FORT WORTH — Ethan Couch, the teenager who used an “affluenza” defense in a drunken-driving crash that killed four people and then violated probation by traveling to Mexico with his mother, was sentenced on Wednesday to nearly two years in jail.

Mr. Couch, who turned 19 on Monday, had previously avoided a harsher punishment because he was sentenced in juvenile court, where the emphasis is on rehabilitation. But after his foray to Mexico last year, prosecutors moved the case to adult court.

On Wednesday, a district court judge, Wayne F. Salvant, ruled that Mr. Couch must spend 720 days in Tarrant County Jail — 180 days for each count of intoxication manslaughter. The judge said the court would reconvene in two weeks to consider modifying the terms after each side submitted additional written arguments.

“Nothing I do is in stone, so I might reconsider,” Judge Salvant said.

Mr. Couch showed no emotion as the sentence was read. He will remain in solitary confinement for 23 hours a day for his protection, Dee Anderson, Tarrant County’s sheriff told reporters after the hearing.