Antimalarial drugs have the obvious connotation of therapeutic utility against malaria, but certain drugs with activity against malaria also are immunomodulators used in rheumatology. Somewhat confusingly, some antibiotics, which are highly active against malaria are not explicitly called antimalarials.
In general usage, the term applies specifically to synthetic analogs of quinine, rather than antibiotics or other drugs with activity against malarial parasites and other protozoa. The major drugs of this type are:
Treatment of malaria
For malaria, chloroquine is the most important drug; quinacrine is no longer in commercial tablet production but, as a third-line agent, is available from compounding pharmacies. Chloroquine remains the drug of choice for chemoprophylaxis when resistance has not been reported.
Their most important use was in systemic lupus erythematosus,  although monoclonal antibodies are now the first-line drugs.  They also have applicability to rheumatoid arthritis, palindromic arthritis and psoriatic arthritis. When DMARDs are indicated, other DMARDs are often preferred, such as methotrexate in rheumatoid arthritis.
In a 1998 study comparing chloroquine and hydrochloroquine,  hydroxychloroquine was less toxic but less effective than chloroquine, but there were no firm recommendations of one over the other. Hydroxychloroquine is considerably more expensive.
Their immunologic mode of action was not understood before their therapeutic use, but current thinking is that they decrease antigen production by macrophages and lymphoid dendritic cells. They do this by increasing their intracytoplasmic pH, leading to changes in the molecular assembly of class II major histocompatibility complex molecules.
Damage to the eyes are the greatest concerns. These drugs may deposit in the melanin of the pigmented epithelial layer of the retina. Since early damage is often reversible, thorough opthalmologic examination is advised every 6 to 12 months.
These drugs can cause hemolytic anemia in patients with glucose-6-phosphate dehydrogenase deficiency.
- Lisa A. Spacek (6 August 2010), Plasmodium, POC-IT Center, Johns Hopkins University
- Hochberg MC et al., ed. (2004), Practical Rheumatology (Third ed.), Mosby, ISBN 0323029396, pp. 440-442
- Monograph: Chloroquine phosphate, American Society of Health System Pharmacists
- J Antonio Aviña-Zubieta et al. (1998), "Long term effectiveness of antimalarial drugs in rheumatic diseases", Ann Rheum Dis 57: 582-587, DOI:10.1136/ard.57.10.582
- Practical Rheumatology, p. 441