Liquid chromatographic assay for the simultaneous determination of pyrazinamide and rifampicin in serum samples from patients with tuberculous meningitis

A simple high-performance liquid chromatographic assay for the simultaneous determination of pyrazinamide and rifampicin in serum from patients with tuberculous meningitis is presented. The drugs and internal standard, p-acetamidobenzoic acid, were extracted from the acidified sample containing 2% ascorbic acid at pH 4.2 into dichloromethane-diethyl ether (2:3). The solvent extract was evaporated to dryness with the aid of nitrogen and the residue redissolved in methanol (75 microliters). The concentrate was analysed by a liquid chromatograph using a reversed-phase 30-microns C8 pre-column linked to a 5-microns C8 analytical column with a gradient solvent programme, which delivered 6% to 48% (v/v) acetonitrile in phosphate buffer (10 mM potassium dihydrogenphosphate, pH 3.5) in 10 min at 1.5 ml/min. The eluate was detected at 215 nm. Twelve patients with tuberculous meningitis were given daily chemotherapy, and their serum samples were assayed for pyrazinamide and rifampicin.

Compliance with oral drug therapy in patients with hematologic malignancy

Compliance with oral self-administered allopurinol (daily medication) and prednisone (intermittent medication) as well as compliance with monthly scheduled clinic appointments, were examined in 108 patients with newly diagnosed hematologic malignancy. Baseline levels of compliance (control group) were compared to results obtained after implementation of three intervention packages, whose aim was to increase compliance. The packages included combinations of education, home psychologic support and restructuring, and training in pill taking. A 24-hour profile of the two drugs and their metabolites was first determined. Serum samples were then obtained monthly over 6 months and analyzed for presence of the drugs. Control patients were fully compliant with allopurinol only 16.8% of the time. This rate increased significantly (44% to 48% of the time) for those who received any one of the intervention programs. With respect to prednisone, control patients were compliant 26.8% of the time, with no real improvement after interventions. Finally, self reports overestimated compliance by a factor of two when compared to drug analysis. The results indicated that full compliance with oral medications was remarkably low among our patients who have treatable and in some cases curable hematologic malignancy. However, compliance can be significantly improved by the use of various intervention packages.

Molecular isolation and sequence determination of the cDNA for the mouse sperm-specific lactate dehydrogenase-X gene

Several cDNA clones for the mouse lactate dehydrogenase-X (LDH-X), a sperm-specific glycolytic enzyme, were isolated from mouse testicular cDNA libraries constructed in the bacteriophage vectors, lambda gt11 and gt10. The largest cDNA clone contains an insert of 1135 base pairs in length and an open reading frame that encodes a 332 amino acid polypeptide with a molecular weight of 35.89 kD. The deduced amino acid sequence of this protein is in close agreement with the published sequence of mouse LDH-X obtained by direct protein sequencing. Northern analysis of RNA isolated from different tissues detected a single size mRNA of 1.5 kilobases in mouse testis but not in brain or liver. The Ldh-x structural gene was estimated to be about 12 kb in size as demonstrated by Southern hybridization analysis of mouse genomic DNA using the full-length cDNA as a probe.

Pharmacokinetics of low-dose intravenous pethidine in patients with renal dysfunction

The kinetics and elimination of pethidine (meperidine) after intravenous administration (150 micrograms/kg) to ten healthy volunteer subjects were compared with those obtained from 18 patients who suffered from varying degrees of renal dysfunction. In both groups of subjects, pethidine was eliminated triexponentially from plasma. However, plasma concentrations in the patients (who were subdivided into patients with severe dysfunction, moderate dysfunction, and mild dysfunction) were consistently higher. The mean +/- SEM elimination half-life (t1/2) of pethidine was significantly longer in the three groups of renal patients: 7.9 +/- 1.1, 20.2 +/- 13.6, 16.6 +/- 5.4, and 14.3 +/- 3.1 hr, respectively, for healthy volunteers, patients with severe, moderate, and mild dysfunction; their mean +/- SEM creatinine clearances were 97.3 +/- 7.5, less than 9.5, 30.0 (3.7), and 63.3 +/- 8.5 mL/min respectively. The mean plasma clearance of the drug was higher in healthy subjects (342.7 +/- 62.5 mL/min) than various groups of renal patients (99.9 +/- 11.6, 120.9 +/- 45.8, and 123.8 +/- 34.1, respectively, for patients with severe, moderate, and mild dysfunction). Impairment of renal function also reduced total plasma protein binding: 58.2 +/- 5.0% in healthy subjects and 31.8 +/- 3.9%, 44.5 +/- 5.0%, and 42.5 +/- 5.6%, respectively, for the three renal patient groups. The percentage of pethidine recovered in the urine was significantly lower in the severe dysfunction group while norpethidine recovery was significantly lower in all three groups of renal patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Disposition of pethidine in man under acidic urinary pH. 3. A comparison of pharmacokinetics among Caucasian, Chinese and Indian subjects

