Liquid Chromatographic Method for Determination of Sulfamethazine Residues in Milk: Collaborative Study

Seven laboratories participated in a collaborative study of a liquid chromatographic (LC) method for determination of sulfamethazine (SMZ) residues in raw milk that were previously frozen. The milk is extracted with chloroform, the chloroform is evaporated, and the residue is suspended in hexane and extracted with 0.1 M KH2P04 (PDP) solution. The PDP extract is analyzed by LC on a C18 column with methanol–0.1M PDP (30 + 70) as mobile phase. Individual laboratories were instructed to analyze 5 replicates each of control milk, fortified control milk at 2 levels, and 3 blind samples. Blind samples included raw milk fortified with SMZ at 10 and 20 ppb and 1 sample containing SMZ residue from a dosed cow. For blind fortified samples containing 10 ppb SMZ, average recovery and relative standard deviations for repeatability and reproducibility (RSDr and RSRR) based on the results from 6 of the 7 participating laboratories were 8.21 ppb, 7.16%, and 23.16%, respectively. Similar data, including results from a seventh participant who reported instrumental problems but was not eliminated by the Dixon outlier test, were 9.13 ppb, 8.38%, and 31.94%, respectively. These results demonstrate that the method is suitable for the determination of SMZ residues in milk at 10 ppb and above. The method was adopted first action by AOAC International.

Assay of Oxolinic Acid Residues in Salmon Muscle by Liquid Chromatography with Fluorescence Detection: Interlaboratory Study

A previously developed method that uses a simplified sample preparation and fluorometric detection of liquid chromatographic eluates for the determination of oxolinic acid in salmon muscle has been collaboratively studied. Five laboratories participated in the study to analyze, in quintuplicate, blank salmon muscle fortified at 10, 20, 50, and 100 μg/kg (ppb), and 2 incurred samples from salmon given feed with medicated oxolinic acid. The tissue, 2 g mixed with 2 g Na2S04, is extracted with ethyl acetate and centrifuged, and the solvent Is evaporated. The residue is partitioned in a mixture of hexane and 0.01 M oxalic acid, and the aqueous phase is chromatographed using fluorescence detection at 327 nm excitation and 369 nm emission. Mean recoveries ranged from 77.2 to 84.5% in spiked samples with reproducibility relative standard deviation (RSDR) ranging from 11.5 to 18.3%. Treated salmon were found to contain 8.71 and 53.8 μg/kg with RSDR of 18.6 and 16.7%, respectively. The corresponding repeatability relative standard deviations (RSDr) were 5.8-12.2%, and 7.7 and 6.2%. The method is recommended for regulatory purposes in Canada.

Dimetridazole Residues in Pork Tissue. I. Assay by Liquid Chromatography with Electrochemical Detector

A liquid chromatographic (LC) method with electrochemical detection in the reductive mode was developed for the quantitative determination of dimetridazole (DMZ) and its major metabolite (HMMNI) at residue levels in pork tissue. For blood plasma, a sample is precipitated with 2 volumes of acetonitrile and centrifuged, and a diluted aliquot of the supernatant liquid is chromatographed. For muscle, a 10 g sample is extracted 3 times with dichloromethane. After evaporation of the combined extracts, the residue is redissolved in a mixture of hexane and mobile phase (0.3% TEA in 0.6M ammonium acetate pH 5.0 and acetonitrile, 85 + 15) and centrifuged, and an aliquot of the lower phase is chromatographed. Chromatography is accomplished using valve switching with 2 liquid circuits, employing the same mobile phase for both. The sample is deaerated by sparging with helium under slight positive pressure to prevent rediffusion of the oxygen. The sample is first loaded into a deoxygenator and the flow is stopped for complete deoxygenation. The flow is then resumed to transfer the sample into the first, low back-pressure column (ODS, 10 μm, 4.6 x 200 mm). Switching the valve at this point removes the deoxygenator from the circuit and connects the first column to a second one (ODS, 5 μm, 4.6 x 150 mm) in tandem. After the effluent is passed through a second deoxygenator to reduce the residual oxygen in the mobile phase, it is monitored by an electrochemical detector with a screened wall jet cell and a gold mercury electrode, set at —1.2 V. The response is linear, in the ranges studied: 100-1000 pg for DMZ and 200-1000 pg for HMMNI. Mean recoveries for the extraction method are 56 and 70% for DMZ and HMMNI, respectively, using spiked meat and plasma samples at 0.26-2 ppb. Essentially 100% recoveries are obtained with spiked (10 ppb) plasma, using the acetonitrile precipitation

