Para-aminosalicylic acid: the return of an old friend

Therapeutic drug monitoring in tuberculosis

PURPOSE

Therapeutic drug monitoring (TDM) is a standard clinical procedure that uses the pharmacokinetic and pharmacodynamic parameters of the drug in the body to determine the optimal dose. The pharmacokinetic variability of the drug(s) is a significant contributor to poor treatment outcomes, including the development of acquired drug resistance. TDM aids in dose optimization and improves outcomes while lessening drug toxicity. TDM is used to manage patients with tuberculosis (TB) who exhibit a slow response to therapy, despite good compliance and drug-susceptible organisms. Additional indications include patients at risk of malabsorption or delayed absorption of TB drugs and patients with drug-drug interaction and drug toxicity, which confirm compliance with therapy. TDM usually requires two blood samples: the 2 h and the 6 h post-dose. This narrative review will discuss the pharmacokinetics and pharmacodynamics of TB drugs, determinants of poor response to therapy, indications of TDM, methods of performing TDM, and its interpretations.

METHODS

This is a narrative review. We searched PubMed, Embase, and the CINAHL from inception to April 2024. We used the following search terms: tuberculosis, therapeutic drug monitoring, anti-TB drugs, pharmacokinetics, pharmacodynamics, limited sample strategies, diabetes and TB, HIV and TB, and multidrug-resistant TB. All types of articles were selected.

RESULTS

TDM is beneficial in managing TB, especially in patients with slow responses, drug-resistance TB, recurrent TB, and comorbidities such as diabetes mellitus and human immunodeficiency virus infection.

CONCLUSION

TDM is beneficial for improving outcomes, reducing the risk of acquired drug resistance, and avoiding side effects.

Simple strategy of the use of pharmaceutically functionalized ionic liquids in a new generation of polymer nanocarriers for the combined delivery of ionic p-aminosalicylate and ampicillin

Single and dual bioactive linear poly(ionic liquid)s (PIL) were synthesized for use as nanocarriers in drug delivery systems (DDS). These PILs were obtained through the (co)polymerization of the choline-based monomeric ionic liquids (MIL) with pharmaceutical anions possessing antibacterial properties, specifically [2-(methacryloyloxy)ethyl]trimethyl-ammonium with ampicillin and p-aminosalicylate (TMAMA/AMP and TMAMA/PAS). The copolymers exhibited varying chain lengths defined by a degree of polymerization (DPn = 122-370), and differing contents of ionic fraction and drugs (TMAMA 61-92 %, AMP 61-93 % and PAS 16-21 %). These parameters were adjustable by the monomer conversion (33-92 %) and the initial ratio of comonomers. In aqueous solution, the polymer particles reached nanosizes, i.e. 190-328 nm for AMP systems and 200-235 nm for AMP/PAS systems. In the release process, the pharmaceutical anions were released through exchange by phosphate anions in PBS at pH 7.4 at 37 °C. Depending on the copolymer composition the release of AMP was attained in 72-100 % (11.1-19.5 µg/mL) within 26 h by the single drug systems, while the dual drug systems released 61-100 % of AMP (14.8-24.7 µg/mL) and 82-100 % of PAS (3.1-4.8 µg/mL) within 72 h. The effectiveness in the drug delivery of the designed TMAMA polymers seems to be promising for future applications in antibiotic therapy and the combined therapy.

Treatment of manganese and lead poisoning with sodium para-aminosalicylic acid: A contemporary update

Sodium para-aminosalicylic acid (PAS-Na) treatment for manganese (Mn) intoxication has shown efficacy in experimental and clinical studies, giving rise to additional studies on its efficacy for lead (Pb) neurotoxicity and its associated mechanisms of neuroprotection. The difference between PAS-Na and other metal complexing agents, such as edetate calcium sodium (CaNa2-EDTA), is firstly that PAS-Na can readily pass through the blood-brain barrier (BBB), and complex and facilitate the excretion of manganese and lead. Secondly, PAS-Na has anti-inflammatory effects. Recent studies have broadened the understanding on the mechanisms associated with efficacy of PAS-Na. The latter has been shown to modulate multifarious manganese- and lead- induced neurotoxicity, via its anti-apoptotic and anti-inflammatory effects, as well as its ability to inhibit pyroptosis, and regulate abnormal autophagic processes. These observations provide novel scientific bases and new concepts for the treatment of lead, mercury, copper, thallium, as well as other toxic encephalopathies, and implicate PAS-Na as a compound with greater prospects for clinical medical application.

An analysis of multidrug multicomponent crystals as tools for drug development

In a typical tablet or capsule formulation, the active drug is often present as a crystalline solid. This solid emerges from the relationships between the individual atoms within the crystal, which confer a distinct set of physical properties. Then, it follows that if we modify the packing arrangement of the individual molecules within these crystals, we can modulate their properties. This can be achieved by crystal engineering. Crystal engineering has also seen teams arrange multiple drug molecules within the same crystal, resulting in dramatic improvements to drug properties in the lab. The success of drugs like SEGLENTIS® and Entresto® have revitalised interest in these forms, but controversy surrounding their translation has prompted this reconsideration of their clinical utility. I reflect on the current academic, clinical, and commercial interest in multidrug multicomponent crystals, drawing parallels with developments pre-Bragg, contributing to a nuanced understanding of the potential and limitations of crystal engineering in pharmaceutical applications.

Drug-induced hypothyroidism in tuberculosis

INTRODUCTION

Adverse reactions to tuberculosis treatment can impact patient adherence and prognosis. Hypothyroidism is a frequent adverse reaction caused using ethionamide, prothionamide, and para-aminosalicylic acid and is often underdiagnosed.

AREAS COVERED

We searched Scielo, Scopus, and EMBASE databases, including 67 articles. Antitubercular drug-induced hypothyroidism has a prevalence of 17%. It occurs after 2 to 3 months of treatment and resolves within 4 to 6 weeks after discontinuation. It is postulated to result from the inhibition of thyroperoxidase function, blocking thyroid hormone synthesis. Symptoms are nonspecific, necessitating individualized thyroid-stimulating hormone measurement for detection. Specific guidelines for management are lacking, but initiation of treatment with levothyroxine, as is customary for primary hypothyroidism, is recommended. Discontinuation of antitubercular drugs is discouraged, as it may lead to unfavorable consequences.

