Isoniazid, Rifampicin, Pyrazinamide and Ethambutol

Introduction, Synthesis and SAR of Anti-Tubercular Drugs

1. ANTI-TUBERCULAR DRUGS (Intro, synthesis, sar…) DEPARTMENT OF PHARMACY UNIVERSITY OF PESHAWAR

2. TUBERCULOSIS An infectious disease caused by the bacterium Mycobacterium tuberculosis. Commonly affect the lungs but can also affect other parts of the body. Symptoms include: Chronic cough Hemoptysis Fever Night sweats Weight loss It is spread through air via cough, sneeze, speak or spit.

3. DRUGS 1 st line: Isoniazid Rifampicin Ethambutol Pyrazinamide Streptomycin 2 nd line: Para amino salicylic acid Capreomycin Ciprofloxacin Cycloserine Ethionamide Amikacin Rifabutin

4. TUBERCULOSIS Recommended treatment of pulmonary T.B is 6 months of combination of drugs. Intensive phase (2 months): Rifampicin Isoniazid Pyrazinamide Ethambutol Continuation phase (4 months): Isoniazid Rifampin Ethambutol (Optional)

5. ISONIAZID Also known as isonicotinylhydrazide, 4-Pyridinecarboxylic acid hydrazide. Isoniazid was first made in the early 20th century but its activity against tuberculosis was first reported in the early 1950s and was marketed in 1952. It is on the World Health Organization's List of Essential Medicines, a list of medicines that constitute the bare minimum for a basic health system.

6. BRANDS NYDRAZIDE (Wilshire) ISONIAZID (Unexo) FAIRZIDE (Ferro)

7. MECHANISM OF ACTION Inhibits synthesis of mycolic acid which is an essential components of mycobacterial cell wall Isoniazid is a prodrug that is activated by KatG, the mycobacterial catalase-peroxidase. The enzyme inhA, is an NADH-dependent, enoyl (acyl carrier protein) reductase protein thought to be involved in double-bond reduction during fatty acid elongation. Isoniazid has bactericidal effect.

8. SYNTHESIS Step 1: 4-methyl pyridine is oxidized to obtain Iso-nicotinic acid.

9. SYNTHESIS Step 2: Iso-nicotinic acid upon heating with anhydrous hydrazine form Isoniazid

10. S.A.R Pyridine ring is essential for activity. Substitution of R-1, R-2 at N-2 leads to variable activity. Addition of isopropyl group at position R-2 results in loss of anti-tubercular activity but exhibit psychomotor stimulant activity, while acetyl isoniazid is inactive. Any substitution (Alkyl) at R-3 results in loss of activity INH is most active derivative.

11. SIDE EFFECT The most frequent reactions are those affecting the nervous system and the liver. Peripheral neuropathy (Dose related) Prophylaxis Pyridoxine: Adult: 100-200mg/day orally for 3 weeks or 25 to 100 mg/day for prophylaxis. Elevated LFT’s Fatal hepatitis Aplastic anemia. Hypersensitivity reaction Dark urine

12. DOSING Active tuberculosis: Oral Adult: 5 mg/kg/day in combination with other drugs. Children: 10-30mg/kg/day in 2 divided doses Prophylaxis: Oral Adult: 300mg once daily Children: 10mg/kg/day SIDE EFFECT: Peripheral neuritis (Pyridoxine): Adult: 100-200mg/day orally for 3 weeks or 25 to 100 mg/day for prophylaxis.

13. RIFAMPICIN Also known as Rifampin. Rifampicin was discovered in 1957 and first sold as a medication in 1971. It’s a semi-synthetic derivative of Rifamycin B, a macrocyclic antibiotic produced by Streptomyces mediteranei.  It is on the World Health Organization's List of Essential Medicines.

14. BRANDS LEDERRIF (Pfizer) UNERIF (Unexo) RIFACIN (Pharmawise)

15. MECHANISM OF ACTION Rifampin has bactericidal effect. Rifampin binds to bacterial DNA-dependent RNA polymerase and thereby inhibits initiation of RNA chain, hence protein synthesis.

16. SYNTHESIS Rifamycin B is obtained from the fermentation liquid of Streptomyces mediterranei (Amycolatopsis rifamycinica). Rifampicin is then obtained by synthetically modifying Rifamycin B.

17. S.A.R Intact macro cyclic molecule is essential for activity. Saturation of double bonds in macro cyclic ring leads to slightly decreased activity. Free hydroxyl (-OH) group present at C-1, C-8, C-21, C-23 are essential for activity. Substitution of hydroxyl group at C-8, C-21, C-23 leads to loss of activity; except C-1 from hydroxyl to carbonyl.

