Spectrofluorometric determination of montelukast in dosage forms and spiked human plasma.

The native fluorescence of montelukast has been studied under different experimental conditions. The highest fluorescence intensity was obtained in methanol at 390 nm using 340 nm for excitation. Surfactants and sensitizers had either a negative or a slightly positive effect on its fluorescence intensity. The fluorescence intensity-concentration plot was rectilinear over the range 0.125 to 5 microg/ml with a lower detection limit of 0.02 microg/ml (3.4 x 10(-8) M). Interference likely to be introduced from co-formulated drugs (such as loratadine) or co-administered drugs (such as verapamil, carbazepam, propranolol) or other common drugs, was studied. The method was successfully applied to the determination of the drug in tablets (pediatric tablets, chewable tablets and adult tablets). The mean % recoveries were in agreement with those provided by the manufacturer. The method was further applied to the in vitro determination of montelukast in spiked human plasma, the mean % recovery (n = 5) was 100.08 +/- 1.40.

Spectrofluorimetric determination of vigabatrin and gabapentin in urine and dosage forms through derivatization with fluorescamine.

A stability-indicating, sensitive, simple and selective spectrofluorimetric method was developed for the determination of vigabatrin (VG) and gabapentin (GB). The method is based on the reaction between the two drugs and fluorescamine in borate buffer of pH 8.2 to give highly fluorescent derivatives that are measured at 472 nm using an excitation wavelength of 390 nm for both drugs. The optimum conditions were ascertained and the method was applied for the determination of VG and GB over the concentration range of 0.20-4.00 and 0.1-1.0 microg/ml, respectively with detection limits of 0.05 microg/ml (2.9 x 10(-7) M) and 0.06 microg/ml (2.3 x 10(-7) M) for VG and GB, respectively. The suggested method was applied, without any interference from the excipients, to the determination of the two drugs in their pharmaceutical formulations. Furthermore, the method was extended to the in-vitro determination of both drugs in spiked human urine. Interference from endogenous amino acids could be eliminated through selective complexation with copper acetate, the % recovery (n=4) is 98.0 +/- 7.05. Co-administered drugs such as lamotrigine, phenobarbitone, valproic acid, clopazam, carbamazepine, clonazepam and cimitidine did not interfere with the assay. The method is also stability-indicating; as the degradation product of vigabatrin: 5-vinylpyrrolidin-2-one, produced no interference with its analysis.

Voltammetric determination of josamycin (a macrolide antibiotic) in dosage forms and spiked human urine.

The voltammetric behaviour of josamycin (a macrolide antibiotic) has been studied using direct current (DC(t)) alternating current (AC(t)) and differential pulse polarography (DPP). In Britton-Robinson buffers, josamycin developed cathodic waves over the pH range 7-12. At pH 10, a well-defined cathodic wave with diffusion current constant of 1.06 +/- 0.19 (n = 5) was obtained. The wave was characterized as being diffusion-controlled; and partially affected by adsorption phenomenon. The current-concentrations plots are rectilinear over the range 10-60 and 6-50 microg/ml using DC(t) mode and DPP mode, respectively. The minimum detectability limit was 1.2 microg/ml (1.9 x 10(-6) M) adopting the DPP mode. A method was proposed for the determination of josamycin in its tablets adopting both DC(t) and DPP modes. The results obtained were in good agreement with those given by the manufacturer. The method was extended to the in-vitro determination of the drug in spiked human urine; the % recovery was 98.06 +/- 1.76% (n = 5). The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented.

Spectrofluorimetric determination of vigabatrin and gabapentin in dosage forms and spiked plasma samples through derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole.

