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The role of metabolites in bioequivalence studies has been a contentious issue for many years. Many papers have published recommendations for the use of metabolite data based on anecdotal evidence from the results of bioequivalence studies. Such anecdotal evidence has validity, but the arguments lack weight because the "correct" answers are always unknown. A more promising area of exploration is recommendations based on simulated bioequivalence studies for which the "correct" answers are known, given the assumptions. A review of the literature, however, reveals scant evidence of attempts to apply to real data the pharmacokinetic principles on which the recommendations from simulated studies relied. We therefore applied those principles (based on estimates of intrinsic clearance after oral administration of the parent drug) to four bioequivalence studies from our archives, in which the parent drug and at least one metabolite were monitored. In each case, the outcome is discussed in the context of the complexity of the metabolic processes that impact on the parent drug and the metabolite(s) during the first passage from the intestinal lumen to the systemic circulation. Our observation is that no simple generalization can be made such that each drug/metabolite combination must be examined individually. Our recommendation, however, is that in the interests of safety, bioequivalence decision-making should be based on the parent drug whenever possible.

Clozapine and its two major metabolites, N-desmethylclozapine and clozapine N-oxide were quantified using a high-performance liquid chromatographic method with UV detection in dog plasma following a single dose of clozapine. The analysis was performed on a 5-micrometer Hypersil CN (CPS-1; 250x4.6 mm) column. The mobile phase consisted of acetonitrile-water-1 M ammonium acetate (50:49:1, v/v/v), which was adjusted to pH 5.0 with acetic acid. The detection wavelength was 254 nm. A liquid-liquid extraction technique was used to extract clozapine and its metabolites from dog plasma. The recovery rates for clozapine, N-desmethylclozapine, and the internal standard (I.S.) were close to 100% using this method. The recovery rate for clozapine N-oxide (62-66%) was lower as expected because it is more polar. The quantitation limits for clozapine, clozapine N-oxide, and N-desmethylclozapine were 0.11, 0.05 and 0.05 microM, respectively. Intra-day reproducibility for concentrations of 0.1, 1.0 and 5.0 microM were 10.0, 4.4 and 4.2%, respectively, for N-oxide; 11.2, 4.3 and 4.9%, respectively, for N-desmethylclozapine; and 10.8, 2.2 and 4.9%, respectively, for clozapine. Inter-day reproducibility was15% for clozapine N-oxide,8% for N-desmethylclozapine and19% for clozapine. This simple method was applied to determine the plasma concentration profiles of clozapine, N-desmethylclozapine and clozapine N-oxide in dog following administration of a 10 mg/kg oral dose of clozapine.

Purpose. To test the hypothesis that the pharmacokinetics of d-meth- ylphenidate (d-MPH) would be altered by food ingested before administration of an immediate release formulation (dl-MPH- IR) but not when food is ingested before a slow release formulation (dl-MPH-SR). Methods. A randomized, four-phase, open label, crossover design was conducted in 24 healthy men who each received, on separate occasions, dl-MPH-IR and dl-MPH-SR taken after an overnight fast and 15 min after a standardized breakfast (20% protein, 21% fat, 59% carbohydrate). Plasma MPH levels were monitored by a validated, stereoselective, GLC-ECD method. Results. For plasma d-MPH, there were significant differences (ANOVA) between dl-MPH-IR and dl-MPH-SR in tmax, Cmax (peak exposure), and Cmax/AUC (sensitive to rate of absorption). Dl-MPH-SR on average delayed tmax from 2.3 to 3.7 h and lowered Cmax 34%. There was no significant difference between the formulations in AUC (extent of absorption). For dl-MPH-IR, food significantly increased Cmax (23%) and AUC (15%) and for dl-MPH-SR the corresponding increases were Cmax (17%) and AUC (14%). After dl-MPH-IR, food delayed average tmax from 2.0 to 2.5 but had no effect on tmax after dl-MPH-SR. There was no effect of food on Cmax/AUC (rate of absorption). Conclusions. Food caused a significant increase in extent of absorption but had no effect on rate of absorption of d-MPH after either dl-MPHIR or dl-MPH-SR.

Purpose. To establish procedures for the effective evaluation of bioequivalence (BE) for highly-variable drugs and drug products (HVD/P). Methods. 2- and 4-period crossover BE studies with 24 subjects were simulated which generally assumed within-subject coefficients of variation of 40%. The relationship between the fraction of studies in which BE was accepted (the statistical power) and the ratio of geometric means (GMR) of the two formulations was evaluated for various methods of analysis. These included, primarily, scaled average BE (ABE), the corresponding approach of expanding BE limits (BEL), and, for comparison, unscaled ABE and scaled individual BE (IBE). Results. Scaled ABE and expanding BEL showed very similar properties in both 2- and 4-period studies. They had steeper power curves than scaled IBE. Unscaled ABE had very low statistical power. The acceptance of BE by unscaled and scaled ABE and expanding BEL was almost independent of subject-by-formulation interaction and the ratio of within-subject variations of the two formulations. By contrast, the conclusions reached by scaled IBE were strongly affected by these parameters. Conclusions. Scaled ABE and expanding BEL evaluate BE effectively for HVD/P in both 2- and 4-period investigations. However, additional, useful information can be obtained from 4-period studies.

Purpose. The release and presystemic absorption of fluphenazine and its decanoate ester from intramuscular depots were investigated.

1. Doxepin is marketed as an irrational mixture of geometric isomers such that the more active Z-isomer comprises only 15% of the total doxepin whereas the less active E-isomer makes up the remaining 85%. 2. The ratio of isomers of the doxepin remains approximately Z:E = 15:85 in the plasma of depressed patients whereas plasma levels of the active Z-N-desmethyl metabolite are similar to those of E-N-desmethyldoxepin. 3. After examination of four animal species (dog, rabbit, guinea pig, rat), rat was closest to human in terms of the Z:E ratio of the geometric isomers of N-desmethyldoxepin excreted in the 0-24-h urine. 4. Changes in the urinary Z:E ratio of the metabolite were observed after oral but not after intravenous or intraperitoneal administration of commercial doxepin to rat. 5. There was no evidence of Z/E interconversion after administration of the pure isomers to rat in vivo, or after incubation of rat or human liver homogenates with pure isomers. 6. In vitro data suggested that the distortion of the Z:E ratio of N-desmethyldoxepin was a consequence of faster metabolism of the E-isomer in comparison with Z-N-desmethyldoxepin rather than 'enrichment' of the Z-isomer at the expense of the E-isomer.

