Glaxo Smith Kline, makers of Combivir and Ziagen have issued a warning regarding criminal tampering of 4 Combivir bottles. The warning states that apparently two bottles of Ziagen were labeled as Combivir. Two other bottles are also under examination.

Glaxo reports that because of potential hypersensitivity reactions to Ziagen, the label changes could be dangerous. In addition, switching from Combivir to Ziagen could lower the effectiveness of a patient's therapy. Glaxo believes this is not just a case of "mislabeling" but one of criminal intent.

Patients are urged to check their Combivir bottles immediately to make sure they have received the proper drug. Pharmacists should open new bottles in front of the customers before the patient leaves the store, Glaxo advised. Patients should check for the following:

• Combivir is a white capsule-shaped tablet engraved with "GX FC3" on one side.
• Ziagen is a yellow capsule-shaped tablet engraved with "GX 623" on one side.
• The Combivir bottles' label shows a photograph of the drug to compare.

Questionable medication should be returned to the pharmacist to be checked, and pharmacies should return suspect bottles to Glaxo for investigation. Patients and pharmacists with questions should call 1-888-825-5249.