Population pharmacokinetic analysis of isoniazid, acetylisoniazid, and isonicotinic acid in healthy volunteers.

In this study, we aimed to quantify the effects of the N-acetyltransferase 2 (NAT2) phenotype on isoniazid (INH) metabolism in vivo and identify other sources of pharmacokinetic variability following single-dose administration in healthy Asian adults. The concentrations of INH and its metabolites acetylisoniazid (AcINH) and isonicotinic acid (INA) in plasma were evaluated in 33 healthy Asians who were also given efavirenz and rifampin. The pharmacokinetics of INH, AcINH, and INA were analyzed using nonlinear mixed-effects modeling (NONMEM) to estimate the population pharmacokinetic parameters and evaluate the relationships between the parameters and the elimination status (fast, intermediate, and slow acetylators), demographic status, and measures of renal and hepatic function. A two-compartment model with first-order absorption best described the INH pharmacokinetics. AcINH and INA data were best described by a two- and a one-compartment model, respectively, linked to the INH model. In the final model for INH, the derived metabolic phenotypes for NAT2 were identified as a significant covariate in the INH clearance, reducing its interindividual variability from 86% to 14%. The INH clearance in fast eliminators was 1.9- and 7.7-fold higher than in intermediate and slow eliminators, respectively (65 versus 35 and 8 liters/h). Creatinine clearance was confirmed as a significant covariate for AcINH clearance. Simulations suggested that the current dosing guidelines (200 mg for 30 to 45 kg and 300 mg for >45 kg) may be suboptimal (3 mg/liter ≤ Cmax ≤ 6 mg/liter) irrespective of the acetylator class. The analysis established a model that adequately characterizes INH, AcINH, and INA pharmacokinetics in healthy Asians. Our results refine the NAT2 phenotype-based predictions of the pharmacokinetics for INH.

LC-UV/MS methods for the analysis of prochelator-boronyl salicylaldehyde isonicotinoyl hydrazone (BSIH) and its active chelator salicylaldehyde isonicotinoyl hydrazone (SIH).

Salicylaldehyde isonicotinoyl hydrazone (SIH) is an intracellular iron chelator with well documented potential to protect against oxidative injury both in vitro and in vivo. However, it suffers from short biological half-life caused by fast hydrolysis of the hydrazone bond. Recently, a concept of boronate prochelators has been introduced as a strategy that might overcome these limitations. This study presents two complementary analytical methods for detecting the prochelator-boronyl salicylaldehyde isonicotinoyl hydrazone-BSIH along with its active metal-binding chelator SIH in different solution matrices and concentration ranges. An LC-UV method for determination of BSIH and SIH in buffer and cell culture medium was validated over concentrations of 7-115 and 4-115 µM, respectively, and applied to BSIH activation experiments in vitro. An LC-MS assay was validated for quantification of BSIH and SIH in plasma over the concentration range of 0.06-23 and 0.24-23 µM, respectively, and applied to stability studies in plasma in vitro as well as analysis of plasma taken after i.v. administration of BSIH to rats. A Zorbax-RP bonus column and mobile phases containing either phosphate buffer with EDTA or ammonium formate and methanol/acetonitrile mixture provided suitable conditions for the LC-UV and LC-MS analysis, respectively. Samples were diluted or precipitated with methanol prior to analysis. These separative analytical techniques establish the first validated protocols to investigate BSIH activation by hydrogen peroxide in multiple matrices, directly compare the stabilities of the prochelator and its chelator in plasma, and provide the first basic pharmacokinetic data of this prochelator. Experiments reveal that BSIH is stable in all media tested and is partially converted to SIH by H2O2. The observed integrity of BSIH in plasma samples from the in vivo study suggests that the concept of prochelation might be a promising strategy for further development of aroylhydrazone cytoprotective agents.

N-isonicotinoyl-(L)-4-aminophenylalanine derivatives as tight binding VLA-4 antagonists.

A series of isonicotinoyl-(L)-aminophenylalanine derivatives was prepared and evaluated as VLA-4 antagonists. These compounds exhibit subnanomolar binding affinity to VLA-4 and significant off-rates. The interplay between off-rate, protein binding and pharmacokinetics is discussed.

Determination of pyridoxal 5'-phosphate in human serum by reversed phase high performance liquid chromatography combined with spectrofluorimetric detection of 4-pyridoxic acid 5'-phosphate as a derivative.

