Sensitive liquid chromatography–tandem mass spectrometry method for the determination of loratadine and its major active metabolite descarboethoxyloratadine in human plasma

A sensitive method for the simultaneous determination of loratadine and its major active metabolite descarboethoxyloratadine (DCL) in plasma was developed, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. The samples were extracted from plasma with toluene followed by back-extraction into formic acid (2%) for DCL after which the toluene containing the loratadine was evaporated, the analyte reconstituted and combined with the DCL back-extract. Chromatography was performed on a Phenomenex Luna C18 (2) 5-microm, 150x2.1-mm column with a mobile phase consisting of acetonitrile-0.1% formic acid using gradient elution (10 to 90% acetonitrile in 2 min) at a flow-rate of 0.3 ml/min. Detection was achieved by a Perkin-Elmer API 2000 mass spectrometer (LC-MS-MS) set at unit resolution in the multiple reaction monitoring mode. TurbolonSpray ionisation was used for ion production. The mean recovery for loratadine and descarboethoxyloratadine was 61 and 100%, respectively, with a lower limit of quantification at 0.10 ng/ml for both the analyte and its metabolite. This is the first assay method described for the simultaneous determination of loratadine and descarboethoxyloratadine in plasma using one chromatographic run. The method is sensitive and reproducible enough to be used in pharmacokinetic studies.

Sensitive liquid chromatographic–tandem mass spectrometric method for the determination of fluoxetine and its primary active metabolite norfluoxetine in human plasma

A sensitive method for the simultaneous determination of fluoxetine and its major active metabolite norfluoxetine in plasma was developed, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. The samples were extracted from alkalised plasma with hexane-isoamyl alcohol (98:2, v/v) followed by back-extraction into formic acid (2%). Chromatography was performed on a Phenomenex Luna C18 (2) 5 microm, 150x2 mm column with a mobile phase consisting of acetonitrile-0.02% formic acid (340:660, v/v) at a flow-rate of 0.35 ml/min. Detection was achieved by a Perkin-Elmer Sciex API 2000 mass spectrometer (LC-MS-MS) set at unit resolution in the multiple reaction monitoring mode. TurbolonSpray ionisation was used for ion production. The mean recoveries for fluoxetine and norfluoxetine were 98 and 97%, respectively, with a lower limit of quantification set at 0.15 ng/ml for the analyte and its metabolite. This assay method makes use of the increased sensitivity and selectivity of mass spectrometric (MS-MS) detection to allow for a more rapid (extraction and chromatography) and sensitive method for the simultaneous determination of fluoxetine and norfluoxetine in human plasma than has previously been described.

Simultaneous determination of cefotaxime and desacetylcefotaxime in human plasma and cerebrospinal fluid by high-performance liquid chromatography

A simple and sensitive HPLC method for the simultaneous determination of cefotaxime (I) and desacetylcefotaxime (II) in human plasma and cerebrospinal fluid (CSF) is described. The assay involves deproteinisation and subsequent separation on a reversed-phase HPLC column, with ultraviolet detection at 262 nm. Retention times were 6.8 and 2.2 min for cefotaxime and desacetylcefotaxime, respectively. Average recoveries for the analytes were 78% (I) and 88% (II) from both matrices. Linear responses were observed over a wide range (0.58-940 microg/ml for (I) in plasma, 0.80-55.8 microg/ml for (I) in CSF, 0.54-148 microg/ml for (II) in plasma and 0.50-36.0 microg/ml for (II) in CSF).

A fast and simple method for the determination of clavulanic acid in human plasma using derivatisation reaction kinetics

A stopped-flow mixing technique is used to determine clavulanic acid in human plasma after plasma deproteinisation with acetonitrile and removal of the organic solvent by extraction with dichloromethane. The reaction kinetic profiles for the reaction between clavulanic acid and imidazole are determined by measuring the absorbance at 312 nm of the imidazole derivative. The reaction rates are proportional to the concentration of the clavulanic acid and by plotting reaction rates against clavulanic acid concentrations linear calibration curves could be constructed over the range 0.30-10.0 microg/ml.

Determination of doxepin and desmethyldoxepin in human plasma using liquid chromatography-tandem mass spectrometry

A sensitive method for the simultaneous determination of doxepin and its active metabolite desmethyldoxepin in plasma was established, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. The samples were extracted with hexane-isoamyl alcohol, separated on a Phenomenex Luna C18 5 microm, 150x2.1 mm column with a mobile phase consisting of methanol-water-formic acid (600:400:0.5, v/v) at a flow-rate of 0.25 ml/min. Detection was achieved by a Perkin-Elmer API 2000 mass spectrometer at unit resolution in multiple reaction monitoring mode monitoring the transition of the protonated molecular ions m/z 280.2, 266.2 and 250.1 to the product ions m/z 107.1, 107.1 and 191.0 for analyte, metabolite and internal standard (benzoctamine-HCl), respectively. TurbolonSpray ionisation was used for ion production. The mean recovery for doxepin and desmethyldoxepin was 90% and 75%, respectively, with a lower limit of quantification at 0.320 ng/ml and 0.178 ng/ml for the analyte and its metabolite, respectively, using 0.5 ml plasma for extraction. This is the first assay method described for the simultaneous determination of doxepin and desmethyldoxepin in plasma using LC-MS-MS. The method is sensitive enough to be used in drug bioavailability studies with doxepin.

Extractionless determination of 6-methoxy-2-naphthylacetic acid, a major metabolite of nabumetone, in human plasma by high-performance liquid chromatography

Following oral administration of the prodrug nabumetone, the major metabolite 6-methoxy-2-naphthylacetic acid (6-MNA) was determined in human plasma. Minimal sample preparation was followed by reversed-phase liquid chromatography and UV detection, affording high sample throughput. The lower limit of quantification (LLOQ) was 70 ng/ml, at a signal-to-noise ratio of 8:1. The assay method displayed good correlation (r=0.997), and can be readily employed in pharmacokinetic and bioequivalence studies.

