Pyrazinamide: Wikis

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Pyrazinamide
Systematic (IUPAC) name
pyrazine-2-carboxamide
Identifiers
CAS number 98-96-4
ATC code J04AK01
PubChem 1046
DrugBank APRD01206
ChemSpider 1017
Chemical data
Formula C5H5N3O 
Mol. mass 123.113 g/mol
Pharmacokinetic data
Bioavailability >90%
Metabolism Hepatic
Half life 9 to 10 hours
Excretion Renal
Therapeutic considerations
Pregnancy cat. C
Legal status  ?
Routes Oral
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Pyrazinamide is a drug used to treat tuberculosis. The drug is largely bacteriostatic, but can be bacteriocidal on actively replicating tuberculosis bacteria.

Contents

Abbreviations

The abbreviations PZA and Z are standard, and used commonly in the medical literature.

Dosing and presentation

  • 20–25 mg/kg daily, or
  • 50–70 mg/kg three times a week.

The British Thoracic Society guidelines are for 1.5 g daily for patients weighing less than 50 kg, and 2 g daily for patients weighing 50 kg or more.

Pyrazinamide is a generic drug and is available in a wide variety of presentations. Pyrazinamide tablets are usually 500 mg and form the bulkiest part of the standard tuberculosis treatment regimen. Pyrazinamide tablets are so large that some patients find them impossible to swallow: pyrazinamide syrup is an option for these patients.

Pyrazinamide is also available as part of fixed dose combinations with other TB drugs such as isoniazid and rifampicin (Rifater is an example).

Pharmacokinetics

Pyrazinamide is well absorbed orally. It crosses inflamed meninges and is an essential part of the treatment of tuberculous meningitis. It is metabolised by the liver and the metabolic products are excreted by the kidneys.

Pyrazinamide is routinely used in pregnancy in the UK and the rest of the world; the WHO recommend its use in pregnancy; and there is extensive clinical experience to show that it is safe. In the U.S., pyrazinamide is not used in pregnancy, citing insufficient evidence of safety.[1] Pyrazinamide is removed by haemodialysis and therefore doses should always be given at the end of a dialysis session.

Medical uses

Pyrazinamide is only used in combination with other drugs such as isoniazid and rifampicin in the treatment of Mycobacterium tuberculosis. It is never used on its own. It has no other indicated medical uses. In particular, it is not used to treat other mycobacteria; Mycobacterium bovis and Mycobacterium leprae are innately resistant to pyrazinamide. Pyrazinamide is used in the first two months of treatment to reduce the duration of treatment required.[2] Regimens not containing pyrazinamide must be taken for nine months or more.

Pyrazinamide in conjunction with rifampin is a preferred treatment for latent tuberculosis.[3]

Pyrazinamide is a potent antiuricosuric drug[4] and consequently has an off-label use in the diagnosis of causes of hyperuricemia and hyperuricosuria.[5] It acts on URAT1.[5]

Mechanism of action

Pyrazinamide is a prodrug that stops the growth of Mycobacterium tuberculosis.

M. tuberculosis has the enzyme pyrazinamidase which is only active in acidic conditions.[6] Pyrazinamidase converts pyrazinamide to the active form, pyrazinoic acid which accumulates in the bacilli. Pyrazinoic acid was thought to inhibit the enzyme fatty acid synthetase I, which is required by the bacterium to synthesise fatty acids[7] although this has been discounted.[8] It was also suggested that the accumulation of pyrazinoic acid disrupts membrane potential and interferes with energy production, necessary for survival of M. tuberculosis at an acidic site of infection. Further studies reproduced the results of FAS I inhibition as the putative mechanism first in whole cell assay of replicating M. tuberculosis bacilli which have shown that pyrazinoic acid and it's ester inhibit the synthesis of fatty acids.[9] This study was followed by in vitro assay of tuberculous FAS I enzyme that tested the activity with pyrazniamide, pyrazinoic acid and several classes of pyrazinamide analogs. Pyrazinamide and it's analogs tested inhibited the activity of purified FAS I.[10] Mutations of the pyrazinamidase gene (pncA) are responsible for pyrazinamide resistance in M. tuberculosis.[11]

Side effects

The most common (approximately 1%) side effect of pyrazinamide is joint pains (arthralgia), but this is not usually so severe that patients need to stop taking the pyrazinamide.[12][13] The arthralgia can be distressing to patients, but is never harmful.[citation needed]

The most dangerous side effect of pyrazinamide is hepatotoxicity, which is dose related. The old dose for pyrazinamide was 40–70 mg/kg daily and the incidence of drug-induced hepatitis has fallen significantly since the recommended dose has been reduced. In the standard four-drug regimen (isoniazid, rifampicin, pyrazinamide, ethambutol), pyrazinamide is the most common cause of drug-induced hepatitis.[14] It is not possible to clinically distinguish pyrazinamide-induced hepatitis from hepatitis caused by isoniazid or rifampicin; test dosing is required (this is discussed in detail in tuberculosis treatment)

Other side effects include nausea and vomiting, anorexia, sideroblastic anemia, skin rash, urticaria, pruritus, hyperuricemia, dysuria, interstitial nephritis, malaise; rarely porphyria, and fever.

