Acetylation of procaine amide in man studied with a new gas chromatographic method

1 A specific gas-chromatographic method was developed for determination of N-acetylprocaine amide in plasma and urine, using 4-amino-N-(2-piperidinoethyl)benzamide as an internal standard. The investigation was performed in 50 cardiac patients who had reached steady-state plasma concentrations of procaine amide. 2 The plasma concentrations of the acetylated metabolite varied between 1.0 and 15.0 μg/ml and were thus of the same order of magnitude as those of the parent drug. Especially high plasma levels of the metabolite were seen in patients with poor kidney function. 3 The urinary excretion of the metabolite varied markedly between individuals and ranged between 6 and 52% of the administered daily dose. There was a clear tendency towards higher rates of acetylation of procaine amide in patients with short plasma half-lives of isoniazid, i.e. the phenotype rapid acetylators. Because of coexisting therapy with other drugs and impaired renal function in some patients studies are required in healthy human volunteers to ascertain whether the acetylation of procaine amide and isoniazid are mediated by the same enzyme system.

Pharmacokinetics of chloral hydrate poisoning treated with hemodialysis and hemoperfusion

In a severe case of chloral hydrate intoxication treated with combined hemodialysis and hemoperfusion the pharmacokinetics of the metabolites trichloroethanol (TCE), trichloroethanol glucuronide (TCE-Glu) and trichloroacetic acid (TCA) were studied. Indications of delayed absorption and some slowing of metabolism were found. At a blood flow rate of 200 ml/min clearances by hemodialysis and hemoperfusion, respectively, in ml/min were estimated to be 188 and 156 for TCE, 184 and 181 for TCE-Glu, 142 and 91 for TCA. Clearance by hemoperfusion declined with time. The half-lives of TCE and TCA were 3.2 and 4.3 hours during combined hemodialysis and hemoperfusion. After termination of treatment the half-life of TCE was 12.8 hours, whereas TCA was metabolized so slowly, that no reliable calculation could be performed. We conclude that hemodialysis and hemoperfusion are equally and highly efficient in the treatment of chloral hydrate poisoning, but hemoperfusion may increase the risk of gastric bleeding more than hemodialysis. Hemodialysis may therefore be preferable and should be tried in spite of low blood pressure.

On-line extraction using an alkyl-diol silica precolumn for racemic citalopram and its metabolites in plasma. Results compared with solid-phase extraction methodology

Sample preparation is usually the most critical and time consuming step when using HPLC for drug analysis in biological matrixes. Sample extracts have to be clean considering both chromatographic interferences and column maintenance. To meet some of these criteria a fully automated on-line extraction (OLE) analysis method was developed for the antidepressant drug citalopram and its two demethylated metabolites, using an RP-C4-ADS extraction column. A comparison between the new OLE method and an off-line solid-phase extraction method showed that the two methodologies were equal in analytical precision but that the OLE method was faster and therefore superior in sample capacity per day.

Bioanalysis of racemic reboxetine and its desethylated metabolite in a therapeutic drug monitoring setting using solid phase extraction and HPLC

Reboxetine is a new antidepressant drug acting as a potent and selective noradrenaline reuptake inhibitor on the noradrenergic neuronal system. Because of an expected interindividual variability in drug metabolism in the clinical practice the need for therapeutic drug monitoring routines in psychiatry is always a prominent feature. In this application, the preferred bioanalytic methodology was solid phase extraction combined with reversed-phase high-performance liquid chromatography and ultraviolet detection at 210 nm. The technique proved reliable, with interday and intraday variation of less than 5% and a quantification limit for reboxetine and one of its main metabolites O-desethylreboxetine (O-reboxetine) at 5 and 30 nmol/L, respectively. The method was applied on serum samples from 38 patients treated chronically with reboxetine. These samples were drawn as trough levels in steady state with a dosage range of 2-16 mg/day. They evidenced a mean reboxetine concentration that was fairly linear and dose proportional, although the variance in concentration was large between patients, even those taking the same dosage. O-reboxetine was detected in quantifiable amounts in only 1 of the 38 patients (<3%). In conclusion, these results suggest that a routine reboxetine therapeutic drug monitoring service that is robust enough to produce reliable and reproducible results may be introduced into everyday clinical practice.

Human pharmacokinetics of L-3,4-dihydroxyphenylalanine studied with microdialysis

BACKGROUND

Intravenous and subcutaneous microdialysis was performed to compare the free concentrations and pharmacokinetics of L-3, 4-dihyroxyphenylalanine (L-dopa) in blood and tissue in healthy subjects and in patients with Parkinson disease.

METHODS

Nine healthy volunteers and 10 patients with Parkinson disease, stage 1. 5-2 according to the Hoehn-Yahr rating scale, took part of the study. In the patient group subcutaneous microdialysis and ordinary blood sampling were performed, whereas in the control group intravenous microdialysis was also performed. Microdialysis samples were collected in fractions of 15 min. The first two fractions were collected for analysis of basal concentrations. A blood sample was also taken. The patients were then given one tablet of Madopar((R)) (100 mg of L-dopa and 25 mg of benserazide), and the microdialysis was continued for another 210 min. Blood samples were obtained at 30-min intervals.

RESULTS

The serum samples gave a significantly higher mean area under the curve (AUC; 491 +/- 139 micromol. min/L) than that for intravenous dialysates (235 +/- 55.3 micromol. min/L), suggesting a protein binding of 50%. The L-dopa concentrations from the subcutaneous dialysates matched those from the intravenous dialysates, indicating rapid distribution of L-dopa to the tissues.

