RESUMO
Safe use of tacrolimus relies on regular whole-blood drug monitoring. Of the methods used to assess whole-blood tacrolimus concentration, antibody-conjugated magnetic immunoassay is mostly used for therapeutic drug monitoring because it requires only a minimal sample preparation and no pretreatment procedure. However, several cases recently have been reported in which abnormally false elevated tacrolimus concentrations were measured by antibody-conjugated magnetic immunoassay (>15 ng/mL), despite the absence of clinical symptoms. We present 2 cases of falsely detected tacrolimus concentrations that did not show abnormally high values within the therapeutic range. Whole-blood tacrolimus concentrations obtained by antibody-conjugated magnetic immunoassay showed well-controlled concentrations (approximately 2-8 ng/mL), whereas those obtained by another immunoassay and in washed erythrocytes were below the assay range (< 1.2 ng/mL). Thus, antibody-conjugated magnetic immunoassay can elicit falsely positive results of tacrolimus concentrations, even though they are within the therapeutic range.
Assuntos
Monitoramento de Medicamentos/métodos , Imunoensaio/métodos , Imunossupressores/sangue , Transplante de Fígado , Magnetismo/métodos , Tacrolimo/sangue , Idoso , Reações Falso-Positivas , Feminino , Humanos , Imunossupressores/administração & dosagem , Pessoa de Meia-Idade , Valor Preditivo dos Testes , Reprodutibilidade dos Testes , Tacrolimo/administração & dosagem , Fatores de Tempo , Resultado do TratamentoRESUMO
The optimal dosage of linezolid to avoid hematologic toxicity is unknown. We report the case of an 87-y-old woman with renal insufficiency who developed a surgical site infection with refractory methicillin-resistant Staphylococcus aureus. The standard dosage of linezolid (1200 mg daily) was not initially tolerated by the patient due to severe thrombocytopenia, but she was successfully treated when the dose was reduced by half (600 mg daily) based on a population pharmacokinetic-pharmacodynamic model. Appropriate dose adjustments can be made to optimize linezolid therapy especially in cases with preexisting renal dysfunction.