UPDATE 1-Cortex to resume Ampakine trial at all dosage levels

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July 17 (Reuters) - Cortex Pharmaceuticals Inc. (COR.A) said it has received approval from U.S. regulators to resume mid-stage trial with Ampakine CX717, a memory-enhancing drug, at all dosage levels in Alzheimer PET-scan study.

The company now has permission from the Food and Drug Administration to resume trial with 600mg and 1200mg doses of the drug in mild-to-moderate Alzheimer's patients.

FDA had previously limited the dosage to lower levels. The study was originally designed with doses of 200mg, 600mg and 1200mg. The company's shares rose more than 25 percent in midday trade, making them the highest percentage gainer on the American Stock Exchange.

The FDA had placed the drug on clinical hold in March 2006 due to concerns over some preclinical animal data. The hold was later lifted in October with Cortex agreeing to an FDA-specified dose range for CX717.

Shares of Cortex rose 68 cents to $3.35 in noon trade. Earlier in the day, it touched a high of $3.46.

Cortex is also studying CX717 for treating Attention Deficit Hyperactivity Disorder. (Reporting by Niveditha Ravi and Jennifer Robin Raj in Bangalore)