CONCLUSIONS

Parkinsonian patients in early stages of the disease have a pharmacokinetic pattern of free L-dopa similar to that of healthy subjects. Comparison of AUCs from microdialysis with ordinary serum analysis revealed data indicating significant protein binding. Microdialysis is a suitable and easily applied tool in pharmacokinetic studies.

Stereoselective pharmacokinetics of S-salbutamol after administration of the racemate in healthy volunteers

Racemic R,S-salbutamol is taken to relieve bronchial constriction. Only the R-enantiomer has bronchodilating properties. The S-enantiomer has been proposed to cause in vitro bronchial hyperreactivity in guinea-pigs. Stereoselective elimination of salbutamol has been shown, with S-salbutamol being eliminated at a slower rate than R-salbutamol. This study questioned whether rates of stereoselective elimination were similar after oral or lung delivery, and whether the S:R ratio would increase after repeated inhalations in a situation resembling a common clinical use. Eighteen healthy volunteers received single-dose racemic salbutamol as a solution instilled in the trachea during anaesthesia, as inhaled micronized powder and/or as ingested tablets. Five volunteers inhaled repeated doses of racemic salbutamol. Concentrations in plasma and urine were measured using a technique which allowed chiral separation of samples with concentrations as low as 0.1 ng x mL(-1). The bioavailability of S-salbutamol was significantly higher than that of R-salbutamol after the different modes of administration. Stereoselective elimination was more pronounced after oral administration than after inhalation. Repeated inhalations resulted in successive increases in the S:R ratio as steady state was approached. In conclusion, the clinical consequences of increasing plasma concentrations of S-salbutamol need to be further assessed.

Cerebrospinal fluid concentrations of propofol during anaesthesia in humans

The concentration of propofol in and surrounding the human brain during propofol anaesthesia is unknown. We measured simultaneously the concentration of propofol in cerebrospinal fluid (CSF) from an indwelling intraventricular catheter and the concentration in arterial blood in five neurosurgical patients before, during induction (at 2.5 and 5 min) and during a maintenance propofol infusion (at 15 and 30 min). After induction of anaesthesia with propofol 2 mg kg-1, anaesthesia was maintained with an infusion of 8 mg kg-1 h-1 for 15 min and then reduced to 6 mg kg-1 h-1. The plasma concentration of propofol increased rapidly during induction and reached a plateau concentration of mean 2.24 (SD 0.66) micrograms ml-1 after 5 min. The concentration of propofol in CSF showed a slower increase during induction and remained almost constant at 35.5 (19.6) ng ml-1 at 15-30 min after induction. The CSF concentration of propofol that we measured was 1.6% of the plasma concentration and consistent with the high protein binding of the drug in plasma.

Low-dose aspirin decreases blood alcohol concentrations by delaying gastric emptying

OBJECTIVE

To determine if treatment with low-dose aspirin (ASA) influences the bioavailability of orally administered alcohol and to assess whether this is caused by altered gastric emptying as measured by the paracetamol absorption test.

METHODS

In a single-center controlled crossover trial, ten healthy male medical students, aged 20-27 years, participated in two experiments in random order. Both times they took paracetamol (1.5 g together with a standardized breakfast) and drank ethanol (0.3 g/kg) 1 h after eating breakfast. On one drinking occasion, no previous medication was given. The other alcohol session was performed after the subjects had taken 75 mg ASA once daily for 7 days. On both occasions, venous blood samples were obtained at exactly timed intervals for a period of 3.5 h.

RESULTS

The blood-ethanol profiles showed large interindividual variations for both experiments. After treatment with ASA, the maximum blood-ethanol concentration was distinctly lower in seven subjects, almost unchanged in two subjects and increased in one subject. Overall, a statistically significant decrease in the peak blood-ethanol concentration was observed. The time required to reach peak blood-ethanol levels was somewhat longer after treatment with ASA. Although the areas under the concentration-time profiles were smaller after ASA treatment, these differences were not statistically significant. The concentrations of paracetamol in plasma were lower when ethanol was ingested after treatment with ASA and the areas under the concentration-time curves (0-170 min) were smaller.

CONCLUSIONS

Intake of low-dose ASA (75 mg daily) tends to delay the absorption of a moderate dose of ethanol, which results in lower peak blood-ethanol concentrations and smaller areas under the concentration-time curves. The underlying mechanism seems to be delayed gastric emptying as indicated by the paracetamol absorption test.

Solid-phase extraction with end-capped C2 columns for the routine measurement of racemic citalopram and metabolites in plasma by high-performance liquid chromatography

An assay based on solid-phase extraction followed by high-performance liquid chromatography (HPLC) was developed for the measurement of citalopram and its main metabolites desmethylcitalopram and didesmethylcitalopram. The best extraction procedure was performed with end-capped C2 column utilising secondary silanol interactions to obtain clean extract. The HPLC analysis was done on a phenyl column with a mobile phase without any amine additives. Fluorescence detection gave a limit of detection of 0.8 nmol/l plasma for the compounds analysed.

