Population Pharmacokinetic Modeling Using Polymyxin B Free Plasma Concentrations From Published Reports and Evaluation of Dosage Regimens Based on Monte Carlo Simulation in Critically Ill Patients

Daily fluid intake as a novel covariate affecting the population pharmacokinetics of polymyxin B in patients with sepsis

BACKGROUND

Polymyxin B dosing in patients with sepsis is difficult because pathophysiological changes and supportive therapies alter drug pharmacokinetics (PK). This study aimed to investigate the impact of fluid management and renal function on the PK of polymyxin B and to propose alternative dosing regimens.

METHODS

Patients (aged ≥ 18 y) with sepsis and receiving intravenous polymyxin B for ≥ 96 h were enrolled. Blood samples were collected at steady state. Plasma concentrations were measured by liquid chromatography-tandem mass spectrometry and subjected to population PK modelling. Monte Carlo simulations were used to optimise dosage regimens.

RESULTS

Eighty-three patients with a median (range) daily fluid intake of 4.2 (1.3-8.4) L and a creatinine clearance (CrCL) of 87.5 (17.3-309.7) mL/min were included. Polymyxin B PK was adequately characterised by a two-compartment model. The PK covariate analysis revealed daily fluid intake statistically significantly affected central volume of distribution and central compartment clearance (CL), and CrCL influenced CL. Simulation indicated that a decreased dosing would be suitable for patients with renal dysfunction (CrCL < 40 mL/min), and therapeutic drug monitoring is recommended to avoid exposure fluctuation when patients have fluid overload.

CONCLUSIONS

Fluid management as well as renal function are essential factors affecting polymyxin B PK for patients with sepsis, which can help optimise dosage regimens.

Remedial Dosing Recommendations for Sirolimus Delayed or Missed Dosages Caused by Poor Medication Compliance in Pediatric Tuberous Sclerosis Complex Patients

BACKGROUND

Delayed or missed dosages caused by poor medication compliance significantly affected the treatment of diseases in children.

AIMS

The present study aimed to investigate the influence of delayed or missed dosages on sirolimus pharmacokinetics (PK) in pediatric tuberous sclerosis complex (TSC) patients and to recommend remedial dosages for nonadherent patients.

METHODS

A published sirolimus population PK model in pediatric TSC patients was used to assess the influence of different nonadherence scenarios and recommend optimally remedial dosages based on Monte Carlo simulation. Thirteen nonadherent scenarios were simulated in this study, including delayed 2h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 23.5 h, and missed one dosage. Remedial dosing strategies contained 10-200% of scheduled dosages. The optimal remedial dosage was that with the maximum probability of returning the individual therapeutic range.

RESULTS

For delayed or missed sirolimus dosages in pediatric TSC patients, when the delayed time was 0-8 h, 8-10 h, 10-18 h, 18-22.7 h, 22.7-24 h, 70%, 60%, 40%, 30%, 20% scheduled dosages were recommended to take immediately. When one dosage was missed, 120% of scheduled dosages were recommended at the next dose.

CONCLUSION

It was the first time to recommend remedial dosages for delayed or missed sirolimus therapy caused by poor medication compliance in pediatric TSC patients based on Monte Carlo simulation. Meanwhile, the present study provided a potential solution for delayed or missed dosages in clinical practice.