A.J. Repta

Factors affecting the stability of fluorescent isoindoles derived from reaction of o-phthalaldehyde and hydroxyalkylthiols with primary amines

The stability of a series of fluorescent isoindole derivatives formed in situ under analytical conditions following the reaction of o-phthalaldehyde (OPA) and 2-mercaptoethanol (2-ME) with a series of primary amines are reported. Increasing the bulk and degree of substitution at C-10 of the resulting isoindole resulted in substantial increases in product stability. The effects of excess OPA and 2-ME on isoindole stability were examined and OPA was observed to catalyze isoindole degradation while 2-ME had no effect. Previously proposed degradation mechanisms were reexamined in light of the present data and an alternate degradation pathway is proposed. 3-Mercapto-1-propanol (3-MP) was found to be a superior thiol for use in the fluorogenic OPA reaction. The OPA/3-MP reagent combination was utilized to derive several amino acids and offered detection limits (S/N = 2) of less than 200 fmol.

Urine analysis of platinum species derived from cis-dichlorodiammineplatinum(II) by high-performance liquid chromatography following derivatization with sodium diethyldithiocarbamate.

A clinically useful method is described for the quantitative analysis of platinum species derived from cis-dichlorodiammineplatinum(II) in urine. The drug and its biodegradation products are derivatized directly in urine by reaction with sodium diethyldithiocarbamate (DDTC) to form a common product, a 2:1 DDTC-platinum adduct. This complex is stable and can be quantitatively extracted into 0.1 volumes of chloroform. An aliquot of the chloroform layer is then subjected to high-performance liquid chromatography on a muBondapak CN column and the eluent monitored spectrophotometrically at 254 nm. At this wavelength the DDTC-platinum adduct has a molar absorptivity of 43,000, and platinum levels of 25 ng/ml or urine can be detected with a precision of +/- 2.5% and an accuracy of +/- 4%.

Controlled drug delivery devices for experimental ocular studies with timolol 2. Ocular and systemic absorption in rabbits

Controlled drug delivery was tested as a means to decrease the potentially dangerous systemic drug concentrations which are associated with timolol eyedrop therapy. l-Tumolol (125 μg) was administered in 0.5% eyedrops (25 μl, pH 6.86) and in controlled release silicone tubing devices (dose 57.6 μ;g; release rate 7.2 μgh for 8 h) in the eyes of pigmented rabbits. [3H]Timolol tracer was used in ocular absorption studies and unlabeled timolol dosage forms in systemic absorption studies. [3H]Timolol concentrations were determined in ocular tissues and tear fluid. Beta blocking activity in plasma was determined using a radioreceptor assay. Comparable timolol concentrations were achieved in the iris-ciliary body with silicone tubing devices (57.6 μg) and with eyedrops (125 μg). The relative ocular timolol bioavailability after controlled drug delivery was about 2-fold greater than from eyedrops. In plasma, peak beta-blocking activity was much higher after eyedrop administration (17.16 ± 2.40 ng/ml) than during controlled timolol delivery (< 1.0 ngml). The results indicate that controlled drug delivery is a viable alternative in improving the therapeutic index of glaucoma therapy with timolol.

High-performance liquid chromatography of cis-dichlorodiammineplatinum(II) using chemically-bonded and solvent-generated ion exchangers

cis-Dichlorodiammineplatinum(II) (cisplatin), a neutral square planar platinum(II) complex useful in the clinical management of a variety of neoplasms, was found to be retained on chemically-bonded and solvent-generated anion exchangers. The solvent-generated anion exchanger was prepared by the adsorption of hexadecyltrimethylammonium bromide onto the surface of a hydrophobic stationary phase. Investigations into the effects of ionic strength, organic modifiers and temperature revealed certain fundamental differences between the two systems. However, the retention mechanism of cisplatin on both types of cationic stationary phases was most readily explained in terms of ion-dipole interaction.

Solubilization and stabilization of an investigational antineoplastic drug (NSC no. 278214) in an intravenous formulation using an emulsion vehicle

Abstract The use of parenteral fat emulsions for development of an extemporaneous preparation of an intravenous formulation of a poorly water-soluble and unstable investigational anticancer agent (NSC no. 278214) is presented. The incorporation into a commercial fat emulsion of the drug, dissolved in dimethylacetamide-cremophor solution, results in a suitable parenteral formulation in which the drug is approximately 100-fold more stable than in simple aqueous solutions.

