Dielectric characterization of thermodynamic first order events in model frozen systems intended for lyophilization.

The degree and ease with which permanent dipoles in a frozen sample orient in an applied electric field is affected during thermal transitions. This motion can be monitored with dielectric analysis (DEA) at low AC frequencies (< approximately 300,000 Hz). The systems characterized with respect to their behavior in the frozen state consisted of common lyophile excipients in aqueous solutions known to exhibit typical thermodynamic first order transitions. Prior to freezing, solution samples were placed on an interdigitated electrodes and served as the dielectric component of the resulting capacitor. Plots of derivative of dielectric permittivity with respect to time (or temperature) showed the presence of frequency independent peaks (signifying a first order event) at temperatures that coincided with eutectic temperatures (ca. -22 degrees C for sodium chloride-water and ca. -5 degrees C for mannitol-water), amorphous to crystalline transition temperatures (ca. -25 degrees C for mannitol-water), and/or freezing point depression values in water. The values obtained by DEA correlated well with differential scanning calorimetry (DSC) and literature values. DEA appears to offer added insight over established techniques by not only determining the temperature at which these events occur, but also by defining the thermodynamic order of the event.

Prediction of lyophile collapse temperature by dielectric analysis.

A new method for predicting lyophile collapse temperatures based upon dielectric analysis (DEA) of frozen two component systems is presented. The method, called the take off frequency model (TOF), relies both on the inherent ability of DEA to detect molecular motion and on the abrupt change in viscosity experienced by a frozen sample undergoing a glass-liquid transition. Collapse temperatures for binary glass forming systems (an antibiotic, sucrose, trehalose, or sorbitol, with water) were in good agreement with the values reported in the literature. DEA was easily able to detect glass transitions poorly defined by differential scanning calorimetry (DSC). Conservative lyophilization cycles for simple systems can be quickly determined on the basis of the TOF model.

Influence of dose range on degree of nonlinearity detected in dose-proportionality studies for drugs with saturable elimination: single-dose and steady-state studies.

Deviation from proportionality occurs when the ratio of area under the curve (AUC) values is not equal to the ratio of administered doses. The degree of nonlinearity (fNL) can be quantitated as the ratio of AUCs divided by the ratio of doses. We explore positive deviation from proportionality (fNL > 1) using the classical Michaelis-Menten model of nonlinear elimination after a single dose (n = 1) or at steady state (ss). The degree of nonlinearity is related to the ratio of the highest dose to the lowest dose (Rd = DH/DL): fn = 1NL = (2 + Rd.epsilon)/(2 + epsilon), fssNL = (Rd.omega - 1)/(Rd.omega - Rd), where epsilon is the ratio of the initial concentration after the lowest dose to the Km (epsilon = DL/Km.V) and omega is the ratio of the Vmax to the average rate of input for the highest dose (omega = Vmax tau/F.DH). From these relationships, we find that (1) for single-dose studies, Km is the important Michaelis-Menten parameter, while Vmax is important at steady state; (2) the degree of nonlinearity cannot exceed the ratio of doses in single-dose studies, and when doses in extreme excess of Km.V are chosen, the degree of nonlinearity is equal to the dose range; and (3) at steady state, the degree of nonlinearity can exceed the ratio of doses and approaches infinity as the average input rate approaches Vmax. Literature data (phenytoin and ethanol) support these findings. We conclude that the degree of nonlinearity is not a useful measure of nonlinearity in and of itself and propose percentage saturation as being more informative.

Effect of physical and chemical properties on drug release from selected thermosoftening vehicles.