A highly sensitive and specific method is proposed for the determination of vigabatrin (I) and gabapentin (II) in their dosage forms and spiked human plasma. The method is based on coupling the drugs with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole in borate buffer at pH 7.1 and measuring the resulting fluorescence at 532 nm after excitation at 465 nm. The fluorescence intensity was a linear function of the concentration of the drugs over the ranges of 1.3-6.5 and 1.7-8.5 microg/mL for I and II, respectively. Minimum detectability values were 0.54 microg/mL (4.2 x 10(-6)M) and 0.97 microg/mL (5.7 x 10(-6)M) for I and II, respectively, under the described conditions. The proposed method was successfully applied to the determination of the 2 drugs in their dosage forms, and the percent recoveries +/- standard deviation (SD) were 104.53 +/- 1.2 and 100.00 +/- 1.32 of the label claim for I and II, respectively. The method was further applied to the determination of vigabatrin in spiked plasma samples. The percent recovery +/- SD was 101.58 +/- 2.68. Interference from endogenous alpha-amino acids was overcome through selective complexation with freshly prepared Cu(OH)2. The interference likely to be encountered from co-administered drugs, such as carbamazepine, cimetidine, clonazepam, clopazam, phenobarbital, valproic acid, and lamotrigine, was also studied. A reaction pathway is suggested.

Spectrofluorometric determination of nimodipine in dosage forms and human urine.

A simple sensitive and specific spectrofluorometric method was developed for the determination of nimodipine (NDP) in pharmaceutical preparations and human urine. The method is based on reduction of nimodipine with Zn/HCl and measuring the obtained fluorescence at 425 nm after excitation at 360 nm. The factors affecting the development of the fluorophore and its stability were studied and optimized. The effect of some surfactants such as beta-cyclodextrin (betaCD), carboxymethylcelullose (CMC), sodium dodecyl sulphate (SDS) and Triton X-100, on the fluorescence intensity was studied. The fluorescence intensity-concentration plot is rectilinear over the range 0.1-5.0 microg/ml in presence of Triton X-100 with a minimum detectability limit of 0.06 microg/ml (1.62 x 10(-7) M). The proposed method was successfully applied to commercial tablets containing NDP, the percentage recovery agreed well with those obtained using the official methods. The method was further extended to the in vitro determination of NDP in spiked human urine samples. The % recovery was 102.1 +/- 2.54 (n = 4). A proposal of the reduction reaction pathway was postulated.

Spectrofluorimetric determination of manzamine A in spiked human urine and plasma.

The native fluorescence of manzamine A (a biologically active beta-carboline marine-derived alkaloid) has been studied under different conditions. The highest fluorescence intensity was obtained in methanol. Two wavelength settings were found to be suitable for excitation, 280 nm and 340 nm; while lambdamax emission was constant in both cases at 387 nm. The fluorescence intensity at 340/387 nm setting was 1.6 greater than that obtained at 280/387 nm settings. The calibration curves were rectilinear over the range 0.1-2.0 and 0.5-2.5 microg/ml for the two settings, respectively. The detection limits were 0.05 microg/ml (9.1 x 10(-9) M) and 0.1 microg/ml (1.82 x 10(-8) M) at 340/387 nm and 280/387 nm, respectively. The proposed method was applied to the determination of manzamine A in spiked human urine and plasma samples adopting the 340/387 nm wavelength setting, the % recoveries (n = 6) were 99.61 +/- 0.90 and 100.25 +/- 1.63, respectively.

Population based data on urinary excretion of various metabolites in children of north western region of Pakistan.

Population based data on urinary excretion of various metabolites of pathological importance, Calcium, Magnesium, Sodium, Potassium, Oxalates, Citrates, Phosphates, Uric acid and urea have been collected from around three hundred children of the Quetta valley. The body weight was in the range of 11-50 kg and the age was in between 4-16 years. The urine excretion average was 987.5 +/- 452.5 ml per 24 hours. There was 11.5% incidence of hypercalciuria, 8.5% incidence of hyperuricosuria, 2.0% hyperphosphaturia, 2.5% hypomagnesuria, 3.5% hypocitraturia, 6.5% hypernatriuria, 43.5% hypokaliurea and 2.1% hyperoxaluria. Urea excretion average was 23.11 +/- 14.99 g per 24 hours. The study provided the basis for childhood reference pattern in urinary excretion of compounds related to various pathological conditions, in particular stone formation in this region.