Retrospective analyses were carried out on 22 analytes involved in nine bioequivalence studies on conventional release products, in which 90% confidence intervals were calculated for partial areas under the plasma concentration versus time curves (AUCs) from the first sampling time to AUC last , The use of partial areas up to 2× the maximum t max among all subjects in any given study gave the same bioequivalence decisions as AUC last .

A bioequivalence study was carried out to compare the bioavailabilities of two formulations containing racemic hydroxychloroquine. The study was based on a single phase parallel design because the enantiomers of hydroxychloroquine have very long terminal phase half lives. A group of n = 72 healthy young men were randomly assigned to receive a single dose of either test ( n = 36 subjects) or the reference ( n = 36 subjects) formulation after which serial blood samples were harvested over 77 days. The two products were found to be bioequivalent in that 90% confidence intervals fell entirely within bioequivalence limits of 80–125% for the log transformed parameters C max and AUC 4 whether calculated from non-chiral or enantioselective blood concentrations. Similarly, 90% confidence intervals for the partial areas from AUC 4 through AUC Inst all fell within 80–125%. These data suggest that enantioselective assays were not required and that blood samples need only have been harvested up to 12 h.

There are few archival data on the impact of stereoisomerism on bioequivalence studies. A bioequivalence study was carried out on two formulations of doxepin containing 15% of the active cis isomer and 85% of the less active trans isomer. Plasma concentrations of cis N-desmethyldoxepin remained at approximately 15% of total in only 2 of 30 healthy volunteers who completed the study. In the remaining 28 subjects, however, the proportion of cis N-desmethyldoxepin steadily increased with time such that by 72 h post dose, cis N-desmethyldoxepin comprised approximately 90% of the metabolite present in plasma. Nevertheless, the 90% confidence intervals (In AUClast, In Cmax and In Cmax/AUClast) for N-desmethyldoxepin fell entirely within bioequivalence li whether stereoselective or non-stereoselective data were analyzed. Thus the results of this study did not support arguments in favor of the use of stereoselective methods in bioequivalence studies.

1. The phase II metabolites in the bile, urine and faeces of rat dosed with clozapine were investigated by means of electrospray mass spectrometry (ESMS) in both positive and negative ion modes. 2. When operated at a cone voltage of 45 V, this soft ionization technique permitted the detection of quasi molecular ions of both sulphate and glucuronide conjugates of hydroxylated phase I metabolites of clozapine. With the cone voltage set at 90 V, however, the ESMS also contained highly diagnostic ions resulting from the loss of 80 Daltons (sulphur trioxide) or 176 Daltons (the glucuronide moiety) from sulphates and O-glucuronides respectively. 3. A sufficient quantity of one metabolite was isolated from rat bile to permit further analysis by 1H-nmr. This metabolite, which was also found in rat urine, was proved to be 7-O-glucuronyl-7-hydroxyclozapine. The analogous sulphate metabolite was also identified in bile by ESMS. 4. Correspondingly glucuronide and sulphate conjugates of a hydroxylated N-desmethyl clozapine were similarly detected in rat bile. There was insufficient material to permit analysis by 1H-NMR, but it appears likely that conjugation was also at the 7-position of N-desmethylclozapine. 5. Finally, the sulphate conjugate of a hydroxy dechlorinated derivative of clozapine was identified by ESMS in both urine and bile. By analogy with a previous report of a similar metabolite in man, the metabolite was tentatively identified as 8-hydroxy-8-deschloroclozapine.

Iloperidone (HP 873) is a D2 and 5-HT2 receptor-antagonist that is under development as a potential atypical antipsychotic agent. Two studies on iloperidone evaluated its safety and tolerability, made a preliminary pharmacokinetic assessment of single 3- and 5-mg doses, and determined the effect of food on its tolerability and pharmacokinetics in healthy volunteers after single 3-mg doses. Iloperidone was well absorbed orally in fasted subjects. The Cmax occurred approximately 2 to 3 hours after administration of a single 3- or 5-mg dose. The pharmacokinetic parameters increased with the dose between 3 and 5 mg (from 2.2 to 5.2 ng/mL for Cmax, and 16 to 50 ng/mL.h for AUC). Iloperidone was eliminated slowly, with a mean t1/2 of 13.5 to 14.0 hours. Coadministration with food did not significantly affect AUC, tmax, or Cmax. These results indicate that the rate of iloperidone's absorption is decreased, but the overall bioavailability is unchanged, when the drug is taken with food. Orthostatic hypotension, dizziness, and somnolence were the most commonly reported adverse events. Coadministration of food reduced the incidence and severity of these events.

Sprague Dawley rats (n = 16) were injected intramuscularly with fluphenazine decanoate (78 mg/kg) in sesame oil. Groups of four rats were surgically prepared on days 1, 7, 15 and 32 post-injection and samples of lymph obtained from the thoracic duct. Fluphenazine was found in similar concentrations in lymph and plasma, although the decanoate was not detected in either body fluid. These data suggest that the lymphatic system plays a role in the presystemic absorption of fluphenazine after i.m. administration of fluphenazine decanoate in the rat. In vitro experiments showed that fluphenazine decanoate was very rapidly hydrolyzed when incubated with rat plasma ( t 1 2 0.6 h ) or muscle homogenates ( t 1 2 1.0 h ). Rates of hydrolysis of fluphenazine decanoate were lower in dog muscle homogenates ( t 1 2 4.3 h ), and very much lower when incubated with plasma from dog 42.9 h) or humans ( t 1 2 50.9 h).

Following a 2-week placebo lead-in, schizophrenic patients were randomly assigned to fluoxetine 20 mg/day or placebo added to depot neuroleptic for a 6-week, double blind trial. All patients had received a stable dose of depot neuroleptic for at least 6 months and did not meet criteria for depression. Serum samples were obtained at baseline and at weeks 4 and 6. Scores on the negative symptom subscale of the Brief Psychiatric Rating Scale (BPRS) were significantly lower at week 6, controlling for baseline scores, in patients receiving fluoxetine (n = 20) compared to patients receiving placebo (n = 21). Measures of psychosis, depression, global functioning and extrapyramidal symptoms (EPS) did not differ between groups at week 6. Fluoxetine administration was associated with a mean 65% increase in serum fluphenazine concentrations in 15 patients and a mean 20% increase in serum haloperidol concentrations in three patients. The change in negative symptoms at week 6 did not correlate with serum concentrations of fluoxetine or norfluoxetine, but did inversely correlate with S-norfluoxetine, an active stereoisomer of fluoxetine. For these chronically ill patients, fluoxetine significantly improved negative symptoms and did not worsen EPS, despite causing substantial elevation in serum concentrations of neuroleptics.

