This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn.

Low dose zidovudine.

Treatment.

Cost-effectiveness analysis.

Asymptomatic HIV-infected people with CD4+ lymphocyte counts.

The study was carried out in the USA.

Price related to 1989.

Single study.

Epidemiological cohort model (model of survival and disease).

Life years gained.

Direct costs were to the health service and included: drugs, physician visits, complete blood counts and three extra 20-test chemistry profiles. Price information related to 1989.

US dollars ($). In the DH Register of Cost-Effectiveness Studies, the original results were converted to UK using GDP purchasing power parities, and reflated to 1991, using the NHS pay and prices index.

Sensitivity analysis was carried out using the method of single parameter variation.

Irrespective of treatment it is assumed that the cost of care once AIDS develops will be $50,000 (at 1989 prices) (34600 at 1991 prices). Delaying this cost produces savings (through discounting). The incremental cost of treating one patient for a year with zidovudine (including monitoring) was estimated at $2653 (1989 prices) (1840, at 1991 prices). Intervention cost and duration was life long.

Outcome duration was life long. Costs and benefits were discounted at 5%. Incremental cost per life year gained for low dose zidovudine and usual care for asymptomatic HIV-infected people with CD4+ lymphocyte counts below 500/mm3 was 6553 to 48,839. The range of incremental cost per life year was 4538 to 48,839 (baseline), with lowest value 1834, and highest value, 173,500. Sensitive parameters were cost and protective effect of zidovudine.

(This commentary was not written by CRD, but by the authors of the DH Register).

1) Zidovudine may delay the development of AIDS in cases of asymptomatic HIV infection, prolonging survival. The evidence for this is one short term study. Low and high estimates are presented based on permanent and one year only protective effect.

2) The sensitivity analysis reflects the uncertainty surrounding the value of this intervention.

Comment in: Annals of InternalMedicine 1991;115(8):655-6.