Pharmacological interactions between rifampicin and antiretroviral drugs: challenges and research priorities for resource-limited settings.

Coadministration of antituberculosis and antiretroviral therapy is often inevitable in high-burden countries where tuberculosis (TB) is the most common opportunistic infection associated with HIV/AIDS. Concurrent use of rifampicin and many antiretroviral drugs is complicated by pharmacokinetic drug-drug interactions. Rifampicin is a very potent enzyme inducer, which can result in subtherapeutic antiretroviral drug concentrations. In addition, TB drugs and antiretroviral drugs have additive (pharmacodynamic) interactions as reflected in overlapping adverse effect profiles. This review provides an overview of the pharmacological interactions between rifampicin-based TB treatment and antiretroviral drugs in adults living in resource-limited settings. Major progress has been made to evaluate the interactions between TB drugs and antiretroviral therapy; however, burning questions remain concerning nevirapine and efavirenz effectiveness during rifampicin-based TB treatment, treatment options for TB-HIV-coinfected patients with nonnucleoside reverse transcriptase inhibitor resistance or intolerance, and exact treatment or dosing schedules for vulnerable patients including children and pregnant women. The current research priorities can be addressed by maximizing the use of already existing data, creating new data by conducting clinical trials and prospective observational studies and to engage a lobby to make currently unavailable drugs available to those most in need.

Reduction of nevirapine-driven HIV mutations by carbamazepine is modulated by CYP3A activity.

OBJECTIVES: The reduction in mother-to-child transmission of HIV-1 by single-dose nevirapine given at birth onset is achieved at the expense of de novo HIV-1 resistance mutations. In the VITA1 study, single-dose carbamazepine accelerated nevirapine elimination, but the accompanying trend towards fewer de novo HIV-1 mutations was statistically non-significant. METHODS: We investigated if the effect of carbamazepine was confounded by the individual variability in nevirapine metabolism and transport. RESULTS: Nine of 34 (26%) single-dose nevirapine-treated women had one or more nevirapine-associated resistance mutations, compared with 3 of 34 (9%) in the single-dose nevirapine/carbamazepine arm. The genetic polymorphisms in CYP2B6 and MRP7 affected neither nevirapine kinetics nor the development of HIV-1 resistance. In contrast, the reduction in HIV-1 mutations by single-dose carbamazepine reached statistical significance at P = 0.04 with an OR of 0.1 (95% CI 0.01-0.90) upon consideration of CYP3A activity, defined as the ratio of 4ß-hydroxycholesterol to cholesterol, and it was more likely in women with higher CYP3A activity. These findings were in agreement with CYP3A induction in carbamazepine-treated patients. Likewise, carbamazepine induced CYP3A4, but not CYP2B6, in vitro when combined with nevirapine. CONCLUSIONS: The induction of nevirapine elimination reduces HIV-1 resistance mutations, but this effect is modulated by individual CYP3A activity. The study suggests that CYP3A4 activity could be monitored using an endogenous marker and, if needed, boosted to improve clinical endpoints.

Nevirapine concentrations in saliva measured by thin layer chromatography and self-reported adherence in patients on antiretroviral therapy at Kilimanjaro Christian Medical Centre, Tanzania.

BACKGROUND: Thin layer chromatography (TLC) can be used to perform therapeutic drug monitoring in resource-limited settings, where more expensive analytical methods, such as high-performance liquid chromatography or liquid chromatography-mass spectrometry, are not feasible. OBJECTIVES: The aim of this cross-sectional study was to compare saliva concentrations of nevirapine (NVP) with self-reported adherence in patients on NVP-containing antiretroviral treatment at Kilimanjaro Christian Medical Centre, Moshi, Tanzania. METHODS: HIV-infected patients using a combination of zidovudine + lamivudine + NVP, or stavudine + lamivudine + NVP, for more than 4 weeks were included. Saliva samples were collected using dental cotton rolls impregnated with citric acid (20 mg). Saliva NVP concentrations were analyzed using TLC. Adherence to ARV medication was assessed by self-reporting using the Morisky scale. RESULTS: Of the 91 study participants, 79 (86.8%) had therapeutic saliva NVP concentrations (ie, >1.75 mg/L) and 12 (13.2%) had subtherapeutic concentrations. Self-reported adherence among the study participants was high in 62 participants (68.1%), moderate in 24 (26.4%), and low in 5 (5.5%). Fifty-seven (91.9%) of the study participants with high self-reported adherence had therapeutic saliva NVP concentrations. Of the 5 participants with low self-reported adherence, 3 had therapeutic NVP concentrations. CONCLUSIONS: A high proportion of patients had therapeutic NVP saliva concentrations as measured by TLC, which showed a good agreement with self-reported adherence.