A bioequivalence study on perphenazine/amitriptyline combination compared three formulations (TST-1, TST-2 and REF) containing the same nominal dose of perphenazine, while TST-2 contained 20% less amitriptyline than the other two formulations. ANOVA-SNK on log-transformed partial areas AUC024 through AUC0∞ showed the intra-subject variabilities of perphenazine to be consistently higher than those of amitriptyline or nortriptyline. There was also a marked increase in intra-subject variability for perphenazine on extrapolating AUC0last to infinity. Thus, whhile the 1–2α confidence intervals (90% CIs) and ratios of geometric means for perphenazine fell within preset limits of 80–125% in all pairwise comparisons, the CIs for AUC0∞ violated the upper limit in comparisons of TST-2 and REF (or TST-2 and TST-1). This outcome could be attributed to high intra-subject variability on AUC0∞. ANOVA-SNK of amitriptyline identified a significant difference in extent of amitriptyline absorbed from TST-2 compared with TST-1 and REF. Thus, in pairwise comparisons between TST-1 and REF, all 90% CIs for amitriptyline partial areas AUC04 through AUC0∞ fell within 80–125% limits. In corresponding comparisons between TST-2 and REF (or TST-2 and TST-1), however, the lower limit of the 90% CIs for AUC01 through AUC0last consistently fell below the 80% cut off. By contrast, 90% CIs associated with the ratios Cmax/AUC04 through Cmax/AUC0∞ all fell within preset limits indicating no differences in absorption rate of amitriptyline, consistent with the theoretical argument that Cmax/AUC is influenced by rate but not extent of absorption. Thus the partial area method is applicable to the evaluation of both relative rate and extent of absorption from conventional release products. Similarly, analyses of nortriptyline data showed that the partial area method is also effective in the evaluation of rate and extent of formation of a metabolite in a bioequivalence study. The partial area method permits a greater number of plasma samples to be devoted to accurate estimation of tmax and Cmax since the necessity to estimate AUC0∞ is obviated.

Whereas some metabolites of antipsychotic drugs are psychoactive and contribute to clinical improvement, recent studies have provided evidence that certain metabolites contribute to side-effects which can be disabling enough to negate clinical improvement as regards the psychosis. The route of administration of the drug can determine the amount of metabolite produced in the body and affect how the patient feels in response to the treatment.

A study was carried out in 11 healthy young men to investigate the pharmacokinetics of chlorpromazine (CPZ) after a bolus intravenous (IV) dose (10 mg) and three single oral doses (25, 50 and 100 mg), with a washout period of two weeks between doses. Plasma levels of CPZ, CPZ N-oxide (CPZNO), CPZ sulfoxide (CPZSO) and both free and conjugated 7-hydroxy-CPZ (7-HOCPZ) were measured by extraction radioimmunoassays. CPZ exhibited multicompartmental pharmacokinetics in most subjects. There was wide between-subject variability in half life (11.05 h), volume of distribution (1215 l), volume of distribution at steady state (642 l) and mean residence time (8.88 h), whereas systemic clearance was somewhat less variable (76.6 l·h−1). All metabolites were present in measurable concentrations in the plasma of 9 of 11 subjects after IV CPZ, whereas free 7-HOCPZ was not detected in the other 2 individuals. With the exception of CPZNO, the biological half lives of the primary metabolites were longer than the half life of CPZ. After oral administration, the percentage of CPZ reaching the systemic circulation intact (F%) was very low (4–38%) and dose dependant. Moreover, both within-subject and between-subject variances were very high. The maximum plasma concentration (Cmax) and area under the plasma concentration versus time curve extrapolated to infinite time (AUC) showed evidence of nonlinearity, whereas half life did not appear to be dose dependant. These data suggest that the high degree of variability in the pharmacokinetics of CPZ is a result of extensive first pass metabolism rather than variation in half life. The mean AUC for the total conjugates of 7-HOCPZ was about two fold higher than that of the parent drug or any other metabolite. This shows that phase II metabolism plays a very significant role in the disposition of CPZ. As a result, the role of CYP2D6 in the 7-hydroxylation of CPZ cannot be fully assessed without taking phase II metabolism into account.

Attempts to investigate relationships between plasma levels of neuroleptics and therapeutic outcome in schizophrenic patients have been hampered due to such factors as the chemical nature of these drugs, their metabolism, and the very heterogeneous nature of the disease states. Two clinical studies are described that investigate the relationship between plasma levels of fluphenazine (FLU) and its metabolites and therapeutic outcome in schizophrenic patients. In the first of these studies the levels of FLU and fluphenazine sulfoxide (FLUSO) in schizophrenics receiving either 5 or 25 mg of fluphenazine decanoate (FLUD) intramuscularly every 2 weeks were monitored. Patients given 25 mg of FLUD required 3 months to reach plasma level steady state. The results suggest that such patients, when being switched from the oral to the depot formulation of FLU, should continue to receive oral supplementation during the 1st 3 months after conversion. The relationship between log-transformed plasma levels at 26 and 38 weeks with subsequent psychotic exacerbation was investigated with the use of logistic regression and survival analysis. Both demonstrated significant relationships between FLU plasma levels and a risk of psychotic exacerbation at 26 and 38 weeks. The possibility of any correlations between neurological side effects and plasma concentrations were also investigated, with statistically significant correlations between FLU levels and akinesia found at 2 and 26 weeks. In the second of these studies the levels of FLU, FLUSO, 7-hydroxyfluphenazine (7-OHFLU), and fluphenazine N4'(-)-oxide (FLUNO) in schizophrenics receiving 5, 10, or 20 mg of oral fluphenazine dihydrochloride daily for 4 weeks were monitored. The relationships between log-transformed plasma levels, disabling side effects, and global improvement were examined by logistic regression for the 4-week period. The study showed a significant correlation between increases in both plasma levels and disabling side effects such that at a plasma level of 2.7 ng/ml, approximately 90% of acutely ill patients experienced disabling side effects. Conversely, the study also showed that at a plasma level of 0.67 ng/ml, 48% of patients experienced improvement without the development of disabling side effects. When relationships between metabolite levels, disabling side effects, and global improvement were examined by logistic regression, a stronger correlation between disabling side effects and FLUNO levels than between side effects and FLU levels was found.(ABSTRACT TRUNCATED AT 400 WORDS)

Chlorpromazine N-oxide, fluphenazine N 4 ’-oxide, prochlor-perazine N 4 ’-oxide, sulforidazine N -oxide, and trifluoperazine N 4 ’-oxide were synthesized by oxidation of the designated nitrogen atom in the N- 10 side chain of the respective parent drug with 3-chloroperoxybenzoic acid. In the case of trifluoperazine, a stepwise increase in the amount of oxidant yielded the N 1 ,N 4 -dioxide and N 1 ’, N 4 ’,S-trioxide. The N’,S- dioxides of chlorpromazine and sulforidazine were obtained by hydrogen peroxide oxidation of the appropriate parent drug.