EXPERT OPINION

Antitubercular drug-induced hypothyroidism is more common than previously thought, affecting one in six MDR-TB patients. Despite diagnostic and treatment recommendations, implementation is hindered in low-income countries due to the lack of certified laboratories. New drugs for tuberculosis treatment may affect thyroid function, requiring vigilant monitoring for complications, including hypothyroidism.

Severe BCG immune reconstitution inflammatory syndrome lymphadenitis successfully managed with pre-antiretroviral counseling and a non-surgical approach: a case report

BACKGROUND

Bacillus Calmette-Guérin (BCG) reactions are the most common cause of immune reconstitution inflammatory syndrome (IRIS) in HIV-positive infants who initiate antiretroviral therapy (ART). There is limited evidence regarding the incidence of BCG-IRIS; however, reports from outpatient cohorts have estimated that 6-9% of infants who initiated ART developed some form of BCG-IRIS within the first 6 months. Various treatment approaches for infants with BCG-IRIS have been reported, but there is currently no widely accepted standard-of-care.

CASE PRESENTATION

A 5-month-old male HIV-exposed infant BCG vaccinated at birth was admitted for refractory oral candidiasis, moderate anemia, and moderate acute malnutrition. He had a HIV DNA-PCR collected at one month of age, but the family never received the results. He was diagnosed with HIV during hospitalization with a point-of-care nucleic acid test and had severe immune suppression with a CD4 of 955 cells/µL (15%) with clinical stage III disease. During pre-ART counseling, the mother was educated on the signs and symptoms of BCG-IRIS and the importance of seeking follow-up care and remaining adherent to ART if symptoms arose. Three weeks after ART initiation, he was readmitted with intermittent subjective fevers, right axillary lymphadenopathy, and an ulcerated papule over the right deltoid region. He was subsequently discharged home with a diagnosis of local BCG-IRIS lymphadenitis. At six weeks post-ART initiation, he returned with suppurative lymphadenitis of the right axillary region that had completely eviscerated through the skin without signs of disseminated BCG disease. He was then started on an outpatient regimen of topical isoniazid, silver nitrate, and oral prednisolone. Throughout this time, the mother maintained good ART adherence despite this complication. After 2.5 months of ART and one month of specific treatment for the lymphadenitis, he had marked mass reduction, improved adenopathy, increased CD4 count, correction of anemia, and resolution of his acute malnutrition. He completely recovered and was symptom free two months after initial treatment without surgical intervention.

CONCLUSIONS

This case details the successful management of severe suppurative BCG-IRIS with a non-surgical approach and underlines the importance of pre-ART counseling on BCG-IRIS for caregivers, particularly for infants who initiate ART with advanced HIV.

The aminosalicylate - folate connection

Two aminosalicylate isomers have been found to possess useful pharmacological behavior: p-aminosalicylate (PAS, 4AS) is an anti-tubercular agent that targets M. tuberculosis, and 5-aminosalicylate (5AS, mesalamine, mesalazine) is used in the treatment of ulcerative colitis (UC) and other inflammatory bowel diseases (IBD). PAS, a structural analog of pABA, is biosynthetically incorporated by bacterial dihydropteroate synthase (DHPS), ultimately yielding a dihydrofolate (DHF) analog containing an additional hydroxyl group in the pABA ring: 2'-hydroxy-7,8-dihydrofolate. It has been reported to perturb folate metabolism in M. tuberculosis, and to selectively target M. tuberculosis dihydrofolate reductase (mtDHFR). Studies of PAS metabolism are reviewed, and possible mechanisms for its mtDHFR inhibition are considered. Although 5AS is a more distant structural relative of pABA, multiple lines of evidence suggest a related role as a pABA antagonist that inhibits bacterial folate biosynthesis. Structural data support the likelihood that 5AS is recognized by the DHPS pABA binding site, and its effects probably range from blocking pABA binding to formation of a dead-end dihydropterin-5AS adduct. These studies suggest that mesalamine acts as a gut bacteria-directed antifolate, that selectively targets faster growing, more folate-dependent species.

Recent Biochemical Advances in Antitubercular Drugs: Challenges and Future

Tuberculosis (TB) is one of the leading causes of death world-wide after AIDS. It infects around one-third of global population and approximately two million people die annually from this disease because it is a very contagious disease spread by Mycobacterium tuberculosis. The increasing number of drug-resistant strains and the failure of conventional treatments against this strain are the challenges of the coming decades. New therapeutic techniques aim to confirm cure without deterioration, to reduce deaths, contagions and the formation of drug-resistant strains. A plethora of new diagnostic tests are available to diagnose the active tuberculosis, screen latent M. tuberculosis infection, and to identify drug-resistant strains of M. tuberculosis. When effective prevention strategies do not prevail, high rates of early case detection and successive cures to control TB emergence would not be possible. In this review, we discussed the structural features of M. tuberculosis, Multi drug resistance tuberculosis (MDR-TB), extremely drug-resistant tuberculosis (XDR-TB), the mechanism of M. tuberculosis infection, the mode of action of first and second-line antitubercular drugs, the mechanism of resistance to the existing drugs, compounds in preclinical and clinical trial and drugs presently available for the treatment of tuberculosis. Moreover, the new diagnostic techniques to detect M. tuberculosis are also discussed in this review.

Micro-nanoemulsion and nanoparticle-assisted drug delivery against drug-resistant tuberculosis: recent developments

Tuberculosis (TB) is a major global health problem and the second most prevalent infectious killer after COVID-19. It is caused by Mycobacterium tuberculosis (Mtb) and has become increasingly challenging to treat due to drug resistance. The World Health Organization declared TB a global health emergency in 1993. Drug resistance in TB is driven by mutations in the bacterial genome that can be influenced by prolonged drug exposure and poor patient adherence. The development of drug-resistant forms of TB, such as multidrug resistant, extensively drug resistant, and totally drug resistant, poses significant therapeutic challenges. Researchers are exploring new drugs and novel drug delivery systems, such as nanotechnology-based therapies, to combat drug resistance. Nanodrug delivery offers targeted and precise drug delivery, improves treatment efficacy, and reduces adverse effects. Along with nanoscale drug delivery, a new generation of antibiotics with potent therapeutic efficacy, drug repurposing, and new treatment regimens (combinations) that can tackle the problem of drug resistance in a shorter duration could be promising therapies in clinical settings. However, the clinical translation of nanomedicines faces challenges such as safety, large-scale production, regulatory frameworks, and intellectual property issues. In this review, we present the current status, most recent findings, challenges, and limiting barriers to the use of emulsions and nanoparticles against drug-resistant TB.

