Analysis of variation in plasma concentrations of nelfinavir and its active metabolite M8 in HIV-positive patients

Pharmacokinetics of Nelfinavir in Children: Influencing Factors and dose Implications

Objectives

The study describes the pharmacokinetics (PK) of the protease inhibitor nelfinavir and its active metabolite M8 in children and evaluates the influence of patient-related factors on nelfinavir plasma levels.

Methods

HIV-1-infected children treated with nelfinavir every 8 h (q8h) were eligible for inclusion in this retrospective study. 0–8 h intensive plasma pharmacokinetics (PK) sampling was performed at steady state. Nelfinavir maximum concentration (Cmax), area under the plasma concentration-time curve in 0–8 h (AUC0-8), trough level at the 8 h time point (C8) and relative apparent oral clearance (Cl*F/kg) were calculated.

Results

Twenty-four children (median age: 4.5 years, median nelfinavir dose: 28 mg/kg q8h) were included. Nelfinavir PK were highly variable: 10/24 children had an AUC0-8 below the value of 12.5 mg/l*h, which has previously been associated with an increased virological failure rate in children. With children aged <2 years and a dose of 20 mg/kg q8h, a non-significant trend was observed to more AUC0-8<12.5 mg/l*h [odds ratio (OR) (95% CI): 2.44 (0.41–14.7) and 8.7 (0.79–95), respectively]. Nelfinavir C8 correlated strongly with AUC0-8 (r=0.89, P<0.001). C8 >0.69 mg/l predicted an AUC0-8 >12.5 mg/l*h with 71% sensitivity and 80% specificity. Dose of nelfinavir per body surface area was a better predictor of AUC0-8 than dose per body weight.

Conclusion

Nelfinavir PK show high interindividual variability in children. Children <2 years old tend to be at increased risk for low nelfinavir levels. These data show that the nelfinavir dose of 20 mg/kg q8h is inadequate in most children. Also, these data suggest that paediatric dosing of nelfinavir based on body surface area should be considered. Therapeutic drug monitoring (TDM) can detect abnormal plasma levels and is therefore useful in optimizing nelfinavir therapy in HIV-infected children. However, further research is needed to more firmly establish a therapeutic range for nelfinavir in children.

Pros and cons of therapeutic drug monitoring of antiretroviral agents

Therapeutic drug monitoring has the promise to become a part of routine patient care in the treatment of HIV infection. It is known that plasma drug concentrations of protease inhibitors and non-nucleoside reverse transcriptase inhibitors are better predictors of antiviral response or toxicity than drug dose is. Furthermore, high interpatient variability is significant. In addition, therapeutic drug monitoring may be used as a direct and objective instrument to measure non-adherence. This review describes possibilities and limitations of therapeutic drug monitoring in HIV treatment.

High-performance liquid chromatography of HIV protease inhibitors in human biological matrices

Methods for HPLC analysis of protease inhibitors (PIs) in human biological matrices were reviewed. Assays have been developed for analysis of single PIs or for simultaneous measurement of multiple PIs in plasma-serum, saliva, cerebrospinal fluid and semen. Liquid-liquid extraction was most often applied for sample pretreatment, but solid-phase extraction and protein precipitation were used as well. Reversed-phase or ion-pair chromatography have been used to separate PIs. Detection of PIs should be sensitive enough for quantitation of plasma concentrations below trough levels of single PIs, or below proposed therapeutic thresholds for PIs. The large majority of assays employs UV detection. As the potential for interferences is large, the selectivity of every method should be evaluated properly. The available high-performance liquid chromatography (HPLC) methods have been applied in clinical pharmacokinetic studies and for therapeutic drug monitoring of PIs. Participation in an interlaboratory quality control program is recommended for every laboratory engaged in the bioanalysis of PIs.