Determination of linsidomine in human plasma by tandem LC-MS with ESI

A sensitive method for the determination of linsidomine in plasma was developed, using high-performance liquid chromatographic (HPLC) separation with tandem mass spectrometric detection. Linsidomine was derivatised with propyl chloroformate and extracted with tert-butyl methyl ether/1,2-dichloroethane (55:45, v/v), back-extracted into HCl (0.01 M) followed by alkalinisation and back-extraction into ether; the final ether extract evaporated, reconstituted in mobile phase and then separated on a Phenomenex Luna C18 (2) 5 micron 2.1 x 150 mm column with a mobile phase consisting of methanol water formic acid (98/100%) (400:600:0.05, v/v/v) at a flow-rate of 0.4 ml min(-1). Detection was achieved by a Finnigan MAT mass spectrometer (LCQ) at unit resolution in the selected reaction monitoring (SRM) mode monitoring the transition of the protonated molecular ion m/z 257.0 to the product ion m/z 86.0. The mean recovery for linsidomine was 51% with a lower limit of quantification of 0.70 ng/ml using 1 ml plasma for extraction. This LC-MS/MS method for the determination of linsidomine in human plasma allows for better specificity and a higher sample throughput than the traditional LC-UV methods. It also demonstrates the profound effect that the composition of acidic modifiers and matrix constituents can have on the electrospray ionisation (ESI) of the analyte.

High-performance liquid chromatographic determination with amperometric detection of piroxicam in human plasma and tissues

After repeated topical application of a piroxicam gel preparation to the knee, piroxicam was quantified in plasma, subcutaneous tissue, synovial capsule and synovial fluid, using specimens obtained during knee surgery. Electrochemical detection was used and the limit of quantification (LOQ) was 0.72 ng/ml in plasma at a signal-to-noise ratio of 10:1. The chromatographic method was optimised to determine piroxicam in all four matrices, and the analyte was quantified using a calibration line constructed from plasma calibration standards. Levels in subcutaneous tissue, synovial capsule and synovial fluid were compared to plasma steady-state levels and expressed as a ratio, in order to ascertain bioavailability.

Determination of fluspirilene in human plasma by liquid chromatography-tandem mass spectrometry with electrospray ionisation

An ultra-sensitive method for the determination of fluspirilene in plasma was established, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. The samples were extracted with hexane/isoamyl alcohol, separated on a Phenomenex Luna C18 5 mu 150 x 2.1 mm column with a mobile phase consisting of methanol-water-acetic acid (600:400:1) at a flow-rate of 0.3 ml/min. Detection was achieved by a Finnigan Matt mass spectrometer (LCQ) at unit resolution in full scan mode scanning the product ion spectrum from m/z 130-500 and monitoring the transition of the protonated molecular ion at m/z 476.2, to the sum of the largest product ions m/z 371, 342 and 274 (MS-MS). Electrospray ionisation was used for ion production. The mean recovery for fluspirilene was 90% with a lower limit of quantification of 21.50 pg/ml using 1 ml plasma for extraction. This is the first chromatographic method described for the determination of fluspirilene in plasma that is accurate and sensitive enough to be used in pharmacokinetic studies.

An evaluation of the interaction of meloxicam with frusemide in patients with compensated chronic cardiac failure

AIMS

To evaluate the interaction of meloxicam with frusemide in patients with compensated cardiac failure.

METHODS

Nineteen patients with Grade II or III compensated chronic cardiac failure completed this randomized, double-blind, cross-over study. The patients received 40 mg frusemide day(-1) for 7 days. Thereafter, patients received either 15 mg meloxicam plus 40 mg frusemide day(-1), or one placebo tablet plus 40 mg frusemide day(-1) for 7 days. After a washout period of 7 days during which patients received 40 mg frusemide day(-1) for 7 days, the patients were crossed over to the alternate treatment. The effect of concomitant ingestion of meloxicam and frusemide on frusemide-induced diuresis, urine and serum electrolytes, urinary frusemide excretion, and plasma frusemide pharmacokinetics was also determined.

RESULTS

The estimate (90% confidence interval) of the '(frusemide + meloxicam)/(frusemide alone)' mean ratio of the variables Cmax, AUC(SS) and Cmax/AUC(SS) for plasma frusemide were 121% (101% to 145%), 106% (96.4% to 117%), and 114% (98.3% to 132%), respectively. Similarly, the estimate (90% confidence interval) of the '(frusemide + meloxicam)/(frusemide alone)' of the mean ratio of the variable cumulative urinary frusemide excretion after multiple doses of frusemide were 123% (101% to 150%) for the period 0-8 h, and 122% (105% to 142%) for the period 0-24 h after drug administration on day 7. The estimate (90% confidence interval) of the '(frusemide + meloxicam)/(frusemide alone)' mean ratio of the pharmacodynamic variables cumulative sodium excretion was 105% (95.2% to 116%) for the period 0-8 h and 108% (96.5% to 121%) for the period 0-24 h after drug administration on day 7.

CONCLUSIONS

Meloxicam may lead to slightly increased maximum concentrations of frusemide in plasma, as well as to slightly increased urinary excretion of frusemide, without affecting the pharmacodynamics of frusemide. Thus there is no clinically significant pharmacokinetic or pharmacodynamic interaction of meloxicam with frusemide following repeated co-administration of meloxicam and frusemide to patients with compensated chronic cardiac failure.

