Solvation enthalpies as descriptors of structure--in vitro percutaneous permeation relationship of benzoxazinones regioisomers.

The aim of this work was to correlate the in vitro human skin permeability, expressed as the permeability coefficient (Kp), and some physicochemical parameters of a new series of benzoxazinones. The in vitro human skin permeability of 14 substances, including regioisomers with CH3, OH, OCH3, and Cl groups in different positions on the aromatic ring, was determined. The modified Franz diffusion cell method was used. The Kp values were in the range 0.14-8.24 cm/h, showing a strong dependence on the position and type of substituent. Physicochemical descriptors usually referred in literature, such as log P, molecular weight and volume (MV), hydrogen bond donor (Hd) and acceptor activity (Ha), and molecular refractivity were considered, with the addition of solvation enthalpy (delta deltaHsolv). Delta deltaHsolv is defined as the difference between formation enthalpies in water and octanol. The algorithm with the best correlation between Kp and physicochemical descriptors was calculated, taking into account the differences observed among the regioisomers. The algorithm obtained with delta deltaHsolv had a good correlation (r2 = 0.749, F = 16.43, P = 0.0005), comparable with the equation, proposed by Potts and Guy, based on MV, Hd and Ha (r2 = 0.830, F = 16.3, P = 0.0004).

Pharmacokinetics of ITF 296 (Sinitrodil) a novel organic nitrate, in healthy volunteers.

ITF 296 is a new orally active nitrate acting selectively on large arterial vessels over a wide range of doses. In healthy volunteers it causes less reduction in vascular resistance and less venodilatation than classic nitrates. Its pharmacokinetic profile was evaluated after intravenous infusion and oral (solution and immediate-release tablet) administration in a randomised cross-over design on 11 healthy volunteers. The plasma levels of ITF 296 and its metabolite ITF 1124 were determined by a HPLC method. The drug is rapidly distributed (mean steady-state distribution volume 53+/-17 liters) and eliminated (half-life of about 25 minutes) both after intravenous and oral administration. The total clearance is 2. 31+/-0.46 l/min. The oral solution of ITF 296 is well absorbed (Cmax=0.057 microg/ml, tmax=30 min) but it undergoes a first-pass effect (F=25%). The tablet, developed only for Phase 1 clinical studies, is characterised by an immediate release (Cmax=0.057 microg/ml, tmax=30 min). The extent of its absolute and relative bioavailability is about 14% and 53% respectively.

In vitro skin permeation of Sinitrodil, a member of a new class of nitrovasodilator drugs.

Clinical trials have shown the potential of benzoxazinones, a new class of organic nitrates, in cardiovascular therapy. In particular Sinitrodil possesses a coronary vascular selectivity greater than that of Nitroglycerin and isosorbide dinitrate. The objective of this study was a preliminary evaluation of the ability of these new organic nitrate derivatives to reach therapeutical steady-state plasma concentrations following a transdermal administration. In vitro permeation studies through human stratum corneum and epidermis have been conducted on two members of this class: Sinitrodil (ITF 296) and ITF 1129. Comparative studies have also been carried out with Nitroglycerin, Isosorbide dinitrate and Nicorandil. Two different fixed concentrations were tested: 0.08% w/v solution and saturated solution. Sinitrodil could be considered a good candidate for transdermal administration on the basis of the in vitro permeation results and of the known therapeutical plasma concentration.

Pharmacokinetic study in rats after single intravenous and oral administrations of [14C]-ITF-296.

