Pharmacokinetics, pharmacodynamics and safety of once-daily versus twice-daily dosing with enfuvirtide in HIV-infected subjects

A 30 kDa polyethylene glycol-enfuvirtide complex enhances the exposure of enfuvirtide in lymphatic viral reservoirs in rats

HIV therapy with anti-retroviral drugs is limited by the poor exposure of viral reservoirs, such as lymphoid tissue, to these small molecule drugs. We therefore investigated the effect of PEGylation on the anti-retroviral activity and subcutaneous lymphatic pharmacokinetics of the peptide-based fusion inhibitor enfuvirtide in thoracic lymph duct cannulated rats. Both the peptide and the PEG were quantified in plasma and lymph via ELISA. Conjugation to a single 5 kDa linear PEG decreased anti-HIV activity three-fold compared to enfuvirtide. Whilst plasma and lymphatic exposure to peptide mass was moderately increased, the loss of anti-viral activity led to an overall decrease in exposure to enfuvirtide activity. A 20 kDa 4-arm branched PEG conjugated with an average of two enfuvirtide peptides decreased peptide activity by six-fold. Plasma and lymph exposure to enfuvirtide, however, increased significantly such that anti-viral activity was increased two- and six-fold respectively. The results suggest that a multi-enfuvirtide-PEG complex may optimally enhance the anti-retroviral activity of the peptide in plasma and lymph.

Reassessment of enfuvirtide's role in the management of HIV-1 infection

BACKGROUND

The development of new protease inhibitors, new non-nucleoside reverse transcriptase inhibitors and novel therapeutic drug classes has dramatically changed the approach to managing HIV-1 patients with multidrug resistant virus. This has led many clinicians to reevaluate the clinical utility of enfuvirtide.

OBJECTIVES

To summarize recent literature on enfuvirtide and to reassess enfuvirtide's role in the management of HIV-1 infection.

METHODS

MEDLINE (1990 to February Week 2 2008) and EMBASE (1990 to 2008 week 8) databases were searched using the following terms: 'enfuvirtide', 'Fuzeon', 'T20', 'HIV fusion inhibitors', and 'HIV entry inhibitor'; limits: English language. Reference lists of articles deemed relevant were hand searched for additional publications. Significant abstracts from recent international HIV conferences were also identified.

CONCLUSION

Enfuvirtide can optimize the response to new combinations of HIV-1 drug regimens in multiresistant patients. Its inclusion as an active agent is effective but use is impacted by its high cost, inconvenient route of administration and cosmetic side-effect profile.

Efficacy and safety of 48 weeks of enfuvirtide 180 mg once-daily dosing versus 90 mg twice-daily dosing in HIV-infected patients

PURPOSE

To evaluate the safety and antiviral activity of once-daily (qd) enfuvirtide (ENF) compared with twice daily (bid) ENF.

METHOD

T20-401 was a phase 2, open-label, randomized, 48-week pilot study comparing ENF 180 mg qd versus ENF 90 mg bid, added to an optimized background (OB) regimen. Patients were randomized 1:1 to receive ENF 180 mg qd given as two 90-mg injections (n = 30) or one 90-mg injection bid (n = 31), plus OB. The primary efficacy endpoint was the proportion of patients achieving a HIV-1 RNA viral load <400 copies/mL. Adherence, pharmacokinetics, safety, and tolerability parameters, including injection site reactions (ISRs), were compared between treatment arms.

RESULTS

At Week 48, 23.3% of patients on once daily versus 22.6% on twice daily (p = .969) reached <400 copies/mL and 13.3% and 22.6% (p = .323), respectively, reached <50 copies/mL. The proportion reporting 1 adverse event or ISRs was comparable between arms, despite an increased incidence of grade 4 erythema (13% vs. 0%), induration (33% vs. 12%), and ecchymosis (7% vs. 0%) on twice daily versus once daily. ENF adherence (95% of prescribed doses) was higher on once daily (80.0%) versus twice daily (58.1%).

CONCLUSION

The antiviral efficacy, safety, and tolerability of 180 mg ENF qd appeared comparable with that of 90 mg ENF bid at Week 48, although the study was not powered to demonstrate the noninferiority of once daily versus twice daily.

Mechanism-based model of the pharmacokinetics of enfuvirtide, an HIV fusion inhibitor

We present a model of the pharmacokinetics of enfuvirtide, a potent inhibitor of the fusion of human immunodeficiency virus type 1 (HIV-1) with target cells. We assume that subcutaneously administered enfuvirtide accumulates in the injection region, diffuses locally, and gets absorbed into blood, where it reversibly associates with lipidic cell membranes and is eventually eliminated. We develop mathematical descriptions of each of these processes and predict the time-evolution of the concentration of enfuvirtide in plasma, C(p). We find, interestingly, that diffusion of enfuvirtide in the subcutaneous region is decoupled from absorption, which enables deduction of analytical expressions for C(p) following single dose administration and ordinary differential equations following multiple dose administration and renders our model amenable to data analysis. Model predictions provide excellent fits to observed plasma concentration-time profiles of enfuvirtide following the intravenous and subcutaneous administration of a single dose and without any adjustable parameters capture quantitatively concentration-time profiles following the administration of multiple doses. Our model thus presents a robust description of the pharmacokinetics of enfuvirtide and may be applied in conjunction with models of viral dynamics to assess responses of HIV-1 patients to alternative enfuvirtide-based therapies. Further, our model reveals that key pharmacokinetic characteristics of enfuvirtide, viz., steady state values of peak and trough concentrations and area under the concentration-time curve, vary nearly linearly with dosage over a broad range of dosages and for different dosing regimens, which enables a priori estimation of enfuvirtide exposure levels for different treatment protocols and may serve to establish guidelines for therapy optimization.