Bioavailability of two selegiline hydrochloride tablet products

The bioavailability of two selegiline HCl (CAS 14611-52-0) tablet products was compared in a single-blind, single-dose, randomised, two-way, cross-over study with 25 healthy volunteers. A test preparation of selegiline HCl (4 x 5 mg tablets) was compared to a reference preparation of selegiline HCl (4 x 5 mg tablets). The volunteers were randomised receiving each treatment once. Two clinic days were separated by a wash-out period of between 6 and 14 days. The variable AUC(0-infinity) was the primary characteristic of the extent of formation (bioavailability) of the selegiline metabolites, desmethylselegiline and methamphetamine. For desmethylselegiline the point estimate (90% confidence interval) of the "test/reference" mean ratio for the variable Cmax is 98.4% (91.2% to 106%), for AUC(0-infinity) 103% (97.6% to 109%), and for Cmax/ AUC(0-infinity) 95.6% (89.4% to 102%). For methamphetamine the point estimate (90% confidence interval) of the "test/reference" mean ratio for the variable Cmax is 101% (96.8% to 105%), for AUC(0-infinity) 102% (95.3% to 109%), and for Cmax/AUC(0-infinity) 99.0% (91.5% to 107%). The results of this study indicate that the test preparation is bioequivalent to the reference preparation with respect to both the rate and extent of formation of desmethylselegiline and methamphetamine.

No influence of pantoprazole on the pharmacokinetics of phenytoin

Twenty-three healthy, male volunteers completed this doubleblind, randomized, placebo controlled, 2-period crossover study to assess the influence of multiple doses of pantoprazole on single-dose phenytoin pharmacokinetics. During each treatment period, the volunteers received either one 40 mg pantoprazole tablet or placebo for 7 days. In addition, a single-dose of 300 mg (3 x 100 mg capsules) phenytoin sodium was administered on day 4 of each treatment period. A 14-day wash-out period was allowed between phenytoin administrations. The results indicate that pantoprazole neither affects the rate nor the extent of absorption, nor the elimination of phenytoin.

Relative bioavailability of four clomipramine hydrochloride tablet products

The relative bioavailability of clomipramine was determined in two single-blind, single-dose, randomized, crossover studies. In the first study, the relative bioavailability of the test product, 2 x 25 mg clomipramine hydrochloride tablets (Noristan Ltd.), with respect to the reference product, Anafranil 2 x 25 mg tablets (clomipramine HCl; Ciba-Geigy (Pty) Ltd.) was determined. In the second study, the relative bioavailability of the test product, 5 x 10 mg clomipramine hydrochloride tablets (Noristan Ltd.), with respect to the reference product, Anafranil 5 x 10 mg tablets (clomipramine HCl; Ciba-Geigy (Pty) Ltd.), was determined. The geometric mean values for the variable Cmax were 31.3 ng mL-1 for the reference and 31.6 ng mL-1 for the test product in study 1. The geometric mean values for the variable AUC were 736 ng h mL-1 and 753 ng h mL-1 for the reference and test, respectively. In study 2, the geometric mean Cmax values were 25.8 ng mL-1 and 23.9 ng mL-1 for the reference and test respectively; the geometric mean AUC values were 569 ng h mL-1 and 547 ng h mL-1. The 90% confidence intervals for the 'test/reference' mean ratios of the plasma clomipramine pharmacokinetic variables Cmax and AUC(0-infinity) (as measures of the rate and extent of absorption of clomipramine, respectively) fall within the conventional bioequivalence range of 80-125% for both studies. The test products (clomipramine HCl) are therefore bioequivalent to the reference products (Anafranil) with respect to the rate and the extent of absorption of clomipramine in both 10 mg and 25 mg strengths.

Study of the effect of miglitol on the pharmacokinetics and pharmacodynamics of warfarin in healthy males

This was a double-blind, randomised, placebo-controlled, cross-over study to determine the possible pharmacodynamic and pharmacokinetic interaction of miglitol (CAS 72432-03-2, Bay m 1099) and warfarin sodium (CAS 129-06-6) in healthy volunteers. The study comprised 2 treatment periods of 8 days each, with a medication-free period of 14 days between the 2 treatment periods. The volunteers received medication for 7 days and were assessed over 8 days in both treatment periods. According to the randomisation, the volunteers received either 100 mg of miglitol or matching placebo, 3 times daily during the treatment periods. On Day 4 of each treatment period the volunteers received a single oral dose of 25 mg warfarin sodium together with miglitol or placebo. The effect of miglitol on both the pharmacokinetics and pharmacodynamics (prothrombin time and clotting factor VII activity) of warfarin sodium was investigated. The study results indicate that the concomitant administration of miglitol and warfarin does not affect the pharmacokinetics of R- and S-warfarin, or the pharmacodynamics of warfarin.

Relative bioavailability of rifampicin, isoniazid and ethambutol from a combination tablet vs. concomitant administration of a capsule containing rifampicin and a tablet containing isoniazid and ethambutol

Twenty male volunteers who were slow metabolisers of isoniazid, completed this single-blind, single-dose, randomised, cross-over study to compare the bioavailability of rifampicin (CAS 13292-46-1), isoniazid (CAS 54-85-3) and ethambutol (CAS 1070-11-7) from Myrin tablets (test preparation) with the bioavailability of these drugs from a combination of capsules containing rifampicin and tablets containing isoniazid and ethambutol (reference). There were 2 treatment periods and on clinic days volunteers were given either the reference (300 mig rifampicin plus 200 mg isoniazid and 600 mg ethambutol HCl), or the test preparation (300 mg rifampicin, 150 mg isoniazid and 600 mg ethambutol HCl). Serial blood samples were drawn from the volunteers and rifampicin, isoniazid and ethambutol assays were performed. The results of this study indicate that the test preparation is equivalent to the reference with respect to both the rate and the extent of absorption of rifampicin, isoniazid (after adjustment for the different doses of isoniazid and ethambutol).