18. SAR Modification at the C-3, C-4 often yield compounds with improved physicochemical and P.K properties.

19. SIDE EFFECTS Hepatotoxicity Flu like symptoms Red and orange colored urine, saliva etc. Rash

20. DOSING Active Tuberculosis: Oral or I/V: 10mg/kg OD (Max 600mg/day) for 6 months in combination with other drugs. Latent Tuberculosis: Oral or I/V: 10mg/kg OD (Max 600mg/day) for 4 months.

21. PYRAZINAMIDE It is a close analog of isoniazid It is a pro-drug (Pyrazinoic acid). The drug is largely bacteriostatic, but can be bactericidal on actively replicating tuberculosis bacteria. It is on the World Health Organization's List of Essential Medicines.

22. BRANDS PYRAZINAMIDE (Pfizer) PZA CIBA 500 (Novartis) PYRAZID (Schazoo zaka)

23. MECHANISM OF ACTION Susceptible organisms produce pyrazinamidase, which is responsible for conversion of pyrazinamide (Prodrug) to Pyrazinoic acid (Active) intracellularly. The protonated Pyrazinoic acid can permeate the mycobacterial membrane to lower the pH of the cytoplasm, hence disrupting basic chemical processes especially energy production.

24. SYNTHESIS Step 1: o- phenylenediamine when reacted with glyoxal; quinoxaline is formed.

25. SYNTHESIS Step 2: Quinoxaline is then oxidized with potassium permanganate to form pyrazin-2,3-dicarboxylic acid.

26. SYNTHESIS Step 3: pyrazin-2,3-dicarboxylic acid is then decarboxylated by heating to get pyrazin-2-carboxylic acid.

27. SYNTHESIS Step 4: pyrazin-2-carboxylic acid is then esterified in presence of methanol and hydrochloric acid to get acetyl ester of pyrazin-2-carboxylic acid.

28. SYNTHESIS Step 5: acetyl ester of pyrazin-2-carboxylic acid is then treated with ammonia to get pyrazinamide.

29. S.A.R The best side chain is amide. Another potential side chain is ester which is activated by bacterial esterase. Nitrogen (Pyrazinoyl) at P-2 is essential for maximum activity. Substitution of “N” with “C” (Nicotinoyl) leads to decreased activity. Any other substitution in the ring will lead to loss of activity.

30. SIDE EFFECTS Arthralgia, Myalgia Gout Hepatotoxicity (Dose related) Rash

31. DOSING Active Tuberculosis: Oral: 15 to 30 mg/kg (Max 2g/day) OD in combination with other drugs. Latent Tuberculosis: Oral: 15 to 20 mg/kg (Max 2g/day) OD for 2 months

32. ETHAMBUTOL Ethambutol was discovered in 1961. It possesses bacteriostatic action against Mycobacterium tuberculosis. Its (+) enantiomer is used as it is more effective. It is on the World Health Organization's List of Essential Medicines.

33. BRANDS MYAMBUTOL (Pfizer) TUBERCURE (Lowitt) ABBUTOL (Abbott)

34. MECHANISM OF ACTION Ethambutol is bacteriostatic against actively growing TB bacilli. It disrupts arabinogalactan (Polymer) synthesis by inhibiting the enzyme arabinosyl transferase leads to increased permeability of the cell wall.

35. SYNTHESIS Step 1: Nitropropane undergoes hydroxymethylation when treated with Formaldehyde to form 2-nitrobutanol.

36. SYNTHESIS Step 2: 2-nitrobutanol is then reduced in presence of Raney’s nickel and hydrogen to form 2-aminobutanol.

37. SYNTHESIS Step 3: (+) 2-aminobutanol is then treated with 2-dichloroethane in presence of sodium hydroxide gives Ethambutol

38. S.A.R Increase in ethylene diamine chain length leads to loss of activity. Replacement of either of the amino group leads to loss of activity. Removal of alcohol groups leads to loss of activity. Substitution of hydroxyl groups with methoxy, ethoxy retains activity but with aromatic group (Phenyl, Pyridine) leads to loss of activity. Increasing the size of N-substituent lead to loss of activity.

39. SIDE EFFECTS Optic neuritis (C.I in children below 6 years) Red-green color blindness Peripheral neuropathy Hyperuricemia

40. DOSING Active Tuberculosis: Oral: 15 mg/kg OD for 2 months in combination with other drugs.

41. BRANDS (Multi ingredient) MYRIN (Pfizer): Isoniazid, Rifampicin, Ethambutol MYRIN-P (Pfizer): Isoniazid, Rifampicin, Ethambutol, Pyrazinamide RIMACTAL-INH (Novartis): Isoniazid, Rifampicin RIFAPIN-H (Schazoo zaka): Isoniazid, Rifampicin

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