The pharmacokinetics of low dose pethidine (150 micrograms kg-1) after intravenous administration were determined in 10 Caucasian, 10 Chinese and 10 Indian healthy volunteers under conditions of acidic urinary pH. Plasma and urine concentrations of pethidine and norpethidine were measured by gas liquid chromatography. In all 3 ethnic groups, the disappearance of pethidine from plasma was best described by a tri-exponential function. No significant differences were observed in the elimination half life, renal clearance and total plasma clearance of the drug. The significantly lower AUC and higher (approaching significance) apparent volume of distribution in the 2 Asian groups may be explained in terms of more readily distribution of the drug (significantly higher K21 rate constants were obtained from both Chinese and Indian subjects according to a 3-compartment open model) due possibly to more frequent movement of these subjects during the early part of experiment. More norpethidine was recovered in the urine of the Chinese and Indian subjects; this may suggest an interethnic difference in the oxidative demethylation of pethidine.

A study of prescribed H1-antihistamine preparations over a period of 12 months in community pharmacy

A survey on the prescribing pattern of H1-antihistamine preparations was carried out in four socio-economic areas in Liverpool: the City Centre, an Affluent Area, a Poor area and a Council Estate. The purpose of this study was to find out which H1-antihistamines were prescribed from the wide range available; to discover if there was a trend in the use of these agents over a 12-month period and to suggest possible explanations for these findings. The majority of H1-antihistamine preparations were prescribed in the Affluent Area followed by the City Centre, Poor Area and the Council Estate. In all four areas, over 7.0% of all total items dispensed in a year contained H1-antihistamine drugs, and the lowest use (3.7-9.2%) fell in the summer months while the highest use was in January (8.2-14.1% of items containing H1-antihistamine dispensed per month). Thus the general trend in the use of these drugs may not follow the trend of the hay fever season and it is probably true that H1-antihistamines were more frequently prescribed for treatment of other conditions (common cough and cold) than rhinitis alone. The most widely prescribed classes of H1-antihistamines were alkylamines and ethanolamines, followed by the phenothiazines and ethylenediamines while the piperazines were not prescribed. Triprolidine, diphenhydramine, promethazine and brompheniramine were the top four most widely prescribed drugs.

Influence of urinary pH on pethidine kinetics in healthy volunteer subjects. 2. A study of ten Chinese subjects

The pharmacokinetics of intravenous pethidine (150 micrograms kg-1) were determined in 10 healthy Chinese subjects under controlled (acidic and alkaline) and uncontrolled urinary pH. Large variations in the 48 hr urinary recoveries of pethidine and norpethidine were induced by change in urinary pH: (mean +/- S.D.): 24.3 +/- 7.3% & 33.0 +/- 11.4%, 0.4 +/- 0.3% & 3.8 +/- 2.2%, 11.4 +/- 6.9% & 13.9 +/- 2.5%, respectively, under acidic, alkaline and uncontrolled urinary pH for pethidine and norpethidine. There was no significant difference in the terminal half-lives, t 1/2 (6.1 to 7.0 hr) of pethidine, although the area under the plasma concentration-time curve under acidic urinary conditions was slightly lower and renal clearance of the drug higher than those under alkaline and uncontrolled urinary conditions. Confirming previous results from Caucasian subjects, under all 3 conditions pethidine disappeared from the plasma tri-exponentially and acidification of the urine may increase body clearance of unchanged pethidine due mainly to greater renal clearance of the drug; this may be useful clinically to treat acute pethidine poisoning. However, under acidic urinary conditions, Chinese subjects excreted more norpethidine than Caucasians (33.0 +/- 11.4% and 23.4 +/- 4.6%, respectively).