Influence of meloxicam on furosemide pharmacokinetics and pharmacodynamics in healthy volunteers

Fifteen healthy male volunteers participated in an open, multiple-dose study to investigate a possible interaction between furosemide and meloxicam, a new non-steroidal anti-inflammatory agent (NSAID). The study comprised three treatment periods. First, furosemide (40 mg) was administered as a single oral daily dose for 3 days. A wash-out day was followed by the administration of meloxicam (15 mg) as a single oral daily dose for 10 days. Thereafter, meloxicam and furosemide were administered concomitantly at the same doses as described above, for 3 days. The effect of concomitant ingestion of meloxicam and furosemide on furosemide-induced diuresis, urine and serum electrolytes, and furosemide pharmacokinetics was determined, after both single and repeated administration of furosemide. Estimates of the "(furosemide+meloxicam)/(furosemide alone)" mean ratio of the variable AUC(0-infinity) for plasma furosemide and the cumulative sodium excretion (0-8 h) were 97.4% (90% confidence interval 89.7-106%) and 88% (90% confidence interval 82-94%), respectively. The study results indicate that meloxicam does not affect the pharmacokinetics of furosemide in healthy volunteers, nor does it affect furosemide-induced diuresis or serum electrolytes. The cumulative urinary electrolyte excretion after concomitant administration of meloxicam and furosemide is somewhat lower than after administration of furosemide alone, in particular for the period 0-8 h after administration of furosemide. This effect of meloxicam on furosemide dynamics is small, and is probably not clinically relevant in healthy volunteers under the dosing regime studied.

Lack of effect of pantoprazole on the pharmacodynamics and pharmacokinetics of warfarin

Twenty-six healthy males took part in this double-blind, randomised, placebo-controlled, two-period, cross-over study. Pantoprazole (40 mg) (test) or placebo (reference) were administered once daily, for 8 days, with a 3 week washout period. A single oral dose of 25 mg warfarin sodium was co-administered with pantoprazole or placebo on Day 2 of each treatment period. The 90% confidence intervals for the 'test/reference' mean ratios of the excess AUC(0.168 h) of prothrombin time and AUC(0.168 h) of factor VII, and of Cmax, AUC and t1/2 of both R- and S-warfarin fell within the equivalence range of 80% to 125%. These results suggest that pantoprazole does not alter the pharmacokinetics or pharmacodynamics of warfarin.

No influence of pantoprazole on the pharmacokinetics of phenytoin

Twenty-three healthy, male volunteers completed this doubleblind, randomized, placebo controlled, 2-period crossover study to assess the influence of multiple doses of pantoprazole on single-dose phenytoin pharmacokinetics. During each treatment period, the volunteers received either one 40 mg pantoprazole tablet or placebo for 7 days. In addition, a single-dose of 300 mg (3 x 100 mg capsules) phenytoin sodium was administered on day 4 of each treatment period. A 14-day wash-out period was allowed between phenytoin administrations. The results indicate that pantoprazole neither affects the rate nor the extent of absorption, nor the elimination of phenytoin.

No pharmacokinetic or pharmacodynamic interaction between rivastatin and warfarin

Twenty-one healthy, male volunteers completed this double-blind, randomized, two-period, crossover study to determine the possible pharmacodynamic and pharmacokinetic interaction of the concomitant administration of rivastatin and warfarin sodium in healthy volunteers. The study comprised 2 treatment periods of 8 days each, with a medication-free period of 14 days between the 2 treatment periods. According to the randomization, the volunteers received either 300 micrograms of rivastatin or matching placebo once daily during the treatment periods. On day 4 of each treatment period, the volunteers also received a single oral dose of 25 mg of warfarin sodium together with rivastatin or matching placebo. The effect of rivastatin on both the pharmacokinetics and pharmacodynamics (prothrombin time and clotting factor VII activity) of warfarin sodium, and the effect of warfarin sodium on the pharmacokinetics of rivastatin were investigated. Blood sample assays included the analysis of both R- and S-warfarin, because it is known that the enantiomers differ in anticoagulant potency. The study results indicate that the concomitant administration of rivastatin and warfarin does not affect the pharmacokinetics of R- and S-warfarin, or the pharmacodynamics of warfarin. Furthermore, the administration of warfarin sodium does not affect the pharmacokinetics of rivastatin.

The effect of fasting on total serum bilirubin concentrations

Thirty-seven healthy volunteers, 19 of whom had consistently elevated total serum bilirubin (TSB) concentrations, took part in an open, randomised cross-over study to determine the effect of fasting on TSB concentrations. The study comprised of two treatments. During one treatment period volunteers ate a standard supper but fasted for 24 h thereafter. During the other treatment period volunteers ate a standard supper, snacks, breakfast and lunch. TSB concentrations were measured at regular intervals. In both the normal and high bilirubin groups, minimum TSB values were recorded 4 h after the supper. A 24 h fast more than doubled TSB concentration from baseline values in both the normal and high bilirubin groups. A clinically relevant rise in TSB took place after 12 h into the fasting period (TSB of 17.3 mumol l-1 in the fasted group vs 14.0 mumol l-1 in the non-fasted group). When designing a clinical trial, selecting volunteers, or judging the tolerance of a new drug, the rise in TSB caused by fasting must therefore be taken into account, particularly in trials where volunteers or patients fast before entering the study.

