension as seen in 0, 0, 17%, 42% and 50% of patients at the respective dose levels. Other side effects were few and mild, and only a single possible extrapyramidal adverse event was observed in a patient at the 60-mg dose. High serum concentrations were not predictive for toxicity, as found on comparison of patients with and without symptoms, but in individual patients symptoms were seen at the time of Cmax. We found that metopimazine was safe with a dosage of 30 mg x 6. This dose is four times higher than that previously recommended for antiemetic use.

Bioavailability of the antiemetic metopimazine given as a microenema.

The absorption of the antiemetic metopimazine (MPZ) given as a single dose of (a) 40 mg microenema, (b) 40 mg orally and (c) 10 mg as a 60 min i.v. continuous infusion was investigated in six healthy volunteers. Blood samples were drawn and the serum concentrations of MPZ and its acid metabolite were measured. The bioavailability of MPZ given orally and as enemas was 22.3 and 19.5% respectively. Partial avoidance of hepatic first pass metabolism was seen with the enemas, which in contrast to suppositories, seems to represent a reliable form of rectal administration.

Stereoselective pharmacokinetics of methadone in chronic pain patients.

Ten patients with chronic pain were randomized to an open, balanced, crossover study. Each patients received two different preparations of racemic methadone, i.e., tablets and intravenous infusion. The pharmacokinetic parameters of the R- and S-enantiomers of the racemate are reported. The analgesically active R-methadone has a significantly longer mean elimination half-life than the optical antipode S-methadone (t1/2 = 37.5 and 28.6 h, respectively). The mean total volume of distribution is 496.6 L for R-methadone and 289.1 L for S-methadone. Significant differences in the mean clearance between R- and S-methadone are seen (0.158 and 0.129 L/min, respectively). However, the lagtime after oral administration and the bioavailability did not show differences between the isomers. The data suggest that both enantiomers of methadone should be measured if correlations between pharmacodynamics and kinetics are made due to the stereoselective differences in half-life, total volume of distribution, and clearance.

High-performance liquid chromatography determination of dapsone, monoacetyldapsone, and pyrimethamine in filter paper blood spots.

A high-performance liquid chromatography method for the simultaneous analysis of dapsone (DDS), the major metabolite of DDS, monoacetyldapsone (MADDS), and pyrimethamine (PYR) was modified for capillary blood samples obtained by finger prick and dried on filter paper. Limit of quantitation using 150 microliters whole blood dried on filter paper was found to be 20 ng/ml for DDS and PYR and 15 ng/ml for MADDS (precision < 15%). The clinically relevant concentrations of DDS are 50-2,000 ng/ml and for PYR 25-150 ng/ml. No interference from several drugs were observed. The accuracy of the filter paper method and the original whole-blood method was almost comparable. Standardization could therefore be obtained by the more simple whole-blood method. Dried filter paper samples stored at 19-22 degrees C were stable for months and for 2 weeks stored at 35 degrees C. The concentrations of simultaneously collected capillary blood and conventional venous blood samples correlated well. The present method using capillary blood dried on filter paper is reliable, simple, sensitive, and applicable in the field with limited technical facilities.

8-methoxypsoralen increases daytime plasma melatonin levels in humans through inhibition of metabolism.

It is well established that in healthy humans oral intake of 5- or 8-methoxypsoralen (5- and 8-MOP) is followed by a significant increase in plasma melatonin concentrations. The effect of psoralen on rat melatonin has been studied in vitro and in vivo and a stimulation of release or secretion from the pineal gland has been suggested. In this study we examined the time-related changes in plasma concentrations of 8-MOP, melatonin and 6-sulfatoxymelatonin in 15 patients admitted for routine psoralen plus UVA therapy. On the first day of treatment blood samples were collected before, and 30, 60, 66 and 90 min after intake of 8-MOP (0.6 mg/kg). Although the rate of 8-MOP absorption varied greatly, a significant increase (P = 0.0002) in melatonin levels was found 60 min after 8-MOP intake. During UVA exposure a strongly correlated decrease in mean melatonin and mean 8-MOP concentrations was found, indicating an effect of UVA radiation, either direct or 8-MOP mediated, on circulating melatonin levels. Plasma 6-sulfatoxymelatonin concentrations decreased significantly between all time points, suggesting inhibition of melatonin metabolism.

Enantioselective high-performance liquid chromatographic method for the determination of methadone in serum using an AGP and a CN column as chiral and analytical column, respectively.

