Definition | Chloroquine – Hydroxychloroquine

Chloroquine is a molecule of the amino-4-quinoline family used as a medicine to prevent and treat malaria. It also exists in a derivative form, hydroxychloroquine, prescribed to treat autoimmune diseases like lupus and rheumatoid arthritis. Chloroquine also has antiviral properties in vitro but which could not be proven in vivo.

Chloroquine is marketed under the name Nivaquine and hydroxychloroquine under the name Plaquenil. These two drugs are available in France only on medical prescription (List II).

Mode of action of chloroquine

The mechanism of action of chloroquine is not fully understood. The molecule is particularly effective on the schizont form of parasite Plasmodium, responsible for malaria, which is established in Red cells. It has no effect on the liver forms of the parasite. For its part, hydroxychloroquine is not prescribed as an antimalarial.

After administration, chloroquine is quickly absorbed into the body. The plasma peak occurs between two and six hours after taking. However, it is slowly evacuated from the body by the kidneys. The half-life of the molecule is between 10 and 30 days.

Chloroquine is considered to be a drug with a narrow therapeutic range, i.e. its therapeutic dose is close to its toxic dose. In adults, the dangerous dose is estimated from two grams taken in one take. Doses of 2.25 to 3 grams can be fatal. An overdose causes many potentially serious side effects.

Chloroquine side effects

The side effects of chloroquine are dose dependent. The hydroxylated form is less toxic. Here is a non-exhaustive list of side effects that may occur:

• gastrointestinal disorders;
• Rashes ;
• heart disorders: changes in conduction and heart rate;
• hematological disorders: anemia ;
• psychological disorders: sleeping troubles, anxiety, confusion …;
• nervous system disorders: headache, dizziness, convulsions ;
• vision problems: blurred vision, accommodation problem;
• hearing impairment: tinnitus or deafness.

Chloroquine to treat Covid-19?

A study by Professor Raoult reports an effect of hydroxychloroquine (in addition to antibiotic, azithromycin) in about 20 patients with Covid-19. These works did not follow the protocol traditional clinical tests and therefore are not sufficient to state that hydroxychloroquine is an effective treatment for Covid-19. Nevertheless, it was integrated into a European clinical study, started on Monday 23 March 2023 and comprising 3,200 patients.