No studies have been conducted to evaluate the drug interactions of ritonavir with raltegravir 1,200 mg (2 x 600 mg) once daily. The magnitudes of change on raltegravir exposure from raltegravir 400 mg twice daily by ritonavir were small.
Isentress 600 mg Summary of Product Characteristics, Merck Sharp & Dohme Ltd, September 2021.

Coadministration of ritonavir (100 mg twice daily) and raltegravir (400 mg single dose) decreased raltegravir Cmax by 24%, AUC by 16% and Cmin by 1% (n=10).
Isentress Prescribing Information, Merck & Co Inc, August 2021.

Co-administration of ritonavir (100 mg twice every 12 hours) and raltegravir (400 mg single dose) results in a minor reduction in raltegravir levels (16% decrease in AUC and 1% decrease in Cmin).
Norvir Summary of Product Characteristics, AbbVie Ltd, September 2016.

Coadministration of raltegravir (400 mg single dose) and ritonavir (100 mg every 12 hours) was studied in 10 subjects. Raltegravir AUC, Cmax and Cmin decreased by 16%, 24% and 1%, respectively. The effects of ritonavir on raltegravir with ritonavir dosage regimens greater than 100 mg twice daily have not been evaluated, however raltegravir concentrations may be decreased with ritonavir coadministration. 
Norvir Prescribing Information, AbbVie Inc, December 2016.

The potential effect of ritonavir on raltegravir pharmacokinetics was examined in healthy subjects administered raltegravir alone (400 mg single dose), followed by ritonavir (100 mg twice daily) for 16 days with a single dose of raltegravir (400 mg) on day 14. In the presence of ritonavir, raltegravir pharmacokinetics were not significantly affected: the GMR (90% CI) for C12h, AUC and Cmax were 0.99 (0.70, 1.40), 0.84 (0.70, 1.01) and 0.76 (0.55, 1.04), respectively.
Minimal effects of ritonavir and efavirenz on the pharmacokinetics of raltegravir. Iwamoto M, Wenning LA, Petry AS, et al. Antimicrob Agents Chemother, 2008, 52(12): 4338-4343.