Solubility and stability of melatonin in propylene glycol and 2-hydroxypropyl-beta-cyclodextrin vehicles

The physicochemical properties of melatonin (MT) in propylene glycol (PG) and 2-hydroxypropyl-beta-cyclodextrin (2-HPbetaCD) vehicles were characterized. MT was endothermally decomposed as determined by differential scanning calorimetry (DSC). Melting point and heat of fusion obtained were 116.9+/-0.24 degrees C and 7249+/-217 cal/mol, respectively. MT as received from a manufacture was very pure, at least 99.9%. The solubility of MT in PG solution increased slowly until reaching 40% PG and then steeply increased. Solubility of MT increased linearly as concentration of 2-HPbetaCD without PG increased (R(2)=0.993). MT solubility in the mixtures of PG and 2-HPbetaCD also increased linearly but was less than the sum of its solubility in 2-HPbetaCD and PG individually. The MT solubility was low in water, simulated gastric or intestinal fluid but the highest in the mixture of PG (40 v/v%) and 2-HPbetaCD (30 w/v%) although efficiency of MT solubilization in 2-HPbetaCD decreased as the concentration of PG increased. MT was degraded in a fashion of the first order kinetics (r(2)>0.90). MT was unstable in strong acidic solution (HCl-NaCl buffer, pH 1.4) but relatively stable in other pH values of 4 approximately 10 at 70 degrees C. In HCl-NaCl buffer, MT in 10% PG was more quickly degraded and then slowed down at a higher concentration. However, the degradation rate constant of MT in 2-HPbetaCD was not changed significantly when compared to the water. The current studies can be applied to the dosage formulations for the purpose of enhancing percutaneous absorption or bioavailability of MT.

Processing factors in development of solid solution formulation of itraconazole for enhancement of drug dissolution and bioavailability

This study investigated solid solutions of itraconazole, a water insoluble antifungal, for improved dissolution and improved bioavailability. Influence of processing factors on drug and carrier properties in solid solution and subsequently on drug dissolution behavior was also studied. An optimized solid solution formulation was compared with marketed product in healthy human subjects under fasted and fed conditions for bioequivalency. Polyethylene glycol (PEG) and drug were made into a solid solution at 120 degrees C. The cooled, solid solution was then ground into granules of different sizes. Solid solutions of lower drug concentration dissolved at a faster rate, and drug dissolution improved considerably with increasing molecular weight of PEG. Initial treatment of itraconazole with the wetting agent/cosolvent glycerol prior to making itraconazole into a solid solution improved drug dissolution, and also reduced the PEG amount required to dissolve drug to form solid solution. Addition of a polymer such as HPMC to the solid solution eliminated precipitation of drug following dissolution. As the granule size of the solid solution was reduced, precipitation of drug during dissolution became prominent. Equivalence of two formulations could not be shown for pharmacokinetic parameters C(max) and AUC, under both fasting and fed conditions.

Preliminary bioequivalence testing of two nicardipine HCl sustained-release formulations with in vitro/in vivo correlations

A new nicardipine HCl oral sustained-release dosage form was evaluated for bioequivalence in comparison with a reference product, Cardene SR. Six healthy subjects, fasted overnight, were enrolled in a single-dose, open-label, randomized, and two-way crossover study. Blood samples were collected over a 12 hour period, and nicardipine plasma concentrations analyzed from plasma. Pharmacokinetic parameters, including Cmax, t(max), and AUC, were obtained from drug plasma concentration-time curves and pharmacokinetic analysis conducted using WinNonlin. The two one-sided t-test was applied in statistical analysis for comparison of the pharmacokinetic parameters between the two products. There was no convincing evidence that nicardipine HCl test product and Cardene SR were bioequivalent. Amounts of nicardipine HCl release in vivo was mathematically obtained by deconvoluting plasma concentration-time data after oral administration using IV bolus injection data as a reference. Plots of percentages of drug release in vitro against those in vivo illustrated triphasic curves. After the in vitro time scale was corrected and then plotted against in vivo data, plots provided a polynomial relationship (R2 of 0.9920 and 0.9954). The in vitro/in vivo correlation may be useful in reformulating this particular test formulation to obtain a product with an in vivo release rate identical to Cardene SR.

Drug release from spray layered and coated drug-containing beads: effects of pH and comparison of different dissolution methods

Based on dissolution profiles of three model drugs on spray layered beads with the same percentage of Aquacoat coating, it was concluded that in vitro dissolution of oral controlled-release formulations should be performed in both gastric and intestinal media for ionizable drugs. Ketoprofen (weak acid, pKa 4.8), nicardipine HCl (salt of weak organic base, pKa 8.6), and acetaminophen (very weak organic acid, pKa 9.7, not ionized at physiologic pH) provided different dissolution characteristics in enzyme-free simulated gastric fluid (pH 1.4) and enzyme-free simulated intestinal fluid (pH 7.4), indicating that the rate of drug release was pH dependent and related to drug ionization even though the solubility of the coating (ethylcellulose) is pH independent. In acidic media, ketoprofen release from the beads containing low-level coating (3%) was slower than that of nicardipine HCl, with the opposite holding true in basic media. Acetaminophen was released at approximately the same rate in both acidic and basic media. A comparison of drug release profiles for nicardipine HCl nude beads was also investigated among three different dissolution methods: USP dissolution apparatus I (basket method, 50 rpm), USP dissolution apparatus II (paddle method, 50 rpm), and USP dissolution apparatus III (Bio-Dis, Van-Kel Industries, 5 and 10 dpm). Release profiles obtained from all methods were similar, indicating that the three dissolution methods were comparable.