Rifampicin concentrations in cerebrospinal fluid and plasma of the rabbit by high performance liquid chromatography

A high performance liquid chromatographic (HPLC) assay has been developed for the measurement of rifampicin in cerebrospinal fluid and plasma samples in the rabbit. The method involved a preliminary organic solvent extraction of the drug and p-dimethylaminobenzoic acid (internal standard) from biological samples and subsequent concentration and analysis by HPLC. An aliquot (25 microliters) of the concentrate was injected into the liquid chromatograph and eluted with acetonitrile-10 mM phosphate buffer of pH 3.5 (48: 52, v/v) on a 30 microns C8 reversed phase column linked to a 5 microns C8 analytical column at ambient temperature (25 +/- 1 degrees C). The eluate was detected at 215 nm. The method has been used to investigate the disposition of rifampicin in plasma and CSF in rabbits.

Rapid high performance liquid chromatographic assay of cephalosporins in biological fluids

A simple isocratic HPLC method is described for the rapid analysis of cephalosporins in body fluids. Sample preparation by protein precipitation takes only five minutes; HPLC analysis is completed within two to ten minutes, using one of two simple solvent mixtures eluted on a single C18 reversed phase column. Nine cephalosporins and nine types of body fluid were formally analysed, but the system was also found to be suitable for the assay of benzyl penicillin, ampicillin, cloxacillin, carbenicillin and chloramphenicol. It is likely that this method, with only minor modifications, would be suitable for the analysis of most beta-lactam antibiotics in most clinical specimens. The method is therefore particularly recommended for use in clinical laboratories.

High-performance liquid chromatographic determination of pyrazinamide in cerebrospinal fluid and plasma in the rabbit

A simple procedure for the determination of pyrazinamide in plasma and cerebrospinal fluid in the rabbit is described. The assay involves a preliminary extraction of the drug and an internal standard, paracetamol, from the acidified sample (pH 4.2). The extract is evaporated to dryness at 45 degrees C and the residue is redissolved in methanol (50 microliters). A 25-microliters aliquot is injected into the liquid chromatograph and eluted with acetonitrile-10 mM phosphate buffer of pH 3.5 (10:90, v/v) on a 30-microns C8 pre-column linked to a 5-microns C8 reversed-phase column at ambient temperature (25 +/- 1 degree C). The eluate is detected at 215 nm. The method has been used to investigate the disposition of pyrazinamide in plasma and cerebrospinal fluid in six rabbits.

High performance liquid chromatographic characterisation and quantitation of p-aminobenzoic acid N-acetylation in Chinese subjects

p-Aminobenzoic acid (PABA), p-acetamidobenzoic acid (PADB) and p-aminohippuric acid (PAH) have been separated and determined by a reversed phase, isocratic high performance liquid chromatographic (HPLC) procedure simultaneously. The mobile phase, at 1.5 ml min-1, used was 10 mM sodium hydrogen phosphate buffer, pH 3.5, containing 40% methanol. The eluent was detected at 270 nm. Linear relationship was obtained from 0 to 2.0 micrograms ml-1 of each compound with the corresponding peak-height ratio using p-methylamino-benzoic acid (PMAB) as the internal standard. Urine samples were obtained from healthy Chinese volunteers after oral dosing of 200 mg PABA which was used as a model substance for metabolic investigation of N-acetylation and other conjugation reactions. The 24 hour urinary recovery, from 43 healthy subjects, of PABA, PABA-COOH conjugates, PADB and PADB-COOH conjugates were (mean +/- S.D.) 2.9 +/- 1.5%, 5.2 +/- 3.3%, 13.9 +/- 4.0% and 42.9 +/- 9.8% of the ingested dose respectively. These accounted for 64.9 +/- 12.0% of total dose ingested in 24 hour. In contrast to previously reported findings on one Caucasian subject, no PAH was identified in the urine, and N-acetylation was the major route of metabolism of PABA apart from conjugation at the -COOH group in this group of Chinese volunteers. It is proposed that PABA metabolism may be a useful probe to study ethnic and geographic variation in N-acetylation.

