Bioequivalence studies with metformin: comparability of reference tablets from different origins.

BACKGROUND: The choice of an appropriate reference product is still a problem within the European Union. When no direct comparisons between originator products in different countries are available, registration authorities are sometimes only prepared to grant registration for a generic product on the basis of a comparison with the originator product in the respective country. The aim of the investigation was therefore to evaluate the bioequivalence of reference products from different origins in two different bioequivalence trials with the same test drug. METHODS: Two separate bioequivalence trials were performed involving the oral administration of one test and two reference products containing 500 mg metformin. Both studies had a randomized, open, single-dose, three-period crossover design and were carried out in 24 healthy volunteers. The reference products in the first trial were Glucophage mite (Germany) and Diabex (Australia). In the second trial the reference drugs were Glucophage mite (France) and Glucophage mite (Switzerland). The results of each trial were analyzed regarding the bioequivalence of the respective reference drugs. FINDINGS: The reference drugs in each of both trials were bioequivalent: the 90% confidence intervals for both AUC(0-tlast) and C(max) were entirely within the acceptance range for bio-equivalence trials (0.80 - 1.25 for both parameters). INTERPRETATION: In the case of metformin, the reference products available in the countries examined were very similar. This retrospective analysis involving two studies, therefore, confirmed bioequivalence between these reference products.

Evaluation of the efficacy of a combined formulation (Grippostad-C) in the therapy of symptoms of common cold: a randomized, double-blind, multicenter trial.

BACKGROUND: The aim of the present trial was to evaluate the efficacy of a combined product in the treatment of common cold and to examine the contribution of the separate components. In the published literature there is conflicting data on the efficacy of agents used in the treatment of common cold, especially when given in drug combinations. METHODS: A prospective, randomized, double-blind, multicenter, 4-arm, controlled trial was carried out in 1,167 patients with common cold treated with one of the following medications: Grippostad-C, a combination of acetaminophen, caffeine, chlorpheniramine and ascorbic acid (verum), ascorbic acid (control), chlorpheniramine and ascorbic acid (reference 1), as well as acetaminophen, caffeine, and ascorbic acid (reference 2). A score of common cold symptoms (headache, throat pain, extremities and joint pain, cough, blocked nose, and disturbances of sleep quality) was the primary outcome. The test drug was first compared with the control using a hierarchic test strategy, then with reference 1, followed by reference 2 with the aim of proving superiority. FINDINGS: A clinically relevant and statistically significant difference was demonstrated at each level of the hierarchy. Grippostad-C was significantly superior to all other treatment groups, the combination of acetaminophen, caffeine, and ascorbic acid was significantly superior to the control, and the combination of chlorpheniramine and ascorbic acid was not statistically different from the control. INTERPRETATION: The efficacy of Grippostad-C for the treatment of common cold was proven. The findings demonstrate that the combination is superior to each of its separate components and each of the components has its own distinctive contribution to the efficacy of the combination product.

Influence of the cytochrome P4502D6*4 allele on the pharmacokinetics of controlled-release metoprolol.

AIM: The aim of the present paper was to compare the pharmacokinetics of metoprolol in homozygous Caucasian volunteers for the wild-type CYP2D6 allele (CYP2D6*1/CYP2D6*1) and heterozygous (CYP2D6*1/CYP2D6*4) Caucasians. METHODS: Thirty-six unrelated healthy male Caucasians were screened for two of the most frequently occurring mutant alleles (CYP2D6*3 and CYP2D6*4) using polymerase chain reaction (PCR). Twenty-four volunteers with a genotype suggesting a rapid hydroxylator phenotype were enrolled in a bioequivalence trial and each received in a randomized, cross-over fashion one of the three formulations compared. Each formulation contained 200 mg metoprolol tartrate/(tablet). In each of the three periods of the trial, one of the formulations was administered under fasting conditions in the morning on 4 consecutive days. Blood for quantification of metoprolol was drawn immediately before the last dose and in selected time intervals thereafter. A sensitive and specific high-performance liquid chromatography (HPLC) method with fluorescence detection was applied for the quantification of metoprolol. Pharmacokinetic parameters were determined for each subject and statistically compared in two groups of 16 homozygous (CYP2D6*1/CYP2D6*1) and six heterozygous (CYP2D6*1/CYP2D6*4) volunteers. RESULTS: Significant differences between homozygous and heterozygous individuals were observed for all pharmacokinetic parameters. The AUC in the course of one those interval of 24 h (AUCtau), minium steady-state concentration (C(min)ss) and average steady-state concentration (C(av)ss) values for heterozygous individuals were more than twice those of individuals. Significantly higher values for C(max)ss, t1/2, half-value duration (HVD) and mean residence time (MRT) were also observed in heterozygous volunteers. The higher concentrations of metoprolol in heterozygous individuals also had pharmacodynamic consequences, namely, greater heart rate and blood pressure reduction.