Bead compacts. II. Evaluation of rapidly disintegrating nonsegregating compressed bead formulations

In this study, three techniques for the prevention or mitigation of polymer coat fracture on compaction of sustained-release beads into tablets were investigated. All techniques in this paper were evaluated without the addition of any cushioning excipients, but rather by spray coating these excipients to avoid segregation during product manufacturing. First, it was shown that use of swellable polymers such as polyethylene oxide (PEO) serves a unique and effective role in preventing polymer coat rupture. PEO was spray coated between the ethylcellulose (EC) and microcrystalline cellulose (MCC) coats to evaluate its cushioning effect. The compacted PEO layered beads, on dissolution, disintegrated into individual beads with sustained drug release of up to 8 hr. It is postulated that the PEO was hydrated and formed a gel that acts as a sealant for the cracks formed in the ruptured polymer coating (sealant-effect compacts). Second, EC-coated drug-layered beads were also overcoated with cushioning excipients such as polyethylene glycol (PEG) and MCC with an additional coating of a disintegrant. These beads were compressed at pressures of 125, 500, and 1000 pounds into caplets and, on dissolution testing, disintegrated into individual beads when the dissolution medium was switched from simulated gastric to intestinal fluid. The dissolution profiles show that the polymer coat was partly disrupted on compaction, leading to a total drug release in 8-10 hr. Third, EC-coated beads were also granulated with cushioning excipient and compressed.

Behavioural mode of action of deet: inhibition of lactic acid attraction

Using the mosquito Aedes aegypti in a novel olfactometer that measures movement towards and away from a stimulus, we could not confirm that 'deet' is a repellent of mosquitoes. In the absence of a host, deet was an attractant and in the presence of a host, it was an inhibitor of attraction. This inhibition occurred in the gaseous phase and was therefore not the result of the physical properties of deet. We determined that L-lactic acid, a component of human sweat that is an attractant to mosquitoes, is the target of this inhibition, implying that lactic acid may be a bottleneck in the behavioural cascade preceding blood-sucking.

Percutaneous absorption and model membrane variations of melatonin in aqueous-based propylene glycol and 2-hydroxypropyl-beta-cyclodextrin vehicles

Percutaneous absorption and model membrane variations of melatonin (MT) in aqueous-based propylene glycol and 2-hydroxypropyl-beta-cyclodextrin vehicles were investigated. The excised hairless mouse skin (HMS) and two synthetic ethylene vinyl acetate (EVA) and microporous polyethylene (MPE) were selected as a model membrane. The solubility of MT was determined by phase equilibrium study. The vertical Franz type cell was used for diffusion study. The concentration of MT was determined using reverse phase HPLC system. The MT solubility was the highest in a mixture of PG and 2-HP beta CD. The percutaneous absorption of MT through excised HMS increased as the solubility increased. However, the permeability coefficient decreased and then slightly increased in a mixture of PG and 2-HP beta CD. On the other hand, both flux and permeability coefficient through EVA membrane decreased as the solubility increased. No MT was detected over 12 h after starting diffusion through MPE membrane. The flux of MT was dependent on the type of membrane selected. Flux of MT was greatest in excised HMS followed by EVA and MPE membrane. Flux of MT through EVA membrane was 5-20 times lower when compared to excised HMS. Interestingly, volumes of donor phase when MPE membrane was used, significantly increased during the study period. The HMS might be applicable to expect plasma concentration of MT in human subjects based on flux and pharmacokinetic parameters as studied previously. The current studies may be applied to deliver MT transdermally using aqueous-based vehicles and to fabricate MT dosage forms.

Bead compacts. I. Effect of compression on maintenance of polymer coat integrity in multilayered bead formulations

Little information is available on the compactability of beads for oral sustained-release dosage forms. It is known that polymer-coated beads may fuse together to produce a non-disintegrating controlled-release matrix tablet when compressed. This study evaluates the effect of compression on beads with multiple layers of polymer and drug coat, and the effect of cushioning excipients and compaction pressure on drug release from compressed bead formulations. The multilayered beads consist of several alternating layers of acetaminophen (APAP) and polymer coats (Aquacoat) with an outer layer of mannitol as a cushioning excipient. Percent drug release versus time profiles showed that the release of drug decreases from noncompacted beads as the amount and number of coatings increases, with only 43% of drug released in 24 hr for coated beads with 10 layers. It was shown that the compacted multilayered beads will disintegrate in gastrointestinal fluids, providing a useful drug release pattern. It was shown that beads of drug prepared by any method can be spray-layered with excipients such as Avicel and mannitol. Spray-layering of the cushioning excipient onto beads can provide an effective way to circumvent segregation issues associated with mixing of the polymer-coated beads and powdered or spherical/nonspherical cushioning excipients. Spray layering of the cushioning excipient can also provide excellent flow properties of the final formulation as visually observed in our experiments. Triple-layered caplets (TLC) were also prepared with outer layers of Avicel PH-101 or polyethylene oxide (PEO), and a center layer of polymer-coated beads. For TLC, the polymer coating on the beads fractured, and nondisintegrating matrix formulations were obtained with both caplet formulations.

