(a) For claims with dates of injury prior to September 1, 2011 (for the purposes of this section, referred to as "legacy claims"), the open formulary as described in §134.500(9) of this title (relating to Definitions) remains in effect until those claims become subject to the closed formulary in accordance with §134.510 of this title (relating to Transition to the Use of the Closed Formulary for Claims with Dates of Injury Prior to September 1, 2011).
(b) Health care, including a prescription drug, for legacy claims not subject to a certified network shall be in accordance with the division's adopted treatment guidelines under §137.100 of this title (relating to Treatment Guidelines) except as provided by subsections (d) and (f) of this section.
(c) Health care, including a prescription drug, for legacy claims subject to a certified network shall be in accordance with the certified network's treatment guidelines pursuant to Insurance Code Chapter 1305 and Chapter 10 of this title (relating to Workers' Compensation Health Care Networks).
(d) Drugs included in the open formulary prescribed and dispensed for legacy claims not subject to a certified network do not require preauthorization, except as required by Labor Code §413.014.
(e) Drugs included in the open formulary prescribed and dispensed for legacy claims subject to a certified network shall be preauthorized in accordance with Insurance Code Chapter 1305 and Chapter 10 of this title.
(f) Drugs included in the open formulary that do not require preauthorization under subsections (d) and (e) of this section and are prescribed and dispensed for legacy claims are subject to retrospective review of medical necessity and reasonableness of health care by the insurance carrier.

Source Note: The provisions of this §134.506 adopted to be effective January 3, 2002, 26 TexReg 10970; amended to be effective January 17, 2011, 35 TexReg 11344