Tuberculosis (TB) continues to be a major health problem, with 9.4 million incident cases and 1.7 million deaths globally in 2009 [1] . Tuberculosis perseveres as an important infectious disease across most of the underdeveloped world. It explains a noteworthy socioeconomic strain. The prevalence of tuberculosis in Pakistan is 350 (158 - 618)/100,000 with a mortality rate of 33 (15 - 60)/100,000 [2] . Despite the declining trend in prevalence and incidence of tuberculosis in the west, the HIV/AIDS rise has set hurdles for its control in developing countries [3] .

TB DILI (Antituberculosis drug-induced liver injury) is defined as the liver injury as a result of antituberculous drugs in accordance to American Thoracic society and international DILI Expert Working Group. TB DILI (Antituberculosis drug-induced liver injury) is multifactorial including metabolic idiosyncrasy to HLA susceptibility and generation of various free radical species. Metabolic idiosyncrasy claims to be the basis of Isoniazid (INH) toxicity where a CYP-generated toxic metabolite of INH induces oxidative stress causing mitochondrial or other key organelles injury. This concept could explain the enhanced risk of severe liver injury with concomitant intake of rifampicin and pyrazinamide [4] . HLA susceptibility with certain HLA haplotypes where HLA- DQB1 0201 antigen is present where HLA-DQA1*0102 is absent, has been linked with INH induced liver injury [5] .

Rifampicin may itself be hepatotoxic, as observed in cases with positive rechallenge and in situations where it is used alone (as to relieve pruritus). The meta-analysis showed that regimens combining isoniazid and rifampicin were associated with a higher rate of hepatotoxicity (2.5%) than regimens without this combination (1.1%) [6] . Pyrazinamide exhibits a wide range hepatotoxicity which includes idiosyncratic dose-dependent, sporting eosinophilia and granulomatous hepatitis. Pyrazinamide modifies nicotinamide acetyl dehydrogenase levels consequently generating free radical species.

Regardless of great advantages with a combination of several antitubercular drugs having synergistic effects, effectivity against different populations of mycobacterium, prevention of drug resistance and the risk of hepatotoxicity of individual drugs is increased. Even though majority of the patients endure the combination of drugs, a few develop adverse effects where anti-tuberculosis treatment induced hepatoxicity is the most significant adversity [7] [8] accounting for more than 7.0% of all undesired effects [9] [10] . The incidence of TB DILI varied from 2.0% to 28.0% which is based on different populations and definitions [7] .

TB DILI includes liver damage ranging from a minimal elevation of ALT or AST without symptoms to acute hepatic failure often fatal or even requiring liver transplantation.

Asymptomatic derangement of liver enzymes is found in 20% of patients (as a consequence of adaptation) [11] [12] . The less favorable outlook has been reported in patients who develop jaundice, acute liver failure, ascites and encephalopathy [13] . Moreover, TB DILI reduces efficacy of anti-TB treatment which could cause non- compliance, treatment failure and eventual recurrence or drug-resistance [14] . These consequences could momentously hamper effective epidemic TB control.

Various risk factors for TB DILI have been evidenced as old age, female gender, high alcohol ingestion, co- administration of enzyme inducers & other hepatotoxic drugs, Asian ethnicity and advanced form of the disease. Prior viral related (HBV & HCV) chronic liver disease, human immunodeficiency virus (HIV) infection and malnutrition are also established risk factors for TB DILI [7] [15] [16] .

Pakistan is an endemic country for TB where various forms of TB are responsible for a mortality rate of 33 (15 - 60)/100,000 [2] . TB DILI leads to treatment failure that may further exacerbate drug resistance causing eventual collapse of TB eradication programme. Critical understanding of clinical features of TB DILI, such as the time of onset, degree of severity, early symptomatology and potential outcomes are of crucial importance in identification of the adverse events with prompt intervention. A primary health care physician should know when to stop anti-tuberculosis treatment (ATT) in case of DILI. Physicians should have comprehensive knowledge of reintroducing strategy as holding ATT even after DILI resolution may lead to rise in TB resistance and can further hamper TB eradication program in Pakistan. The study is designed to:

・ Determine the frequency, types, severity and patterns of TB DILI.

・ Evaluate various risk factors for TB DILI.

This is a prospective cohort study of 278 patients with a diagnosis of Tuberculosis. Local institutional ethics committee approval was sought before commencing the study. The study was conducted at Civil Hospital Karachi, Pakistan. All confirmed cases of Tuberculosis of age ≥ 18 years who had given informed consent were included over a period of eight months after commencement of study. Patient with prior history, evidence of liver injury, suspected multi-drug resistant (MDR) and extensively drug resistant (XDR) TB were excluded.

