We Have Some Trouble with Special Characters and Displaying Monographs

We have some trouble with special characters and displaying monographs. 22.09.2018

ATC code: N06AA09 Classification: PNP - Probably not porphyrinogenic Substance: Amitriptyline Rationale for risk classification: Amitriptylin does not inhibit or induce CYP2C9. It is not listed as an inhibitor or inducer of any major CYP enzymes in vivo. Risk for gastrointestinal adverse events in the form of obstipation and nausea motivates vigilance against insufficient intake of food, especially of carbohydrate. Amitriptylin is metabolised to nortriptylin, which is classified as Probably not porphyrinogenic (PNP). For more information please refer to the monograph of nortriptylin (ATC code: N06A A10). Therapeutic characteristics: Amitriptyline is indicated for the treatment of depression and chronic pain. Very common side effects that can be potentially porphyrinogenic through reduction in carbohydrate intake and that also can be confused with an acute porphyria attack are obstipation and nausea. Another very common side effect is tachycardia. A common side effect is fatigue. Metabolism and pharmacokinetics: Amitriptyline is metabolised by CYP2D6 (Hisaka 2010 and SPC) to nortriptyline, E-10-hydroxyamitriptyline and E-10-hydroxynortriptyline (Zhou 2009). CYP3A4 (Gharahmani 1997 and Zhou 2009), CYP2C9, CYP1A2 (Flockhart 2007 and Zhou 2009) and CYP2C19 (Pelkonen 2008 and Zhou 2009) are listed in addition to CYP2D6, to contribute to the metabolism of amitriptyline (Zhou 2009). In vivo studies have shown that CYP3A plays a relatively minor role in amitriptyline clearance (Venkatakrishnan 2001). Co-administration of amitriptyline with two CYP2C9 substrates, warfarin and tolbutamide, showed that amitriptyline had no effect on the plasma half-lives of the substrates (Pond 1975). This indicates that amitriptyline does not inhibit or induce CYP2C9.

Copyright 2007-2018 The Drug Database. All rights reserved.Page 1/3 Tricyclic antidepressants, which include amitriptyline, does appear to have minimal potential for mechanism-based inhibition of human liver microsomal CYP enzymes involved in drug metabolism (Polasek 2008). Amitriptyline also demonstrated no response in an hPXR transactivation assay (Sinz 2006). It is listed as a weak inhibitor of CYP2C19 in vivo. It is however, not listed as an inhibitor or inducer of any major CYP enzymes in vivo (Isoherranen 2009). No drug-drug interactions with amitriptyline as a perpetrator regarding CYP enzymes are observed (Interaksjoner and Interaktionsdatabasen), which indicate that amitriptyline is not an inhibitor or inducer of CYP enzymes in vivo. Summary of other guidance on prescribing (porphyria drug lists): European Porphyria Network: not listed. Porphyria South Africa: use only with extreme caution and if no alternative. Personal communications: Thunell, patient inquiry: tolerated. (n=1) Published clinical experience: There are conflicting experiences on whether amitriptyline is safe or not. Amitriptyline is listed as unsafe for patients with acute porphyria (Moore 1997, 2000). Amitriptyline is listed as safe for patients with acute porphyria (Eales 1979). EPNET drug reports: Uneventful use reported in 12 patients with acute porphyria. One report of the worsening of an attack leading to hospitalisation of a previously undiagnosed female AIP patient, but the patient was also exposed to other probably porphyrinogenic drugs and other factors that could have contributed to the attack. References: Disler PB, Blekkenhorst GH, et al. Guidelines for drug prescription in patients with the acute porphyrias. S Afr Med J. 1982 May 1;61(18):656-60. Eales L. Porphyria and the dangerous life-threatening drugs. S Afr Med J. 1979 Nov 24;56(22):914-7. Flockhart DA. Drug Interactions: Cytochrome P450 Drug Interaction Table. Indiana University School of Medicine (2007). http://medicine.iupui.edu/clinpharm/ddis/table.aspx. Accessed 19.09.2013 Ghahramani P, Ellis SW,et al. Cytochromes P450 mediating the N-demethylation of amitriptyline. Br J Clin Pharmacol. 1997 Feb;43(2):137-44. Hisaka A, Ohno Y, et al. Prediction of pharmacokinetic drug-drug interaction caused by changes in

Copyright 2007-2018 The Drug Database. All rights reserved.Page 2/3 cytochrome P450 activity using in vivo information. Pharmacol Ther. 2010 Feb;125(2):230-48. Interaksjoner. Available from: http://www.interaksjoner.no amitriptylin. Accessed: 27.09.2013 Interaktionsdatabasen. Available from: http://www.interaktionsdatabasen.dk amitriptylin. Accessed: 27.09.2013 Isoherranen N, Hachad H, et al. Qualitative analysis of the role of metabolites in inhibitory drug-drug interactions: literature evaluation based on the metabolism and transport drug interaction database. Chem Res Toxicol. 2009 Feb;22(2):294-8. Moore AW 3rd, Coke JM. Acute porphyric disorders. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2000 Sep;90(3):257-62. Moore MR, Hift RJ. Drugs in the acute porphyrias--toxicogenetic diseases. Cell Mol Biol (Noisy-le-grand). 1997 Feb;43(1):89-94. Norwegian medicines agency. Summary of Product Characteristics (SPC). Amitriptyline. http://www.legemiddelverket.no/ Last edition: 26.07.2010 Pelkonen O, Turpeinen M, et al. Inhibition and induction of human cytochrome P450 enzymes: current status. Arch Toxicol. 2008 Oct;82(10):667-715. Polasek TM, Miners JO. Time-dependent inhibition of human drug metabolizing cytochromes P450 by tricyclic antidepressants. Br J Clin Pharmacol. 2008 Jan;65(1):87-97. Pond SM, Graham GG, et al. Effects of tricyclic antidepressants on drug metabolism. Clin Pharmacol Ther. 1975 Aug;18(2):191-9. Sinz M, Kim S, et al. Evaluation of 170 xenobiotics as transactivators of human pregnane X receptor (hPXR) and correlation to known CYP3A4 drug interactions. Curr Drug Metab. 2006 May;7(4):375-88. Venkatakrishnan K, Schmider J, et al. Relative contribution of CYP3A to amitriptyline clearance in humans: in vitro and in vivo studies. J Clin Pharmacol. 2001 Oct;41(10):1043-54. Zhou SF, Zhou ZW, et al. Substrates, inducers, inhibitors and structure-activity relationships of human Cytochrome P450 2C9 and implications in drug development. Curr Med Chem. 2009;16(27):3480-675.