Multiple-layer compression-coated tablets: formulation and humidity studies of novel chewable amoxicillin/clavulanate tablet formulations

The purpose of this study was to produce novel multiple-layer, compression-coated, chewable tablet formulations containing amoxicillin trihydrate, and clavulanic acid as potassium clavulanate, and to test in vitro dissolution characteristics and the effect of humidity stability compared to Augmentin chewable tablets as a reference. Double- and triple-layer tablets were manufactured on a laboratory scale by multiple-layer dry compression, and dissolution profiles of both active ingredients were determined. Tablets were subjected to stability evaluation in laboratory-scale humidity tanks maintained at constant humidity. Assay of content was determined by HPLC or UV spectroscopy. Physical characteristics of the powder mixture, such as angle of repose, and of tablets for hardness and friability, were also determined. Chewable tablets showed similar dissolution profiles in vitro for both active ingredients, compared to the marketed reference, Augmentin. The stability of clavulanic acid, but not amoxicillin, was increased in the novel triple or bilayer formulation. The tablets showed suitable friability, hardness, and angle of repose for starting materials to suggest that industrial scale-up is feasible. This approach to formulation of drugs containing multiple or moisture-sensitive ingredients has been shown to increase the stability of the central core drug without changing the dissolution pattern of the active ingredients. This formulation is expected to be bioequivalent in vivo based on these in vitro results.

Evaluation of commercial insect repellents on human skin against Aedes aegypti (Diptera: Culicidae)

An olfactometer was used to evaluate the efficacy of selected commercial insect repellent products against Aedes aegypti (L.). A comparison of 12 commercial repellent products was made on human skin. The products tested included 2 natural oil insect repellent formulations (Buzz Away and Green Ban) containing plant extracts, 2 proprietary products (Skin-So-Soft lotion and bath oil), and 8 commercial deet preparations in various concentrations and forms of spray, aerosol, stick, cream, and lotion. Behavioral responses and time to probe were determined in triplicate using 10 female mosquito challenges per replicate for each product. Generally, products with higher concentrations of deet were found to have longer repellence times. OFF spray and Muskol lotion offered the longest repellence times. However, there was no significant difference in time for mosquitoes to probe among the formulations. Skin-So-Soft lotion and bath oil were not as effective as deet in repelling Ae. aegypti. Natural oil insect repellent formulations offered essentially no repellency against Ae. aegypti. This is a simple and reproducible method to evaluate the efficacy of insect repellents and is recommended for preliminary screening of new insect repellents or formulations.

Transmucosal, oral controlled-release, and transdermal drug administration in human subjects: a crossover study with melatonin

The effect of oral controlled-release (CR), oral transmucosal (buccal; TMD) and transdermal (TDD) drug delivery systems on plasma concentrations of melatonin (MT) and its principal metabolite in human subjects using a crossover, single dose design was evaluated. Twelve adult male volunteers participated in the study and received all three dosage forms on three separate occasions. All patch dosage forms were removed after 10 h of wear. Plasma concentrations of the parent drug and its metabolite, 6-sulfatoxymelatonin (MT6s) were measured by radioimmunoassay. Between-subject plasma concentrations of MT were very variable following both oral CR and TDD. Use of the oral CR system gave plasma MT profiles in some subjects that were initially similar to physiological levels, but then differed substantially from physiological in the rate of MT offset; in a few subjects, plasma MT levels remained consistently much below normal nocturnal physiological levels. Also, the ratio of metabolite to parent drug by the oral CR route was many times greater than physiological. TDD resulted in a significant delay in systemic drug levels and a gradual decline in drug delivery after patch removal, possibly due to deposition of melatonin in the skin. TDD failed to simulate the physiological plasma profile of MT (rapid achievement of steady-state blood levels and rapid decline after removal of the patch; i.e., so-called "square-wave" profile). TMD provided prompt systemic drug levels with less variability than oral CR or TDD delivery. Also, plasma MT levels fell promptly and rapidly after removal of the patch. No indication of mucosal deposition was observed. TMD was able to mimic the physiological plasma profiles of both MT and its principal metabolite.

Preliminary evaluation of transdermal delivery of melatonin in human subjects

A transdermal delivery device (TDD)1 was applied to four human subjects to investigate whether melatonin (MT) could penetrate through human skin. The TDD (total surface area of 3.80 cm2) was applied to the forearm of each subject. Plasma MT concentrations increased above baseline in approximately 2-4 hours, although steady state was not achieved in the 8-hour study period. Intersubject variation of plasma MT among four subjects was noted. Urinary excretion of 6-sulphatoxymelatonin (6-STMT), a major metabolite of MT in humans, increased as plasma MT concentrations increased. Cumulative amounts of urinary 6-STMT increased over a 6-hour period when the TDD was applied and were three times greater than in controls. The urinary excretion rate of 6-STMT was statistically correlated with plasma MT concentration among subjects (r2 = 0.77). These data suggest that the urinary excretion rate of 6-STMT can be used as an index of MT plasma concentrations in human subjects. Although an intersubject variability in both plasma MT concentration and urinary excretion rate of 6-STMT was noted, it was evident that MT can be delivered transdermally in human subjects.

