Ethambutol in tuberculosis: time to reconsider?

[Ethambutol-induced toxic optic neuropathy during treatment of tuberculosis meningitis in a child]

INTRODUCTION

Toxic optic neuropathy is a severe optic nerve injury that can compromise the prognosis for vision, justifying early clinical and ancillary diagnosis.

CASE DESCRIPTION

We report the case of an 11-year-old child being treated for tuberculous meningitis with a combination of ethambutol and three other anti-bacillary drugs, referred for a rapidly progressive bilateral decline in visual acuity. On ophthalmologic examination, the visual acuity was counting fingers within 1ft in both eyes, and bilateral optic disc pallor was noted, without other associated abnormalities. Neurological imaging was unremarkable, with red-green dyschromatopsia and a bilateral cecocentral scotoma. Faced with this clinical and paraclinical picture, we arrived at the diagnosis of ethambutol toxic optic neuropathy, with a multidisciplinary decision leading to a change in the antibacillary treatment protocol. No clinical improvement was noted after 3 months of follow-up.

DISCUSSION

Optic nerve toxicity is rare in children and is classically described as dose- and time-dependent.

CONCLUSION

Ethambutol ocular toxicity is extremely rare in children, and the required action when detected is to discontinue the drug. Reversibility is not always assured, which requires early detection of toxic optic neuropathy by close clinical and ancillary monitoring and, above all, sensitization of the treating physicians (pediatricians, pulmonologists and neurologists).

Anti-tuberculosis drug delivery for tuberculous bone defects

INTRODUCTION

Traditional therapy methods for treating tuberculous bone defects have several limitations. Furthermore, systemic toxicity and disease recurrence in tuberculosis (TB) have not been effectively addressed.

AREAS COVERED

This review is based on references from September 1998 to September 2021 and summarizes the classification and drug-loading methods of anti-TB drugs. The application of different types of biological scaffolds loaded with anti-TB drugs as a novel drug delivery strategy for tuberculous bone defects has been deeply analyzed. Furthermore, the limitations of the existing studies are summarized.

EXPERT OPINION

Loading anti-TB drugs into the scaffold through various drug-loading techniques can effectively improve the efficiency of anti-TB treatment and provide an effective means of treating tuberculous bone defects. This methodology also has good application prospects and provides directions for future research.

Monocarbonyl curcuminoids as antituberculosis agents with their moderate in-vitro metabolic stability on human liver microsomes

Tuberculosis, an airborne infectious disease, results in a high morbidity and mortality rate. The continuous emergence of TB resistance strains including MDR (multidrug-resistant tuberculosis), XDR (extensive drug-resistant tuberculosis), and especially TDR (totally drug-resistant tuberculosis) is a major public health threat and has intensified the need to develop new antitubercular agents. A natural product, curcumin, possesses diverse biological activities but suffers due to a lack of water solubility and bioavailability. To overcome these limitations, a series of 17 water-soluble monocarbonyl curcuminoids was synthesized and evaluated for antimycobacterial activity. All compounds exhibited good to moderate anti-TB activity with MIC₉₉ in the range of 3.12-25.0 µM, out of which 7c and 7p were found the most potent compounds with MIC₉₉ in the range of 3.12-6.25 µM. Furthermore, these compounds were observed to be nonhaemolytic, nontoxic, and stable under both physiological as well as reducing conditions. In-vitro metabolic stability data of the representative compound 7p with the human liver microsome revealed that these compounds possess a moderate metabolism with a half-life of 1.2 h and an intrinsic clearance of 1.12 ml/h/mg.

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.

Drug-resistant tuberculosis: controversies and challenges in pediatrics

Tuberculosis remains one of the top two causes of death caused by a single infectious disease worldwide, despite curative therapy. Children with tuberculosis are especially difficult to detect, since acid fast bacilli smears and cultures are usually negative and clinical signs are nonspecific or lacking. Multidrug-resistant tuberculosis, or tuberculosis resistant to at least isoniazid and rifampin, has emerged in most areas of the world over the past 20 years. Treatment of multidrug-resistant tuberculosis is more expensive and difficult. The second-line tuberculosis medications required for treatment are more toxic and less efficacious than standard treatment. These medications are not readily available in many areas of the world where drug resistance is most common. Fluoroquinolones are one of the most promising classes of second-line medications, but are not generally recommended for use in children. Ethambutol is recommended in the initial treatment of tuberculosis in children treated in areas where there is a risk of drug-resistant disease and the susceptibility of the source case is not known. Some experts have been hesitant to use ethambutol due to the risk of visual impairment associated with the drug and the difficulties in monitoring vision in young children. Pediatric drug formulations are not available for most antituberculosis medications, even the first-line tuberculosis drugs. Treatment of children exposed, infected or ill with multidrug-resistant tuberculosis is reviewed with special emphasis on second-line drugs, including recommended dosage, available formulations and necessary monitoring. While new cases of multidrug-resistant tuberculosis have decreased in most developed countries over the past 10 years, cases continue to increase in many developing countries and among immigrants from high-risk areas. Tuberculosis and multidrug-resistant tuberculosis are serious threats requiring worldwide strategies to control and treat. Better diagnostic tests, medications, public health strategies and vaccines will all be needed to eliminate tuberculosis.

