Dose Fractionation of Moxifloxacin for Treatment of Tuberculosis: Impact of Dosing Interval and Elimination Half-Life on Microbial Kill and Resistance Suppression.

The repurposed agent moxifloxacin has become an important addition to the physician's armamentarium for the therapy of Mycobacterium tuberculosis When a drug is administered, we need to have metrics for success. As for most antimicrobial chemotherapy, we contend that for Mycobacterium tuberculosis therapy, these metrics should be a decline in the susceptible bacterial burden and the suppression of amplification of less-susceptible populations. To achieve optimal outcomes relative to these metrics, a dose and schedule of administration need to be chosen. For large populations of patients, there are true between-patient differences in important pharmacokinetic parameters. These distributions of parameter values may have an impact on these metrics, depending on what measure of drug exposure drives the metrics. To optimize dose and schedule choice of moxifloxacin, we performed a dose fractionation experiment in the hollow fiber infection model. We examined 12-, 24-, and 48-h dosing intervals with doses of 200, 400, and 800 mg for each interval, respectively. Within each interval, we had an arm where half-lives of 12, 8, and 4 h were simulated. We attempted to keep the average concentration (Cavg) or area under the concentration-time curve (AUC) constant across arms. We found that susceptible bacterial load decline was linked to Cavg, as we had indicated previously. Resistance suppression, a nonmonotonic function, had minimum concentration (Cmin) as the linked index. The 48-h interval with the 4-h half-life had the largest less-susceptible population. Balancing bacterial kill, resistance suppression, toxicity (linked to peak concentration [Cpeak]), and adherence, we conclude that the dose of 400 mg daily is optimal for moxifloxacin.

The Funnel: a Screening Technique for Identifying Optimal Two-Drug Combination Chemotherapy Regimens.

The Mycobacterium tuberculosis drug discovery effort has generated a substantial number of new/repurposed drugs for therapy for this pathogen. The arrival of these drugs is welcome, but another layer of difficulty has emerged. Single agent therapy is insufficient for patients with late-stage tuberculosis because of resistance emergence. To achieve our therapeutic ends, it is requisite to identify optimal combination regimens. These regimens go through a lengthy and expensive evaluative process. If we have a modest group of 6 to 8 new or repurposed agents, this translates into 15 to 28 possible 2-drug combinations. There is neither time nor resources to give an extensive evaluation for all combinations. We sought a screening procedure that would identify combinations that had a high likelihood of achieving good bacterial burden decline. We examined pretomanid, moxifloxacin, linezolid, and bedaquiline in log-phase growth, acid-phase growth, and nonreplicative persister (NRP) phase in the Greco interaction model. We employed the interaction term α and the calculated bacterial burden decline as metrics to rank different regimens in different metabolic states. No relationship was found between α and bacterial kill. We chose bacterial kill as the prime metric. The combination of pretomanid plus moxifloxacin emerged as the clear frontrunner, as the largest bacterial declines were seen in log phase and acid phase with this regimen and it was second best in NRP phase. Bedaquiline also produced good kill. This screening process may identify optimal combinations that can be further evaluated in both the hollow-fiber infection model and in animal models of Mycobacterium tuberculosis infection.

Clinical Outcomes Among Patients With Drug-resistant Tuberculosis Receiving Bedaquiline- or Delamanid-Containing Regimens.

