System functionality and physicochemical model of fentanyl transdermal system

Fentanyl is an opioid traditionally administered by infusion or injection and more recently in a rate-controlled transdermal dosage form. This system is a four-layer laminate on a protective liner. A backing layer seals and protects the drug reservoir, the source for continuous delivery of fentanyl. A membrane controls the release rate of fentanyl from the system. An adhesive layer attaches the system to skin and releases an initial loading dose of fentanyl. The rate of fentanyl delivery through skin is determined by the system and the skin at the application site. The release rate from the system is approximated by Fick's first law of diffusion and is controlled by the rate-controlling membrane. A complete simulation model that combines both in vitro release data and the pharmacokinetic model has been developed and used to show the influence of various physiologic and system variables on serum fentanyl concentrations.

Identification of the envelope V3 loop as the primary determinant of cell tropism in HIV-1

Cells of the monocyte-macrophage lineage are targets for human immunodeficiency virus-1 (HIV-1) infection in vivo. However, many laboratory strains of HIV-1 that efficiently infect transformed T cell lines replicate poorly in macrophages. A 20-amino acid sequence from the macrophage-tropic BaL isolate of HIV-1 was sufficient to confer macrophage tropism on HTLV-IIIB, a T cell line--tropic isolate. This small sequence element is in the V3 loop, the envelope domain that is the principal neutralizing determinant of HIV-1. Thus, the V3 loop not only serves as a target of the host immune response but is also pivotal in determining HIV-1 tissue tropism.

A mutant poliovirus containing a novel proteolytic cleavage site in VP3 is altered in viral maturation

A six-amino-acid insertion containing a Q-G amino acid pair was introduced into the carboxy terminus of the capsid protein VP3 (between residues 236 and 237). Transfection of monkey cells with full-length poliovirus cDNA containing the insertion described above yields a mutant virus (Sel-1C-02) in which cleavage occurs almost entirely at the inserted Q-G amino acid pair instead of at the wild-type VP3-VP1 cleavage site. Mutant Sel-1C-02 is delayed in the kinetics of virus production at 39 degrees C and exhibits a defect in VP0 cleavage into VP2 and VP4 at 39 degrees C. Sucrose gradient analysis of HeLa cell extracts prepared from cells infected by Sel-1C-02 at 39 degrees C shows an accumulation of fast-sedimenting replication-packaging complexes and a significant amount of uncleaved VP0 present in fractions containing mature virions. Our data provide in vivo evidence for the importance of determinants other than the conserved amino acid pair (Q-G) for recognition and cleavage of the P1 precursor by proteinase 3CD and show that an alteration in the carboxy terminus of VP3 or the amino terminus of VP1 affects the process of viral maturation.

Absorption characteristics of transdermally administered fentanyl

Fentanyl was administered intravenously and transdermally to eight surgical patients to determine the systemic bioavailability and rate of absorption of the transdermally administered drug. Serum fentanyl concentrations reached a plateau approximately 14 h after placement of the transdermal fentanyl delivery system. This plateau was maintained until removal of the system at 24 h. The decline in serum fentanyl concentrations after removal of the transdermal system had a terminal half-life of 17.0 +/- 2.3 h (mean +/- SD), considerably longer than the terminal elimination half-life seen after intravenous administration of fentanyl in the same patients (6.1 +/- 2.0 h). The rate of fentanyl absorption, predicted to be 100 micrograms/h from in vitro data, appeared to be relatively constant during a period starting 4-8 h after placement of the transdermal system until removal of the system at 24 h. The rate of absorption during this period was 91.7 +/- 25.7 micrograms/h. After removal of the transdermal fentanyl delivery system, absorption continued at a declining rate. This indicates that the long terminal half-life of serum fentanyl concentrations after transdermal system removal is due to continued slow absorption of fentanyl, probably from a cutaneous depot of drug at the site of prior transdermal system placement. At the time of removal of the transdermal fentanyl system, 1.07 +/- 0.43 mg of drug remained in this depot. Systemic fentanyl bioavailability was found to be 0.92 +/- 0.33, with no evidence of significant cutaneous metabolism or degradation by the skin's bacterial flora. The transdermal administration of fentanyl produces relatively constant serum fentanyl concentrations for significant periods of time in the postsurgical patient requiring analgesic therapy.

Simultaneous quantification of cycloserine and its prodrug acetylacetonylcycloserine in plasma and urine by high-performance liquid chromatography using ultraviolet absorbance and fluorescence after post-column derivatization

D-Cycloserine is a broad-spectrum antibiotic used with other antibiotics to treat various forms of tuberculosis. Its prodrug sodium (R)-4-[(1-methyl-3-oxo-1-butenyl)amino]-3-isoxazolidinone hemihydrate, developed for better aqueous stability and solubility, is combined with another broad-spectrum antibiotic, fludalanine. An ion-pair, reversed-phase high-performance liquid chromatographic assay has been developed to simultaneously detect cycloserine and its prodrug in plasma and urine. The prodrug is detected directly by ultraviolet absorbance and cycloserine by fluorescence following post-column derivatization.

