Quantification of myo-inositol, 1,5-anhydro- D-sorbitol, and D-chiro-inositol using high-performance liquid chromatography with electrochemical detection in very small volume clinical samples.

Inositol is a six-carbon sugar alcohol and is one of nine biologically significant isomers of hexahydroxycyclohexane. Myo-inositol is the primary biologically active form and is present in higher concentrations in the fetus and newborn than in adults. It is currently being examined for the prevention of retinopathy of prematurity in newborn preterm infants. A robust method for quantifying myo-inositol (MI), D-chiro-inositol (DCI) and 1,5-anhydro- D-sorbitol (ADS) in very small-volume (25 µL) urine, blood serum and/or plasma samples was developed. Using a multiple-column, multiple mobile phase liquid chromatographic system with electrochemical detection, the method was validated with respect to (a) selectivity, (b) accuracy/recovery, (c) precision/reproducibility, (d) sensitivity, (e) stability and (f) ruggedness. The standard curve was linear and ranged from 0.5 to 30 mg/L for each of the three analytes. Above-mentioned performance measures were within acceptable limits described in the Food and Drug Administration's Guidance for Industry: Bioanalytical Method Validation. The method was validated using blood serum and plasma collected using four common anticoagulants, and also by quantifying the accuracy and sensitivity of MI measured in simulated urine samples recovered from preterm infant diaper systems. The method performs satisfactorily measuring the three most common inositol isomers on 25 µL clinical samples of serum, plasma, milk, and/or urine. Similar performance is seen testing larger volume samples of infant formulas and infant formula ingredients. MI, ADS and DCI may be accurately tested in urine samples collected from five different preterm infant diapers if the urine volume is greater than 2-5 mL.

In vivo impact of prodrug isosorbide-5-nicotinate-2-aspirinate on lipids and prostaglandin D2: is this a new immediate-release therapeutic option for niacin?

OBJECTIVES: To evaluate the pharmacokinetics and effects of the first immediate-release (IR) niacin-aspirin prodrug (ST0702) on lipid, prostaglandin and thromboxane levels in non-human primates (NHPs). METHODS: We compared 28 mg/kg crystalline IR niacin, equimolar doses of crystalline IR ST0702 and control on low density lipoprotein cholesterol (LDL-C), apolipoprotein B (ApoB) and triglycerides (Tg) in NHPs (6 per group) over 48 h (daily oral gavage). In addition, we compared IR niacin and ST0702 effects on prostaglandin (PG)D(2), ex vivo thromboxane B(2) (TXB(2)) levels and plasma pharmacokinetics. RESULTS: ST0702 is metabolised in vivo to aspirin, niacin and salicylic acid with T(max) values of 30, 45 and 95 min respectively using a non-compartmental model. ST0702 resulted in 38% and 40% reductions in LDL-C and ApoB levels compared to control over the 48 h period (p = 0.027 and p = 0.012 respectively). Corresponding values were 32% and 25% for niacin (both p = NS vs control). ST0702, but not niacin, decreased Tg levels (p = 0.017 for between group difference). Post prandial glycaemia was attenuated vs baseline in the ST0702 group only. Ex vivo serum TXB(2) generation was suppressed at 15 min and complete suppression of TXB(2) was sustained at 24h (p<0.01 vs niacin). ST0702 suppressed PGD(2) exposure eightfold (p = 0.012) compared to niacin over the first 24h. CONCLUSIONS: This two-dose study in NHPs suggests that ST0702 is more effective than IR niacin on lipid profiles, while suppressing TXB(2) and PGD(2) increases and prevents post-prandial glycaemia. ST0702 shows promise as a new IR therapeutic option for niacin.

Clean-up of plasma extracts by gel permeation chromatography during analysis of isosorbide nitrates by capillary gas chromatography.

This work describes how gel permeation chromatography (GPC) can be used for sample clean-up to reduce the fouling of the column in an automated on-column injector. The analytes were isolated from plasma together with the internal standard (isomannide dinitrate) by liquid-liquid extraction on Extrelut silica columns. The extracts were evaporated and reconstituted in tetrahydrofuran for separation of the analytes from non-volatile plasma components by GPC on a styrene-divinylbenzene column with 100 A pore size. A programmable autosampler with an additional three-way valve was used for injection and fraction collection. The molecular weight fraction between 100 and 700 a.m.u. was collected and transferred to the on-column autosampler for capillary gas chromatography on a 30-m column butt-connected to a 0.2-m pre-column. The pre-column was replaced after 50 sample injections. When the GPC purification was excluded from the work-up procedure a deposit of non-volatile components was formed at the injection zone of the pre-column which resulted in excessive peak-tailing after only five or six injections of plasma extract. The limit of determination was 0.2 ng/ml plasma for isosorbide dinitrate and 0.4 ng/ml for the mononitrates.

Metabolic fact of 14C-isosorbide 5-mononitrate in humans.

Single oral doses of 20 mg of the carbon-14 labelled form of the antianginal drug isosorbide 5-mononitrate (5-ISMN, Elantan) were essentially completely absorbed and excreted fairly rapidly in the urine. Means of 24, 52, 78, 93 and 96% dose were excreted during 6, 12, 24, 48 and 120 h, respectively. Concentrations of 14C reached peak levels at about 1-2 h when about 86% of the 14C was associated with the parent drug, 5-ISMN (peak mean level 430 ng/ml), and the remainder mainly with the pharmacologically-inactive denitrated product isosorbide. Because the plasma (and urinary) half-life of isosorbide was longer (about 8-9 h) than that of 5-ISMN (about 4.5 h), the proportions of the former in plasma increased relative to the latter. Concentrations of 14C in whole-blood and plasma were similar, implying that 5-ISMN diffused into blood cells. Concentrations of 5-ISMN in saliva and plasma were almost identical, presumably because of the almost negligible plasma protein binding of the drug (less than 5%). At least five metabolites of 5-ISMN were detected in urine - these were isosorbide (about 37% dose), conjugated material (about 25% dose) presumably mainly 5-ISMN-glucuronide, sorbitol (about 7% dose), the parent drug 5-ISMN (about 2% dose) and two unidentified metabolites (about 7 and 4% dose, respectively). The conjugated material was excreted in the urine relatively more rapidly than the denitrated product, isosorbide.

Determination of isosorbide dinitrate and its mononitrate metabolites in human plasma by high-performance liquid chromatography-thermal energy analysis.

An accurate and sensitive method for the simultaneous determination of isosorbide dinitrate and its 2- and 5-mononitrates in human plasma has been developed. Following extraction of 3.0 ml of plasma with 12.0 ml of dichloromethane-ethyl acetate (1:1) the extract is subjected to high-performance liquid chromatography employing a Zorbax NH2 column. The eluent stream is introduced into a thermal energy analyser, employing chemiluminescence as a specific means of detection. The minimum quantifiable level of the compound in plasma is 200 pg/ml allowing the quantitation of isosorbide dinitrate in human plasma following single oral administration. Nitroglycerin is employed as internal standard.

Simultaneous determination of isosorbide dinitrate and its mononitrates in human plasma by capillary column GLC.

A previously described electron-capture GLC method for determination of isosorbide dinitrate in human plasma was adapted for the simultaneous determination of isosorbide dinitrate, isosorbide 2-mononitrate, and isosorbide 5-mononitrate using a capillary column. Quantitation was done with two internal standards. The lower limits of detection were approximately 0.5 ng/ml of plasma for isosorbide dinitrate, 2 ng/ml for isosorbide 2-mononitrate, and 20 ng/ml for isosorbide 5-mononitrate.