Tuberculosis in special populations

The susceptibility to infection, the pathogenesis and the clinical manifestations of tuberculosis (TB) depend on the immunological status of the host. Immunological status is largely determined by age and comorbidities, but is also affected by other less well known factors. In Spain, most incidental cases of TB arise from the reactivation of remotely acquired latent infections and are favored by the aging of the population and the use of aggressive immunosuppressive therapies. The diagnosis and management of TB in these circumstances is often challenging. On the one hand, the atypical presentation with extrapulmonary involvement may delay diagnosis, and on the other, the toxicity and interactions of the antituberculous drugs frequently make treatment difficult. Immigration from resource-poor, high incidence TB countries, where the social and economic conditions are often suboptimal, adds a new challenge to the control of the disease in Spain. This chapter summarizes our current knowledge of epidemiological, clinical and treatment aspects of TB in particularly susceptible populations.

Treatment of paediatric TB: revised WHO guidelines

The World Health Organization has recently revised the recommended dosages of the main first-line anti-tuberculosis drugs for use in children. The recommended dosages and range of isoniazid, rifampicin, pyrazinamide and ethambutol have been increased from the previous recommended dosages. Ethambutol is now recommended for use in children of all ages including those of less than 5 years of age. This review explains the rationale for these recent revisions. Children require higher dosages than adults to achieve the same serum concentrations. Available data in HIV-uninfected children suggest that the revised dosages are within limits that have a very low risk of toxicity. An important challenge will be to examine the impact of higher dosages on clinical response, drug-drug interactions and risk of toxicity in HIV-infected children.

The outcome of infants younger than 6 months requiring ventilation for pneumonia caused by Mycobacterium tuberculosis

INTRODUCTION

The outcome of young infants (<6 months) being ventilated for respiratory failure caused by Mycobacterium tuberculosis (MTB) has not been recorded.

PATIENTS AND METHODS

A descriptive study of children <6 months admitted to the PICU from 1 February 1999 to 31 December 2005 with MTB causing respiratory failure.

RESULTS

Seventeen infants were ventilated for respiratory failure caused by MTB: ten had ventilatory respiratory failure and seven had hypoxic failure. An index case was found in 47%. All chest radiographs (CXRs) were highly suggestive of tuberculosis. MTB was cultured in 15 cases. In the other two cases MTB was confirmed by histopathology. The median duration of ventilation was 6 days (range: 1-35 days) with a median PaO2/FiO2 of 85 and ventilatory index of 58. Transthoracic glandular enucleation was required to facilitate extubation in six babies. All the infants survived. At 6-month follow-up 35% had a normal CXR and all were asymptomatic. One child had CXR changes suggestive of bronchiectasis but was asymptomatic.

CONCLUSION

The outcome of infants <6 months ventilated for respiratory failure caused by MTB is very good if TB is recognized timeously and appropriate management started. The diagnosis of TB in these infants can be made with a high index of suspicion and careful evaluation of the CXR.

[Multidrug-resistant tuberculosis in the pediatric age group]

AIMS

To study the clinical and epidemiological features in eight pediatric patients with multidrug-resistant tuberculosis (MDR-TB) diagnosed from 1994 to 2005 in three hospitals in Madrid (Spain).

METHODS

A retrospective study was performed in patients aged less than 15 years old with positive culture for multidrug-resistant Mycobacterium tuberculosis and patients with negative cultures diagnosed after contact with MDR-TB.