Pharmacokinetics of [14C]-ITF-296 and its metabolites, ITF-1124 and ITF-1577, were studied in rats after a single intravenous (2.5 mg/kg) and oral (10 mg/kg) administration. Radioactivity was measured by LSC while unchanged drug and its metabolites in plasma were assayed by an HPLC-UV method. The absorption of [14C]-ITF-296 after oral administration is practically complete. Elimination of radioactivity occurs mainly in urine (higher than 80%) and the recovery of the dose (higher than 95%) takes place up to 96 h after both treatments. Both by i.v. and p.o. route the results show that the radioactivity is largely excreted in the bile and reabsorbed in the intestine. The tissue distribution study indicates that there is no accumulation or localization of radioactivity in the major organs or blood and no radioactivity levels are found 96 h after either treatment. In addition, whole body autoradiography confirms the tissue distribution pattern, showing no differences between albino and pigmented rats.

Pharmacokinetic study in dogs and monkeys after single intravenous and oral administrations of [14C]-ITF-296.

Pharmacokinetics of [14C]-ITF-296 and its metabolites, ITF-1124 and ITF-1577, were studied in dogs and monkeys after a single intravenous (2.5 mg/kg) and oral (10 mg/kg) administration. Radioactivity was measured by LSC while unchanged drug and its metabolites in plasma were assayed by an HPLC-UV method. The absorption of [14C]-ITF-296 after oral administration is practically complete both in dogs and in monkeys. The determination of unchanged drug and its metabolites shows quite a similar profile in dogs and monkeys for ITF-296 and ITF-1124 and a different time-course for ITF-1577. Elimination of radioactivity occurs mainly in urine (namely 70-80%) for both species and the recovery of the dose (higher than 90%) takes place up to 96 h after both treatments.

Simultaneous determination of ITF 296 and two metabolites in plasma by a validated HPLC method.

A simple and sensitive HPLC validated method was developed for the simultaneous determination of ITF 296 (a new orally active nitrate) and its metabolites ITF 1124 and ITF 1577 in biological samples. Quantitation was performed by peak height ratios between the three compounds and the internal standard (ITF 1721). Detection limit of the method was 0.005 microgram/ml using 1 ml of plasma. The results indicated that the method is reproducible, accurate, precise, sensitive and specific for the measurement of the three compounds in plasma samples. Those characteristics allowed us to conclude that the method is suitable for analysing samples obtained after administration of ITF 296 to humans at therapeutic dosage and to animals for formulation studies.

HPLC determination of ITF 188 and its metabolite ITF 1078 in urine after intranasal administration of new heparin salt ITF 1300 to dogs.

Heparin salt ITF 1300 in which low molecular weight heparin is salified with a new counterion, di-[3-(N,N-dibutylamino)]propyl carbonate (ITF 188), was selected for the pharmacological development. A specific, sensitive and reproducible HPLC method for the determination of ITF 188 and its alcoholic metabolite ITF 1078 in urine was developed. The method was employed for the study of urinary excretion of the counterion after intranasal administration of ITF 1300 to dogs. The total amount of ITF 188 and ITF 1078 found in urine within 72 hours after the nasal instillation of ITF 1300 accounts for about 5% of the administered dose.

Pharmacokinetic profile of ITF 296 in rats and dogs.

The pharmacokinetic profile of ITF 296 was studied after a single oral or i.v. dose administered to rats and dogs. ITF 296 and its first metabolite, ITF 1124, were measured in plasma and urine by a validated HPLC method with UV detection. Similar results were obtained in both animal species. After i.v. administration, the initial decline in plasma levels (distribution phase) was rapid, followed by a slower elimination phase. After oral administration, ITF 296 was rapidly and almost completely absorbed from the gastrointestinal tract, the maximal plasma levels being reached between 10 min and 1 h after administration in both species. Only traces of the parent compound were found in the urine of the two species, suggesting that ITF 296 was extensively metabolized. Preliminary data indicate that renal excretion is the major route of elimination of the biotransformed products. The denitrated metabolite was present in plasma from the earliest sampling time after either the i.v. or the oral route. After oral administration the drug was not significantly metabolized during passage through the liver, suggesting good bioavailability. The development of ITF 296 as a new orally active nitrate is supported by its pharmacokinetic profile in rats and dogs.