Safe use of the CXCR4 inhibitor ALX40-4C in humans.

ALX40-4C is a small peptide inhibitor of the chemokine receptor CXCR4 that can inhibit X4 strains of HIV-1. Prior to the discovery of chemokine receptors as the HIV coreceptors, ALX40-4C was used in phase I/II clinical trials to evaluate its therapeutic potential against HIV-1, making ALX40-4C the first anticoreceptor inhibitor to be tested in humans against HIV-1. Patients in the highest dose groups achieved ALX40-4C levels above the effective concentration of the drug for nearly the entire 1-month treatment period. ALX40-4C was well tolerated by 39 of 40 asymptomatic HIV-infected patients, despite the critical role of CXCR4 in normal development and hematopoiesis. No significant or consistent reductions in viral load were observed, but only 12 of the enrolled patients harbored virus types that used CXCR4. We also found that ALX40-4C interacts with the second extracellular loop of CXCR4 and inhibits infection exclusively by blocking direct virus-CXCR4 interactions.

Induction of zidovudine glucuronidation and amination pathways by rifampicin in HIV-infected patients.

AIMS: The objective of the study was to determine the effect of multiple doses of rifampicin on the steady-state pharmacokinetics of zidovudine and its 5'-glucuronosyl (GZDV) and 3'-amino (AMT) metabolites. METHODS: Eight asymptomatic HIV-infected patients (seven male, one female) participated in this three-period longitudinal study. Each patient received zidovudine (200 mg every 8 h) for 14 days (period 1), followed by rifampicin (600 mg every 24 h) with zidovudine for 14 days (period 2), and then zidovudine alone for a further 14 days (period 3). Blood and urine samples were collected over 6 h on the last day of each period for measurements of zidovudine and GZDV by h.p.l.c.-u.v. and AMT by h.p.l.c.-m.s-m.s. RESULTS: Compared with zidovudine-alone values in period 1, 14 days of coadministration with rifampicin significantly increased zidovudine oral clearance (89%) and formation clearances to GZDV (100%) and AMT (82%). Correspondingly, there were decreases in maximum plasma concentration (43%), AUC (47%) and urine recovery (37%) of zidovudine. GZDV/zidovudine and AMT/zidovudine AUC ratios increased by 99% and 36%, respectively, despite a significant 29% decrease in AMT AUC. After stopping rifampicin for 14 days, values of these pharmacokinetic parameters returned to within 26% of baseline. Over the three periods AMT plasma levels were <18 ng ml-1 (n=6) and <40 ng ml-1 (n=2), and molar AMT/zidovudine AUC ratios ranged from 1.7% to 4.5%. CONCLUSIONS: Rifampicin induced zidovudine glucuronidation and amination pathways resulting in decreased plasma and urine exposures to zidovudine. AMT plasma exposure decreased because induction was more pronounced for the major GZDV metabolite. The magnitude of the residual inductive effect was minimal at 14 days after stopping rifampicin.

Reduced plasma concentrations of antituberculosis drugs in patients with HIV infection.

BACKGROUND: Reports suggest that antituberculosis drugs are malabsorbed in patients with advanced HIV disease. OBJECTIVE: To evaluate the pharmacokinetics of antituberculosis agents in HIV-seropositive patients at different stages of disease. DESIGN: Parallel study. SETTING: Two hospital outpatient clinics. PARTICIPANTS: 12 healthy volunteers, 12 patients with asymptomatic HIV disease, 12 patients with symptomatic HIV disease, and 12 patients with symptomatic HIV disease and diarrhea. MEASUREMENTS: Drug plasma concentrations were measured over 24 hours on day 4 of concurrent therapy. INTERVENTION: Oral isoniazid (300 mg/d), rifampin (600 mg/d), pyrazinamide (1000 mg/d), and ethambutol (1000 mg/d). RESULTS: Reduced total drug exposure to rifampin and pyrazinamide was associated with D-xylose malabsorption in persons with HIV infection or AIDS. Peak drug exposure to isoniazid was lower in patients with diarrhea. CONCLUSIONS: Reduced total drug exposure may be related to malabsorption in persons with HIV infection or AIDS.

