Multiple molecular targets mediated antioxidant activity, molecular docking, ADMET, QSAR and bioactivity studies of halo substituted urea derivatives of α-Methyl-l-DOPA.

A series of novel α-methyl-l-DOPA urea derivatives viz., 3-(3,4-dihydroxyphenyl)-2-methyl-2-(3-halo/trifluoromethyl substituted phenyl ureido)propanoic acids (6a-e) have been synthesized from the reaction of α-methyl-l-DOPA (3) with various aryl isocyanates (4a-e) by using triethylamine (5, TEA) as a base catalyst in THF at reflux conditions. The synthesized compounds are structurally characterized by spectral (IR, 1H &13C NMR and MASS) and elemental analysis studies and screened for their in-vitro antioxidant activity against DPPH, NO and H2O2 free radical scavenging assays and identified compounds 6c &6d as potential antioxidants. The acquired in vitro results were correlated with the results of molecular docking, ADMET, QSAR and bioactivity studies performed for them and predicted that the recorded in silico binding affinities are in good correlation with the in vitro antioxidant activity results. The molecular docking analysis has comprehended the strong hydrogen bonding interactions of 6a-e with 1CB4, 1N8Q, 3MNG, 1OG5, 1DNU, 3NRZ, 2CDU, 1HD2 and 2HCK proteins of their respective SOD, LO, PRXS5, CP450, MP, XO, NO, PRY5 and HCK enzymes. This has sustained the effective binding of 6a-e and resulted in functional inhibition of selective aminoacid residues to be pronounced as multiple molecular targets mediated antioxidant potent compounds. In addition, the evaluated toxicology risks of 6a-e are identified with in the potential limits of drug candidates. The conformational analysis of 6c & 6d prominently infers that urea moiety uniting α-methyl-l-DOPA with halo substituted aryl units into a distinctive orientation to comply good structure-activity to inhibit the proliferation of reactive oxygen species in vivo.

Monitoring simultaneous photocatalytic-ozonation of mixture of pharmaceuticals in the presence of immobilized TiO2 nanoparticles using MCR-ALS: Identification of intermediates and multi-response optimization approach.

The present study has focused on the degradation of a mixture of three pharmaceuticals, i.e. methyldopa (MDP), nalidixic acid (NAD) and famotidine (FAM) which were quantified simultaneously during photocatalytic-ozonation process. The experiments were conducted in a semi-batch reactor where TiO2 nanoparticles (crystallites mean size 8nm) were immobilized on ceramic plates irradiated by UV-A light in the proximity of oxygen and/or ozone. The surface morphology and roughness of the bare and TiO2-coated ceramic plates were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). An analytical methodology was successfully developed based on both recording ultraviolet-visible (UV-Vis) spectra during the degradation process and a data analysis using multivariate curve resolution with alternating least squares (MCR-ALS). This methodology enabled the researchers to obtain the concentration and spectral profiles of the chemical compounds which were involved in the process. A central composite design was used to study the effect of several factors on multiple responses namely MDP removal (Y1), NAD removal (Y2) and FAM removal (Y3) in the simultaneous photocatalytic-ozonation of these pharmaceuticals. A multi-response optimization procedure based on global desirability of the factors was used to simultaneously maximize Y1, Y2 and Y3. The results of the global desirability revealed that 8mg/L MAD, 8mg/L NAD, 8mg/L FAM, 6L/h ozone flow rate and a 30min-reaction time were the best conditions under which the optimized values of various responses were Y1=95.03%, Y2=84.93% and Y3=99.15%. Also, the intermediate products of pharmaceuticals generated in the photocatalytic-ozonation process were identified by gas chromatography coupled to mass spectrometry.

Development and validation of a simple spectrophotometric method for the determination of methyldopa in both bulk and marketed dosage formulations

A simple, precise, sensitive, rapid, specific and economical spectrophotometric method was developed to determine methyldopa (MTD) content in bulk and pharmaceutical dosage formulations. The proposed method was based on the formation of a colored product from the nitrosation reaction of MTD with sodium nitrite in an acid medium. The resultant nitroso derivative species reacts further with sodium hydroxide and is converted it into a more stable compound. This yellow nitrosation product exhibited an absorption maximum at 430 nm. Beer's Law was obeyed in a concentration range of 6.37 to 82.81 μg mL-1 MTD with an excellent coefficient of determination (R 2 = 0.9998). No interference was observed from common excipients in formulations. The results showed the method to be simple, accurate and readily applied for the determination of MTD in pure form and in pharmaceutical preparations. The analytical results obtained for these products using the proposed method are in agreement with those of the Brazilian Pharmacopoeia procedure at a 95% confidence level.

