Coadministration of methadone and raltegravir (400 mg twice daily) had no significant effect on methadone AUC and Cmax. These findings can be extended to raltegravir 1,200 mg once daily. No dose adjustment required for raltegravir (400 mg twice daily and 1,200 mg once daily) or methadone.
Isentress 600 mg Summary of Product Characteristics, Merck Sharp & Dohme Ltd, September 2021.

In drug interaction studies performed using raltegravir film-coated tablets 400 mg twice daily dose, raltegravir did not have a clinically meaningful effect on the pharmacokinetics of methadone. No dose adjustment is required when raltegravir 400 mg twice daily or 1200 mg once daily is coadministered.
Isentress Prescribing Information, Merck & Co Inc, August 2021.

The effect of raltegravir (400 mg twice daily) on the pharmacokinetics of methadone were investigated in 12 HIV- subjects stable on methadone. There was no change in either methadone AUC or Cmax in the presence of raltegravir and no dose adjustment is required for methadone when coadministered with raltegravir.
Effect of raltegravir on the pharmacokinetics of methadone. Anderson MS, Luk JAM, Hanley WD, et al. J Clin Pharm, 2010, in press.