What is the appropriate interval to obtain a hydroxychloroquine level after making a dosage adjustment?

Hydroxychloroquine has an initial whole-blood half-life of around 5 days, while its terminal half-life is around 40 days (Costedeau-Chalumeau et al., PMID 27745934). The former is relevant to evaluating whole blood levels after a dose change.

This was confirmed in the PLUS study (see figure 2 in Costedoat-Chalumeau et al., PMID 23144449). One can see a steady state beginning at 1 month after dosage change.

Due to these results, I remeasure a trough whole blood HCQ drug level 1 month or later after any dose change before making decisions on dose changes.

Personal communication with Dr. Costedoat-Chalumeau confirms that she does the same. She states that after first starting someone on HCQ, she waits 1 to 1 1/2 months before testing.