A Canadian perspective on the revised 2020 ASHP-IDSA-PIDS-SIDP guidelines for vancomycin AUC-based therapeutic drug monitoring for serious MRSA infections.

Background: A revised consensus guideline on therapeutic drug monitoring (TDM) of vancomycin for serious methicillin-resistant Staphylococcus aureus (MRSA) infections was recently published with endorsement of numerous American pharmacy and medical societies. Changing practice from trough TDM to area-under-the-curve-(AUC)-guided dosing was suggested. Methods: Recent literature was critically appraised to determine whether AUC TDM is appropriate for Canadian hospital practice. Results: Previous 2009 vancomycin consensus guidelines recommended trough levels of 15-20 mg/L for serious MRSA infections, based on relatively poor evidence for efficacy or safety. In the past decade, aggressive trough targets have led to unnecessary toxicity. Adoption of a TDM strategy using an alternative parameter (AUC) has been suggested, although the evidence for any outcome benefits is low quality. In addition, implementation would require greater resources at health care institutions in the forms of more frequent serum levels or acquisition of costly Bayesian software programs. Most studies on this subject have been observational and retrospective; therefore, relationships between TDM parameters and outcomes have not been convincingly and consistently demonstrated to be causal in nature. Despite claims to the contrary, based on few in silico experiments, available clinical data suggest correlation of trough levels and AUC is high. TDM with lower target trough levels is a simpler solution to reduce risk of toxicity. Conclusions: There are serious concerns with adoption of AUC TDM of vancomycin into routine practice in Canada. Trough-based monitoring with modest reduction in target levels remains the most evidence-informed practice at this time.

Historique: De nombreuses sociétés pharmaceutiques et médicales américaines ont récemment publié et avalisé des lignes directrices consensuelles révisées sur le suivi thérapeutique pharmacologique (STP) de la vancomycine en cas de graves infections par le Staphylococcus aureus résistant à la méthicilline (SARM). Ces lignes directrices préconisent de passer de la STP des creux à une posologie déterminée par l'aire sous la courbe (ASC). Méthodologie: Les chercheurs ont procédé à une évaluation critique des publications récentes pour déterminer si la STP selon l'ASC est adaptée à la pratique hospitalière au Canada. Résultats: Les lignes directrices consensuelles de 2009 sur la vancomycine recommandaient un creux de 15 mg/L à 20 mg/L en cas d'infection grave par le SARM, en fonction de données probantes d'efficacité et d'innocuité relativement faibles. Depuis dix ans, des creux cibles trop ambitieux ont été responsables de toxicités inutiles. Il est proposé de revoir la stratégie du STP d'après un autre paramètre (l'ASC), même si les données probantes en démontrant les bienfaits sont de faible qualité. De plus, sa mise en œuvre exigerait des ressources plus importantes dans les établissements de santé, soit le dosage plus fréquent des concentrations plasmatiques ou l'acquisition de logiciels bayésiens coûteux. La plupart des articles sur le sujet sont des études d'observation et des études rétrospectives. Par conséquent, la nature causale des relations entre les paramètres et les résultats du STP n'a pas été démontrée de manière convaincante ni systématique. Malgré les prétentions contraires, selon quelques expériences in silico, les données cliniques disponibles font foi d'une corrélation élevée entre les concentrations minimales et l'ASC. Il serait plus simple d'assurer le STP par des concentrations minimales cibles plus basses pour réduire le taux de toxicité. Conclusions: L'adoption du STP de la vancomycine selon l'ASC dans la pratique quotidienne soulève de vives préoccupations au Canada. Pour l'instant, la surveillance des creux assortie à de modestes réductions des concentrations cibles demeure la pratique la plus respectueuse des données probantes.

Serotonergic and adrenergic drug interactions associated with linezolid: a critical review and practical management approach.

OBJECTIVE: To describe the evidence for serotonergic and adrenergic drug interactions with linezolid and discuss clinical management strategies. DATA SOURCES: A literature search of PubMed (1947-November 2012), MEDLINE (1946-November 2012), EMBASE (1974-November 2012), and International Pharmaceutical Abstracts (1970-November 2012) was conducted using the terms linezolid, drug interaction, serotonin syndrome, serotonin toxicity, sympathomimetic, serotonergic agents, and adrenergic agents. Citations of retrieved articles were also reviewed. STUDY SELECTION AND DATA EXTRACTION: English-language articles describing coadministration of serotonergic or adrenergic agents with linezolid to humans were included. Studies published only in abstract form were excluded. DATA SYNTHESIS: One prospective study, 6 retrospective studies, and 24 case reports were identified describing a serotonergic or adrenergic drug interaction. Incidence of serotonin syndrome in patients on linezolid and serotonergic agents ranged between 0.24% and 4%. Serotonergic agents determined to have probable (according to the Horn Drug Interaction Probability Scale) linezolid interactions in case reports included meperidine, citalopram, escitalopram, fluoxetine, paroxetine, sertraline, duloxetine, and venlafaxine. Serotonergic agent dose and duration of coadministration with linezolid did not appear to influence the occurrence of serotonin syndrome. Adrenergic medication coadministration was associated with a possible drug interaction as determined by the Horn Drug Interaction Probability Scale but did not appear to result in clinically significant drug interactions with linezolid. CONCLUSIONS: Linezolid-associated serotonergic drug interactions occur more commonly than adrenergic interactions. Serotonergic interactions considered probable according to the Horn Drug Interaction Probability Scale do not appear to correlate with drug dosage; time of onset ranges from <1 to 20 days, and effect resolves in <1 to 5 days after discontinuation of offending agents. If coadministration of linezolid and a serotonergic agent cannot be avoided, clinicians should be aware of the symptoms and management of serotonergic toxicity; close monitoring is recommended and additional serotonergic agents should not be used. While adrenergic drug interactions with linezolid are less common in clinical practice, monitoring for signs of hypertension remains important.