Opening the door on entry inhibitors in HIV: Redefining the use of entry inhibitors in heavily treatment experienced and treatment-limited individuals living with HIV

INTRODUCTION

Entry inhibitors are a relatively new class of antiretroviral therapy and are typically indicated in heavily treatment experienced individuals living with HIV. Despite this, there is no formal definition of 'heavily treatment experienced'. Interpretation of this term generally includes acknowledgement of multidrug resistance and reflects the fact that patients in need of further treatment options may have experienced multiple lines of therapy. However, it fails to recognize treatment limiting factors including contraindications, age-associated comorbidities, and difficulty adhering to regimens.

METHODS

This manuscript follows a roundtable discussion and aims to identify the unmet needs of those living with HIV who are in need of further treatment options, to broaden the definition of heavily treatment experienced and to clarify the use of newer agents, with an emphasis on the potential role of entry inhibitors, in this population.

RESULTS/CONCLUSIONS

Within the entry inhibitor class, mechanisms of action differ between agents; resistance to one subclass does not confer resistance to others. Combinations of entry inhibitors should be considered in the same regimen, and if lack of response is seen to one entry inhibitor another can be tried. When selecting an entry inhibitor, physicians should account for patient preferences and needs as well as agent-specific clinical characteristics. Absence of documented multidrug resistance should not exclude an individual from treatment with an entry inhibitor; entry inhibitors are a valuable treatment option for all individuals who are treatment limited or treatment exhausted. We should advocate for additional clinical trials that help define the role of entry inhibitors in people with exhausted/limited ART options other than drug resistance.

Enfuvirtide: from basic investigations to current clinical use

IMPORTANCE OF THE FIELD

Drug resistance is a major challenge in the treatment of HIV infection. Enfuvirtide is the first entry inhibitor to have been approved for clinical use.

AREAS COVERED IN THIS REVIEW

Relevant information through searches of MEDLINE (1998 to June 2010) and meeting abstracts of major HIV/AIDS conferences (2003 - June 2010) using the search terms 'enfuvirtide', 'T-20' and 'fusion inhibitor'.

WHAT THE READER WILL GAIN

Enfuvirtide blocks HIV fusion to host cells. It works against the different HIV-1 variants but is not active against HIV-2. The recommended dosage of enfuvirtide is 90 mg b.i.d. subcutaneously. The two large Phase III pivotal clinical trials TORO 1 and 2 showed that enfuvirtide is an effective therapeutic option as rescue therapy in combination with other active antiretroviral drugs. Resistance to enfuvirtide is conferred by mutations in the HR1 region of gp41. Single and double mutations have been shown to result in high-level resistance to enfuvirtide. Postmarketing studies have been helpful to define more precisely the place of enfuvirtide in the sequence of antiretroviral therapy.

TAKE HOME MESSAGE

The emergence of new compounds and new classes of drugs, highly active against multiresistant virus but more convenient to administer than enfuvirtide, will probably prevent the extensive use of enfuvirtide. This drug remains attractive in some subgroups of patients because of its excellent systemic tolerance and the lack of interactions with the major cytochrome P450 isoenzymes.

The fusion inhibitor enfuvirtide in recent antiretroviral strategies

PURPOSE OF REVIEW

The purpose of this review is to discuss recent pharmacological, virological, and clinical data that concern enfuvirtide usage in different antiretroviral combinations.

RECENT FINDINGS

Randomized, recent trials in multidrug-experienced patients suggest that antiretroviral combinations with enfuvirtide have excellent virological responses with new antiretroviral compounds, including darunavir, etravirine, raltegravir, vicriviroc, and maraviroc. Trials confirm long-term safety, in spite of moderate injection-site reactions or pain, and lack of significant interactions. Preliminary data suggest that switching from enfuvirtide to raltegravir is effective and using enfuvirtide in prophylaxis of mother-to-child transmission is well tolerated. To administer enfuvirtide in an intensification strategy in antiretroviral-naïve or experienced populations may accelerate virological decline.

SUMMARY

Dosage adaptations to renal insufficiency are not necessary with enfuvirtide. Spinal fluid concentrations and ombilic cord passage are negligible. Durability of virological responses with enfuvirtide in combinations has been confirmed, in spite of injection-site reactions and twice daily subcutaneous administration. Enfuvirtide should be used with at least one other fully active drug in optimized background therapy in multidrug-experienced populations, a possible exception being with entry inhibitors, which may further benefit from the addition of a third active drug. Data concerning enfuvirtide in antiretroviral combinations show accelerated viral load decline, and the possibility of switching from enfuvirtide to raltegravir without modification of optimized background therapy.