BACKGROUND: Bedaquiline and delamanid are newly available drugs for treating multidrug-resistant tuberculosis (MDR-TB); however, there are limited data guiding their use and no comparison studies. METHODS: We conducted a prospective, observational study among patients with MDR-TB in Georgia who were receiving a bedaquiline- or delamanid-based treatment regimen. Monthly sputum cultures, minimal inhibitory concentration testing, and adverse event monitoring were performed. Primary outcomes were culture conversion rates and clinical outcomes. Targeted maximum likelihood estimation and super learning were utilized to produce a covariate-adjusted proportion of outcomes for each regimen. RESULTS: Among 156 patients with MDR-TB, 100 were enrolled and 95 were receiving a bedaquiline-based (n = 64) or delamanid-based (n = 31) regimen. Most were male (82%) and the median age was 38 years. Rates of previous treatment (56%) and cavitary disease (61%) were high. The most common companion drugs included linezolid, clofazimine, cycloserine, and a fluoroquinolone. The median numbers of effective drugs received among patients on bedaquiline-based (4; interquartile range [IQR], 4-4) and delamanid-based (4; IQR, 3.5-5) regimens were similar. Rates of acquired drug resistance were significantly higher among patients receiving delamanid versus bedaquiline (36% vs 10%, respectively; P < .01). Adjusted rates of sputum culture conversion at 2 months (67% vs 47%, respectively; P = .10) and 6 months (95% vs 74%, respectively; P < .01), as well as more favorable clinical outcomes (96% vs 72%, respectively; P < .01), were higher among patients receiving bedaquiline versus delamanid. CONCLUSIONS: Among patients with MDR-TB, bedaquiline-based regimens were associated with higher rates of sputum culture conversion, more favorable outcomes, and a lower rate of acquired drug resistance versus delamanid-based regimens.

Developing New Drugs for Mycobacterium tuberculosis Therapy: What Information Do We Get from Preclinical Animal Models?

Preclinical animal models of infection are employed to develop new agents but also to screen among molecules to rank them. There are often major differences between human pharmacokinetic (PK) profiles and those developed by animal models of infection, and these may lead to substantial differences in efficacy relative to that seen in humans. Linezolid is a repurposed agent employed to great effect for therapy of Mycobacterium tuberculosis In this study, we used the hollow-fiber infection model (HFIM) to evaluate the impact of different pharmacokinetic profiles of mice and nonhuman primates (NHP) versus humans on bacterial cell kill as well as resistance suppression. We examined both plasma and epithelial lining fluid (ELF) profiles. We examined simulated exposures equivalent to 600 mg and 900 mg daily of linezolid in humans. For both plasma and ELF exposures, the murine PK profile provided estimates of effect that were biased low relative to human and NHP PK profiles. Mathematical modeling identified a linkage between minimum concentrations (Cmin) and bacterial kill and peak concentrations (Cpeak) and resistance suppression, with the latter being supported by a prospective validation study. Finding new agents with novel mechanisms of action against M. tuberculosis is difficult. It would be a tragedy to discard a new agent because of a biased estimate of effect in a preclinical animal system. The HFIM provides a system to benchmark evaluation of new compounds in preclinical animal model systems against human PK effects (species scale-up estimates of PK), to safeguard against unwarranted rejection of promising new agents.

Perspectives for personalized therapy for patients with multidrug-resistant tuberculosis.

According to the World Health Organization (WHO), tuberculosis is the leading cause of death attributed to a single microbial pathogen worldwide. In addition to the large number of patients affected by tuberculosis, the emergence of Mycobacterium tuberculosis drug-resistance is complicating tuberculosis control in many high-burden countries. During the past 5 years, the global number of patients identified with multidrug-resistant tuberculosis (MDR-TB), defined as bacillary resistance at least against rifampicin and isoniazid, the two most active drugs in a treatment regimen, has increased by more than 20% annually. Today we experience a historical peak in the number of patients affected by MDR-TB. The management of MDR-TB is characterized by delayed diagnosis, uncertainty of the extent of bacillary drug-resistance, imprecise standardized drug regimens and dosages, very long duration of therapy and high frequency of adverse events which all translate into a poor prognosis for many of the affected patients. Major scientific and technological advances in recent years provide new perspectives through treatment regimens tailor-made to individual needs. Where available, such personalized treatment has major implications on the treatment outcomes of patients with MDR-TB. The challenge now is to bring these adances to those patients that need them most.

Pharmacokinetic Evidence from the HIRIF Trial To Support Increased Doses of Rifampin for Tuberculosis.

