Extravasation of poly(amidoamine) (PAMAM) dendrimers across microvascular network endothelium.

PURPOSE: To study the influence of a controlled incremental increase in size and molecular weight of a series of poly(amidoamine) (PAMAM) dendrimers on their extravasation across the microvascular network endothelium. METHODS: A series of PAMAM dendrimers (generations 0-4) were fluorescently labeled using fluorescein isothiocyanate (FITC). Purification and fractionation of the fluorescently labeled polymers were done using size exclusion chromatography. The hamster cremaster muscle preparation was used as an in vivo model to study the extravasation process of the fluorescently labeled polymers. The extravasation process was visualized and recorded using intravital microscopy techniques. Analysis of the recorded experiments was done using Metamorph Imaging System. Extravasation of the fluorescently labeled polymers is reported in terms of their extravasation time (tau), i.e., the time needed for the fluorescence intensity in the interstitial tissue to reach 90% of the fluorescence intensity in the neighboring microvessels. RESULTS: Extravasation time (tau) describes the rate of microvascular extravasation of polymeric drug carriers across the microvascular endothelium into the interstitial tissue. Extravasation time (tau) of the studied PAMAM dendrimers showed size and molecular weight dependence. An increase in size and/or molecular weight of PAMAM dendrimers resulted in a corresponding exponential increase in the extravasation time (tau). CONCLUSIONS: Extravasation of PAMAM dendrimers across the microvascular endothelium showed size and molecular weight dependence. Results suggest that in addition to size and molecular weight, other physicochemical properties of polymeric drug carriers such as molecular geometry and charge may influence their microvascular extravasation. Systematic studies of the influence of the physico-chemical properties of polymeric drug carriers on their microvascular extravasation will aid in the design of novel macromolecular drug carriers with controlled extravasation profiles.

Administration of crushed extended-release pentoxifylline tablets: bioavailability and adverse effects.

The pharmacokinetics of crushed and intact pentoxifylline tablets were compared, and the frequency of adverse effects was evaluated. Intact 400-mg extended-release pentoxifylline tablets, crushed 400-mg tablets, intact 600-mg tablets, and crushed 600-mg tablets were given sequentially to 10 healthy male volunteers. Blood samples were collected at time 0, at 30-minute intervals for the first three hours, and at 4, 6, 8, 12, and 24 hours after the dose and analyzed by capillary gas chromatography for pentoxifylline and three major metabolites. The bioavailability of the crushed tablets relative to the intact tablets was 156% for the 400-mg strength and 137% for the 600-mg strength. The area under the plasma drug concentration-time curve from 0 to 24 hours (AUC0-24) for the 400-mg tablets (crushed and intact) differed significantly from that for the 600-mg tablets; there was no significant difference between intact 400-mg and intact 600-mg tablets or crushed 400-mg and crushed 600-mg tablets. The maximum plasma drug concentration (Cmax) was significantly greater and the time to maximum concentration (t(max)) significantly shorter for crushed tablets than intact tablets. The 400-mg crushed tablet caused mild nausea in three subjects. The 600-mg crushed tablet caused both moderate nausea and dizziness in seven subjects and diaphoresis, headache, and vomiting in one subject each. Cmax was higher and tmax shorter when pentoxifylline tablets were administered crushed rather than intact, and the increase in maximum plasma concentrations appeared to cause dose-related adverse effects; crushing the tablets did not decrease the relative bioavailability.

Toxicokinetics of trimethyltin in four inbred strains of mice.

Sixteen week old male AKR/J, Balb/cByJ, C57B1/6J and DBA/2J mice received single i.p. injections of trimethyltin (TMT). The toxic effects were weight loss, hyperexcitability, tremor, clonic-tonic convulsion, posterior paresis and death. The minimum toxic dose was 1.8 mg/kg, for the AKR strain and 2.3 mg/kg for the other strains. The highest non-lethal dose was 2.7 mg/kg for the AKR, DBA/2 and C57B1/6 strains and 3.0 mg/kg for the Balb/c strain. Blood levels of TMT peaked within 1 h and declined with half-lives of approximately 1.5 days. Blood levels of TMT were lower in the C57B1/6 mice due to greater tissue binding of TMT in C57B1/6 mice. Some of the toxic endpoints showed different rank orders among the strains, leading us to conclude that more than one biological process is responsible for the acute toxic effects of TMT in mice.

