The pharmaceutical executive on trial for murdering her severely autistic son with a fatal dose of pills admitted on the stand Friday that she tended to mundane tasks as her 8-year-old’s life drained away beside her.

Gigi Jordan, 53, testified that she already knew she was going to kill little Jude Mirra when she checked into the posh Peninsula hotel on Feb. 3, 2010.

She coolly recalled how Jude tilted his head back and let her plop about eight pills in his mouth — their typical nightly routine.

Except this time she fed him about 50, she said.

Jordan then crushed Vicodin tablets and mixed them with vodka and orange juice before squirting the brew into his mouth.

“How long after that did Jude pass out?” asked Assistant District Attorney Matthew Bogdanos.

“Ten or 15 minutes later,” she answered. “He was on the bed, laying down and watching a movie on his iPad Touch.”

Then it was business as usual for Jordan, who appeared unmoved by her son’s vanishing existence.

She e-mailed her financial ­adviser, asking him to transfer $125,000 from an account set up for Jude into her own, she said.

The next morning, she called the front desk and asked for an employee come to her room to pick up some letters and deliver them.

“You told her how to mail them, where to mail them, which post office was open late, you then told her to slip the receipt under your door when she was done?” asked Bogdanos.

“Yes,” she answered.

“And when you were doing that where was Jude?” he asked.

“In the bed.”

“Was he alive or dead?”

“I don’t know,” she answered.

That evening, Jordan had a conversation with the hotel manager in the hallway outside her room about extending her stay.

As little Jude’s lifeless body decomposed in their room, the calm, collected mother asked the manager to have room service send up a bottle of water.

“When you were having that conversation, where was Jude?” asked Bogdanos.

“On the bed,” she answered.

“Was he alive or dead?” he asked.

“I believe he was dead,” she said.

With her grim task complete, Jordan tried to ingest a fatal dose of pills, she told jurors.

She was discovered on Feb. 5 a little groggy but alive — just arm’s length from her son’s corpse.