Assay of Oxytetracycline Residues in Salmon Muscle by Liquid Chromatography with Ultraviolet Detection

A novel method for the assay of oxytetracycline residues in salmon muscle is described. Tissue is homogenized with 4 volumes of 1 % metaphosphoric acid in the presence of a small amount of dichloromethane (0.4 volume), shaken, and centrifuged. The residue is washed twice (4 and 2 volumes, respectively) with 1 % metaphosphoric acid, and the combined aqueous supernatants are concentrated to about 2 mL by flash evaporation and then diluted to 5 mL. Filtered aliquots of the extract are subjected to liquid chromatography using a C18 column with a mobile phase of acetonitrile-tetrahydrofuran- 0.025M aqueous oxalic acid (9 + 1 + 30) containing octanesulfonic acid at a final concentration of 10mM. Eluted peaks are monitored at 355 nm. Calibration and standard curves were linear from 0.01 to 0.5 μg on-column, with a limit of quantitation better than 0.05 μg/g. Recoveries from spiked blanks varied from 85.8 to 90.3% (relative standard deviation, 13.1-2.4%) in the 0.05-1.00 μg/g concentration range and were 21.1% at 0.02 μg/g.

A pharmacokinetic study of intermittent rifabutin dosing with a combination of ritonavir and saquinavir in patients infected with human immunodeficiency virus

AIM

Our primary aim was to evaluate the plasma exposures and safety of rifabutin and its active 25-O-desacetyl metabolite during concomitant therapy of intermittent rifabutin dosing regimens with a combination of ritonavir and saquinavir.

METHODS

Twenty-four patients without mycobacterial infection who were human immunodeficiency virus seropositive and who were receiving 400 mg each of ritonavir and saquinavir twice daily participated in a 3-period, 2-group longitudinal pharmacokinetic study. Patients were equally randomized to receive 300 mg of rifabutin every 7 days (group 1) or 150 mg of rifabutin every 3 days (group 2) for 8 weeks. Blood samples were collected over the dosing intervals of the protease inhibitors at baseline (period 1) and of the 3 drugs after 4 weeks (period 2) and 8 weeks (period 3) for HPLC measurement of plasma concentrations of the 3 drugs and 25-O-desacetylrifabutin.

RESULTS

Nineteen patients (group 1, n = 10; group 2, n = 9) completed the study. Five individuals withdrew from the study; 3 of them experienced side effects, and 2 were lost to follow-up. For combined groups, mean saquinavir and ritonavir overall (area under the concentration-time curve [AUC]) and peak (C(max)) plasma exposures averaged over periods 2 and 3 did not change significantly (8% to 19%; P > .05) compared with those in period 1 (90% confidence intervals, -7% to 26% for ritonavir and -2% to 38% for saquinavir). Rifabutin and metabolite AUC and C(max) exposures were stable over the 8 weeks, with intraindividual coefficients of variation of 12% to 19%. Oral clearance of rifabutin was similar in both groups (321 mL/min in group 2 versus 372 mL/min in group 1; P = .34). Rifabutin C(max) values were significantly lower in group 2 (310 ng/mL versus 496 ng/mL in group 1; P = .004). Rifabutin and metabolite predose levels were significantly higher in group 2 (rifabutin: 54 ng/mL versus 17 ng/mL; desacetyl rifabutin: 55 ng/mL versus 28 ng/mL; P < .002).

CONCLUSIONS

Rifabutin exposures were similar at 4 and 8 weeks and had minimal effect on ritonavir and saquinavir exposures. Intermittent rifabutin dosing over 8 weeks provided a safe and manageable regimen for concurrent therapy with a combination of ritonavir and saquinavir.

Pharmacokinetic interaction between mefloquine and ritonavir in healthy volunteers

AIMS

To evaluate the pharmacokinetic interaction between ritonavir and mefloquine.

