Application of chronopotentiometry to determine the thickness of diffusion layer adjacent to an ion-exchange membrane under natural convection.

A brief review of the evolution of the diffusion boundary layer (DBL) conception inspired by the works of Nernst, Levich and Amatore is presented. Experimental methods for studying the DBL in electrode and membrane systems are considered. The electrochemical behaviour of a CM2 cation-exchange membrane in NaCl and KCl solutions is studied by chronopotentiometry at constant under-limiting current. Chronopotentiometric curves are described theoretically by applying the Kedem-Katchalsky equations in differential form to a three-layer system including the membrane and two adjoining DBLs. The conductance coefficients entering the equations are found by treating the results of membrane characterisation: the electrical conductivity, transport numbers of ions and water, electrolyte uptake, as functions of the equilibrium electrolyte solution. The two-phase microheterogeneous model is used for this treatment resulting in presentation of the conductance coefficients as functions of (virtual) electrolyte solution concentration in the membrane. The steady-state DBL thickness (delta) is found by fitting experimental potential drop at sufficiently high times. It is found that delta is proportional to (Delta c)(-0.2), where Delta c is the difference between the electrolyte concentration in the solution bulk and at the interface. This result differs from the Levich equation, which gives the power equal to -0.25 for Delta c. This deviation is explained by the fact that the theory of Levich does not take into account microscopic chaotic convection motion recently described by Amatore et al. It is shown that the treatment of experimental chronopotentiometric curves with the model developed allows one to observe the role of streaming potential in the membrane. Different mechanisms of streaming potential and their effect on the shape of chronopotentiograms are discussed. A simple analytical solution of Navier-Stokes equations applied to natural convection near an infinite vertical ion-exchange membrane is found. It is shown that the formation of DBL induced by electric current is quasi-stationary. This fact allows the empirical expression found earlier and linking delta with Delta c under steady-state conditions to be used in transient regimes. The numerical solution of the non-stationary Kedem-Katchalsky equations together with this empirical expression results in quantitative description of the potential difference (pd) and delta as functions of time in chronopotentiometric experiments. The comparison of theoretical and experimental chronopotentiometric curves shows an excellent agreement, especially for the part after switching off the current. The reasons of a small deviation observed just before the curves attain steady state under a constant current applied are discussed.

Pharmacokinetics of ethambutol in children and adults with tuberculosis.

SETTING: Five hospitals in the United States. OBJECTIVE: To describe ethambutol pharmacokinetics in children and adults with active tuberculosis (TB). DESIGN: Prospective, open-labeled study in 56 adults and 14 children with active tuberculosis who received ethambutol as part of their multidrug TB regimens. RESULTS: Most serum samples were collected up to 10 h post dose and assayed using a validated gas chromatography assay with mass selective detection (GC/MS). Concentration data were analyzed using non-compartmental and population pharmacokinetic methods. Drug exposure increased with dose, but less than proportionally at doses >3000 mg. Lower than expected maximum serum concentrations (Cmax <2 microg/ml) were common in adults. Very low Cmax (<1 microg/ml) were common in children, as was delayed absorption (time to Cmax >3 h). Many Cmax were at or below typical TB minimal inhibitory concentrations. Cmax values for HIV-positive patients were 20% lower than HIV-negative patients with daily doses, but were similar with larger twice-weekly doses. CONCLUSIONS: Adult TB patients often had lower than expected ethambutol serum concentrations, and most pediatric TB patients had very low ethambutol serum concentrations. Higher doses and therapeutic drug monitoring may be indicated for many of these patients.

Pharmacokinetics of ethionamide administered under fasting conditions or with orange juice, food, or antacids.

