Few mechanisms by which anti TB drugs causeshepatotoxiciy have been described and they are idiosyncratic damage ,dose-dependenttoxicity; induction of hepatic enzymes, drug-induced acute hepatitis andallergic reactions. Idiosyncratic hepatotoxiciy occur independent of the drugdose administered and dose dependent hepatotoxiciy is the hepato-cellulardamage depends on the drug dosage used 67. Although baseline liver function tests recommended inall patients before starting antiTB drugs, due to limited resources, it is recommendedto be done in at least those who are at risk of developing hepatotoxicity as inpatients chronically consume alcohol, take concomitant hepatotoxic drugs, haveviral hepatitis, other pre-existing liver disease or abnormal baseline liverchemistry, pregnant or within 3 months postpartum and in HIV co infection.Liver function tests should be arranged if they develop toxic features ofhepatitis like nausea, vomiting, icterus with or without hepatomegaly while on ATT8.Diagnosis of drug induced liver injury ( DILI) isbased on presence of symptoms along with increase level of either transaminasesor serum bilirubin or both and should besuspected if at least one of the following criteria is present910 I. A rise of five times the upper limit ofnormal levels (50 IU/L) of AST and/or alanine aminotransferase (ALT) withoutany clinical symptoms. II.
Arise in the level of serum total bilirubin 1.5 mg/dl( >27umol/l) III. A rise of three times the upper limit ofnormal levels (50 IU/L) of AST and/or alanine aminotransferase (ALT) withclinical symptoms.
IV. Any rise of AST/ALTfrom pre-treatment level with toxic symptoms such as anorexia, nausea, vomitingand jaundice. It is important torule out other possible causes of hepatitis like viral hepatitisbefore the diagnosis of anti -TB drug induced hepatitis is made. However it isimportant not to withhold ATT prematurely as well as not to wait till patient develophepatic encephalopathy. If ATT induced hepatotoxicity is suspected, all ATTdrugs should be withheld and if it is considered insecure to stop ATT, analternative non-hepatotoxic regimen consisting of streptomycin, ethambutol anda fluoroquinolone should be initiated.It is essential to waitfor liver function tests to drop up to base line and clinical symptoms toresolve before reintroducing the anti-TB drugs.
Once patient improve clinicallyand biochemically, drugs are introduced one at a time while monitoring clinicalsymptoms and L