Assay and purity analysis of diatrizoate sodium in drug product by LC.

An LC procedure was developed to separate diatrizoate sodium from three known impurities. These impurities are 2,4- and 2,6-diiodo-3,5-diacetamidobenzoic acid (DDZA), and the free amine (5-acetamido-3-amino-2,4,6-triiodobenzoic acid). The separation was achieved using a Hamilton, PRP-X100, anion exchange column. The retention of diatrizoate sodium and the impurities was dependent on pH, potassium chloride concentration and phosphate concentration. Increasing any of these mobile phase modifiers decreased the retention time of all of the components. The eluent for assay and purity determination of drug product consisted of 0.1 M potassium chloride and 0.05 M potassium phosphate dibasic in water/acetonitrile (900:100). The mean concentration of diatrizoate sodium in Hypaque Sodium 50% determined over 3 days was 102.3% of label claim with an R.S.D. of 1.3. The accuracy of the purity method, determined by spiking known amounts of the impurities at five concentrations ranging from 0.025 to 0.06% (w/w) into drug product, was 100.1% for DDZA and 94.2% for the free amine. The decomposition of diatrizoate sodium in 0.1 N potassium hydroxide at 85 degrees C followed pseudo first-order kinetics. The calculated half-life was 2 days.

Binding constant determination of WIN 22169, a novel polymeric ligand.

WIN 22169 is a co-polymer containing approximately 11 repeating units of polyoxyethylene and diethylenetriamine pentaacetic acid (DTPA). WIN 66368, a magnetic resonance imaging (MRI) contrast agent, is the gadolinium III complex of WIN 22169. WIN 22169 has been characterized with respect to its equivalent weight, acidity constants and excess acid or base, as well as its metal ion binding constants. The logs of the equilibrium binding constants of the ligand to Gd3+, Ca2+, Zn2+ and Cu2+ were found to be 16.6, 7.47, 12.2 and 14.0. The Gd selectivity constant, a measure of the preferential binding of the ligand toward Gd3+ versus the three in vivo ions: Ca2+, Zn2+ and Cu2+, of WIN 66368 was calculated to be 7.9. This value compares favourably to that for Gd DTPA which has a Gd selectivity constant of 7.04.

An LC method for measuring complex formation equilibria by competitive chelation.

A method, entailing the use of a competitor ligand, is described for measuring complex formation constants by HPLC. The log of the formation constant of Gd(III) 2,6-bis(aminomethyl)pyridinetetraacetate was determined to be 18.6, a previously unreported value.

The effect of mobile phase modifiers on the simultaneous LC elution of a gadolinium complex and free ligand.

A liquid chromatographic method was developed for simultaneous separation of a gadolinium complex and corresponding ligand using a reversed-phase anion-exchange column. The effect of mobile phase pH, EDTA and chloride ion concentration, added to the mobile phase as counter-ions, on the elution of a metal complex and ligand were investigated. Decreasing the mobile phase pH from 9.4 to 7.4 decreased the retention time of the free ligand but had little effect on changing the retention time of the complex. Increasing the EDTA concentration of the mobile phase from 0 to 0.5 mM decreased the retention of the free ligand but had little effect on changing the retention time of the metal complex. Both the retention times of the metal complex and free ligand decreased as the chloride ion concentration was increased from 0 to 0.2 M.

Benzoyl peroxide solubility and stability in hydric solvents.

Saturated solubility and reaction rate constants for the decomposition of benzoyl peroxide in solution and suspension were determined for use in formulation development. The solvents studied included ethanol, propylene glycol, and cosolvent mixtures of PEG 400 and water. The solubility of benzoyl peroxide was inversely related to the solvent polarity, with greater solubility occurring with semipolar solvents. The stability of benzoyl peroxide in solution was dependent on the solvent, concentration of benzoyl peroxide, and temperature. The compound was least stable in PEG 400. Stability was improved when water was added to PEG 400. Similar solvent effects were observed in suspension. In benzoyl peroxide suspensions of PEG 400 and PEG 400/water blends, benzoyl peroxide stability was dependent on solubility, with improved stability occurring in blends where the benzoyl peroxide was least soluble. Thus, solution formulations of benzoyl peroxide in pharmaceutically acceptable solvents are unlikely to show good stability; however, suspension formulations should be reasonably stable if the vehicle is selected to provide low benzoyl peroxide solubility.

