Assay of unbound teicoplanin in human plasma by centrifugal ultrafiltration combined with ultra performance liquid chromatography-tandem mass spectrometry / 药学实践杂志

Objective To establish an assay method for unbound teicoplanin in plasma by centrifugal ultrafiltration combined with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Methods Protein was removed from plasma by a Centrifree® ultrafiltration device. The ultrafiltrate was injected to determine the unbound concentration of teicoplanin. EndeadvorsilTM C18 column (1.8 μm, 50 mm×2.1 mm) was used with gradient elution of acetonitrile and 0.02 mol/L ammonium acetate solution (containing 0.1% formic acid). The detection was performed on a triple-quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM)mode via electro spray ionization (ESI). Results The calibration curve of unbound teicoplanin in plasma was linear over the range of 0.10 to 8.00 μg/ml (r=0.999). The intra-assay precision and the inter-assay precision of samples didn't exceed 7.00%. The average relative recovery ratio was 97.9%, and the matrix effect factor was 0.97. The samples had good stability after being stored at room temperature for 10 h or at −20 ℃ for 15 days, and freeze-thawed 3 times (RSDs were all within 6.50%). Conclusion This method is convenient, fast, sensitive and accurate. It provided a basis for clinical development of teicoplanin unbound concentration monitoring.

Potency and plasma protein binding of drugs in vitro—a potentially misleading pair for predicting in vivo efficacious concentrations in humans

In drug discovery or preclinical stages of development, potency parameters such as IC₅₀, K(i), or K(d) in vitro have been routinely used to predict the parameters of efficacious exposure (AUC, C(min), etc.) in humans. However, to our knowledge, the fundamental assumption that the potency in vitro is correlated with the efficacious concentration in vivo in humans has not been investigated extensively. Thus, the present review examined this assumption by comparing a wide range of published pharmacokinetic (PK) and potency data. If the drug potency in vitro and its in vivo effectiveness in humans are well correlated, the steady-state average unbound concentrations in humans [C(u_ss.avg) = f(u)·F·Dose/(CL·τ) = f(u)·AUCss/τ] after treatment with approved dosage regimens should be higher than, or at least comparable to, the potency parameters assessed in vitro. We reviewed the ratios of C(u_ss.avg)/potency in vitro for a total of 54 drug entities (13 major therapeutic classes) using the dosage, PK, and in vitro potency reported in the published literature. For 54 drugs, the C(u_ss.avg)/in vitro potency ratios were < 1 for 38 (69%) and < 0.1 for 22 (34%) drugs. When the ratios were plotted against f(u) (unbound fraction), “ratio < 1” was predominant for drugs with high protein binding (90% of drugs with f(u) ≤ 5%; i.e., 28 of 31 drugs). Thus, predicting the in vivo efficacious unbound concentrations in humans using only in vitro potency data and f(u) should be avoided, especially for molecules with high protein binding.

Total, unbound plasma and salivary phenytoin levels in critically ill patients / Níveis totais, livres em plasma, e salivares de fenitoína em doentes graves

OBJECTIVE: To assess the reliability of salivary phenytoin (PHT) concentrations and predicted free PHT levels by Sheiner-Tozer equation in order to substitute measured free PHT concentrations in critically ill patients. METHODOLOGY: Twenty-four neurocritically ill adult patients receiving intravenous PHT were included in the study. Analyses of total, free plasma and saliva PHT concentrations were performed by fluorescence polarization immunoassay. Plasma albumin levels were also determined. RESULTS: Free PHT concentrations as well as salivary levels better correlate to clinical effect than total drug concentrations. Linear regression analysis showed a strong correlation between estimated free PHT concentrations by Sheiner-Tozer and measured free PHT levels (r=0.835; p<0.001) and salivary PHT concentrations and measured free PHT concentrations (r=0.964; p<0.001). Sheiner-Tozer equation could be misleading in the presence of displacing drugs. CONCLUSIONS: Saliva may serve as a feasible fluid to plasma in order to be used as a surrogate for free concentration monitoring of PHT in this population.

OBJETIVO: Avaliar a confiabilidade de concentrações salivares de fenitoina (PHT) e níveis livres de PHT pronosticado por equação de Sheiner-Tozer, o efeito da substituição das concentrações medidas livres de PHT em doentes graves. MÉTODO: Vinte e quatro doentes adultos que recebem PHT intravenoso forem incluídos no estudo. Análises de PHT total, livre em plasma e saliva foram realizadas por uma técnica de imune fluorescência polarizassem. Os níveis de albumina em plasma foram também determinados. RESULTADOS: Concentrações livres de PHT em plasma e saliva correlacionam melhor ao efeito clínico que concentrações de fármaco total. Análise de regressão lineal mostrou uma correlação forte entre concentrações livres de PHT estimadas por Sheiner-Tozer e os níveis livres de PHT medidos (r=0.835; p<0.001), e entre concentrações em saliva de PHT e concentrações livres medidas de PHT (r=0.964; p<0.001). A equação de Sheiner-Tozer poderia ser inadequada na presença de fármacos competidores da ligação às proteínas. CONCLUSÕES: Saliva pode servir como substituto do plasma para ser utilizado no controle de concentração livre de PHT em plasma nesta população.