Calcium alginate beads as core carriers of 5-aminosalicylic acid

The utilization of calcium alginate beads as core carriers for delayed dissolution followed by burst release as a potential method of intestinal site specific drug delivery was investigated. 5-Aminosalicylic acid was spray-coated on dried calcium alginate beads and then coated with different percentages of enteric coating polymer and/or sustained-release polymer. Beads coated with more than 6% (w/w) methacrylic copolymer plastisized with dibutyl sebacate and triethyl citrate resisted release in 2-hr acid fluid challenge and allowed immediate dissolution upon transfer to simulated intestinal fluid. With 6% (w/w) methacrylic copolymer on top of 4% (w/w) ethylcellulose polymer, the major portion of drug did not release in 2 hr of acid treatment or the next 3 hr of simulated intestinal fluid treatment. This dosage form provides the possibility to deliver drug to the lower intestinal tract with minimal early release, followed by sustained release in the colon.

Pharmacokinetics and pharmacodynamics in the design of controlled-release beads with acetaminophen as model drug

Relationships between pharmacodynamics (drug concentration and effect) and pharmacokinetics were used to develop an oral, controlled-release-bead dosage form. Reported pharmacodynamic data were used with pharmacokinetic curves to identify effective therapeutic drug concentrations for optimum therapy for a drug with a "deep tissue" effective compartment. The commonly used, over-the-counter, non-narcotic, analgesic-antipyretic acetaminophen (APAP) was used as the model drug. Data reported in the literature were used to compare analgesic and antipyretic efficacy. Computer simulations were performed with MAXSIM (version 3.01) to suggest a zero-order drug release useful for a 12-h, oral, sustained-dosage form for antipyretic therapy in children, on the basis of current pediatric dosing of APAP. Coated APAP beads with the desired release rate were then developed with fluid-bed coating technology.

Multiple-dose acetaminophen pharmacokinetics

Four different treatments of acetaminophen (Tylenol) were administered in multiple doses to eight healthy volunteers. Each treatment (325, 650, 825, and 1000 mg) was administered five times at 6-h intervals. Saliva acetaminophen concentration versus time profiles were determined. Noncompartmental pharmacokinetic parameters were calculated and compared to determine whether acetaminophen exhibited linear or dose-dependent pharmacokinetics. For doses less than or equal to 18 mg/kg, area under the curve (AUC), half-life (t1/2), mean residence time (MRT), and ratio of AUC to dose for the first dose were compared with the last dose. No statistically significant differences were observed in dose-corrected AUC for the first or last dose among subjects or treatments. Half-lives and MRT were not significantly different among treatments for the first or the last dose. Statistically significant differences in t1/2 and MRT were noted (p less than 0.05) among subjects for the last dose. A plot of AUC versus dose for the first and the last doses exhibited a linear relationship. Dose-corrected saliva concentration versus time curves for the treatments were superimposable. Thus, acetaminophen exhibits linear pharmacokinetics for doses of 18 mg/kg or less. Plots of AUC versus dose for one subject who received doses higher than 18 mg/kg were curved, suggesting nonlinear behavior of acetaminophen in this subject.

Antimicrobial activity of Microgard against food spoilage and pathogenic microorganisms

Microgard, a commercially available fermented milk product containing antimicrobial metabolites, was a potent inhibitor for Gram-negative bacteria such as Pseudomonas, Salmonella, and Yersinia when 1% concentration was incorporated into agar media. Gram-positive Bacillus cereus, Staphylococcus aureus, and Listeria monocytogenes were insensitive to Microgard. Kluyveromyces marxianus, an unidentified black yeast, and Penicillium expansum were partially suppressed, whereas Aspergillus niger and a yogurt spoilage yeast were tolerant to 5% Microgard. Optimum activity of Microgard was at pH 5.3 and below; the concentration that gave complete inhibition depended upon the number of bacteria present as well as the genus tested. Blood agar base reversed the antagonistic activity of Microgard against Pseudomonas putida compared with plate count agar.

Gastrointestinal transit of nondisintegrating, nonerodible oral dosage forms in pigs

Gastrointestinal (GI) transit data necessary as "baseline" or "control" information were collected using pigs as animal models preliminary to bioavailability studies of new sustained action formulations. Density and size effects of nondisintegrating dosage forms on GI transit were investigated. Initially, enteric-coated nondisintegrating magnesium hydroxide caplets (density, 1.5 g/ml; size, 19.6 x 9.5 mm; weight, 1.2 g) were utilized in seven pigs. Prolonged gastric residence (greater than 5 days) occurred in every case for this dosage form. Therefore, nondisintegrating caplets of three densities (1.25, 1.45, and 2.3 g/ml) and three different sizes (large, 20 x 10 mm; medium, 10 x 10 mm; small, 5 x 10 mm) were studied in two more pigs. Roentgenography was used to visualize passage of caplets through the GI tract. Heidelberg pH capsules (size, 8 x 20 mm; density, 1.61 g/ml) were also used in this study. Total GI transit times range from 2 to 33 days for 22 administrations of these nondisintegrating dosage forms. Pigs are found to not be an appropriate model for evaluating bioavailability of nondisintegrating controlled-release dosage forms because total GI transit time (especially gastric transit) is much too long.

