Zinc(II) in saliva: determination of concentrations produced by different formulations of zinc gluconate lozenges containing common excipients.

A study of the pH of saliva produced by humans sucking hard candy lozenges containing zinc gluconate and citric acid demonstrated the probability that the formulation delivered an insignificant amount of the contained zinc as Zn2+. This could account for the negative results of several clinical studies of this lozenge and similar formulations as treatment for the common cold. Direct measurement of unbound Zn2+ in saliva from this and other zinc gluconate formulations was required to substantiate the inference from the pH study. A specific-ion-electrode assay method was developed. Using this method, it was found that saliva completely suppresses the ionization of zinc to free Zn2+ in the presence of citric acid or a 30-fold molar excess of mannitol plus sorbitol. Under the same conditions, however, the presence of an excess of glycine does not interfere with ionization to produce Zn2+. This finding supports the hypothesis that the positive clinical results of three studies were due to the use of formulations which release ionic zinc.

Analytical methods for drugs in the next decade.

Today's research for new drug substances is moving toward molecules of much larger molecular weight and complexity than the small, modern drug molecules, e.g., polypeptides, interferon, slow-releasing substances, and blood and plasma components. The complexity of natural products derived from human or other animal bodies requires a new analytical chemistry. Simple tests for drug stability, dissolution, and bioavailability will no longer suffice to provide and ensure purity and structural identity of such drugs. During the next decade, the demands on analytical chemists will increase; more biological organic and physical chemistry will be required by analysts to perform their jobs. Criteria for purity will require even greater chromatographic involvement but this will have to be complemented by nuclear magnetic resonance and mass spectrometry. The demands made on AOAC to validate and approve methods to assay drugs and determine their purity will increase enormously in this next decade. The understanding of drug purity will take on a new meaning because of the complex nature of natural products. Stability indication will be significant only when chemical and biological tests can complement and define the active components and the impurities. AOAC will be required to play a major role in assuring the manufacturer and the public that their drugs are adequately tested, safe, and efficacious.

Reverse phase high speed liquid chromatography of antibiotics. III. Use of ultra high performance columns and ion-pairing techniques.

Improved methods for the separation and quantitation of cephalosporin, penicillin, aminoglycoside and anthracycline antibiotics are presented. The use of ultra high performance 5 micrometer phase columns combined with the added dimension of ion-pairing greatly increases the ease of separation and speed of analysis of complex antibiotic mixtures. Antibiotics in a variety of dosage forms and in fermentation broths have been examined in order to provide the maximum data on impurities to meet regulatory requirements for drug safety, purity and efficacy. Mixtures of antibiotics have been analyzed to demonstrate the improved separations, increased efficiency and shortened analysis times possible with ultra thin performance columns. Under these improved conditions, the danger of multiple components in a single peak are markedly reduced.

Preparation and properties of bilirubin photoisomers.

Polar photoisomers of bilirubin were formed by irradiation of bilirubin in chloroform solution in the absence of O2. Two pairs of compounds were isolated with molecular weights identical with bilirubin. One pair reverted to bilirubin in polar media and gave chemical reactions similar to bilirubin; the other pair were not reconverted into bilirubin by chemical means and gave reactions distinct from those of bilirubin. However, both groups were reconverted into bilirubin by irradiation in chloroform solution in the absence of O2. The probable role of these photoisomers in the catabolism of bilirubin during phototherapy of neonatal jaundice is discussed.

Quantitative determination of cephalexin in cephradine by NMR spectroscopy.

An NMR method to determine quantitatively the presence of cephalexin in cephradine was developed. The method is applicable to the chemical itself as well as to capsules and oral suspension formulations. The determination is based on the NMR signal arising from the five aromatic protons of the cephalexin molecule. Integration of this signal relative to a signal from cephradine provides the data necessary to determine the percentage of cephalexin present. The precision at the 2% cephalexin levels is +/- 0.18%. The time required to carry out a single analysis is about 10 min, and five analyses can be done in about 0.5 hr.

Quantitative determination of chlorpromazine. HCl in tablets, spansules, injectables, and bulk chemical by nuclear magnetic resonance spectroscopy.

A nuclear magnetic resonance (NMR) procedure is described for the quantitative analysis of chlorpromazine. HCl in bulk chemical as well as in final dosage forms--tablets, spansules, and injectables. The method is based on measurement of a characteristic signal of chlorpromazine relative to an internal standard. Three different internal standards are specified: Cyclohexane was selected because of the convenience and rapidity with which samples could be prepared for assay. Piperonal was used to verify the method and to show that precision and accuracy were not affected by the volatility of the cyclohexane. Tetramethylammonium bromide was used as an internal standard for Thorazine injectable. No interferences were found from stearates and other tablet excipients. The NMR procedure provides a simple, direct, and specific assay with a precision of +/- 1-2%.