Pharmacokinetic characteristics for extent of absorption and clearance in drug/drug interaction studies

Many aspects of drug/drug interaction studies, including aspects of the design, choice of pharmacokinetic characteristics, and statistical analysis can be adapted from bioequivalence studies [Steinijans et al. 1991]. However, an important difference between drug/drug interaction studies and bioequivalence studies is that two formulations in bioequivalence studies generally do not differ with respect to the clearance of the drug under investigation, but in drug/drug interaction studies an effect of one drug on the clearance of another drug is not only possible, but the likely mechanism of interaction for many classes of drugs. Thus, while in bioequivalence studies two formulations are conventionally compared with respect to the rate and extent of absorption of the drug, in drug/drug interaction studies equivalence has to be shown with respect to not only the rate and extent of absorption, but also, and in particular, with respect to the clearance of the drug. Consequently, in drug/drug interaction studies the area under the curve is not a pure characteristic of the extent of absorption, but a composite characteristic of extent of absorption and clearance. This should be taken into account when interpreting the results of drug/drug interaction studies. Apart from standard characteristics such as Cmax and AUC used in bioequivalence studies, for drug/drug interaction studies we suggest the elimination half-life as a characteristic for the clearance, and the ratio of AUC and the elimination half-life as a characteristic for the extent of absorption of a drug.

Absolute bioavailability of a new high dose methylprednisolone tablet formulation

This was a single-blind, single-dose, randomized crossover study to determine the absolute bioavailability of Medrol, a new high dose (100 mg) methylprednisolone tablet product, by comparing it with 100 mg methylprednisolone from an intravenous formulation, Solu-Medrol. Fourteen healthy, non-smoking, Caucasian male volunteers took part. On treatment days volunteers remained recumbent for 4 hours after drug administration, with food and fluid intake standardized over this period. Serial blood samples were drawn over a 14-hour period after drug administration. Plasma methylprednisolone concentrations were determined by high performance liquid chromatography. The geometric means of AUCi.v. and AUCtablet were 4,049 and 3,334 ng.h/ml, respectively. The absolute bioavailability of the tablet product was 82%, which is in agreement with published data for other oral dosage forms of methylprednisolone. Volunteers displayed the expected rise in peripheral blood neutrophil count, but no other clinically relevant changes in hematology or clinical chemistry were observed. No adverse drug reactions were recorded. It is concluded that the tablet product can be used as a substitute for parenteral methylprednisolone in situations requiring high-dose therapy.

Relative bioavailability of four controlled-release nifedipine products

Four controlled-release nifedipine products were investigated in two clinical studies. In study 1, 22 healthy male volunteers took part in an open, multiple-dose, randomized, crossover study to determine the relative bioavailability of two 10 mg controlled-release nifedipine tablets (Adalat Retard, Bayer), administered 12 hourly, and one 20 mg controlled-release nifedipine tablet (Adalat Retard, Bayer) administered 12 hourly. In study 2, 24 healthy male volunteers took part in an open, multiple-dose, randomized, three-period, crossover study to determine the relative bioavailability of (i) two 30 mg nifedipine gastro-intestinal therapeutic system (GITS) tablets (Adalat XL, Bayer) administered once daily; (ii) one 60 mg nifedipine GITS tablet (Adalat XL, Bayer) administered once daily; and (iii) one 20 mg plus one 10 mg nifedipine controlled-release tablet (Adalat Retard, Bayer), administered 12 hourly. In both studies detailed pharmacokinetic data, in particular with respect to the controlled-release characteristics of the different formulations, were collected. Results of both studies indicate that all nifedipine products investigated are bioequivalent with respect to the extent of absorption of nifedipine. The nifedipine GITS products (Adalat XL) have better controlled-release properties than the Adalat Retard product, and are suitable for once-a-day administration.

Automated high-performance liquid chromatographic method for the determination of acyclovir in plasma

Owing to the low plasma concentrations of acyclovir obtained during pharmacokinetic studies after low-dosage oral administration, a sensitive, automated HPLC method had to be developed for determining acyclovir in a large number of plasma samples. Extraction and injection of the samples were done automatically by a Gilson ASPEC system using tC18, 100-mg Sep-Pak Vac extraction columns. The extracts were chromatographed on a Nova-Pak C18 column with sodium octanesulphonate and methanol in the mobile phase. The analyte was detected at 250 nm. The calibration graphs were linear up to at least 1200 ng/ml and the limit of quantification was 10 ng/ml.

Antithrombotic activity of Bay u3405, a thromboxane A2-antagonist, in patients with Dacron aortic grafts: a random controlled clinical trial

Twelve patients with Dacron aortic grafts participated in a placebo controlled, crossover trial to investigate the effect of Bay u3405, a thromboxane A2 receptor antagonist, on graft thrombogenicity. During each treatment period (seven days, Bay u3405 or placebo), 111In-platelet survival and platelet deposition on the grafts were measured daily by gamma-camera imaging and blood radioactivity analysis. Bay u3405 substantially reduced the deposition of platelets and the thrombogenic index, while platelet survival remained unchanged. The ex vivo platelet aggregation response to ADP and epinephrine was significantly inhibited. The bleeding time increased slightly but not to any clinically relevant extent, and no adverse side effects were recorded. Bay u3405 seems to be a safe and effective drug for the inhibition of platelet deposition on aortic Dacron grafts. The use of quantitative imaging techniques is also more sensitive than the measurement of platelet survival for the assessment of antiplatelet drug efficacy in patients with aortic grafts.

Steady-state pharmacokinetics of phentermine extended-release capsules

Twenty-one healthy, caucasian, male volunteers completed this randomized single blind, multiple-dose, crossover bioavailability study during which either phentermine HCl capsules (Minobese Forte, reference product) or phentermine base capsules (Duromine, test product) were ingested once daily for 14 days. A washout period of 14 days was allowed between the two treatment phases. On profile days (day 14 of each treatment phase) subjects remained recumbent for 24 hours after drug administration. Serial venous blood samples were drawn over the 24 hour dosing interval for plasma phentermine assay by gas chromatography. The 90% confidence intervals for the "test/reference" mean ratios of the pharmacokinetic variables Cmax,norm, Cmin,norm, AUCnorm (normalized for difference in the dose of phentermine base), %PTF and T75% Cmax, all fell within the bioequivalence range of 80% to 125%. With the aid of trough plasma phentermine concentrations, it was established that steady-state was reached after 14 days of once daily administration of either product. Adverse events experienced on both treatments included prolonged or recurrent episodes of insomnia, nausea, headache, dry mouth and dizziness. No clinically relevant changes in clinical chemistry or hematology variables occurred during the study.

