GlaxoSmithKline announced Friday that the company has received four reports of suspect bottles containing 60 tablets of Combivir (lamivudine plus zidovudine) that actually contained another medicine, Ziagen (abacavir sulfate) Tablets. The company has determined that counterfeit labels for Combivir Tablets were placed on two bottles of Ziagen and labels on another two bottles are suspect. Both medicines are used as part of combination regimens to treat HIV infection.

The incidents appear to be isolated and limited in scope. No injuries or adverse reactions have been reported. Company tests have shown no problems with the medicine itself.

GlaxoSmithKline and the U.S. Food and Drug Administration (FDA) are both investigating. The company also is contacting health-care providers and pharmacists to alert them to the situation and is alerting patients to check their medicine to be sure they have received the correct tablets.

Pharmacists, physicians and patients should immediately examine the contents of each Combivir bottle to confirm they do not contain Ziagen tablets. The two kinds of tablets are easily distinguishable. Combivir is a white capsule-shaped tablet engraved with "GX FC3" on one side; the other side of the tablet is plain. Ziagen is a yellow capsule-shaped tablet engraved with "GX 623" on one face; the other side is plain. The Combivir label shows a color photo of the tablet.

The risk to patients is primarily due to the fact that approximately 5% of individuals who receive abacavir sulfate in Ziagen or Trizivir (abacavir sulfate, lamivudine and zidovudine) Tablets have developed a potentially life-threatening hypersensitivity reaction. Symptoms generally resolve after discontinuing the medication, however, patients who have had a hypersensitivity reaction to Ziagen are advised to never take the medication again.

Patients taking Combivir would not have been advised about the hypersensitivity reaction and how to take Ziagen safely because Combivir does not contain abacavir sulfate. Patients who have had a hypersensitivity reaction to abacavir yet take Ziagen or Trizivir again experience more severe symptoms within hours that may include life-threatening hypotension (lowering of the blood pressure) and death. In addition, the replacement of Combivir which contains two antiviral drugs with Ziagen, a single antiviral, may decrease the effectiveness of a patient's treatment regimen.

Patients should always confirm they have the right medication; for patients taking Combivir this is especially important now.

"While we cannot determine the extent of counterfeit labeling, we believe this unfortunate situation can be addressed by watchful pharmacists checking products before dispensing them and careful patients double-checking their medications," said Peter Traber, senior vice president clinical development and medical affairs at GSK. "Both patients and pharmacists can easily recognize the difference between the two tablets and can identify if they have received the wrong medicine before they take it." These steps should minimize the risk to patients.

Involved in the counterfeit labeling cases were 60-count bottles of Combivir Tablets, which contain 150-milligrams of lamivudine and 300 milligrams of zidovudine, and 60-count bottles of 300-milligram tablets of Ziagen.