Self-Assembling Polymers with p-Aminosalicylate Anions Supported by Encapsulation of p-Aminosalicylate for the Improvement of Drug Content and Release Efficiency

Bioactive linear choline-based copolymers were developed as micellar carriers for drug delivery systems (DDSs). The polymethacrylates containing trimethylammonium groups with p-aminosalicylate anions (PAS-based copolymers: series 1) or chloride anions (Cl-based copolymers: series 2) differing in ionic content and chain length were selected for drug loading. The diverse structures of amphiphilic copolymers made it possible to adjust the encapsulation efficiency of a well-known antibiotic, i.e., p-aminosalicylate in the form of sodium salt (PASNa) or acid (PASA), providing single drug systems. Goniometry was applied to verify the self-assembly capacity of the copolymers using the critical micelle concentration (CMC = 0.03-0.18 mg/mL) and the hydrophilicity level quantifying the surface wettability of polymer film using the water contact angle (WCA = 30-53°). Both parameters were regulated by the copolymer composition, indicating that the increase in ionic content caused higher CMC and lower WCA, but the latter was also modified to a less hydrophilic surface by drug encapsulation. The drug content (DC) in the PAS-based polymers was increased twice by encapsulation of PASNa and PASA (47-96% and 86-104%), whereas in the chloride-based polymer systems, the drug was loaded in 43-96% and 73-100%, respectively. Efficient drug release was detected for PASNa (80-100% series 1; 50-100% series 2) and PASA as complete in both series. The strategy of loading extra drug by encapsulation, which enhances the drug content in the copolymers containing anions of the same pharmaceutics, provided promising characteristics, which highlight the potential of PAS-loaded micellar copolymers for drug delivery.

Site-selective post-modification of short α/γ hybrid foldamers: a powerful approach for molecular diversification towards biomedical applications

The extensive research work in the exhilarating area of foldamers (artificial oligomers possessing well-defined conformation in solution) has shown them to be promising candidates in biomedical research and materials science. The post-modification approach is successful in peptides, proteins, and polymers to modulate their functions. To the best of our knowledge, site-selective post-modification of a foldamer affording molecules with different pendant functional groups within a molecular scaffold has not yet been reported. We demonstrate for the first time that late-stage site-selective functionalization of short hybrid oligomers is an efficient approach to afford molecules with diverse functional groups. In this article, we report the design and synthesis of hybrid peptides with repeating units of leucine (Leu) and 5-amino salicylic acid (ASA), regioselective post-modification, conformational analyses (based on solution-state NMR, circular dichroism and computational studies) and morphological studies of the peptide nanostructures. As a proof-of-concept, we demonstrate the applications of differently modified peptides as drug delivery agents, imaging probes, and anticancer agents. The novel feature of the work is that the difference in reactivity of two phenolic OH groups in short biomimetic peptides was utilized to achieve site-selective post-modification. It is challenging to apply the same approach to short α-peptides having a poor folding tendency, and their post-functionalization may considerably affect their conformation.

Synthesis and Characterization of Linear Copolymers Based on Pharmaceutically Functionalized Monomeric Choline Ionic Liquid for Delivery of p-Aminosalicylate

Bioactive linear poly(ionic liquid)s (PIL) were designed as carriers in drug delivery systems (DDS). Their synthesis was based on a monomeric ionic liquid (MIL) with a relevant pharmaceutical anion to create therapeutically functionalized monomers, which further can be used in the controlled atom transfer radical polymerization (ATRP). The presence of chloride counterions in the quaternary ammonium groups of choline MIL, e.g., [2-(methacryloyloxy)ethyl]trimethyl-ammonium chloride (ChMACl), was stimulated to undergo the anion exchange with p-aminosalicylate sodium salt (NaPAS) as the source of the pharmaceutical anion with antibacterial activity. The resultant [2-(methacryloyloxy)ethyl]trimethylammonium p-aminosalicylate (ChMAPAS) was copolymerized to attain the well-defined linear choline-based copolymers with various contents of PAS anions (24–42%), which were regulated by the initial ratio of ChMAPAS to MMA and conversion degree. The length of polymeric chains was evaluated by the total monomer conversion (31–66%) yielding degree of polymerization (DPn = 133–272). Depending on the polymer carrier composition, PAS anions were exchanged by 60–100% within 1 h, 80–100% within 4 h, and completely after 24 h by phosphate anions in PBS imitating a physiological fluid.

Hybridization Approach Toward Novel Antituberculars: Design, Synthesis, and Biological Evaluation of Compounds Combining Pyrazinamide and 4-Aminosalicylic Acid

Apart from the SARS-CoV-2 virus, tuberculosis remains the leading cause of death from a single infectious agent according to the World Health Organization. As part of our long-term research, we prepared a series of hybrid compounds combining pyrazinamide, a first-line antitubercular agent, and 4-aminosalicylic acid (PAS), a second-line agent. Compound 11 was found to be the most potent, with a broad spectrum of antimycobacterial activity and selectivity toward mycobacterial strains over other pathogens. It also retained its in vitro activity against multiple-drug-resistant mycobacterial strains. Several structural modifications were attempted to improve the in vitro antimycobacterial activity. The δ-lactone form of compound 11 (11') had more potent in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv. Compound 11 was advanced for in vivo studies, where it was proved to be nontoxic in Galleria mellonella and zebrafish models, and it reduced the number of colony-forming units in spleens in the murine model of tuberculosis. Biochemical studies showed that compound 11 targets mycobacterial dihydrofolate reductases (DHFR). An in silico docking study combined with molecular dynamics identified a viable binding mode of compound 11 in mycobacterial DHFR. The lactone 11' opens in human plasma to its parent compound 11 (t_1/2 = 21.4 min). Compound 11 was metabolized by human liver fraction by slow hydrolysis of the amidic bond (t_1/2 = 187 min) to yield PAS and its starting 6-chloropyrazinoic acid. The long t_1/2 of compound 11 overcomes the main drawback of PAS (short t_1/2 necessitating frequent administration of high doses of PAS).