Rifamycins exhibit concentration-dependent killing of Mycobacterium tuberculosis; higher exposures potentially induce better outcomes. We randomized 180 tuberculosis patients in Peru to receive rifampin at 10, 15, or 20 mg/kg/day. A total of 168 had noncompartmental pharmacokinetic analyses; 67% were sampled twice, and 33% were sampled six times. The doses administered were well tolerated. The median area under the concentration-time curve from 0 to 6 h (interquartile range) was 24.9 (17.6 to 32.1), 43.1 (30.3 to 57.5), or 55.5 (35.7 to 73.2) h · µg/ml. The median maximum drug concentration in serum in the experimental arms reached the target of 8 µg/ml. Continued investigation of higher rifampin doses is warranted. (This study has been registered at ClinicalTrials.gov under registration no. NCT01408914.).

Population pharmacokinetics of rifampin in the treatment of Mycobacterium tuberculosis in Asian elephants.

The objective of this study was to develop a population pharmacokinetic model for rifampin in elephants. Rifampin concentration data from three sources were pooled to provide a total of 233 oral concentrations from 37 Asian elephants. The population pharmacokinetic models were created using Monolix (version 4.2). Simulations were conducted using ModelRisk. We examined the influence of age, food, sex, and weight as model covariates. We further optimized the dosing of rifampin based upon simulations using the population pharmacokinetic model. Rifampin pharmacokinetics were best described by a one-compartment open model including first-order absorption with a lag time and first-order elimination. Body weight was a significant covariate for volume of distribution, and food intake was a significant covariate for lag time. The median Cmax of 6.07 µg/mL was below the target range of 8-24 µg/mL. Monte Carlo simulations predicted the highest treatable MIC of 0.25 µg/mL with the current initial dosing recommendation of 10 mg/kg, based upon a previously published target AUC0-24/MIC > 271 (fAUC > 41). Simulations from the population model indicate that the current dose of 10 mg/kg may be adequate for MICs up to 0.25 µg/mL. While the targeted AUC/MIC may be adequate for most MICs, the median Cmax for all elephants is below the human and elephant targeted ranges.

The pharmacokinetics of a single oral or rectal dose of concurrently administered isoniazid, rifampin, pyrazinamide, and ethambutol in Asian elephants (Elephas maximus).

Tuberculosis, caused by Mycobacterium tuberculosis, is a disease of concern in captive Asian elephants (Elephas maximus). Treatment for tuberculosis in elephants utilizes multidrug protocols combining isoniazid, rifampin, pyrazinamide, and/or ethambutol. In this study, a single, coformulated dose of isoniazid 5 mg/kg, rifampin 10 mg/kg, pyrazinamide 30 mg/kg, and ethambutol 30 mg/kg was administered orally to six Asian elephants, and rectally to five elephants using a cross-over design. Blood samples were collected serially over 24 h. Pyrazinamide and ethambutol concentrations were determined using validated gas chromatography assays. Isoniazid and rifampin concentrations were determined using validated high-performance liquid chromatography assays. Rectal isoniazid produced an earlier Tmax compared with oral administration. Oral isoniazid resulted in a comparatively lower Cmax , but higher AUC values compared with rectal isoniazid. Oral rifampin and oral ethambutol were well absorbed while rectal rifampin was not. Oral pyrazinamide produced comparatively higher Cmax and AUC values compared with rectal pyrazinamide. Results of this study indicate that currently recommended therapeutic monitoring sample collection times for rectal isoniazid and oral rifampin do not provide an accurate assessment of exposure for these drugs. This study demonstrates notable individual variability, indicating that dosing of these medications requires individual monitoring and provides additional information to guide the clinician when treating elephants.

Isoniazid urine spectrophotometry for prediction of serum pharmacokinetics in adults with TB.