A definitive enantioselective pharmacokinetic evaluation of dl-threo-methylphenidate (MPH) was carried out in 11 healthy volunteers, all of whom received, in a randomized crossover design, three oral administrations of MPH: immediate release (IR), slow release (SR), and SR chewed before swallowing (CH). In addition, all subjects received MPH intravenously (IV) on a separate occasion. Both plasma and urine samples were collected for up to 16 hr after each drug administration. Significant enantioselective differences were found in pharmacokinetic parameters such as CL, MRT, Vdss, AUC infinity 0, and t1/2. A profound distortion of the enantiomeric ratio for MPH (d >> 1) was evident in all plasma samples harvested after oral administration. After IV MPH, however, there was no significant distortion in the plasma d/l ratio until 1.5 hr after dosing, whereafter there was a divergence of the plasma levels of the enantiomers. After oral administration of dl-MPH, the absolute bioavailability (F) of d-MPH was 0.23 and that of l-MPH was 0.05. There were no significant differences in renal clearance for d- or l-MPH after oral or IV administration, although the fraction of the dose excreted unchanged in the urine was significantly greater after IV MPH. These data suggest that enantioselective differences in the pharmacokinetics of oral MPH are the result of enantioselectivity in presystemic metabolism rather than in renal excretion, such that l-MPH is preferentially converted into l-ritalinic acid. Finally, it was found that chewing the slow release formulation led to a pharmacokinetic profile very similar to that of MPH-IR, suggesting that MPH-SR should not be prescribed for children who chew tablets.

Commercial preparations of the tricyclic anti-depressant doxepin contain 15% of the more active cis-doxepin and 85% of the trans-isomer. The single dose pharmacokinetics of doxepin and its major metabolite N-desmethyldoxepin were examined in 30 healthy young men. Results for total doxepin showed wide intersubject variation in all pharmacokinetic parameters except tmax and Cmax. Plasma levels of cis-doxepin were extremely low and it was only possible to estimate the stereoselective pharmacokinetics of the parent drug in 3 subjects. The data from those particular subjects resulted in an average ratio of cis- to trans-doxepin isomers in plasma of 15:85. In contrast, the mean plasma levels of cis-N-desmethyldoxepin in 28 subjects exceeded those of the trans-isomer at every time point after 10 h, such that the areas under the plasma concentration versus time curves (AUC) of cis-N-desmethyldoxepin were significantly higher than those of the corresponding trans-isomer. This phenomenon may play an important role in the therapeutic action of doxepin since it has been suggested that cis-N-desmethyldoxepin is pharmacologically active. In 2 subjects, however, the AUC0-inf of trans-N-desmethyldoxepin were respectively 4 and 8 fold higher than those of the cis-isomer.

This study was designed to investigate whether the addition of fenfluramine to neuroleptic therapy could produce an improvement in chronic schizophrenics who were limited responders to neuroleptics. Initially, each of 9 inpatients received at least 6 weeks’ treatment with placebo fenfluramine for baseline data collection. Thereafter, active fenfluramine therapy commenced at 60 mg/day with increments of 20 mg/day implemented every 2 weeks until a maximum daily dose of 120mg of fenfluramine was attained. This dosage level was maintained until fenfluramine was withdrawn by stepwise decrements, so that the duration of fenfluramine treatment did not exceed 12 weeks. The patients then continued to receive placebo fenfluramine for a minimum of 4 weeks for further evaluation and data collection. Throughout the study each patient was maintained on a constant dose of a neuroleptic drug. The stepwise addition of fenfluramine revealed significant correlations between dose and plasma concentrations for both isomers of fenfluramine and its pharmacologically active metabolite, nor-fenfluramine. Dose proportionality with the plasma concentrations of the isomers of parent and metabolite was also maintained during dose tapering. The plasma concentrations of the l-isomers of both fenfluramine and norfenfluramine were significantly higher than those of the corresponding d-isomers. Moreover, the l: d optical isomer ratios were constant at 1.9 for fenfluramine and 1.4 for norfenfluramine. Thus, it would appear that the enantioselective aspects of fenfluramine and its metabolite norfenfluramine were not affected by changes in the dose of fenfluramine. The presence of fenfluramine had no consistent effects on the steady-state plasma concentrations of either the neuroleptic drugs or metabolites.

Dehalogenation reactions of selected phenothiazine antipsychotic and tricyclic antidepressant drugs were studied during fast atom bombardment (FAB) mass spectral analysis. All of these halogenated compounds demonstrated the presence of ions corresponding to the loss of a halogen and its replacement by a hydrogen atom. The structure of the dechlorinated ion for chlorpromazine and the source of the hydrogen atoms replacing the chlorine were studied using perdeuterio-glycerol, accurate mass measurement and comparison of the spectrum with its authentic dechlorinated analog. In addition tandem mass spectrometric studies illustrated identical daughter ion spectra for the dechlorinated ion arising during FAB mass spectrometry of chlorpromazine and the analogous ion present in its unhalogenated analog promazine. The dechlorination process once started by exposure to the atom beam during static FAB mass spectrometry demonstrates an accumulation of dechlorinated ion with time. During continuous flow FAB where the sample is refurbished with time the extent of dechlorination remains relatively constant. The extent of dehalogenation was greater for chlorinated compounds as compared to fluorinated derivatives. The percentage exchange of chlorinated compounds ranged from 7.2% to 32.6% while the percentage exchange for triflupromazine was 3.3%. The recognition that such ions can arise during FAB mass spectrometry avoids the possible misinterpretation of such ions as being due to sample contamination or due to in vivo metabolic dehalogenation during metabolism studies.

1. The metabolism of chlorpromazine N-oxide was studied in female rats after a 20 mg/kg single i.p. dose. 2. Metabolites identified in urine and faeces were chlorpromazine, 7-hydroxychlorpromazine, chlorpromazine sulphoxide, N-desmethylchlorpromazine and N-desmethylchlorpromazine sulphoxide. As these same five metabolites were previously shown to be present after oral administration this indicates that reduction of chlorpromazine N-oxide occurs not only in the gastrointestinal tract but also at other sites. 3. The metabolism of chlorpromazine N-oxide was studied following its administration by either i.p., i.v. or oral routes to female rats in which the bile duct was cannulated. 4. There were no qualitative differences between the three routes of administration with respect to the metabolites identified. With the exception of the absence of N-desmethylchlorpromazine and N-desmethylchlorpromazine sulphoxide, all metabolites previously identified in urine and faeces were also present in bile. 5. Additionally there were three compounds present in rat bile which were not identified in urine or faeces. These were chlorpromazine N-oxide, chlorpromazine N,S-dioxide and 7-hydroxychlorpromazine O-glucuronide. This is the first unequivocal evidence for the identification of intact 7-hydroxychlorpromazine O-glucuronide in any species. 6. The inability to detect chlorpromazine N-oxide and chlorpromazine N,S-dioxide in the faeces of rats is likely to be due to the reduction of the N-oxide group on the passage of these biliary metabolites down the intestinal tract.