Treatment options for children with multi-drug resistant tuberculosis

INTRODUCTION

According to the latest report from the World Health Organization (WHO), approximately 10.0 million people fell ill with tuberculosis (TB) in 2020, 12% of which were children aged under 15 years. There is very few experience on treatment of multi-drug resistant (MDR)-TB in pediatrics.

AREAS COVERED

The aim of this review is to analyze and summarize therapeutic options available for children experiencing MDR-TB. We also focused on management of MDR-TB prophylaxis.

EXPERT OPINION

The therapeutic management of children with MDR-TB or MDR-TB contacts is complicated by a lack of knowledge, and the fact that many potentially useful drugs are not registered for pediatric use and there are no formulations suitable for children in the first years of life. Furthermore, most of the available drugs are burdened by major adverse events that need to be taken into account, particularly in the case of prolonged therapy. A close follow-up with a standardized timeline and a comprehensive assessment of clinical, laboratory, microbiologic and radiologic data is extremely important in these patients. Due to the complexity of their management, pediatric patients with confirmed or suspected MDR-TB should always be referred to a specialized center.

Structure-Based Optimization of Coumestan Derivatives as Polyketide Synthase 13-Thioesterase(Pks13-TE) Inhibitors with Improved hERG Profiles for Mycobacterium tuberculosis Treatment

Pks13 was identified as a key enzyme involved in the final step of mycolic acid biosynthesis. We previously identified antitubercular coumestans that targeted Pks13-TE, and these compounds exhibited high potency both in vitro and in vivo. However, lead compound 8 presented potential safety concerns because it inhibits the hERG potassium channel in electrophysiology patch-clamp assays (IC₅₀ = 0.52 μM). By comparing the Pks13-TE-compound 8 complex and the ligand-binding pocket of the hERG ion channel, fluoro-substituted and oxazine-containing coumestans were designed and synthesized. Fluoro-substituted compound 23 and oxazine-containing coumestan 32 showed excellent antitubercular activity against both drug-susceptible and drug-resistant Mtb strains (MIC = 0.0039-0.0078 μg/mL) and exhibited limited hERG inhibition (IC₅₀ ≥ 25 μM). Moreover, 32 exhibited improved metabolic stability relative to parent compound 8 while showing favorable bioavailability in mouse models via serum inhibition titration assays.

DFT calculations, structural analysis, solvent effects, and non-covalent interaction study on the para-aminosalicylic acid complex as a tuberculosis drug: AIM, NBO, and NMR analyses

In this study, the effect of non-covalent interactions on the para-aminosalicylic acid complex is explored using density functional theory (DFT) in the gas phase and the solution. Our findings exhibit that the achieved binding energies considerably change on going from the gas phase to the solution. Based on the obtained results, the absolute value of the binding energy of the complex in the polar solvents is lower than the non-polar ones while in the gas phase it is higher than the solution. The atoms in molecules (AIM) and the natural bond orbital (NBO) analyses are applied to estimate the topological properties and the charge transfer during complexation, respectively. The results indicate that the presence of the cation-π interaction increases the strength of the intramolecular hydrogen bond in the studied complex. Finally, the various electronic descriptors such as energy gap, hardness, softness, and electronic chemical potential are investigated to gain further insight into these interactions. According to the achieved results, the high energy gap of the complex in the water solvent indicates high chemical stability and low reactivity compared to the others. On the other hand, the most reactive as well as the softest complex belongs to the gas phase.

Cocrystals of tuberculosis antibiotics: Challenges and missed opportunities

Cocrystals have been extensively used to improve the physicochemical properties and bioavailability of active pharmaceutical ingredients. Cocrystals of anti-tuberculosis medications are among those commonly reported. This review provides a summary of the tuberculosis antibiotic cocrystals reported in the literature, providing the main results on current tuberculosis medications utilized in cocrystals. Moreover, anti-tuberculosis cocrystals limitations and advantages are described, including evidence for enhanced solubility, stability and effect. Opportunities to enhance anti-tuberculosis medications and fixed dose combinations using cocrystals are given. Several cocrystal pairs are suggested to enhance the effectiveness of anti-tuberculosis drugs.

Pharmacokinetics and Dose Optimization Strategies of Para-Aminosalicylic Acid in Children with Rifampicin-Resistant Tuberculosis

Treatment options for children with Rifampicin-resistant tuberculosis (RR-TB) remain limited, and para-aminosalicylic acid (PAS) is still a relevant component of treatment regimens. Prevention of resistance to companion drugs by PAS is dose related, and at higher concentrations, PAS may exhibit significant bactericidal activity in addition to its bacteriostatic properties. The optimal dosing of PAS in children is uncertain, specifically for delayed-release granule preparations, which are the most used. A population pharmacokinetic model was developed describing PAS pharmacokinetics in children receiving routine RR-TB treatment. Model-based simulations evaluated current World Health Organization (WHO) weight-band doses against the adult pharmacokinetic target of 50 to 100 mg/liter for peak concentrations. Of 27 children included, the median (range) age and weight were 3.87 (0.58 to 13.7) years and 13.3 (7.15 to 30.5) kg, respectively; 4 (14.8%) were HIV positive. PAS followed one-compartment kinetics with first-order elimination and transit compartment absorption. The typical clearance in a 13-kg child was 9.79 liters/h. Increased PAS clearance was observed in both pharmacokinetic profiles from the only patient receiving efavirenz. No effect of renal function, sex, ethnicity, nutritional status, HIV status, antiretrovirals (lamivudine, abacavir, and lopinavir-ritonavir), or RR-TB drugs was detected. In simulations, target concentrations were achieved only using the higher WHO dose range of 300 mg/kg once daily. A transit compartment adequately describes absorption for the slow-release PAS formulation. Children should be dosed at the higher range of current WHO-recommended PAS doses and in a once-daily dose to optimize treatment.

