Coadministration of ritonavir (200 mg every 6 hours for 4 days) with fluconazole (400 mg single dose on day 1 followed by 200 mg daily doses for 4 days) to 8 subjects resulted in increases of 12%, 15% and 14% in ritonavir AUC, Cmax and Cmin, respectively.
Norvir Prescribing Information, AbbVie Inc, December 2016.

Coadministration of fluconazole (200 mg once daily) and ritonavir (200 mg every 6 h) to eight healthy volunteers resulted in a 12% increase in ritonavir AUC and a 15% increase in Cmax. The changes in ritonavir pharmacokinetics are probably of limited clinical significance and do not necessitate dosage adjustment of ritonavir when fluconazole is added to the regimen.
Evaluation of the effect of fluconazole on the pharmacokinetics of ritonavir. Cato A, Cao G, Hsu A, et al. Drug Metab Dis, 1997,25:1104–6.

Three HIV + individuals received ritonavir (600 mg twice daily) and fluconazole (400 mg on day 2 and 200 mg on days 3–8). There were no detectable changes in the pharmacokinetics of ritonavir and no dosage adjustment is required.
The effect of fluconazole on ritonavir and saquinavir pharmacokinetics in HIV-1 infected individuals. Koks CHW, Crommentuyn KML, Hoetelmans RMW, et al. Br J Clin Pharmacol, 2001, 51:631–5.