Out of 278 patients with a diagnosis of TB, 95 (34.14%) had TB DILI. Most of the patients were male 192 (69.0%). The most common type of TB was pulmonary 59.39% followed by extrapulmonary forms like intestinal, peritoneal, lymph nodes, etc. The demographic detail of patients with comorbids is given in Table 1.

The incidence of hepatotoxicity is more common with multidrug regimens for TB compared to INH monotherapy in anti-TB prophylaxis. In this study TB DILI was manifested in 34.17% which is greater than earlier studies where the frequency was 8% - 19.8% [20] [21] . A recent Iranian study has shown similar frequency (31.37%) of TB DILI [22] . Low frequency of TB DILI (5%) was reported in a meta-analysis from the west [23] Pulmonary TB was the commonest form of TB in this study whereas an earlier study [24] had lesser frequency of pulmonary TB.

Nausea, anorexia, and vomiting are the main clinical presentation of TB DILI in this study which is congruent to the former studies [25] [26] . All three types of DILI were observed here including asymptomatic patients with raised aminotransferase, symptomatic with raised aminotransferase and patients with acute liver failure/encephalopathy. An earlier study showed various types of TB DILI with acute uncomplicated hepatitis (72.7%), fulminant hepatic failure (9.1%) and hepatic encephalopathy (18.2%) [26] . Kumar et al. reported low frequency (5.7%) of ATT induced acute liver failure with high mortality [13] .

All three major patterns of DILI (hepatocellular, Cholestatic, mixed) were present in this study. Most prevalent (63.15%) DILI pattern was hepatocellular followed by 23.15% mixed and 13.68% Cholestatic type. ATT DILI severity was noted from mild to severe in this study. Majority of patients having TB DILI 41 (43.15%) had mild DILI, 29 (30.52%) had moderate DILI while 20 (20.01%) and 05 (5.26%) patients had severe and very severe DILI respectively. Khalili et al. [22] have shown moderate (18.7%), severe (7.8%) and very severe (4.9%) hepatotoxicity with ATT. Maukof et al. [24] have shown the severity of TB DILI by using modestly different cut off values for transaminases. In above study mild, moderate and severe DILI were present in 66%, 26.67% and 13.33% patients respectively. The difference in DILI severity from above study to ours was owing to different cut off values for transaminases used in those two studies. A large Chinese study also showed similarly severe TB DILI [25] Locally published study on TB DILI showed severity according to elevated level of trans-

SGA, Subjective global assessment. TB DILI, Antituberculosis drug-induced liver injury.

aminases (ALT/AST > 2) 22.3%, (ALT/AST > 3) 14.44% and (ALT/AST > 5) 2.22% although hepatotoxicity or DILI grading was not in accordance to the International DILI Expert Working Group which includes bilirubin in grading system [27] .

DILI was also documented after reintroduction of ATT in this study. 20% patients had mild DILI with INH whereas rifampicin and PZA produced DILI in 13.68% and 5.26% on reintroduction. Sharma et al. analyzed rechallenge of 3 antituberculosis regimens in patients with TB DILI [28] . In this study reintroducing strategy of ATT were compared in three management groups where group I patients were reintroduced with highest doses of isoniazid, rifampicin, pyrazinamide simultaneously while group II patients were given therapy according to ATS guidelines (RIF trailed by isoniazid for 7 days, followed by pyrazinamide for 7 days, all in the maximum dosages). Patients in group III were reintroduced ATT as British Thoracic Society (BTS) guidelines where isoniazid, Rifampicin, and pyrazinamide were given sequentially by achieving the highest dose of each agent. Sharma et al. accomplished that the re-emergence of DILI was comparable amid the three treatment groups, (p = 0.69) [28] . The frequency of DILI over the reintroduction strategy by American thoracic society as used in this study was 3.42%.

In contrast, to study by Sharma et al., the Tahaoglu et al. in their study [29] compare the reintroduction regimens of ATT with maximum doses of antituberculosis agents like pyrazinamide and slow reintroduction of ATT without Pyrazinamide. The above study concluded that reintroduction of ATT with maximum doses were more hepatotoxic [29] . The dissimilarity between the above mentioned studies could be owing to a lesser sample size, the lesser treatment restraining limits and possible adaptation [30] . Khalili et al. [22] has shown the overall hepatotoxicity of RIF, INH and PZA were 1%, 3% and 9% respectively.

Advance stage of TB, underlying acute or chronic liver disease, various degrees of malnutrition and indiscriminate use of drugs are considered as major factors for higher prevalence of TB DILI in developing countries. Conversely, it is imprecise whether they are independent risk factors for hepatotoxicity.