Pharmacokinetics of antimycobacterial drugs in patients with tuberculosis, AIDS, and diarrhea.

To test the hypothesis that antituberculous drug disposition is altered in patients with AIDS, we studied the steady-state pharmacokinetics of isoniazid (300 mg/d), rifampin (600 mg/d), and pyrazinamide (1,500 mg/d) in 29 adults (14 patients infected with human immunodeficiency virus [HIV] and 15 non-HIV-infected patients) with tuberculosis in Nairobi, Kenya. Intestinal integrity was assessed with xylose. Neither HIV infection nor diarrhea accounted for the interpatient variability in the area-under-the-plasma concentration vs. time curve (AUC), the maximum concentration, or the terminal half-life (t1/2) of isoniazid, rifampin, and pyrazinamide. No significant association between HIV infection or diarrhea and pharmacokinetics was seen for any of the compounds. In addition, neither the AUC nor the t1/2 of any of these drugs reflected interpatient differences in CD4 lymphocyte counts. Xylose absorption was uniformly low. We did not demonstrate that HIV infection, diarrhea, or CD4 lymphocyte counts contributed significantly to the variability in pharmacokinetics of isoniazid, rifampin, and pyrazinamide in TB patients in Nairobi.

Rifabutin absorption in the gut unaltered by concomitant administration of didanosine in AIDS patients.

Didanosine (ddI) is currently used in the management of patients infected by the human immunodeficiency virus. Rifabutin (RBT) is being extensively used for prophylaxis against Mycobacterium avium complex (MAC) infections. Due to its acid-labile characteristics, ddI must be administered with a buffer. Recent reports have indicated that absorption of ketoconazole, ciprofloxacin, and dapsone, etc., in the gut is altered by concomitant ddI dosing. We have assessed whether concomitant dosing of ddI as antiretroviral therapy modifies RBT absorption in the gut, its steady-state pharmacokinetics, and/or safety in 15 patients with AIDS. Of the 15 patients enrolled, 12 completed the study and 3 receiving 600 mg of RBT with concomitant ddI administration withdrew prematurely from the study. Steady-state RBT pharmacokinetics were assessed on day 13 (ddI plus RBT) and day 16 (RBT alone). The ddI doses (adjusted for body weight) were 167 to 375 mg twice daily, while RBT was administered as a single 300- or 600-mg daily dose. No statistically significant (P > 0.05) differences were seen in RBT absorption parameter estimates between days 13 and 16: maximum concentration in plasma (Cmax; 511 +/- 341 ng/ml versus 525 +/- 254 ng/ml) and the time at which Cmax was observed (3.0 versus 2.5 h). The mean RBT estimates for area under the concentration-time curve from 0 to 24 h (AUC(0-tau)) (5,650 versus 5,023 ng x h/ml) and for oral clearance (1.28 versus 1.18 liter/h/kg) on both study days were also similar. Assessment based on urinary recovery of RBT (3.1 versus 3.7 mg) and its predominant deacetyl metabolite, LM565 (1.6 versus 1.4 mg), showed no apparent effect of ddI. The fraction of the RBT dose converted to LM565, as suggested by the ratio of AUC of the metabolite to AUC of the parent drug, was also unaltered (0.15 versus 0.12). A ratio analysis (day 13/day 16) of the RBT pharmacokinetic estimates showed that the 95% confidence intervals for all parameters were inclusive of one. Furthermore, the brief interruption of ddI therapy over this short study period at steady state produced no clinically significant changes in body weight, hematology, and renal and pancreatic functions. Therefore, concomitant administration of ddI appears not to affect RBT absorption in the gut and its disposition or safety in patients with AIDS.

Development of an enzyme-linked immunosorbent assay for measurement of serum-associated ALX40-4C.

