Effects of interleukin 3 and interleukin 6 on platelet recovery in mice treated with 5-fluorouracil.

We have studied the effects of murine recombinant interleukin 3 (IL-3) and human recombinant interleukin 6 (IL-6) on platelet recovery after administration of 5-fluorouracil (5-FU) to mice. 5-FU at 250 mg/kg body weight was administered as a single i.p. injection, and treatment with IL-3 alone, IL-6 alone, or a combination of IL-3 plus IL-6 was initiated immediately following the 5-FU or after a delay of 2 days. In addition, the effects of the combination of IL-3 plus IL-6 were evaluated following delays in initiation of their administration until 4 or 6 days after 5-FU treatment. In all schedules, the IL-3 and IL-6 treatments were discontinued 8 days following 5-FU. IL-3 and IL-6 were given s.c. three times daily; each injection of IL-3 was 80,000 U, each injection of IL-6 was 5000 U, and the combination comprised separate injections of IL-3 and IL-6 at the same respective doses. The combination of IL-3 and IL-6, initiated immediately or 2 days following 5-FU, diminished the platelet nadir and increased platelet counts on individual days during the recovery phase, thus apparently decreasing the time required for recovery to a normal platelet level. However, using self-modeling nonlinear regression, in order to analyze variability in the duration of thrombocytopenia, statistically significant shortening of the period of thrombocytopenia could not be consistently demonstrated. Neither IL-3 alone nor IL-6 alone had any effect on the above parameters. Recovery of hematocrit values and white blood cell levels was unaffected by administration of either IL-3 or IL-6 alone or the combination of both cytokines. We propose that IL-3 and IL-6 can act synergistically to enhance platelet recovery following 5-FU-mediated thrombocytopenia, but their modification of the response to 5-FU is modest.

Chronopharmacokinetics of nicotine.

RATIONALE: For high-clearance drugs such as nicotine, hemodynamic changes throughout the day may be expected to influence the rate of metabolism. MATERIAL AND METHODS: To assess the effects of meals and diurnal rhythms on nicotine clearance, an intravenous infusion of nicotine bitartrate was administered for 48 hours to 11 subjects. Two models to determine nicotine clearance variation throughout the day are described. Both models were used to estimate the mean effect of meal and diurnal rhythms on nicotine clearance and individual parameters that were regressed against baseline covariates. Clearance was modeled as a function of time [CL(t)] and split it in three components: a (constant) baseline value (theta 1), its circadian (diurnal) variation, and the effect of meal: CL(t) = [theta 1 + circadian(t)] [1 + meal(t)]. A two-compartmental (time-variant) model incorporating CL(t) was then fitted to the data providing estimates of CL(t) conditional on literature values of the time-invariant parameters (volume of distribution and intercompartmental clearances). RESULTS: The estimated circadian(t) showed a maximum at approximately 11 AM and a flat minimum from 6 PM to 3 AM; the estimated meal(t) showed a sharp increase up to 1 hour (after the meal), at which point clearance is increased 42%, and a slower decrease thereafter, returning to baseline (zero) after 2.8 hours. Individual estimates of baseline clearance are found to have a linear relationship with body weight. No other covariate, sex in particular, effect could be found.

Passive versus electrotransport-facilitated transdermal absorption of ketorolac.

OBJECTIVE: To investigate the bioavailability (extent and rate of absorption) of ketorolac from two cutaneous absorption sources, active electrotransport and passive transdermal, and to examine the enantiomeric selectivity of bioavailability for each source. METHODS: Based on a crossover study in 12 healthy volunteers, the extent and rate of absorption of ketorolac, delivered by a patch, were found by estimating the input rate function of the drug. For that purpose, deconvolution was used in two steps. First, intravenous data were analyzed to estimate the ketorolac disposition function, and second, postpatch data were deconvolved to estimate the unknown patch input profile given the disposition function estimated in the first step. Because the input rate function curves to be estimated for the patches may be of arbitrary shape, a spline was used to model the patch input function, whereas intravenous data were modeled with use of a sum of exponentials. Differences in the extent of absorption (F) for the four treatment-enantiomer combinations were further examined with a mixed-effect regression model, based on the sets of four individual estimates of bioavailability. RESULTS: On average, the F value for the active electrotransport treatment, which exhibited the faster absorption rate, was four times greater than the F for the passive transdermal treatment. Further, during the passive treatment, R-ketorolac yielded an average F that is 42% greater than that for S-ketorolac and also exhibited a smaller absorption lag-time. During the active treatment, there was no important enantiomeric difference in either extent or rate of absorption.