Primate eta-globin DNA sequences and man's place among the great apes

Molecular studies indicate that chimpanzee and gorilla are the closest relatives of man (refs 1-7 and refs therein). The small molecular distances found point to late ancestral separations, with the most recent being between chimpanzee and man, as judged by DNA hybridization. Kluge and Schwartz contest these conclusions: morphological characters group a chimpanzee-gorilla clade with the Asian ape orang-utan in Kluge's cladistic study and with an orang-utan-human clade in Schwartz's study. Clearly, extensive sequencing of nuclear DNA is needed to resolve by cladistic analysis the branching order within Hominoidea. Towards this goal, we are sequencing orthologues of the primate psi eta-globin locus. Here, we compare the newly completed sequences of orang-utan and rhesus monkey with human, chimpanzee, gorilla, owl monkey, lemur and goat orthologues. Our findings substantially increase the evidence indicative of a human-chimpanzee-gorilla clade with ancestral separations around 8 to 6 Myr ago. We also verify that neutral hominoid DNA evolved at markedly retarded rates.

Pharmacokinetics of low-dose 1-beta-D-arabinofuranosylcytosine given by continuous intravenous infusion over twenty-one days

The pharmacokinetic parameters of low dose 1-beta-D-arabinofuranosylcytosine (ara-C) infusions were studied in 11 patients, 6 males and 5 females, with a mean age of 68.5 +/- 13.8 (SD) years. The drug was infused to 4 patients with pre-leukemia (refractory anemia with excess blasts), 5 patients with acute myelogenous leukemia, and 2 patients with secondary leukemia due to chemotherapy, at a dosage of 20 mg/m2/day over 21 days. The patients' blood and urine were analyzed for ara-C content by radioimmunoassay. Mean steady state plasma levels of 7.7 +/- 4.7 ng/ml (31.7 +/- 19.3 nM) (n = 189) and a range 0.6 (2.5 nM) (lower limit of assay) to 29.7 ng/ml (122.1 nM), with significant inter- and intra-patient variations, were reached within about 2.7 h. The plasma levels of ara-C decreased rapidly, with a t1/2 alpha of about 12 min following discontinuation of the infusion, followed by a very slow t 1/2 beta of about 19 h. Other parameters (mean values of 10 or 11 patients) were: area under the curve, 182.1 +/- 64.8 ng X day/ml; total body clearance, 188.7 +/- 54.8 liters/h; renal clearance, 3.1 +/- 1.4 liters/h; volume of distribution at steady state, 53,913 +/- 17,626 liters; and recovery of ara-C in urine, 1.43 +/- 0.69% (n = 226) of daily administered ara-C. A linear relationship was observed with administered dose when the mean plasma levels of our study were compared with the ones reported for conventional ara-C infusions. Plasma clearance was comparable to that observed in conventional dose, when the observed values were extrapolated to the dose administered in this study.

An improved gas liquid chromatographic assay for plasma valproic acid concentrations in mentally handicapped epileptic children

A gas liquid chromatographic (GLC) method is described for the determination of valproic acid concentrations in plasma. This simple, rapid and reproducible assay involved chloroform (500 microliter) extraction of the drug and internal standard (octanoic acid) from acidified plasma samples. An aliquot (1 microliter) of the unconcentrated organic extract was injected directly into the GLC system (a coiled glass column 1 m long, 6 mm OD packed with 5% diethylene-glycol-succinate-phosphate on 100/120 mesh Supelcoport) with detection by flame-ionization. This assay was successfully employed to measure plasma concentrations of valproic acid in 42 mentally handicapped, epileptic children of Chinese origin, most of whom were on multiple anti-epileptic agents.

Pharmacokinetic contributions to drug use

Fundamental research in pharmacokinetics help to identify the causes of inter-subject variability in response to drugs. An understanding of these causes may permit the development of an individual dosage schedule and improve drug therapy. All professionals who are involved with drug use in patients should have a good knowledge of drug disposition and clinical pharmacokinetics.