Bioanalysis and disposition of alpha-fluoromethylhistidine, a new histidine decarboxylase inhibitor

A sensitive, selective, and rapid high-performance liquid chromatographic procedure was developed for the determination of alpha-fluoromethylhistidine (alpha-FMH) in human biological samples. The plasma assay required isolation of the drug using a weak cation-exchange resin prior to HPLC analysis with UV detection. The urine assay employed postcolumn derivatization with o-phthalaldehyde (without a thiol) and fluorescence detection. The extent of metabolism of alpha-FMH in humans was studied in four healthy volunteers using tritium-labeled material. No significant differences in the plasma and urine concentrations of radioactivity and unchanged drug were detected. In addition, the radiochromatograms of selected urine samples revealed a single peak with a retention time corresponding to the unchanged drug. The evidence presented suggests negligible biotransformation of alpha-FMH in humans.

General method for evaluating the fraction of the irreversible organ clearance due to conversion of drug to a primary metabolite

An expression for the fractional metabolic clearance of a drug across an organ has been developed. The expression is a function of areas under the temporal profiles of the drug and metabolite concentrations in the sampling compartment. Formation of the metabolite of interest is permitted throughout the linear systems analyzed. The expression is shown to be applicable to any linear system provided there is only a single direct feed from the organ of interest (compartment where formation of the particular metabolite is being investigated) to the drug-sampling compartment.

Effect of nonlinear protein binding on equilibration times for different initial conditions

The dynamics in the equilibration of free drug in a two-compartment closed system, exhibiting nonlinear binding in one of the compartments, are elucidated. The dynamics of the free drug in the compartment containing the binding sites are first studied under the two initial conditions when the drug is added to the same and the other compartment; the dynamics of the drug in the compartment devoid of binding sites are then studied under the two initial conditions. Dynamic asymmetries are shown to exist among the four cases in the nonlinear region using an equilibrium limit which symmetrizes the dynamics for all four cases in the linear region. In the two cases where the dynamics are viewed in the compartment devoid of binding sites, the dynamic asymmetry is manifested by a reduction in the time required to reach the limit for the drug added to the compartment containing the binding sites compared with the other compartment. The time difference between these two cases becomes magnified when limits, reflective of the relative error in the estimate of the equilibrium value, are applied. In the linear region, application of these limits results in a time difference. This time difference again favors addition to the compartment containing the binding sites from a time-conservation perspective.

An assessment of the accuracy of a regional economic-demographic projection model

A large number of regional economic-demographic projection models have been developed but their accuracy has seldom been evaluated. This article examines the accuracy of one such model in projecting total populations for 1980, using 1970 base data, for 106 counties and 553 places in two states. Comparisons of the model's projections to 1980 Census counts reveal mean percentage absolute differences of 10 percent for counties and 14 percent for places. In addition, the model's accuracy was comparable to that for alternative projection systems. When projections for places of less than 1,000 are excluded, differences are substantially reduced. Economic-demographic models appear to be quite useful and deserve further attention.

Kinetics of the tissue distributions of sulindac and metabolites. Relevance to sites and rates of bioactivation

Sulindac (sulfoxide) is a prodrug in reversible metabolic equilibrium with its pharmacologically active metabolite, the corresponding sulfide. Following simultaneous parenteral injection of sulfoxide-14C and sulfide-3H at equivalent dosage, all labeled species in the plasma of rats and guinea pigs and in representative tissues were determined at various times. Rate constants for sulfoxide in equilibrium or formed from sulfide, calculated from the rates of interchange of the two labels in plasma, are still higher than those approximated from earlier, single-label studies, and indicate turnovers of total body pools every 45 and 8.5 min in rat and guinea pig, respectively. From the time-course of tissue/plasma ratios of endogenous labeled species, it can be concluded that kidney and liver are major sites of bioactivation of the prodrug, with significant sulfoxide leads to sulfide activity present in all tissues examined. At steady state, tissue concentrations of each redox form are determined by the ratio of the metabolic rate constants for the two opposing biotransformations and by unique tissue/plasma distributive constants for each redox form, resulting in all tissues, except lung, and at all times examined, in a sulfide/sulfoxide ratio greater than one.

Vaginal drug absorption in rhesus monkeys I: development of methodology

Earlier reports from these laboratories described a procedure for determining vaginal drug absorption in the rabbit based upon a perfusion system, and data on the vaginal absorption of the straight-chain aliphatic alcohols and carboxylic acids were given. These studies have been extended to the rhesus monkey. Rib-cage-type cells were designed for intravaginal insertion through the vulval orifice and to fit the specific dimensions of the monkey vagina. The general design of the cell was similar to that used in the rabbit vaginal absorption studies. The persusion system was checked by using 3H-polyethylene glycol 4000, and no significant leaks from the cell were found. The absorption of the alcohols followed first-order kinetics. The computed apparent permeability coefficients for the alcohols were of comparable magnitude to those previously reported for the rabbit vaginal membrane.