Updated from 2:36 p.m. EDT

Shares of

Cardiac Science

(DFIB)

were among the best-performing health and pharmaceutical stocks Thursday after the company received a $3 million purchase order from the Department of Health in England.

Under the agreement, Cardiac Science will be the sole provider of automated defibrillators under England's National Defibrillation Programme, which is the world's largest government-sponsored defibrillation program. The $3 million order represents the single largest order in Cardiac Science's history. The order is expected to ship during the fourth quarter. Shares of Cardiac Science traded up 12 cents, or 8.1%, to $1.61.

Gilead Sciences

(GILD) - Get Report

rose after the company released preliminary results from an ongoing study to test the effectiveness of its drugs Viread and Emtriva, which are used to control HIV. The early results show that Viread and Emtriva, which are combined in the company's Truvada drug, showed that 88% of patients taking its drugs saw their HIV levels reduced, versus 80% for those who took

GlaxoSmithKline's

(GSK) - Get Report

Combivir drug. Gilead termed the results statistically significant. Shares of Gilead Sciences traded up $2.42, or 3.6%, to $69.24.

Shares of

Merck

(MRK) - Get Report

fell after a study funded by the Food and Drug Administration showed that people who take a high dose of its Vioxx arthritis drug have

a 50% greater chance of suffering from a heart attack or sudden cardiac death than those who use

Pfizer's

(PFE) - Get Report

Celebrex drug. Merck executives strongly disagreed with the findings, saying "this analysis is a retrospective database analysis -- not a clinical trial. Observational analyses have limitations, often conflict with each other, and must be interpreted within the context of data from large, randomized, controlled clinical trials." The drugmaker was also quick to point out that although the analysis was funded by the FDA, the results and conclusions "do not necessarily reflect the views of the FDA." Shares of Merck traded down 97 cents, or 2.1%, to $45.05.

Impac Medical Systems

(IMPCE)

fell after

Nasdaq

representatives warned that Impac's shares could be delisted as soon as Sept. 2. The health care information technology company, which has not filed its quarterly results with the

Securities and Exchange Commission

, said it intends to request a hearing before the Nasdaq Listing Qualifications Panel. Effective Aug. 26 the company's stock will trade with the letter "E" at the end of its ticker symbol, indicating the company's delinquent filing status. Shares of Impac Medical Systems traded down 71 cents, or 5.3%, to $12.60.

Other health care volume movers included

Amgen

(AMGN) - Get Report

, down 15 cents to $59.16;

Schering-Plough

(SGP)

, up 7 cents to $19.06;

Johnson & Johnson

(JNJ) - Get Report

, down 14 cents to $57.52;

Genentech

(DNA)

down 36 cents to $48.80; and

Biogen Idec

(BIIB) - Get Report

, down 20 cents to $59.63.