Considerable cost savings through the analysis of pooled plasma samples in bioequivalence studies that fail to show bioequivalence

A major part of the cost of bioequivalence studies is due to the drug assays of the individual plasma samples collected from each volunteer. Considerable savings in manpower, time, and especially costs could be achieved if it could be determined before the individual plasma samples are assayed that bioequivalence can not be shown. Such information can in fact be obtained through the analysis of pooled plasma samples. We propose an approach where pooled plasma samples are assayed and the resulting pooled drug concentration profiles for the test and reference product are compared. If this comparison indicates that one will not be able to show bioequivalence in the statistical analysis of the individual data, the individual plasma samples are not assayed. Thus more than 40% of the cost of a bioequivalence study that fails to show bioequivalence can be saved.

The effect of benzbromarone on allopurinol/oxypurinol kinetics in patients with gout

The objectives of this study were to establish if, and to what extent, benzbromarone affects allopurinol/oxypurinol kinetics, and to compare the uric acid lowering capabilities of Allomaron (allopurinol 100 mg plus benzbromarone 20 mg) with the effects of allopurinol alone in patients with confirmed gout. We studied 14 adult men in an open randomized cross-over study. After a 14 day run-in period with Zyloprim (2 x 100 mg allopurinol tablets in the morning), the patients were randomly allocated to morning doses of either Allomaron (2 tablets) or Zyloprim (2 tablets). Seven days later cross-over was effected and the alternative treatment was taken for a further 7 days. On days 7 and 14 the patients came into hospital and venous blood samples were taken over 24 h for allopurinol and oxypurinol assays by HPLC. Serum uric acid was determined on days -14, 1, 7, and 14. Benzbromarone lowered plasma oxypurinol concentrations (Allomaron/Zyloprim mean ratio of AUC0-->24 was 59%; 95% confidence interval 54-64%), but did not affect plasma allopurinol concentrations. Despite this pharmacokinetic interaction of benzbromarone with allopurinol, resulting in lower plasma concentrations of oxypurinol, Allomaron was superior to allopurinol alone in lowering serum uric acid, probably because of the added uricosuric effect of benzbromarone.

Automated high-performance liquid chromatographic method for the determination of mianserin in plasma using electrochemical detection

An automated high-performance liquid chromatographic method for the determination of mianserin in plasma is described. Extraction and injection of the samples were automatically done by the Gilson ASPEC system using C8, 100-mg Supelclean solid-phase extraction columns. The extracts were chromatographed on a reversed-phase C18 column (150 mm x 3.9 mm I.D.) with a phosphate buffer-acetonitrile-methanol mobile phase and the analytes detected electrochemically. Calibration curves were linear to at least 53.7 ng/ml at which the between-day relative standard deviation was 5% and the recovery 101%. The limit of quantification was 1.67 ng/ml at which the between-day relative standard deviation was 9% and the recovery 92% using a sample volume of 0.5 ml. The method was applied to the determination of mianserin in the plasma of normal human volunteers participating in a comparative bioavailability study.

The effects of felodipine on the pharmacokinetics of diazepam

Twelve consenting, caucasian male volunteers participated in a double-blind, randomized, crossover study of the effects of felodipine, a calcium antagonist, on the pharmacokinetics of diazepam. There were two trial periods of 12 days each with a wash-out period of 9 days between them (total duration: 12 + 12 + 9 = 33 days). During the 12-day periods they received either felodipine or placebo each morning under fasting conditions. On day 6 of each of the two 12-day periods, diazepam, 10 mg was injected i.v. 30 minutes after the felodipine/placebo. Diazepam and desmethyldiazepam concentrations were measured in plasma up to 168 hours after the injection. Diazepam plasma concentrations and pharmacokinetic parameters were not affected by the concomitant medication with felodipine. However, the co-administration of felodipine increased desmethyldiazepam plasma concentrations relative to placebo: mean area under the plasma concentration-time curve of 4,910 vs 5,581 ng.h/ml and mean peak concentrations of 40 vs 47 ng/ml. Felodipine might cause a retarded elimination of desmethyldiazepam, possibly by obtruding the formation of oxazepam. The clinical relevance of these findings remains to be elucidated.

Aflatoxin exposure and its relationship to kwashiorkor in African children

The urinary excretion of aflatoxins in normal children from a periurban area, as well as those hospitalized with kwashiorkor and marasmus was assessed. In no case was aflatoxin isolated from the urine. It is concluded that aflatoxin exposure is unusual in this population and that aflatoxins do not play a primary role in the pathogenesis of kwashiorkor.

Post-mortem serum concentration of cantharidin in a fatal case of cantharides poisoning

A patient admitted to hospital died shortly after admission without a proper diagnosis having been made. Symptoms as well as the presence of a brown powder found in the possession of the deceased indicated the possibility of cantharidin intoxication. Cantharidin was positively identified by means of a GC/MS analysis, utilizing the selected ion monitoring technique (SIM), for m/z = 197.0813, (M + H+) for cantharidin, under positive chemical ionization conditions at a resolution of 7000 and a mass window of 30 ppm. Quantitation was done by means of a GC/MS SIM analysis of a toluene extract of acidified post-mortem serum under El+ conditions at a resolution of 3000, using clofibrate as internal standard and monitoring m/z = 128.0473 and 128.0029 for cantharidin and clofibrate respectively. The post-mortem serum was found to contain cantharidin at a concentration of 72.3 ng/ml whilst the cantharides powder contained 0.87% cantharidin.

