La. Stat. tit. 38 § 375
The court may direct that one or two jurors in addition to the regular panel be called and empanelled to sit as alternate jurors. Alternate jurors, in the order in which they are called, shall replace jurors who, prior to the time the jury retires to consider its verdict, become unable or disqualified to perform their duties. Alternate jurors shall be drawn in the same manner, shall have the same qualifications, shall be subject to the same examination and challenges, shall take the same oath, and shall have the same functions, powers, facilities, and privileges as the principal jurors. An alternate juror who does not replace a principal juror shall be discharged when the jury retires to consider its verdict. If one or two alternate jurors are called, each side shall have an equal number of peremptory challenges. The court shall determine how many challenges shall be allowed and shall allocate them among the parties on each side. The additional peremptory challenges may be used only against an alternate juror, and the other peremptory challenges allowed by law shall not be used against the alternate jurors.
La. R.S. § 38:375