Simultaneous determination of carbamazepine and its epoxide metabolite in plasma and urine by high-performance liquid chromatography

A simple procedure for the simultaneous determination of carbamazepine and its major metabolite, carbamazepine epoxide, in plasma and urine is described. The assay involves two extractions of the drugs and an internal marker, clonazepam, from the alkalinized sample. The extract is evaporated to dryness at 45 degrees C and the residue is redissolved in methanol (30 microliters). A 25-microliters aliquot is injected into the liquid chromatograph and eluted with acetonitrile-water (40:60, v/v) on a C18 pre-column linked to a 5-microns C8 reversed-phase column. The eluent is detected at 215 nm. The method has been used to investigate the steady-state concentrations of carbamazepine and carbamazepine epoxide in the plasma and urine of a manic-depressive patient.

Influence of urinary pH on pethidine kinetics in healthy volunteer subjects

The kinetics of intravenous pethidine (150 micrograms kg-1) were determined in 10 healthy Caucasian subjects under uncontrolled and controlled (acidic and alkaline) urinary pH. Although large variations in the 48 hr urinary recovery of pethidine and norpethidine (26.9 +/- 5.9% & 23.4 +/- 4.6%, 0.6 +/- 0.3% & 3.6 +/- 1.6%, 6.9 +/- 3.2% & 17.4 +/- 6.6%, respectively, under acidic, alkaline and uncontrolled urinary pH were induced by change in urinary pH, the terminal t1/2 (7-8 hr), the AUC and the plasma concentration-time profiles were not affected. Under all these conditions, the disappearance of pethidine from the plasma was described by a triexponential function. A 3-compartment open model with input into the central compartment and elimination from both the central and the fast accessible (metabolising) compartment was proposed to interpret pethidine distribution in the body. This model explains the complimentary elimination of pethidine by renal excretion and metabolism. Under alkaline urinary pH, the hydrolytic route predominates as recovery of pethidine and norpethidine in the urine is significantly lower under this condition. Acidification of the urine may increase body clearance of the unchanged drug due mainly to greater renal clearance, and this may be useful clinically to treat acute pethidine poisoning and when the complimentary hepatic metabolism is impaired.

The simultaneous determination of five anti-epileptic drugs in plasma by high performance liquid chromatography

A high performance liquid chromatographic (HPLC) method is described for the simultaneous determination in plasma of carbamazepine, ethosuximide, phenobarbitone, phenytoin and primidone. The procedure involved the preliminary extraction of the drugs and the internal standard (hexobarbitone) into a mixture of organic solvents at pH 2. The dried extract was dissolved in methanol and 25 microliter of the concentrate was injected into a liquid chromatograph linked to a reverse-phase column. The drugs and internal standard were eluted from the column by a mixture of methanol and water, as the mobile phase, and detected with a UV spectrophotometer at 204 nm. This HPLC assay, which required 0.5 ml of plasma, was used to determine anti-epileptic drugs levels in 136 mentally-handicapped children suffering from epilepsy. Comparison between different batches of assays showed that recovery of the drugs from plasma varied from 60 to 98% and with a coefficient of variance between 3.8 to 9.8%. Detection limit of the method ranged from 2 micrograms ml-1 for primidone, to 1 microgram ml-1 for the remainder of the anti-epileptic drugs.

Elimination of phenoperidine in liver disease

The disposition and elimination of phenoperidine was studied in five normal subjects, and in six patients with hepatic disease. Plasma concentrations of phenoperidine were generally higher in patients with hepatic dysfunction. Secondary peaks were observed between 15 and 105 min (particularly in patients with liver disease). In the patients the terminal half-life of phenoperidine was prolonged by approximately 50%, mainly because of a decrease in the clearance of the drug. There was little or no change in the total apparent volume of distribution. However, the differences between normal subjects and patients with hepatic disease were not statistically significant. The results suggest that slight or moderate impairment of hepatic function does not significantly affect the kinetics of the drug, and that modification of its dosage may not be required.

Quantitative capillary column gas chromatographic method for the determination of glycopyrronium in human plasma

A new sensitive and selective capillary column gas chromatographic method for the anti-cholinergic agent glycopyrronium bromide in human plasma is described. The procedure involves preliminary ion-pair extraction of the drug into dichloromethane, followed by concentration and analysis of the ion-pair complex by capillary column gas chromatography using a nitrogen-sensitive detector. The method depends on the thermal dequaternisation of the quaternary ammonium compound and can be used to detect 5 ng/ml in a 3-ml plasma sample. The assay procedure has been applied to the determination of the plasma concentration of glycopyrronium after intravenous administration to an anaesthetised patient.