Coupled-column chromatography on a Chiral-AGP phase for determination of amlodipine enantiomers in human plasma: an HPLC assay with electrochemical detection

A sensitive enantioselective high performance liquid chromatographic assay for determination of the dihydropyridine-type calcium antagonist amlodipine in human plasma samples is described. Chiral chromatography is performed on an alpha 1-acid glycoprotein column (i.e. Chiral-AGP) and the eluted enantiomers are trapped and compressed on two short columns before final achiral chromatography on a narrow bore column (i.e. Zorbax SB-Ph) using electrochemical detection. Both stereoselective quantitative analysis and enantiomeric ratio analysis, for samples with a known total concentration of amlodipine are described. The quantitative assay shows linearity over the range 0.5-10 ng ml-1 for the two enantiomers and the limit of detection is about 0.2 ng ml-1. The method has been applied to a pharmacokinetic study of the enantiomers of amlodipine in human subjects.

Sensitive high-performance liquid chromatographic analysis of amlodipine in human plasma with amperometric detection and a single-step solid-phase sample preparation

A narrow-bore HPLC assay with electrochemical detection for the determination of the calcium antagonist amlodipine in human plasma samples is presented. By using a single-step solid-phase extraction procedure on Bond Elut C2 columns, the sample preparation step has been considerably simplified and less time-consuming compared to earlier presented works. With a linear and reproducible calibration curve over the range 0.5-20 ng ml-1 plasma, the assay has successfully been used in the analysis of more than 500 plasma samples from a multicenter trial.

Tissue disposition of glyceryl trinitrate, 1,2-glyceryl dinitrate, and 1,3-glyceryl dinitrate in tolerant and nontolerant rats

The tissue distribution of glyceryl trinitrate (GTN) and its two dinitrate metabolites 1,2-glyceryl dinitrate (1,2-GDN) and 1,3-glyceryl trinitrate (1,3-GDN), was studied in GTN-tolerant and nontolerant male Sprague-Dawley rats. The concentrations of GTN, 1,2-GDN, and 1,3-GDN were measured in plasma, heart, brain, liver, aortic tissue, and adipose tissue at various time points after a subcutaneous dose of GTN (50 mg/kg). At the first time point (5 hr), concentrations of GTN, 1,2-GDN, and 1,3-GDN in plasma were equal for tolerant and nontolerant rats, but the elimination rate was altered for the tolerant rats as compared with nontolerant rats. In adipose tissue, the concentration of GTN was significantly higher as compared with concentrations of the dinitrate metabolites. In contrast, the other tissues studied showed significantly higher concentrations of the GDNs when compared with GTN. The 1,3-GDN/1,2-GDN ratio decreased with time for both tolerant and nontolerant rats. This study indicates that long-term GTN administration results not only in tolerance development, but also in altered pharmacokinetics of GTN, 1,2-GDN, and 1,3-GDN. The results also show that the 1,3-GDN/1,2-GDN ratio is dependent on the GTN concentration.

Tissue levels of glyceryl trinitrate and cGMP after in vivo administration in rat, and the effect of tolerance development

The present study compares the tissue distribution of glyceryl trinitrate (GTN) in plasma, heart, brain, aortic tissue, and adipose tissue from GTN tolerant and GTN nontolerant rats at various time points. Furthermore, the cGMP levels in brain, heart, and aortic tissue were studied at various time points as well as the concentration-effect relationship for GTN in aorta isolated at different time points after the last exposure to GTN. Concentrations of GTN were found to be higher in all tissues studied as compared with plasma, and the concentrations of GTN were higher in tissues from tolerant rats as compared with nontolerant rats, except for aortic tissue. Concentration-effect curves obtained in vitro showed that aortic smooth muscle was still tolerant 24 h after the last dose of GTN. The cGMP level in brain was significantly increased by 40% 2 h after a single dose of GTN (50 mg/kg) and in aortic tissue by 50% at 15 min and at 2 h after a single dose of GTN (50 mg/kg). There was no effect on cGMP in brain, while an increase was seen in aortic tissue 15 min after the last dose in tolerant animals. No change in cGMP level was seen in heart neither in nontolerant nor in tolerant animals at 15 min and at 2 h. No effect on cGMP levels in brain, heart, and aortic tissue was seen 8, 16, and 24 h after exposure to GTN in either tolerant or nontolerant rats. In conclusion, GTN does not involve the cGMP system in heart, and tolerance development caused a less pronounced GTN-induced cGMP increase in aortic tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Steady-state pharmacokinetics of enteric coated 5-amino-salicylic acid tablets in healthy volunteers and in patients with Crohn's disease or ulcerative colitis

An Eudragit-L coated oral 5-aminosalicylic acid (5-ASA; mesalazine) product (Mesasal), has been formulated to deliver 5-ASA to the distal small bowel and colon for the treatment of inflammatory bowel disease. The purpose of this study was to compare the pharmacokinetic profile of this product at steady-state between healthy volunteers and two different patient groups with inflammation of either the small or the large bowel. Two carefully selected groups of patients, nine with Crohn's disease restricted to the small intestine and ten with total ulcerative colitis and one group of ten healthy volunteers received two 250 mg Mesasal tablets three times daily for 10 days to reach steady-state. Plasma 5-ASA and acetyl-5-ASA concentrations were followed for 48 h and urinary excretion for 72 h. There was a great variation in most pharmacokinetic parameters within each group and no significant differences were noticed between the groups. The location of the inflammatory process probably does not influence the pharmacokinetics of 5-ASA in any significant way in patients with either Crohn's disease in the small bowel or total ulcerative colitis.