METHODS

Healthy volunteers participated in two separate, nonfasted, three-treatment, three-period, longitudinal pharmacokinetic studies. Study 1 (12 completed): ritonavir 200 mg twice daily for 7 days, 7 day washout, mefloquine 250 mg once daily for 3 days then once weekly for 4 weeks, ritonavir restarted for 7 days simultaneously with the last mefloquine dose. Study 2 (11 completed): ritonavir 200 mg single dose, mefloquine 250 mg once daily for 3 days then once weekly for 2 weeks, ritonavir single dose repeated 2 days after the last mefloquine dose. Erythromycin breath test (ERMBT) was administered with and without drug treatments in study 2.

RESULTS

Study 1: Ritonavir caused less than 7% changes with high precision (90% CIs: -12% to 11%) in overall plasma exposure (AUC(0,168 h)) and peak concentration (Cmax) of mefloquine, its two enantiomers, and carboxylic acid metabolite, and in the metabolite/mefloquine and enantiomeric AUC ratios. Mefloquine significantly decreased steady-state ritonavir plasma AUC(0,12 h) by 31%, Cmax by 36%, and predose levels by 43%, and did not affect ritonavir binding to plasma proteins. Study 2: Mefloquine did not alter single-dose ritonavir pharmacokinetics. Less than 8% changes in AUC and Cmax were observed with high variability (90%CIs: -26% to 45%). Mefloquine had no effect on the ERMBT whereas ritonavir decreased activity by 98%.

CONCLUSIONS

Ritonavir minimally affected mefloquine pharmacokinetics despite strong inhibition of CYP3A4 activity from a single 200 mg dose. Mefloquine had variable effects on ritonavir pharmacokinetics that were not explained by hepatic CYP3A4 activity or ritonavir protein binding.

Single and multiple dose pharmacokinetics of nelfinavir and CYP2C19 activity in human immunodeficiency virus-infected patients with chronic liver disease

AIMS

To evaluate the single-dose and multiple-dose pharmacokinetics of nelfinavir and its active M8 metabolite in eight HIV-seropositive patients with liver disease, and to examine the relationship between CYP2C19 activity (genotype and plasma M8/nelfinavir metabolic ratio) and the severity of liver disease in these patients.

METHODS

Nelfinavir was given as a single dose (500 or 750 mg) to patients beginning therapy and twice (500, 750 or 1000 mg) or three times (250 or 750 mg) daily during chronic therapy. Single-dose pharmacokinetic values were used to predict multiple-dose regimens. Peak and total plasma exposures between 2-4 microg ml-1 and 45-75 microg ml-1 h, respectively, and predose levels > 0.7 microg ml-1 were targeted for multidose nelfinavir. Genotype was determined by analysis for CYP2C19*1, CYP2C19*2, and CYP2C19*3. Individuals were grouped according to their genotype, molar M8/nelfinavir AUC ratio (low: < 0.1, intermediate: 0.1-0.3, high > 0.3), and Child-Pugh classification for severity of liver disease.

RESULTS

Nelfinavir pharmacokinetics were characterized by wide interindividual variability, low clearance (181-496 ml min-1 70 kg-1, n = 7), and prolonged half-life (5-20 h, n = 7). M8/nelfinavir AUC ratio increased 58% (n = 4) and alpha 1-acid glycoprotein levels decreased up to 39% (n = 5) from single to multiple dosing. CYP2C19 activity was low (metabolic AUC ratio < 0.1) in four patients with moderate to severe liver disease even though they were genetically extensive CYP2C19 metabolizers (*1/*1 or *1/*2). Three patients required lower daily doses than the standard regimen of 750 mg every 8 h to achieve target concentrations and maintain virologic suppression at < 50 RNA copies ml-1 (up to 20 months).

CONCLUSIONS

Acquired CYP2C19 deficiency from moderate or severe liver disease resulted in decreased M8 formation. Long-term HIV suppression is possible using low nelfinavir doses in patients with liver disease.

Pharmacokinetic and pharmacodynamic interactions between diltiazem and quinidine

OBJECTIVES

To examine the pharmacokinetic and pharmacodynamic interactions between quinidine and diltiazem because both drugs can inhibit drug metabolism.