Effect of 7 days of phenytoin on the pharmacokinetics of and the development of resistance to single-dose nevirapine for perinatal HIV prevention: a randomized pilot trial.

OBJECTIVES: To confirm whether 7 days of phenytoin, an enzyme inducer, would decrease the elimination half-life of single-dose nevirapine and to investigate its effect on the development of nevirapine resistance in pregnant, HIV-infected women. METHODS: In a pharmacokinetic pilot trial (NCT01187719), HIV-infected, antiretroviral (ARV)-naive pregnant women ≥18 years old from Zambia and Tanzania and with CD4 cell counts >350 cells/mm(3) were randomized 1 : 1 to a control (zidovudine pre-delivery, single-dose nevirapine/zidovudine/lamivudine at delivery and zidovudine/lamivudine for 7 days post-delivery) or an intervention (control plus 184 mg of phenytoin once daily for 7 days post-delivery) group. Primary endpoints were the pharmacokinetics of and resistance to nevirapine. RESULTS: Thirty-five and 37 women were allocated to the control and intervention groups, with median (IQR) ages of 27 (23-31) and 27 (23-33) years, respectively. Twenty-three and 23 women had detectable nevirapine levels at delivery and subsequent samples in the control and the intervention groups, respectively. Geometric mean (GM) (95% CI) plasma levels of nevirapine at delivery were 1.02 (0.58-1.78) mg/L and 1.14 (0.70-1.86) mg/L in the control and intervention groups, respectively (P = 0.76). One week after delivery, 0/23 (0%) and 15/22 (68%) control and intervention mothers, respectively, had undetectable levels of nevirapine (<0.05 mg/L; P<0.001). One week later, the figures were 10/21 (48%) and 18/19 (95%) mothers, respectively (P = 0.002). The GM (95% CI) half-life of nevirapine was 63.2 (52.8-75.7) versus 25.5 (21.6-30.1) h in the control group versus the intervention group (P < 0.001). New nevirapine mutations were found in 0/20 (0%) intervention-group mothers versus 1/21 (5%) control-group mothers. Overall, there was no difference in adverse events reported between the control and intervention arms (P > 0.28). CONCLUSIONS: Adding 7 days of an enzyme inducer to single-dose nevirapine to prevent mother-to-child transmission of HIV significantly reduced subtherapeutic nevirapine levels by shortening the half-life of nevirapine. As prolonged subtherapeutic nevirapine dosage leads to the emergence of resistance, single-dose nevirapine could be used with phenytoin as an alternative if other ARVs were unavailable.

Induction of hepatic drug-metabolising enzymes and tamoxifen metabolite profile in relation to administration route during low-dose treatment in nude rats.

Tamoxifen is the most used anticancer drug and is approved for chemoprevention. Little is known about the enzyme inducing properties of low-dose regimens and the influence of route of administration. In this study, nude rats received 5 mg/kg/day of tamoxifen orally or a 50 mg continuous-release pellet subcutaneously. The mRNAs for cytochrome P450-enzymes (CYPs), flavin-containing monooxygenase 1 (FMO1) and phase II drug-metabolising enzymes were quantified by real-time RT-PCR. Tamoxifen and metabolite concentrations were measured using HPLC. We observed a significant increase in CYP3A18 and FMO1 mRNA expression levels in the orally treated animals, whereas the increase in CYP3A2 expression did not reach statistical significance (p=0.057). No significant induction of enzyme expression was observed in rats that received subcutaneous (S.c.) treatment. After 33 days the serum levels of 4-hydroxytamoxifen (4OHtam), tamoxifen and N-desmethyltamoxifen (NDtam) in orally treated animals were 1.8+/-0.7, 11.1+/-3.2 and 11.4+/-3.8 ng/ml, respectively. In subcutaneously treated animals, tamoxifen and N-desmethyltamoxifen were detected in tissues, but not in serum. These data demonstrate that in contrast to the subcutaneous administration, low-dose oral tamoxifen induced tamoxifen-metabolising enzymes. Furthermore, the different routes of administration resulted in different serum and tissue levels of tamoxifen and metabolites.