Steady-state pharmacokinetics of a new 4-gram 5-aminosalicylic acid retention enema in patients with ulcerative colitis in remission

The pharmacokinetic profile of a new 4-g 5-aminosalicyclic acid (5-ASA) retention enema, Mesasal, was investigated. Nine patients with ulcerative colitis in remission and one patient with mild disease activity received one enema for seven consecutive nights. They were admitted to hospital for administration of the eighth enema. Plasma concentration and urinary excretion of 5-ASA and acetyl-5-aminosalicyclic acid (Ac-5-ASA) were studied for 45 h and faecal excretion for 24 h after administration of the last enema. The median peak plasma concentration of 5-ASA was 0.92 (range, 0.59-1.87) micrograms/ml at a median of 11 h after administration, and of Ac-5-ASA 1.62 (range, 1.03-4.36) micrograms/ml at a median of 12 h after administration. On average, the plasma concentration of Ac-5-ASA was almost twice that of 5-ASA at each sampling period. At 24 h after administration the median plasma concentration for 5-ASA was 0.12 (range, 0-0.77) micrograms/ml and for Ac-5-ASA 0.36 (range, 0.01-1.6) micrograms/ml. At 45 h after administration low levels of both 5-ASA (less than 0.2 micrograms/ml) and Ac-5-ASA (less than 0.3 microgram/ml) were noted in two patients, low levels of only Ac-5-ASA (less than 0.1 microgram/ml) in two patients, and neither 5-ASA nor Ac-5-ASA in the other six patients. All patients had detectable urinary levels of both 5-ASA and Ac-5-ASA during the first 4 h after administration. Median urinary recovery during 45 h was 12.6% (range, 5.6-22.2%), indicating a low absorption at steady-state conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of a 5-aminosalicylic acid enteric-coated tablet in patients with Crohn's disease or ulcerative colitis and in healthy volunteers

An Eudragit-L coated oral 5-aminosalicylic acid (5-ASA; mesalazine) product (Mesasal), has been formulated to deliver 5-ASA to the distal small bowel and colon for the treatment of inflammatory bowel disease. The purpose of this study was to compare the pharmacokinetic profile of this drug between two patient groups, with either inflamed small or large bowel and with volunteers. Two carefully selected patient groups (one with nine patients suffering from Crohn's disease restricted to the small intestine, and one with ten patients suffering from total ulcerative colitis) and a group of ten volunteers received two 250 mg Mesasal tablets in the morning, on a fasting stomach. Plasma 5-ASA and acetyl-5-ASA concentrations were followed for 48 h, and urine and faecal excretion for 72 h. There was a great variation in most pharmacokinetic parameters within each group. Numerically, however, the data suggests a somewhat higher systemic absorption in patients with Crohn's disease than in healthy volunteers or patients with ulcerative colitis. The location of the inflammatory process might have some influence on the pharmacokinetics of 5-ASA in inflammatory bowel disease.

An estimation of the annual incidence of poisoning using automated telephone polling

An automated telephone poll was conducted in Bernalillo County NM during February, 1988. The equipment made 33,458 telephone calls and 2,703 households responded to the eight items included in the poll. The results included a minimum of 810 poisoning incidents in these households in the previous year, giving an annual incidence of poisoning in this population of 108 per 1,000. This rate is considerably higher than previous estimates. Other results included a trend toward delaying poisoning therapy until symptoms developed or taking the poisoned patient directly to an emergency department. If these results are confirmed by conventional polling, poisoning is a major public health problem. Furthermore, confirmation would establish automated telephone polling as a valuable tool for rapidly and inexpensively surveying large populations.

Pharmacokinetics of a 5-aminosalicylic acid enteric-coated tablet and suppository dosage form

An Eudragit-L coated oral 5-aminosalicylic acid (5-ASA; mesalazine) product (Mesasal), has been formulated to deliver 5-ASA to the distal small intestine and colon for the treatment of inflammatory bowel disease. The purpose of this study was to compare the pharmacokinetic profile of this product to sulphasalazine (SASP; Salazopyrin) and to assess the pharmacokinetics of a suppository 5-ASA dosage form. Twelve healthy volunteers randomly received four single doses of 5-ASA delivering formulations not less than 1 week apart. (a) Mesasal tablets, 2 x 250 mg, fasting; (b) Mesasal tablets, 2 x 250 mg, fed; (c) Salazopyrin tablets, 3 x 500 mg (corresponding to 576 mg 5-ASA), fasting; and (d) Mesasal suppository, 1 x 500 mg, fasting. Plasma 5-ASA and acetyl-5-ASA (Ac-5-ASA) concentrations were followed for 48 h and urine and faecal concentrations for 72 h. Mesasal tablets (fasting) produced a greater area under the concentration-time curve (AUC), peak and time to peak for both plasma 5-ASA and Ac-5-ASA than Salazopyrin. Median urinary recovery values were 21.7% for Salazopyrin and 35.5% for Mesasal (fasting) (P less than 0.01). This means that the systemic absorption was higher after Mesasal than after Salazopyrin. The total faecal recovery values were 38.3 and 26.5%, respectively (NS). Except for a delay of 1.5-.3 h in the time to peak of 5-ASA and Ac-5-ASA plasma levels, the pharmacokinetics of Mesasal tablets were essentially the same in fasting or fed subjects. Suppository administration of 5-ASA resulted in a low median urinary recovery of 10.8%.