METHODS

Twelve fasting, healthy male volunteers (age, 24 +/- 5 years; weight, 75 +/- 10 kg) received a single oral dose of diltiazem (60 mg) or quinidine (200 mg), alone and on a background of the other drug, in a crossover study. Background treatment consisted of 100 mg quinidine twice a day or 90 mg sustained-release diltiazem twice a day for 2 day before the study day.

RESULTS

Pretreatment with diltiazem significantly (p < 0.05) increased the area under the curve of quinidine from 7414 +/- 1965 to 11,213 +/- 2610 ng.hr/ml and increased its terminal elimination half-life (t1/2) from 6.8 +/- 1.1 to 9.3 +/- 1.5 hours. Its oral clearance was decreased from 0.39 +/- 0.1 to 0.25 +/- 0.1 L/hr/kg, whereas the maximal concentration was not significantly affected. Diltiazem disposition was not significantly affected by pretreatment with quinidine. Diltiazem pretreatment increased QTc and PR intervals and decreased heart rate and diastolic blood pressure. No significant pharmacodynamic differences were shown for diltiazem alone versus quinidine pretreatment.

CONCLUSION

Diltiazem significantly decreased the clearance and increased the t1/2 of quinidine, but quinidine did not alter the kinetics of diltiazem with the dose used. No significant pharmacodynamic interaction was shown for the combination that would not be predicted from individual drug administration.

Simultaneous determination of diltiazem and quinidine in human plasma by liquid chromatography

A novel method for simultaneous determination of diltiazem and quinidine in human plasma is described. Plasma is alkalinized and extracted with methyl tert.-butyl ether. The ether phase is separated and evaporated. The residue is reconstituted in 0.2 ml of mobile phase containing 56 mM octanesulfonic acid then washed twice with n-hexane. Aliquots are chromatographed on a silanol-deactivated reversed-phase column using a mobile phase containing aqueous H2SO4 (0.01 M, pH 2)-methanol-acetonitrile (45:45:10) and 10 mM octanesulfonic acid. Peaks are monitored with a UV detector set at 237 nm and a fluorescence detector using an excitation set at 247 nm and a 270 nm UV cut-off filter at the emission. Calibration and standard curves were linear from 1 to 130 ng on-column for diltiazem and from 2 to 600 ng on-column for quinidine. Limits of quantitation were 2 and 4 ng/ml for diltiazem and quinidine, respectively. Recoveries from spiked plasma were 94.0 to 102.5% (R.S.D. 6.0-11.4%) for diltiazem and 98.5% to 104.1 (R.S.D. 7.7-8.7%) for quinidine over the ranges studied. In vitro stability was studied in spiked plasma samples stored at -80 degrees C for sixteen months. Both diltiazem and quinidine remained within 10% from nominal values. For ex vivo stability at -80 degrees C, a plasma sample obtained from a volunteer 2 h after oral administration of diltiazem (60 mg) was analysed for two days after sampling and eighteen months later. The mean deviation from initial measured was 4.7%.

Assay of oxolinic acid residues in salmon muscle by liquid chromatography with fluorescence detection: interlaboratory study

A previously developed method that uses a simplified sample preparation and fluorometric detection of liquid chromatographic eluates for the determination of oxolinic acid in salmon muscle has been collaboratively studied. Five laboratories participated in the study to analyze, in quintuplicate, blank salmon muscle fortified at 10, 20, 50, and 100 micrograms/kg (ppb), and 2 incurred samples from salmon given feed with medicated oxolinic acid. The tissue, 2 g mixed with 2 g Na2SO4, is extracted with ethyl acetate and centrifuged, and the solvent is evaporated. The residue is partitioned in a mixture of hexane and 0.01 M oxalic acid, and the aqueous phase is chromatographed using fluorescence detection at 327 nm excitation and 369 nm emission. Mean recoveries ranged from 77.2 to 84.5% in spiked samples with reproducibility relative standard deviation (RSDR) ranging from 11.5 to 18.3%. Treated salmon were found to contain 8.71 and 53.8 micrograms/kg with RSDR of 18.6 and 16.7%, respectively. The corresponding repeatability relative standard deviations (RSDR) were 5.8-12.2%, and 7.7 and 6.2%. The method is recommended for regulatory purposes in Canada.

