Four macaques (Macaca nemestrina; 1 female and 3 males) were administered dideoxyinosine (DDI) at three dose levels (3.2 mg/kg i.v., 10 mg/kg i.v., and 20 mg/kg s.c.). Blood and urine samples were ...collected during 6-8 h and 24 h after drug administration, respectively. The mean plasma clearance (16.7 +/- 4.9 ml/min/kg), steady-state volume of distribution (1.5 +/- 0.4 L/kg), and terminal plasma half-life (96.8 +/- 7.5 min) did not differ significantly between the two i.v. doses. DDI was eliminated from the body primarily by excretion of the unchanged drug in the urine (74%). The absorption of DDI from the subcutaneous site was complete (bioavailability of 0.91 +/- 0.13) and rapid, with peak plasma concentration obtained at 30 min.
We have characterized the ability of a simian immunodeficiency virus, SIVmne strain E11S, to infect macaque placental trophoblast and Hofbauer cells. These primary placental cells were permissive to ...SIVmne infection, regardless of gestational age. Virus production by the infected cells was determined as time-dependent viral core antigen p27 production, followed by verification of the proviral gag/LTR DNA sequences in the infected cells using a polymerase chain reaction assay. Of more than six placentas tested, SIVmne infection of placental cells at an early gestational age (i.e., days 55 or 78) produced more than 10-fold the amount of virus core antigen p27 than did placental cells infected at a late gestational age (i.e., days 135 or 165). In addition, SIVmne infection of trophoblast cells was inhibited by SIVmac neutralizing macaque serum but not by normal serum, indicating the specificity of virus infection. Furthermore, the amount of SIV core antigen p27 produced by the virus-infected trophoblast and Hofbauer cells was shown to be dependent on the multiplicity of virus infection. Collectively, our results indicate that macaque trophoblast and Hofbauer cells can be infected by SIV and that both gestational age and viral dose may play a role in the extent of viral infection.
The objective of the study was to determine the identity and kinetic characteristics of nucleoside transporters present in the brush-border membrane of the human jejunum. With use of brush-border ...membrane vesicles, uptake of 3Huridine was stimulated two- to threefold by an inwardly directed Na+ gradient and was inhibited by both 100 microM thymidine and 100 microM guanosine nucleosides, which serve as model substrates for purine (N1, cif) and pyrimidine (N2, cit) transporters, respectively. 3Hthymidine and 3Hguanosine transport exhibited an overshoot phenomenon only in the presence of a Na+ gradient. Na(+)-thymidine uptake was inhibited by 100 microM cytidine or thymidine but not by guanosine, inosine, formycin B, or hypoxanthine. 3Hguanosine uptake was inhibited by 100 microM inosine, guanosine, or formycin B but not by thymidine or cytidine. Both adenosine and uridine inhibited uptake of 3Hthymidine and 3Hguanosine to a similar extent, indicating that both N1, cif and N2, cit Na(+)-nucleoside transporters are expressed in human jejunum. Enhanced uptake of Na(+)-thymidine by an inside-negative potential difference generated by K+ and valinomycin provides evidence that nucleoside transport is rheogenic, involving net transfer of a positive charge. The Hill coefficient was unity for all three substrates, indicating a Na(+)-nucleoside coupling stoichiometry of 1:1. At saturating Na+ concentration (150 mM) the kinetic parameters (n = 3-4) Michaelis-Menten constant and maximum velocity for uridine, thymidine, and guanosine uptake were 4.15 +/- 1.79, 2.74 +/- 0.58, 12.02 +/- 1.34 microM and 25.93 +/- 7.38, 16.10 +/- 3.64, 63.92 +/- 10.23 pmol.mg-1.10 s-1, respectively. These results suggest that, in contrast to the human kidney that expresses the N4 nucleoside transporter, the human jejunum expresses both N1 and N2 Na(+)-nucleoside transporters.
The specific aims of this work were to: (1) evaluate the therapeutic strategy of using fluconazole to suppress sulfamethoxazole hydroxylamine formation in HIV-infected patients and provide the basis ...for future toxicity prevention trials; (2) examine the effect of the commonly co-administered drugs for opportunistic infections, rifabutin (300mg OD), clarithromycin (500mg BD) and fluconazole (200mg OD) on the pharmacokinetics of both dapsone (100mg OD) and sulfamethoxazole (800mg OD) and their respective hydroxylamine production in HIV-infected patients; (3) identify a potentially clinically useful inhibitor of sulfadiazine hydroxylamine production in vitro and (4) determine the inhibitory potential of the protease inhibitors indinavir, nelfinavir, ritonavir and saquinavir on dapsone and sulfamethoxazole hydroxylamine production. Fluconazole was an effective inhibitor of both dapsone and sulfamethoxazole hydroxylamine exposure in HIV-infected patients and suppressed hydroxylamine exposure approximately 50%. Rifabutin increased sulfamethoxazole hydroxylamine exposure by approximately 50% compared to controls, but had no effect on dapsone hydroxylamine exposure. Clarithromycin had no effect on exposure to either dapsone or sulfamethoxazole hydroxylamine. Fluconazole was also found to substantially inhibit sulfadiazine hydroxylamine production in vitro with Ki's ranging from 19–62μM and would be predicted to inhibit hydroxylamine exposure by 40–70% in vivo. Of the protease inhibitors examined only ritonavir has the potential to inhibit sulfamethoxazole and dapsone hydroxylamine production with a Ki for reversible inhibition of 1.44 ± 0.41 μM and IC50 of 1.82 ± 0.35μM, respectively. This work demonstrates the utility of in vitro drug metabolism data to prospectively predict significant drug-drug interactions in vivo. The strategy of using fluconazole to inhibit dapsone and sulfamethoxazole hydroxylamine exposure in HIV-infected patients to decrease rates of adverse reactions should now be examined in much larger toxicity trials.