Tissue distribution of glyceryl trinitrate and the effect on cGMP levels in rat

In order to study distribution in tissue, rats were treated subcutaneously with glyceryl trinitrate, GTN, (50 mg/kg). The concentrations of GTN were measured in plasma, brain, heart, adipose tissue and aortic tissue at different sampling times by a gas chromatographic method with electron-capture detection. The peak GTN-concentration was reached after 2 hours in all tissues examined. The highest concentration of GTN was found in adipose tissue, where the level was approximately forty times higher than in plasma. The concentration of GTN in brain, heart and aortic tissue was about 2-3 times as high as in plasma. The cGMP level was measured in heart and brain. An increase of the cGMP level was found in brain 2 hours after GTN administration. No cGMP increase was found in heart tissue. The results indicate a substantial distribution of GTN to tissue, and an increase of cGMP in brain. The distribution of the substance in the tissues as shown, might have both pharmacokinetic and pharmacodynamic implications.

Variable bioavailability of papaverine

The plasma concentration curves of papaverine have been studied in nine healthy males and seven patients after administration of single intravenous (80 mg) and oral (80 mg) doses. The bioavailability of the drug was highly variable with a mean of 28% (range 5-99%) but reproducible within the same individual (4 of the volunteers) after a repeated (80 mg) oral dose. The calculated half-life after intravenous administration ranged between 1.2-6.6 hours (mean 3.0). The mean apparent volume of distribution was 3.1 l/kg and the mean total plasma clearance was 836 ml/min. It is concluded that papaverine shows an unacceptable inter-individual variation in the bioavailability after oral administration of 80 mg tablets.

Retention and subsequent liberation of glyceryl trinitrate in organ baths influences the relaxation of bovine mesenteric arteries contracted by various agents

The present study compares the relaxant effect of glyceryl trinitrate (GTN) on isolated bovine mesenteric artery in commonly used organ baths made of glass and in disposable vials made of polyethylene, a material known to be inert to GTN. It is shown that the EC50-value for the GTN-induced relaxation is about 1000-fold lower when polyethylene vials are used. The study also shows that the reason for this is that the materials previously used in the experimental equipment retain and subsequently liberate GTN at re-use. In organ baths of glass with holders of acrylics, GTN concentrations of about 20 nM were found during equilibration, i.e. before start of the experiment. The vessel specimens become partly tolerant during equilibration in such organ baths and thus the vessels are less sensitive to GTN. The findings may explain the discrepancy between previous in vitro and in vivo studies. Low concentrations known to be effective in vivo have not been demonstrated to have a relaxant effect in earlier in vitro studies.

Sensitive assay of methadone in plasma by using capillary gas chromatography with photoionization detection

A new gas chromatographic assay for methadone, utilizing a fused-silica capillary column, is presented. Extreme sensitivity was reached, compared to nitrogen-phosphorus and mass spectrometry detection, by employing a photoionization detector. Plasma concentrations of methadone as low as 1 ng/ml can easily be detected and, by further optimization, 0.1 ng/ml was reached. The minimum detectable amount of methadone reaching the detector was 70 fg. The results indicate that the photoionization detector has potential as a tool in drug monitoring.

Repeated pentagastrin-stimulated gastric acid secretory tests carried out in the evaluation of the pharmacodynamics of a new histamine H2-receptor antagonist, SK&F 93479

Single doses of 10 mg or 20 mg intravenously or 25 mg or 40 mg orally of a new histamine H2-receptor antagonist, SK&F 93479, have been administered to 31 patients with peptic ulcer disease. BAO and MAO were measured before and repeated during a 26-h period after drug administration. In a separate group of 17 patients the mean coefficients of variation of BAO and MAO measured in this manner were 53% and 20%, respectively. If this variation in the placebo group is taken into account, BAO was significantly inhibited at all dose levels during the 3rd h after dosing, and a significant effect was still seen during the 25th h after 40 mg orally with a mean reduction of 77%. Mean inhibitions of MAO during the 4th h after dosing of SK&F 93479 were significant at all dose levels, and a significant effect could still be seen during the 26th h for the two oral doses. The mean inhibitions of MAO measured during the 4th and 10th h after dosing were after 10 mg intravenously 44% and 11%, after 20 mg intravenously 59% and 11%, after 25 mg orally 57% and 21%, and after 40 mg orally 75% and 46%. The percentage inhibition of MAO during the 10th h correlated with plasma concentrations (r = 0.64, p less than 0.01). SK&F 93479 is a potent inhibitor of acid secretion with a long duration of action.

Effect of cimetidine and oxmetidine on 24-h gastric acid and pepsin in patients

The 24-h intragastric pH, titrated hydrogen ion concentration, and pepsin concentration were studied in nine peptic ulcer patients during administration of placebo and of 800 mg cimetidine given as two or four equal doses. Cimetidine, 400 mg twice daily, was more effective in reducing acidity during morning (p less than 0.05) and overnight (p less than 0.01) than cimetidine, 200 mg four times daily, which, however, was the most effective regimen during the afternoon (p less than 0.05-0.01). During the 24-h period pH values equal to or above 5 were observed for less than 1 h with placebo treatment, for 1.8 h with cimetidine, 200 mg four times daily, and for 4.7 h with cimetidine, 400 mg twice daily. A new histamine H2-receptor antagonist, oxmetidine, was studied in six other patients, also during a 24-h period. Both 400 mg twice daily and 200 mg four times daily of oxmetidine were superior to placebo (p less than 0.05) in reducing intragastric acidity during the entire 24-h period.