Warfarin bio-availability. A comparison of 4 products

The bio-availability of four warfarin tablet formulations--Marevan (Allen & Hanburys); Warfarin (Petersen); Coumadin (Boots) and Warfarin (Lennon)--administered as a single 10 mg oral dose, was compared in a single-blind cross-over study. Twelve healthy adult male volunteers participated in a clinical trial in which 95% confidence intervals for the true ratio (of the means) of each test product with respect to the reference product (Marevan) were calculated for maximum concentration and area under the plasma concentration time curve. The three test products differed by less than 20% from the reference product, suggesting that all four can be used interchangeably without risk of compromising safety and efficacy.

Gas chromatographic-mass spectrometric method for the quantitation of cantharidin in human serum

A gas chromatographic-mass spectrometric (GC-MS) method utilising single-ion monitoring at a resolution of 3000 to quantitate cantharidin in post-mortem serum is described. Serum was acidified, extracted with toluene, and 1 microliter of the toluene extract subjected to GC-MS analysis. Clofibrate was used as internal standard. The method displayed a high degree of specificity and was accurate and precise, with a linear response in the concentration range 15-150 ng/ml. A cantharidin concentration of 72.3 ng/ml was found in the post-mortem serum.

[Epidemiology of poisonings in the Bloemfontein area, 1980-1985]

An epidemiological study of human poisoning in the Bloemfontein area over a recent 6-year period was performed. Deliberate and accidental poisonings were studied relative to: (i) age of poisoned persons; (ii) sex of poisoned persons; (iii) type of poison involved; and (iv) the time the poisoning occurred. The study also included the number of patients admitted to hospital after poisoning. The incidences of some agents involved were compared with those in two previous studies done in the same area.

Drugs in sport. The first 5 years of testing in South Africa

Since 1983 screening procedures have been developed to detect prohibited substances in urine specimens collected from competitors in sport. Gas chromatography is used for the detection of stimulant drugs and gas chromatography/mass spectrometry for the detection of anabolic steroids. Of 679 urine samples analysed, a positive result was obtained for 45 (6.6%). Fencamfamine was the stimulant most frequently detected, while the ephedrines as a group accounted for 18 positive samples. These findings indicate the necessity to continue the monitoring of drug use and abuse in sport.

Effects of HOE 760 (histamine H2-receptor antagonist) on diazepam pharmacokinetics

A double-blind cross-over study of the effects of HOE 760 (histamine H2-receptor blocker) on diazepam pharmacokinetics was conducted in 12 healthy men. HOE 760 or placebo was given daily for 12 days and, after a wash-out period of 9 days, the alternate medication was given for 12 days. Diazepam 10 mg was given intravenously on day 6 of each of the 12-day periods. Blood was taken up to 1 week after the diazepam injections for assay of diazepam and desmethyldiazepam. The co-administration of HOE 760 did not affect the pharmacokinetics of diazepam and desmethyldiazepam.

Comparative bio-availability of theophylline whole and halved sustained-release tablets

In a randomised, multiple-dose, cross-over study in 14 healthy volunteers, plasma theophylline concentrations were compared during a 12-hour dosing interval after repeated administration of theophylline (Euphyllin Retard; Byk Gulden) as whole and halved tablets. Bio-availability of theophylline from the halved tablets relative to the whole tablets was: 116% (100%, 134%) for the extent of absorption as judged by the area under the concentration time curve (AUC) and 115% (99%, 135%) for the rate of absorption as judged by maximum concentration (Cmax). The confidence levels for the 80-120% bio-equivalence range were 72% (AUC) and 76% (Cmax), those for the 80 and 125% range were 91% (AUC) and 91% (Cmax). The plateau times T75% Cmax, which characterise the sustained-released properties, were 8.5 +/- 2.9 hours (halved) and 8.3 +/- 2.5 hours (whole) during the 12-hour dosing interval. It is concluded that no clinically relevant deviations in steady-state plasma theophylline concentration and sustained-release properties are likely to result from breaking (halving) the film-coated tablets.

Pharmacokinetics of temazepam after day-time and night-time oral administration

The pharmacokinetic disposition of temazepam was compared after a day-time and night-time dose in an open randomised crossover study. Twelve healthy male volunteers received a single oral dose of 20 mg temazepam in a soft gelatine capsule at 0900 h or 2200 h. Blood samples were taken immediately before dosing and at selected times over the 36-h period after each dose. The absorption of temazepam was slower after evening administration; the absorption half-life and time to reach maximal plasma concentration being 0.53 h and 1.67 h respectively, compared to 0.38 h and 1.02 h following morning administration. Considering distribution characteristics, evening administration produced a lower peak plasma temazepam concentration (362 ng/ml) compared with a day-time level of 510 ng/ml. Distribution half-life after night-time administration was increased compared with day-time administration (1.76 h vs 1.03 h). A significantly higher percentage of the drug, relative to Cmax, remained in the plasma at 8 and 24 h after evening dosing (39.3 and 15.4% compared to 24.7 and 11.2% following day-time administration). In spite of the half-lives of absorption, distribution and elimination all being longer after the evening dose, the overall bioavailability, as measured by the area under the curve (AUC) was comparable after the two times of administration. Similarly the difference in the mean residence time (MRT) of the two doses was within accepted limits. It is concluded that a chronopharmacokinetic effect was seen for temazepam; however it is unlikely to be of any clinical significance.