Desenvolveu-se método espectrofotométrico simples, preciso, sensível, rápido, específico e econômico para a determinação do teor de metildopa (MTD) em matéria-prima e em formulações farmacêuticas. O método proposto baseia-se na formação de um produto colorido resultante da reação de nitrosação da MTD com nitrito de sódio em meio ácido. A espécie resultante (nitroso derivado) reage com hidróxido de sódio e é convertida a um composto mais estável de cor amarela. Este produto exibiu máximo de absorção a 430 nm. A lei de Beer foi obedecida na faixa de concentração de 6,37 a 82,81 μg mL-1 de MTD com excelente coeficiente de determinação (R 2 = 0,9998). Não se observou interferência de excipientes comumente encontrados em formulações farmacêuticas comerciais. Os resultados demonstraram que o método proposto apresenta simplicidade, excelentes precisão e exatidão e pode ser aplicado para a determinação de MTD na sua forma pura e em preparações farmacêuticas. Os resultados analíticos obtidos pelo método proposto estão de acordo com aqueles obtidos pelo método oficial descrito na Farmacopéia Brasileira, a um nível de confiança de 95%.

Development and validation of a high-performance liquid chromatography-electrospray ionization-MS/MS method for the simultaneous quantitation of levodopa and carbidopa in human plasma.

A sensitive and fast high-performance liquid chromatography-electrospray ionization-MS/MS method for the simultaneous quantitation of levodopa and carbidopa in human plasma was developed and validated. A simple protein precipitation step with perchloric acid was used for the cleanup of plasma, and methyldopa was added as an internal standard. The analyses were carried out using an ACE C(18) column (50 × 4.6 mm i.d.; 5 µm particle size) and a mobile phase consisting of 0.2% formic acid and acetonitrile (90:10). The triple-quadrupole mass spectrometer equipped with an electrospray source in positive mode was set up in the selective reaction monitoring mode to detect the ion transitions m/z 198.1 → m/z 107.0, m/z 227.2 → m/z 181.0, and m/z 212.1 → m/z 139.2 for levodopa, carbidopa, and methyldopa, respectively. The method was validated and proved to be linear, accurate, and precise over the range 50-5000 ng/mL for levodopa and 3-600 ng/mL for carbidopa. The proposed method was successfully applied in a pharmacokinetic study with a levodopa/carbidopa tablet formulation in healthy volunteers.

Simultaneous quantitation of levodopa and 3-O-methyldopa in human plasma by HPLC-ESI-MS/MS: application for a pharmacokinetic study with a levodopa/benserazide formulation.

A sensitive and simple method was developed for the quantitation of levodopa and its metabolite 3-O-methyldopa, in human plasma, after oral administration of tablet formulations containing levodopa (200 mg) and benserazide (50 mg). The analytes were extracted by a protein precipitation procedure, using carbidopa as an internal standard. A mobile phase consisting of 0.2% formic acid and acetonitrile (94:6, v/v) was used and chromatographic separation was achieved using ACE C(18) column (50 mm×4.6 mm i.d.; 5 µm particle size). Selected reaction monitoring was performed using the fragmentation transitions m/z 198→m/z 107, m/z 212→m/z 166 and m/z 227→m/z 181 for levodopa, 3-O-methyldopa and carbidopa, respectively. Calibration curves were constructed over the range 50.0-6000.0 ng/mL for levodopa and 25.0-4000.0 ng/mL for 3-O-methyldopa. The method shown to be specific, precise, accurate and provided recovery rates higher than 85% for all analytes. No matrix effect was detected in the samples. The validated method was applied in a pharmacokinetic study with a levodopa/benserazide tablet formulation in healthy volunteers.

Determination of L-dopa, carbidopa, 3-O-methyldopa and entacapone in human plasma by HPLC-ED.