Prednisone and prednisolone are two most widely prescribed corticosteroids in clinical practice. Pharmacokinetic variability has been attributed as a cause of variability in response between ...individuals to standard dosage forms. The pharmacokinetics of prednisone and prednisolone are complicated by the reported nonlinear disposition and the reversible metabolism in vivo of these two steroids. In this project, attempts to derivatise the steroids using a fluorescent label to improve the lower limits of sensitivity of the conventional method of analysis of these steroids failed due to the presence of unwanted reaction products produced in the derivatisation procedure. The pharmacokinetics of the corticosteroids were therefore studied using a conventional normal phase HPLC method based on the intrinsic U.V. absorption of these corticosteroids. A reverse phase HPLC method of analysing cortisol and prednisolone simultaneously was also developed. The corticosteroids were administered to rabbits, as the water soluble esters, in dose ranging infusion studies. From measurement of the plasma concentration at steady-state, and the fraction unbound, measured by equilibrium dialysis, the plasma clearance of the total and the unbound steroids were computed. Our results indicate that prednisone is not completely available from prednisone succinate while the hydrolysis of prednisolone phosphate toprednisolone is complete. The plasma clearance of the total and unbound prednisolone was found to increase with an increase in the rate of infusion of prednisolone phosphate. The ratio of the plasma concentration of prednisolone to prednisone, at steady-state, remained constant over a ten-fold range of prednisone succinate infusion, indicating that at least the interconversion between these two steroids appears to be linear. In vitro binding studies, using rabbit plasma, indicate concentration dependent binding of prednisone and prednisolone to plasma proteins and a definite interaction between these two steroids for binding sites on corticosteroid binding globulin (CBG). Equations for a perfusion and compartmental model were derived to aid in the analysis and interpretation of the results on the disposition of a drug and metabolite undergoing reversible metabolism. In Part B of the thesis, a "single-point single-dose" method for predicting individual dosage requirement is explored. Such a method would be helpful when an intermediary measure of the pharmacological activity of the corticosteroids is available which bears a simple relationship to the plasma concentration of these corticosteroids.
The "single-point, single-dose" method for predicting individual maintenance dosage is examined. Data available in the literature on nortriptyline is used to illustrate the method. Optimal use of the ...method requires knowledge of the pharmacokinetics, especially the elimination rate constant, within the patient population requiring the drug. The method is applicable to intravenous and extravascular administration, when absorption is rapid relative to elimination, for those drugs whose disposition kinetics can be described by a linear one-compartment model. As a reasonable approximation, the optimal sampling time after the single test dose is 1.5 times the population half-life. Error in chemical analysis needs to be considered when applying the method. One method of evaluating the prediction and subsequent adjustment of dosage is discussed.
The toxicity of azidothymidine (AZT) was studied in monkey dams and fetuses that were exposed to the drug over the entire gestational period. Fourteen virus-free female macaques (Macaca nemestrina) ...were randomly assigned to AZT or control groups. AZT animals received the drug through a gastric catheter at a dose of 1.5 mg/kg every 4 hours, which produced plasma concentrations similar to those in humans taking 500 to 600 mg/day of AZT. Control animals received water placebo, also through gastric catheter. Some animals participated in both groups. All females were mated with the same male; 41 matings produced 20 pregnancies, of which 16 were carried to term (9 in AZT females; 7 in control females). The AZT animals developed an asymptomatic macrocytic anemia, but hematologic parameters returned to normal when AZT was discontinued. Total leukocyte count decreased during pregnancy and was further affected by AZT administration. AZT-exposed infants were mildly anemic at birth. AZT caused deficits in growth, rooting and snouting reflexes, and the ability to fixate and follow near stimuli visually, but the deficits disappeared over time. These data indicate that early exposure to AZT in utero should have no irreversible adverse effects on the fetus.
A diaper method, used in pediatric medicine, has been adapted and validated for total urine collection from infant macaques (Macaca nemestrina). The device consists of cellulose sponges and ...polyethylene sheets. The method proposed is non-invasive, simple, and does not significantly hinder the movement of the infant. The method should be useful when one is conducting pharmacokinetic studies in which total urine collection is required.
The use of illicit and licit drugs during pregnancy is a major public health concern because of potential adverse effects on the fetus and the risk to maternal health. Because the placenta is the ...primary link between the mother and the conceptus and is essential for the growth and survival of the fetus, abnormalities in placental formation and function resulting from drug use could have a major influence on pregnancy outcome. At present, little information is available on the impact of abused drugs on placental biology alone or in combination with other “host” factors (eg, stress, infections). This prompted the National Institute on Drug Abuse (NIDA) to convene a meeting of experts in placental biology to review cutting-edge research with the mission to translate existing information to new clinical and research initiatives in the drug abuse field. This report summarizes the presentations and research recommendations resulting from the workshop discussions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
