Infectious disease. Combating emerging viral threats

Most approved antiviral therapeutics selectively inhibit proteins encoded by a single virus, thereby providing a “one drug-one bug” solution. As a result of this narrow spectrum of coverage and the high cost of drug development, therapies are currently approved for fewer than ten viruses out of the hundreds known to cause human disease. This perspective summarizes progress and challenges in the development of broad-spectrum antiviral therapies. These strategies include targeting enzymatic functions shared by multiple viruses and host cell machinery by newly discovered compounds or by repurposing approved drugs. These approaches offer new practical means for developing therapeutics against existing and emerging viral threats.

Economic evaluation of systemic treatments for cytomegalovirus retinitis in patients with AIDS

OBJECTIVE

To determine the cost of using systemic therapy to treat newly diagnosed cytomegalovirus (CMV) retinitis in persons with AIDS.

DESIGN

Incidence-based simulation model of CMV treatment from a government payer perspective.

SETTING

Swiss healthcare system.

PATIENTS AND PARTICIPANTS

Patients with AIDS and newly diagnosed CMV retinitis.

INTERVENTIONS

Patients were assigned to 1 of 4 treatment regimens for induction and maintenance therapy: (i) intravenous (IV) cidofovir induction and maintenance (cidofovir IV/IV); (ii) IV foscarnet induction and maintenance (foscarnet IV/IV); (iii) IV ganciclovir induction and maintenance (ganciclovir IV/IV); and (iv) IV ganciclovir induction and oral (PO) ganciclovir maintenance (ganciclovir IV/PO). Following a second relapse, patients were assigned to one of the other regimens.

MAIN OUTCOME MEASURES

Time to first and subsequent progression, duration of maintenance treatment and direct medical expenditures [1998 Swiss francs (SwF)] .

RESULTS

The median time to first progression was longest for cidofovir IV/IV, followed by foscarnet IV/IV, ganciclovir IV/IV and ganciclovir IV/PO. Mean survival was 13 months and mean costs for this period in the base case were lowest in those initially treated with cidofovir (SwF146,742), followed by initial treatment with foscarnet IV/IV (SwF194,809), ganciclovir IV/PO (SwF195,190) and ganciclovir IV/IV (SwF243,964). Costs were most sensitive to changes in efficacy estimates.

CONCLUSIONS

Of the regimens studied, initiation of treatment with systemic cidofovir appears least costly over a 13-month period.

Cidofovir in the treatment of cytomegaloviral disease

OBJECTIVE

To review the clinical pharmacology and microbiology of cidofovir in the therapy of cytomegalovirus (CMV) disease.

DATA SOURCES

Pertinent literature was identified via a MEDLINE search (October 1986-February 1997), and data from abstracts presented at recent scientific meetings were also included; unpublished information was provided by the manufacturer.

STUDY SELECTION

Antiviral activity data were included if widely accepted methodology was used. All clinical data currently available from human studies were also included.

DATA SYNTHESIS

Cidofovir is similar to ganciclovir in mechanism of action; however, cidofovir does not require viral enzymes for activation. Although the half-life of cidofovir in plasma is only 2.6 hours, the intracellular half-life may be much longer, allowing efficacy with biweekly maintenance dosing. In vitro, cidofovir appears to be equally or more effective than the other agents currently available for the treatment of CMV. In vivo, cidofovir appears to be effective in delaying the progression of CMV retinitis, although no clinical trials to date have directly compared cidofovir with either ganciclovir or foscarnet. Current intravenous dose recommendations are 5 mg/kg once weekly for two doses (induction), and then 5 mg/kg once every other week (maintenance). Since cidofovir is cleared almost entirely by the kidneys, dosage adjustments must be made in patients with impaired renal function. Disadvantages of cidofovir primarily include its risks of adverse drug reactions, such as nephrotoxicity, which is likely to occur in up to 50% of patients if appropriate preventative measures are not taken. Neutropenia and constitutional reactions to probenecid are also commonly encountered during the course of cidofovir therapy.

CONCLUSIONS

Cidofovir is the first acyclic phosphonate nucleoside antiviral agent to be approved for general use in the US. In addition to delaying the progression of CMV retinitis, cidofovir may provide some protective benefits to patients at risk for developing the disease and may be active against certain strains of virus resistant to other currently available therapies. Another advantage of cidofovir is its infrequent dosage schedule, which may prove beneficial in patients who are not compliant with daily intravenous dosing regimens. When determining the appropriate treatment for a patient with CMV retinitis, the benefits of using cidofovir must be weighed carefully against the risk of potentially serious adverse effects.