Excretion of hydroxylated metabolites of tamoxifen in human bile and urine.

The selective oestrogen-receptor modulator tamoxifen is the most commonly used drug against breast cancer. It has potent metabolites, such as 4-hydroxytamoxifen. Recently, the metabolite 4-hydroxy-N-desmethyltamoxifen has received increased attention as it may be a major contributor to the overall effects of tamoxifen. The excretion of tamoxifen and its metabolites was examined in a patient with biliary drainage after an oral dose of [14C]tamoxifen. During the first 10 days after oral dosing, 11.5, 26.7 and 24.7% of the radioactivity was excreted in the bile, urine and faeces, respectively. After deconjugation with beta-glucuronidase, the concentrations of tamoxifen and 4 of its metabolites were measured, and it was observed that the hydroxylated metabolites were excreted in the bile and urine. 4-Hydroxytamoxifen was the dominant compound, being detected during the first day of observation, whereas 4-hydroxy-N-desmethyltamoxifen was first observed in the urine and bile after 4 days. This is the first report on tamoxifen excretion in human bile and urine demonstrating that 4-hydroxytamoxifen may be a first-pass metabolite. In contrast, the potent metabolite 4-hydroxy-N-desmethyltamoxifen was first detected 4 days after administration of a single oral dose.

Tamoxifen and metabolite concentrations in serum and breast cancer tissue during three dose regimens in a randomized preoperative trial.

PURPOSE: Both therapeutic and adverse effects of tamoxifen may be related to its tissue concentrations. We investigated concentrations of tamoxifen, 4-hydroxytamoxifen, N-desmethyltamoxifen, and N-didesmethyltamoxifen in serum, normal breast, and breast cancer tissues during conventional dosage and two low-dose regimens. Furthermore we studied tamoxifen effects on the cancer proliferation marker Ki-67, and on sex hormone-binding globulin (SHBG). EXPERIMENTAL DESIGN: From September 1999 to August 2001, 120 breast cancer patients were randomized to 20-, 5-, or 1-mg tamoxifen daily. We measured serum and tissue concentrations of tamoxifen and three metabolites after 28 days of treatment, and the changes between baseline and post-treatment levels of SHBG and Ki-67. RESULTS: The median (range) tamoxifen concentrations (ng/ml) at doses of 1, 5, and 20 mg daily (n = 38, 37, and 36) were 7.5 (2.9-120.9), 25.2 (1.9-180.9), and 83.6 (8.7-134.4) in serum, and 78.2 (35.9-184), 272.3 (122-641), and 744.4 (208.6-2556) in breast cancer tissue, respectively. Tamoxifen levels followed a dose-concentration relationship. The concentrations of tamoxifen and metabolites were related to each other. Serum and tissue concentrations of tamoxifen were associated with corresponding changes of SHBG levels, whereas changes of Ki-67 levels were not related. CONCLUSIONS: Estrogen agonistic effects of tamoxifen on SHBG decreased with lower dosage, whereas tamoxifen effects on Ki-67 expression did not change. This together with a >10-fold variation in serum tamoxifen concentrations and a serum to tissue concentration relationship suggest that tamoxifen treatment may be improved by administration of lower doses and therapeutic drug monitoring.

Efavirenz, tenofovir and emtricitabine combined with first-line tuberculosis treatment in tuberculosis-HIV-coinfected Tanzanian patients: a pharmacokinetic and safety study.