Characterization of drug release from liposomal formulations in ocular fluid.

The successful application of liposomes in topical ophthalmic drug delivery requires knowledge of vesicle stabilization in the presence of tear fluid. The release of procaine hydrochloride (PCH) from large unilamellar liposomes in the presence of simulated tear fluid was studied in vitro as a function of bilayer lipid content and tear protein composition. Reverse-phase evaporation vesicles were prepared from egg phosphatidylcholine, stearylamine or dicetyl phosphate, and cholesterol. The relationship between lipid composition and encapsulation efficiency, vesicle size, drug leakage upon storage at 4 degrees C, and the release of PCH-loaded liposomes was studied. The encapsulation efficiency was found to be dependent upon the lipid composition used in the liposome preparation. In particular, phosphatidylcholine vesicles containing cholesterol and/or charged lipids had a lower entrapment efficiency than liposomes prepared with phosphatidylcholine alone. However, the drug release rate was reduced significantly by inclusion of cholesterol and/or charged lipids in the liposomes. The release kinetics of the entrapped agent seemed to be a biphasic process and the drug-release in both simulated tear fluid (STF) and pH 7.4 phosphate buffered saline (PBS) solutions followed pseudo first-order kinetics in the early stage of the release profile. The drug-release appeared to be diffusion and/or partition controlled. Drug release from liposomes into STF, pH 7.4 PBS, and five different modified tear formulations was also evaluated. While serum-induced leakage is attributed to high-density lipoprotein-mediated destabilization, it was determined that lactoferrin might be the protein component in tear fluid that has the primary influence on the liposome-entrapped drug release rate. Five local anesthetics, benoxinate, proparacaine, procaine, tetracaine, and benzocaine were entrapped in liposomal vesicles by a reverse-phase evaporation (REV) technique. The release of these structurally similar topical anesthetics entrapped in positively charged liposomes (egg phosphatidylcholine, stearylamine, and cholesterol in a 7:2:1 molar ratio) was evaluated in a simulated tear fluid and pH 7.4 phosphate buffered saline solution. The liposomes appeared to be useful carriers for these drugs to retard their in vitro release in tear fluid and perhaps sustain or control their release in the eye for better therapeutic efficacy. An analysis of the release data demonstrated that for this series of drugs, drug partition coefficient has the largest effect on release rate, with molecular weight exhibiting a smaller effect. Release rate was found to decrease with increased lipophilicity or increased molecular weight.

Sustained release of acetaminophen from heterogeneous matrix tablets: influence of polymer ratio, polymer loading, and co-active on drug release.

The aim of this research was to investigate the effect of pseudoephedrine (PE), polymer ratio, and polymer loading on the release of acetaminophen (APAP) from hydroxypropyl methyl cellulose (HPMC)/polyvinylpyrrolidone (PVP) matrices. Granules formulated with APAP or both APAP and PE, and various blends of HPMC and PVP were compressed into tablets at varying compression forces ranging from 2000 to 6000 Ib. In vitro drug release from the matrix tablets was determined and the results correlated with those of tablet water uptake and erosion studies. Drug release from the formulations containing both APAP and PE was slower than those containing only APAP (P < 0.05, F = 3.10). Drug release from tablets formulated with APAP only showed an initial burst at pH 1.16 or 7.45, and at high total polymer loading (> or = 9.6%). Formulations containing both APAP and PE showed slower drug release at pH 1.16 than at pH 7.45. At pH 1.16, a decline in the percentage of APAP released occurred after 18 hours. This was due to the hydrolysis of APAP to p-aminophenol. The drug dissolution data showed good fit to the Korsmeyer and Peppas model, and the values of the release exponents ranged from 0.20 to 0.62, indicating a complex drug release pattern. Tablet erosion studies indicated that the amount of APAP released was linearly related to the percentage of tablet weight loss. The kinetics of tablet water uptake was consistent with a diffusion and stress relaxation controlled mechanism. Overall, the results of this study indicated that PE, as a co-active in the formulation, modified the matrix, and hence retarded APAP release.

In a drug discrimination procedure isolation-reared rats generalize to lower doses of cocaine and amphetamine than rats reared in an enriched environment.

