## 1 Introduction
### Anti-Tuberculosis Agents and Their Potential Side Effects  
There have been numerous anti-tuberculosis drugs or agents (Table 1) used to treat TB. The most common drugs are ethambutol, Isoniazid, linezolid, pyrazinamide, rifampicin, and streptomycin (Figure 2). A comprehensive description of these antituberculosis agents together with their potential side effects is given below. Ethambutol, an essential first-line antituberculosis drug, possesses bacteriostatic action against _Mycobacterium tuberculosis_[12]. It is also used as part of a combination regimen to treat non-tuberculous mycobacterial infections [13]. This medication works by blocking the bacteria that cause TB from growing or increasing in number [13]. Although the exact mechanism of action of ethambutol is not fully known, evidence suggests that ethambutol performs its bacteriostatic activity against TB bacilli by exhibiting inhibition against arabinosyl [13]. Disruption of arabingalactan formation inhibits the synthesis of the mycolic-arabinogalactan-peptidoglycan complex, thereby leading to increased permeability of the cell wall. However, several reports have indicated that ethambutol causes serious side effects that can reduce its usage for the treatment of TB. Some of the most common side effects of the drug include vomiting, swelling of the face, blurred vision, rash, breathlessness and nausea [14]. Isoniazid is one of the more potent antimicrobial agents mostly used to treat tuberculosis. It is used to treat both active and latent TB. This drug was recommended in 1963 for use as monotherapy in the deterrence of activation of tuberculosis in patients suffering  
Figure 2: The chemical structure of antituberculosis drugs. from latent tuberculosis [15]. It is listed as one of the vital medicines for the treatment of TB in the WHO's list of essential medicines. Isoniazid works by inhibiting the lipid and DNA synthesis of _M. tuberculosis_, thereby resulting in the inhibition of cell wall formation and development [16]. However, this drug is frequently used together with other antituberculosis agents such as rifampicin, pyrazinamide, and either streptomycin or ethambutol. The common side effects of isoniazid include liver inflammation, numbness in the hand and feet, liver failure and increased blood levels of liver enzymes [17]. Linezolid is the first in a new class of oxazolidinone antibiotic drugs used to treat various types of infections, including drug-resistant TB [18]. It is among the list of essential drugs recommended by WHO against the activity of _M. tuberculosis_[19]. Linezolid works by disrupting bacterial growth, thereby inhibiting bacterial protein production [20]. This mechanism of action is unique in that it prevents the start of bacterial protein synthesis. Despite the effectiveness of this drug in the treatment of TB, safety is one of the key concerns. Some of the potential side effects of linezolid are headache, nausea, difficulty breathing, swelling in your face or throat, discoloration of the tongue and diarrhea [21]  
Pyrazinamide is another anti-tuberculosis agent that is structurally related to nicotinamide and very effective against _M. tuberculosis_ and other mycobacterium strains [22]. Recently, pyrazinamide was reinstated as first-line therapy to solve challenges related to resistant strains as the incidence of tuberculosis is surging [23]. Though the mechanism of action of pyrazinamide is not fully known, its structure is similar to that of nicotinamide, and so it is assumed that pyrazinamide intervenes with the nucleic acid metabolism of bacterial cells. However, one of the major therapeutic limitations of the use of pyrazinamide is hepatotoxicity [23]. Other limitations include gastrointestinal upset, and skin rashes can be associated with pyrazinamide administration [24]. In addition, the use of pyrazinamide treatment has also been linked to liver injury, notably resulting in a hepatitis-like liver injury in a patient suffering from tuberculosis [25; 26].