BACKGROUND: Isoniazid (INH) is an important drug in many TB regimens, and unfavorable treatment outcomes can be caused by suboptimal pharmacokinetics. Dose adjustment can be personalized by measuring peak serum concentrations; however, the process involves cold-chain preservation and laboratory techniques such as liquid chromatography (LC)/mass spectrometry (MS), which are unavailable in many high-burden settings. Urine spectrophotometry could provide a low-cost alternative with simple sampling and quantification methods. METHODS: We enrolled 56 adult patients on treatment for active TB. Serum was collected at 0, 1, 2, 4, 6, and 8 h for measurement of INH concentrations using validated LC-MS/MS methods. Urine was collected at 0-4, 4-8, and 8-24 h intervals, with INH concentrations measured using colorimetric methods. RESULTS: The median peak serum concentration and total serum exposure over 24 h were 4.8 mg/L and 16.4 mg*hour/L, respectively. Area under the receiver operator characteristic curves for urine values predicting a subtherapeutic serum concentration (peak <3.0 mg/L) were as follows: 0-4 h interval (AUC 0.85, 95% CI 0.7-0.96), 0-8 h interval (AUC 0.85, 95% CI 0.71-0.96), and 0-24 h urine collection interval (AUC 0.84, 95% CI 0.68-0.96). CONCLUSION: Urine spectrophotometry may improve feasibility of personalized dosing in high TB burden regions but requires further study of target attainment following dose adjustment based on a urine threshold.

CONTEXTE: L'isoniazide (INH) est un médicament important dans de nombreux schémas thérapeutiques contre la TB, et des résultats thérapeutiques défavorables peuvent être dus à une pharmacocinétique sous-optimale. L'ajustement de la dose peut être personnalisé en mesurant les concentrations sériques maximales ; cependant, le processus implique la conservation de la chaîne du froid et des techniques de laboratoire telles que la chromatographie liquide (LC)/spectrométrie de masse (MS), qui ne sont pas disponibles dans de nombreuses régions à forte charge de morbidité. La spec-trophotométrie urinaire pourrait constituer une alternative peu coûteuse avec des méthodes d'échantillonnage et de quantification simples. MÉTHODES: Nous avons recruté 56 patients adultes sous traitement pour une TB active. Le sérum a été prélevé à 0, 1, 2, 4, 6 et 8 h pour mesurer les concentrations d'INH à l'aide de méthodes LC-MS/MS validées. L'urine a été prélevée à des intervalles de 0­4, 4­8 et 8­24 h, et les concentrations d'INH ont été mesurées à l'aide de méthodes colorimétriques. RÉSULTATS: La concentration sérique maximale médiane et l'exposition sérique totale sur 24 h étaient respectivement de 4,8 mg/L et de 16,4 mg*heure/L. L'aire sous les courbes caractéristiques de l'opérateur récepteur a été mesurée à l'aide de méthodes color-imétriques. Les aires sous les courbes caractéristiques des récepteurs pour les valeurs urinaires prédisant une concentration sérique sous-thérapeutique (pic <3,0 mg/L) étaient les suivantes : intervalle 0­4 h (AUC 0,85 ; IC 95% 0,7­0,96), intervalle 0­8 h (AUC 0,85 ; IC 95% 0,71­0,96), et intervalle de collecte d'urine 0­24 h (AUC 0,84 ; IC 95% 0,68­0,96). CONCLUSION: La spectrophotométrie urinaire peut améliorer la faisabilité d'un dosage personnalisé dans les régions à forte charge de TB, mais nécessite une étude plus approfondie de l'atteinte de la cible après l'ajustement de la dose sur la base d'un seuil urinaire.

Vitamin D, race, and experimental pain sensitivity in older adults with knee osteoarthritis.

