Nitroglycerin sublingual tablets. II. Preparation and stability of a new, stabilized, sublingual, molded nitroglycerin tablet

Sublingual nitroglycerin. I. Comparative evaluation of the physical stability of commercially available tablets

The physical stability of one type of stabilized molded and three types of compressed nitroglycerin tablets was studied. The evaporation rate of nitroglycerin was controlled by its vapour pressure and by the matrix effect of the dosage forms. The four products showed different vapour pressures and matrix effects. In time nitroglycerin escapes from the outmost layers of the tablets; the dosage form in which the drug showed the lowest vapour pressure (the stabilized molded tablet) was found to be the most stable one. However, from the time when the drug had escaped from the outmost layers of the dosage form, the matrix effect became dominant. When nitroglycerin tablets were stored in tightly closed containers at room temperature potency loss was minimal. Even when the bottles were opened regularly this did not result in a significant loss of the drug. Measures are suggested to minimize drug evaporation.

Effect of nitroglycerin-soluble additives on the stability of molded nitroglycerin tablets

Nitroglycerin vapor pressures at 25 degrees C were determined for additive-nitroglycerin systems over the additive-nitroglycerin weight ratio range of 0.5 to 3.0 for 16 additives exhibiting solubility in nitroglycerin. The effects of the additives on nitroglycerin chemical stability at 25 degrees C and 50 degrees C were also studied. Tablet stability characteristics, i.e., content uniformity, open-dish stability, and chemical decomposition were evaluated for selected tablet formulations. Most additives lowered the vapor pressure of nitroglycerin sufficiently to stabilize content uniformity when used at additive-nitroglycerin weight ratios near 1. Higher additive levels are needed for significant potency stabilization in open-dish stability tests, but these levels normally decrease the chemical stability of nitroglycerin. However, stabilization of content uniformity, a twofold reduction of potency loss in an open-dish stability test, and chemical stability are possible with at least three of the additives studied.

Stability of intravenous nitroglycerin solutions

The stability of intravenous nitroglycerin solutions prepared from either sublingual tablets or a 10% nitroglycerin-lactose adsorbate (powder) was examined under various conditions. Nitroglycerin concentration was measured by high-pressure liquid chromatography. Nitroglycerin stock solutions (0.8-1.0 mg/ml) prepared from tablets or powder in either 0.9% saline were stored upright in refrigerated multidose vials for 6 months without a significant decrease in concentration. Storage of the solutions at room temperature resulted in a 20% loss after 3 months. Intravenous nitroglycerin solutions (0.2 mg/ml) prepared from tablets or powder in 0.9% saline or 5% dextrose in water were stored in glass intravenous bottles at temperatures between 6 and 38 degrees for 24 hr with a maximum loss of 18%. Stability was not affected by light. Solutions in contact with rubber stoppers, plastic intravenous bags, or plastic administration sets exhibited decreased nitroglycerin concentration characteristic of sorption. Nitroglycerin concentrations decreased to a greater extent when the administration sets were equipped with plastic burets. Brief contact of nitroglycerin solutions with a plastic syringe did not result in decreased concentration. The stability of intravenous nitroglycerin solutions packaged in glass was not dependent on light, the vehicle, or the source of nitroglycerin. Contact with rubber or plastic surfaces should be minimized.

Nitroglycerin stability in polyethylene glycol 400 and povidone solutions

The stability of solutions of nitroglycerin in several common pharmaceutical solvents and compounds used as tablet excipients was investigated using a UV spectrophoto metric assay. Included in the study were povidone (I), polyethylene glycol 400 (II), and solvents such as absolute alcohol, propylene glycol, and glycerol. At the elevatted temperatures of the accelerated stability studies, only II demonstrated a considerable adverse effect on the stability of the nitroglycerin solution. It is postulated that a "reaction compound" was formed between nitroglycerin and II which regenerated nitroglycerin depending on hydrolysis conditions. Based on the Arrhenius equation and with initial rates of up to 6 hr of degradation, the predicted stability for a II solution of nitroglycerin in terms of its 10% decomposition at 25 degrees was approximately 7 days.

