Although Roxane believes the problem may be limited to a single bottle, which was not dispensed to a patient, the decision was taken to call for a nationwide voluntary recall of the lot 558470A in which the bottle was found based on the severe implications of a wrong pill reaching a patient.
Indeed, if methotrexate 2.5mg tablets are taken in place of azathioprine 50mg tablets in accordance with dosing instructions that may be prescribed for azathioprine, serious toxic effects can occur.
These include decreased resistance to infection, mouth ulcers, reduced blood counts, vomiting, diarrhea, liver, kidney or lung injury.
There have even been recorded cases of death at high doses of Methotrexate, such as might result from a substitution of methotrexate 2.5mg tablets for azathioprine 50mg tablets.
Azathioprine is used to help prevent rejection in kidney transplant patients and can also be used to manage severe rheumatoid arthritis, while methotrexate is used to treat various forms of cancer as well as psoriasis and rheumatoid arthritis.
Both kind of tablets are circular with a tannish coulour but they can be distinguished by the numbers printed on them, with methotrexate tablets marked with the numbers 54 and 323.
No injuries have yet been reported in relation to this incident which is bound to deal a severe blow to Roxane's status as one of America's largest generic manufacturers, losing ground to the branded version of azathioprine in the US - Azasan made by Salix.
Roxane rejected a request by In-PharmaTechnologist.com for information on the errors in the manufacturing process that led to the incident and the circumstances under which the bottle with the wrong pills was discovered on the basis that any details released would harm the investigation the company is conducting with the oversight of the US Food and Drug Administration (FDA).
The incident took place at Roxane's headquarters in Columbus, Ohio, where 800 employees work in a modern 250,000-square-foot laboratory, manufacturing and office complex.
Acquired by Boehringer Ingelheim in 1978, 80 per cent of Roxane's manufacturing is generics, specialising in anticancer and respiratory therapies.
Last month the FDA authorized Roxane to produce a generic liquid concentrate version of Zoloft, the top-selling antidepressant in the United States that has now gone off patent.
An FDA spokeswoman would not comment on the actions the agency is planning to take in response to Roxane's manufacturing mistake.