Lactobacillus effects on cholesterol: in vitro and in vivo results

A double blind investigation was conducted on the influence of a commercially available tablet containing Lactobacillus acidophilus and Lactobacillus bulgaricus (Lactinex Becton Dickinson Microbiology Systems, Cockeysville, MD) on human serum lipoprotein concentrations. Tablets containing about 2 X 10(6) viable bacteria of Lactobacillus mixtures or placebo tablets were ingested by 354 nonfasting informed subjects in a dose of one tablet each, taken four times a day. There was a 3-wk washout period between two 6-wk treatment periods. The number of viable lactobacillus in unused returned tablets was the same at the end of the study as in the beginning. Analysis of paired data using Wilcoxon signed ranks test showed no major effects on lipoprotein concentrations for either the placebo-treated group or the lactobacilli-treated group. There were no statistically significant differences for low density lipoprotein concentrations between the lactobacilli-treated group and the placebo-treated group. The high density lipoprotein concentrations increased 1.8 to 3.0 mg/dl in both groups for both study periods. For total cholesterol the placebo-treated group experienced a statistically significant increase in the first period according to the Wilcoxon signed ranks test (from 208.0 to 215.0 mg/dl, P less than .001) but not according to a two-sample Student t test. Total cholesterol did not change significantly for the Lactobacillus-treated group in either period. Cardiac risk factor (ratio of total cholesterol to high density cholesterol) did not vary during the study. Lipoprotein values increased immediately following vigorous exercise compared with following 15 min of resting without either placebo or treatment. Sample controls for assay and reassay gave virtually identical values (coefficient of variation 1.6%), confirming that assay results were quite reliable. Thus, ingestion of commercially available Lactobacillus tablets, which contain about 2 X 10(6) cfu/tablet of L. acidophilus and L. bulgaricus cells in a dose of four tablets daily did not affect serum lipoprotein concentrations.

Chlorpheniramine dissolution and relative urinary excretion from commercial products

Dissolution profiles were determined for seven commercially available nonprescription solid dosage forms containing chlorpheniramine (four sustained release and three immediate release). An in vitro pH change method used to simulate GI transit produced dissolution profiles for some similarly labeled products which were significantly nonequivalent. One product failed to release its chlorpheniramine even when ground in a mortar and pestle in HCl solution, but did release drug in H3PO4 solution. A small (four subjects) relative bioavailability study based on average cumulative excretion of intact drug in urine gave results in parallel with substantially nonequivalent dissolution data for three products.

Dyphylline prodrugs: plasma hydrolysis and dyphylline release in rabbits

Ester hydrolysis of prodrugs of dyphylline [7-(2,3-dihydroxypropyl)theophylline] followed first-order kinetics in both human and rabbit plasma. Rate constants were estimated by linear regression analysis of initial conversion rates, determined at different initial prodrug concentrations. Release of dyphylline from different prodrugs was 1.3 to 13 times faster in rabbit plasma than human plasma. However, relative rates of drug release (lability order) followed the same patterns in rabbit and human plasma. Dyphylline concentrations in rabbit plasma were extended slightly following intravenous administration of dyphylline 2',3'-dipivaloate. Oral dosing of the prodrug in rabbits greatly sustained plasma dyphylline concentrations.

Theophylline and dyphylline pharmacokinetics in the horse

The pharmacokinetics of theophylline and dyphylline were determined after IV administration in horses. In a preliminary experiment, the usual human dosage (milligram per kilogram) of each drug was given to 1 horse. Results were used to calculate dosages for a cross-over study, using 6 horses for each drug. Theophylline plasma concentrations decreased triexponentially in 5 of 6 healthy horses after IV infusion of 10 mg of aminophylline/kg of body weight for 16 to 32 minutes. In the 6 horses, total body elimination rate constants were variable, and the half-life of theophylline was 9.7 to 19.3 hours. Clearance was 42.3 to 69.2 ml/hr/kg. The initial distribution phase was rapid (t1/2 approx 3.5 to 4 minutes); a 2nd distribution phase was slower (t1/2 approx 1.5 to 2 hours). Plasma concentrations of theophylline were in the assumed effective range (10 to 20 micrograms/ml) from 15 minutes until 40 minutes after time zero. The mean apparent volume of distribution was 1.02 L/kg. After bolus IV injection of dyphylline (20 mg/kg), pharmacokinetics were best described by a 2-compartment open model in 2 horses and by a 3-compartment open model in 4 horses. In the 6 horses, elimination half-life of dyphylline was 1.9 to 2.9 hours, and clearance was 200 to 320 ml/hr/kg. Plasma concentrations (approx 50 micrograms/ml) were observed at 10 minutes after injection without adverse effects. Concentrations greater than 10 micrograms/ml were observed from time zero to about 1.5 hours after injection. Theophylline induced significant increases in heart rate, but dyphylline did not affect heart rate significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of cheese for histamine, tyramine, tryptamine, histidine, tyrosine, and tryptophane

A method is described for determining the content of selected biologically active amines (histamine, tyramine, tryptamine) and amino acids (histidine, tyrosine, tryptophane) in cheeses by high performance liquid chromatography. The amines and amino acids were quantified by employing a counter ion-containing mobile phase and by comparing peak areas of high performance liquid chromatography charts for sample cheeses versus standard cheeses containing known amounts of added amines based on dual injections of samples and standards. Recovery of amines and amino acids varied from 87.5 to 111%. Histamine, which has been associated with food poisoning in concentrations of 185 mg/100 g in Swiss cheese and 180 to 500 mg/100 g in fish, was found in concentrations above 500 mg/100 g in Swiss cheese. The high performance liquid chromatography analytical method should be useful for screening to detect cheese samples containing toxic amounts of histamine and for research studies designed to determine the cause and effect relationships for histamine production in cheese.