The metabolism of atropine in man

A metabolic pattern of atropine in man, based on the detection of radiolabelled products in urine by high performance liquid chromatography after administration of [3H]atropine sulphate to a normal volunteer is proposed. Noratropine (24%), atropine-N-oxide (equatorial isomer) (15%), tropine (2%) and tropic acid (3%) appear to be the major metabolites, while 50% of the administered dose is excreted as apparently unchanged atropine. No conjugates were detectable. Evidence that atropine is present as (+)-hyoscyamine was found, suggesting that stereoselective metabolism of atropine probably occurs.

Ibuprofen bio-availability. A comparison of Brufen and Inza

Ibuprofen in the form of Brufen 200 mg tablets and Inza 200 mg and 400 mg tablets was administered to 18 healthy adult volunteers (9 men and 9 women) in a single-dose (800 mg ibuprofen) open randomized cross-over bio-availability study. Tests revealed increased time required for 50% dissolution to take place for Inza tablets (40-47 minutes) relative to Brufen tablets (7 minutes). Maximum concentration and time to maximum concentration differed significantly (over 20%) between Inza and Brufen, being approximately 30% lower and 67% greater respectively in the case of Inza tablets. Area under plasma concentration time curves were comparable. These data suggest that the Inza tablets tested are not bioequivalent to Brufen 200 mg tablets. Clinical implications are discussed.

The microbial metabolism of condensed (+)-catechins by rat-caecal microflora

The metabolism of 2,3-trans-3,4-trans-3,5,7,3',4'-pentahydroxy-4-(2,4,6-trihydrox yphenyl)-flavan and 2,3-trans-3,4-trans-3,5,7,3',4',-pentahydroxy-4-(2,3-trans-3,5,7,3 ', 4'-pentahydroxyflavanyl-[8])-flavan in vitro by rat-caecal microflora was investigated. Metabolites were extracted and enriched by column chromatography and preparative h.p.l.c., while structural determination was carried out using comparative g.l.c.-mass spectrometry and p.m.r. spectrometry. The metabolites identified were derivatives of benzoic acid, phenylacetic acid, phenylpropionic acid and phenyllactic acid in addition to phloroglucinol, delta-(3-hydroxyphenyl)-gamma-valerolactone and 1-(3-hydroxyphenyl)-3-(2,4,6-trihydroxyphenyl)-propan-2-ol. An additional metabolic route, which differs from the expected severance of the (+)-catechin-phloroglucinol bond and well-documented total heterocyclic ring degradation of flavanoids, is proposed.

Pharmacokinetic study of a paediatric formulation of amoxycillin and clavulanic acid in children

A combination of amoxycillin and clavulanic acid 4:1 was administered to 35 children (aged 2 to 10 years) with infections. The combination was administered orally as a suspension, every 8 h for 5 to 7 days. Sixteen children (aged 2 to 5 years), received 125 mg amoxycillin and 31.25 mg clavulanic acid, and 19 (6 to 10 years) received 250 mg amoxycillin and 62.5 mg clavulanic acid per dose. Following the first dose serum concentrations of amoxycillin and clavulanic acid were determined by microbiological assay. In the younger group receiving the lower dosage (mean: amoxycillin 9.11 mg/kg and clavulanic acid 2.34 mg/kg), the mean peak concentration of amoxycillin was 3.5 mg/l and of clavulanic acid 1.2 mg/l, occurring 1.32 h and 1.39 h, respectively, after administration. In the older group receiving the higher dosage (mean: amoxycillin 12.35 mg/kg and clavulanic acid 3.14 mg/kg) the mean peak serum level of amoxycillin was 4.0 mg/l and of clavulanic acid 1.3 mg/l, occurring 1.43 h and 1.23 h, respectively, after administration. The higher dose per kilogram body weight resulted in a higher peak serum concentration both of amoxycillin and clavulanic acid. The formulation was well tolerated by all the children and no serious side-effects were recorded. Treatment was considered clinically effective in all cases.

Physostigmine and the adrenergic/antimuscarinic syndrome. A case report

A 14-year-old White boy was recently admitted to the Universitas Hospital, Bloemfontein, with an adrenergic/antimuscarinic syndrome following drug overdose. The causation of the syndrome and successful management with physostigmine salicylate are discussed.

Drugs in sport. A report of laboratory investigations into the prevalence of their use in South Africa

Screening procedures utilizing two-dimensional thin-layer chromatography, gas-liquid chromatography and gas chromatography-mass spectrometry were carried out in an attempt to detect stimulant drugs in urine specimens collected from competitors in three major sporting events held during 1983. Drugs classified as forbidden stimulants by the International Olympics Committee were detected in 4% of the specimens collected from competitors in the South African Athletics Championships and in 28% of the specimens collected from competitors in the 1983 Rapport Cycling Tour, while none were detected in specimens collected from competitors in the South African Senior Swimming Championships.

Metabolism of (+)-catechin and some of its C-6 and C-8 substituted derivatives in the isolated perfused pig liver

The metabolism of (+)-catechin, 8-benzyl-(+)-catechin, 6-bromo-, 8-bromo- and 6,8-dibromo-(+)-catechin and 6- and 8-carboxymethyl-(+)-catechin by the isolated perfused pig liver resulted in the formation of the corresponding 3'-O-methyl derivatives. The position of O-methylation was determined by alkaline fusion. The bromo derivatives also underwent debromination. Unmetabolized material and metabolites were present as two glucuronides, a 3,4'-diglucuronide and a 3,5 (or 7)-diglucuronide, both in serum and bile. The position of conjugation was determined by methylation of free hydroxyl groups in the conjugates followed by unmasking of the conjugated hydroxyl groups by enzymic hydrolysis. Results indicate that substitution on the A-ring of (+)-catechin has little influence on the type of metabolites obtained.