Discovery and Development of Antibacterial Agents: Fortuitous and Designed

Today, antibacterial drug resistance has turned into a significant public health issue. Repeated intake, suboptimal and/or unnecessary use of antibiotics, and, additionally, the transfer of resistance genes are the critical elements that make microorganisms resistant to conventional antibiotics. A substantial number of antibacterials that were successfully utilized earlier for prophylaxis and therapeutic purposes have been rendered inadequate due to this phenomenon. Therefore, the exploration of new molecules has become a continuous endeavour. Many such molecules are at various stages of investigation. A surprisingly high number of new molecules are currently in the stage of phase 3 clinical trials. A few new agents have been commercialized in the last decade. These include solithromycin, plazomicin, lefamulin, omadacycline, eravacycline, delafloxacin, zabofloxacin, finafloxacin, nemonoxacin, gepotidacin, zoliflodacin, cefiderocol, BAL30072, avycaz, zerbaxa, vabomere, relebactam, tedizolid, cadazolid, sutezolid, triclosan and afabiacin. This article aims to review the investigational and recently approved antibacterials with a focus on their structure, mechanisms of action/resistance, and spectrum of activity. Delving deep, their success or otherwise in various phases of clinical trials is also discussed while attributing the same to various causal factors.

Therapeutic drug monitoring in patients with tuberculosis and concurrent medical problems

INTRODUCTION

Therapeutic drug monitoring (TDM) has been recommended for treatment optimization in tuberculosis (TB) but is only is used in certain countries e.g. USA, Germany, the Netherlands, Sweden and Tanzania. Recently, new drugs have emerged and PK studies in TB are continuing, which contributes further evidence for TDM in TB. The aim of this review is to provide an update on drugs used in TB, treatment strategies for these drugs, and TDM to support broader implementation.

AREAS COVERED

This review describes the different drug classes used for TB, multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB), along with their pharmacokinetics, dosing strategies, TDM and sampling strategies. Moreover, the review discusses TDM for patient TB and renal or liver impairment, patients co-infected with HIV or hepatitis, and special patient populations - children and pregnant women.

EXPERT OPINION

TB treatment has a long history of using 'one size fits all.' This has contributed to treatment failures, treatment relapses, and the selection of drug-resistant isolates. While challenging in resource-limited circumstances, TDM offers the clinician the opportunity to individualize and optimize treatment early in treatment. This approach may help to refine treatment and thereby reduce adverse effects and poor treatment outcomes. Funding, training, and randomized controlled trials are needed to advance the use of TDM for patients with TB.

The pharmacokinetics of para-aminosalicylic acid and its relationship to efficacy and intolerance

Following its introduction as an antituberculosis agent close to 75 years ago, the use of para-aminosalicylic acid (PAS) has been limited by gastrointestinal intolerance and multiple formulations were produced in attempts to reduce its occurrence. More recently, an enteric-coated, granular, slow-release PAS formulation (PASER) was introduced and is now in wide-spread use for the treatment of drug-resistant tuberculosis. The current PASER dosing regimen is based on recommendations derived from older studies using a variety of different PAS formulations and relegate PAS to a role as an exclusively bacteriostatic agent. However, there is ample evidence that if sufficiently high serum concentrations are reached, PAS can be bactericidal and that intolerance following once daily dosing, that aids the achievement of such concentrations, is no worse than that following intermittent daily dosing. In particular, prevention of resistance to companion drugs appears to be dependent on the size of the single dose, and hence the peak concentrations, and not on maintaining serum levels consistently above minimum inhibitory concentration. We present a narrative review of the development of PAS formulations, dosing practices, and published data regarding pharmacokinetics and pharmacodynamics and the relationship of PAS dosage to intolerance and efficacy. Our conclusions suggests that we are at present not using PAS to its maximum ability to contribute to regimen efficacy and protect companion drugs.

Role of Whole-Genome Sequencing in Characterizing the Mechanism of Action of para-Aminosalicylic Acid and Its Resistance

para-Aminosalicylic acid (PAS) remains one of the drugs of last resort for the treatment of tuberculosis, but its mechanism of action is still not completely understood. The main aim of this project was to identify new potential mechanisms of action and resistance to PAS by performing whole-genome sequencing on PAS-resistant laboratory mutants. A new variant in the folC gene was identified, as well as some other mutations that require further study.

Probability of mycobactericidal activity of para-aminosalicylic acid with novel dosing regimens

PURPOSE

Para-aminosalicylic acid (PAS) is currently one of the add-on group C medicines recommended by the World Health Organization for multidrug-resistant tuberculosis treatment. At the recommended doses (8-12 g per day in two to three divided doses) of the widely available slow-release PAS formulation, studies suggest PAS exposures are lower than those reached with older PAS salt formulations and do not generate bactericidal activity. Understanding the PASER dose-exposure-response relationship is crucial for dose optimization. The objective of our study was to establish a representative population pharmacokinetics model for PASER and evaluate the probability of bactericidal and bacteriostatic target attainment with different dosing regimens.

METHODS

To this end, we validated and optimized a previously published population pharmacokinetic model on an extended dataset. The probability of target attainment was evaluated for once-daily doses of 12 g, 14 g, 16 g and 20 g PASER.

RESULTS

The final optimized model included the addition of variability in bioavailability and allometric scaling with body weight on disposition parameters. Peak PAS concentrations over minimum inhibitory concentration of 100, which is required for bactericidal activity are achieved in 53%, 65%, 72% and 84% of patients administered 12, 14, 16 and 20 g once-daily PASER, respectively, when MIC is 1 mg/L. For the typical individual, the exposure remained above 1 mg/L for ≥ 98% of the dosing interval in all the evaluated PASER regimens.

CONCLUSION

The pharmacokinetic/pharmacodynamic parameters linked to bactericidal activity should be determined for 14 g, 16 g and 20 g once-daily doses of PASER.

Treatment of Drug-Resistant Tuberculosis. An Official ATS/CDC/ERS/IDSA Clinical Practice Guideline

Background: The American Thoracic Society, U.S. Centers for Disease Control and Prevention, European Respiratory Society, and Infectious Diseases Society of America jointly sponsored this new practice guideline on the treatment of drug-resistant tuberculosis (DR-TB). The document includes recommendations on the treatment of multidrug-resistant TB (MDR-TB) as well as isoniazid-resistant but rifampin-susceptible TB.Methods: Published systematic reviews, meta-analyses, and a new individual patient data meta-analysis from 12,030 patients, in 50 studies, across 25 countries with confirmed pulmonary rifampin-resistant TB were used for this guideline. Meta-analytic approaches included propensity score matching to reduce confounding. Each recommendation was discussed by an expert committee, screened for conflicts of interest, according to the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology.Results: Twenty-one Population, Intervention, Comparator, and Outcomes questions were addressed, generating 25 GRADE-based recommendations. Certainty in the evidence was judged to be very low, because the data came from observational studies with significant loss to follow-up and imbalance in background regimens between comparator groups. Good practices in the management of MDR-TB are described. On the basis of the evidence review, a clinical strategy tool for building a treatment regimen for MDR-TB is also provided.Conclusions: New recommendations are made for the choice and number of drugs in a regimen, the duration of intensive and continuation phases, and the role of injectable drugs for MDR-TB. On the basis of these recommendations, an effective all-oral regimen for MDR-TB can be assembled. Recommendations are also provided on the role of surgery in treatment of MDR-TB and for treatment of contacts exposed to MDR-TB and treatment of isoniazid-resistant TB.