Ethyl lactate-ethanol-water cosolvent for intravenous theophylline

Theophylline was dissolved in an ethyl lactate-ethanol-water cosolvent system and administered intravenously to rabbits. There were no observed differences in theophylline pharmacokinetics in rabbits administered in the cosolvent system when compared to theophylline administered as Aminophylline Injection USP, with the half-life being 4.5 hours and 4.3 hours respectively. Theophylline dissolved in the cosolvent system caused less erythrocyte hemolysis when exposed to blood in vitro than Aminophylline Injection USP. There were no observed toxicities in any rabbits during intravenous administration of theophylline dissolved in the cosolvent system or for Aminophylline Injection USP.

Effect of food and tablet age on relative bioavailability and pharmacodynamics of two tolbutamide products

Relative bioavailability and pharmacodynamics of tolbutamide from two different commercially available tablet products have been evaluated in healthy subjects in a single-dose crossover study. "Fresh" tablets and tablets aged by exposure to 98% relative humidity for 3 d at ambient temperature were studied. Aging was found to differentially affect both the rate and extent of absorption for the two products. Differences were reflected by log AUC (generic product AUC 10% lower than the product of the innovator, p = 0.047), peak concentration (generic product 27% lower than the product of the innovator, p = 0.0001), mean absorption time (generic product 119% longer than the product of the innovator, p = 0.0008), and mean residence time (generic product 17% longer than the product of the innovator, p = 0.011). Aged product from the innovator produced statistically significantly higher serum tolbutamide concentrations for the first 8 h postdose and a greater glucose depression than aged generic product. Administration of unaged tablets with food produced differences in the rate of absorption, manifested in time-to-peak (generic product 69% later than the product of the innovator, p = 0.006), peak concentration (generic product 18% lower than the product of the innovator, p = 0.001), and mean absorption time (generic product 104% greater than the product of the innovator, p = 0.007), which resulted in statistically significantly higher tolbutamide concentrations for the product of the innovator than for the generic product for the first 3 h postdose.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation and characterization of potential prodrugs of dyphylline

Four diesters and four monoesters of dyphylline were synthesized as prodrugs proposed to prolong the duration of action of dyphylline. They were characterized by IR, 1H NMR, HPLC, and MS. Appropriate solvent-programming conditions for the HPLC separation of dyphylline and the newly synthesized mono- and diesters were developed. It was confirmed by low-temperature 1H NMR at approximately -40 degrees C that all four monoesters were located on the primary hydroxy position. Attempts to produce the secondary monoesters yielded the primary monoesters during purification. Monoesters were shown by HPLC and MS to migrate between the primary and secondary hydroxy groups in aqueous solution.

Neutron activation of iron tablets to evaluate the effects of glycine on iron absorption

Neutron bombardment (neutron flux, 3 X 10(12) neutrons/cm2/s) of prepared iron tablets containing glycine-iron or iron alone was performed to prepare radioactive tablets to assess the effects of glycine on iron absorption from tableted formulations. No interfering isotopes of sufficient quantity were generated during neutron activation of the iron tablets. Cobalt-60 was the major trace mineral detected and accounted for only 1.3% of the total activity. There may have been trace amounts of zinc-65 or chromium-51 present, but they were not detectable above background radioactivity in the final tablet produced. Iron-59 represented greater than 98% of the radioactivity present in the tablets used in the study. Glycine-containing iron tablets produced dramatically higher amounts of iron in blood and tissues of rabbits (p less than 0.05) than did the same tablet formulations without glycine. The area under the iron blood concentration-time curve over 4 h increased by 67% with glycine added to the formulation over control iron tablets. Iron concentrations in tissues 4 h after iron administration was in the order of blood greater than liver greater than heart greater than kidney greater than muscle.

Generic tolbutamide tablet dissolution: intralot and interlot variation

Dissolution profiles for 62 lots of tolbutamide tablets from six manufacturers have been characterized using the USP paddle-stirrer apparatus. Results of paddle-stirrer dissolution for percent drug dissolved at 10, 20, and 30 min correlated well (r2 = 0.7444) with results from the USP rotating-basket test for 39 lots of tolbutamide. Interlot and intralot variability in tolbutamide dissolution was highly dependent on the manufacturer. For one product, the intralot range (for six paddle-stirred tablets) of percent drug dissolved after 30 min was 50-68% while the maximum interlot range for mean dissolution was 58-104%. One lot failed to meet both the rotating-basket and the paddle-stirrer dissolution specifications. Tablet response to aging at 60, 75, and 98% relative humidity over time was also highly manufacturer specific. The innovator's product repeatedly dissolved well when fresh or aged at all humidities. Dissolution from some generic tablets was dramatically depressed by humidity aging, even after only 3 d. Pretreatment of tablets with simulated gastric fluid modified the dissolution profile of one poorly dissolving lot of tablets. Results indicate that manufacturing quality control is highly variable among tolbutamide tablets.

Effects of divalent amino acids on iron absorption

Solutions of each of 10 amino acids or ascorbic acid were mixed with iron and orally administered to rats. Iron was absorbed to a statistically significantly greater extent (p less than 0.05) when mixed with asparagine, glycine, serine, or ascorbic acid as compared with a control solution of iron. The largest effects were for asparagine and glycine, which also increased iron absorption to a significantly greater extent (p less than 0.001) than did serine or ascorbic acid. No statistically significant increase in iron absorption occurred when any of the other amino acids was mixed with iron. The extent of iron absorption from each test solution, as measured by area under the concentration of iron-59 in the blood-time curve (r2 = 0.0002), and the initial rate of iron absorption for each test solution (r2 = 0.01) showed no correlation with the stability constant of the amino acid-iron complex.

