Table 1 Key selected inclusion and exclusion trial criteria for patients

1. Men and women from 40 to 80 years of age.

1. Patients who are currently treated with hydroxychloroquine (HCQ) or have received HCQ in the past due to OA of the hands.

2. Presence of clinical hand osteoarthritis (OA) according to American College of Rheumatology (ACR) criteria.

2. Patients who have not tolerated HCQ (for example, skin disease or malaria prophylaxis) or patients for whom HCQ was discontinued due to an eye disease.

3. Conforming to the ACR criteria for hand OA supported by X-ray of both hands, dating less than 6 months previous, X-ray of the hands showing radiological signs of digital erosive OA in one or more joints. This criterion is checked by a central assessment.

3. Existence of a pain syndrome of the upper limbs, which would interfere with the monitoring of pain.

4. Symptoms of digital inflammatory OA (pressure pain of the joint and/or florid joint swelling and/or redness and/or warmth) with more than three fingers’ joints for more than 3 months (at least every other day) despite taking analgesics and non-steroidal anti-inflammatory drugs (NSAIDs).

4. Patients suffering or having suffered from secondary OA after one of the following disease (for example, infectious arthritis, acromegaly, ochronosis, hemochromatosis, gout, etcetera) or inflammatory joint diseases.

5. Pain above 4 as evaluated by the Australian-Canadian OA Index (AUSCAN)-numeric rating score (NRS) (0-10).

5. Planned surgery.

6. Function as co-primary clinical outcome with ≥26 using the AUSCAN.

6. Local injection of finger or hand joints with glucocorticoids or other medications in the previous 3 months.

7. The ability to understand the trial information for patients (Arzneimittelgesetz, German Medicinal Products Act (AMG) §40(1) and 3b).

7. Current intake of oral, intra-articular (i.a.) or systematic glucocorticoids (intravenous (i.v.), intramuscular (i.m.)).

8. The ability to sign the written informed consent form including the data protection form (according AMG §40(1) and 3b).

8. Presence of retinopathy.

9. Known hypersensitivity to HCQ or to one of the drugs in this study protocol.

10. Treatment with digoxin

11. Any unstable medical condition or other serious clinical situations that expose the patient to risk in the opinion of the local investigator.

12. Current participation in another clinical trial or undergoing an experimental treatment.

13. Patients who are underage or incapable of understanding the aim, importance and consequences of the study or of giving legal informed consent (according to AMG §40(4) and 42(2) and (3)).

14. Prisoners and persons who are institutionalized due to AMG §40(1), no. 4

15. Pregnant and breastfeeding women