RESULTS

Pulmonary tuberculosis was diagnosed in seven patients and arthritis in one. Fifty percent of the patients were immigrants and an adult source case was found in four (50%). M. tuberculosis was isolated in gastric juice in four patients and in synovial biopsy in one. In three patients cultures were negative but these patients had previously been in contact with MDR-TB. Two strains were resistant to isoniazid and rifampicin, four were resistant to isoniazid, rifampicin and streptomycin, one was resistant to isoniazid, rifampicin, streptomycin and pyrazinamide, and one was resistant to 11 drugs. Six patients initially received conventional treatment without improvement. Patients received therapy for 15 months (range: 12 to 18) with 3 to 5 drugs according to the sensitivity study. The following adverse effects were observed: creatine phosphokinase increase (one patient), tendinitis (one patient), alteration of visual evoked responses (one patient) and transitory psychosis (one patient). One patient required pulmonary lobectomy. All patients responded satisfactorily to medical treatment.

CONCLUSIONS

MDR-TB should be suspected in patients not responding to TB treatment, especially those from countries with high resistance rates. In patients with negative cultures, treatment should rely on the results of a sensitivity study in the adult source case. MDR-TB requires the use of second-line anti-TB drugs for prolonged periods with possible toxic effects.

Challenges of Childhood TB/HIV Management in Malawi

The diagnosis and management of childhood tuberculosis (TB) are major challenges in countries such as Malawi with high incidence of TB and human immunodeficiency virus (HIV) infection. Diagnosis of TB in children often relies only on clinical features but clinical overlap with the presentation of HIV and other HIV-related lung disease is common. The tuberculin skin test (TST), the standard marker of M. tuberculosis infection in immune competent children, has poor sensitivity in HIV-infected children and is not usually available in Malawi. HIV test should be routine in children with suspected TB as it improves clinical management. HIV-infected children are at increased risk of developing active disease following TB exposure which justifies the use of isoniazid preventive therapy (IPT) once active disease has been excluded but this is difficult to implement and appropriate duration of IPT is unknown. HIV-infected children with active TB experience higher mortality and relapse rates on standard TB treatment compared to HIV-uninfected children, highlighting the need for further research to define optimal treatment regimens. HIV-infected children should also receive appropriate supportive care including cotrimoxazole prophylaxis and anti-retroviral treatment (ART) if indicated. There are concerns about concurrent use of some anti-TB drugs such as rifampicin with some ARTs.

In search of cyclooxygenase inhibitors, anti-Mycobacterium tuberculosis and anti-malarial drugs from Thai flora and microbes

Malaria continues to be a major infectious disease of the developing world and the problem is compounded not only by the emergence of drug resistant strains but also from a lack of a vaccine. The situation for tuberculosis (TB) infection is equally problematic. Once considered a "treatable" disease for which eradication was predicted, TB has re-emerged as highly lethal, multi-drug resistant strains after the outbreak of AIDS. Worldwide, the disease causes millions of deaths annually. Similarly, treatments for chronic inflammatory diseases such as arthritis have been impeded due to the potentially lethal side effects of the new and widely prescribed non-steroidal anti-inflammatory compounds. Thais have utilized bioresources from plants and some microorganisms for medicine for thousands of years. Because of the need for new drugs to fight malaria and TB, with radically different chemical structures and mode of actions other than existing drugs, efforts have been directed towards searching for new drugs from bioresources. This is also true for anti-inflammatories. Although Thailand is considered species-rich, only a small number of potential bioresources has been investigated. This article briefly describes the pathogenesis of 2 infectious diseases, malaria and TB, and modern medicines employed in chemotherapy. Diversities of Thai flora and fungi and their chemical constituents with antagonistic properties against these 2 diseases are described in detail. Similarly, anti-inflammatory compounds, mostly cyclooxygenase (COX) inhibitors, are also described herein to demonstrate the potential of Thai bioresources to provide a wide array of compounds for treatment of diseases of a different nature.

Low levels of pyrazinamide and ethambutol in children with tuberculosis and impact of age, nutritional status, and human immunodeficiency virus infection