The release profile of several drugs, (chlorpheniramine maleate, salicylic acid, hydrochlorothiazide, p-hydroxy benzoic acid, sulphafurazole, anhydrous theophylline) and the marker (D&C yellow No. 10) was detailed to determine the effect of physical and chemical properties on release from selected thermosoftening matrices (Gelucire 50/02 and 50/13). At a concentration of drug or marker of 2.5% w/w, hydrochlorothiazide showed the slowest release from G50/02, due to its low aqueous solubility, while theophylline showed the highest release owing to its low mol. wt and moderate aqueous solubility. Release reflected two of the selection criteria, aqueous solubility and mol. wt, set forth for the drug/markers used in the study. The hydrophobic matrix, G50/02, offered no enhancement in drug release and functioned in a manner commensurate with other hydrophobic matrices. No hydrogen bonding was noted between any of the drugs or markers and the matrix. As drug or marker concentration increased from 2.5 to 15% w/w, potential hydrogen bonding was noted between p-hydroxy benzoic acid and the matrix. Theophylline no longer had the highest release being replaced by chlorpheniramine maleate and D&C yellow No. 10. With Gelucire excipient G50/13, chlorpheniramine maleate showed the highest release; it dissolved within the matrix at experimental temperature and lowered the matrix melting point. The matrix swelled upon exposure to the dissolution medium and it was from this swollen layer that release occurred. Sulphafurazole, hydrochlorothiazide, salicylic acid and p-hydroxy benzoic acid exerted a similar effect to chlorpheniramine maleate on the matrix. No hydrogen bonding was observed between the drugs and matrix.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of release from selected thermosoftening vehicles.

Release of D&C Yellow No. 10 and anhydrous theophylline have been determined from a thermosoftening, hydrophilic matrix, Gelucire 50/13, incorporating a water-soluble additive, polyethylene glycol 4000. As additive level increased, release also increased. The effect of mixtures of Gelucire 50/13 (G50/13) and Gelucire 50/02 (G50/02) on release was also investigated as a function of temperature and pH. As the level of G50/02 increased, release decreased and became predominantly diffusional. As temperature was increased, release changed from diffusion to a mixed model of both diffusion and erosion. At basic pH, release from these composite systems became more erosional in character, possibly reflecting partial hydrolysis of the ester-linked matrices. Diffusion coefficients and apparent diffusion coefficients were calculated in G50/02 and G50/13 matrices, respectively, and were in agreement with published data.

Evaluation of methodology for assessing release characteristics of thermosoftening vehicles.

Methodology has been devised for the testing and evaluation of the mechanistic release of drug or markers from thermosoftening materials, as represented by the Gelucire class of excipients, which could be predictive. Release of a drug (anhydrous theophylline) and a marker (D&C yellow No. 10) was determined using a calibrated stationary disc/rotating fluid system. Of the fourteen commercially available Gelucire excipients, six were investigated in detail (G46/07, G48/09, G50/02, G50/13, G53/10, G62/05) and found to have biphasic release profiles. Lipid soluble materials demonstrated predominantly diffusion-controlled release, while water-dispersible materials absorbed water and showed signs of swelling which led to erosion as an additional component of the release characteristics.

Quantitative and mechanistic measurements of container/closure integrity. Bubble, liquid, and microbial leakage tests.

The parenteral vial/closure seal interface is tested for leakage of gas, liquids, and microorganisms. Gas leakage is determined using a bubble test, liquid leakage is detected by atomic absorption of a copper ion tracer solution, and microbial leakage is verified using a liquid-borne microbial suspension challenge test. Leakage performance by these methods is compared to gaseous leakage rates quantitatively determined for the same package systems. The establishment of leakage rate specifications based on these results is discussed.

Quantitative and mechanistic measurements of parenteral vial container/closure integrity. Leakage quantitation.

Leakage across the parenteral vial/closure seal interface is quantitatively measured in terms of mass of gas per unit time using a differential pressure method of leakage measurement. With this test system, uncoated, Purcoat coated, and film coated closures are compared for their ability to seal nondefective and defective vial surfaces. Correlations are made between closure sealing performance and rubber viscoelasticity, closure coating material type and thickness, and crimped vial residual seal force.

Comparative dissolution performance of internationally available piroxicam products.

Piroxicam is a widely used nonsteroidal antiinflammatory drug available worldwide under various trade names by several manufacturers. Only one brand of piroxicam (Feldene) is currently marketed in the U.S., and the United States Pharmacopeial Convention established an official dissolution requirement for piroxicam in 1985. The purpose of this study was to evaluate and compare the dissolution performance of several internationally available piroxicam products using the United States Pharmacopeia (USP) dissolution test for piroxicam capsules. Of 25 brands of piroxicam capsules evaluated, 72 percent of the brands failed to meet the USP requirement, several by a wide margin. Although there is no specific USP dissolution test for tablets, the test for capsules was applied to five different brands of piroxicam tablets, and 80 percent of the tablet brands tested failed to meet the USP requirement. Although comparative bioavailability studies would be required to establish any definitive relationship between dissolution test performance and bioavailability, the failure of most of these products to meet the USP requirement for dissolution indicates formulation differences that could result in altered bioavailability. The substantial differences in dissolution performance observed among the piroxicam oral dosage forms tested have implications concerning the equivalency and standards of multisource products available on the international market, and should be taken into account by health care providers worldwide.