ALX40-4C is an antiretrovirus agent that has been found to have some inhibitory properties against human immunodeficiency virus (HIV) replication in vitro. The compound was designed as a competitor of the HIV Tat protein for TAR binding. In addition to its anti-HIV properties, it has demonstrated the ability to inhibit in vitro replication of herpes simplex virus types 1 and 2 as well as human cytomegalovirus. Subsequently, in vivo pharmacokinetic evaluation of ALX40-4C necessitated the establishment of a detection system for the measurement of ALX40-4C in subject serum. For this purpose, an indirect-competition enzyme-linked immunosorbent assay with generated rabbit anti-ALX40-4C antiserum was developed. The original assay took 12 h to complete and required many manipulations. Herein, we describe alterations to the system that resulted in the overall reduction in assay time and manipulation. We demonstrate that our alterations do not affect the specificity or sensitivity of the assay compared to that of the original system. ALX40-4C levels in spiked serum samples as well as drug levels from patient samples were used to validate the assay.

Lack of gender effect on ciprofloxacin pharmacokinetics in humans.

The influence of gender on the single-dose pharmacokinetics of oral ciprofloxacin was investigated in a parallel designed study in 24 healthy, fasted volunteers. Ciprofloxacin (750 mg) was administered as a single tablet to 10 women and 14 men. All subjects were Caucasian except for one African American man. The mean age was 36 years for men and 33 years for women. Women received the drug during the nonmenstruating phase of their menstrual cycle and were not taking oral contraceptives at the time of the study. Plasma samples were collected over a 24 h period and assayed by h.p.l.c. The 90% confidence limits for the ratio of geometric means of maximum plasma concentration, apparent terminal half-life, and apparent oral plasma clearance (corrected for body weight) were between 80% and 125%, and those for the area under the plasma concentration-time curve were 71% and 101%. Results suggest that there were no gender-related differences in ciprofloxacin pharmacokinetics in men and nonmenstruating women of middle age.

Risks and synergies from drug interactions.

AIM: To review what is known from in vitro and in vivo studies about the interactions, both potentially beneficial and potentially harmful, of antiretroviral agents with each other and with other classes of drugs. INTERACTIONS WITH NUCLEOSIDE ANALOGUES: Some interactions between nucleoside HIV reverse transcriptase inhibitors and between nucleoside analogues and HIV protease inhibitors result in greater antiretroviral activity (e.g. zalcitabine with saquinavir). Others may increase the risks of toxicity and there are a number of combinations of nucleoside agents with other drugs that should be used with caution or avoided completely. INTERACTIONS WITH PROTEASE INHIBITORS: These drugs are metabolized by cytochrome P450 CYP3A4 in the liver; because they have the potential to inhibit this enzyme they may interact with many other drugs that are metabolized by this pathway. Ritonavir also inhibits other cytochrome P450 enzymes and so interacts with numerous drugs from a range of classes. Potentially beneficial interactions between protease inhibitors include the increase in saquinavir levels brought about by ritonavir. CONCLUSIONS: Knowledge of additive and synergistic interactions between antiretroviral agents should facilitate development of therapeutic regimens with prolonged antiretroviral activity. Thorough investigation of possibly harmful interactions with co-administered drugs and education of clinicians and patients about the risks of these interactions is required.

Effects of the antacids in didanosine tablets on dapsone pharmacokinetics.

OBJECTIVE: To investigate 1) the effects of the magnesium-aluminum antacids in didanosine tablets on dapsone absorption in healthy volunteers and 2) the effects of the antacid formulation of active didanosine tablets on dapsone pharmacokinetics in patients seropositive for human immunodeficiency virus (HIV). DESIGN: Two separate, randomized, two-period, two-treatment, crossover studies with a 21-day washout period between treatments. SETTING: Clinical investigation unit of a university hospital. PARTICIPANTS: Six healthy men and six HIV-positive men. MEASUREMENTS: Serial dapsone plasma concentrations were measured when dapsone, 100 mg, was administered alone and with either the third of four doses of didanosine placebo tablets (group 1) or the 27th of 28 doses of active didanosine tablets (group 2). In each study, pharmacokinetic variables were determined using noncompartmental methods and compared by analysis of variance. RESULTS: When dapsone was administered alone, pharmacokinetic variables did not significantly differ from those with dapsone given in either combination (P > 0.10 for all comparisons). CONCLUSIONS: Didanosine, antacids, and other excipients in the currently used didanosine chewable tablets did not significantly affect plasma concentrations of dapsone.