Absorption measurement of nu2 + 2nu3 band of CH4 at 1.33 microm using an InGaAsP light emitting diode

The combination band of nu2 + 2nu3 of CH4 at 1.33 microm (7512 cm(-1)) was observed at 0.3-cm(-1) resolution by a simple experimental arrangement using a near-infrared high-radiant InGaAsP light emitting diode (LED) and a Ge detector. Forty-six line centers were measured with accuracies of 0.03 cm(-1). The assignment of these manifolds was made by inspection of the P, Q, and R branches. The experimental result indicates that the nu2 + 2nu3 band can be used for fully optical remote monitoring of methane using InGaAsP optical sources in conjunction with an ultralow-loss optical fiber network.

The dissolution and oral bioavailability of mexiletine capsules modified for clinical trial. A preliminary report

The dissolution and bioavailability of two preparations of mexiletine hydrochloride (200 mg), one available commercially as Mexitil and one modified by the Hospital Pharmacy for a clinical trial, were investigated in a cross-over study with healthy volunteer subjects. The evaluation of bioavailability was based on comparisons of the mean residence time (MRTp.o.) and mean absorption time (MATp.o.), areas under the plasma mexiletine concentration time-curve (AUC) and urinary recovery of unchanged mexiletine under controlled condition of acidic urinary pH after oral administration of single doses of either 400 mg or 200 mg as mexiletine hydrochloride. Three different methods of calculation were used to account for possible changes in clearance of the drug in between treatments. Bioavailability data were available from 3 cross-over studies as the investigation was terminated because one subject experienced idiosyncratic reactions to mexiletine. The mean-transit-time, T DISSOLVED-IN VITRO, for the hospital-modified capsules (2.8 min) was longer than that of the Mexitil capsule (2.0 min) in 0.1 HCl. This delay in dissolution was complemented by an increase in MATp.o. (0.43 and 0.58 hr respectively for Mexitil and hospital-modified capsules) obtained in one subject. The bioavailabilities of the two preparations were comparable from AUC between 0 to 6 hr, but the plasma curves from 6 to 48 hr were not followed. The mean times in vivo, T MEAN-IN VIVO (determined from urinary elimination curves in a cross-over study of 3 subjects) were consistently shorter after ingestion of Mexitil capsules though the significance was difficult to obtain due to small sample size.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of urine pH on the elimination of phenoperidine

The effect of urine pH on the plasma concentration and elimination of phenoperidine and its main metabolites was studied in six volunteers. The clearance of unchanged phenoperidine in acid urine was significantly greater than in neutral or alkaline urine. By contrast, the elimination of its basic metabolites was enhanced in uncontrolled or alkaline urine. Other pharmacokinetic parameters were not significantly affected.

Effect of antacids on the plasma concentration of phenoperidine

The effect of antacids on the plasma concentration of phenoperidine was studied in six volunteers. All subjects received the same dose of phenoperidine (15 micrograms kg-1) on different occasions in the presence, and absence of, an antacid preparation. In control studies, secondary peaks in the plasma concentration of phenoperidine were invariably observed; these were entirely eliminated, or modified substantially, by the concurrent administration of antacids. In the latter conditions, plasma concentrations of phenoperidine were greater during the first 20 min, and the area under the plasma concentration--time curve between 0 and 20 min was significantly greater than in control studies. In contrast, the plasma clearance of the drug was almost identical in control conditions and during treatment with antacids. After the oral administration of phenoperidine to two subjects, the systemic bioavailability of the drug was 9.9% and 13.9% respectively.

Plasma concentration of pyridostigmine during the antagonism of neuromuscular block

The plasma concentrations of pyridostigmine were measured in eight patients during the antagonism of non-depolarizing neuromuscular blockade. After the injection i.v. of pyridostigmine bromide 14.6 mg/70 kg, the concentration of the drug rapidly decreased between 2 and 7 min, and then declined more slowly. After 2 h, significant amounts of pyridostigmine were still present in the plasma of all subjects. In the eight patients studied, the initial half-life was 1.0 +/- 0.3 min and the terminal half-life was 46.4 +/- 6.5 min (mean +/- SEM). Total body clearance of pyridostigmine was 8.7 +/- 1.5 ml min-1 kg-1, and the total apparent volume of distribution was 536 +/- 80 ml kg-1. Possible explanations for the differences between these results and previous studies are considered.