This study was conducted in order to (i) determine the effect of food, orange juice, or antacids on the absorption of a single oral 500-mg dose of ethionamide (ETA) in healthy volunteers, including an assessment of bioequivalence, and (ii) determine ETA population pharmacokinetic (PK) parameters. The pharmacokinetics of ETA in serum was determined for 12 healthy males and females in a randomized, four-period crossover study. Volunteers received single 500-mg doses of ETA either on an empty stomach (reference) or with food, orange juice, or antacids. Serum samples were collected for 48 h and assayed by high-performance liquid chromatography. Data were analyzed by noncompartmental and population methods. Mean test/reference ratios and 90% confidence intervals were determined. No statistically significant differences were seen in the maximum concentration of ETA (C(max)), time to maximum concentration (T(max)), or area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)) between the four treatments (P > 0.05 by analysis of variance). The least-squares mean ratios (with confidence intervals in parentheses) for C(max) were 105% (81.2 to 135%) after orange juice, 94% (72.8 to 121%) after food, and 88% (68.4 to 114%) after antacids. The least-squares mean ratios (with confidence intervals is in parentheses) for AUC(0-infinity) were 91% (72.7 to 115%) after orange juice, 96% (76.4 to 121%) after food, and 95% (75.5 to 120%) after antacids. The mean T(max) was slightly prolonged following antacid or food administration (2.3 to 2.6 h) compared to administration on an empty stomach or with juice (1.7 to 1.9 h). The median population PK parameters were as follows: K(a) = 0.37 to 0.48 h(-1), V/F = 2.0 to 2.8 liters/kg, CL/F = 56.5 to 72.2 liters/h, and terminal half-life = 1.7 to 2.1 h, where K(a) is the absorption rate constant, V is the volume of distribution, and CL is clearance. The PK behavior of ETA was not significantly modified by the different conditions studied. Mean ratios for AUC ranged from 0.91 to 0.96 for the orange juice, food, and antacid treatments, indicating a minimal effect on relative bioavailability. ETA can, therefore, be administered with food if tolerance is an issue.

A population analysis of nebulized (R)-albuterol in dogs using a novel mixed gut-lung absorption PK-PD model.

PURPOSE: The objectives of this study were to 1) construct a pharmacokinetic-pharmacodynamic (PK-PD) model, and 2) determine the PKs and PDs of (R)-albuterol when given by nebulization to 8 dogs for 7 consecutive days. METHODS: Four doses were evaluated (0.002, 0.02, 0.1, and 0.4 mg/kg/ day). Blood samples were obtained after drug administration on days 1 and 7. Heart rates (HR) were obtained during treatment days 1, 4 and 7. All (R)-albuterol plasma concentrations were fitted using a mixed gut-lung absorption 2-compartment PK model. Day-1, 4, and 7 HR data were co-modeled using a direct response model with Hilltype equations, including a necessary tolerance phenomenon. The population PK-PD analysis was performed with an iterative 2-stage methodology (IT2S). RESULTS: No chiral inversion was seen, and double absorption peaks on the plasma concentration versus time curves were observed in the majority of dogs. These were hypothesized to be the result of combined gut and lung absorption of (R)-Albuterol. Results indicated that 67% (range: 57-89%) of (R)-albuterol systemic exposure after nebulized administration is due to gut absorption. Mean population PK parameters were KaGI (10+/-5.7 h(-1)), KaLUNG (21+/-9.5 h(-1)), CLc/F (0.6+/-0.2 L/h/kg), CLd/F (1.4+/-0.5 L/h/kg), Vc/F (1.4+/-0.9 L/kg), and Vp/F (4.8+/-2.4 L/kg). (R)-albuterol administration was associated with an increase in the dogs heart rates. A tolerance effect related to the cumulative dose was observed and modeled. CONCLUSIONS: The presented PK-PD model appears to differentiate gut from lung absorption when (R)-albuterol is given by 15-minute nebulization to dogs. These results agree with the accepted hypothesis that most of the systemic exposure of (R)-albuterol after nebulized administration is due to gut absorption.

Potential interaction between itraconazole and clarithromycin.

Three patients negative for human immunodeficiency virus infection were admitted for pulmonary Mycobacterium avium complex (MAC) and aspergillosis infections. They were treated with different drug combinations, but all regimens included clarithromycin for MAC and itraconazole for aspergillosis. All patients experienced an increase in clarithromycin concentrations and clarithromycin: 14-OH-clarithromycin ratio compared with expected range values. They had no clinical side effects. The time course suggested a possible interaction between clarithromycin and itraconazole, presumably through itraconazole's effects on cytochrome P450 3A4 activity. A bidirectional interaction cannot be ruled out. The data suggest that, when necessary, these two drugs can be administered together safely. Further investigation is necessary to determine the extent and clinical consequences of coadministration in humans.