The aim of the study was the development of analytical methods suitable for the quantification of L-dopa, carbidopa and entacapone in plasma of Parkinsonian patients treated with Stalevo(®). The metabolite 3-O-methyldopa was also determined to obtain some indications on the pharmacokinetics of L-dopa. For the simultaneous analysis of L-dopa, 3-O-methyldopa and carbidopa, a RP C18 column as the stationary phase and a mixture of methanol and a pH 2.88 phosphate buffer (8:92, v/v) as the mobile phase were used. A feasible plasma pre-treatment based on protein precipitation was implemented, obtaining extraction yield higher than 94% for all the analytes. For the analysis of entacapone a RP C8 column and a mixture of methanol, acetonitrile and a pH 1.90 phosphate buffer as the mobile phase (17.5:22.5:60, v/v/v) were used. A plasma pre-treatment procedure was developed, based on solid phase extraction of entacapone using Oasis HLB cartridges. Extraction yields were good, being always higher than 96%. Both methods, based on HPLC-ED (V=+0.8V), have been fully validated. Good linearity was obtained over the following concentration ranges: 100-4000 ng mL(-1) for L-dopa, 200-10,000 ng mL(-1) for 3-O-methyldopa, 25-4000 ng mL(-1) for carbidopa and 20-4000 ng mL(-1) for entacapone. Precision data were satisfactory, being R.S.D.% values lower than 5.64%; accuracy also resulted very good with recovery data higher than 90%. The proposed methods have been successfully applied to the analysis of patient plasma samples and seem to be suitable for therapeutic drug monitoring purposes.

Single dose bioequivalence study of alpha-methyldopa tablet formulations using a modified HPLC method.

BACKGROUND AND OBJECTIVE: The purpose of the present study was to compare the bioavailability of a new methyldopa (CAS 555-30-6) tablet formulation with that of a reference formulation in 12 healthy male subjects using a modified HPLC method. METHODS: The study was designed as an open label, single-dose, randomized study with a cross-over design. Under fasting conditions, each subject received one 250-mg tablet orally as a single dose of a test or reference formulation on two treatment days. The treatment periods were separated by a one-week washout period. The blood samples were collected at different time points after each administration and determined using a rapid and reliable modified HPLC method. The method used was validated for specificity, accuracy, precision and sensitivity. The pharmacokinetic parameters (Cmax, AUC0-t, AUC0-infinity) were statistically compared by analysis of variance (ANOVA) for test and reference formulations. RESULTS AND DISCUSSION: All validation criteria for the developed HPLC method were in acceptable range. The maximum plasma concentration (Cmax) of alpha-methyldopa was 270.3-1864.9 ng/ml for the test and 224.5-1585.6 ng/ml for the reference formulation. The mean AUC0-infinity of alpha-methyldopa was 2002.1-10614.8 and 2076.8- 9056.3 ng x h/ml for the test and reference formulation, respectively. The calculated 90% confidence intervals for the mean test/reference ratios of mentioned parameters were 92.48-115.94, and 88.82-101.13 which are in the bioequivalence range. The statistical tests did not show any statistical differences between formulations suggesting that methyldopa tablet of test and reference can be considered as bioequivalent preparations. CONCLUSION: A rapid and reliable HPLC method with fluorescence detector was developed to analyze alpha-methyldopa in human plasma. Based on the obtained results the test formulation of alpha-methyldopa is bioequivalent to the reference formulation.

Levodopa and 3-OMD levels in Parkinson patients treated with Duodopa.