The influence of urinary pH on the disposition of indomethacin in healthy volunteers

The influence of urinary pH on the plasma levels and renal elimination of unchanged indomethacin has been studied in seven healthy volunteers with the use of a specific and sensitive gas-liquid chromatographic method assay for indomethacin in plasma and urine. There is a wide variation in the terminal t1/2 (2.5-10.3 h) and the AUC (5264-12693 ng/ml h) of indomethacin after a standard oral dose (50 mg) under 'normal' urinary condition. Such variation is probably, in part, due to an intersubject difference in extrarenal elimination of the drug. The urinary recovery of unchanged indomethacin is highest at alkaline pH (15.7 +/- 5.3%), lowest at acidic pH (3.5 +/- 2.0%) and the 'normal' value is 7.1 +/- 1.6%. These differences are statistically significant. Despite such influence there is no apparent change in plasma levels of the drug under uncontrolled and controlled (acidic and alkaline) conditions of urinary pH. The clinical implication is that possible changes in urinary pH during long-term treatment of arthritic patients may not affect the overall kinetics of indomethacin which is extensively eliminated by the extrarenal route.

The relationship of plasma levels of pyridostigmine to clinical effect in patients with myasthenia gravis

The relationship between plasma levels of pyridostigmine to clinical evaluation of muscle power was examined in nine patients with myasthenia gravis during treatment with pyridostigmine in doses of 60 to 1040 mg daily. Five of the nine subjects demonstrated a trend towards a positive correlation, but in only two of them was this statistically significant at p < 0.05. In addition, the presence or absence of a possible correlation between muscle power and plasma concentration was not related to the duration of the disease, additional prednisolone therapy or thymectomy.

The effect of neostigmine on pyridostigmine bioavailability in myasthenic patients after oral administration

Plasma levels of pyridostigmine and/or neostigmine were monitored in 8 myasthenic patients who were stabilised on oral pyridostigmine bromide only (60-540 mg per day), and in 9 patients who were stabilised on both neostigmine bromide (15-480 mg per day) and pyridostigmine bromide (240-1080 mg per day), over a period of 12 hr (8.00 a.m. - 8.00 p.m.). Maximum plasma concentrations of pyridostigmine in the first and second groups of patients ranged from 12.4 to 64.5 ng per ml and 15.3 to 144.0 ng per ml respectively. Despite this general intersubject variation in bioavailability of pyridostigmine, there was a direct relationship between the area under plasma concentration-time curves (AUC) and total daily dose in the first group of myasthenic patients (r = 0.95). However, no such observation was noticed neither in all 17 patients nor in the 9 patients who were treated with both drugs. Neostigmine was detected in only one of the second group of patients. It was suggested that neostigmine might interfere with the bioavailability of pyridostigmine when both drugs are concurrently administered orally.

Disposition of pethidine in man under acidic urinary PH. I. Plasma level and urinary elimination of pethidine and norpethidine

A detailed study on the plasma and urine levels of pethidine and its major basic metabolite, norpethidine, was carried out after intravenous and oral administration of pethidine, under conditions of controlled acidic urinary pH, to two healthy subjects who had previously shown significant difference in the urinary recovery of pethidine after the intramuscular administration of a standard dose. Utilizing the data of area under plasma concentration-time curve and cumulative urinary excretion of pethidine, similar values of renal clearance of the drug were obtained after separate intravenous and oral administration to the same subject. There is an overall difference in the renal clearance and metabolic pattern of the drug between these two subjects under conditions of controlled acidic urinary pH. It is postulated that variation in the overall elimination of pethidine and other weakly basic drugs can only be elucidated under conditions and may be interpreted in terms of differences in the renal clearance and hepatic biotransformation of the drug.