1. Two pilot studies were carried out to investigate the enantioselective pharmacokinetics of methylphenidate (MPH) in children with attention deficit-hyperactivity disorder (ADHD). A more definitive study, which included administration of an intravenous dose, was carried out in healthy young men. 2. Serial plasma samples were harvested from predose to 8 hours in the first pilot study, predose to 12 hours in the second pilot study and predose to 16 hours in the definitive study. Plasma levels of the separate isomers d-MPH and 1-MPH were determined by an enantioselective gas chromatographic method. 3. In the first pilot study, 6 boys with ADHD each received his regular dose of MPH (10mg n = 5, 5mg n = 1), which contained equal proportions of d-MPH and 1-MPH in an immediate release formulation (MPH-IR). No MPH was detectable in the predose plasma. Thereafter, plasma levels of the more active d-MPH were 4 to 10 fold higher than those of 1-MPH. Plasma levels of 1-MPH were so low that it was not possible to monitor them beyond 4 hours in some children. 4. In the second pilot study, 5 boys and 1 girl with ADHD each received their regular dose (20mg) of a slow release formulation (MPH-SR). No MPH was detectable in the predose plasma. Thereafter, plasma levels of the more active d-MPH were 5 to 10 fold higher than those of 1-MPH. It was possible to monitor plasma levels of 1-MPH over the full 12 hour period of study in 5 of the 6 children.(ABSTRACT TRUNCATED AT 250 WORDS)

HP 818 (1-benzoyl-6-fluoro-3-(1-methyl-4-piperidinyl)-1H-indazole) exhibits the profile of a potent nonnarcotic analgesic with neuroleptic properties. HP 818 blocks the effects of chemical (phenylquinone), pressure (tail clip), and radiant heat (tail flick) painful stimuli in mice (ED50 values of 0.3, 1.2, and 4.1 mg/kg s.c., respectively). This compound displays antinociceptive activity by the subcutaneous, oral, and intravenous routes of administration. It is also effective in the shock titration assay in squirrel monkeys and in a model of surgically induced pain. The rank order of potency of HP 818 and several other standard compounds in these tests for analgesia was Innovar > fentanyl > HP 818 > codeine > droperidol. In addition to its antinociceptive effects, HP 818 possesses neuroleptic properties. It is active in the climbing mouse, pole climb avoidance, and intracranial self-stimulation assays (ED50 values of 1.8, 1.7, and 2.5 mg/kg i.p., respectively). Moreover, HP 818 inhibits amphetamine- and apomorphine-induced stereotypy, indicative of D2-dopaminergic blocking properties. HP 818, unlike typical neuroleptic agents, does not induce supersensitivity to the effects of apomorphine when administered chronically in mice. In contrast to the clinical standard neuroleptanalgesic Innovar, HP 818 (1.0–3.0 mg/kg i.v.) produces no significant cardiovascular or respiratory changes in the anesthetized dog. Thus, HP 818 is potentially an effective presurgical medication due to its nonnarcotic analgesic activity and sedative neuroleptic effects, along with its lack of limiting cardiorespiratory side effects.

The comparative bioavailability of a new tablet formulation of fluphenazine dihydrochloride (5 mg) and a reference product (fluphenazine dihydrochloride, Prolixin, 5 mg) was assessed in drug-free psychiatric patients. Twenty-six patients were initially entered in the study, of whom 22 completed the protocol. Each patient received the test (T) and the reference formulation (R) in a balanced two-way crossover design. Plasma concentrations of fluphenazine were monitored over a period of 48 h after drug administration using a sensitive HPLC method. One patient did not show any measurable plasma concentration for one formulation at any sampling time and, therefore, bioavailability was assessed in the remaining 21 patients. All pharmacokinetic parameters showed wide intersubject variation. The maximum plasma concentration (Cmax), time to Cmax, and area under the curve up to the last measurable concentration (AUClast0), infinity (AUCinfinity0), or truncated areas (such as AUC16(0), AUC24(0) were compared by analyses of variance and found not to be significantly different in each case across the formulations. Except for AUC24(0), AUC32(0), and AUC48(0), ANOVA of all other parameters showed a high power (greater than 80%) to detect a 20% difference in the mean value of each bioequivalence parameter between T and R. The two formulations were found to be bioequivalent in that confidence intervals of the mean values of AUCinfinity0, AUClast0, truncated AUCs, or Cmax for T:R ratios were, in each case, well within the acceptable range of 100 +/- 20%.

Addressing the need for research on the nature of refractoriness to antipsychotic drug therapy exhibited by a substantial minority of schizophrenic patients, Philip R.A. May and Sven Jonas Dencker instigated an international study group to discuss this problem, beginning with the International Congress of Neuropsychopharmacology in Goteborg, Sweden, in 1980. The study group subsequently met in Haar, Federal Republic of Germany, in 1985; in Banff, Canada, in 1986; and again in Telfs, Austria, in 1988. The study group set three objectives: (1) to clarify the concept of treatment resistance or refractoriness; (2) to suggest criteria for defining or rating the degree of treatment refractoriness; and (3) to explore the role of psychosocial and drug therapies in increasing the responsiveness of the treatment refractory patient. This position article represents a distillation of the study group's efforts to define treatment refractoriness in schizophrenia.

1. Commercial doxepin contains geometric isomers in the proportions Z:E = 15:85. Z-doxepin and its metabolite Z-N-desmethyldoxepin are both active antidepressants, whereas the corresponding E-isomers are less active therapeutically. 2. The present pharmacokinetic study was a balanced, randomized, two-treatment, two-period, two-sequence crossover design in which 12 healthy male volunteers were given single doses of commercial doxepin intravenously and orally on two occasions separated by a washout period. 3. A two-compartment model with no lag time and first-order elimination fitted the plasma concentration-time curves after intravenous dosing. Pharmacokinetic parameters estimated from the model were comparable with those estimated by non-compartmental methods. 4. All pharmacokinetic parameters displayed a wide between-subject variability. Both isomers of doxepin showed large volumes of distribution and relatively short half-lives in plasma, suggestive of extensive distribution and/or tissue binding. The mean fraction absorbed after oral administration was 0.29 for each isomer. Renal clearances of each isomer were very low after either oral or intravenous dosing, although all four analytes were quantifiable in the urine for prolonged periods. 5. After oral dosing, plasma concentrations of the doxepin isomers remained roughly in the ratio Z:E = 15:85, whereas those of N-desmethyldoxepin were closer to 1:1 in all but two outliers, who had high levels E-N-desmethyldoxepin.