Distribution and fate of diethyl malonate and diisopropyl fluorophosphate on pig skin in vitro.

The in vitro distribution and fate of [14C]diethyl malonate and [14C]diisopropyl fluorophosphate were evaluated on normal and heat-treated pig skin. The extent of hydrolysis from the skin surface, skin, and receptor fluid was determined. A significant skin-mediated hydrolysis (15-35% of applied dose) was observed for diethyl malonate in normal skin, but not in heat-treated skin. These results indicated that a heat labile process (e.g., enzymatic hydrolysis) was in part responsible for the degradation of diethyl malonate after topical application to normal skin. Heat treatment tripled the skin penetration of diisopropyl fluorophosphate and reduced the amount of recovered hydrolysis product, diisopropyl phosphoric acid. Enzymatic and spontaneous hydrolysis, as well as impurity, accounted for the presence of degradation product.

Percutaneous penetration in the hairless dog, weanling pig and grafted athymic nude mouse: evaluation of models for predicting skin penetration in man.

The human skin grafted congenitally athymic (nude) mouse, pig skin grafted nude mouse, hairless dog, and weanling Yorkshire pig were evaluated as models for predicting skin penetration in man. Nine radiolabelled compounds previously tested on man were applied topically (4 micrograms/cm2) to each model. These compounds included caffeine, benzoic acid, N, N-diethyl-m-toluamide, three steroids, and three insecticides. To correct for incomplete excretion of the label following topical absorption, per cent penetration was calculated by dividing the per cent of the topically applied radioactive dose recovered in the excreta by the corresponding percentage after parenteral administration and multiplication by 100. Calculated values of per cent penetration were confirmed in the case of the grafted nude mouse because significant correlations (r = 0.78 for human skin grafted athymic nude mouse and r = 0.97 for pig skin grafted athymic nude mouse) were found between the calculated values and the actual values obtained by summing the radioactivity recovered in the urine, faeces, tissues, and carcass. The results also revealed a significant correlation between human skin grafted athymic nude mouse values and human values (r = 0.74, P = 0.05) and between weanling Yorkshire pig values and human values (r = 0.83, P = 0.05). In contrast, no significant correlation existed between human values and those of the hairless dog and the pig skin grafted athymic nude mouse.

Evaluation of animal models for predicting skin penetration in man.

The human skin grafted athymic nude mouse, pig skin grafted athymic nude mouse, hairless dog, and weanling Yorkshire pig were evaluated as models for predicting skin penetration in man. Nine radiolabeled compounds previously tested on man were applied topically (4 micrograms/cm2) to each animal. These compounds included caffeine, benzoic acid, N,N-diethyl-m-toluamide, three steroids, and three insecticides. To correct for incomplete excretion of the label following topical absorption, percentage penetration was calculated by dividing the percentage of the topically applied radioactive dose recovered in the excreta by the corresponding percentage after parenteral administration and multiplication by 100. In the case of the grafted athymic nude mouse, calculated values of percentage penetration were confirmed because significant correlations (r = 0.78 for the human skin grafted athymic nude mouse and r = 0.97 for the pig skin grafted athymic nude mouse) were found between the calculated values and percentage penetration determined by summing radioactivity recovered in the urine, feces, tissues, and carcass. The results revealed a significant correlation between human skin grafted athymic nude mouse values and human values (r = 0.74, p = 0.05), and between weanling Yorkshire pig values and human values (r = 0.83, p = 0.05). In contrast, no significant correlation existed between human values and those of the hairless dog and pig skin grafted athymic nude mouse. The disposition of radioactivity following topical application of the radiolabeled nerve agent analog ( diisopropylfluorophosphonate ) and simulant (diethyl malonate) was determined in the weanling pig and the human skin grafted athymic nude mouse.(ABSTRACT TRUNCATED AT 250 WORDS)