Reverse phase high speed liquid chromatography of antibiotics. II. Use of high efficiency small particle columns.

Improved methods for the separation and quantitation of cephalosporins, penicillins, tetracyclines and several miscellaneous antibiotics by reverse phase high speed liquid chromatography are presented. The methods have been improved significantly by the substitution of high efficiency, small particle (approximately 10 micrometer reverse phase columns in place of the previously used medium efficiency, pellicular columns. The conditions and procedures described here illustrate that considerable improvements in separation and sensitivity of detection of antibiotics are achieved. Pure compounds, complex mixtures of antibiotics in a variety of dosage forms and fermentation broths are routinely analyzed by the described procedures.

The determination of cephradine and cephalexin by reverse phase high-performance liquid chromatography.

The application of reverse phase high-performance liquid chromatography to the separation and analysis of cephradine and cephalexin is demonstrated. The procedure has been applied to chemicals, pharmaceutical formulations and reaction solutions. The preparation of samples is simple and rapid. Chromatographic conditions are described for both pellicular and small particle columns. The feasibility of determing cephradine and cephalexin in physiological fluids has also been demonstrated.

Quantitative NMR analysis of a four-component mixture of phenylglycine derivatives.

A rapid, accurate, and precise NMR analytical method for the analysis of phenylglycine, dihydrophenylglycine, tetrahydrophenylglycine, and cyclohexylglycine in combination with each other was developed. The method is based on the integration of the NMR signal characteristic of each component relative to the signal from tetramethylammonium bromide, which is added as an internal standard. No prior separation of the four components is required.

Effect of phototherapy on bilirubin excretion in man and the rat.

Further evidence that the bilirubin excreted by Gunn rats during phototherapy is unconjugated is presented. The unconjugated bilirubin is not carried into bile as a water-soluble complex with rapidly excreted bilirubin derivatives, nor as a result of leakage of plasma protein into bile. Phototherapy does not augment biliary excretion of bilirubin in normal nonjaundiced rats, but does increase the concentration of conjugated bilirubin in the bile of patients with alcoholic cirrhosis, although their serum bilirubin concentrations are unaffected. The mechanism for augmented excretion of unconjugated bilirubin during phototherapy remains unexplained.

Inhibition of prostaglandin synthetase and carrageenan-induced edema by tricyclic analogs of flufenamic acid.

A group of tricyclic analogs of flufenamic acid were tested for their ability to inhibit both the biosynthesis of prostaglandin and carrageenan-induced inflammation of the rat paw. All had activity greater than phenylbutazone as inhibitors of prostaglandin synthetase, with SK&F 22908 being as active as flufenamic acid. The anti-inflammatory activities of these compounds correlated only to a minor degree with the inhibition of prostaglandin biosynthesis. The data support the position that within this series of compounds inhibition of prostaglandin synthetase and non-steroidal antiinflammatory activity, as well as ulcerogenic liability, may be an expression of different mechanisms.

NMR spectroscopic analysis of 2-mercapto-5-methyl-1,3,4-thiadiazole in cefazolin.

A rapid, sensitive, and accurate method for the quantitative analysis of 2-mercapto-5-methyl-1,3,4-thiadiazole in cefazolin is presented. The method utilizes NMR spectroscopy and is based on the difference in the chemical shift of the methyl protons on free thiadiazole and the thiadiazole moiety of cefazolin.

Reverse phase high speed liquid chromatography of antibiotics.

Reverse phase high speed liquid chromatographic methods are presented for the separation and detection of cephalosporins, penicillins, tetracyclines and other miscellaneous antibiotics. The reverse phase approach is superior to ion-exchange liquid chromatography and spectrophotometric, chemical and microbiological procedures currently in use. In addition to being simple and easy to control, the technique is rapid, convenient and precise and provides the basis for the direct analysis of pure compounds, stability samples, complex mixtures and dosage forms of all types. Preparative chromatography has been used in our laboratory for the separation and isolation of up to 500 mg of antibiotics. Using this approach, we have separated and isolated small impurities as well as pure feference compounds. The methodology reported here can be extensively applied to the separation, quantitation and isolation of both naturally occurring and synthetically produced antibiotics in a variety of media including physiological fluids.

Cholesterol solubility in lecithin-bile salt systems.

The method of sample preparation can markedly influence the rate of dissolution and attainment of supersaturated states of cholesterol. The equilibrium solubility of cholesterol, studied as a function of its physical state in a model bile system, is almost half that of previously accepted values. Slow attainment of the equilibrium state may have acted to bias previous studies. Extrapolation of our data to the clinical situation reveals that many persons considered normal by present standards actually possess bile that is supersaturated with respect to cholesterol and are thus potential gallstone formers.