Pharmacokinetics of Para-Aminosalicylic Acid and Its 2 Major Metabolites: A Potential Relationship to the Development of Gastrointestinal Intolerance

Para-aminosalicylic acid (PAS), often the last drug remaining for treatment of drug-resistant tuberculosis, is notorious for causing gastrointestinal intolerance; however, the cause of PAS intolerance is uncertain. The objective of this study was to assess relationships between peak concentrations of PAS administered as a granular slow-release enteric coated formulation, and its metabolites acetyl-PAS and glycine-PAS, and intolerance. PAS and its metabolites were measured in 29 adult patients with drug-resistant tuberculosis at Brooklyn Hospital, Cape Town, randomized to receive granular slow-release enteric-coated PAS 4 g twice daily or 8 g once daily for 1 week, followed by the alternative regimen. Concentrations of PAS and its metabolites were determined by liquid chromatography and tandem mass spectrometry, and a visual analogue scale evaluated intolerance. Spearman's correlation test assessed the relationship between maximum plasma concentrations (C_max ) and intolerance scores. A large interindividual variability was observed for the PAS C_max (40.42-68.55 mg/L) following 4 g twice daily; (62.69-102.41 mg/L) for 8 g once daily and a similar wide C_max range found for the metabolites acetyl-PAS and glycine-PAS. Twenty-six patients reported at least 1 intolerance episode, but most visual analogue scale scores clustered around 0. Significant inverse associations were found between acetyl-PAS C_max and bloating (rho = -0.448; P = .025) and diarrhea (rho = -0.407; P = .044) for the twice-daily regimen and a similar inverse association found for glycine-PAS and diarrhea (rho = -0.412; P = .041). Plasma concentrations of the metabolites did not correlate with the occurrence of gastrointestinal symptoms, but higher metabolite concentrations correlated with lower intolerance scores; slow metabolism of PAS and its continued presence in the intestinal tract may be the main cause of intolerance.

Analysis of mutations leading to para-aminosalicylic acid resistance in Mycobacterium tuberculosis

Thymidylate synthase A (ThyA) is the key enzyme involved in the folate pathway in Mycobacterium tuberculosis. Mutation of key residues of ThyA enzyme which are involved in interaction with substrate 2′-deoxyuridine-5′-monophosphate (dUMP), cofactor 5,10-methylenetetrahydrofolate (MTHF), and catalytic site have caused para-aminosalicylic acid (PAS) resistance in TB patients. Focusing on R127L, L143P, C146R, L172P, A182P, and V261G mutations, including wild-type, we performed long molecular dynamics (MD) simulations in explicit solvent to investigate the molecular principles underlying PAS resistance due to missense mutations. We found that these mutations lead to (i) extensive changes in the dUMP and MTHF binding sites, (ii) weak interaction of ThyA enzyme with dUMP and MTHF by inducing conformational changes in the structure, (iii) loss of the hydrogen bond and other atomic interactions and (iv) enhanced movement of protein atoms indicated by principal component analysis (PCA). In this study, MD simulations framework has provided considerable insight into mutation induced conformational changes in the ThyA enzyme of Mycobacterium.

A Pharmacology Perspective of Simultaneous Tuberculosis and Hepatitis C Treatment

Tuberculosis (TB) and hepatitis C virus (HCV) infection are both major public health problems. Despite high rates of co-infection there is scarce literature addressing the convergence of the two diseases. One particularly unexplored area is the potential for simultaneous treatment of TB and HCV which would allow for leveraging an extensive global TB treatment infrastructure to help scale up HCV treatment. We review the drug metabolism of anti-TB and HCV drugs and the known and potential drug-drug interactions between recommended HCV regimens and individual anti-TB drugs. Rifampin is the only anti-TB drug to have been formally studied for potential drug interactions with anti-HCV direct-acting antivirals (DAAs) and existing data precludes these combinations. However, based on known pathways of drug metabolism and enzyme effects, the combination of HCV DAA regimens with all other anti-TB drugs may be feasible. Pharmacokinetic studies are needed next to help move co treatment regimens forward for clinical use among patients coinfected with TB and HCV.

Methionine Antagonizes para-Aminosalicylic Acid Activity via Affecting Folate Precursor Biosynthesis in Mycobacterium tuberculosis

para-Aminosalicylic acid (PAS) is a second-line anti-tubercular drug that is used for the treatment of drug-resistant tuberculosis (TB). PAS efficacy in the treatment of TB is limited by its lower potency against Mycobacterium tuberculosis relative to many other drugs in the TB treatment arsenal. It is known that intrinsic metabolites, such as, para-aminobenzoic acid (PABA) and methionine, antagonize PAS and structurally related anti-folate drugs. While the basis for PABA-mediated antagonism of anti-folates is understood, the mechanism for methionine-based antagonism remains undefined. In the present study, we used both targeted and untargeted approaches to identify factors associated with methionine-mediated antagonism of PAS activity. We found that synthesis of folate precursors as well as a putative amino acid transporter, designated MetM, play crucial roles in this process. Disruption of metM by transposon insertion resulted in a ≥30-fold decrease in uptake of methionine in M. bovis BCG, indicating that metM is the major facilitator of methionine transport. We also discovered that intracellular biotin confers intrinsic PAS resistance in a methionine-independent manner. Collectively, our results demonstrate that methionine-mediated antagonism of anti-folate drugs occurs through sustained production of folate precursors.

Utility of para-aminosalicylic acid in drug-resistant tuberculosis: Should it be classified as Group D3 or Group C?

Background

The World Health Organization drug-resistant tuberculosis (DR-TB) 2016 guidelines reclassified para-aminosalicylic acid (PAS) as Group D3 "add-on" drug. We studied our DR-TB data wherein PAS was widely and preferably used as a substitute in the standardized regimen in varied situations and report its utility in DR-TB.