A physiological computer model was designed to simulate the metabolic drug-drug interactions between two orally co-administered drugs due to reversible enzyme inhibition using drug concentrations in the portal vein. The extent of interactions was compared at steady-state for the effects of a delay in time between the administration of the substrate and the inhibitor. It was demonstrated that the extent of the interactions can be strongly affected by a time interval between the two drug administrations. By delaying the administration of the inhibitor until after the absorption phase of the substrate, one can significantly reduce the extent of the drug--drug interactions. This is because drug concentrations in the portal vein and the liver are much higher than that in the systemic circulation during the absorption phase. The model also showed that interactions involving substrates with a high extraction ratio (E(H)), i.e., drugs with higher first-pass effect, can be more strongly affected by dose staggering. Substrates with a low absorption rate constant (k(a)) require a longer interval with the inhibitor in order to reduce the extent of the interactions. This observation suggests dose staggering as a simple and cost-effective way to reduce the extent of unwanted drug--drug interactions in clinical practice.

The potential utility of a pulse dose of a deuterium-labeled isotopomer (FLU-D(4)) in elucidating the pharmacokinetics of fluphenazine (FLU) at steady state was investigated in dogs. The single-dose oral pharmacokinetics of FLU in dogs were established. After resting the dogs for 3 weeks, the animals were dosed to steady state with oral FLU administered at 12-h intervals. Following 15 doses, one dose of FLU was replaced by a pulse dose of FLU-D(4), after which dosing with FLU was resumed. FLU and FLU-D(4) plasma concentrations were determined by tandem mass spectrometry. Comparable estimates of apparent oral clearance were calculated from (i) a single dose of FLU, (ii) a pulse dose of FLU-D(4), and (iii) over a dosing interval at steady state. Average steady-state plasma concentrations were reliably predictable from a pulse dose of FLU-D(4).

This study demonstrated that the mere fact that two multisource drug formulations are bioequivalent with the same reference formulation does not guarantee that they are bioequivalent with each other. The present unscaled bioequivalence limits (BEL) of 0.80 to 1.25 permitted far greater deviation from unity of the geometric mean ratio (GMR) for multisource formulations with low within-subject variabilities than for drugs with high variabilities. Scaling the BEL drastically reduced the maximum deviation from unity of GMRs for two multisource formulations each bioequivalent with the same reference product while broadening the BEL for highly variable drugs. It was concluded that scaling was consistent with the principle of switchability for toxic drugs with low variability and for safe, highly variable drugs. On the other hand, scaling need not be applied to safe drugs with low variability and should not be applied in the unusual case of a highly variable drug with a narrow therapeutic range.

Doxepin is a tricyclic antidepressant marketed as an irrational mixture of cis- and trans-geometric isomers in the ratio of 15:85. A convenient high-performance liquid chromatographic (HPLC) procedure for simultaneous quantitation of geometric isomers of doxepin and N-desmethyldoxepin in plasma and urine is described. The HPLC procedure employed a normal phase system with a silica column and a mobile phase consisting of hexane-methanol-nonylamine (95:5:0.3, v/v/v), a UV detector and nortriptyline as the internal standard. The liquid-liquid extraction solvent was a mixture of n-pentane-isopropanol (95:5, v/v). The limit of quantitation was 1 ng/ml for each isomer. The calibration curves were linear over the ranges 1-200 ng/ml (plasma) and 1-400 ng/ml (urine). In plasma, the accuracy (mean +/- S.D.) (97.53 +/- 1.67%) and precision (3.89 +/- 1.65%) data for trans-doxepin were similar to corresponding values for urine, i.e., 97.10 +/- 2.40 and 3.82 +/- 1.14%. Accuracy and precision data for trans-N-desmethyldoxepin in plasma were 97.57 +/- 2.06 and 4.38 +/- 3.24%, and in urine were 97.64 +/- 3.32 and 5.26 +/- 1.83%, respectively. Stability tests under three different conditions of storage indicated no evidence of degradation. The recovery of doxepin was 61-64% from plasma and 63-68% from urine. The method has been applied to analyses of plasma and urine samples from human volunteers and animals dosed with doxepin.

A highly sensitive and specific high-performance liquid chromatographic method with coulometric detection was developed for the simultaneous assay of fluphenazine decanoate and fluphenazine in plasma. The extraction and sample clean-up procedures are simple, rapid to execute, yet yield chromatograms relatively free of any interference from endogenous plasma constituents, such that the extraordinary sensitivity of the coulometric detector can be exploited fully. This is the first analytical procedure for the simultaneous determination of fluphenazine decanoate and fluphenazine. The detection limits for both fluphenazine decanoate and fluphenazine were 0.1 ng/ml plasma and the limits of quantitation were 0.25 ng/ml plasma. Standard curves from 0.25 to 10 ng/ml were linear with coefficients of variation < 10%. The method was applied to measure plasma levels of fluphenazine decanoate and fluphenazine in patients under medication with 25-50 mg biweekly intramuscular (i.m.) injections of fluphenazine decanoate. It was possible to monitor the plasma levels of fluphenazine in all cases. Fluphenazine decanoate was present in measurable concentration in the plasma of 4 out of 5 patients who received biweekly i.m. injections of 50 mg fluphenazine decanoate. In a pilot experiment with a dog, the method was used to follow fluphenazine decanoate and fluphenazine plasma levels up to 13 days, at least, after i.m. single dose (10 mg/kg).