OBJECTIVE: Low circulating serum levels of 25-hydroxyvitamin D (referred to hereafter as vitamin D) have been correlated with many health conditions, including chronic pain. Recent clinical practice guidelines define vitamin D levels <20 ng/ml as deficient and levels of 21-29 ng/ml as insufficient. Vitamin D insufficiency, including the most severe levels of deficiency, is more prevalent in black Americans. Ethnic and race group differences have been reported in both clinical and experimental pain, with black Americans reporting increased pain. The purpose of this study was to examine whether variations in vitamin D levels contribute to race differences in knee osteoarthritis pain. METHODS: The sample consisted of 94 participants (74% women), including 45 blacks and 49 whites with symptomatic knee osteoarthritis. Their average age was 55.8 years (range 45-71 years). Participants completed a questionnaire on knee osteoarthritis symptoms and underwent quantitative sensory testing, including measures of sensitivity to heat-induced and mechanically induced pain. RESULTS: Blacks had significantly lower levels of vitamin D compared to whites, demonstrated greater clinical pain, and showed greater sensitivity to heat-induced and mechanically induced pain. Low levels of vitamin D predicted increased experimental pain sensitivity, but did not predict self-reported clinical pain. Group differences in vitamin D levels significantly predicted group differences in heat pain and pressure pain thresholds at the index knee and ipsilateral forearm. CONCLUSION: These data demonstrate that race differences in experimental pain are mediated by differences in the vitamin D level. Vitamin D deficiency may be a risk factor for increased knee osteoarthritis pain in black Americans.

Therapeutic drug monitoring and TB treatment outcomes in patients with diabetes mellitus.

BACKGROUND: Diabetes mellitus (DM) increases the risk of TB disease and poor treatment outcomes such as delayed sputum culture conversion due to inadequate drug exposure. Therapeutic drug monitoring (TDM) has improved these outcomes in some settings.METHODS: To compare treatment outcomes in programs with routine TDM vs. programs that did not use TDM, we conducted a retrospective study among people with DM and TB at health departments in four US states.RESULTS: A total of 170 patients were enrolled (73 patients in the non-TDM group and 97 patients in the TDM group). Days to sputum culture conversion and total treatment duration were significantly shorter in the TDM group vs. the non-TDM group. In adjusted analyses, patients who underwent TDM were significantly more likely to achieve sputum culture conversion at 2 months (P = 0.007).CONCLUSION: TDM hastened microbiological cure from TB among people with DM and a high risk for poor treatment outcomes in the programmatic setting.

Adequacy of WHO weight-band dosing and fixed-dose combinations for the treatment of TB in children.

BACKGROUND: We examined whether the updated WHO weight-band dosing recommendations and fixed-dose combination tablets for the treatment of TB in children achieves recommended calculated dosages and adequate drug plasma exposure.DESIGN/METHODS: Children on first-line TB treatment per WHO guidelines were enrolled. Blood sampling at pre-dose, 1, 2, 4, 8, and 12 h post-dose after at least 4 weeks of treatment was performed. Drugs concentrations were measured using validated liquid chromatography tandem with mass spectrometry and pharmacokinetic parameters calculated using noncompartmental analysis. Plasma drug exposure below the lower limit of the 95% confidence interval of the mean for children was considered low and above the upper limit was high.RESULTS: Of 71 participants, 34 (47.9%) had HIV coinfection. The median calculated dose for isoniazid (INH), rifampin (RIF), pyrazinamide (PZA), and ethambutol (EMB) was 10.0 (range 4.3-13.3), 15.0 (range 8.6-20.0), 30.0 (range 21.0-40.0), and 20.4 (range 14.3-26.7) mg/kg, respectively. Overall, most patients had under-exposure for RIF and PZA and over-exposure for INH and EMB. Drug dose and weight-for-age Z-score were associated with area under the curve from time 0-24 h for all drugs.CONCLUSIONS: Despite adherence to WHO dosing guidelines, low PZA and RIF plasma exposures were frequent in our study population. Higher than currently recommended dosages of RIF and PZA may be needed in children.

Effect of HIV infection on plasma exposure to first-line TB drugs and target attainment in children.