Piperacillin and tazobactam exhibit linear pharmacokinetics after multiple standard clinical doses.

A population pharmacokinetic (PK) analysis was conducted to determine if piperacillin and tazobactam exhibited linear or nonlinear PKs and if incremental changes in the daily dosage of piperacillin affected tazobactam PKs. Four dosage groups were evaluated after multiple dosing regimens. Concentrations of drug in plasma and amounts in urine were best fitted by using a linear two-compartment PK model. No significant difference between dosing groups was seen for any piperacillin or tazobactam PK parameters. Both drugs exhibited linear PKs when given at usual clinical doses. Tazobactam PKs did not appear to be affected by the different dosing regimens of piperacillin.

Population pharmacokinetics of nitroglycerin and of its two metabolites after a single 24-hour application of a nitroglycerin transdermal matrix delivery system.

The purpose of this study was to assess the ability of our previously constructed pharmacokinetic (PK) model to describe nitroglycerin (GTN), 1,2-dinitroglycerin (1,2-GDN), and 1,3-dinitroglycerin (1,3-GDN) plasma concentrations after a single-dose application of a GTN transdermal matrix delivery system. GTN, 1,2-GDN, and 1,3-GDN plasma concentrations were simultaneously fitted using a first-pass, mixed-order release, one-compartment PK model. Population PK parameter values were derived using an iterative two-stage methodology (IT2S). Some of the mean PK parameters estimates and their interindividual variability (CV%) were the percentage of the delivered GTN dose reaching the systemic circulation released by a first-order process A, 53% (44); the 1,2-GDN and 1,3-GDN formation rate constants, k(f1)9 h(-1) (67) and k(f2) 0.5 h(-1) (38), respectively; the metabolite elimination rate constant, k(m) 1 h(-1) (27); GTN, 1,2-GDN, and 1,3-GDN volumes of distribution (Vc/F 6 L [45]), V2/F 78 L [51]), and V3/F 29 L [40]), respectively). Mean calculated elimination half-lives (t1/2+/-standard deviation [SD]) for GTN and the GDN metabolites were 7+/-4 minutes and 33+/-7 minutes, respectively. The proposed PK model fitted the observed plasma concentrations of GTN, 1,2-GDN, and 1,3-GDN very well. This new transdermal matrix delivery system appears to behave pharmacokinetically in the same manner as a transdermal reservoir delivery system (Transderm-Nitro, Ciba-Geigy, Mississauga, Canada).

Novel pharmacokinetic modelling of transdermal nitroglycerin.

PURPOSE: To construct a pharmacokinetic (PK) model and to determine population PK parameters of nitroglycerin (GTN), 1,2-dinitroglycerin (1,2-GDN), and 1,3-dinitroglycerin (1,3-GDN). METHODS: Data were obtained in thirty healthy volunteers following a single dose of a GTN reservoir transdermal patch. Blood samples were obtained just before and at 0.5, 1, 2, 3, 4, 6, 8, 12, 14, and 24 hours after the patch application and 1 hour after its removal. GTN, 1,2-GDN, and 1,3-GDN concentrations were determined using HPLC and simultaneously best fitted using a first-pass mixed-order release one-compartment PK model. Individual estimates (ADAPT-II) were used as priors for a population PK analysis (IT2S). Fitted parameters included the percentage (A) of the nitroglycerin dose reaching the systemic circulation that was released from the patch by a first-order process (K1); two absorption (ka1 and ka2), two metabolite formation (kf1 and kf2) and one metabolite elimination (k(m)) rate constants; and three volumes of distribution Vc/F, V2/F and V3/F. RESULTS: Nitroglycerin mean population parameter estimates and inter-individual variability (CV%) were: A 35% (65), K1 0.06 h-1(91), ka1 5 h-1(46), ka2 0.47 h-1(39), kf1 11 h-1(42), kf2 0.6 h-1(34), k(m) 1.4 h-1(29), V0/F 6 L(31), V2/F 73 L(34), and V3/F 23 L(29). The average elimination half-lives for GTN and the two metabolites were 5 and 32 minutes, respectively. CONCLUSIONS: The proposed PK model fitted observed concentrations of GTN, 1,2-GDN and 1,3-GDN very well. This model should be useful to predict drug and metabolite concentrations and to assess bioequivalence of two transdermal formulations.

