Pharmacokinetic calculations
Specific pharmacokinetic parameters were used to evaluate the effect of TPE on CFP/SUL including the amount of drug eliminated during TPE (QPE); the fraction eliminated by TPE (fe %); Apparent volume of distribution (Vd); Area under the plasma level versus time curve (AUC); Elimination rate constant (Kel); Half-life (T1/2) and Drug clearance (CL).
QPE was calculated as total volume of efluent port (Vep)×concentration of CFP or SUL concentration from effluent port (Cep); In the equation: QPE= Vep×Cep[12].
fe % can be calculated as QPE/TBS × 100%. Total Body Stores (TBS)=Vd×concentration before plasma exchange [13].
Kel=(ln Ca-ln Cb)/(Tb-Ta). Tb-Ta, duration of two blood collection time points, ln Ca and ln Cb, natural log of plasma drug concentrations at the corresponding time points Ta and Tb. KelTotal=(ln C1-ln C3)/(T3-T1). ln C1, natural log of plasma concentration at start of TPE. ln C3, natural log of plasma concentration at the end of TPE; KelPatient=(ln C1-ln C3)/(T3-T1) on session II [4]; Definitions, the Elimination rate constant during TPE (KelTotal) represents the contribution of durg removed due to TPE and patient; The contribution of durg eliminated due to patient is Kelpatient. T1/2 can be calculated as 0.693/Kel [4].
Drug clearance while off TPE (CLpatient) was calculated for the values of KelPatient×Vd [13, 14]. The Drug clearance due to TPE (CLPE) was calculated using the equation: CLPE=QPE/AUCPE. AUCPE, the AUC during TPE [12, 13]. Total drug clearance (CLTotal) = CLPE+CLpatient; The proportion of %CLPE was determined by CLPE/CLTotal×100%. Creatinine clearance (Ccr) was calculated using the Cockroft-Gault equation [15].
Data were analyzed using the SPSS statistic version 22 (IBM; New York, NY, United). The Paired-samples t-test was used to compare the pharmacokinetics of the day with and without TPE. Calculated values of <0.05 were considered to be statistically significant. The correlation between plasma drug concentration before TPE and QPE were analyzed by Pearson’s correlation coefficient.