Chloroquine has a very large volume of distribution of 65,000 L (VD is total drug in body/plasma conc.). This means that significantly more chloroquine is distributed into the tissue than the blood. It is a very lipophilic drug and distributes into the tissues with a long residence time (~ 900 hours). It is readily absorbed into the blood as referenced in the label info you provided with peak blood plasma levels in a couple hours. Then it distributes to the tissue and stays there for a prolonged time (weeks). It takes awhile for the chloroquine levels in the tissue to build up to therapeutic levels. It can take 1 - 3 months to see effects of Plaquenil. Likewise, it has prolonged effects after discontinuation because it is retained for a long time ( hence why the half life, which reflects the rate at which it is cleared from the body, is relevant to therapeutic levels in this case. It is the levels distributed in the tissues are what is important for therapeutic effect not the blood levels. If taken daily the blood levels will be the roughly the same on day 1 as on day 30 but don’t see effect for lupus or RA right away.
In fact, Kaiser Permanente stated that for hydroxychloroquine that “extensive experience and research show that hydroxychloroquinine builds up in the body and continues to work for a average of 40 days after the last dose is taken” in explaining why the weren’t filling routine prescriptions until the temporary shortage is resolved.
Perhaps you like to to read some too, so here you go.
https://doi.org/10.1038/s41584-020-0372-x