The simultaneous determination of pethidine and norpethidine in biofluids by nitrogen selective gas chromatography

A rapid sensitive and selective gas chromatographic method has been developed for the simultaneous determination of pethidine and its major basic metabolite, norpethidine, using a nitrogen selective detector. The procedure involved a preliminary ethereal extraction of the drug, its metabolite and internal marker (lignocaine) from the alkalinised biological fluids (plasma or urine). The extract, after concentration, was analysed by a GC system (3 per cent OV 17 on Gas Chrom Q, 80-100 mesh) linked to a nitrogen selective detector. The calibration graphs (relating peak height ratios of the drug to internal marker and concentration) of pethidine and norepethidine were linear and reproducible over the ranges of 5 ng/ml to 100 ng/ml for plasma samples and 50 ng/ml to 1000 ng/ml for urine samples. The recovery of the drug and metabolite from plasma samples at 5 ng/ml and 100 ng/ml is 100 per cent and 84.9 per cent respectively for pethidine, and 100 per cent and 90.9 per cent respectively for norpethidine. Similar recovery from urine samples of pethidine and norpethidine is also achieved at 50 ng/ml and 1000 ng/ml levels. The reproducibility of the assay procedure for pethidine and norpethidine is 100 +/- 0.02 per cent and 100 +/- 0.04 per cent at 100 ng/ml level, and 100 +/- 0.15 per cent and 100 +/- 0.12 per cent at 5 ng/ml level.

Algal single cell protein production from sewage effluent with high salinity

Laboratory studies indicate that the unicellular green alga Chlorella salina CU-1 could be cultivated in treated sewage effluent with high salinity. The high protein content (51% dry weight), and the relatively complete amino acid profile of the cells, suggest that this alga might be an ideal organism to be used for single cell protein production from high-salinity sewage.

Kinetics and metabolism of intramuscular neostigmine in myasthenia gravis

Neostigmine kinetics and metabolism were studied after intracellular administration to 8 patients with myasthenia gravis. The plasma neostigmine level declined monoexponentially from 21 +/- 2 to 9 +/- 1 ng/ml between 30 and 120 min. The data were interpreted in terms of a 1-compartment model. Estimates of plasma half-life (t1/2) ranged from 51.1 to 90.5 min; apparent volume of distribution varied from 32.0 to 60.6 1; and total body clearance from 434 to 549 ml/min. Approximately 80% of the drug was eliminated in urine within 24 hr either as unchanged neostigmine or its metabolites. Approximately 50% of the dose was eliminated as the unchanged drug, 15% as 3-hydroxyphenyltrimethylammonium, and 15% as other unidentified metabolites. The neostigmine t1/2, based on the urinary excretion of the unchanged drug, ranged from 90.2 to 118.7 min. It was concluded that neostigmine was eliminated by renal and extrarenal mechanisms.

Plasma concentration and metabolism of phenoperidine in man

The plasma concentrations of phenoperidine were measured in five patients during general anaesthesia. The concentration of the drug decreased rapidly between 2 and 40 min and then declined more slowly. Detectable concentrations of phenoperidine were present in plasma for at least 3 h. In the five patients, the distribution half-life of the drug ranged from 3.19 to 14.23 min and the elimination half-life from 47.31 to 162.30 min. Unchanged phenoperidine and two identified metabolites (pethidine and norpethidine) were present in urine.

The simultaneous monitoring of plasma levels of neostigmine and pyridostigmine in man

The synthesis of a series of pyridostigmine analogues wa reported. From these analogues N,N-dipropylcarbamoyloxy-1-methylpyridinium bromide was considered the most suitable compound for use as a common internal marker for the simultaneous determination of neostigmine and pyridostigmine in human plasma. The assay involved a preliminary ion-pair extraction of the drugs and the internal marker from plasma using potassium-iodide glycine buffer. The extract was analysed by a GC system (10% OV-17 on chromosorb W-AW, 100-120 mesh) linked to a nitrogensensitive detector. The calibration graphs of neostigmine and pyridostigmine were linear and reproducible over the range 5 ng to 100 ng per ml in 3 ml plasma samples. This assay procedure has been used to monitor simultaneously the plasma levels of neostigmine (4.7 to 33 ng per ml) and pyridostigmine (2.7 to 18.6 ng per ml) of a myasthenic patient over a period of twelve hours with repeated dosing of neostigmine bromide (30 mg) and pyridostigmine bromide (60 mg).