Editing Phenytoin (section)

===Skin===
[[Hypertrichosis]], [[Stevens–Johnson syndrome]], [[purple glove syndrome]], rash, [[exfoliative dermatitis]], [[pruritis|itching]], [[hirsutism|excessive hairiness]], and coarsening of facial features can be seen in those taking phenytoin.

Phenytoin therapy has been linked to the life-threatening skin reactions [[Stevens–Johnson syndrome]] (SJS) and [[toxic epidermal necrolysis]] (TEN). These conditions are significantly more common in patients with a particular [[HLA-B]] [[allele]], [[HLA-B75|HLA-B*1502]].<ref name="pmid17509004">{{cite journal | vauthors = Man CB, Kwan P, Baum L, Yu E, Lau KM, Cheng AS, Ng MH | title = Association between HLA-B*1502 allele and antiepileptic drug-induced cutaneous reactions in Han Chinese | journal = Epilepsia | volume = 48 | issue = 5 | pages = 1015–1018 | date = May 2007 | pmid = 17509004 | doi = 10.1111/j.1528-1167.2007.01022.x | s2cid = 34728720 | doi-access = free }}</ref> This allele occurs almost exclusively in patients with ancestry across broad areas of Asia, including South Asian Indians.

Phenytoin is primarily metabolized to its inactive form by the enzyme [[CYP2C9]]. Variations within the CYP2C9 gene that result in decreased enzymatic activity have been associated with increased phenytoin concentrations, as well as reports of drug toxicities due to these increased concentrations.<ref>{{cite journal | vauthors = Caudle KE, Rettie AE, Whirl-Carrillo M, Smith LH, Mintzer S, Lee MT, Klein TE, Callaghan JT | title = Clinical pharmacogenetics implementation consortium guidelines for CYP2C9 and HLA-B genotypes and phenytoin dosing | journal = Clinical Pharmacology and Therapeutics | volume = 96 | issue = 5 | pages = 542–548 | date = November 2014 | pmid = 25099164 | pmc = 4206662 | doi = 10.1038/clpt.2014.159 }}</ref> The [[U.S. Food and Drug Administration]] (FDA) notes on the phenytoin drug label that since strong evidence exists linking HLA-B*1502 with the risk of developing SJS or TEN in patients taking [[carbamazepine]], consideration should be given to avoiding phenytoin as an alternative to carbamazepine in patients carrying this allele.<ref>{{cite web|title=DILANTIN- phenytoin sodium capsule, extended release|url=http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8848de76-8d74-4620-bcc7-a86a596e5dd9|access-date=12 March 2015|url-status=live|archive-url=https://web.archive.org/web/20150402175051/http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8848de76-8d74-4620-bcc7-a86a596e5dd9|archive-date=2 April 2015}}</ref>