When tenofovir disoproxil fumarate was administered with low dose ritonavir (as lopinavir/ritonavir), there was no significant effect on lopinavir/ritonavir PK parameters; tenofovir AUC and Cmin increased by 32% and 51%, but there was no change in Cmax. Coadministration as darunavir/ritonavir had no significant effect on darunavir/ritonavir PK parameters, but increased tenofovir AUC and Cmin by 22% and 37%. A higher risk of renal impairment has been reported in patients receiving tenofovir disoproxil fumarate in combination with a ritonavir or cobicistat boosted protease inhibitor. A close monitoring of renal function is required in these patients. In patients with renal risk factors, the co-administration of tenofovir disoproxil fumarate with a boosted protease inhibitor should be carefully evaluated.
Viread Summary of Product Characteristics, Gilead Sciences Ltd, September 2016.

Coadministration of low dose ritonavir (coformulated as lopinavir/ritonavir, 400/100 mg twice times daily for 14 days) and tenofovir-DF (300 mg once daily) was investigated in 24 healthy volunteers. There was no change in tenofovir Cmax; AUC and Cmin increased by 32% and 51% respectively. There was no change in Cmax, AUC or Cmin for lopinavir or ritonavir. When low dose ritonavir (100 mg twice daily for 14 days) was coadministered with saquinavir (1000 mg twice daily ) and tenofovir (300 mg once daily) in 35 healthy volunteers, there was no change in tenofovir AUC or Cmax, but Cmin increased by 23%. There was no change in ritonavir Cmax or AUC, but Cmin increased by 23%.
Viread Prescribing Information, Gilead Sciences Inc, February 2016.

The coadministration of tenofovir diproxil fumarate (300 mg once daily) was investigated in 18 HIV-1 infected individuals receiving saquinavir hard gel/ritonavir combination (1000/100 mg twice daily). On day 1, 12 h pharmacokinetic profiles for saquinavir and ritonavir were obtained, tenofovir was then added to the regimen and blood sampling repeated at days 3 and 14. Following the addition of tenofovir, saquinavir and ritonavir plasma concentrations were not significantly different compared with day 1. Geometric mean ratios (95% confidence intervals) for the AUC on days 3 and 14 were 1.16 (0.97, 1.59) and 0.99 (0.87, 1.30) for saquinavir and 1.05 (0.92, 1.28) and 1.08 (0.97, 1.30) for ritonavir.
Pharmacokinetics of saquinavir hard gel/ritonavir (1000/100 mg twice daily) when administered with tenofovir diproxil fumarate in HIV-1-infected subjects. Boffito M, Back D, Stainsby-Tron M, et al. Br J Clin Pharmacol, 2005, 59: 38-42.

The effect of tenofovir on the pharmacokinetics of lopinavir and ritonavir was investigated in 18 treatment experienced HIV+ patients. Lopinavir concentrations decreased in the presence of tenofovir (Cmin from 4.61 to 3.06 µg/ml; Cmax from 10.68 to 9.65 µg/ml). Decreases in ritonavir concentrations were also observed (Cmin from 0.63 to 0.35 µg/ml; Cmax from 1.02 to 0.72 µg/ml). Therapeutic drug monitoring of lopinavir when coadministered with tenofovir may be useful to indicate if individual dose modification of lopinavir and/or ritonavir is required.
Pharmacokinetic drug interaction of lopinavir/ritonavir in combination with tenofovir in experienced HIV+ patients. Breilh D, Rouzes A, Djabarouti S, et al. 44th Interscience Conference on Antimicrobial Agents and Chemotherapy, Washington, October/November 2004, abstract A-445.

Coadministration of hard gel saquinavir/ritonavir (1000/100 mg twice daily) alone and with tenofovir (300 mg once daily) was studied in 40 healthy subjects. The pharmacokinetics of tenofovir were not substantially effected by saquinavir/ritonavir (Cmin, Cmax and AUC increased by 23%, 15% and 14% respectively). Ritonavir exposure was slightly increased; Cmin, Cmax and AUC increased by 23%, 10% and 11% respectively. Saquinavir Cmin was moderately enhanced (47% increase); Cmax and AUC increased by 22% and 29% respectively. All subjects achieved a SQV Cmin above 100 ng/ml.
Pharmacokinetic assessment of tenofovir DF and ritonavir-boosted saquinavir in healthy subjects. Zong J, Chittick G, Blum MR, et al. 44th Interscience Conference on Antimicrobial Agents and Chemotherapy, Washington, October/November 2004, abstract A-444.

Coadministration of ritonavir (100 mg once daily, given with atazanavir) and tenofovir (300 mg once daily) was investigated in 10 male HIV+ subjects. In the presence of tenofovir, there were decreases in ritonavir AUC (7011 to 5217 ng/ml.h), Cmax (886 to 642 ng/ml) and Cmin (43 to 39 ng/ml). Atazanavir concentrations were also decreased in the presence of tenofovir.
Pharmacokinetic parameters of atazanavir/ritonavir when combined to tenofovir in HIV-infected patients with multiple treatment failures: a sub-study of PUZZLE2-ANRS 107 trial. Taburet AM, Piketty C, Gerard L, et al. 10th Conference on Retroviruses and Opportunistic Infections, Boston, February 2003. Abstract 537.