Schering-Plough Corp. (SGP) is gearing up for the potential launch of a new antipsychotic drug.

The Kenilworth, N.J., drug maker recently told employees it will probably hire a small number of new workers for the launch of asenapine - under the proposed brand name Saphris - which is currently under review by U.S. regulators. Merck & Co. (MRK), Whitehouse Station, N.J., which agreed in March to acquire Schering-Plough in a cash-and-stock deal then valued at about $41 billion, disclosed Schering's hiring plans in a regulatory filing Friday.

The hirings would be notable because the merger partners said in March they would institute hiring freezes in connection with their pending combination, which is expected to close by the end of this year. Merck has said it expects to then reduce the combined entity's work force by about 15%, or nearly 16,000 employees.

The exception to the current hiring freeze is for "critical business needs," according to Merck's regulatory filing, and Schering's potential new hires for asenapine would fall into this category.

"There are various positions you might need to fill even in the planning, pre-launch" phase, said Schering-Plough spokesman Robert Consalvo, who declined to specify the number of positions in question, or say when Schering expects a regulatory decision.

Just four months ago, the U.S. Food and Drug Administration declined to approve asenapine for treatment of schizophrenia and bipolar disorder, and asked Schering for more information from existing clinical databases. The FDA proposed language for a prescribing label, and didn't request additional clinical trials - which some analysts saw as a good sign. Schering responded to the FDA's request in February, and an agency decision is pending.

Schering inherited asenapine with its 2007 acquisition of Organon BioSciences from Akzo Nobel NV (AKZOY). Akzo had previously been in a partnership with Pfizer Inc. (PFE) to develop and commercialize the drug, but Pfizer backed out of the alliance in 2006 for commercial reasons.

Schering believes asenapine is effective but with a less severe side effect of weight gain that is associated with some other antipsychotics. Schering has predicted the drug's peak annual sales could exceed $1 billion.

But some analysts have had low expectations, citing unimpressive clinical data and the perception that a cautious FDA had raised the bar for approval of mental-health drugs. Even if the drug gets approved, it would enter a crowded antipsychotic market dominated by AstraZeneca PLC's (AZN) Seroquel and relatively cheap generic versions of Johnson & Johnson's (JNJ) Risperdal.

Doubts about asenapine's prospects were reinforced last year when the FDA rejected another experimental antipsychotic, iloperidone from Vanda Pharmaceuticals Inc. (VNDA), signaling the FDA was taking a tough stance toward new antipsychotics.

But last week the FDA reversed course and approved Vanda's drug, which will be sold under the brand Fanapt. The Fanapt approval doesn't guarantee the FDA will do the same for Schering's asenapine, but it does show that the FDA's bar for new antipsychotics isn't insurmountable.

Schering-Plough shares rose 32 cents to $23.00 Tuesday. Merck shares rose 57 cents to $24.97.

-Peter Loftus; Dow Jones Newswires; 215-656-8289; peter.loftus@dowjones.com