Separation, identification and determination of lumichrome in swine feed and kidney

During surveillance of hog carcasses from Manitoba for antibiotic residues by the Health of Animals Laboratory, Agriculture Canada, Saskatoon, an unknown substance was found which produced tetracycline-like results with the methods used. This same substance was found in an implicated swine feed premix. Using various HPLC systems and columns, UV spectroscopy, reverse-phase TLC, and mass spectrometry, the substance was isolated from the feed premix, and identified as lumichrome, a photodegradation product of riboflavin. Traces of the same substance were found in riboflavin standard. Analysis of swine kidney, previously found to contain the unknown, showed the same substance was present at a level of about 1 ppm.

The identification and assay of 2-methyl-5-nitroimidazole in pigs treated with dimetridazole

An unidentified metabolite of dimetridazole (DMZ), found in pig plasma, muscle and kidney, was shown by chromatography and spectroscopy to be 2-methyl-5-nitroimidazole (2-MNI), resulting from N-demethylation of DMZ. This route of degradation competes with the oxidation pathway previously described. The concentration of 2-MNI in the plasma of pig fed medicated diet (DMZ 0.0125%) ranged from 29 to 83 ppb, 2 hours after the morning meal, similar to DMZ, but lower than that of the major metabolite, 2-hydroxymethyl-1-methyl-5-nitroimidazole (HMMNI). Its elimination profile in plasma was biphasic, similar to those of HMMNI and DMZ. Early and terminal half lives were 2.6 and 9.1 h respectively. None of the metabolites could be detected in any of the tissues studied 49 hours after withdrawal.

Quantitation and Confirmation of Sulfamethazine Residues in Swine Muscle and Liver by LC and GC/MS

The present paper describes a liquid chromatographic (LC) method for purification of crude swine tissue extracts before gas chromatographic/mass spectrometric (GC/MS) quantitation and confirmation of sulfamethazine at low ppb levels. Fractions corresponding to sulfamethazine were collected, evaporated to dryness, ^methylated with diazomethane, concentrated, and analyzed by GC/MS. A mass spectrometer was set to selected ion monitoring (SIM) mode. Ions 233, 227, 228, and 92 m/z were detected. Ratio 227/233 m/z (sulfamethazine/internal standard, [pheny| 13C6] sulfamethazine) was used for quantitation, while ratios 228/227 and 92/ 227 m/z, respectively, were used for confirmation. Quantitation in spiked blank muscle tissue was tested from 100 to 1 ppb and found acceptable at all concentrations studied; coefficients of variation ranged from 4.9 to 14.4%. Similar results were obtained for liver tissue from 5 to 20 ppb; coefficients of variation ranged from 1.2 to 9.1 %.

Quantitation and confirmation of sulfamethazine residues in swine muscle and liver by LC and GC/MS

The present paper describes a liquid chromatographic (LC) method for purification of crude swine tissue extracts before gas chromatographic/mass spectrometric (GC/MS) quantitation and confirmation of sulfamethazine at low ppb levels. Fractions corresponding to sulfamethazine were collected, evaporated to dryness, N-methylated with diazomethane, concentrated, and analyzed by GC/MS. A mass spectrometer was set to selected ion monitoring (SIM) mode. Ions 233, 227, 228, and 92 m/z were detected. Ratio 227/233 m/z (sulfamethazine/internal standard, [phenyl 13C6] sulfamethazine) was used for quantitation, while ratios 228/227 and 92/227 m/z, respectively, were used for confirmation. Quantitation in spiked blank muscle tissue was tested from 100 to 1 ppb and found acceptable at all concentrations studied; coefficients of variations ranged from 4.9 to 14.4%. Similar results were obtained for liver tissue from 5 to 20 ppb; coefficients of variation ranged from 1.2 to 9.1%.

