Updated from 6:07 p.m. EST

Cephalon's ( CEPH) drug for attention deficit hyperactivity disorder was rejected in a stunning decision by a panel of medical advisers to the Food and Drug Administration.

The advisory committee said Thursday the ADHD medication Sparlon needed more tests to assure safety against a rare and potentially fatal skin disease, even though the experts said the drug was effective. Additional tests could add at least a year to the regulatory process.

The advisory committee voted 12-to-1 against recommending Sparlon's approval, citing its concerns about Stevens-Johnson syndrome, a rare and vicious blistering of the skin that can be caused by certain drugs. The FDA isn't bound to follow its advisers' recommendations, but it usually does so.

"We are obviously disappointed with the recommendation of the advisory committee," said Dr. Paul Blake, Cephalon's executive vice president for worldwide medical and regulatory operations. "We will continue our discussions with the FDA to determine the next steps in the review of this drug application."

In September, an FDA staff member called attention to one case of the rare disease and two other cases of severe skin rash. He recommended that Sparlon be rejected. One month later, the agency granted Cephalon conditional approval for Sparlon, asking the company to provide more data on the skin problems and several other matters.

The advisory committee's decision is a major blow to Cephalon, which was seeking FDA approval for Sparlon to treat children ages 6 to 17. Cephalon's stock was halted Thursday while the panel deliberated, and the decision came after the markets had closed. A dramatic decline in its shares can be expected when trading resumes Friday.

The panel's ruling concluded two days of FDA hearings -- on Wednesday another advisory committee examined ADHD drugs in general -- and several roller-coaster weeks for Cephalon.

The Frazer, Pa., company's stock has bounced from the low $70s, to the low $80s, to the mid $60s and back to the low $70s as bits and pieces of clinical research and FDA analysis have become public.

Cepahlon's previously issued 2006 basic adjusted income per common share guidance of $3.80 to $4 remains unchanged, but the company is reducing its sales forecast by $100 million to a range of $1.45 billion to $1.50 billion. The sales projection for its central nervous system drug franchise was also lowered by $100 million, to a range of $665 million to $715 million.

Frank Baldino Jr., the company's chairman and CEO, said he couldn't predict what additional tests might be needed, or how long they might last, until Cepahlon executives meet with FDA representatives. Like other Cephalon executives commenting during an early evening telephone conference call, Baldino sounded shocked by the committee's decision.

Baldino said he thought Cephalon had provided an adequate response to the FDA about Stevens-Johnson syndrome and two other cases of serious rash after the agency granted conditional approval for Sparlon in October.

Blake said he believed the committee's vote reflected "a general heightened sense of concern" among regulators for all drugs. He, too, was surprised by the committee's vote, noting that the 7-year-old child who contracted Stevens-Johnson wasn't hospitalized and wasn't kept out of school.

Thankfully for the child, he added, this was a "relatively benign case" of the disease, which lasted two weeks. The child took Sparlon for 16 days until symptoms appeared.

Analysts also were jolted by the committee's vote. They had expected the committee to recommend approval for Sparlon, perhaps with certain restrictions. Some predicted Sparlon might be saddled with a black box warning for the skin rash or for some psychiatric side-effects that appeared in some tests.

A black box warning is the FDA's strongest message to doctors and patients. Black box warnings can affect sales because they may discourage physicians from prescribing the drug, or at least encourage them to first prescribe competitors' products.

Sparlon contains the ingredient modafinil, the same ingredient found in Provigil, a sleep-disorders drug that also is Cephalon's best-selling product. Sparlon contains a higher dose of the ingredient than does Provigil.

Provigil doesn't have any black box warnings nor does it have any alerts for dangerous skin problems.

No ADHD drug has such a warning for the dangerous skin rashes. Strattera, from Eli Lilly ( LLY), has a black box warning about suicidal thinking in adolescents. The label also alerts patients to potential liver damage.

Adderall and Adderall XR, from Shire PLC ( SHPGY) have a black box regarding potential amphetamine abuse.

Last month, another FDA advisory committee recommended that all stimulant-type ADHD drugs carry a black box warning for cardiovascular risk. The vote was 8-7, with one abstention, covering drugs such as Shire's medications, Ritalin from Novartis ( NVS), generic versions of Ritalin, and Concerta from Johnson & Johnson ( JNJ).

Several smaller brands also would be affected because they are stimulants. Neither Strattera nor Cephalon is viewed as a stimulant by the FDA.

Stevens-Johnson syndrome played a role in the FDA's requesting the removal from the market of Bextra, a Pfizer ( PFE) arthritis drug that was withdrawn last April.

Bextra's label already had a black box warning for this disease when the FDA asked Pfizer to pull it, saying the drug's risks outweighed its benefits. The agency also cited a "potential increased risk" of serious cardiovascular injury in asking Pfizer to withdraw Bextra.

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