Pharmacokinetics of nitroglycerin in rats

The plasma nitroglycerin levels obtained after intracardial (0.7 mg/kg), oral (7 mg/kg), and topical (7--14 mg/kg) doses of nitroglycerin in rats are reported. Nitroglycerin followed essentially one-compartment kinetics after intracardial administration, showing a mean half-life of about 4 min and a mean apparent volume of distribution of about 3 liters/kg. After oral drug administration, "flip-flop" kinetics were evident. The mean oral bioavailability was determined to be 1.6%, firmly supporting the contention that nitroglycerin is extensively metabolized during first passage through the liver. Under the experimental conditions studied, no detectable levels of nitroglycerin were observed after topical application.

Polymer sorption of nitroglycerin and stability of molded nitroglycerin tablets in unit-dose packaging

The sorption of nitroglycerin by thermoplastic polymers and the stability of molded nitroglycerin tablets in strip packaging were studied. The polymers investigated varied greatly in their affinity for nitroglycerin, the order of decreasing affinity being: vinyls greater than low density polyethylene greater than ionomers greater than high density polyethylene. With the proper choice of packaging, molded nitroglycerin tablets stabilized with povidone maintained acceptable potency for up to 2 years at 26 degrees when strip packaged in unit doses. Chemical decomposition (hydrolysis) of nitroglycerin also was investigated. Povidone accelerated the decomposition of nitroglycerin; at high temperature, decomposition was a significant factor in tablet stability for tablets containing povidone.

Rapid determination of nitroglycerin volatility using thermogravimetric analysis

The effect of selected tablet components on the volatility of nitroglycerin from compressed sublingual tablets was studied by thermogravimetric analysis. The results, confirmed by chemical analyses, showed that nitroglycerin volatility is significantly reduced by the use of povidone USP and microcrystalline cellulose NF in tablet formulations. In general, the stabilizing effect of these materials was dependent on the presence and the concentration of each other. These studies demonstrated the utility of thermogravimetric analysis as a rapid and reliable means of screening nitroglycerin formulations for stability purposes.

The effect of tablet formulation on the haemodynamic properties of glyceryl trinitrate

A non-invasive haemodynamic study was carried out in 13 normal subjects to compare the pharmacodynamics of glyceryl trinitrate when formulated as a moulded tablet ('Nitrostat') rather than as a generic compressed tablet. The glyceryl trinitrate moulded tablet, with a much more rapid and predictable dissolution time, produced an earlier onset of systolic blood pressure fall (p less than 0.01) and a greater maximum percentage change in peripheral blood flow (p less than 0.02). No other significant differences in effect on pulse rate, blood pressure or peripheral blood flow were noted.

A comparison of solute migration in a test granulation dried by fluidization and other methods

The intragranular migration of sodium chloride in granules made by the wet massing of heavy kaolin B.P. with salt solution has been studied in batches dried by fluidization and a vacuum tumbling method. The larger granules from the fluidized batch exhibited considerable intragranular variation with the outer crust containing over twice the average salt concentration. Solute loss from this layer by abrasion on prolonged fluidization was slight but the dust eluted from the dryer had a salt content above average. Analysis of sieved fractions of the dust showed that this enrichment was concentrated in the fine material passing a 53 mum mesh. The vacuum dried granules had less migration and were less resistant to crushing than those dried by fluidization. The dust produced had a salt content only slightly greater than the average composition and the overall solute content of the sized fractions were all close to this average. The same system was used to study intergranular migration in a fixed bed when the granules were dried by infrared radiation, by microwave radiation, by convection from air and in a vacuum. The greatest migration occurred in samples dried by infrared radiation and the maximum solute concentration was near the middle of the bed. The air dried granules had less migration and the maximum concentration was in the surface layer. The granules dried in a vacuum and by microwave radiation were fairly uniform in composition throughout the bed. The above results are explained on the basis of the capillary theory of drying together with the modifying influence of the drying method on the probable heat and mass transfer rates.