Prizidilol, a combined vasodilatory and beta-adrenoceptor blocking drug, in primary hypertension. A long-term efficacy, tolerance and pharmacokinetic study

After an initial placebo period of four weeks 24 patients with primary hypertension were treated with prizidilol, a hydrazinopyridazine derivative with combined vasodilator and non-selective beta-adrenoceptor blocking actions, for a dose titration period of 14 weeks. Prizidilol 200 to 800 mg was given once daily to achieve a target supine diastolic blood pressure (BP) less than 90 mmHg. Supine and standing BP recorded 24-27 h after drug intake decreased from 172 +/- 17/106 +/- 6 mmHg (mean +/- SD) and 167 +/- 18/111 +/- 8 mmHg, respectively, after placebo to 159 +/- 16/99 +/- 8 and 154 +/- 18/101 +/- 9 mmHg after active treatment for six weeks (mean dose 447 mg), and to 154 +/- 16/97 +/- 7 and 148 +/- 14/97 +/- 7 mmHg after treatment for 14 weeks (mean dose 687 mg/day). A slight reduction in HR was seen after treatment for six weeks and in plasma renin activity and urinary methoxycatecholamine excretion after treatment for 14 weeks. A sustained decrease in BP was observed for 10 h after prizidilol 800 mg (n = 9), with a maximum antihypertensive effect (mean reduction in supine BP 33/18 mmHg) 2.5 h after dosing, which coincided with the mean peak plasma concentration. The plasma elimination half-life of the drug was 3.9 h (range 2.0-8.9 h). Changing to a twice daily regimen in 17 patients (mean daily dose 748 mg at six months) did not produce any further reduction in the BP (recorded 12-15 h after dosing) as compared to the once daily regimen at 14 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of oxmetidine, a new histamine H2-receptor antagonist, after single oral and intravenous doses

The plasma concentration curves and urinary excretion of oxmetidine after administration of single i.v. (100 mg) and oral (200 mg) doses have been studied in 11 patients with peptic ulcer disease. The mean bioavailability of the drug was 70% (range 53-91%). After intravenous administration, the mean plasma t 1/2 beta was 3.0 h, the mean apparent volume of distribution 0.7 l/kg, the mean total plasma clearance 12.3 l/h and the mean plasma renal clearance was 0.7 l/h. Following intravenous and oral administration an average of 6% and 3%, respectively, of unchanged drug was found in the urine. The plasma concentration curve after oral administration in most patients exhibited two maxima, with peak concentrations appearing between 45 and 210 min after dosing.

Cimetidine, but not oxmetidine, penetrates into the cerebrospinal fluid after a single intravenous dose

1 Thirty-six patients with various neurological diseases or symptoms received single intravenous doses of either cimetidine 400 mg (n = 19) or oxmetidine 200 mg (n = 17), 15 or 60 min before a diagnostic lumbar puncture. 2 In the 15 min CSF samples concentrations of cimetidine were detectable but not measurable in 5 and non-detectable in 3 patients. 3 In the 60 min CSF samples the concentrations of cimetidine were detectable in all 11 patients and were measurable in 8 of these patients with a mean +/- s.e. mean of 0.12 +/- 0.01 microgram/ml. These CSF concentrations were correlated to simultaneously measured plasma concentrations (P less than 0.01). The mean ratio CSF/plasma concentration was 0.03. 4 No detectable concentrations of oxmetidine were found either in the 15 min (n = 9) or in the 60 min (n = 8) liquor samples. 5 Cimetidine penetrates the blood-drain barrier slowly and not freely after a single dose. Our data suggest that the new histamine H2-receptor antagonist oxmetidine does not cross this barrier.

The pharmacokinetics of cimetidine and its sulphoxide metabolite in patients with normal and impaired renal function

1 The pharmacokinetics of cimetidine and its sulphoxide metabolite was studied after a single intravenous dose of 200 mg cimetidine in nine patients with normal renal function and ten patients with severe renal failure on regular haemodialysis and during continuous oral cimetidine treatment in ten patients with normal renal function and 31 patients with different degrees of renal failure. 2 In normal renal function a mean of 47.3% of the single intravenous dose was excreted as unchanged drug and 12.8% as cimetidine sulphoxide. The mean plasma elimination half-life (T1/2) of cimetidine was 2.0 h and of cimetidine sulphoxide 1.7 h. 3 In severe renal failure a mean of 2.2% of the single intravenous dose was excreted as unchanged drug and 0.5% as cimetidine sulphoxide. The mean plasma T1/2 of cimetidine was 3.9 h. The plasma concentrations of the sulphoxide metabolite increased successively with time after dosing and no elimination phase was observed still 9 h after dose. The mean non-renal clearance of cimetidine was 210 ml/min and lower than in normal renal function, suggesting decreased metabolism of cimetidine in uraemia. 4 During continuous oral cimetidine treatment in patients with normal renal function and in patients g and no elimination phase was observed still 9 h after dose. The mean non-renal clearance of cimetidine was 210 ml/min and lower than in normal renal function, suggesting decreased metabolism of cimetidine in uraemia. 4 During continuous oral cimetidine treatment in patients with normal renal function and in patients g and no elimination phase was observed still 9 h after dose. The mean non-renal clearance of cimetidine was 210 ml/min and lower than in normal renal function, suggesting decreased metabolism of cimetidine in uraemia. 4 During continuous oral cimetidine treatment in patients with normal renal function and in patients with different degrees of renal failure given reduced doses of cimetidine the plasma concentrations of the sulphoxide metabolite were higher with decreasing renal function. The mean plasma T1/2 of cimetidine was 3.1 h in mild renal dysfunction (creatinine clearance 50-75 ml/min) and 4.5 h in severe renal failure (creatinine clearance 5-15 ml/min) and of cimetidine sulphoxide 5.3 and 14.4 h respectively. 5 Toxicity studies of cimetidine sulphoxide may be needed to assess if high plasma concentrations of the sulphoxide metabolite in severe renal failure are of clinical significance.