Lot-to-lot variation in dissolution of tolbutamide tablets

The dissolution characteristics of tolbutamide tablets made by two manufacturers were compared. Six tablets selected from six lots of each manufacturer were subjected to the USP rotating-basket and paddle-stirrer dissolution tests. Samples were drawn after 10, 20, 30, and 45 minutes for the rotating-basket test and after 10, 20, and 30 minutes for the paddle-stirrer test. Drug concentrations of the dissolution samples were measured by ultraviolet spectroscopy or high-pressure liquid chromatography. All lots passed the disintegration, assay, content uniformity, and tablet weight variation tests; however, there was considerable interlot and intralot variation in the dissolution characteristics of the tablets. The range of interlot differences in the average amount of tolbutamide dissolved using the rotating-basket test was 55.6% for one manufacturer's product and less than 1% for the other's. The ranges were 40.5% and 2.4%, respectively, using the paddle-stirrer test. Similar differences for intralot variation between the two manufacturers' products also existed. Constant patient monitoring appears prudent when products with highly variable dissolution characteristics are used. It is recommended that, for a given patient, the chosen brand of tolbutamide not be changed without careful evaluation.

Comparison of two dissolution apparatuses with correlation of in vitro-in vivo data for prednisone and prednisolone tablets

Dissolution profiles in 0.1N hydrochloric acid using both the paddle stirrer apparatus and the spin filter apparatus were obtained for prednisone tablets made by seven different manufacturers and prednisolone tablets made by eight different manufacturers. Dissolution parameters were correlated with results obtained in three human bioavailability trials which were previously reported. Also, results obtained in one apparatus were correlated with those obtained in the other apparatus. Such correlations may be useful in the setting of in vitro dissolution rate specifications for commerical prednisone and prednisolone tablets.

Paired-ion reversed-phase high-pressure liquid chromatographic assay of pentobarbital-pyrilamine suppositories

The assay of suppositories containing pentobarbital and/or pyrilamine in a water-soluble polyethylene glycol base by high-pressure liquid chromatography is described. No extraction is required. The suppository is dissolved in the mobile phase. This solution is diluted with an internal standard stock solution containing phenobarbital. Chromatographic conditions include a C18 bonded microporous silica column and a mobile phase of 65% 4 x 10(-3) M n-butyl sodium sulfonate in 1% acetic acid and 35% acetonitrile. The procedure using commercial products gave results comparable to those obtained by GLC.

Development of an estriol-releasing intrauterine device

Estriol-releasing intrauterine devices were developed for experimental use in animals and humans. The devices consist of a reservior containing the steroid surrounded by a rate-limiting polyurethane membrane. After an initial transient, the drug is released from the device at a constant rate for 1 year or more; devices with a much longer release period can be fabricated readily. A constant release rate is achieved by maintaining solid drug in the reservoir and good physical contact between the drug and the inside wall of the device. The methods used to fabricate the devices are described along with release rate and stability data.

Influence of kaolin--pectin suspension on digoxin bioavailability

The effect of a kaolin--pectin suspension on the bioavailability of orally administered digoxin was evaluated when both drugs were given concomitantly and when their time of administration was separated by 2 hr. Coadministration of the antidiarrheal with the cardiac glycoside delayed absorption of the latter and, at the same time, decreased by 62% the amount of drug absorbed. Intersubject variation in digoxin bioavailability also was increased more than twofold. When the kaolin--pectin suspension was given 2 hr before the cardiac glycoside, the digoxin absorption rate was not affected, although its relative extent of absorption was reduced by about 20%. In contrast, when the antidiarrheal was given 2 hr after digoxin, neither the rate nor the extent of absorption of the cardiac glycoside was perturbed. No change in the intersubject variability in digoxin bioavailability was noted whether the antidiarrheal was given 2 hr before or 2 hr after the cardiac glycoside.

tert-Butoxycarbanyl as a convenient protecting group in synthesis of potential centrally active dopamine derivatives

Several pivaloyl and pivaloyloxy esters and amides of dopamine were synthesized for possible antiparkinson activity. The compounds were synthesized by select O- and N-acylation and N-methylation procedures. The tert-butoxycarbonyl function is an effective and easily removed nitrogen-protecting group for dopamine. Preliminary biological testing results showed that all compounds tested elicited a hypothermic response in mice, while only O,O-dipivaloyl-N,N-dimethyldopamine reversed reserpine-induced motor depression in mice. However, it is difficult to conclude from the preliminary data that the observed biological effects were due to central dopaminergic receptor stimulation.

Circadian rhythm of urinary pH in man with and without chronic antacid administration

In normal human volunteers, when urinary pH was plotted versus time, the circadian sine-wave type curve was not altered by chronic administration of a commercially available suspension containing a mixture of magnesium and aluminum hydroxides, although the antacid perturbed the entire curve in a more alkaline direction. A single dose of the antacid had little effect on urinary pH. There was a highly significant linear relationship between the change in hydrogen ion concentration during chronic antacid treatment and the initial control urinary hydrogen ion concentration, but there was no significant correlation between change in urinary pH and initial control urinary pH as has been previously reported. The above results were based on the evaluation of the hydrogen ion concentrations of 1562 separate urine samples collected from 24 normal subjects in a three treatment crossover study. It is recommended that: (1) research studies involving drug-drug interactions with antacids be designed to consider the effect of the antacid on the circadian rhythm of urinary pH, and (2) pH values not be averaged as commonly reported in the literature, but rather the pH values be converted to hydrogen ion concentrations before statistical analysis.