A very sensitive spectrofluorimetric method for the determination of pyridoxal 5'-phosphate (PLP) in human serum is described. The specificity is based on the selective oxidation of PLP to 4-pyridoxic acid 5'-phosphate with potassium cyanide. Separation of the highly fluorescent 4-pyridoxic acid 5'-phosphate is achieved by reversed-phase high-performance liquid chromatography. Specificity is improved by a careful choice of fluorescence filters, maximised at the excitation (325 nm) and emission (418 nm) wavelengths of 4-pyridoxic acid 5'-phosphate. The detection limit for the reaction is 0.22 ng ml(-1). For quantification, the serum is spiked with PLP before protein precipitation with 3.3% m/V trichloroacetic acid. The method can be used for the determination of PLP in serum, even in vitamin B6 deficient patients. The mean value for human serum PLP from 30 healthy adults was found to be 14.6 +/- 4.8 ng ml(-1) (mean +/- standard deviation).

Plasma B6 vitamer and 4-pyridoxic acid concentrations of men fed controlled diets.

A rapid and sensitive procedure is described for the analysis of all the B6 vitamers and 4-pyridoxic acid in human plasma utilizing reversed-phase high-performance liquid chromatography with ultraviolet and fluorometric detection. Pyridoxal phosphate values obtained by radiometric and chromatographic, ultraviolet and fluorometric, assays were highly correlated as were pyridoxine phosphate values determined using both detectors. Plasma B6 vitamer and 4-pyridoxic acid concentrations of 22 men fed diets containing 0.75-0.98 mg of vitamin B6 daily for eight weeks were in the range of reported values; pyridoxal phosphate was their predominant plasma B6 vitamer. This methodology should be useful in the assessment of vitamin B6 requirements.

Simultaneous and direct determination of pyridoxal, pyridoxal-5'-phosphate, and pyridoxic acid in serum by derivative synchronous fluorescence spectroscopy.

Simultaneous and direct assays of pyridoxal, pyridoxal-5'-phosphate, and pyridoxic acid in human serum are described. The method applied is based on the reaction of these compounds with beryllium in an ammoniacal medium to yield highly fluorescent derivatives. Overlapping of conventional fluorescence spectra is resolved by using second-derivative fluorescence spectroscopy, thus making the use of separation techniques unnecessary. The proposed method is simple (only beryllium and an ammoniacal buffer are needed to develop fluorescence), rapid (the derivative formation is instantaneous and serum treatment only requires deproteinization), and inexpensive (no sophisticated detection equipment is necessary, any conventional modern spectrofluorimeter being adequate for use). The analytical recovery achieved was of about 96% for pyridoxal, 97% for pyridoxal-5'-phosphate, and 100% for pyridoxic acid. Measurements were carried out in a single scan.

A comparison of the blood levels and urinary excretion of ethionamide and prothionamide in man.

The blood levels and urinary excretion of the anti-mycobacterial drugs ethionamide and prothionamide have been compared after oral dosage in man. High pressure liquid chromatographic methods were used to determine the two closely related thioamides and their microbiologically active sulphoxide metabolites after the ingestion of both single and combined doses of the two drugs. Both drugs were rapidly eliminated from the body, the half-life for the urinary excretion and removal from the plasma of prothionamide being slightly less than that of ethionamide. Less than 0.1% of the orally administered doses were excreted unchanged in the faeces. Plasma concentrations of ethionamide and its sulphoxide metabolite were substantially higher than those of prothionamide and prothionamide sulphoxide. The implications of these findings for the use of ethionamide or prothionamide in the treatment of lepromatous leprosy are discussed.

A study of interaction of a low-dose combination oral contraceptive with anti-tubercular drugs.

Low-dose combination contraceptive (containing norethisterone acetate 1 mg and ethinyl estradiol 30 micrograms) was administered to women receiving concurrent therapy with either Rifampicin or "triple" antitubercular treatment consisting of paraaminosalicylic acid (PAS), isonicotinic acid hydrazide (INH) and streptomycin. Plasma levels of norethisterone (NET) and ethinyl estradiol (EE), PAS and INH were measured and the area under curve (AUC) was calculated for NET and EE. Rifampicin treatment (9 women) caused a statistically significant reduction of the plasma NET levels as well as the AUC of NET. In this group of women, though a trend for reduction in EE levels was observed in individual subjects, it was not statistically significant. Out of 7 regularly menstruating women on Rifampicin therapy, 2 showed a premenstrual rise of plasma progesterone (P) levels (> 4 ng/ml) suggesting an ovulatory cycle and 3 experienced menstrual irregularities. In contrast, plasma levels of NET and EE as well as their AUCs were not altered in 8 women receiving "triple" antitubercular therapy. Only one woman out of 8, had menstrual irregularity and all women had P levels in the anovulatory range. Furthermore, oral contraceptive treatment did not alter the plasma levels of PAS and INH.

A radioimmunoassay for isoniazid.

A sensitive radioimmunoassay is described, for measuring isoniazid in therapeutic and subtherapeutic concentrations. This radioimmunoassay was used in an exploratory clinical study to measure, as a function of time, the concentration of this drug in plasma of patients receiving isoniazid therapy.