Rats with different behavioral histories, defined by rearing and housing in either an enriched condition (EC) or an isolation condition (IC), were trained in a two-lever operant procedure to discriminate 5.0 mg/kg cocaine from saline. In cocaine dose-generalization tests, the IC rats exhibited an ED50 (1.01 mg/kg) significantly lower than the EC rats (ED50: 1.55 mg/kg). The cocaine-appropriate responding was emitted when the rats were treated with d-amphetamine, and for the d-amphetamine test doses the ED50 (0.19 mg/kg) was again significantly lower for the IC rats compared to the ECs (ED50: 0.33 mg/kg). These data suggest that IC rats are more sensitive to the stimulus properties of indirect dopaminergic agonists than EC rats and highlight the importance of environmental variables in governing an organism's response to the stimulus properties of abused drugs.

Development and evaluation of a novel dissolution apparatus for medicated chewing gum products.

A novel dissolution apparatus was developed for medicated chewing gum products. A prototype gum product containing phenylpropanolamine hydrochloride (PPA) was used to evaluate the apparatus. The apparatus consists of a conical Teflon base and a rotating, ribbed Teflon plunger suspended in a dissolution vessel. Parameters evaluated were rotation speed, plunger frequency, medium volume, medium type, medium sampling location, number of plunger ribs, and number of gum pieces. Samples were taken over a 20-min period and samples were analyzed by HPLC. Cumulative percentage released-versus-time profiles were obtained for each parameter evaluated. Statistical analysis of the gum product indicated that the only significant differences occurred at the lowest rotation speed and lowest plunger frequencies. A Level A correlation was found between the in vitro release profile for the 20-rpm and 30-cycles/min plunger frequency and the in vivo chew-out study.

Pharmacokinetics of diltiazem absorption in the rat gastrointestinal tract.

The absorption of diltiazem (CAS 42399-41-7) from the stomach, small intestine, and colon of the rat has been studied, using an in situ cannulation procedure. Diltiazem solutions (1 mg/ml) were prepared in isotonic buffers at pH 3.5 (stomach), 6.2 (small intestine), or 7.5 (colon). 10 ml of drug solution was used in the small intestine, 4 ml was used in the stomach and colon. Aliquot (100 microliters) of the solution was withdrawn at 5-min intervals for a period of 30 min, and assayed by HPLC. A semilog plot of percent remaining vs. time showed that absorption followed apparent first order kinetics with absorption rate constant, ka, equal 0.07 min-1, 0.02 min-1, and 0.01 min-1, in the small intestine, colon, and stomach, respectively.

Rectal bioavailability of delta-9-tetrahydrocannabinol from the hemisuccinate ester in monkeys.

Oral administration of delta-9-tetrahydrocannabinal (delta 9-THC) was shown to result in low and erratic bioavailability, while the drug showed no bioavailability from various suppository formulations. delta 9-THC-Hemisuccinate was formulated as a prodrug for delta 9-THC in suppositories using Witepsol H15 base. The bioavailability of delta 9-THC from this formulation was evaluated in monkeys. The plasma levels of delta 9-THC and its metabolite 11-nor-delta 9-THC-9-COOH were determined using GC/MS analysis. The calculated bioavailability of delta 9-THC from this formulation was found to be 13.5%. Non-compartmental analysis of the plasma concentration data using statistical moments showed the mean residence time (MRT) for delta 9-THC in the body to be 3 h following iv administration of delta 9-THC or its hemisuccinate ester (3.4 and 2.7 h, respectively), as compared with 5.8 h following rectal administration of the delta 9-THC hemisuccinate. The observed rectal bioavailability of delta 9-THC from suppositories containing the hemisuccinate ester as a prodrug is of significant importance in developing an alternative approach to oral administration of the drug.

Determination of amino acids in different regions of the rat brain. Application to the acute effects of tetrahydrocannabinol (THC) and trimethyltin (TMT).