BACKGROUND: Whether HIV infection adversely affects exposure to first-line TB drugs in children is debatable. It is also not known whether HIV infection increases the risk of plasma underexposure or overexposure to TB drugs. This study sought to address these questions.DESIGN/METHODS: Children on TB treatment were enrolled. After 4 weeks on therapy, blood samples were collected at pre-dose, 1, 2, 4, 8, and 12 h post-dose for pharmacokinetic analysis. Plasma drug exposure below and above the lower and upper bounds of the 95% confidence intervals of the reference mean for children were considered underexposure and overexposure, respectively. The effect of HIV infection on drugs exposure and risk of underexposure were examined using multivariate analysis.RESULTS: Of 86 participants (median age: 4.9 years), 45 had HIV coinfection. HIV coinfection was associated with lower pyrazinamide (PZA) and ethambutol exposures in adjusted analysis. Patients with TB-HIV coinfection were three times more likely to have PZA underexposure than those with TB only. Underexposure of rifampin was common irrespective of HIV coinfection status.CONCLUSIONS: HIV coinfection was associated with a higher risk for PZA underexposure in children. This effect should be accounted for in models and simulations to determine optimal PZA dose for children.

Clinical standards for the management of adverse effects during treatment for TB.

BACKGROUND: Adverse effects (AE) to TB treatment cause morbidity, mortality and treatment interruption. The aim of these clinical standards is to encourage best practise for the diagnosis and management of AE.METHODS: 65/81 invited experts participated in a Delphi process using a 5-point Likert scale to score draft standards.RESULTS: We identified eight clinical standards. Each person commencing treatment for TB should: Standard 1, be counselled regarding AE before and during treatment; Standard 2, be evaluated for factors that might increase AE risk with regular review to actively identify and manage these; Standard 3, when AE occur, carefully assessed and possible allergic or hypersensitivity reactions considered; Standard 4, receive appropriate care to minimise morbidity and mortality associated with AE; Standard 5, be restarted on TB drugs after a serious AE according to a standardised protocol that includes active drug safety monitoring. In addition: Standard 6, healthcare workers should be trained on AE including how to counsel people undertaking TB treatment, as well as active AE monitoring and management; Standard 7, there should be active AE monitoring and reporting for all new TB drugs and regimens; and Standard 8, knowledge gaps identified from active AE monitoring should be systematically addressed through clinical research.CONCLUSION: These standards provide a person-centred, consensus-based approach to minimise the impact of AE during TB treatment.

Administration and monitoring of clofazimine for NTM infections in children with and without cystic fibrosis.

Few studies have evaluated clofazimine (CLOF) drug monitoring and safety in children. We treated 10 children, 8 with CF, for NTM infection with multiple antimicrobials, including CLOF. All had serial blood CLOF concentrations measured and were followed for adverse events. Despite CLOF dose escalation, most children with CF did not reach a target CLOF concentration. Our data suggest that children with CF may require earlier initiation of CLOF at higher doses than is currently recommended.

Clinical standards for the dosing and management of TB drugs.

BACKGROUND: Optimal drug dosing is important to ensure adequate response to treatment, prevent development of drug resistance and reduce drug toxicity. The aim of these clinical standards is to provide guidance on 'best practice´ for dosing and management of TB drugs.METHODS: A panel of 57 global experts in the fields of microbiology, pharmacology and TB care were identified; 51 participated in a Delphi process. A 5-point Likert scale was used to score draft standards. The final document represents the broad consensus and was approved by all participants.RESULTS: Six clinical standards were defined: Standard 1, defining the most appropriate initial dose for TB treatment; Standard 2, identifying patients who may be at risk of sub-optimal drug exposure; Standard 3, identifying patients at risk of developing drug-related toxicity and how best to manage this risk; Standard 4, identifying patients who can benefit from therapeutic drug monitoring (TDM); Standard 5, highlighting education and counselling that should be provided to people initiating TB treatment; and Standard 6, providing essential education for healthcare professionals. In addition, consensus research priorities were identified.CONCLUSION: This is the first consensus-based Clinical Standards for the dosing and management of TB drugs to guide clinicians and programme managers in planning and implementation of locally appropriate measures for optimal person-centred treatment to improve patient care.

Effect of malnutrition on the pharmacokinetics of anti-TB drugs in Ghanaian children.