Methodology

This retrospective observational study enrolled both pulmonary and extrapulmonary DR-TB patients receiving PAS in the programmatic management of DR-TB from March 2012 to June 2013. They were divided into seven subgroups on the basis of indication for PAS substitution in the standardized regimen for DR-TB cases. The clinical profile and outcomes were analyzed.

Results

PAS was substituted in 250 cases (225 - pulmonary DR-TB and 25 - extrapulmonary DR-TB). PAS was used in (1) pre-extensively drug-resistant TB (XDR-TB) fluoroquinolones (FQs) - 136 (54.4%), (2) XDR-TB - 15 (6%), (3) substitute drug for serious adverse events - 3 (1.2%), (4) pregnant DR-TB patients - 5 (2%), (5) patients on successful private-based second-line therapy adopted under the Revised National Tuberculosis Control Program - 10 (4%), (6) substitute drug for previous FQ exposure - 5 (2%), and (7) Category V - 76 (30.4%). Although 51.2% had an unfavorable response (UFR) against 48.8% with FR, wide disparity was noted in subgroups. FR was observed in 68.4% pre-XDR-TB (FQ), 80% pregnant patients, 90% adopted from private on successful second-line therapy, 80% previous FQ exposure against 40% XDR-TB, 7.9% Category V, and 0% PAS substitution for adverse drug reactions (ADRs). UFR was seen in 31.6% pre-XDR-TB (FQ), 20% pregnant patients, 10% adopted from private on successful second-line therapy, 20% of previous FQ exposure against 60% XDR-TB, 92.1% Category V, and 100% on PAS substitution for ADR.

Conclusion

In view of the safety and efficacy of PAS in our DR-TB patients except for XDR and Category V group, we recommend larger studies with PAS and consider its reclassification into Group C rather than Group D3.

Prevalence of drug-resistant tuberculosis and imputed burden in South Africa: a national and sub-national cross-sectional survey

BACKGROUND

Globally, per-capita, South Africa reports a disproportionately high number of cases of multidrug-resistant (MDR) tuberculosis and extensively drug-resistant (XDR) tuberculosis. We sought to estimate the prevalence of resistance to tuberculosis drugs in newly diagnosed and retreated patients with tuberculosis provincially and nationally, and compared these with the 2001-02 estimates.

METHODS

A cross-sectional survey was done between June 15, 2012-June 14, 2014, using population proportionate randomised cluster sampling in the nine provinces in South Africa. 343 clusters were included, ranging between 31 and 48 per province. A patient was eligible for inclusion in the survey if he or she presented as a presumptive case during the intake period at a drug resistance survey enrolling facility. Consenting participants (≥18 years old) completed a questionnaire and had a sputum sample tested for resistance to first-line and second-line drugs. Analysis was by logistic regression with robust SEs, inverse probability weighted against routine data, and estimates were derived using a random effects model.

FINDINGS

101 422 participants were tested in 2012-14. Nationally, the prevalence of MDR tuberculosis was 2·1% (95% CI 1·5-2·7) among new tuberculosis cases and 4·6% (3·2-6·0) among retreatment cases. The provincial point prevalence of MDR tuberculosis ranged between 1·6% (95% CI 0·9-2·9) and 5·1% (3·7-7·0). Overall, the prevalence of rifampicin-resistant tuberculosis (4·6%, 95% CI 3·5-5·7) was higher than the prevalence of MDR tuberculosis (2·8%, 2·0-3·6; p=0·01). Comparing the current survey with the previous (2001-02) survey, the overall MDR tuberculosis prevalence was 2·8% versus 2·9% and prevalance of rifampicin-resistant tuberculosis was 3·4% versus 1·8%, respectively. The prevalence of isoniazid mono-resistant tuberculosis was above 5% in all provinces. The prevalence of ethionamide and pyrazinamide resistance among MDR tuberculosis cases was 44·7% (95% CI 25·9-63·6) and 59·1% (49·0-69·1), respectively. The prevalence of XDR tuberculosis was 4·9% (95% CI 1·0-8·8). Nationally, the estimated numbers of cases of rifampicin-resistant tuberculosis, MDR tuberculosis, and isoniazid mono-resistant tuberculosis for 2014 were 13 551, 8249, and 17 970, respectively.

INTERPRETATION

The overall prevalence of MDR tuberculosis in South Africa in 2012-14 was similar to that in 2001-02; however, prevalence of rifampicin-resistant tuberculosis almost doubled among new cases. Furthermore, the high prevalence of isoniazid mono-resistant tuberculosis, not routinely screened for, and resistance to second-line drugs has implications for empirical management.

FUNDING

President's Emergency Plan for AIDS Relief through the Centers for Disease Control and Prevention under the terms of 1U19GH000571.

Current therapies for the treatment of multidrug-resistant tuberculosis in children in India

INTRODUCTION

Multidrug-resistant tuberculosis (MDR-TB) is a serious life threatening condition affecting children as well as adults worldwide. Timely diagnosis and effective treatment, both of which are complex in children, are the prerogatives for a favorable outcome. Areas covered: This review covers epidemiology, treatment regimen and duration, newer drugs and adverse events in children with MDR-TB. Special note has been made of epidemiology and principles of treatment followed in Indian children. Expert opinion: High index of suspicion is essential for diagnosing childhood MDR-TB. If there is high probability, a child can be diagnosed as presumptive MDR-TB and started on empiric treatment in consultation with experts. However, every effort should be made to confirm the diagnosis. Backbone of an effective MDR-TB regimen consists of four 2nd line anti-TB drugs plus pyrazinamide; duration being 18-24 months. The newer drugs delamanid and bedaquiline can be used in younger children if no other alternatives are available after consultation with experts. Wider availability of these drugs should be ensured for benefit to all concerned. More research is required for development of new and repurposed drugs to combat MDR-TB. Children need to be included in clinical trials for such life-saving drugs, so that nobody is denied the benefits.