We studied 19 patients (14 men, 5 women, Hoehn and Yahr (H&Y)> or =3) with advanced Parkinson's disease (PD) attending the Parkinson Institute, Milan, whose motor fluctuations and dyskinesia were not controlled by oral medications. After all oral PD medications had been withdrawn, they received a duodenal levodopa infusions (Duodopa, Solvay Pharmaceuticals) for 14h/day through a transabdominal port; levodopa boluses were administered in the morning and during "off" periods. The patients were evaluated by means of the UPDRS in the morning ("off") and 60-120min after the infusion ("on") at baseline and for a mean follow-up of 13.5+/-12.5months (up to 36months in 10 patients:). Levodopa (l-DOPA) and its metabolites were determined by HPLC with electrochemical detection. l-DOPA concentrations tended to higher in the afternoon (2008+/-345 vs 1713+/-274ng/mL) and correlated with the daily dose. O-methyldopa (OMD) levels correlated with l-DOPA levels, and the OMD/l-DOPA ratios were stable over the day. There was a relationship between decreasing UPDRS III scores and decreasing OMD/l-DOPA ratios. Dyskinesia (UPDRS IV, items 32-34) showed a clear improvement over time but there was no clear relationship with l-DOPA and OMD levels, or the OMD/l-DOPA ratio. The l-DOPA/dose ratio was stable over time, whereas OMD levels and the OMD/l-DOPA ratio decreased. It is conceivable that continuous infusion decreases metabolism possibly due to a reduction in methyl donor availability, as demonstrated by the increase in total homocysteine levels. Our results do not support the development of tolerance even after several months of continuous infusion, and indicate that pharmacodynamic factors play a role in afternoon off periods.

[Methyldopa-induced acute reactive hepatitis in pregnancy, drug-metabolizing capacity of the liver]. / Methyldopa által indukált akut reaktív hepatitis terhességben, a máj gyógyszer-metabolizáló képességének alakulása.

Alpha-methyldopa is a regularly used antihypertensive drug during pregnancy. Methyldopa, which decreases the sympathoadrenal system, is the first drug of choice since decades. The reactive hepatitis is not frequent, but known serious side effect of alpha-methyldopa. In non-pregnant women the estimated rate of manifest hepatotoxicity is 2.5-10%. In our case, gestation hypertension developed at the 21st gestation week of a 35 year-old pregnant woman. Oral methyldopa, a central alpha adrenergic blocker therapy was introduced. On the 23rd gestation week acute hepatitis developed. During differential diagnosis of hepatitis, the etiology of methyldopa was taken into account. Viral and autoimmune origin was rolled out. No fetal aberration was found during ultrasound examination. The function of drug metabolizing function from blood was measured by CYP phenotyping (CYP gene expression analysis). CYP3A4 enzyme plays a primary role in the metabolism of nifedipine. Antihypertensive therapy was changed from methyldopa to nifedipine. Nifedipine dosage was based on the value of CYP3A4 gene expression. With the reduced nifedipine therapy (30 mg daily), blood pressure was successfully under control. The diagnosis of alpha-methyldopa induced hepatitis was based on anamnesis, clinical picture and the results of chemical and radiological examination and confirmed by the level of drug-metabolizing capacity. The gestation hepatotoxicity of alpha-methyldopa was reported first in 1969 by Elkington Smith, who suggested the monitoring of serum aminotransferase during alpha-methyldopa therapy in pregnancy in their case report. Our case report confirms that monitoring of serum aminotransferase level is still valuable when treating a pregnant woman with alpha-methyldopa.

A rapid high performance liquid chromatographic determination of methyldopa in human serum with fluorescence detection and alumina extraction: application to a bioequivalence study.

A simple and ultra rapid high performance liquid chromatographic (HPLC) method coupled with alumina extraction and fluorescence detection was described for determination of methyldopa in human serum. The drug and an internal standard were adsorbed onto alumina and eluted using acidic methanol. The eluate was directly injected onto ODS reverse phase column using a mixture of phosphate buffer (0.05 M) containing triethylamine (100 microl/l, v/v; pH 2.3) and methanol (92:8, v/v) at a flow rate of 2.1 ml/min as the mobile phase. The fluorescence detector excitation and emission wavelengths were set at 270 and 320 nm, respectively. No interference in the assay from any endogenous substances or other concurrently used drugs was observed and the retention times of I.S. and the drug were 1.7 and 2.4 min, respectively with total run time (injection to injection) of less than 3.5 min. The limit of quantification was evaluated to be 2 ng/ml. Validity of the method was studied and the method was precise and accurate with a linearity range from 20 ng/ml to 5000 ng/ml. This method has been used in a randomized crossover bioequivalence study of two different methyldopa preparations in 24 healthy volunteers.

Mediated exodus of L-dopa from human epidermal Langerhans cells.