Effect of cimetidine on the pharmacokinetics of the metabolites of metamizol.

Metamizol (dipyrone) is hydrolyzed in the gastrointestinal tract to the pharmacologically active metabolite 4-methyl-amino-antipyrine (4-MAA), which is transformed by both, oxidation to 4-formyl-amino-antipyrine (4-FAA) and demethylation to 4-amino-antipyrine (4-AA). 4-AA is acetylated to 4-acetyl-amino-antipyrine (4-AcAA). The aim of the present study was to investigate whether cimetidine will alter the pharmacokinetics of the metabolites of metamizol due to cimetidine-induced inhibition of the metabolic transformation of 4-MAA. The study was carried out in 12 patients with duodenal ulcer treated with cimetidine 1,000 mg daily over 20 days. A single oral dose of metamizol 1,500 mg was administered 2 days prior to commencement of cimetidine therapy to all patients. Two further doses of 750 and 1,500 mg of metamizol were given in a randomized order on days 8 and 13 during cimetidine treatment. Blood samples for determination of metamizol metabolites were drown over 48 hours post dose. Drug assays for metamizol metabolites and cimetidine were performed using HPLC methods. The patients were phenotyped for CYP2D6 and acetylation polymorphism. The results revealed that cimetidine interacted with 4-MAA by increasing the systemic availability, prolonging the elimination half-life and decreasing the systemic clearance of 4-MAA, whereas the renal clearances of 4-MAA remained unchanged. Consistent with cimetidine-induced changes in the oxidation of 4-MAA to 4-FAA, as well as in the demethylation of 4-MAA to 4-AA, were the decreased rates of production and the lower maximum concentrations of 4-FAA and 4-AA when metamizol was administered during cimetidine treatment (p < 0.05). No correlation was found between the decrease in the production rates of 4-FAA induced by cimetidine and the hydroxylation abilities of the patients, this suggesting that CYP2D6 is not involved in the metabolism of 4-MAA to 4-FAA. The acetylation of 4-AA to 4-AcAA was not affected by cimetidine. Cimetidine produced an increase not proportional to the dose in the systemic availability only of 4-MAA, whereas the kinetics of the other metabolites changed proportionally to the increasing dose of metamizol.

Double-blind randomized multicenter study on the efficacy of trapidil versus isosorbide dinitrate in stable angina pectoris.

BACKGROUND: Trapidil is an inhibitor of phosphodiesterase I-IV with resulting positive lusitropic, vasodilating, and antiplatelet effects. HYPOTHESIS: This study was undertaken to compare the antianginal efficacy of trapidil with that of isosorbide dinitrate (ISDN) in patients with stable angina pectoris. METHODS: We studied 95 patients with stable angina pectoris who were randomized into a double-blind parallel group study with either oral trapidil or ISDN. After a 1-week run-in period and a 2-week wash-out phase, the patients received either trapidil 200 mg t.i.d. (n = 48) or ISDN 20 mg t.i.d. (n = 47) for 12 weeks. All antianginal medication, except sublingual glyceryl trinitrate (GTN), was discontinued during the study. Patients underwent an exercise electrocardiogram on an ergometer bicycle according to a modified Bruce protocol before and at 6 and 12 weeks during treatment. RESULTS: The workload capacity increased from 583 +/- 281 W.min before treatment to 833 +/- 444 W.min after 12 weeks of treatment in the trapidil group (p < 0.01) and from 555 +/- 276 W.min to 827 +/- 361 W.min in the ISDN group (p < 0.01). The anginal attacks per week as well as the use of GTN decreased significantly in both groups. After 12 weeks of therapy, the cumulative ST-segment depression during exercise decreased by 67% in the trapidil patients and by 23% in the ISDN patients. Compared with baseline, the double product at the 75 W level was reduced in both groups after 12 weeks of treatment. Blood pressure and heart rate at rest remained nearly unchanged. Overall, no statistical difference was found between the two study groups. The tolerability was good. CONCLUSION: Oral trapidil therapy is safe and effective in stable angina pectoris and is equivalent to standard therapy with ISDN.