A simple and sensitive HPLC method with ultraviolet absorption detection at 200 nm is described for the determination of methadone enantiomers in human serum, using dextropropoxyphene as an internal standard and organic solvent extraction. Separation was performed on two serially coupled columns, CN and Chiral AGP, with a mobile phase consisting of acetonitrile, dimethylocytlamine and phosphate buffer. Using 1.0 ml of serum, 5 nmol/1 of each enantiomer could be determined with an acceptable precision. No interactions from several drugs were observed. The method has been successfully used in a pharmacokinetic study. More than 2500 serum samples have been separated on the same AGP column with acceptable selectivity and resolution.

Skin pigmentation as a predictor of minimal phototoxic dose after oral methoxsalen.

BACKGROUND AND DESIGN: Twenty-eight subjects were phototested to determine their erythemal responses to oral methoxsalen with UV-A and UV-B irradiation. Skin pigmentation was measured by skin reflectance at 550 and 660 nm before irradiation. The smallest UV radiation dose to produce erythema (minimal phototoxic dose and minimal erythema dose, respectively) was determined. The serum concentration of methoxsalen was measured at the time of UV-A irradiation. RESULTS: There was a positive correlation between skin pigmentation and both 72-hour minimal phototoxic dose and 24-hour minimal erythema dose. No correlation was demonstrated between methoxsalen serum concentration and minimal phototoxic dose. The combination of skin pigmentation and methoxsalen level did not give a better prediction of minimal phototoxic dose than skin pigmentation alone. CONCLUSIONS: Skin pigmentation measurements can be used to predict the minimal phototoxic and erythema doses. Skin pigmentation measurements are easy to perform and should be included in both phototherapy and photochemotherapy to improve the efficiency and reliability of the treatment.

[Detection of morphine after ingestion of poppy seeds]. / Påvisning af morfika efter indtagelse af birkes.

The aim of this study was to investigate whether morphine can be detected in urine after the ingestion of poppy seeds bought in Denmark. Morphine and codeine were determined in 10 different poppy seed specimens bought in Denmark. Ten and 25 g of the specimens containing the highest amount of morphine and codeine were consumed by respectively six and seven volunteers. Urine samples were collected for analysis at intervals up to 24 h. All samples were found positive by radioimmunoassay up to 24 h after ingestion. Using the less sensitive thin layer chromatography method, one of six and two of seven were positive, two to four hours after intake of respectively 10 and 25 g of the specimens. We conclude that the detection of morphine in urine does not necessarily indicate an illegal drug use.

The influence of food on 8-methoxypsoralen serum concentration and minimal phototoxic dose.

Ten adult volunteers were given three oral doses of 0.46-0.56 mg/kg body weight of 8-methoxypsoralen (8-MOP) in a liquid formulation under fasting conditions, and after ingestion of a low-fat or fat-rich breakfast. 8-MOP serum levels and photosensitivity were measured 0.5-4 h after drug ingestion. The 1-h 8-MOP serum levels and photosensitivity were significantly higher in fasting conditions than after ingestion of a low-fat or fat-rich meal (intra-individual median difference in photosensitivity 7.5 J/cm2). On 12 of 20 occasions when the drug was taken after food ingestion, the 1-h 8-MOP serum concentration was below 30 ng/ml. A survey of 43 out-patients undergoing regular PUVA treatment showed that the frequency of erythemal reactions was significantly higher when 8-MOP was ingested with a > 50% smaller quantity of food than usual (P < 0.005). This study demonstrated food-induced variations in 8-MOP photosensitivity both in an experimental situation and in an out-patient survey. In order to optimize the therapeutic effect of PUVA, the quantity of food taken before 8-MOP should remain constant, and the timing of UVA irradiation should be adjusted according to the preceding food intake.

Determination of isradipine and its pyridine metabolite in serum by capillary column gas chromatography with nitrogen-selective detection.

A relatively simple, sensitive and precise gas chromatographic method for the determination of isradipine, a calcium antagonist of the dihydropyridine type, and its main metabolite in serum is described. Using a one-step extraction procedure, a wide-bore column and a nitrogen-phosphorus detector, a limit of quantitation of 0.5 and 2.0 nM for isradipine and the metabolite was found. No interferences from several drugs were observed. The method was successfully used in a pharmacokinetic study in hypertensive women during pregnancy.