L-3,4-dihydroxyphenylalanine (L-dopa) is not metabolized within human epidermal Langerhans cells (LC); yet they can take up substantial amounts of this amino acid which subsequently can be released into the extracellular space. We recently reported that human epidermal energy metabolism is predominantly anaerobic and that the influx mechanism is a unidirectional L-dopa/proton counter-transport system and now we describe conditions for the mediated transport of L-dopa out of the LC. It is demonstrated that certain amino acids and one dipeptide can effectively trigger the efflux of L-dopa taken up by the LC.Thus, alpha-methyl-dopa (alpha-m-dopa), D-dopa and the dipeptide, met-ala at the outside of the plasma membrane stimulated the efflux of L-dopa from L-dopa loaded LC. Similar effects were achieved by a variety of other amino acids in the extracellular fluid while some other amino acids were inactive. The time required for 50% D-methionine-induced exodus of L-dopa from L-dopa loaded LC was in the range of 5-7 min and a complete exodus of L-dopa was attained at about 20 min of incubation. This dislocation of L-dopa to the extracellular fluid is interpreted as an expression of trans-stimulation. In the case of alpha-m-dopa, D-dopa and met-ala, which admittedly were not able to penetrate the plasma membrane of LC, the concept of trans-stimulation was given a new purport, since none of them were able to participate in an exchange reaction. Finally, it could be concluded that L-dopa escaped by a route different from the one responsible for L-dopa uptake in LC.Thus, while the influx of L-dopa supports extrusion of protons deriving from anaerobic glycolysis in the LC, L-dopa efflux can provide the cells with useful amino acids in an energy-saving way, altogether a remarkable biological process. From this follows that L-dopa has a biological function of its own, besides being a precursor in the catecholamine and pigment syntheses.

Pharmacokinetic profile of methyldopa in the brain of sinaortic-denervated rats.

Pharmacokinetics of methyldopa (MD) and the effect on the dopaminergic metabolism was studied in anesthetized sham-operated (SO) and sinoaortic-denervated (SAD) rats by using the microdialysis technique. A concentric microdialysis probe was placed in the striatum or in the posterior hypothalamus. Levels of MD, homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured by high pressure liquid chromatography coupled to electrochemical detection (HPLC-EC). Following the i.p. administration of MD (50 mg x kg(-1), i.p.), striatal dialysates showed that this drug rapidly reaches the brain. However, in SAD rats the MD levels of dialysates were lower and decreased more rapidly compared to SO rats. On the other hand, dialysates of posterior hypothalamus showed that in SAD animals the accumulation of MD was significantly greater than in SO rats.MD does not significantly reduce the striatal production of dopaminergic metabolite DOPAC in both groups of rats. The drug also induces a decrease of DOPAC levels in hypothalamic dialysates of SO and SAD animals. On the other hand, a no significative decay of HVA levels was seen in the striatal dialysate of both groups of experimental animals. In conclusion, this study by using a microdialysis technique shows that MD has different kinetic profiles in dialysates from posterior hypothalamus and striatum of SO and SAD rats at a dose that alters dopaminergic metabolism.

Comparative single- and multiple-dose pharmacokinetics of levodopa and 3-O-methyldopa following a new dual-release and a conventional slow-release formulation of levodopa and benserazide in healthy volunteers.

The objective was to assess the single- and multiple-dose pharmacokinetics of levodopa and 3-O-methyldopa following administration of a new dual-release and conventional slow-release formulation of levodopa/benserazide in the dose ratio of 4:1. In an open-label, two-way cross-over study, 20 healthy volunteers were randomized to receive first either Madopar DR or Madopar HBS for 8 days. Then they crossed over to the other formulation. A first dose of 200 mg levodopa and 50 mg benserazide ('250' mg) was given on day 1, '125' mg t.i.d. on the subsequent 6 days (days 2-7), followed by '250' mg on day 8. The two treatment periods of 8 days were separated by a wash-out period of at least 7 days. Blood samples were taken at specific times over a 12-hour period (day 1) or a 36-hour period (day 8). Plasma concentrations of levodopa and 3-O-methyldopa were measured by high-performance liquid chromatography for pharmacokinetic evaluation. The pharmacokinetics of levodopa after a single-dose administration (day 1) of Madopar DR and Madopar HBS were significantly different as reflected by the respective mean values of maximum plasma concentration (C(max) 1.99 vs. 0.82 mg x l-1), time to reach maximum concentration (t(max) 0.7 vs. 2.6 h) and area under the plasma concentration-time curve (AUC(0- infinity ) 4.52 vs. 3.18 mg x h x l-1). The respective values after multiple doses (day 8) were: C(max) 1.98 vs. 0.93 mg x l-1, t(max) 0.7 vs. 2.3 h and AUC(0-infinity ) 4.84 vs. 3.96 mg x h x l-1. The relative bioavailability (Madopar DR vs. Madopar HBS) was 1.73 on day 1 and 1.32 on day 8. Bioequivalence could not be demonstrated for log-transformed data of AUC and C(max) within a predefined range of 80-125 and 70-143%, respectively. In conclusion, the observed differences in C(max), t(max) and AUC are consistent with a faster rate and higher extent of levodopa absorption after administration of Madopar DR. Statistical evaluation of these kinetic data showed that Madopar DR is not bioequivalent to Madopar HBS.