Genetic factors and risk of agranulocytosis from metamizol.

The role of genetic factors in the pathogenesis of agranulocytosis was investigated in agranulocytosis patients by phenotyping for N-acetyltransferase and glucose-6-phosphate polymorphism; by typing for gene products of the major histocompatability complex, ABO- and RH-blood groups, and haemoglobins; and by performing cytogenetic analysis of chromosome aberrations. Nine persons were identified as agranulocytosis cases in the period from 1982 to 1987 among the population of Sofia. They were contacted again 10 years after recovery from the disease. Five of them were associated with metamizol (dipyrone) use. The results obtained revealed significant differences between the agranulocytosis patients and the healthy population in the human lymphocyte antigen (HLA) allele frequencies, and in the degree and the frequency of chromosome aberrations. A higher frequency of the HLA24 antigen (relative risk 13.60, p = 0.05) and a lower frequency of the DQA1*0501 allele were evident for the ex-agranulocytosis patients as compared to the controls (11% versus 57% respectively, p = 0.05). In the patients exposed to metamizol, an A24-B7 haplotype was found with a frequency higher than that in the non-exposed patients and the reference group (p < 0.05). The HLA-DQwl antigen and metamizol-related agranulocytosis were evidently associated in all cases (5/5;100%) in contrast to the patients not exposed to metamizol and the controls. The HL-A2 antigen was absent in four of the five metamizol-associated agranulocytosis cases (20%), while in the control group it was present in 56%. The degree of structural rearrangements (0.62 +/- 0.2%) and the frequency of chromosome breakages (7.75 +/- 0.68%) in agranulocytosis patients were higher than those in the healthy population (0.3 +/- 0.12%, p < 0.05 and 1.42 +/- 0.27%, p < 0.01, respectively). The abnormalities affected predominantly chromosomes 1(1p13), 2(2p12) and 5(5p12). No differences were found between the agranulocytosis patients and the healthy population when considering the haemoglobin subtypes, ABO-and RH-blood groups, glucose-6-phosphate dehydrogenase activity and the rates of slow and rapid acetylators.

Comparative bioavailability of two oral metamizole formulations. Influence of the acetylation phenotype.

The bioavailability of the four metabolites of metamizole (CAS 68-89-3), 4-methyl-amino-antipyrine (4-MAA), 4-formyl-amino-antipyrine (4-FAA), 4-amino-antipyrine (4-AA) and 4-acetyl-amino-antipyrine (4-AcAA) was compared after oral administration of a test (Analgin) and a reference formulation, both containing 1 g of metamizole. The study was conducted in 12 healthy volunteers according to an open, randomized, cross-over design. The geometric mean of the area under the serum concentration-time curves (AUC) of 4-MAA for the test formulation was 87.61 (57.58-133.30) micrograms.h/ml and was similar to that for the reference formulation (86.83; 53.86-139.92 micrograms.h/ml). No statistically significant differences between test and reference formulation were found with respect to the rate of absorption (Cmax, tmax, 100 Cmax/AUC) of 4-MAA. For 4-FAA, 4-AA and 4-AcAA, the 90% confidence intervals of the bioavailability parameters lay also within the bioequivalence ranges. Four of the subjects were rapid and eight were slow acetylators. No differences were found between slow and rapid acetylators in the bioavailability of 4-MAA, the pharmacologically active metabolite of metamizole.

Effect of verapamil and diltiazem on the rCBF and the rCBF autoregulation in cortex and thalamus of cats.