Rational design and evaluation of improved o-phthalaldehyde-like fluorogenic reagents

Evidence was presented suggesting that the fluorescent isoindole produced by reaction of o-phthalaldehyde (OPA), ethanethiol, and primary amine was formed by initial imine formation followed by conversion to an alpha-alkylaminobenzylsulfide and subsequent ring closure to form the isoindole nucleus. This mechanism suggested that the minimum structural requirement for condensation to an isoindole was an o-diacyl benzene in which one of the carbonyl groups was aldehydic. A major drawback of OPA as an analytical reagent is the limited stability of the fluorescent 1,2-disubstituted isoindole. Since isoindole instability is related to autoxidation at C-3, the use of o-(formyl) arylketones as alternatives to OPA is attractive in increasing the lifetime of the fluorescent species in that such reagents would form 1,2,3-trisubstituted isoindoles. Two compounds, o-acetylbenzaldehyde (OAB) and o-benzoylbenzaldehyde (OBB), were synthesized and evaluated as potential fluorogenic reagents. Both formed fluorescent products. The rate of formation of isoindole from the latter was too slow to make it of practical analytical value; however, OAB formed isoindoles with t1/2 less than 10 s and offered markedly improved stability over that observed with OPA.

Pharmacokinetics of intact cisplatin in plasma. Infusion versus bolus dosing

Abstract Plasma levels of total platinum, total filterable platinum and intact cisplatin were monitored in 4 patients who received cisplatin in a regimen consisting of 20 mg/m 2 by i.v. bolus followed immediately by 80 mg/m 2 by 6 h infusion. Baseline pharmacokinetic parameters were obtained from a previous study in which 100 mg/m 2 of cisplatin was administered by a single i.v. bolus. These baseline pharmacokinetic parameters were used in an attempt to predict the pharmacokinetic behavior of cisplatin in the present study. The results demonstrated close agreement between observed and predicted plasma level-time profiles and the area under the plasma concentration-time profiles for cisplatin. The ratios of the various platinum species in plasma over the time course of the study were also consistent with those previously reported. These findings suggest that at a dose of 100 mg/m 2 , the pharmacokinetics of cisplatin and its conversion to other species in plasma are independent of dosage schedule. Since 100 mg/m 2 is a relatively high dose of cisplatin, it is likely that this approach is applicable to other doses and schedules, and ultimately might prove useful in designing optimum cisplatin dosage regimens.

Assessment of cisplatin reactivity with peptides and proteins using reverse-phase high-performance liquid chromatography and flameless atomic absorption spectroscopy.

Abstract Methodology based on gradient elution reverse-phase high-performance liquid chromatography has been developed to permit monitoring of reactions of cisplatin, a noble metal-containing antineoplastic agent, with peptides, polypeptides, and proteins. Such reactions have been implicated in biotransformation of eisplatin. Specificity is provided by both the chromatographic column and the use of on-line uv and off-line atomic absorption spectroscopic detectors placed in series postcolumn. chromatographic conditions were optimized to maximize resolution of nitrogenous components. In some cases, however, resolution of platinum-containing components and those devoid of metal was not possible. This chromatographic overlap could be deconvoluted by sequentially monitoring the eluant with a uv detector (responsive to all proteinaceous material) and on atomic absorption spectrophotometer (specific for platinum detection). This technique has been applied to a kinetic investigation of cisplatin reactivity toward Met-enkephalin.

Buccal drug absorption. I. Comparative levels of esterase and peptidase activities in rat and hamster buccal and intestinal homogenates

Abstract Esterase, aminopeptidase, carboxypeptidase, and endopeptidase activities were quantitated in homogenates of rat and hamster buccal and intestinal tissues. Whole homogenates (cytosol + cell membranes) of both tissues from the rat had higher esterase activity than supernatants of these homogenates. In both species intestinal homogenates showed significantly higher esterase and amino-peptidase activities than buccal homogenates, while carboxypeptidase activity in buccal homogenates was significantly higher than intestinal homogenates. Although hamster buccal and intestinal homogenates had similar levels of endopeptidase activity, rat intestinal homogenates had significantly higher endopeptidase activity than buccal homogenates. The results suggest that the utility of the buccal mucosa as a delivery route for some drugs may be compromised - as with the intestinal mucosa - by the presence of drug-degrading enzymes in the mucosa.

High-performance liquid chromatography of platinum complexes on solvent generated anion exchangers : III. Application to the analysis of cisplatin in urine using automated column switching

Platinum complexes are retained on solvent generated anion exchangers, prepared by coating reversed-phase (C-18) supports with a monolayer of hexadecyltrimethylammonium bromide. The retention mechanism is described in terms of ion--dipole interactions in the stationary phase, reinforced by a hydrophobic effect. The high degree of ligand selectivity exhibited by these systems arises from the use of purely aqueous mobile phases which maximize the differences in solute dipole and hydrophobic surface area. By using stationary phases of different surface characteristics and the application of automated column switching, the technique is applicable to the clinical analysis of cisplatin in urine. After chromatography, the purified cisplatin fractions area determined by atomic absorption spectrophotometry. The recovery of cisplatin from urine is 101.1% with a relative standard deviation of 3.6% and the limit of detection is 2 micrograms/ml.