Excretion of antihypertensive medication into human breast milk: a systematic review.

OBJECTIVE: To establish which antihypertensive medications are safe for use while breastfeeding, by reviewing the available evidence. METHODS: Reports of studies examining the transfer of antihypertensive medications to breastmilk were identified from multiple MEDLINE and EMBASE searches, manual review of bibliographies of articles and textbooks on drug use during lactation. The reports were reviewed and the results were compiled. RESULTS: Prospective cohort studies and case reports constituted the only available evidence. Compilation of these results found that the milk to plasma (M/P) ratios varied widely across the beta-blocker family, the beta-blockers with low protein binding having the highest M/P ratios. The angiotensin-converting enzyme (ACE) inhibitors, methyldopa, and some calcium channel blockers had low M/P ratios. CONCLUSION: The available data to date indicate that ACE inhibitors, methyldopa, beta-blockers with high protein binding, and some calcium channel blockers all appear to be safe treatments of hypertension in a nursing mother. The data suggest that drugs to be avoided are beta-blockers with low protein binding. However, the available evidence is limited and further studies are needed to confirm these findings.

Quantification of methyldopa in human plasma by high-performance liquid chromatography-electrospray tandem mass spectrometry application to a bioequivalence study.

A method based on LC-MS-MS is described for the determination of methyldopa in human plasma using dopa-phenyl-D3 as the internal standard. The method has a chromatographic run time of 5.5 min and was linear in the range of 20-5000 ng/ml. The limit of quantitation was 20 ng/ml, the intra-day precisions were 7.3, 5.4 and 4.3% and the intra-day accuracies were -8.0, -1.3 and -2.0% for 30, 600 and 3000 ng/ml, respectively. The inter-day precisions were 7.7, 0.5 and 0.7% and the inter-day accuracies were 0.2, -1.1 and -2.3%, respectively, for the above concentrations. This method was employed in a bioequivalence study of two tablet formulations of methyldopa.

Pharmacokinetic and pharmacodynamic alterations of methyldopa in rats with aortic coarctation. A study using microdialysis.

A pharmacokinetic-pharmacodynamic study of methyldopa (MD) was made in anesthetized sham operated (SO) and aortic coarctated (ACo) rats by using a vascular shunt probe for arterial microdialysis and simultaneous blood pressure recording. Anesthetized Wistar rats were used 7 days after aortic coarctation or sham operation. A vascular shunt probe was inserted into the carotid artery and a concentric probe was placed into the striatum or posterior hypothalamus. MD and 3,4-dihydroxyphenylacetic acid (DOPAC) were determined in the dialysates by HPLC-EC. MD (50 mg kg(-1)i.p.) induced an increase of heart rate in SO (Delta HR: 108 +/- 22 bpm, n= 6) and in ACo rats (Delta HR: 55 +/- 10 bpm, n= 6, P< 0.05, one way ANOVA). Moreover, MD also reduced the mean arterial pressure (MAP) of SO rats (Delta MAP: -10 +/- 4 mmHg, n= 6) and ACo animals (Delta MAP: -51 +/- 9 mmHg, n= 6, P< 0.05, one way ANOVA). Analysis of the arterial blood dialysates showed a lower half-life of MD in ACo rats (t(1/2): 1.5 +/- 0.3 h, n= 6, P< 0.05, 't' test) than in SO rats (t(1/2): 3.7 +/- 1.0 h, n= 6). A low accumulation and a fast decay of striatal MD levels were seen in ACo rats. However, peak levels of drug were greater in the hypothalamic dialysates of ACo rats than in SO animals samples. On the other hand, MD also induced an increase of DOPAC levels in the hypothalamic dialysates of ACo rats. In conclusion, the aortic coarctation modifies the pharmacokinetic and cardiovascular effect of MD in the rat. The action of this drug on dopaminergic neurotransmission is also altered in the ACo animals.

