With the recent announcement by US President Donald Trump that Chloroquine or Hydroxychloroquine may be useful for the treatment of the new pandemic virus COVID-19, there have been questions about the safety of these medications and the difference between the two medications.

I will attempt to describe these medications as simply as possible while pointing out precautions, side effects, similarities and differences.


Chloroquine is a synthetic drug which was studied and researched as early as 1934 by the Germans under the name of Resochin. It has been used and is still being used around the world for the prevention and treatment of Malaria especially where the risk of chloroquine-resistant malaria is still low. It has also been widely used to treat Rheumatoid arthritis and Lupus erythematous.

Chloroquine is available as tablets, capsules, syrups and injections. It is important to note that oral formulations may be either Chloroquine Phosphate or Chloroquine Sulfate while the injection is Chloroquine hydrochloride. Therefore, it would be wise for prescribers to write the prescription clearly and state the dose as the chloroquine base or the Chloroquine salt.

****To avoid excessive dosage in obese patients, the doses of Chloroquine and Hydroxychloroquine should be calculated on the basis of ideal body-weight.****

Hydroxychloroquine on the other hand is a hydroxylated form of chloroquine with similar actions and attributes of chloroquine. It is generally less toxic than Chloroquine especially with long term use.

Toxicity, precautions and side effects

The same toxicity, precautions and side effects apply to both Chloroquine and Hydroxychloroquine. However, they are usually less with Hydroxychloroquine.

Taken in proper doses, Chloroquine is a very safe drug; however a single dose of 30mg/kg (13.61mg/lb.) may be fatal.


Use with caution in patients with psoriasis, history of epilepsy, myasthenia gravis, and severe gastrointestinal disorders. Avoid using with other hepatotoxic medications and patients with G6PD deficiency should use with care. Other precautions include patients with hepatic (liver) or renal (kidney) impairment.

For pregnant and breast-feeding patients, the prescriber should weigh the benefits versus the risks. In this case, just like in malaria; the benefits of treating COVID-19 most likely outweigh the risks.

*****To avoid excessive dosage in obese patients, the doses of Chloroquine and Hydroxychloroquine should be calculated on the basis of ideal body-weight.*****

These include gastrointestinal disturbances, headache, hypotension, visual disturbances, depigmentation or loss of hair, rashes and pruritus to mention a few.

For COVID-19

Hydroxychloroquine is widely prescribed in the United States and a lot of US prescribers are familiar with Hydroxychloroquine so I would think that would be a wise choice for US patients. On the other hand Chloroquine is widely prescribed in Africa and some other continents; so their prescribers can start with Chloroquine and later move to the less toxic Hydroxychloroquine.

The only dosage I could find was from the WHO and is the proposed dose of hydroxychloroquine 400mg per day for 5 days and it is still undergoing Clinical trials


Hopefully, these two affordable and widely available medications will prove successful in the fight against the COVID-19 virus.


British National Formulary 66 pg 432 (bnf.org)

Goodman & Gilman, The Pharmacological Basis of Therapeutics, 11th edition 2006


Leave a Reply

Your email address will not be published. Required fields are marked *