Determination of methylprednisolone and hydrocortisone in plasma using high pressure liquid chromatography

A method for quantitative determination of methylprednisolone and hydrocortisone in plasma using added methylprednisolone acetate as internal standard and high pressure liquid chromatography is presented. The standard curves were evaluated statistically and logarithmic parabolic equation is preferred over the usual standard curve mathematical relationships. The method was applied to samples of one subject's plasma containing methylprednisolone and endogenous hydrocortisone after oral dosing with multiple doses of methylprednisolone.

Degradation of carmustine in aqueous media

The degradation rate of carmustine was investigated in buffered aqueous media at several pH values. The buffering agents studied were those with potential use in parenteral formulations of this drug: acetate, citrate, and phosphate. The apparent first-order degradation rate constants were calculated using a linear regression procedure. A pH range over which minimum degradation occurred was ascertained. General acid and specific base catalysis was demonstrated for the degradation of carmustine. From the data at 5, 22, and 37 degrees, the apparent activation energies for carmustine degradation in buffered aqueous media were computed and were strongly pH dependent.

Degradation of carmustine in mixed solvent and nonaqueous media

The degradation rate of carmustine in several solvent mixtures and in mannitol solution was investigated at 5, 22, and 37 degrees. The solvents chosen were those utilized as parenteral diluents. The apparent first-order degradation rate constants were computed using a linear regression procedure. The most nonaqueous solvent mixtures demonstrated minimum apparent degradation rates. The apparent degradation rate constant decreased with a decrease in the macroscopic dielectric constant. From the data at several temperatures, the apparent activation energies for carmustine degradation in the several solvent mixtures were calculated. There was no evidence for a relationship between the apparent activation energy and the dielectric constant.

Linear and nonlinear assessment of tolmetin pharmacokinetics

Plasma concentration-time data in man after oral dosing of the nonsteroidal antiinflammatory agent, tolmetin sodium, were fitted to both linear and nonlinear pharmacokinetic equations. The apparent elimination half-life of tolmetin is shown to be 4.5 to 6.0 hours. An analytical method is presented which allows measurement of plasma concentrations for at least 32 hr (compared with a previous limit of about 8 hr) after a single oral dose of the equivalent of 400 mg of tolmetin acid.

Sensitive radioimmunoassay for digoxin in plasma and urine

A reproducible and sensitive radioimmunoassay for digoxin in either serum, plasma or urine is described. Using 0.5 ml of serum or plasma, the assay sensitivity is 0.05 ng of digoxin/ml. The antiserum and tracer solutions employed are available in a kit sold in the United States. All other reagents were prepared in the laboratory. The assay allows measurement of digoxin in plasma or serum for 96 hours after single 0.5 mg doses of digoxin; this is necessary in human bioavailability studies to accurately estimate the total area under the digoxin concentration, time curve from zero to infinite time. In contrast, with the kit assay, employing 0.2 ml of plasma or serum, it has been reported that the 12 hr serum digoxin levels, after single 0.5 mg doses, are, in most subjects, below the sensitivity limit (about 0.5 ng/ml) of the assay.

Diffusion model for drug release from suspensions I: theoretical considerations

A new mathematical model based on physicochemical principles is presented; it does not require a "diffusion layer" for the release of a suspended drug from a semisolid vehicle. This general model has wide range application to systems where release is controlled by the diffusion rate or dissolution rate of a drug. The appropriate mathematical relationships are derived and evaluated. Theoretical drug concentration distributions in the vehicle and a membrane and the predicted cumulative drug mass uptake by blood under specified conditions are presented. The dissolution rate of solid drug in the vehicle markedly influences predicted drug release using the model presented. It is anticipated that the model will stimulate further research to confirm or reject the assumption that the dissolution rate may be slow enough to be important in the systems studied.

Plasma prednisolone concentrations: comparison of radioimmunoassay and competitive protein binding assay

A comparison was made between plasma concentrations of prednisolone measured by both competitive protein binding radioassay (CPB) and radioimmunoassay (RIA) and, with each assay, using a calibration curve generated from individual subject data and from pooling the individual calibration curva data. The plasma samples were obtained from six normal adult male volunteers who were pretreated with dexamethasone to suppress endogenous hydrocortisone and who then ingested 10 mg of prednisolone. Both the standard curve data and the plasma concentrations were evaluated statistically. It was shown that the CPB method has considerably greater precision than the RIA method and could be employed in bioavailability and pharmacokinetic studies of both prednisolone and prednisone. It was also shown that corticosteroid binding globulin cross-reacts considerably less with the major metabolite of prednisolone, 20beta-dihydroprednisolone, than the particular antiserum used in the RIA.

Diffusion model for drug release from suspensions II: release to a perfect sink

Numerical mathematical methods are applied to a diffusion model based on physicochemical principles to predict drug release from suspensions of drug in semisolid vehicles. The predicted mass of drug released versus time curves using this model are in agreement with some reported experimental data but differ from predictions using the classical model for semisolid suspensions. The differences are discussed in relation to the drug dissolution rate and diffusion rate in the vehicle.