Age > 35 year was proven as a risk factor for TB DILI in this study. Latest studies are harmonious to this study where patients over 35 years have 4 fold increased possibility of developing TB DILI [31] . A study reported that the rate of TB DILI encompasses 2% to 8% on aging, with an average of 5% [32] . Other studies accounted that DILI ranges from 22% to 33% in patients over 35 years compared with a range from 8% to 17% in those younger [4] [33] . Mahmood et al. [20] expressed that older age group was affected more with TB DILI than the younger ones (25.8% and 14.4%, respectively). In contrast Steele et al. [34] observed liver injury (hepatitis) in 1% - 6.9% of children contrasted to 1.6% - 2.5% of adult’s instituted isoniazid and rifampicin combination; involving all age groups at threat of emerging DILI. Shakya et al. reported that the rate of TB DILI is more in younger sufferers [35] . This could be elucidated by the fact that the majority of patients in their study were young. A prior Iranian [22] study disapproved age > 35 year to be a risk for developing TB DILI.

The feminine gender is conventionally considered more liable to develop TB DILI. Numerous studies reported increased risk of hepatotoxicity, neither treatment limiting nor the statistically significant [36] [37] . Papastavros et al. showed a 4-fold rise in the risk of treatment limiting TB DILI in females with an overall incidence of 2% [37] . Mahmood et al. [20] reported a higher frequency of TB DILI in females than males (26.3% vs. 19.7%). In contrast, this study along with other recent studies [38] - [40] did not show female gender to be a threat for developing TB DILI. In this study, diabetes was established to be a risk factor for TB DILI. Srivastava RK, et al. [41] also reported that diabetes amplifies TB DILI likewise our study. Earlier studies [42] [43] on the subject also depicted diabetes as a risk factor for hepatotoxicity. An earlier study [22] defined our study and did not prove diabetes as a risk factor. Malnutrition is considered to be a risk factor for TB DILI since long. Current reports keep on validating the significance of low albumin to be a risk factor as well as an indicator of malnutrition mutually for TB DILI. In this study various degree of malnutrition were assessed by SGA scheme and patients were categorized into stage A, B and C. Malnourished patients with SGA B (Odd ratio = 0.29, 95% CI 0.19 - 0.65 p = 0.001) and SGA C (odd ratio = 6.69, 95% CI, 3.63 - 14.41, p = 0.001) category were at greater risk of TB DILI in this study. The SGA technique uses the clinical information collected during history taking and physical examination to determine nutritional status without resorting to objective measurements like anthropometry [19] [44] . SGA method of assessment has been used successfully to assess nutritional status, in general medical and surgical patients. Earlier studies demonstrated three-fold elevated risk of increasing TB DILI in patients with hypoalbuminemia (<3.5 mg/dl) [5] [31] . Recently weight loss has been implicated as a significant risk factor for DILI [45] .

Concomitant use of hepatotoxic drugs with ATT were also instituted to be a significant risk factor for DILI (Odd ratio = 5.34, CI 95%, 2.69 - 10.68, p = 0.000). Previous studies [22] [46] also proved parallel hepatotoxic drugs as a risk factor for TB DILI. In current study, extrapulmonary TB was found to be a risk factor for TB DILI. An earlier study also showed a superior risk of TB DILI in extrapulmonary TB when compared to pulmonary TB [47] . A recent Indian study has also shown that extrapulmonary TB has more ATT DILI compared to pulmonary TB [48] . Concomitant hepatotoxic drugs and severe malnutrition were found to be independently associated with TB DILI when assessed by multivariate analysis. Earlier studies [22] [25] [48] were also congruent with this study for independent risk factors but malnutrition was assessed by low serum albumin rather than SGA staging. Among the risk factors for TB DILI, oxidative stress parameters like Malondialdehyde (MDA), Glutathione (GSH) and Superoxide dismutase (SOD) are also important. The oxidative stress parameters were not determined here, main shortcoming in this study as their serum level also should have been determined before and during the treatment. This would have helped in further understanding of endogenous factors for TB DILI.

TB DILI is a frequently reported medical problem in patients with various types of tuberculosis. All patterns of DILI were present where hepatocellular and mixed were elaborated the commonest. TB DILI ranges from mild injury to very severe or fatal liver damage. Age more than 35 years, malnutrition, extra pulmonary TB and concomitant use of hepatotoxic drugs were identified risk factors for TB DILI. Severe degree of malnutrition and concomitant use of hepatotoxic drugs were found to be an independent risk factor for TB DILI.

Authors have no conflict of interest.

Iftikhar HaiderNaqvi,KhalidMahmood,AbuTalib,AamerMahmood, (2015) Antituberculosis Drug-Induced Liver Injury: An Ignored Fact, Assessment of Frequency, Patterns, Severity and Risk Factors. Open Journal of Gastroenterology,05,173-184. doi: 10.4236/ojgas.2015.512027