BACKGROUND: To evaluate the effect of rifampicin-based tuberculosis (TB) treatment on the pharmacokinetics of efavirenz/tenofovir/emtricitabine in a fixed-dose combination tablet, and vice versa, in Tanzanian TB-HIV-coinfected patients. METHODS: This was a Phase II open-label multiple dose pharmacokinetic and safety study. This study was conducted in TB-HIV-coinfected Tanzanian patients who started TB treatment (rifampicin/isoniazid/pyrazinamide/ethambutol) at week 1 to week 8 and continued with rifampicin and isoniazid for another 16 weeks. Antiretroviral treatment (ART) of efavirenz/tenofovir/emtricitabine in a fixed-dose combination tablet was started at week 4 after initiation of TB treatment. A 24-h pharmacokinetic sampling curve was recorded at week 8 (with TB treatment) and week 28 (ART alone). For TB drugs, blood samples at 2 and 5 h post-dose were taken at week 3 (TB treatment alone) and week 8 (with ART). RESULTS: A total of 25 patients (56% male) completed the study; 21 had evaluable pharmacokinetic profiles. The area under the concentration-time curve 0-24 h post-dose of efavirenz, tenofovir and emtricitabine were slightly higher when these drugs were coadministered with TB drugs; geometric mean ratios (90% CI) were 1.08 (0.90, 1.30), 1.13 (0.93, 1.38) and 1.05 (0.85, 1.29), respectively. For TB drugs, equivalence was suggested for peak plasma concentrations when administered with and without efavirenz/tenofovir/emtricitabine. Adverse events were mostly mild and no serious adverse events or drug discontinuations were reported. CONCLUSIONS: Coadministration of efavirenz, tenofovir and emtricitabine with a standard first-line TB treatment regimen did not significantly alter the pharmacokinetic parameters of these drugs and was tolerated well by Tanzanian TB patients who are coinfected with HIV.

Antibiotic prescribing practice in management of cough and/or diarrhoea in Moshi Municipality, Northern Tanzania: cross-sectional descriptive study.

INTRODUCTION: The increase in resistance of many pathogens to currently available antibiotics has been recognized as life-threatening problem. The development of drug resistance is promoted by irrational prescribing behavior. Inappropriate use of antibiotics is attributed by over-prescription, inadequate dosage and use for non-bacterial infections. The purpose of this study was to assess antibiotic prescribing practices in the management of diarrhoea and cough among children attending hospitals in Moshi municipal, Tanzania. METHODS: We conducted a cross-sectional descriptive hospital based study, from September 2010 to March 2011. All children presenting with diarrhoea and cough, aged between one month and 5 years attended at the two hospitals were enrolled. Data were collected by a standard questionnaire. Information on the prescribed drugs was obtained from patient files. RESULTS: A total of 384 children were enrolled. Of these, 326 (84.9%) received antibiotics; common prescribed antibiotics were penicillins, sulphonamides, aminoglycosides and macrolides. Eighty percent of children with acute watery diarrhoea and 68.9% with common cold were given antibiotics inappropriately. Inappropriate antibiotic prescription was significantly associated with prescriber being a clinical officer and assistant medical officer, and child having diarrhoea. Inappropriate antibiotic dosage was significantly occurred when prescriber was clinical officer with reference to medical officer. CONCLUSION: This study observed a high antibiotic prescription rate by clinicians and treatment guidelines for management of patients who presented with cough and/or diarrhoea are followed. Continuing professional development programmes for clinicians on prescription would help in reducing irrational prescribing practices.

Intrapartum single-dose carbamazepine reduces nevirapine levels faster and may decrease resistance after a single dose of nevirapine for perinatal HIV prevention.

BACKGROUND: World Health Organization guidelines recommend zidovudine + lamivudine for 7 days from labor onset in HIV-infected women receiving single-dose nevirapine (sdNVP) to cover prolonged subtherapeutic nevirapine concentrations. Although effective, this is complicated and does not eliminate resistance; alternative strategies could add benefit. METHODS: Antiretroviral-naive HIV-infected pregnant women aged 18-40 years, with CD4 >200 cells per cubic millimeter, able to regularly attend the antenatal clinics in Moshi, Tanzania, were enrolled 1:1 by alternate allocation to receive 200 mg sdNVP alone or in combination with open-label 400-mg single-dose carbamazepine (sdNVP/CBZ) at delivery (ClinicalTrials.gov NCT00294892). The coprimary outcomes were nevirapine plasma concentrations 1 week and nevirapine resistance mutations 6 weeks postpartum. Analyses were based on those still eligible at delivery. RESULTS: Ninety-seven women were assigned to sdNVP and 95 to sdNVP/CBZ during pregnancy, of whom 75 sdNVP and 83 sdNVP/CBZ were still eligible at delivery at study sites. The median (interquartile range) nevirapine plasma concentration was 1.55 (0.88-1.84) mg/L in sdNVP (n = 61) and 1.40 (0.93-1.97) mg/L in sdNVP/CBZ (n = 72) at delivery (P = 0.91), but 1 week later was significantly lower in sdNVP/CBZ [n = 63; 0.09 (0.05-0.20) mg/L] than in sdNVP [n = 52; 0.20 (0.09-0.31) mg/L; rank-sum: P = 0.004] (geometric mean ratio: 0.64, 95% confidence interval: 0.43 to 0.96; P = 0.03). Six weeks postpartum, nevirapine mutations were observed in 11 of 52 (21%) in sdNVP and 6 of 55 (11%) in sdNVP/CBZ (odds ratio = 0.46, 95% confidence interval: 0.16 to 1.34; P = 0.15). CONCLUSIONS: Addition of single-dose carbamazepine to sdNVP at labor onset in HIV-infected, pregnant women did not affect nevirapine plasma concentration at delivery, but significantly reduced it 1 week postpartum, with a trend toward fewer nevirapine resistance mutations.