Recent pharmacokinetic studies that included children found that serum drug levels were low compared to those of adults for whom the same dosages were used. This study aimed to characterize the pharmacokinetics of pyrazinamide and ethambutol in Malawian children and to examine the impact of age, nutritional status, and human immunodeficiency virus (HIV) infection. We conducted a pharmacokinetic study of children treated for tuberculosis with thrice-weekly pyrazinamide (n = 27; mean age, 5.7 years) and of a separate group of children treated with thrice-weekly ethambutol (n = 18; mean age, 5.5 years) as portions of tablets according to national guidelines. Malnutrition and HIV infection were common in both groups. Blood samples were taken just prior to oral administration of the first dose, and subsequent samples were taken at intervals of 2, 3, 4, 7, 24, and 48 h after drug administration. Serum drug levels were low in all children for both drugs; in almost all cases, the maximum concentration of the drug in serum (Cmax) failed to reach the MIC for Mycobacterium tuberculosis. The Cmax of pyrazinamide was significantly lower in younger children (<5 years) than in older children. The Cmax of pyrazinamide was also lower for HIV-infected children and children with severe malnutrition, but these differences did not reach statistical significance. No differences were found for ethambutol in relation to age, HIV infection, or malnutrition, but the Cmax was <2 mg/liter in all cases. Studies of pharmacokinetic parameters and clinical outcomes obtained by using higher dosages of drugs for treatment of childhood tuberculosis are needed, and recommended dosages may need to be increased.

Tuberculosis in children

The epidemiology of pediatric tuberculosis (TB) is shaped by risk factors such as age, race, immigration, poverty, overcrowding, and HIV/AIDS. Once infected, young children are at increased risk of TB disease and progression to extrapulmonary disease. Primary disease and its complications are more common in children than in adults, leading to differences in clinical and radiographic manifestations. Difficulties in diagnosing children stem from the low yield of mycobacteriology cultures and the subsequent reliance on clinical case definitions. Inadequately treated TB infection and TB disease in children today is the future source of disease in adults.

Impact of human immunodeficiency virus 1 infection on clinical presentation, treatment outcome and survival in a cohort of Ethiopian children with tuberculosis

BACKGROUND

Childhood tuberculosis (TB) is difficult to diagnose reliably because signs and symptoms are nonspecific and sputum for direct microscopy is difficult to obtain, especially in very young children. This diagnostic dilemma is thought to have increased with the HIV pandemic. Few studies on treatment outcome of dually infected children in high endemic countries have been reported. This study examines the impact of HIV infection on clinical presentation, diagnostic criteria and treatment outcome of TB in Ethiopian children.

METHODS

A prospective cohort study of children with TB diagnosed in Addis Ababa from December 1995 to January 1997 in which HIV-positive children were compared with HIV-negative children with regard to medical history, signs and symptoms, nutritional status, chest radiography, tuberculin skin test, response to TB treatment and final outcome. Mycobacterium tuberculosis was cultured in children with pulmonary manifestations.

RESULTS

HIV-positive children were younger, were underweight and had a 6-fold higher mortality than HIV-negative children. The tuberculin skin test was less sensitive and chest radiography was less specific in HIV-infected patients. Adherence to treatment was high (96%), and the cure rate was 58% for HIV-positive and 89% for HIV-negative TB patients.

CONCLUSION

HIV-positive children are at risk of diagnostic error as well as delayed diagnosis of TB. TB manifestations are more severe and progression to death is more rapid than in HIV-negative children. Weight for age may be used to identify children at high risk of a fatal outcome.

Evaluation of young children in contact with adult multidrug-resistant pulmonary tuberculosis: a 30-month follow-up

SETTING

The Western Cape Province of South Africa, an area with a high tuberculosis (TB) incidence, where initial multidrug resistance (MDR) among adult TB cases was 1.1% during 1992-1993.

OBJECTIVE

To determine the long-term prevalence of TB infection and disease in children in household contact with adults with MDR pulmonary TB, and to establish the efficacy of chemoprophylaxis in preventing disease in these children.

METHOD

Children <5 years old in contact with 73 MDR TB adults were evaluated. Disease was treated by prescribing at least 2 drugs to which the adult's strain was susceptible. The remaining children were classified as infected or noninfected and received chemoprophylaxis according to the index's strain susceptibility or were followed up and treated when indicated. All were followed up for 30 months.

RESULTS

At the initial evaluation 125 children were seen, median age 27.5 months. Of these, 119 were followed up. Fourteen (12%) had disease, 61 (51%) were infected only, and 44 (37%) were noninfected. By 30-month follow-up, 29 (24%) had developed disease and 64 (54%) were infected only. Four adult-child pair Mycobacterium tuberculosis isolates were compared by DNA fingerprinting; 3 were identical. All children who developed TB disease were clinically cured. Two (5%) of 41 children who received appropriate chemoprophylaxis and 13 (20%) of 64 who did not, developed TB during follow-up (odds ratio: 4.97).

CONCLUSION

The study confirms MDR TB transmission to childhood contacts. Seventy-eight percent of children were infected or developed disease. Appropriate chemoprophylaxis may prevent disease in these children.