Pfizer's experimental rheumatoid arthritis pill tofacitinib has suffered a glitch on its path to market, after US regulators said they need more time to review new information in support of its marketing application.

Last month it was reported that the US Food and Drug Administration was after extra analysis of clinical data provided in the drug's New Drug Application, giving the first indication that the decision could be delayed.

Now, according to the FDA, the new data provided by Pfizer in response "constitute a major amendment to the application", which will require extra time to review.

Consequently, the Prescription Drug User Fee Act date has been put back by three months, which means that Pfizer may not get a decision until November 21, 2012. 

Back in May, FDA advisors voted 8-2 that tofacitinib should get the green light as a treatment for adults with moderate-to-severely active RA who have failed to respond to another disease-modifying anti-rheumatic drug (DMARD), such as Abbott's Humira (adalimumab) and Johnson & Johnson's Remicade (infliximab). 

However, prior documents published by FDA staffers also expressed concern that the medicine increased risks of serious infections and malignancies, as well as higher chance of lymphoma, with some panelists specifically worried about over-immunosuppression with the higher 10mg dose of the drug.

Extensive clinical programme

Still, the medication has been evaluated in a comprehensive, multi-study, global clinical development program involving around 5,000 patients in 44 countries, and Pfizer remains confident in its future.

"We believe that the results from the comprehensive multi-study clinical development program for tofacitinib have demonstrated a favorable benefit-risk profile, and we remain committed to working expeditiously with the FDA to make tofacitinib available to patients,” said Yvonne Greenstreet, senior vice president and head of the Medicines Development Group for Pfizer Specialty Care.

If approved, tofacitinib would be the first new oral DMARD for RA in more than 10 years, as well as the first JAK inhibitor to get the thumbs-up for the disease.

RA affects approximately 1.6 million Americans and 23.7 million people worldwide, and it is thought that the target population for tofacitinib amounts to about a third of patients.

Leerink Swann & Co analyst Seamus Fernandez has estimated that, if approved, the drug could pull in sales of $2.3 billion in annual sales by 2018, according to Bloomberg.