BACKGROUND: Anti-TB drugs dosing based on weight alone may contribute to suboptimal drug concentrations and poor treatment outcomes in malnourished children. We examined the effect of malnutrition on the pharmacokinetics (PK) of first-line anti-TB drugs in children.METHODS: Drug concentrations were measured in Ghanaian children during the intensive phase of TB treatment. Weight-for-age (WFA), height-for-age (HFA), weight-for-height (WFH) and body mass index-for-age (BFA) were calculated and children with Z-scores < -2 SD (standard deviations) were considered as having malnutrition. PK differences of anti-TB drugs were compared by nutritional status.RESULTS: Of 100 participants, 24/48 (50.0%) of those younger than 5 years had wasting, 58/86 (67.4%) were underweight, and 56/99 (56.6%) had stunting; 22/51 (43.1%) children aged ≥5 years had low BFA. Children with stunting were more likely than controls to have lower mean peak concentration (Cmax) and area under the curve (AUC0-8h) of rifampin (RIF) and pyrazinamide (PZA), as well as a higher frequency of Cmax below the normal range. Wasting and underweight were associated with lower mean ethambutol (EMB) Cmax and AUC0-8h.CONCLUSIONS: The current WHO-recommended dosages were associated with lower plasma exposure of RIF, PZA and EMB in children with stunting, wasting and underweight. Anti-TB drugs dosing models for children may need to include height.

Steady-state amprenavir and tenofovir pharmacokinetics after coadministration of unboosted or ritonavir-boosted fosamprenavir with tenofovir disoproxil fumarate in healthy volunteers.

Objective An open-label, three-period pharmacokinetic study was conducted to investigate the drug interaction potential between fosamprenavir (FPV) and tenofovir disoproxil fumarate (TDF). Methods Thirty-six healthy subjects received TDF 300 mg once daily (qd) for 7 days (period 1), and then were randomized to 14 days of either FPV 1400 mg twice daily (bid) or FPV/ritonavir (RTV) 700/100 mg bid alone or with TDF (period 2). Subjects continued their randomized dose of FPV for 14 more days, adding or removing TDF based upon its receipt in period 2 (period 3). Twenty-four-hour pharmacokinetic sampling was carried out on day 7 of period 1 and on day 14 of periods 2 and 3. Steady-state plasma amprenavir (APV) and tenofovir (TFV) pharmacokinetics were assessed by noncompartmental analysis and parameter values observed with each regimen were compared using geometric mean ratios with 90% confidence intervals. Results After TDF coadministration, APV geometric mean minimum concentration (C(min)), maximum concentration (C(max)), and area under the plasma concentration-time curve (AUC) increased by 31, 3 and 7% above values observed with unboosted FPV alone; they also increased by 31, 4 and 16% above values observed with FPV/RTV alone. TFV C(min), C(max) and AUC decreased by 12, 25 and 15% after FPV coadministration and by 9, 18 and 7% after FPV/RTV coadministration. No significant changes in RTV pharmacokinetics were observed. No differences were noted in adverse events among dosing periods. Conclusions In this evaluation of the interaction between FPV and TDF, increases in APV exposures and modest decreases in TFV exposures were observed. These were unlikely to be clinically significant.

How to design a study to evaluate therapeutic drug monitoring in infectious diseases?

BACKGROUND: Therapeutic drug monitoring (TDM) is a tool to personalize and optimize dosing by measuring the drug concentration and subsequently adjusting the dose to reach a target concentration or exposure. The evidence to support TDM is however often ranked as expert opinion. Limitations in study design and sample size have hampered definitive conclusions of the potential added value of TDM. OBJECTIVES: We aim to give expert opinion and discuss the main points and limitations of available data from antibiotic TDM trials and emphasize key elements for consideration in design of future clinical studies to quantify the benefits of TDM. SOURCES: The sources were peer-reviewed publications, guidelines and expert opinions from the field of TDM. CONTENT: This review focuses on key aspects of antimicrobial TDM study design: describing the rationale for a TDM study, assessing the exposure of a drug, assessing susceptibility of pathogens and selecting appropriate clinical endpoints. Moreover we provide guidance on appropriate study design. IMPLICATIONS: This is an overview of different aspects relevant for the conduct of a TDM study. We believe that this paper will help researchers and clinicians to design and conduct high-quality TDM studies.