Effect of rifabutin on the pharmacokinetics of zidovudine in patients infected with human immunodeficiency virus.

We investigated the effects of rifabutin (300 mg daily administered for 7 or 14 days) on the pharmacokinetics of zidovudine in nine patients who were infected with human immunodeficiency virus (HIV). Serial blood and urine samples were collected over a 6-hour period on each day that the pharmacokinetics of zidovudine were studied. Pharmacokinetic parameters were determined for zidovudine and its glucuronide metabolite and compared with use of analysis of variance (ANOVA) appropriate for a repeated-measures design. Except for a statistically significant decrease (28%) in the terminal half-life of zidovudine from 1.5 to 1.1 hours (P = .005) after coadministration of both agents for 14 days, concurrent administration of rifabutin for 7 or 14 days had no statistically significant effects on zidovudine plasma and urine pharmacokinetic parameters (the difference among treatment means was < 25%). Treatment with rifabutin is unlikely to influence the effectiveness of treating HIV-infected patients with zidovudine because of any pharmacokinetic interaction between these drugs.

Pharmacokinetics of simultaneously administered zidovudine and didanosine in HIV-seropositive male patients.

Our objective was to determine whether a pharmacokinetic interaction exists between zidovudine and didanosine when they are coadministered. This was designed as a randomized, three-period, three-treatment, six-sequence, crossover study with a 1-week washout period between treatments. The patients were six men infected with human immunodeficiency virus who were asymptomatic. On three separate occasions, patients received zidovudine alone (200 mg every 8 h) for 3 days, didanosine alone (200 mg every 12 h) for 3 days, or zidovudine and didanosine for 3 days. On the fourth day, each patient received the final dose of each regimen, and blood and urine were serially collected for 8 h. Pharmacokinetic parameters were assessed for zidovudine, its glucuronide metabolite (GZDV), and didanosine. Coadministration of zidovudine had no significant effect on didanosine pharmacokinetic parameters (< 12% difference between treatment means, p > 0.1). Coadministration of didanosine did not significantly alter zidovudine pharmacokinetic parameters but did cause statistically significant increases in the renal and apparent formation clearances of GZDV (18.5% and 30.5% difference between the treatment means, respectively, p < 0.025). Therapeutic doses of zidovudine did not alter didanosine pharmacokinetic parameters. Coadministration of didanosine did not affect zidovudine parameters but did cause small alterations in GZDV pharmacokinetic values. These changes are unlikely to be clinically significant.

A phase I evaluation of concomitant rifabutin and didanosine in symptomatic HIV-infected patients.

It has been suggested that didanosine (ddI) may undergo hepatic metabolism. Rifabutin is an inducer of drug metabolism. Fifteen human immunodeficiency virus-infected patients whose conditions were stabilized on twice-daily doses of ddI participated in a Phase I, open-label, pharmacokinetic and safety drug interaction study between rifabutin and ddI. Twelve patients completed the study. All patients received their regular ddI dose (167-375 mg) on day 1. On days 2-13 they received once-daily rifabutin (600 mg, three patients; 300 mg, nine patients) with their regular twice-daily ddI regimen. On days 14-16 they received rifabutin alone. Serial blood and urine samples were collected for 12 h on day 1 and for 24 h on days 13 and 16, and safety evaluations were made throughout the study. Average day 1/day 13 ddI pharmacokinetic ratios and 95% confidence interval values for Cmax, AUC0-infinity, Cls/F, and t 1/2, lambda z were 1.17 (0.96-1.38), 1.13 (0.99-1.27), 0.91 (0.81-1.01), and 0.97 (0.79-1.15), respectively (p > 0.05 for all comparisons; paired t test). A 20% difference in AUC0-infinity could be detected with 90% power. Also, there were no significant changes in laboratory values or electrocardiograms, or in rifabutin pharmacokinetic parameters when the two agents were coadministered. Based on the safety and pharmacokinetic assessments, rifabutin did not appear to interact with ddI.