Chromatographic and spectroscopic characterization of sulphur-bound dimetridazole and ranidazole derivatives

The 5-nitroimidazoles, dimetridazole and ronidazole, two important veterinary drugs, were reacted under reductive conditions with the sulfhydryl-containing substrates cysteine and glutathione to yield 5-amino-4-S-substituted imidazoles. After purification by reversed-phase liquid chromatography (RP-LC), the four adducts were characterized by RP-LC with photodiode array detection using conditions where their parent drugs were not eluted from the column. Structural identification was conducted by spectroscopic techniques, mainly 1-dimensional and 2-dimensional NMR. While the dimetridazole adducts were found to be monosubstituted at the C-4 position, the two ronidazole products contained two units of the sulfhydryl substrate, located at the C-4 and C-6 positions.

Sulfamethazine (Sulfadimidine) Residues In Canadian Consumer Milk

A survey on the presence of sulfamethazine (sulfadimidine) residues In consumer milk has been conducted In 10 cities across Canada. In each city, homogenized milk was purchased at 3 different retail outlets, each supplied by different processing plants. A total of 30 samples was analyzed by a liquid chromatographic method. The limit of quantitation was 5 ppb. In addition to automatic integration, visual inspection of the chromatograms was required to distinguish between low concentrations of sulfamethazine and 2 unknown interfering peaks. Two samples, from different cities, contained 11.4 and 5.24 ppb of the drug. Drug Identity was confirmed by mass spectrometry. All other samples appeared to be free of the drug.

Sulfamethazine (sulfadimidine) residues in Canadian consumer milk

A survey on the presence of sulfamethazine (sulfadimidine) residues in consumer milk has been conducted in 10 cities across Canada. In each city, homogenized milk was purchased at 3 different retail outlets, each supplied by different processing plants. A total of 30 samples was analyzed by a liquid chromatographic method. The limit of quantitation was 5 ppb. In addition to automatic integration, visual inspection of the chromatograms was required to distinguish between low concentrations of sulfamethazine and 2 unknown interfering peaks. Two samples, from different cities, contained 11.4 and 5.24 ppb of the drug. Drug identity was confirmed by mass spectrometry. All other samples appeared to be free of the drug.

Dimetridazole residues in pork tissue. II. Application of liquid chromatographic method to monitor elimination of drug and its major metabolite

A study was conducted to monitor the elimination of dimetridazole (DMZ) and its major metabolite 2-hydroxymethyl-1-methyl-5-nitroimidazole (HMMNI) in swine plasma and tissue, using a liquid chromatographic method with electrochemical detector sensitive to 0.5 ppb. The study consisted of 2 experiments. In the preliminary experiment, one young female piglet was fed medicated ration containing 125 ppm dimetridazole (DMZ) for 2 weeks, followed by a withdrawal period using regular ration for 5 days. Another, control, piglet was given regular diet throughout. Plasma concentrations of DMZ and its most important residue, HMMNI, were measured daily at 2 h after the morning feeding and, on days 8 and 15, several times during the day. The 2 h concentrations after 3 days loading ranged from 47 to 77 ppb for DMZ and 424 to 1081 ppb for HMMNI. A daily cycle in the plasma levels was seen for both substances. Upon withdrawal of medication, elimination of drug and metabolite was biexponential with a terminal half-life of 6.7 h. In the second experiment, 5 piglets were medicated as above and slaughtered 2, 6, 12, 25, and 49 h after withdrawal of the medication; the concentration of DMZ and HMMNI was measured in plasma, muscle, kidney, and liver. DMZ in the plasma amounted to 22 and 1.8 ppb at 2 and 6 h, while HMMNI declined from 535 ppb at 2 h to 0.75 ppb at 25 h. Most values for both substances found in muscle were close to those in the plasma; in kidney they amounted to 9-17% of the plasma levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Dimetridazole residues in pork tissue. I. Assay by liquid chromatography with electrochemical detector