HP 749 was absorbed slowly in the conscious monkey after single oral doses (10, 20, and 40 mg/kg), with gradual metabolism to the N-despropyl metabolite, P86-7480. The tmax was 2 to 4 hours after dosing, with nonlinear increases in Cmax and the AUC0-4th for HP 749. The calculated elimination half life (t1/2) after oral administration was 7.4 +/- 2.1 hours; however, absorption appeared to influence the terminal phase because the t1/2 after intravenous administration of 10 mg/kg was 1.5 hours. Plasma concentration of HP 749 2 minutes after intravenous bolus was 26.08 micrograms/mL. The HP 749 was rapidly distributed (t1/2 alpha = 0.064 +/- 0.033 hours) after intravenous administration, and displayed a VZ of 2.6 +/- 0.85 L/kg. The CL of HP 749 was 20.8 +/- 6.9 mL/min/kg, whereas renal clearance (CLR) of unchanged drug was only 0.13 +/- 0.04 mL/min/kg. Thus, only about 1% of the administered dose was excreted unchanged by the kidney. The P86-7480 also was rapidly distributed and eliminated after an intravenous bolus, but was less extensively distributed than HP 749. HP 749 administered either as an intravenous bolus or orally caused a significant pressor effect soon after dosing. A significant tachycardia resulted from intravenous administration, but not after oral administration of the drug. An intravenous bolus of P86-7480 (0.1 mg/kg) resulted in an immediate increase in MAP and decreased heart rate. The duration of these cardiovascular events was significantly shorter after intravenous administration of P86-7480 than with intravenous or oral administration of the parent drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Pooled plasma from healthy volunteers was spiked with pure, synthetic clozapine or clozapine N-oxide and then made alkaline with either sodium hydroxide or sodium carbonate. The alkalized samples were allowed to stand at room temperature for various time intervals before extraction with organic solvent and then analyzed by high-performance liquid chromatography. It was found that clozapine N-oxide was reduced to clozapine in plasma made alkaline with sodium hydroxide, but such reduction was negligible in the plasma made alkaline with sodium carbonate. The amount of clozapine produced from clozapine N-oxide depended upon both the strength of the alkali added to the plasma and the duration of exposure of the plasma proteins plus clozapine N-oxide to the alkali. The reduction appears to take place through reducing equivalents generated by the action of strong alkali on plasma proteins. The thermal lability of clozapine N-oxide during gas chromatography-mass spectrometric analysis was also investigated. It was found that clozapine N-oxide was quantitatively decomposed to clozapine during gas chromatography-mass spectrometric analysis.

The rationale for using the logarithmic transformation on concentration-dependent pharmacokinetic parameters a priori is presented. This rationale is based on theoretical pharmacokinetic and statistical grounds, but is also applicable to the practice of physicians in dealing with variations of drug treatment within and between patients. The implications of the transformation on data analysis, specifically analysis of variance, and estimation and inference from the analysis as it pertains to bioequivalence decisions are explored. Implementation of the transformation is shown, with an example of two perphenazine formulations in a single-dose crossover study. It is concluded that the transformation has to be accepted on theoretical grounds because sample sizes are too small in bioequivalence studies and too susceptible to extreme values to state with any certainty the actual distribution of pharmacokinetic parameters or their differences within a subject.

Haloperidol (HAL) is a potent butyrophenone antipsychotic agent which is reversibly metabolized to reduced haloperidol (RHAL). In order to determine if this reversible metabolic pathway is linked to the debrisoquine 4-hydroxylase isozyme of cytochrome P-450 (P450IID6). HAL (5 mg) or RHAL (5 mg) was orally administered to healthy male volunteers in a randomized crossover design both with and without a prior (1 h) oral dose of quinidine (250 mg bisulfate), a potent inhibitor of this isozyme. Thirteen volunteers, 11 extensive metabolizers, 2 poor metabolizers, completed all four phases of the study. Plasma samples harvested over seven days were analysed for HAL and RHAL. An expression for the apparent fractional availability of metabolite from the parent compound given (Fapppm) was derived and was used to determine whether HAL or RHAL is the preferred metabolite, and whether quinidine co-administration alters Fapp for either compound. The AUC (0-t) for both HAL and RHAL were significantly greater following the administration of either compound with quinidine compared with AUC (0-t) values obtained in the absence of quinidine. The maximum plasma concentration (Cmax) of the administered compound was also greater following the administration of quinidine. Quinidine had no effect on the half-lives of the administered compounds. The Fapp for HAL and RHAL were not significantly affected by the administration of quinidine, indicating that the interconversion of HAL and RHAl is not linked to P450IID6. The Fapp of RHAL after administration of HAL was significantly greater than the Fapp of HAL after RHAL administration, indicating that RHAL is the preferred metabolic form. This difference was not affected by quinidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Nine boys with attention-deficit hyperactivity disorder took part in a study in which d-methylphenidate, l-methylphenidate, dl-methylphenidate, or placebo were administered in a double-blind, four-way, randomized, crossover design. Plasma levels of the isomers of methylphenidate were monitored by means of an enantioselective assay method. The ability of the children to perform tasks that required sustained attention was monitored by a battery of computer tests. There was no evidence of interconversion between the enantiomers in vivo, although the presence of the d-isomer significantly altered the pharmacokinetics of the l-antipode. The presence of the l-isomer did not affect the pharmacokinetics of d-methylphenidate. The computer tests revealed a drug-induced improvement in sustained attention that was entirely attributable to the d-enantiomer. There was no evidence to suggest that the effectiveness of d-methylphenidate was in any way compromised by the presence of its antipode. Clinical Pharmacology and Therapeutics (1992) 52, 561–568; doi:10.1038/clpt.1992.185

Stereoselective urinary pharmacokinetics of dl-threo -methylphenidate (MPH) and its major metabolite, dl -ritalinic acid (RA), were examined in a cohort of healthy subjects. On two occasions, separated by one week, each subject received MPH · HCl either intravenously (10 mg) or orally (40 mg). Urine was collected in six time segments, up to 16 h after each dosing. In the first 2 h after oral administration of MPH, d -MPH found in the urine was 10-fold greater than the l -antipode, whereas there was no significant difference between the amounts of MPH enantiomers excreted after the intravenous dose. Examination of RA content in the 0-2-h urine samples after oral administration of MPH indicated the presence of higher levels of l -RA ( d -RA: l -RA, 0.37), whereas after intravenous MPH, there was no significant difference between the amounts of RA enantiomers. Moreover, after oral administration of MPH, the ratio of d -MPH to l -MPH was ~10 in urine samples from each of the time segments. By contrast, after intravenous administration of MPH, the d:l ratio changed progressively from 1.16 in the 0-2-h urine sample to 9.06 in the 12–16-h sample. These observations suggest that, after oral administration of dl -MPH, the distortion in the ratio of MPH or RA enantiomers in urine samples was attributable to enantioselective presystemic conversion of MPH to RA rather than to enantioselective excretion.

An observer-blind randomized, placebo-controlled, crossover study was conducted in 22 healthy male subjects. They received 2 g cefpirome or placebo intravenously following an overnight fast. One hour later they consumed a single 0.5 g/kg dose of alcohol. The treatments were reversed after a seven-day 'washout' period. Subjects were evaluated for any adverse events or 'disulfiram-like' symptoms. The effects of cefpirome on the pharmacokinetics of alcohol were also studied. There were no statistically significant differences in mean values for the various pharmacokinetic parameters for plasma alcohol between the cefpirome and placebo treatment groups. There were no side effects or 'disulfiram-like' reactions following consumption of alcohol in either group. A single iv dose of 2 g cefpirome was well-tolerated in healthy males and, moreover, pre-treatment with cefpirome did not adversely affect the metabolism of alcohol in these subjects.

