Shoukry K.W. Khalil

A Sensitive HPLC Method for the Determination of Terfenadine and Its Metabolite in Human Plasma

Abstract A sensitive and selective HPLC assay with fluorescence detection was developed for the analysis of terfenadine and its acid metabolite in human plasma. The compounds were isolated from plasma by liquid extraction with methyl-t-butyl ether:isopropyl alcohol (95:5% v/v). The chromatographic separation was carried on cyanopropylsilane column (15 cm × 4,6 mm) with a mobile phase consisting of 0.001 M acetate buffer, pH 4.0 : acetonitrile (25:75% v/v). The eluent was monitored at 230 nm excitation and 300 nm emission wavelengths with a 270 nm cut-off filter. The range of quantification was 2 to 1000 ng/ml for terfenadine and 5 to 1000 ng/ml for acid metabolite, respectively. The assay showed linearity over the range of quantification (r2 > 0.998). This method has been applied to the analysis of human plasma samples.

HPLC Determination of Valproic Acid in Human Serum Using Ultraviolet Detection

Abstract A sensitive HPLC method with minimal sample preparation and good reproducibility for the determination of valproic acid in serum is described. Serum samples were precipitated using acetonitrile containing diazepam as the internal standard. Chromatography was performed on a Hewlett Packard model 1090 equipped with an octadecylsilane column and a Beckman model 163 variable wavelength detector. The drug and internal standard were eluted isocratically using a mobile phase consisting of 0.01M sodium phosphate monobasic solution, pH 2.3 and acetonitrile (63:37 v/v) followed by a gradient to flush the column before the next sample injection. The flow rate was 2.5 mL/min, the injection volume was 25 μL and the effluent was monitored at 210 nm. The serum standard curve was linear from 2.5-200.0 μg/mL with a correlation coefficient of 0.9994. Day-to-day precision for quality control samples (10.0, 25.0, 75.0 μg/mL serum) ranged from 5.6-9.6% CV. Possible interferences from other drugs which might be admini...

Steady-State Pharmacokinetics of Hydroxychloroquine in Rheumatoid Arthritis Patients

Steady-state pharmacokinetics of hydroxychloroquine (HC) sulfate (Plaquenil) were studied in five volunteers with rheumatoid arthritis who had taken 6 mg/kg/d of the drug for at least six months. Blood samples were drawn at 0, 1, 2, 4, 6, 8, 12, and 24 hours following an oral dose. Both whole blood and plasma were assayed by an HPLC method for HC and its metabolites desethylhydroxychloroquine, desethylchloroquine, and didesethylchloroquine. A 24-hour urine collection was obtained and assayed for the same compounds. The pharmacokinetics of HC and its metabolites conformed to the model predicted by single-dose studies. During the 24-hour period the absorption phase and both early and late distribution phases were seen. Variation in mean maximum/minimum concentration was 40 percent. Renal clearance accounted for only 16 percent of unchanged HC (22 percent of total drug and metabolites) and did not correlate with creatinine clearance.

An Improved HPLC Method for the Determination of Furosemide in Plasma and Urine

Abstract A sensitive HPLC method with minimal sample preparation and good reproducibility for the determination of furosemide in plasma and urine is described. Acidified plasma samples were extracted using CH2Cl2 containing desmethylnaproxen as internal standard (IS). Fresh urine samples were incubated with β-gluc-uronidase for 15 minutes and then treated with CH3CN containing IS. Chromatography was performed on a C18 column with 10 mcl sample injection, Mobile phases were: a) for plasma: 0.01 M NaH2PO4, pH 3.5 - CH3OH (65:35), and b) for urine: acetic acid, pH 3.5 - CHS3OH (60:40) at 3 ml/min and fluorescence detection at Ex 235/Em 389 nm. The plasma standard curve was linear from 0.01 to 15.0 mcg/ml and the urine from 0.5 to 200.0 mcg/ml. The within run CVs were 3,2% at 0.74 mcg/ml plasma and 2.0% at 10.7 mcg/ml urine. Recovery from plasma was 69.9% at 2.0 mcg/ml and 98.6% from urine at 5.0 mcg/ml. The stability of furosemide and its glucuronide were studied. Both methods have been applied to the analy...

A HPLC method for the separation and quantification of the enantiomers of hydroxychloroquine and its three major metabolites

Abstract A two step HPLC method for analysis of the enantiomers of Hydroxychloroquine (HCQ) and its three major metabolites, Desethylhydroxychloroquine (DHCQ), Desethylchloroquine (DCQ) and Bisdesethylchloroquine (BDCQ), was developed. Fluorescence detection was used at λex=230nm and λem=385nm with a 370nm cut-off filter. This method has higher sensitivity and better resolution of the parent drug and its three metabolites when compared to published methods. In the first step, a cyano column was used to separate and collect fractions containing HCQ and its three metabolites. The mobile phase was 20% pH 6.0 (0.015M K2HPO4) buffer, 30% methanol and 50% acetonitrile at a flow rate of 2 ml/min and 50°C. This method was linear over the concentration ranges of 2–20, 20–300 and 200–2000 ng/ml of blood (r>0.99) and was used for quantitation. In a second step, chiral separation was performed on a chiral-AGP column using a mobile phase of 94% pH 7.0 (0.05M NH4H2PO4, 0.005M dihexylamine) buffer, 5% isopropanol and 1%...

A Simple HPLC Method for the Determination of Trazodone Human Serum

Abstract A simple HPLC method with minimal sample preparation and good reproducibility for the determination of trazodone in serum is described. Basified serum samples were extracted using ethyl acetate containing diazepam as the internal standard (IS). Chromatography was performed on a cyanopropylsilane column with 15 μL sample injection. The mobile phase consisted of 0.02 M ammonium phosphate, pH 7.5 : acetonitrile (70:30 v/v). The eluent was monitored at 220 nm. The serum standard curve was linear from 10.0 to 8000.0 ng/mL serum. The overall within-run quality control CV was 6.3% for five concentrations (20.0, 40.0, 100.0, 250.0 and 1000.0 ng/mL) and the overall recovery from serum was 85.4%. This method has been applied to the analysis of human serum samples.