WASHINGTON (AP) -- The number of serious problems and deaths linked to medications reported to the government set a record in the first three months of this year, a health industry watchdog group said Wednesday.

The Food and Drug Administration received nearly 21,000 reports of serious drug reactions, including over 4,800 deaths, said an analysis of federal data by the nonprofit Institute for Safe Medication Practices, which scrutinized data going back to 2004, and yearly totals dating to the 1990s.

Two drugs accounted for a disproportionately large share of the latest reports. One was heparin, the tainted blood thinner from China that caused an international safety scandal. The other was Chantix, a new kind of anti-smoking drug from Pfizer.

Chantix, which had the most reports of any medication, works directly in a smoker's brain to ease withdrawal symptoms. It also blocks the pleasurable effects of nicotine if the patient tries to light up again. But earlier this year, the FDA warned that Chantix may be linked to psychiatric problems, including suicidal behavior and vivid dreams. The government banned it for pilots. Pfizer said Wednesday it stands by Chantix, and that the volume of reports might be linked to publicity about the drug's side effects.

The FDA had no immediate response to the report.

The watchdog group, known as ISMP, has served hospitals and pharmacists for years as a clearinghouse for information on drug safety and medication errors. It is now reaching out to consumers with regular reports on drug safety trends, drawn from FDA records.

"We believe that one of the most important tools to promote is to monitor trends on a regular basis," said Thomas J. Moore, a senior scientist with the group. "Knowing which drugs are causing injuries and how many people are being hurt is the raw material we need to fashion sound measures to promote patient safety."

The FDA defines serious drug reactions as ones that cause hospitalization, require medical intervention, or place a life in jeopardy. The agency's monitoring system relies on voluntary reports from doctors and is only believed to capture a fraction of overall problems.

The total of 20,745 cases reported from Jan.-March was 38 percent higher than the average for the previous four calendar quarters, and the highest for any quarter, the report said.

Fatalities accounted for 23 percent of the cases. The total number of deaths, 4,824, was an increase of nearly 3 percent from the last calendar quarter of 2007.

Previous research from ISMP has shown that serious drug safety problems reported to the FDA increased markedly from 1998-2005. The FDA case reports provide a signal of possible problems with a drug, but a cause-and-effect connection can only be established through painstaking investigation. If the FDA were a police agency, the reports would indicate "probable cause," but not neccesarily "guilt beyond a reasonable doubt."

The ISMP study found that heparin accounted for 779 reports of serious problems, including 102 deaths. The FDA, using data that covers a longer time period has reported 238 deaths possibly linked to heparin.

Heparin "illustrates an example of a significant drug safety problem that was promptly and effectively resolved by the drug manufacturers and the FDA once the issue was detected and understood," the report said.

Not so with Chantix, it concluded.

The FDA should forcefully warn patients taking Chantix that they may have blackouts and other problems that could lead to accidents, the report said. The current warnings say that patients may be too impaired to drive or operate heavy machinery, but such language is standard for many medications.

The report found 15 cases of Chantix patients who appeared to have been involved in traffic accidents, and 52 additional cases involving blackouts or loss of consciousness. The FDA received 1,001 reports of serious injuries possibly linked to Chantix, more than for the ten best-selling brand name drugs combined.

Chantix "continued to provide a striking signal of safety issues that require investigation and action," the report said. The authors acknowledged Pfizer's concern that publicity may be driving up the number of reports, but nonetheless concluded that there are enough to warrant further action by the FDA.

Pfizer said the total sum of its data on Chantix, including results from clinical trials, show that the drug's benefits clearly outweigh its risks.

"We stand by the efficacy and safety profile of Chantix," the company said in a statement. "There are few things that provide greater health benefits than quitting smoking. Pfizer is committed to reducing the prevalence of smoking globablly. As part of that mission, we want to increase peoples' understanding of the dangers of smoking and the benefits of quitting."