Pharmacokinetics of cimetidine and its sulphoxide metabolite during haemodialysis

A single intravenous dose of cimetidine 200mg was administered to 6 patients with severe chronic renal failure one hour prior to haemodialysis. The plasma concentrations of cimetidine and its sulphoxide metabolite at the start of haemodialysis were 2.74 +/- 0.12 and 0.76 +/- 0.08 microgram/ml, and after dialysis for 4h 1.08 +/- 0.10 and 0.51 +/- 0.08 microgram/ml, respectively (mean +/- SE). The average haemodialysis clearance (ClHDa) of cimetidine during dialysis was 46-92 ml/min at a dialysate flow rate of 320 ml/min and blood flow rates in the 6 patients between 160-240 ml/min. The mean ClHDa of the sulphoxide metabolite was 44% higher than that of cimetidine, and ranged between 49-148 ml/min. During haemodialysis the mean plasma elimination half-life (t 1/2) of cimetidine was 3.24h (range 2.08-5.08) and of the sulphoxide metabolite 9.49h (range 4.70-14.39). There was a significant relationship between the elimination rate constant (beta) and ClHDa of the sulphoxide metabolite (p less than 0.01), but no such relationship was found between beta and ClHDa of cimetidine. The mean total amount of cimetidine eliminated during dialysis was 27.3mg (range 17.9-31.8), which was 9.0-15.9% of the given dose. Between 12.2-21.2mg (mean 15.3) of the sulphoxide metabolite was eliminated in the dialysate. Major adjustment of the dose of cimetidine on days of dialysis is not necessary.

Pharmacokinetics of cimetidine after single doses and during continuous treatment

The plasma concentration-time curve and urinary excretion of cimetidine were followed in 10 patients after single 200mg doses given intravenously, in 9 patients after 400 and 800mg single oral doses, and in 10 patients over a 24-hour period during continuous oral treatment with 1000mg daily. The bioavailability of cimetidine measured as the ratio between the areas under the plasma concentration-time curves (AUC) after oral and intravenous administration was 76%. The mean excretion of cimetidine in the urine as unchanged drug, expressed as a percentage of administered dose, was 58% after 200mg intravenously and between 37 and 41% after single oral doses of 200, 400 and 800mg and during continuous treatment with 1.0g/day. Since there were no significant differences between the oral doses, the relative bioavailability of cimetidine does not appear to be dose-dependent. The AUC after the 800mg dose was 2.1 times that of the 400mg dose. No dose-dependent kinetics were observed. There were also no significant differences in the AUCs after 200 and 400mg doses during continuous treatment compared with the AUCs after the same single doses. Thus, cimetidine does not appear to induce or inhibit its own metabolism during treatment. Following intravenous administration, the mean volume of distribution was 1.39L/kg and the mean total body clearance and the mean plasma renal clearance of cimetidine were 655 and 375ml/min, respectively. A renal clearance of cimetidine more than 3 times higher than the creatinine clearance demonstrates that the renal excretion of cimetidine is mainly by tubular secretion. Plasma concentrations of cimetidine during continuous treatment with 1.0g/day were above 1.0 microgram/ml-the plasma concentration associated with 50% inhibition of stimulated acid secretion in peptic ulcer patients-for 9 out of the 24 hours. A morning plasma concentration above 0.6 microgram/ml before the next morning dose has been taken during treatment with cimetidine 1.0g/day is only seen in patients with some degree of renal failure. Measurement of plasma half-life during continuous treatment shows that the plasma half-life is longer than the mean 1.79 hours estimated after intravenous administration of a single dose.

Steady-state kinetics and dosage requirements of cimetidine in renal failure

25 patients with different degrees of chronic stable renal failure received oral treatment with cimetidine over 6 days and a final dose in the morning of day 7. The doses of cimetidine were reduced according to the degree of renal failure. Plasma concentrations of cimetidine were determined before the morning dose on days 2,3,6 and before the final morning dose and during the day on day 7. 24-hour excretions of cimetidine were measured during the study and on day 7, 6 to 9 hours after the final morning dose. There were significant linear relationships between the values of creatinine clearance and plasma elimination rate constant of cimetidine (p less than 0.0025) and between the values of creatinine clearance and renal clearance of cimetidine (p less than 0.05). On the basis of the morning plasma concentrations before and the plasma concentration curve after the final morning dose on day 7 the following dose recommendations according to pretrial values of creatinine clearance are recommended for cimetidine treatment in renal failure: 5 to 15ml/min 200mg 2 or 3 times daily, 15 to 30ml/min 200mg 3 times daily and 30 to 75ml/min 200mg 4 times daily.

