Generic competition to

Shire Pharmaceuticals'

( SHPGY) best-selling drug Adderall just got closer, adding to the Anglo-U.S. drug company's mounting challenges.

Name Dropping?
Shire's Wednesday wallop (top), and year-long rally

Cambrex

(CBM) - Get Report

, a New Jersey chemical maker, said Wednesday it now has the capability to make a generic version of Adderall, the mainstay of the Anglo-U.S. drug maker. Adderall is the top branded drug in the $700 million market to treat attention deficit hyperactivity disorder and accounted for 45% of Shire's 1999 sales of $137.8 million. Shire shares slid $4.81, or 9%, to $48.81 Wednesday.

Shire has maintained for years that Adderall, while composed of four off-patent amphetamines, would present a major challenge to duplicate. That has kept generic competitors off the market. Adderall, which has around a third of the ADHD market, competes with drugs including

Novartis'

(NVS) - Get Report

Ritalin and Concerta from

Alza

( AZA) and

Johnson & Johnson

(JNJ) - Get Report

. (

TheStreet.com

examined Shire's

Adderall worries in a story this week.)

Getting Riskier?

But a spokesman for Cambrex said the company is now making generic Adderall and is pitching proposals to supply several major generic drug companies, which would market the drug to doctors. Industry officials said they are believed to include

Teva

(TEVA) - Get Report

,

Watson

(WPI)

and

Andrx

( ADRX).

"The risk profile for Shire just went up," says Genghis Lloyd-Harris, biotech analyst for

Credit Suisse First Boston

, who rates Shire a hold and whose firm doesn't underwritten for the company. Now a generic company can seek U.S. approval for a chemical equivalent version of the drug, a process that could take a year or more from filing.

Cambrex's announcement comes as Shire is facing a major threat to sales of Adderall from Concerta, which was launched in August and has garnered nearly 10% of the market to treat schoolchildren and others with ADHD, also called hyperactivity.

Sales of Adderall, which have grown to take about 33% of the market in the last five years, flattened out after Concerta hit the market, and analysts said it was only a matter of time before a generic equivalent to Adderall hit the market.