A modified HPLC method is described for the determination of amino acids [aspartic acid, glutamic acid, glutamine, glycine, taurine, and gamma-aminobutyric acid (GABA)] in brain tissue utilizing precolumn derivatization with o-phthalaldehyde (OPA)-tert-butyl-thiol and electrochemical detection. A simple extraction procedure was employed and DL-homoserine used as internal standard. A neurotoxin previously shown to affect brain amino acids (trimethyltin, TMT) and a psychoactive compound hypothesized to act on these neurochemicals (delta-9-tetrahydrocannabinol, THC) were administered to adult male rats and amino acids were measured. Results revealed a gradient of distribution of most amino acids, with lowest levels posteriorly in the brain stem and increasing to the highest values in anterior cortical regions. TMT increased glutamine significantly in all brain regions examined, but increased glycine and decreased taurine only in the frontal cortex and hippocampus. No significant changes in any amino acid were found in hippocampus after THC treatment. The results establish the validity and usefulness of this HPLC method for detecting neurotoxicity-related changes in brain amino acid metabolism.

Comparison of serum progesterone levels in dogs after administration of progesterone by vaginal tablet and vaginal suppositories.

Serum progesterone levels from a vaginal tablet formulation and six different vaginal suppository formulations, each containing 25 mg of progesterone, were evaluated in mongrel dogs. Bioavailabilities relative to an intravenous dose of progesterone were calculated. The vaginal tablet was found to have a significantly higher bioavailability compared with the vaginal suppositories.

An in vitro method of evaluating tolnaftate release from topical powder.

A dissolution apparatus was constructed to evaluate tolnaftate release from topical powders. It consisted of a mesh unit to support the powder, a receptor phase, and a sink. This report describes three parameters that were used to evaluate this technique. First, three different areas of contact were examined using 52-, 41-, or 30-µm mesh supports. Second, the effect of the pH on the dissolution rate was studied, using aqueous buffers of pH 3, 5, 7, or 8 as the receptor phase. Finally, different topical powder formulations containing different amounts of tolnaftate were tested. The results obtained showed that the percentage of tolnaftate released from topical powders increased at low pH levels and with the larger mesh support. The percentage released was greater in a starch-talc preparation than in a talc-only preparation. The mesh was replaced by a semipermeable membrane (2.5- to 4 nm pore size) to function as an in vitro model for intradermal diffusion. The results showed that a cream initially released more drug than powder formulations.

Dissolution of meprobamate from various tablet formulations.

The effect of some formulation variables on the release of meprobamate from compressed tablets has been investigated. Possible interaction among the various variables was also studied. As a diluent, lactose produced a better dissolution rate than did starch. Tablets made with starch paste as the binder produced a faster release of meprobamate than those made with gelatin solution. Acacia proved to be the best disintegrating agent when compared to microcrystalline cellulose or starch, especially when the formulation already contained starch as the diluent. Under these conditions, microcrystalline cellulose was a better disintegrating agent than starch. Magnesium stearate or talc when used as a lubricant did not reduce the rate of release of meprobamate. Formulations containing a large proportion of starch (about 50%) did not produce a fast release of meprobamate.

Determination of sodium fusidate and fusidic acid in dosage forms by high-performance liquid chromatography and a microbiological method.

A new High-performance liquid chromatographic (HPLC) method for the assay of sodium fusidate (I) or fusidic acid in dosage forms was developed and compared to a microbiological assay. A linear relationship was obtained between absolute peak area and amount of I(r = 0.99+) in the 50-1000-microgram/ml range. In the microbiological assay, Staphylococcus aureus (NCTC 6571) was the test organism, using an agar diffusion technique. With five test levels of the standard, potencies were interpolated from standard curve using a log transformation straight-line method with least-squares fitting (r = 0.99+). Both methods were applied to assay I (or fusidic acid) in tablets, a suspension, and an ointment. Excellent agreement was observed between results of the two methods.

In vitro availability profiles of oral methoxsalen commercial products.

The in vitro release rate of methoxsalen from three commercially available tablets and an experimental tablet were evaluated at pH 2 and 7, using the USP dissolution test. The experimental tablet and one commercial product showed that 74% of the labeled amount is released in 1 h and almost completely released after 3 h at pH 2 and 7. Two products showed that only 12 and 10% of the labeled amount was released in 1 h and a maximum of 25 and 23% after 3 h at pH 2. At pH 7, the percent released from these two products were slightly higher. These results correlate with the reported clinical effectiveness of one of the products showing fast methoxsalen release. Since exposure to long-wave UV radiation is carried out 1-3 h following methoxsalen oral administration, delayed release might explain the failure of some products to give satisfactory clinical results.