Effect of bismuth subsalicylate on ciprofloxacin bioavailability.

A single oral dose of 528 mg of bismuth subsalicylate (30 ml of Pepto-Bismol) had no significant effect on the plasma pharmacokinetics of a single oral dose of 750 mg of ciprofloxacin administered to 12 healthy volunteers (six men and six women). These results suggest that ciprofloxacin bioavailability will not be significantly decreased by single doses of bismuth subsalicylate when the two medications are administered simultaneously.

Relationship between body weight, body surface area and serum zidovudine pharmacokinetic parameters in adult, male HIV-infected patients.

OBJECTIVE: To determine whether there is a simple relationship between body weight or body surface area (BSA) and serum zidovudine pharmacokinetic parameters in patients receiving oral zidovudine. DESIGN: Single-dose, pharmacokinetic study. PATIENTS: Fifty-three asymptomatic and symptomatic HIV-infected men (CD4+ cell count < 500 x 10(6)/l) participated in the study. Results of renal function and haematology tests were within normal limits and all hepatic function tests were up to three times the upper limit of normal. Patients received 200 mg oral zidovudine and serial blood samples were collected for 4 h (18 patients) or 8 h (35 patients). Serum zidovudine concentrations were measured by high-performance liquid chromatography (12 patients) or radioimmunoassay (41 patients). Pharmacokinetic parameters were calculated by non-compartmental methods. The relationships between body weight or BSA and maximum serum concentration (Cmax), area under the concentration-time curve (AUC), apparent serum clearance (CL/F), and apparent terminal volume of distribution (Vz/F) were determined by simple least-squares linear regression. RESULTS: There were no significant relationships between either body weight or BSA and Cmax, AUC, Vz/F (corrected for weight), and clearance (P > 0.07; R2 < 0.06 for all comparisons). A significant positive association between Vz/F, uncorrected for weight, and either weight (P = 0.011; R2 = 0.121) or BSA (P = 0.022; R2 = 0.098) was observed. The interindividual coefficients of variation of CL/F and Vz/F values were only marginally reduced when the parameters were corrected for weight (31.3 versus 30.8% and 28.0 versus 26.0% respectively). CONCLUSIONS: There is little or no linear association between either body weight or BSA and observed serum zidovudine concentrations following administration of 200 mg zidovudine in adult male patients who are within 20% of their ideal weight.

Effect of fluconazole on zidovudine pharmacokinetics in patients infected with human immunodeficiency virus.

The effect of a therapeutic dose of fluconazole on the disposition of zidovudine was evaluated in 12 men infected with human immunodeficiency virus. The study was designed as a randomized, two-period, two-treatment, crossover trial. On two occasions, 21 days apart, patients received either zidovudine alone or zidovudine (each, 200 mg every 8 h) and fluconazole (400 mg daily) for 7 days. Fluconazole coadministration decreased (P < .001) the apparent oral serum clearance of zidovudine by 43% and the apparent oral formation clearance to zidovudine glucuronide (GZDV) by 48%, resulting in increases (P < .002) in the area under the serum concentration time curve (74%), the maximum serum concentration (84%), and the terminal half-life (128%) of zidovudine. The molar ratio of GZDV to zidovudine recovered in urine was reduced by 34% with fluconazole (P < .001). These pharmacokinetic changes suggest that 400 mg of fluconazole inhibited the conversion of zidovudine to GZDV. Patients receiving this combination should be monitored for the development of zidovudine-related adverse reactions.

Effect of antacids in didanosine tablet on bioavailability of isoniazid.

The antacids in two didanosine placebo tablets had no significant effect on the plasma pharmacokinetics of a single oral dose of 300 mg of isoniazid administered to 12 healthy volunteers. These results suggest that isoniazid bioavailability will be unaffected by the antacids in didanosine tablets when the two medications are administered simultaneously to human immunodeficiency virus-seropositive patients.