Prizidilol, an antihypertensive with precapillary vasodilator and beta-adrenoceptor blocking actions, in primary hypertension

Single oral doses of 1.5, 3.0, 4.5 and 6.0 mg/kg prizidilol HCl, an antihypertensive with vasodilator and beta-adrenoceptor blocking actions, were given to 12 patients with primary hypertension on separate days. Systolic and diastolic blood pressure (BP) decreased after 4.5 and 6.0 mg/kg and systolic BP also after 3.0 mg/kg. The antihypertensive effect was evident in 1 to 2 hr with maximum effect in 4 to 5 hr (supine systolic BP 20 and diastolic 13 mm Hg after 6.0 mg/kg); the effect was sustained for more than 8 hr. An initial slight reduction in heart rate (HR) after 1 to 2 hr was followed by a slight rise after 6 to 8 hr. There were higher plasma drug levels and greater antihypertensive effects after the 6.0-mg/kg dose in slow acetylators (n = 5) than in rapid acetylators (n = 7). Due to its hydrazine moiety, prizidilol, like hydralazine, seems to be a substrate for the polymorphic N-acetyltransferase enzyme system.

The influence of trichloroethylene and related drugs on the vestibular system

A previously described experimental model for studying the effect of industrial solvents on the vestibular system of rabbits has been applied to trichloroethylene. Estimation of trichloroethylene and its metabolites in blood and cerebrospinal fluid was performed by gas chromatography. Vestibular function was studied by recording nystagmus, induced by positional changes or accelerated rotation. At blood levels of trichloroethylene above 30 p.p.m. "positional nystagmus" develops. Two metabolites of trichloroethylene, chloral hydrate and trichloroethanol, which are known as central nervous system (CNS) depressants, did not induce this abnormal nystagmus. However, alpha-chloralose, a derivative of chloral hydrate, induced positional nystagmus and also a markedly exaggerated nystagmus developed during rotatory acceleration. It is suggested that solvents like trichloroethylene elicit vestibular disturbances by stimulation of central subcortical vestibulo-oculomotor connections. The stimulation may be caused by a blockage of inhibitory systems.

Oral absorption of cimetidine and its clearance in patients with renal failure

The plasma concentration curve after a single oral dose of cimetidine 200 mg was followed in 27 patients with varying degrees of chronic renal failure (creatinine clearance 1--52 ml/min) and in 46 patients with normal serum creatinine. Compared to the latter patients, the plasma concentration was higher and the elimination rate was slower in all uraemic subjects, including a group with moderate renal impairment. The preliminary recommendations of dosage for patients with a creatinine clearance below 5 ml/min, and for patients on regular haemodialysis, is cimetidine 200 mg every 12 h, 5-15 ml/min 200 mg every 12 to 8 h, 15-30 ml/min 200 mg every 8 h and 30-52 ml/min 200 mg every 6 h.

The absorption of cimetidine before and during maintenance treatment with cimetidine and the influence of a meal on the absorption of cimetidine--studies in patients with peptic ulcer disease

1 The absorption of a single oral dose of cimetidine taken on a fasting stomach or together with a meal was studied in 28 patients before and during 12 weeks treatment with cimetidine. 2 No significant changes in bioavailability were seen during treatment measured as the area under the blood concentration curve (AUC). 3 AUC after a single dose of 400 mg cimetidine was 2.05 times the area after a 200 mg dose. 4 There was a good correlation between AUC and the dose of cimetidine given corrected for body weight (r=0.89). 5 There was no difference in bioavailability if 200 mg cimetidine was taken on a fasting stomach or together with a beef steak meal. 6. During fasting conditions there was a peak in blood concentration at about one hour followed by a second unexplained peak during the third to fifth hour after dose administration. 7 With food the initial rise in blood concentrations was slower and there was only one peak occurring about 2 h after dose administration.

Studies on hexachlorophene-induced myelin lesions in the trigeminal root transitional region in developing and adult mice

Hexachlorophene (HCP)-induced intramyelinic vacuolation was studied in the transitional region of the trigeminal root of suckling and adult mice. HCP produced an extensive vacuolation in the central compartment of the region in both suckling and adult mice, while in the peripheral compartment myelin lesions were only seen in mice less than 16 days of age. Gas chromatographic measurements showed that in suckling mice the blood concentration of HCP decreased with age, apparently reflecting a faster elimination of HCP from the blood. By substantially increasing the HCP dose, higher blood concentrations were obtained in adult than less the 16-day-old mice; in spite of this, PNS myelin changes occurred only in the latter. Thus, by observing the HCP effect on the transitional region, where CNS and PNS directly meet, it is concluded that CNS of both suckling and adult mice is more severely effected by HCP than PNS, and that the reaction of the PNS myelin is age-dependent during the period of myelinogenesis; it is particularly vulnerable to a cytotoxic edema inducing substance.

Acetylation of procaine amide in man. A preliminary communication

The metabolism of procaine amide was studied in 41 cardiac patients who had achieved steady state plasma concentrations of the drug. Acetylated procaine amide accounted for 31 +/- 12% (range 16-63%) of the overall urinary recovery of the drug and is therefore a main metabolite in man. Plasma levels of the metabolite were usually lower but sometimes exceeded those of the parent compound with variations between 1 and 15 mug/ml. The metabolite had a weaker effect than procaine amide on the maximal electrical driving velocity of isolated atrial strips from guinea pig.

Gas chromatographic determination of ethosuximide and phensuximide in plasma and urine of man

Ethosuximide and phensuximide in plasma and urine can be assayed to a concentration of 2–5 μg ml−1 by a rapid and specific gas chromatographic assay. The method can be used to monitor plasma concentrations in patients with petit mal treated with these drugs alone or in combination with other antiepileptic drugs. The steady-state plasma concentrations of ethosuximide in children given 10–45 mg kg−1 day−1 varied between 10 and 150 μg ml−1 indicating marked interindividual differences in pharmacokinetics.