A pooled analysis of CD4 response to zidovudine and zalcitabine treatment in patients with AIDS and AIDS-related complex.

INTRODUCTION: This article reports a meta-analysis focused on the efficacy of zalcitabine and zidovudine alone or in combination as reported by three AIDS Clinical Trial Group trials. We analyzed the log CD4 count (LCD4) response to therapy up to 1 year after the beginning of therapy. One of the purposes of this article was to illustrate a meta-analysis method that permits pooling of original data from trials with different designs. METHODS: To effectively eliminate obvious differences due to design, we first estimated complete (1 year) individual LCD4 versus time curves using a sophisticated smoothing technique. Then several summary descriptors were computed from the completed LCD4 curves. Those descriptors were corrected for baseline covariate differences, and the corrected values were then related to measures of drug exposure. RESULTS: Significant baseline covariates were LCD4 baseline count and AIDS-related complex or AIDS diagnosis. The predictor, corrected for baseline covariates, that correlated best with drug exposure was intensity, the initial rate of rise of LCD4, estimated as the slope of LCD4 between pretreatment and peak LCD4. CONCLUSION: Using intensity as a single response measure, we found weak evidence for synergism of zalcitabine and zidovudine: combination therapy increased response by 20% over that expected from a purely additive interaction.

The pharmacokinetics and pharmacodynamics of diltiazem and its metabolites in healthy adults after a single oral dose.

A potential complicating factor in the characterization of the pharmacokinetics and pharmacodynamics of diltiazem after an oral dose in the presence of two metabolites, N-demethyldiltiazem and desacetyldiltiazem, in plasma. Both N-demethyldiltiazem and desacetylditiazem have been shown to have pharmacologic activity in animal tissues. It is therefore possible that these metabolites contribute to the pharmacologic effect of diltiazem, but this possibility has not been explored. The purpose of this study was to investigate the pharmacokinetics and pharmacodynamics of diltiazem, N-demethyldiltiazem, and desacetyldiltiazem. Particular attention was paid to the effect of diltiazem on atrioventricular conduction. Six healthy men received a 120 mg oral dose of diltiazem. Concentrations of diltiazem, N-demethyldiltiazem, and desacetyldiltiazem in plasma and urine were measured by a sensitive HPLC method. Measures of pharmacologic response (heart rate, blood pressure, and PR interval) were obtained at each blood sampling time. Mean (+/- SD) peak plasma concentrations of diltiazem, N-demethyldiltiazem, and desacetyldiltiazem were 174.3 +/- 72.7, 42.6 +/- 10.0, and 14.9 +/- 3.3 ng/ml, respectively. The apparent half-lives of diltiazem, N-demethyldiltiazem, and desacetyldiltiazem were 6.5 +/- 1.4 hours, 9.4 +/- 2.2 hours, and 18 +/- 6.2 hours, respectively. Both N-demethyldiltiazem and diltiazem were eliminated by net secretion, whereas the renal clearance of desacetyldiltiazem did not exceed clearance by filtration. Both N-demethyldiltiazem and desacetyldiltiazem are bound to plasma proteins, with unbound fractions of 0.323 +/- 0.035 and 0.230 +/- 0.021. These values are similar to the unbound fraction of diltiazem (0.254 +/- 0.027). No significant effect of diltiazem on blood pressure or heart rate was noted. However, a prolongation of the PR interval was observed in all six subjects. Furthermore, an apparent clockwise hysteresis in the concentration-effect relationship was found in four of the six subjects. These findings suggest that some form of acute tolerance to the electrophysiologic effect of diltiazem develops, but the results of pharmacodynamic modeling suggest that this is not caused by the antagonistic effects the metabolites.

Semiparametric models for antagonistic drug interactions.