A liquid chromatographic (LC) method with electrochemical detection in the reductive mode was developed for the quantitative determination of dimetridazole (DMZ) and its major metabolite (HMMNI) at residue levels in pork tissue. For blood plasma, a sample is precipitated with 2 volumes of acetonitrile and centrifuged, and a diluted aliquot of the supernatant liquid is chromatographed. For muscle, a 10 g sample is extracted 3 times with dichloromethane. After evaporation of the combined extracts, the residue is redissolved in a mixture of hexane and mobile phase (0.3% TEA in 0.6M ammonium acetate pH 5.0 and acetonitrile, 85 + 15) and centrifuged, and an aliquot of the lower phase is chromatographed. Chromatography is accomplished using valve switching with 2 liquid circuits, employing the same mobile phase for both. The sample is deaerated by sparging with helium under slight positive pressure to prevent rediffusion of the oxygen. The sample is first loaded into a deoxygenator and the flow is stopped for complete deoxygenation. The flow is then resumed to transfer the sample into the first, low back-pressure column (ODS, 10 microns, 4.6 x 200 mm). Switching the valve at this point removes the deoxygenator from the circuit and connects the first column to a second one (ODS, 5 microns, 4.6 x 150 mm) in tandem. After the effluent is passed through a second deoxygenator to reduce the residual oxygen in the mobile phase, it is monitored by an electrochemical detector with a screened wall jet cell and a gold mercury electrode, set at -1.2 V.(ABSTRACT TRUNCATED AT 250 WORDS)

Dimetridazole Residues in Pork Tissue. II. Application of Liquid Chromatographic Method to Monitor Elimination of Drug and its Major Metabolite

A study was conducted to monitor the elimination of dimetridazole (DMZ) and its major metabolite 2-hydroxymethyl-l-methyl-5-nitroimidazole (HMMNI) in swine plasma and tissue, using a liquid chromatographic method with electrochemical detector sensitive to 0.5 ppb. The study consisted of 2 experiments. In the preliminary experiment, one young female piglet was fed medicated ration containing 125 ppm dimetridazole (DMZ) for 2 weeks, followed by a withdrawal period using regular ration for 5 days. Another, control, piglet was given regular diet throughout. Plasma concentrations of DMZ and its most important residue, HMMNI, were measured daily at 2 h after the morning feeding and, on days 8 and 15, several times during the day. The 2 h concentrations after 3 days loading ranged from 47 to 77 ppb for DMZ and 424 to 1081 ppb for HMMNI. A daily cycle in the plasma levels was seen for both substances. Upon withdrawal of medication, elimination of drug and metabolite was biexponential with a terminal half-life of 6.7 h. In the second experiment, 5 piglets were medicated as above and slaughtered 2, 6, 12,25, and 49 h after withdrawal of the medication; the concentration of DMZ and HMMNI was measured in plasma, muscle, kidney, and liver. DMZ in the plasma amounted to 22 and 1.8 ppb at 2 and 6 h, while HMMNI declined from 535 ppb at 2 h to 0.75 ppb at 25 h. Most values for both substances found in muscle were close to those in the plasma; in kidney they amounted to 9-17% of the plasma levels. Very little HMMNI and no DMZ was found in the liver at 2 h. No drug or metabolite could be detected at 49 h in any of the tissues studied

Quantitative analysis of ethynodiol diacetate and ethinyl estradiol/mestranol in oral contraceptive tablets by high-performance liquid chromatography

A procedure is described for the assay of ethynodiol diacetate and ethinyl estradiol/mestranol by HPLC using two UV detectors at 210 and 280 nm. The system was acetonitrile 38% (v/v) in water as mobile phase on a 250 x 3.2-mm i.d. RP-2 column, with butylated hydroxytoluene as the internal standard. There was greater than 99% recovery from synthetic preparations and the coefficient of variation was greater than 2.0% for formulations.

Comparison of acidic and enzymatic hydrolysis procedures for identification of natural estrogens in pharmaceutical preparations

The usefulness of a distinct enzyme-hydrolyzed preparation for the identification of conjugated and esterified estrogens USP was studied. No significant differences were found when the GLC identification test was performed on the acid-hydrolyzed assay preparation.

High-performance liquid chromatographic analysis of testosterone esters in oily solution

High-performance liquid chromatography was used to analyze testosterone esters in oily solution. The procedure was based on a microparticulate silica column, with a chemically bonded hydrocarbon phase, using methanol-tetrahydrofuran-water (57:11:32 v/v/v) as the mobile phase and 240 nm as the detection wavelength.