The purpose of this clinical trial is to characterize drug interactions between one medicinal herb widely used by HIV infected patients: Echinacea sp. and the protease inhibitor darunavir/ritonavir.

15 patients on antiretroviral therapy with darunavir/ritonavir 600/100 mg twice a day during four weeks will be recruited. The patients will receive treatment with Echinacea purpurea for 14 days, 500 mg every 6 hours. A 12 hour pharmacokinetic curve will be obtained at baseline and on day 14.

Inclusion Criteria:

1. Patients infected with HIV-1 (at least one documented positive Western-Blot).
2. Age =/+ 18 years.
3. Patients receiving antiretroviral therapy containing darunavir / ritonavir at the approved dose of 600/100 mg twice daily for at least 4 weeks
4. HIV viral load in plasma <50 copies / mL
5. Absence of acute infections and / or tumors in the three months prior to inclusion.
6. Subject able to follow the treatment period, without suspicion of poor adherence in previous antiretroviral treatments.
7. Voluntary written informed consent.

Exclusion Criteria:

1. Any clinical or historical observation that could interfere with the pharmacokinetics of medications, such as gastrointestinal illness or surgery (except for herniotomy and appendectomy), changes in the composition of plasma proteins, some indication of hepatic or renal dysfunction.
2. Active alcohol consumption (> 50 g / day) or illicit drugs (except cannabis).
3. Pregnancy or lactation