A new class of models to describe antagonistic drug interactions are presented. They are semiparametric in that they use nonparametric functions (splines) but are forced to obey certain constraints corresponding to reasonable assumptions. We propose the models primarily for exploratory data analysis, but they may also be definitive models for such purposes as predicting future responses. Certain problems that arise in semiparametric modeling, such as model selection, are addressed so that we can propose a relatively automatic and objective approach to model determination. We demonstrate the applicability of the class of models we propose to two real data set examples involving pain relief response to opioid agonists/antagonists. The results suggest that the semiparametric approach is particularly useful when unusual shapes link dose to response.

Differential postnatal development of mu-, delta- and kappa-opioid binding sites in rat brain.

With selective labelling techniques and analysis of saturation curves it is shown that in rat brain the concentrations of mu-, delta- and kappa-binding sites increase differentially during postnatal development. There are no changes in the binding affinities. The concentration (pmol/g brain) of kappa-sites are first to reach adult levels, namely between 7 and 14 days after birth. Adult levels of mu-sites are attained between 14 and 21 days after birth. The most striking finding is that development of delta-sites, which are not detectable 3 days after birth by the method used, lags markedly behind that of mu- and kappa-sites. The profile of development in rat brain is compared to that found previously in mouse brain.

Concepts, properties, and applications of linear systems to describe distribution, identify input, and control endogenous substances and drugs in biological systems.

The response at time t (R(t)) of a (causal linear time invariant) system to an input A(t) is represented by: [equation: see text] where K(t) is called the unit impulse response function of the system, and the integration on the right side of the equation (above) is called the convolution (from the latin cum volvere: to interwine) of A(t) and K(t). The system described by this equation is at zero (initial conditions) when t = 0. Although it does not even begin to describe the incredible variety of possible responses of biological systems to inputs, this representation has large applicability in biology. One of the most frequently used applications is known as deconvolution: to deinterwine R(t) given a known K(t) (or A(t)) and observations of R(t), to obtain A(t) (or K(t)). In this paper attention is focused on a greater variety of aspects associated with the use of linear systems to describe biological systems. In particular I define causal linear time-invariant systems and their properties and review the most important classes of methods to solve the deconvolution problem, address. The problem of model selection, the problem of obtaining statistics and in particular confidence bands for the estimated A(t) (and K(t)), and the problem of deconvolution in a population context is also addressed, and so is the application of linear system analysis to determine fraction of input absorbed (bioavailability). A general model to do so in a multiinput-site linear system is presented. Finally the application of linear system analysis to control a biological system, and in particular to target a desired response level, is described, and a general method to do so is presented. Applications to simulated, endocrinology, and pharmacokinetics data are reported.

D-optimal design applied to binding saturation curves of an enkephalin analog in rat brain.

The D-optimal design, a minimal sample design that minimizes the volume of the joint confidence region for the parameters, was used to evaluate binding parameters in a saturation curve with a view to reducing the number of experimental points without loosing accuracy in binding parameter estimates. Binding saturation experiments were performed in rat brain crude membrane preparations with the opioid mu-selective ligand [3H]-[D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO), using a sequential procedure. The first experiment consisted of a wide-range saturation curve, which confirmed that [3H]-DAGO binds only one class of specific sites and non-specific sites, and gave information on the experimental range and a first estimate of binding affinity (Ka), capacity (Bmax) and non-specific constant (k). On this basis the D-optimal design was computed and sequential experiments were performed each covering a wide-range traditional saturation curve, the D-optimal design and a splitting of the D-optimal design with the addition of 2 points (+/- 15% of the central point). No appreciable differences were obtained with these designs in parameter estimates and their accuracy. Thus sequential experiments based on D-optimal design seem a valid method for accurate determination of binding parameters, using far fewer points with no loss in parameter estimation accuracy.

A semiparametric deconvolution model to establish in vivo-in vitro correlation applied to OROS oxybutynin.