Efficacy of pentosan polysulfate in the treatment of interstitial cystitis: a meta-analysis.

OBJECTIVES: To determine the efficacy of pentosan polysulfate (Elmiron) compared to placebo in the treatment of interstitial cystitis. METHODS: The data sources used were MEDLINE, Excerpta Medica, and International Pharmaceutical Abstracts databases, and the manufacturer. Bibliographies of articles obtained were reviewed. The keywords used were pentosanpolysulfate, pentosanpolysulfate sodium, and pentosan. Inclusion criteria were blinded selection of English language, prospective, randomized, placebo-controlled comparative trials; > or = 8 weeks' duration; > or = 300 mg daily; adult humans with > or = 1 symptoms including pain, urgency, frequency, and nocturia; symptoms for > or = 12 months; normal urinalysis; negative findings for urine culture and cytology. Exclusion criteria were hemorrhagic cystitis; drug-, microbial-, or radiation-induced cystitis; carcinoma in situ; other influencing diseases. The outcome of success was defined as a > or = 50% decrease in pain, urgency, frequency, and nocturia. The number of successes was extracted by blinded investigators, treating withdrawals as failures. The percentage difference in success rates of pentosan polysulfate and placebo, and the number needed to treat (NNT) were determined for each variable; P values and 95% confidence intervals (CIs) were determined for combined data. Homogeneity of effect was determined by calculating Q (chi-squared). Article quality was assessed using the Chalmers scale to determine if quality affected outcome. Effective inter-rater reliability was determined using Rosenthal's method. Significance was set at P < 0.05. RESULTS: Four studies were included. Data were extracted from all four studies for pain (n = 398), three for urgency (n = 306), two for frequency (n = 160), and one study for nocturia (n = 106). The differences (95% confidence limits) were pain: 16.6% (95% CI 8%, 25%), NNT = 7; urgency: 13.0% (1.0%, 25%), NNT = 7.5; frequency: 16.7% (2.3%, 31.1%), NNT = 6; nocturia: -1% (-19.8%, 21.8%). P values from homogeneity tests were not significant. Mean quality scores were 63.8%, 48.1%, 50.4%, and 65.6%, respectively, in the four studies; the effective inter-rater reliability was 0.96. Results did not differ when weighted by quality score. CONCLUSIONS: Pentosan polysulfate is more efficacious than placebo in the treatment of pain, urgency, and frequency associated with interstitial cystitis. Pentosan polysulfate is not significantly different from placebo in treating nocturia associated with interstitial cystitis.

B-complex recombinants and sarcoma regression: role of B-L/B-F region genes.

The anti-sarcoma response of three B complex recombinant haplotypes BR1(F24-G23), BR2(F2-G23), and BR3(F2-G23) was investigated. In a preliminary experiment, one male heterozygous for the BR1 recombinant haplotype and another heterozygous for the BR2 recombinant haplotype were each mated to females, some of which carried the respective recombinant. The anti-sarcoma response of progeny carrying the BR1 recombinant differed significantly from that of progeny carrying the BR2 recombinant. Subsequently, each of the three recombinant haplotypes was placed on each of four B haplotype complex backgrounds, and compared to B-G and B-L/B-F region controls on the same background haplotype. For each recombinant, significant differences in tumor growth were found between the recombinant and B-L/B-F control chickens on either one, two, or three of the four genetic backgrounds tested. For each recombinant, no differences were found between chickens carrying the recombinant and B-G region controls, which is further evidence that the gene(s) controlling Rous sarcoma growth lies in or near the B-L/B-F chromosomal region. Moreover, although the BR2 and BR3 recombinants appear to be identical serologically, they differed significantly in tumor growth suggesting that the two haplotypes are genetically different.