The effects of Verapamil and Diltiazem, administered at a dose of 0.3 mg/kg i.v., on the autoregulation of the regional cerebral blood flow (rCBF) in the cortex and the thalamus were studied on 28 cats. The animals were anesthetized with ether and alfa-chloralose. The rCBF was registered by the hydrogen clearance method with locally generated hydrogen. The mean arterial blood pressure (MABP) elevation was performed by an i.v. infusion of angiotensin (0.2 microgram/min). The mean initial values of the cortical rCBF were 71.15 ml/100g/min and of the thalamic rCBF -46.85 ml/100 g/min. The mean limits of the cortical rCBF autoregulation were: 137.5 mm Hg for the absolute limit (La) and 31.25 mm Hg for the relative limit (Lr). The mean limits of the thalamic rCBF autoregulation were: 157.75 mm Hg for the (La) and 46.5 mm Hg for the (Lr). Verapamil increased the cortical rCBF by 40% and the thalamic rCBF by 24%. The absolute limits of rCBF autoregulation were decreased by 22% in the cortex, and by 15% in the thalamus. The relative limits were decreased by 31% in the cortex and by 35% in the thalamus. Diltiazem increased the cortical rCBF by 42% and the thalamic rCBF by 6%. The absolute limits of rCBF autoregulation were decreased by 21% in the cortex and the thalamus. The relative limits were decreased by 52% in the cortex, and by 38% in the thalamus.

Effects of nimodipine and flunarizine on the regional autoregulation of the CBF in cats.

The effects of nimodipine (3 micrograms/kg/min) and flunarizine (60 micrograms/kg/min) on the autoregulation of the regional cerebral blood flow (rCBF) in the cortex and thalamus of 28 cats were studied. The animals were anaesthetized with ether and alfa-chloralose. The rCBF was registered by the hydrogen clearance method with locally generated hydrogen. MABP elevation was performed by i.v. angiotensin infusion (0.2 +/- g/min). The initial values of the rCBF in the cortex were 71.1 ml/100g/min, and in the thalamus - 49.1 ml/100g/min. The limits of rCBF autoregulation in the cortex were: the absolute limit of autoregulation (La) 139 +/- 11 mm Hg, and the relative limit of autoregulation (Lr), 28 +/- 6 mm Hg. In the thalamus these values were: La 160 +/- 11 mm Hg, and Lr 47 +/- 7 mm Hg. Nimodipine increased the rCBF in the cortex by 58 per cent, and in the thalamus, by 38 per cent as compared to the initial values (p < 0.01). The limits of rCBF autoregulation in the cortex changed to 88 +/- 8 mm Hg for the La, and to 10 +/- 4 mm Hg for the Lr (p < 0.01); and in the thalamus, to 92 +/- 8 mm Hg for the La, and to 19 +/- 5 mm Hg for the Lr (p < 0.01). Flunarizine increased the rCBF in the cortex by 28 per cent, and in the thalamus by 24 per cent, as compared to the initial values (p < 0.01). The rCBF autoregulation in both cerebral structures was not influenced by flunarizine.

The distribution of ciprofloxacin and its metabolites in human plasma, pulmonary and bronchial tissues.

The disposition of ciprofloxacin and its pharmacologically active metabolites (sulfociprofloxacin, oxociprofloxacin, and desethylenciprofloxacin) in plasma, lung and bronchial tissues was studied in 24 patients undergoing a partial or total resection of the lung. The patients were divided into four groups, a control group and groups in which ciprofloxacin (200 mg) was given i.v. 1, 2 and 3 h before surgery. The concentrations of ciprofloxacin and its metabolites were determined by high performance liquid chromatography (HPLC). Ciprofloxacin concentrations in lung tissue were four times and in bronchial tissue twice those in plasma (p less than 0.01). The individual tissue concentrations of ciprofloxacin correlated with the individual plasma concentrations (r = 0.95 for lung; r = 0.94 for bronchi; p less than 0.001). Metabolite concentrations in both tissues and plasma were 10- to 100-fold lower than the concentrations of ciprofloxacin. These data suggest that the concentrations of the parent compound are essential for the therapeutic efficacy of ciprofloxacin.

Pharmacokinetics and biliary concentrations of fleroxacin in cholecystectomized patients.