Effect of HMG-CoA reductase inhibitors on proliferation and protein synthesis by rat hepatic stellate cells.

BACKGROUND/AIMS: 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors called statins, have besides their cholesterol-lowering function, therapeutic value in conditions such as neo-angiogenesis and atherosclerosis. We investigated the effect of two statins on the proliferation rate and protein steady state levels of hepatic stellate cells (HSC). METHODS: Cellular DNA synthesis under the influence of statins and/or platelet derived growth factor (PDGF) and mevalonate was evaluated by measuring BrdU incorporation. Synthesis of collagens type I, III, IV and fibronectin was quantified by ELISA. Additionally, we examined the influence of simvastatin on isoprenylation of Ras and RhoA proteins. RESULTS: Lovastatin and simvastatin induced a dose-dependent inhibition of the proliferation rate of HSC. Subsequent addition of PDGF and/or mevalonate, after long-term exposure of simvastatin to HSC, did not reverse simvastatins' antiproliferative effect. Lovastatin and simvastatin reduced the protein steady state level of collagens type I (-40%), III (-45%) and IV (-27%). Membrane bound Ras steady state levels decreased under the influence of simvastatin. Membrane bound RhoA remained unaltered, whereas, cytosolic RhoA protein level was strongly reduced. CONCLUSIONS: Our data showed that lovastatin and simvastatin inhibited HSC proliferation and collagen steady state levels by mechanisms independent of their lipid reducing activities.

A randomized trial of low-dose tamoxifen on breast cancer proliferation and blood estrogenic biomarkers.

BACKGROUND: Tamoxifen reduces the risk of breast cancer in women at high risk for the disease but increases the risk for endometrial tumors and venous thromboembolisms, possibly in a dose-dependent fashion. We compared the effects of tamoxifen at 1 mg/day and 5 mg/day with those of the standard dose of 20 mg/day on breast cancer proliferation using a surrogate endpoint marker (Ki-67 expression) and blood biomarkers associated with breast cancer, cardiovascular disease, and bone fracture risk. METHODS: We randomly assigned 120 women with estrogen receptor (ER)-positive breast cancer to tamoxifen at 1, 5, or 20 mg/day for 4 weeks. Expression of the tumor proliferation marker Ki-67 and of biomarkers of breast cancer (insulin-like growth factor-I, sex hormone-binding globulin), cardiovascular disease (cholesterol, triglycerides, ultrasensitive C-reactive protein, fibrinogen, antithrombin-III), and bone fracture (type I collagen C-telopeptide) risk were determined before (baseline) and after treatment. All levels were compared with those in two nonrandomized control groups (34 women with ER-negative breast cancer and 29 additional women with ER-positive breast cancer). Data were analyzed by analysis of covariance. All statistical tests were two-sided. RESULTS: Expression of Ki-67 decreased in all three tamoxifen groups, with no difference in the magnitude of reduction among groups (P =.81). Relative to baseline, Ki-67 expression decreased by a median of 15.0% (95% confidence interval = 0.0% to 24.1%) among the tamoxifen groups but increased by 12.8% (95% confidence interval = 0.0% to 19.6%) among the nonrandomized control groups. Several blood biomarkers showed dose-response relationships with tamoxifen, including decreased insulin-like growth factor-I, increased sex hormone-binding globulin, and decreased low-density lipoprotein-cholesterol, ultrasensitive C-reactive protein, fibrinogen, and antithrombin-III levels. CONCLUSIONS: The effects on Ki-67 expression of lower doses of tamoxifen were comparable to those achieved with the standard dose, although the effects on blood biomarkers were variable. The effects of lower doses of tamoxifen should be assessed further in randomized trials.