Comparative bioavailability of alpha-methyldopa normal and film tablet formulations after single oral administration in healthy volunteers.

In a single dose, randomized, cross-over study, with one week of wash-out period, the relative bioavailability of Dopegyt tablets containing 250 mg alpha-methyldopa (AMD) and Presinol film tablets with identical active ingredient content was examined in 24 healthy volunteers. Since technologically two completely different preparations (a film-tablet and a non-film-tablet) having significantly different in vitro dissolution were to be compared, both preparations were compared to a third one, AMD solution (Dopegyt solution) with 250 mg/50 ml concentration. Plasma concentrations of the drug were measured for 24 hours post-dose, applying HPLC with fluorometric detection. Pharmacokinetic parameters calculated from individual data (AUC0-infinity, AUC0-t, Cmax, Cmax/AUC0-infinity, t(max)) were evaluated statistically. Wilcoxon's nonparametric test and the four-way variance analysis could not detect any significant difference at the usual a=95% probability level in these pharmacokinetic parameters of the two tablet preparations. For AUC0-infinity at the 90% probability level, the confidence interval was 0.883-1.237 (with an estimated geometric mean of 1.045), for the test/reference ratio of Dopegyt and Presinol tablets, thus the two preparations proved to be bioequivalent. The relative bioavailability of Dopegyt (test preparation) and Presinol (reference preparation) calculated from the AUC0-infinity values was 116.7+/-56.7% that also confirmed bioequivalence. The results of all the applied statistical tests suggest that Dopegyt and Presinol can be considered as bioequivalent preparations.

Pharmacokinetic study of methyldopa in aorta-coarctated rats using a microdialysis technique.

The pharmacokinetics of methyldopa (12.5, 25 and 50 mg kg(-1), i.p.) was studied in anesthetized sham-operated (SO) and abdominal aorta-coarctated (ACo) rats using a microdialysis technique. A non-linear relationship between the area under the curve (AUC) and dose was observed in SO rats. However, in ACo rats the AUC showed a proportional increase with dose. Abdominal aortic coarctation produced significant differences in the estimates of clearance (Cl) and the elimination rate constant from the dialysate (K(ed)) after the administration of 50 mg kg(-1)of methyldopa (K(ed)SO, 0.31 +/- 0.09; ACo, 0.66 +/- 0.09(*)h(-1): Cl SO, 30.8 +/- 10.1; ACo, 78.6 +/- 13.3(*)mlkg(-1)min(-1);n= 6,(*)P< 0.05 vs SO). In conclusion, this study, by using a microdialysis technique, suggests that abdominal aortic coarctation seems to produce changes in the pharmacokinetics of methyldopa in rats.

Study of the evolution of blood and striatal levels of methyldopa: a microdialysis study in sinaortic denervated rats.

Pharmacokinetic of methyldopa (50 mg kg(-1)i.p.) was studied in anesthetized sham operated and sinoaortic denervated (SAD) rats by using the microdialysis technique. Vascular shunt probe was inserted into the carotid artery and concentric probe was placed in the striatum. Levels of methyldopa were measured by HPLC-EC. The number of animals in each group was six and normal distribution of the variables of the study was assumed. Peak concentrations in arterial blood of methyldopa were similar in both groups of rats but the elimination rate constant was 0.31+/-0.09 h(-1)for sham rats (n =6) and 1.28+/-0.31 h(-1)for SAD rats (n =6, P<0.05). Low levels of methyldopa and a more pronounced decrease were seen in striatum of sinoaortic denervated rats. In conclusion, by using a microdialysis technique, different kinetic profiles of methyldopa were observed in sham operated and sinoaortic denervated rats.