Patients with biliary tract infections received 800 mg of fleroxacin orally once daily on five consecutive days; cholecystectomy was on day 3. Starting on the day when dose 5 was administered, serial blood and T-drain bile samples were taken for 72 h and urine was collected for 96 h. The mean (+/- the standard deviation) peak concentration in plasma was 8.2 +/- 4.0 mg/liter at 8.3 h. The harmonic mean elimination half-life was 10.5 h, which is comparable to that reported for healthy volunteers. This increase resulted from reduced renal clearance (mean [+/- standard deviation], 38 +/- 22 ml/min), as the volume of distribution in the patients (1.4 +/- 0.7 liter/kg) did not differ from that reported for healthy subjects. Maximum concentrations in T-drain bile were high (median, 22.1 mg/liter) and exceeded those measured in plasma by a factor of 2 to 3; the individual ratios of the area under the curve for bile divided by that for plasma ranged from 1.3 to 9.9. As observed in healthy volunteers, the major pathway for elimination of fleroxacin was via the kidneys. The fraction of dose 5 eliminated in the 0- to 24-h urine was reduced, however, and the fraction of the dose in the urine as the N-demethyl and N-oxide metabolites was elevated. At the dose regimen used in this study, the MICs for most pathogens that cause biliary tract infections were surpassed in plasma and bile for more than 24 h.

Cisapride and cimetidine in the treatment of erosive esophagitis.

The efficacy of cisapride, as compared with cimetidine, in the treatment of erosive esophagitis was studied in a double-blind trial. One hundred and twenty-nine patients were assigned to one of four dosage schedules: cisapride 10 mg b.i.d. (20 mg group) or q.i.d. (40 mg group), or cimetidine 400 mg b.i.d. (800 mg group) or q.i.d. (1600 mg group). Treatment lasted 8 to 12 weeks. The degree of esophagitis and the severity of diurnal and nocturnal heartburn and regurgitation were significantly (p less than 0.01) reduced in the four treatment groups. Endoscopy did not show any significant differences among the four groups, although cisapride tended to be more effective in moderate to severe esophagitis, in which cases mucosal healing (i.e. absence of erosions and ulcers) was observed in 69%, 64%, 55% and 55% of the patients treated with cisapride 40 mg, cisapride 20 mg, cimetidine 1600 mg and cimetidine 800 mg. Improvement in reflux symptoms in the two cisapride groups was not significantly different from that in the cimetidine 1600 mg group, but was better (p less than 0.05) than that in the cimetidine 800 mg patients. The severity score for all reflux symptoms had decreased by 79%, 74% (cisapride 40 mg and 20 mg), 69% and 57% (cimetidine 1600 mg and 800 mg) by the end of treatment. These results show that cisapride is at least as effective as acid-suppressing therapy in patients with reflux esophagitis, and is therefore a valuable alternative to it.

Pharmacokinetics of metamizol metabolites in healthy subjects after a single oral dose of metamizol sodium.

The linearity of the pharmacokinetics of the metamizol metabolites 4-methyl-amino-antipyrine (4-MAA), 4-amino-antipyrine (4-AA), 4-formyl-aminoantipyrine (4-FAA), and 4-acetyl-amino-antipyrine (4-AcAA) has been studied after administration to 15 healthy male volunteers of single oral doses of 750, 1500, and 3000 mg metamizol. The trial was open, randomized, and cross-over, with a one-week interval between dosing days. Metabolite concentrations in serum and urine were measured using reverse-phase HPLC. The mean Cmax of 4-MAA increased linearly with dose whereas its AUC was not proportional to dose after administration of 1500 and 3000 mg. With 4-AA, the increase in mean Cmax was linear, but the increase in AUC was not. The increases in mean Cmax and AUC for 4-FAA after doses of 1500 and 3000 mg were not proportional to the dose. The increases in mean Cmax and AUC for 4-AcAA were roughly proportional to the increase in dose. There were no significant differences in renal clearance between doses for any of the four metabolites. The observed non-linearities reflect the saturability of metabolic pathways. However, although they were statistically significant, the deviations from linearity were marginal and should not be of clinical relevance to the analgesic efficacy of metamizol in the dose range tested.

Protective effect of rioprostil on indomethacin-induced lesions of gastric and duodenal mucosa in healthy volunteers.