Wikipedia articles

References

  1. ^ American Thoracic Society, Centers for Disease Control, Infectious Diseases Society of America (2003). "Treatment of Tuberculosis". Am J Respir Crit Care Med 167 (602–662). 
  2. ^ Hong Kong Chest Service, Medical Research Council. "Controlled trial of four thrice weekly regimens and a daily regimen given for 6 months for pulmonary tuberculosis". Lancet 1 (8213): 171–4. PMID 6109855. 
  3. ^ Centers for Disease Control and Prevention. "Targeted tuberculin testing and treatment of latent tuberculosis infection". MMWR 49 (No. RR-6): 31–32. 
  4. ^ Spaia S, Magoula I, Tsapas G, Vayonas G (2000). "Effect of pyrazinamide and probenecid on peritoneal urate transport kinetics during continuous ambulatory peritoneal dialysis". Perit Dial Int 20 (1): 47–52. PMID 10716583. http://www.pdiconnect.com/cgi/pmidlookup?view=long&pmid=10716583. 
  5. ^ a b Ichida K, Hosoyamada M, Hisatome I, Enomoto A, Hikita M, Endou H, Hosoya T (January 2004). "Clinical and molecular analysis of patients with renal hypouricemia in Japan-influence of URAT1 gene on urinary urate excretion". J. Am. Soc. Nephrol. 15 (1): 164–73. doi:10.1097/01.ASN.0000105320.04395.D0. PMID 14694169. http://jasn.asnjournals.org/cgi/pmidlookup?view=long&pmid=14694169. 
  6. ^ Zhang Y, Mitchison D (January 2003). "The curious characteristics of pyrazinamide: a review". Int. J. Tuberc. Lung Dis. 7 (1): 6–21. PMID 12701830. http://openurl.ingenta.com/content/nlm?genre=article&issn=1027-3719&volume=7&issue=1&spage=6&aulast=Zhang. 
  7. ^ Zimhony O, Cox JS, Welch JT, Vilchèze C, Jacobs WR (2000). "Pyrazinamide inhibits the eukaryotic-like fatty acid synthetase I (FASI) of Mycobacterium tuberculosis" (abstract). Nature Medicine 6 (9): 1043–47. doi:10.1038/79558. PMID 10973326. http://www.nature.com/nm/journal/v6/n9/abs/nm0900_1043.html;jsessionid=AFEEF16483CA23196C7729EBE644297C. 
  8. ^ Boshoff HI, Mizrahi V, Barry CE (2002). "Effects of Pyrazinamide on Fatty Acid Synthesis by Whole Mycobacterial Cells and Purified Fatty Acid Synthase I". Journal of Bacteriology 184 (8): 2167-72. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC134955/. 
  9. ^ Zimhony O, Vilcheze C, Arai M, Welch J, Jacobs WR pi. Pyrazinoic acid and its n'Propyl Ester Inhibit Fatty Acid Synthase I in Replicating Tubercle Bacilli. Antimicrob Agents Chemother. 2007 51 752-754
  10. ^ Ngo SC., Zimhony O, Chung WJ Sayahi, H, Jacobs WR. and JT. Welchpi. Inhibition of Isolated Mycobacterium tuberculosis Fatty Acid Synthase I by Pyrazinamide Analogs. Antimicrob Agents Chemother AntimicrobAgents Chemother. 2007; 1 2430-5
  11. ^ Scorpio A, Zhang Y (1996). "Mutations in pncA, a gene encoding pyrazinamidase/nicotinamidase, cause resistance to the antituberculous drug pyrazinamide in tubercle bacillus". Nature Medicine 2: 662–7. doi:10.1038/nm0696-662. PMID 8640557. 
  12. ^ East and Central African/Medical Research Council Fifth Collaborative Study (1983). "Controlled clinical trial of 4 short-course regimens of chemotherapy (three 6-month and one 9-month) for pulmonary tuberculosis". Tubercle 64: 153–166. doi:10.1016/0041-3879(83)90011-9. PMID 6356538. 
  13. ^ British Thoracic Society (1984). "A controlled trial of 6 months chemotherapy in pulmonary tuberculosis, final report: results during the 36 months after the end of chemotherapy and beyond". Br J Dis Chest 78 (4): 330–336. PMID 6386028. 
  14. ^ Yee D et al. (2003). "Incidence of serious side effects from first-line antituberculosis drugs among patients treated for active tuberculosis". Am J Resp Crit Care Med 167 (11): 1472–7. doi:10.1164/rccm.200206-626OC. PMID 12569078. http://ajrccm.atsjournals.org/cgi/content/full/167/11/1472. 
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