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In general, the intraventricular administration of cytotoxic antitumor drugs provides a high drug concentration in the cerebrospinal fluid with a reduced risk of systemic adverse reactions. Methotrexate (MTX) high-dose therapy requires close monitoring when performed in combination with trimethoprim-sulfamethoxazole (ST) therapy and proton pump inhibitor (PPI) and nonsteroidal anti-inflammatory drug administration for excretion delay and toxicity enhancement. While the frequency of systemic side effects is thought to be low with intrathecal administration, such effects do rarely but occasionally occur. We must consider drug interactions with combination therapy as a potential factor inducing such effects. We examined the patients who received MTX intrathecal administration at Fukuoka University Hospital from January 2013 to December 2014 with respect to the onset of side effects and combination therapy. MTX intrathecal administration was performed a total of 79 times in 27 patients. In five of these 27 patients, MTX intrathecal administration was performed twice a week, and hematotoxicity and non-hematotoxicity developed in two patients in whom ST was also administered. On the other hand, even if ST and/or PPI was administered, no side effects were observed in the patients administered levofolinate.

Warfarin (WF) shows a number of interactions with other drugs, which alter its anticoagulant effects. The albumin binding interaction is one such pharmacokinetic mechanism of drug interaction with WF, which induces a rise in the free WF concentration and thus increases the risk of WF toxicity. Teicoplanin (TEIC) is an anti-methicillin-resistant Staphylococcus aureus drug, which also binds strongly to albumin in the plasma. Therefore, co-administration of TEIC may displace WF from the albumin binding site, and possibly result in a toxicity. The present study was performed to investigate the drug-drug interaction between WF and TEIC in comparison with controls treated with vancomycin (VCM), which has the same spectrum of activity as TEIC but a lower albumin binding ratio.The records of 49 patients treated with WF and TEIC or VCM at Fukuoka University Hospital between 2010 and 2015 were retrospectively reviewed. These 49 patients consisted of 18 treated with TEIC in combination with WF, while 31 received VCM in combination with WF. Prothrombin time-international normalized ratio (PT-INR) showed a significant increase of 80.9 (52.0-155.3) % after co-administration of TEIC with WF. In contrast, the rate of PT-INR elevation associated with VCM plus WF was 30.6 (4.5-44.1) %. These observations suggested that TEIC can cause a rise in free WF concentration by albumin binding interaction. Therefore, careful monitoring of PT-INR elevation is necessary in patients receiving WF plus TEIC.

BACKGROUND Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome is a potentially life-threatening syndrome comprising severe skin eruption, fever, eosinophilia, lymphadenopathy, and involvement of internal organs. Here, we describe a case of DRESS syndrome caused by cross-reactivity between vancomycin and subsequent teicoplanin administration. CASE REPORT A 79-year-old male was admitted to our hospital for the treatment of injuries incurred in a traffic accident. Eosinophilia and lung dysfunction appeared after vancomycin administration. These symptoms were improved temporarily by withdrawal of vancomycin and administration of corticosteroid, but exacerbated by subsequent teicoplanin administration. These symptoms disappeared after discontinuation of teicoplanin. Based on comprehensive assessment of the overall clinical course, we judged that DRESS syndrome was induced by cross-reactivity between vancomycin and subsequent teicoplanin administration. Using the European Registry of Severe Cutaneous Adverse Reactions (RegiSCAR) scoring system, we categorized DRESS syndrome related to vancomycin and teicoplanin as "probable." We describe, for the first time, DRESS syndrome (defined using the RegiSCAR scoring system) caused by cross-reactivity between vancomycin and subsequent teicoplanin administration. CONCLUSIONS Clinicians should be aware that DRESS syndrome can be induced by cross-reactivity between vancomycin and teicoplanin.