Histological, biochemical, and ultrastructural studies on hyperpigmented human skin xenografts.

The mechanisms for hyperpigmentation observed in human cutaneous xenografts placed on athymic nude mice was investigated. Histologic, biochemical, histochemical, and ultrastructural examinations were performed on human skin prior to grafting and at various times ranging from 2 weeks to 30 weeks post-grafting (PG). Hyperpigmentation was macroscopically visible on the graft as early as 4-6 weeks. The number of Dopa-positive melanocytes per unit area was increased at 2 weeks PG and remained elevated until 20 weeks PG. The surface area of the melanocytes, a measure of the activity of the cells, also increased significantly and remained above the pre-grafting size throughout the study. Western blot analysis using tyrosinase specific antibody (alpha Ty-SP) revealed the presence of tyrosinase exclusively in the grafted skin from 2 weeks to 12 weeks PG tested. Histological and ultrastructural observations revealed the presence of numerous dendritic melanocytes, indeterminant clear cells suggestive of Langerhans cells, and dermal melanophages. The results of this study suggest that the observed hyperpigmentation in grafted tissue is caused by an increase in the number of Dopa-positive melanocytes and probably from enhanced melanin production. Extracts of proteins from the xenografts exhibited prominent differences in low and high molecular proteins between pre- and post-grafted skin. Among them, the exclusive appearance of a protein doublet with apparent mw approximately 14 kDa was found in grafted skin, and subsequent studies indicate it has potent effects on melanocyte function.

Influence of non-MHC T lymphocyte alloantigens on regression of Rous sarcomas in the chicken.

Chickens of Regional Poultry Research Laboratory (RPRL) inbred line 6(3) regress sarcomas induced by Bryan high-titer Rous sarcoma virus to a greater extent than chickens of line 7(2), although these lines are identical for the major histocompatibility complex (MHC, B complex). They differ, however, at two independent autosomal loci, Ly-4 and Th-1, which determine surface alloantigens of partly overlapping subsets of T lymphocytes. Association of genotypes at these loci with quantitative variation in ability to regress Rous sarcomas was tested in segregating progeny derived from crosses of lines 6(3) and 7(2). In the F4 generation chickens of the Ly-4a/Ly-4a, Th-1a/Th-1a genotype (symbolized aa/aa) had significantly higher regressor ability than any of the other three double homozygous genotypes. In F5, all nine genotypes formed by combinations of homozygotes and heterozygotes were tested, and higher regressor ability was shown by the aa/aa, ab/aa, and aa/ab genotypes. These results indicate that higher regression is associated with: (1) interaction between the line 6(3) Ly-4a and Th-1a alleles in homozygous form; and (2) dominance x dominance interaction, in that the a allele at each locus is dominant for higher regression only within the homozygous aa genotype at the other locus.

Endrocrine factors and the growth and spread of B16 melanoma.

B16 melanomas grew more slowly in female than in male syngeneic C57BL/6J mice. After oophorectomy, the growth rate was similar to that in normal and castrated male mice and was not altered in pregnant mice. The growth in vitro was similar in the presence of serum from normal and castrated male and female mice.

The distribution and fate of blood-borne 125IUdR-labelled tumour cells in immune syngeneic rats.

Radiolabelled sarcoma cells injected into the tail veins of normal rats were held up almost exclusively in the lung, and were not observed to pass through into the systemic circulation. Intramuscularly injected tumour cells were retained at the site of injection. Radioactivity was lost from both sites though more rapidly from the lung than from muscular tissue and was probably the result of tumour-cell death. Alveolar macrophages did not take part in the destruction of tumour cells in the lung. There was an increased rate of radiolabel loss from the lungs of hyperimmune, post-excision and tumour-bearing rats, as compared with normal rats. The destruction was immunologically specific; it was detected earlier, was more comprehensive in the hyperimmune and post-excision animals than in tumour-bearing animals, and correlated with the ability of the hyperimmune and post-excision animals to reject larger numbers of intravenous unlabelled tumour cells, than the tumour-bearing rats.