Variations in the Blood Phenytoin Levels during Long-Term Combined Treatment with S-1 and Phenytoin
Although combination therapy with the oral fluoropyrimidine anticancer drug S-1 and the anticonvulsant phenytoin (PHT) is known to increase blood levels of PHT and the risk of intoxication, reports on long-term monitoring of blood levels of PHT during combined S-1 and PHT treatment and a thorough un...
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doaj-f75f7e887b0e42cfaf622d6f033fd23b2020-11-24T23:04:28ZengKarger PublishersCase Reports in Oncology1662-65752014-09-017365666110.1159/000368077368077Variations in the Blood Phenytoin Levels during Long-Term Combined Treatment with S-1 and PhenytoinYutaka NegoroTakashi HigashiHiroaki MatsuokaKyohei WatanabeToshiaki IgarashiYuichiro KayanoRyoichi YanoToshiaki NakamuraMikio MasadaAlthough combination therapy with the oral fluoropyrimidine anticancer drug S-1 and the anticonvulsant phenytoin (PHT) is known to increase blood levels of PHT and the risk of intoxication, reports on long-term monitoring of blood levels of PHT during combined S-1 and PHT treatment and a thorough understanding of their interaction are lacking. This report aims to describe interactive effects of S-1 and PHT through long-term therapeutic drug monitoring of PHT. A 72-year-old male had been prescribed oral PHT (130 mg/day) for over 20 years and started receiving S-1 therapy (80 mg/day for 4 weeks, followed by a 2-week rest) as postoperative adjuvant chemotherapy for gastric cancer. The blood PHT level was continuously monitored. Prior to receiving S-1, the patient's blood PHT concentration was 6.0 μg/ml, but it increased during S-1 therapy, reaching 22.9 μg/ml on day 84 (during a rest period of second cycle S-1 therapy). After reducing his PHT dosage to 100 mg/day, it never reached toxic levels (4.0-10.4 μg/ml). It was difficult to keep blood PHT concentrations constant because of the time lag between the period of combined use of S-1 and PHT and the timing of manifestation and disappearance of the drug interaction. The DIPS probability scale indicated a highly probable interaction between S-1 and PHT. We conclude that, when S-1 and PHT are used concurrently, occurrence and disappearance time of their interaction need to be predicted to maintain an effective and safe PHT concentration.http://www.karger.com/Article/FullText/368077S-1PhenytoinDrug interactionTherapeutic drug monitoring |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Yutaka Negoro Takashi Higashi Hiroaki Matsuoka Kyohei Watanabe Toshiaki Igarashi Yuichiro Kayano Ryoichi Yano Toshiaki Nakamura Mikio Masada |
spellingShingle |
Yutaka Negoro Takashi Higashi Hiroaki Matsuoka Kyohei Watanabe Toshiaki Igarashi Yuichiro Kayano Ryoichi Yano Toshiaki Nakamura Mikio Masada Variations in the Blood Phenytoin Levels during Long-Term Combined Treatment with S-1 and Phenytoin Case Reports in Oncology S-1 Phenytoin Drug interaction Therapeutic drug monitoring |
author_facet |
Yutaka Negoro Takashi Higashi Hiroaki Matsuoka Kyohei Watanabe Toshiaki Igarashi Yuichiro Kayano Ryoichi Yano Toshiaki Nakamura Mikio Masada |
author_sort |
Yutaka Negoro |
title |
Variations in the Blood Phenytoin Levels during Long-Term Combined Treatment with S-1 and Phenytoin |
title_short |
Variations in the Blood Phenytoin Levels during Long-Term Combined Treatment with S-1 and Phenytoin |
title_full |
Variations in the Blood Phenytoin Levels during Long-Term Combined Treatment with S-1 and Phenytoin |
title_fullStr |
Variations in the Blood Phenytoin Levels during Long-Term Combined Treatment with S-1 and Phenytoin |
title_full_unstemmed |
Variations in the Blood Phenytoin Levels during Long-Term Combined Treatment with S-1 and Phenytoin |
title_sort |
variations in the blood phenytoin levels during long-term combined treatment with s-1 and phenytoin |
publisher |
Karger Publishers |
series |
Case Reports in Oncology |
issn |
1662-6575 |
publishDate |
2014-09-01 |
description |
Although combination therapy with the oral fluoropyrimidine anticancer drug S-1 and the anticonvulsant phenytoin (PHT) is known to increase blood levels of PHT and the risk of intoxication, reports on long-term monitoring of blood levels of PHT during combined S-1 and PHT treatment and a thorough understanding of their interaction are lacking. This report aims to describe interactive effects of S-1 and PHT through long-term therapeutic drug monitoring of PHT. A 72-year-old male had been prescribed oral PHT (130 mg/day) for over 20 years and started receiving S-1 therapy (80 mg/day for 4 weeks, followed by a 2-week rest) as postoperative adjuvant chemotherapy for gastric cancer. The blood PHT level was continuously monitored. Prior to receiving S-1, the patient's blood PHT concentration was 6.0 μg/ml, but it increased during S-1 therapy, reaching 22.9 μg/ml on day 84 (during a rest period of second cycle S-1 therapy). After reducing his PHT dosage to 100 mg/day, it never reached toxic levels (4.0-10.4 μg/ml). It was difficult to keep blood PHT concentrations constant because of the time lag between the period of combined use of S-1 and PHT and the timing of manifestation and disappearance of the drug interaction. The DIPS probability scale indicated a highly probable interaction between S-1 and PHT. We conclude that, when S-1 and PHT are used concurrently, occurrence and disappearance time of their interaction need to be predicted to maintain an effective and safe PHT concentration. |
topic |
S-1 Phenytoin Drug interaction Therapeutic drug monitoring |
url |
http://www.karger.com/Article/FullText/368077 |
work_keys_str_mv |
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