In vitro-in vivo correlation (IVIVC) models may be used to predict in vivo drug concentration-time profiles given in vitro release characteristics of a drug. This prediction is accomplished by incorporating in vitro release characteristics as an input function (A(vitro)) to a pharmacokinetics model. This simple approach often results in biased predictions of observed in vivo drug concentrations, and it can result in rejecting IVIVC. To solve this problem we propose a population IVIVC model that incorporates the in vitro information and allows one to quantify possibly changed in vivo release characteristic. The model assumes linear kinetics and describes the in vivo release as a sum of A(vitro) and a nonparametric function (A(d), a spline) representing the difference in release due to in vivo conditions. The function A(vitro) and its variability enter the model as a prior distribution. The function A(d) is estimated together with its intersubject variability. The number of parameters associated with A(d) defines the model: no parameters indicates perfect IVIVC, a large number of parameters indicates poor IVIVC. The number of parameters is determined using statistical model selection criteria. We demonstrate the approach to solve the IVIVC problem of an oral extended release oxybutynin form (OROS), administered in three pharmacokinetic studies. These studies present a particular challenging case; that is, the relative bioavailability for the OROS administration is >100% compared with that of the immediate-release form. The result of our modeling shows that the apparent lack of IVIVC can be overcome: in vivo concentration can be predicted (within or across data sets) based on in vitro release rate together with a simple form of systematic deviation from the in vitro release.

A descriptive tool to characterize nonlinear kinetics, with applications to meperidine and lidocaine.

We describe an explorative data analysis tool which can detect and describe the presence of nonlinearities in multiple dose kinetics studies. The method is nonparametric (i.e. not dependent on modeling assumptions), uses regression to estimate the functions representing the kinetics, and makes the detection of nonlinearity a part of the model selection process. Flexible functions (splines) are used to describe the kinetics corresponding to the lowest given dose, and to describe the (possible) departure of the kinetics corresponding to higher doses from the reference kinetics. The estimated kinetics and departures can be examined to offer possible insight into the nature of the nonlinearity. The methodology is applied to the analysis of meperidine and lidocaine kinetics through the lungs and the heart. We find that the lung kinetics of lidocaine and meperidine are linear. However their myocardial kinetics are complex and nonlinear.

A new criterion for selection of pharmacokinetic multiexponential equations.

In linear pharmacokinetics, the time course of the plasma concentration of a drug, Ct, is expressed by the sum of exponential terms, (formula; see text) This article proposes a new statistical criterion for discriminating between alternate polyexponential models. According to this new criterion, the model that best interprets a set of experimental data points is that which minimizes the area between the approximate confidence limits of Ct.

A general solution for nonparametric control of a linear system using computer-controlled infusion pumps.

Investigators have developed algorithms for use in computer-controlled infusion pumps (CCIP's) which dose intravenous drugs assuming multiexponential unit impulse response (UIR) function. However for many UIR multiexponential functions are at best an approximation. For almost all substances the early times after an impulse administration show complex profiles hardly described by multiexponential functions. For many later times also show departures from exponential decline. We derive a general approach for a CCIP which can be used with an arbitrary UIR function. A particular instance of the approach is based on a nonparametric representation of an UIR which uses spline functions. The approach is computationally simple, it can take into account desired constraints (for example no overshoot to avoid toxicity) and presents a solution to control concentrations of substances in a site different from the input site. Examples based on real lodocaine, veralipride, and thiopental data demonstrate the approach.

An application of the D-optimal criterion to define the experimental design for a particular class of semi-parametric models.

An updated version of the computer program EXCAD [1] allows the user to optimize experimental design to estimate parameters of particular semi-parametric models. The semi-parametric models take the general form of a function of time (t): Y(t) = NL (c(t,alpha),beta). The function NL(C(t,alpha),beta), is, in general, a non-linear transformation of a function, C(t,alpha), that in turn is the convolution of two others. One of these two functions is expressed in a non-parametric form, and is not of direct interest to the experimenter. The other is of direct interest: it is a parametric function depending on a set of parameters alpha. This semi-parametric model applies to numerous kinds of biological experiments, such as pharmacokinetic/pharmacodynamic, physiological, circulatory flow experiments. This paper presents a new method for determining an optimal experimental design to estimate the parameters alpha and beta. The new approach adopts the D-optimal criterion, and is illustrated using real thiopental data.

Software for experimental design: the computer program EXCAD.

A computer program (EXCAD) dedicated to the optimization of experimental designs to estimate parameters of a mathematical model, is presented. EXCAD computes D-optimal designs and sequentially augmented designs. D-optimal designs minimize the determinant of the variance-covariance matrix and parameters, thus obtaining the average most accurate estimate of parameters. D-optimal designs have generally as many support points as the number of parameters in the mathematical model, so sample scheduling is minimal, not extensive. Augmented designs add to an original design the point that maximizes the decrement of the determinant of the variance-covariance matrix. The general model, linearly or not linearly parametrized Y = F(X,P), that relates two independent variables and P parameters to different responses may be written in the program, while a set of prewritten models is provided.

