Ritonavir dosed as an antiretroviral agent is likely to inhibit CYP2D6 and as a result is expected to increase concentrations of fluoxetine. Careful monitoring of therapeutic and adverse effects is recommended when this medicine is concomitantly administered with antiretroviral doses of ritonavir.
Norvir Summary of Product Characteristics, AbbVie Ltd, September 2016.

When ritonavir is coadministered with SSRIs, plasma concentrations of SSRIs may be increased and a decrease in dose may be needed. Coadministration of ritonavir (600 mg single dose) with fluoxetine (30 mg every 12 hours for 8 days), in 16 subjects, increased ritonavir AUC by 19% and did not alter the Cmax. Cardiac and neurologic events have been reported when ritonavir has been co-administered with fluoxetine. The possibility of drug interaction cannot be excluded. 
Norvir Prescribing Information, AbbVie Inc, December 2016.

Coadministration of fluoxetine (30 mg 12 hourly) and ritonavir (600 mg) was studied in 16 healthy volunteers. There was a 19% increase in the AUC of ritonavir and little or no effect on Cmax. The interaction was not studied at steady-state and therefore it would be expected that the effect of fluoxetine on steady-state pharmacokinetics would be smaller than that observed. No ritonavir dose adjustment is recommended.
Effect of fluoxetine on pharmacokinetics of ritonavir. Ouellet D, Hsu A, Qian, J et al. Antimicrob Agents Chemother, 1998, 42: 3107–12.