Enantioselective in vitro hydrolysis of methylphenidate (MPH) by the blood esterases of seven mammalian species is reported. The species included rats, rabbits, dogs, cattle, horses, monkeys, and humans. In vitro incubations up to 8 h were carried out in plasma, red blood cells, and whole blood of the various species. Enantioselective differences were evident among the different species on comparison of the data obtained from the three biological fluids. The esterases present in plasma appeared to show greater activity in the hydrolysis of MPH in all species where comparison with the other two biofluids was possible. Only in the case of humans did esterases present in plasma and red blood cells demonstrate opposite enantioselectivity in the hydrolysis of MPH. Thus after 8 h incubation, the RR-MPH/SS-MPH ratios in plasma and red blood cells were 0.31 and 1.16, respectively.

The in vivo metabolism of compounds which contain N-oxide groups, either aliphatic or heteroaromatic tertiary amines, has not been extensively studied. Just as there are differences in the enzymes involved in the oxidation of the two different types of tertiary amines to their N-oxides, it might be expected that there will be differences in the effect such a group has on the overall metabolism of substrates. Therefore, in order to simplify discussion, the focus in this chapter will be on only one type, namely the N-oxides of aliphatic tertiary amines. However, it should be realized that compounds containing a heteroaromatic tertiary amine group are important as is illustrated by two drugs which possess such a functionality, namely chlordiazepoxide and minoxidil. In both these cases some of the major metabolites in man either retain the N-oxide group as such or form conjugates thereof (Thomas and Harpootlian, 1975; Johnson et al., 1983; Boxenbaum et al., 1977; also see Chapter 4).

When undertaking development of methodology to analyse a compound containing an N-oxide, it is important to consider whether the compound is the N-oxide of a tertiary aliphatic amine such as trimethylamine, or tertiary arylalkylamine such as dimethylphenylamine, or heteroaromatic amine such as pyridine or quinoline. The first two types are referred to here as aliphatic tertiary amines. It is established that there are chemical and metabolic differences between these two types of amine oxides. Generally the N-oxides of heteroaromatic amines are more stable both chemically than the N-oxides of aliphatic amines (Ochiai, 1967; Bickel, 1969; Jenner, 1971; Lindsay, 1979; Damani, 1985). A comparison of the stability of the two types of N-oxides to heat and some reducing agents is given in Table 3.1.

Enantioselective gas chromatographic assays for the quantitation of methylphenidate and its major metabolite ritalinic acid in plasma are described. The procedures involved the extraction of methylphenidate enantiomers from alkanised plasma. The plasma was then washed to ensure complete removal of methylphenidate before saturation with sodium carbonate to promote the extraction of ritalinic acid enantiomers with ethyl acetate-isopropanol (60:40) solvent mixture. Subsequently, ritalinic acid enantiomers were converted back into methylphenidate enantiomers by Fisher-Speier esterification. N-Heptafluorobutyryl-L-prolyl chloride, a chiral acylating reagent, was used to convert the enantiomers of methylphenidate into their corresponding diastereomeric amide derivatives, which were separated cleanly on an achiral capillary column (OV-225) and quantitated with electron-capture detection. The assays were sensitive, reliable and reproducible.

Highly specific and sensitive antisera for fluphenazine-N4'-oxide (FLUNO) were obtained from New Zealand white rabbits immunized with a bovine serum albumin conjugate of 7-(3-carboxypropionyl)propchlorperazine-N4'-oxide. One of the antisera was used to develop a radioimmunoassay (RIA) procedure that enabled for the first time the determination of steady-state plasma levels of FLUNO, an active metabolite, in patients treated with oral or intramuscular (i.m.) fluphenazine (FLU). This method has sufficient sensitivity to quantitate accurately 20 pg of FLUNO in 200 microliters of plasma extract with a coefficient of variation of less than 8%. The antiserum had negligible cross-reactivity (less than 2%) with FLU and its major metabolites such as FLU sulfoxide, 7-hydroxy-FLU, and N-deshydroxyethyl-FLU. To confirm that the developed RIA procedure specifically quantitated FLUNO, FLUNO was selectively reduced to FLU by sodium dithionite in plasma samples from patients. A good correlation (r2 = 0.9646) was observed between the total FLU level and the sum of FLU and FLU equivalent to FLUNO determined separately in the same plasma. The steady-state plasma concentrations of FLUNO in patients receiving a daily oral dose of 5 to 20 mg of FLU dihydrochloride ranged from 13 to 378% of that of FLU, whereas this value ranged from 10 to 214% in plasma samples from patients treated with a biweekly intramuscular (i.m.) dose of 5 mg of FLU decanoate.

Two analytical methods for the analysis of chlorpromazine (CPZ), a radioimmunoassay (RIA) and a GLC-MS method, were compared in a bioequivalence study of two CPZ tablet formulations (Thorazine: film coated and sugar coated). Thirty-six nonsmoking, healthy, male volunteers completed the study. Each subject ingested single doses (2 × 25 mg) of the test (T) and the reference (R) formulations in a two-way crossover design with a two-week drug-free interval between doses. Following each administration, plasma concentrations of CPZ were monitored over a period of 24 h by both RIA and GLC-MS methods. Plasma concentrations and pharmacokinetic parameters determined by either analytical method showed wide intersubject variation, with the GLC-MS data showing relatively higher magnitude of intersubject variation than the RIA data. In general, plasma concentrations measured by RIA were significantly different from those measured by GLC-MS (paired t tests: p 0.75: p < 0.0001). Similar statistical relationships were found between the plasma concentrations of CPZ determined by the two methods at each sampling time and the bioequivalence parameters area under the plasma level versus time curves up to the last measurable concentration (AUC0t) and the maximum plasma concentration (Cmax). Bioequivalence parameters AUC0t, AUC0∞, and (Cmax). determined separately from the data obtained by the two methods for the two formulations were examined by analyses of variance (ANOVA) and other criteria and tests for bioequivalence. Results of ANOVA, confidence intervals of test/reference ratios of AUC0t, AUC0∞, and Cmax, and statistical tests for bioequivalence indicated that, except for Cmax by GLC-MS, data generated by both methods indicated bioequivalence of the two formulations (i.e., test/reference ratio was within 100 ± 20%). The experiments suggest that despite significant differences between the absolute plasma concentration values obtained, both methods yielded data for the two formulations which demonstrated that they were bioequivalent.