Physical stability of semisynthetic suppository bases.

Changes in the melting range of several semisynthetic suppository bases were studied over time. X-ray diffraction studies characterized the changes as amorphous to crystalline transitions, with likely polymorphic effects occurring concurrently. Use of a modified Krowczynski apparatus to test pure base and single-ingredient suppositories showed dramatic hardening of the materials over periods as short as 6 weeks. Data were obtained by differential scanning calorimetry on freshly solidified, incrementally aged, and equilibrated samples. These methods may be used as both predictive and ongoing physical stability tests in the evaluation of suppository bases and formulas.

Compatibility of verapamil hydrochloride injection in commonly used large-volume parenterals.

The visual and chemical compatibilities of verapamil hydrochloride injection in 10 commonly used large-volume solutions packaged in glass, polyolefin, or polyvinyl chloride containers were studied. The mixtures, each containing 40 mg/liter of verapamil hydrochloride, were stored away from light for up to 48 hours at 25 degrees C. The solutions were examined visually for haze, precipitate formation, color change, and evolution of gas immediately after mixing and at 0.25, 1, 3, 8, 24, and 48 hours. Spectrophotometry and thin-layer chromatography were used to test for drug decomposition or chemical incompatibilities. All test methods used showed that no significant degradation of verapamil hydrochloride had taken place in the solutions or through contact with the containers. Slightly higher spectrophotometric readings for dextrose-containing solutions, though within experimental error, could have indicated the presence of dextrose degradation products. Evidence from this study suggests that verapamil hydrocholoride is compatible with the large-volume parenterals studied.

Conductivity and hardness changes in aged compacts.

Batches of sodium, potassium, and ammonium chloride tablets containing no excipients and spray-dried lactose tablets containing 0.5% magnesium stearate were stored at 20 and 76% relative humidity. Electrical resistance and hardness measurements were made within 1 hr after compression and at intervals during a 45-day period. Hardness values of sodium, potassium, and ammonium chloride tablets stored at 20% relative humidity increased from 70 to 200% at 45 days, while conductances decreased 10-fold. Tablets stored at 76% relative humidity showed no increases or slight decreases in hardness with slight increases in conductance. Lactose tablets decreased slightly in hardness with corresponding increases in conductance.

Thermal characterization of citric acid solid dispersions with benzoic acid and phenobarbital.

The glass transition temperatures of citric temperatures of citric acid glass were determined by differential scanning calorimetry to be 10.2 and 13.5 degrees for in situ and bulk-prepared samples, respectively. Mechanical stress on citric acid glass induced foci for crystallization. Benzoic acid addition to citric acid glass decreased its glass transition temperature while phenobarbital addition increased its glass transition temperature, the latter forming a glass solution.

Electrical conductance of directly compressible materials under pressure.

An electrometer that allowed direct recording of resistance changes during compression was used to measure the conductances of sodium chloride, potassium chloride, ammonium chloride, and sodium citrate. The effects of initial particle size, lubricant level, moisture content, and compaction pressure were determined. Direct compression tableting diluents also studied were dextrose, sucrose, lactose, microcrystalline cellulose, and dibasic calcium phosphate. Distinctive conductance patterns were observed and are rationalized in terms of previously proposed bondign machanisms.

In vitro evaluation of three commercial sustained-release papaverine hydrochloride products.

Three commercial sustained-release papaverine hydrochloride products in the form of microencapsulated pellets were evaluated. Three different dissolution apparatuses were used: a continuous flow apparatus, the USP rotating basket apparatus, and a modified reciprocating basket apparatus. The frequency rate of the reciprocating basket apparatus could be varied from 0 to 31 strokes/min. Salicylic acid compacts were used as a standard to characterize each apparatus. A linear log--log correlation between dissolution rate and apparatus speed or flow rate was obtained. Release of papaverine hydrochloride from the commercial preparations was affected significantly by the pH of the dissolution media but not by the agitation intensity.