The protective effect of rioprostil against gastroduodenal mucosal lesions induced by indomethacin is investigated in a double-blind controlled trial on 36 healthy adult volunteers, divided into three groups. All the volunteers are treated with indomethacin, 50 mg t.d.s. during a period of 5 days. The first group is treated with placebo, the second with rioprostil, 300 micrograms, and the third with rioprostil, 600 micrograms. Endoscopies are performed before and after treatment. Blood samples for high performance liquid chromatography determination of indomethacin plasma concentrations are taken on the 6th day, before the last dose of indomethacin is administered, and 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 12 and 24 h after the last dose of indomethacin. It is found that in both doses rioprostil exerts a protective effect against indomethacin-induced lesions, reducing the appearance rate of erosions from 67% to 17% statistically significant in the 600 micrograms group. The bioavailability of indomethacin in the three groups does not differ significantly.

Effects of beta-adrenergic agents on the regional cerebral blood flow in cortex and thalamus of the cat.

The effects of the beta-adrenergic agents isoprenaline, terbutaline, l,d-propranolol, acebutolol, as well as d-propranolol, on the regional cerebral blood flow (rCBF) in cortex and thalamus and arterial blood pressure (ABP) were investigated following i.v. administration. The experiments were performed in 64 cats anaesthetized with ether and chloralose. The rCBF was measured using the thermistor thermoclearance technique. Isoprenaline, as well as terbutaline (1, 3, 5 micrograms/kg) decreased the cortical rCBF and the ABP (p less than .05). Both adrenergic agonists increased the thalamic rCBF despite the decrease in ABP (p less than .05). L,d-propranolol (1 mg/kg) abolished the effects of isoprenaline and terbutaline on thalamic rCBF. Acebutolol (0.6 mg/kg) or d-propranolol (0.5 mg/kg) did not alter isoprenaline- and terbutaline-induced effects on rCBF in thalamus. L,d-propranolol decreased the thalamic rCBF, whereas d-propranolol increased the rCBF in thalamus (p less than .05). Acebutolol did not change the thalamic rCBF significantly. The results obtained indicate that beta-adrenergic agents have heterogeneous effects on rCBF in cortex and thalamus. Their effects on thalamic rCBF seem to be accomplished by beta 2-adrenoceptor stimulation.

Comparison of the antihypertensive effects of celiprolol and acebutolol.

The antihypertensive effects of the new cardioselective beta-blocker celiprolol and acebutolol have been compared. Thirty patients with arterial hypertension WHO Grade I-II were treated in a double-blind fashion with celiprolol or acebutolol. Before starting the treatment and on Days 15 and 29, before the morning dose, blood samples were taken for measurement of the plasma level of celiprolol. At the same times physical examinations, and clinical and urine chemistry analyses were performed. At the 99% probability level both drugs had significantly lowered the systolic and diastolic blood pressures to normal values at the end of the second and fourth weeks. There was no significant difference between their antihypertensive efficacy. The decrease in diastolic blood pressure at the end of the second week was significantly correlated with the reciprocal of the plasma celiprolol concentration at steady-state at the end of the dosage interval.

Autoregulation of the regional cortical and thalamic cerebral blood flow in cats.

The autoregulation of regional cerebral blood flow (rCBF) in cortex and thalamus upon an increase in systemic arterial blood pressure (ABP) was investigated in 27 cats before and after pretreatment with phentolamine (1 mg/kg, i.v.), propranolol (1 mg/kg, i.v.) or acebutolol (1.2 mg/kg, i.v.). The animals were anaesthetized with ether and chloralose. rCBF was measured by thermistor thermoclearance technique. ABP elevation was produced by angiotensin i.v. infusion. rCBF autoregulation was evaluated using different criteria--limits and indices of autoregulation. The data obtained indicate that thalamic rCBF is more resistant to ABP elevation than cortical rCBF. Phentolamine did not change rCBF autoregulation in cortex and thalamus. Propranolol did not change the cortical but increased the thalamic rCBF resistance to ABP elevation. Acebutolol did not influence rCBF autoregulation in thalamus. The results suggest that different mechanisms are involved in rCBF autoregulation in cortex and thalamus. They can be selectively influenced by pharmacological agents.