MODDIS: a microcomputer program for model discrimination.

A computer program for a microcomputer (HP 86) is presented to discriminate between different models and to design new experiments for model discrimination. By a non-linear fitting algorithm a set of experimental data is fitted with different models suggested by the user. The parameters characterizing each model are estimated by minimizing the sum of squared residuals; different criteria are used to test the choice between two or more models at different levels of probability and the smallest number of additional experiments required for discrimination is computed. If discrimination is not achieved a direct search method is used to find the local maxima of the divergence (or information for discrimination) over a user-chosen domain of independent variables (x R'''). The x value corresponding to the absolute maximum of the divergence is the best choice to run a new experiment for discrimination.

Pharmacokinetic and pharmacodynamic modelling of metoprolol in rabbits with liver failure.

The pharmacokinetic and pharmacodynamic profiles of metoprolol were studied in adult male rabbits given 3.2 mg/kg i.v. before and during liver failure. The partition of metoprolol between blood cells and plasma averaged 1.14 in both conditions. Plasma protein binding, concentration-independent, was 32% and 17% in normal and pathological status, respectively. With normal liver function the terminal elimination half-life for the drug was 0.54-0.96 h, rising to 1.0-2.1 h in liver failure. Differences of the same order were observed for total plasma drug clearance (average 3.7 vs 1.5 1/h/kg), MRT (0.77 vs 1.92 h), AUC (0.9 vs 2.2 mg h/l) and k10 (3.17 vs 1.80 h-1). Liver impairment did not affect the volume of distribution of the central compartment, the steady-state volume of distribution and the other intercompartmental rate constants. Although metoprolol was eliminated in the urine, the amount excreted was low (1.5% of the administered dose) in both conditions. The pharmacokinetic model was extended by an 'effect compartment', which has no influence on the predetermined mass of drug in the body, to analyse the relationship between heart rate fall and changes in metoprolol plasma concentrations. After drug administration, heart rate fell rapidly about 90 beats in both states. The mean unbound plasma concentration producing 50% of this reduction was double during liver failure compared to normal condition (0.03 vs 0.07 mg/l), but the temporal aspects of drug equilibration with site of action were similar.

Every 36-h gentamicin dosing in neonates with hypoxic-ischemic encephalopathy receiving hypothermia.

OBJECTIVE: To examine the impact of a change in the empiric gentamicin dose from 5 mg kg(-1) every 24 h (Q24 h period) to 5 mg kg every 36 h (Q36 h period) on target drug concentration achievement in neonates with hypoxic ischemic encephalopathy (HIE) receiving therapeutic hypothermia. STUDY DESIGN: Gentamicin drug concentrations in neonates with HIE receiving therapeutic hypothermia were examined during two time periods in a retrospective chart review. During the initial treatment period (November 2007 to March 2010; n=29), neonates received Q24 h period. During the second treatment period (January 2011 to May 2012; n=23), the dose was changed to Q36 h period. Cooling criteria and protocol remained the same between treatment periods. Gentamicin drug concentrations including achievement of target trough concentrations (<2 mg l(-1)) were compared between treatment periods. Individual Bayesian estimates of gentamicin clearance were also compared. RESULT: Neonates with an elevated trough concentration >2 mg l(-1) decreased from 38 to 4% with implementation of a Q36-h dosing interval (P<0.007). The mean gentamicin trough concentration was 2.0 ± 0.8 mg l(-1) during the Q24 h period and 0.9 ± 0.4 mg l(-1) during the Q36 h period (P<0.001). Peak concentrations were minimally impacted (Q24 h 11.4 ± 2.3 mg l(-1) vs Q36 h 10.0 ± 1.9 mg l(-1); P=0.05). The change in gentamicin trough concentration could not be accounted for by differences in gentamicin clearance between treatment periods (P=0.9). CONCLUSION: A 5 mg kg(-1) every 36-h gentamicin dosing strategy in neonates with HIE receiving therapeutic hypothermia improved achievement of target trough concentration <2 mg l(-1), while still providing high peak concentration exposure.