Pharmacokinetics of zidovudine after the initial single dose and during chronic-dose therapy in HIV-infected patients.

The pharmacokinetics of zidovudine in 10 symptomatic HIV-infected men were assessed after administration of the initial 200 mg oral dose at the start of therapy (day 1) and on one occasion during non steady-state conditions of chronic-dose therapy (200 mg every 4 h while awake on day 21-66; 5 doses per day). The following mean (+/- s.d.) pharmacokinetic parameters were determined on day 1 and during chronic therapy, respectively: Cmax (4.09 +/- 2.54 vs 3.82 +/- 1.03 mumol l-1), oral clearance (40.7 +/- 12.9 vs 41.1 +/- 8.4 ml min-1 kg-1) and terminal half-life (68.4 +/- 29.4 vs 65.1 +/- 13.1 min). Mean pharmacokinetic parameters on day 1 were < 10% different (P > 0.34) from those determined during chronic therapy. Differences in means of 21% for clearance and 36% for Cmax could be detected with a power of 80% at the 5% significance level. Intra-subject coefficients of variation were 17% for clearance and 32% for Cmax, respectively. This study suggests that within a group of patients whose stage of HIV infection and general health are relatively stable, first-dose pharmacokinetic parameters provide a good estimate of multiple-dose pharmacokinetic parameters.

Overview of the immune and hematopoietic systems.

Current knowledge of the immune and hematopoietic systems is reviewed. All blood cells are derived from the totipotent stem cell, also known as the pluripotent stem cell. The differentiation of pluripotent peripheral stem cells into blood cells is controlled by a variety of biologic response modifiers, including colony-stimulating factors (CSFs) and interleukins. Among the known CSFs are stem cell growth factor, granulocyte-macrophage CSF, multilineage CSF (interleukin-3), granulocyte CSF, macrophage CSF, and erythropoietin. CSFs are categorized as class I (those that stimulate the production of several types of blood cells; also called pluripotent) and class II (those that stimulate only one cell line; also called unipotent). Effects of CSFs can be studied using laboratory tests of colony-forming-unit activity. Pathogens entering the body through damaged skin or mucous membranes are met with both a cellular response (neutrophils, macrophages, cytotoxic T lymphocytes, and natural killer cells) and a humoral response (antibodies and complement). There is interplay between these two arms of the immune system to defend against foreign antigens. This interplay can occur by cell-to-cell contact and by cytokines. Hematopoietic and immune cells of the body are produced and destroyed under precise control of many different biologic response modifiers, including the colony-stimulating factors, interleukins, and interferons.

Cations in the didanosine tablet reduce ciprofloxacin bioavailability.

The effect of the magnesium-aluminum cations contained in didanosine chewable tablets on ciprofloxacin pharmacokinetics was evaluated in 12 healthy volunteers. The study was designed as a randomized, balanced, open, two-period, two-treatment crossover trial with a 7-day washout period between treatments. In one phase, subjects received a single 750 mg ciprofloxacin tablet alone. In the didanosinecation regimen, subjects received two didanosine-placebo tablets every 12 hours for two doses. On day 2, they received two didanosine-placebo tablets immediately followed by a single 750 mg ciprofloxacin tablet. Serial blood samples were collected for 24 hours after administration of each ciprofloxacin dose. The average maximum concentration of ciprofloxacin alone was 3.38 +/- 0.63 (SD) micrograms/ml compared with 0.25 +/- 0.21 (SD) micrograms/ml when ciprofloxacin was administered with the didanosine placebo (p < 0.0001). The mean (+/- SD) area under the plasma drug concentration-time curve from time 0 to the last measurable concentration for ciprofloxacin alone was 15.50 +/- 2.69 micrograms.hr/ml compared with 0.26 +/- 0.21 micrograms.hr/ml when ciprofloxacin was coadministered with the didanosine-placebo (p < 0.0001). The mean time to maximum concentration of ciprofloxacin alone decreased from 1.56 +/- 0.62 to 0.75 +/- 0.38 hours with buffer administration (p = 0.0012). The simultaneous administration of ciprofloxacin and didanosine should be avoided.