Revisiting the mutant prevention concentration to guide dosing in childhood tuberculosis

The mutant prevention concentration (MPC) is a well-known concept in the chemotherapy of many bacterial infections, but is seldom considered in relation to tuberculosis (TB) treatment, as the required concentrations are generally viewed as unachievable without undue toxicity. Early studies revealed single mutations conferring high MICs of first- and second-line anti-TB agents; however, the growing application of genomics and quantitative drug susceptibility testing in TB suggests a wide range of MICs often determined by specific mutations and strain type. In paediatric TB, pharmacokinetic studies indicate that despite increasing dose recommendations, a proportion of children still do not achieve adult-derived targets. When considering the next stage in anti-TB drug dosing and the introduction of novel therapies for children, we suggest consideration of MPC and its incorporation into pharmacokinetic studies to more accurately determine appropriate concentration targets in children, to restrict the growth of resistant mutants and better manage drug-resistant TB.

Structural and functional effects of nucleotide variation on the human TB drug metabolizing enzyme arylamine N-acetyltransferase 1

The human arylamine N-acetyltransferase 1 (NAT1) enzyme plays a vital role in determining the duration of action of amine-containing drugs such as para-aminobenzoic acid (PABA) by influencing the balance between detoxification and metabolic activation of these drugs. Recently, four novel single nucleotide polymorphisms (SNPs) were identified within a South African mixed ancestry population. Modeling the effects of these SNPs within the structural protein was done to assess possible structure and function changes in the enzyme. The use of molecular dynamics simulations and stability predictions indicated less thermodynamically stable protein structures containing E264K and V231G, while the N245I change showed a stabilizing effect. Coincidently the N245I change displayed a similar free energy landscape profile to the known R64W amino acid substitution (slow acetylator), while the R242M displayed a similar profile to the published variant, I263V (proposed fast acetylator), and the wild type protein structure. Similarly, principal component analysis indicated that two amino acid substitutions (E264K and V231G) occupied less conformational clusters of folded states as compared to the WT and were found to be destabilizing (may affect protein function). However, two of the four novel SNPs that result in amino acid changes: (V231G and N245I) were predicted by both SIFT and POLYPHEN-2 algorithms to affect NAT1 protein function, while two other SNPs that result in R242M and E264K substitutions showed contradictory results based on SIFT and POLYPHEN-2 analysis. In conclusion, the structural methods were able to verify that two non-synonymous substitutions (E264K and V231G) can destabilize the protein structure, and are in agreement with mCSM predictions, and should therefore be experimentally tested for NAT1 activity. These findings could inform a strategy of incorporating genotypic data (i.e., functional SNP alleles) with phenotypic information (slow or fast acetylator) to better prescribe effective treatment using drugs metabolized by NAT1.

Population pharmacokinetics of moxifloxacin, cycloserine, p-aminosalicylic acid and kanamycin for the treatment of multi-drug-resistant tuberculosis

Control of multi-drug-resistant tuberculosis (MDR-TB) requires extensive, supervised chemotherapy because second-line anti-TB drugs have a narrower therapeutic range than first-line drugs. This study aimed to develop population pharmacokinetic (PK) models for second-line drugs in patients with MDR-TB, evaluate the recommended dosage regimens and, if necessary, suggest new dosage regimens. A prospective, single-centre PK study was performed on second-line anti-TB drugs in patients with MDR-TB. Moxifloxacin, cycloserine, p-aminosalicylic acid (PAS), kanamycin and other second-line drugs were administered to the patients. Plasma concentrations were analysed using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Population PK models were developed using non-linear mixed effect modelling (NONMEM, Version 7.30; ICON Development Solutions, Ellicott City, MD, USA). Simulations were performed using the calculated PK parameters. The respective absorption rate constant, apparent clearance and apparent volume of distribution values were as follows: 0.305/h, 9.37 L/h and 56.7 L for moxifloxacin; 0.135/h, 1.38 L/h and 10.5 L for cycloserine; 0.510/h, 30.8 L/h and 79.4 L for PAS; and 1.67/h, 3.75 L/h and 15.2 L for kanamycin. The simulations showed that the following dosage regimens were more likely to be within the recommended concentration ranges than the raw data in this study: 200 mg of moxifloxacin once daily (QD) (patient weight <50 kg) and 400 mg of moxifloxacin QD (patient weight ≥50 kg), 500-750 mg of cycloserine QD, 4.95-6.6 g of PAS twice daily and 750-1000 mg of intramuscular kanamycin QD. These findings indicate that the recommended doses should be revised to improve the clinical outcomes of MDR-TB treatment.

Adverse effects of oral second-line antituberculosis drugs in children

INTRODUCTION

Increasing numbers of children with drug-resistant tuberculosis are accessing second-line antituberculosis drugs; these are more toxic than first-line drugs. Little is known about the safety of new antituberculosis drugs in children. Knowledge of adverse effects, and how to assess and manage these, is important to ensure good adherence and treatment outcomes.

AREAS COVERED

A Pubmed search was performed to identify articles addressing adverse effects of second-line antituberculosis drugs; a general search was done for the new drugs delamanid and bedaquiline. This review discusses adverse effects associated with oral second-line antituberculosis drugs. The spectrum of adverse effects caused by antituberculosis drugs is wide; the majority are mild or moderate, but these are important to manage as it could lead to non-adherence to treatment. Adverse effects may be more common in HIV-infected than in HIV-uninfected children.

EXPERT OPINION

Although children may experience fewer adverse effects from oral second-line antituberculosis drugs than adults, evidence from prospective studies of the incidence of adverse events in children is limited. Higher doses of second-line drugs, new antituberculosis drugs, and new drug regimens are being evaluated in children: these call for strict pharmacovigilance in children treated in the near future, as adverse effect profiles may change.

Extensively drug-resistant tuberculosis in a young child after travel to India

Extensively drug-resistant (XDR) tuberculosis is becoming increasingly prevalent worldwide, but little is known about XDR tuberculosis in young children. In this Grand Round we describe a 2-year-old child from the USA who developed pneumonia after a 3 month visit to India. Symptoms resolved with empirical first-line tuberculosis treatment; however, a XDR strain of Mycobacterium tuberculosis grew in culture. In the absence of clinical or microbiological markers, low-radiation exposure pulmonary CT imaging was used to monitor treatment response, and guide an individualised drug regimen. Management was complicated by delays in diagnosis, uncertainties about drug selection, and a scarcity of child-friendly formulations. Treatment has been successful so far, and the child is in remission. This report of XDR tuberculosis in a young child in the USA highlights the risks of acquiring drug-resistant tuberculosis overseas, and the unique challenges in management of tuberculosis in this susceptible population.