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Do You Know the Drug Interactions Related to Hydroxychloroquine and Chloroquine?

Anti-malarial medications like Hydroxychloroquine and Chloroquine are potential treatments for the symptoms of COVID-19. Are you aware of related drug interactions? Did you know that rapid lab tests for these drug levels can be performed in unique specimen types: serum/plasma, blood, fluids (purge, gastric, synovial, vitreous, bile) and tissue? Learn this and the importance of Therapeutic Drug Monitoring with our new infographic.

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Hydroxychloroquine is an antimalarial medication known more commonly by doctors and patients as Plaquenil®. The drug was approved for use in the United States in 1994, and indications were later broadened to include rheumatoid and psoriatic arthritis, discoid and systemic lupus erythematosus and prevention and treatment of malaria1.

Recent media reports and publications have reported the use of hydroxychloroquine and chloroquine in treating patients with COVID-19. As reported by the Center for Disease Control (CDC), chloroquine and hydroxychloroquine have demonstrated in-vitro activity against SARS-COV, SARS-CoV-2 and other coronaviruses with the latter showing a higher level of potency2,3. A limited small scale study in China reported that chloroquine treatment of COVID-19 patients resulted in clinical and virologic improvement versus the comparator group4. As stated on the CDC website “based upon limited in-vitro and anecdotal data, chloroquine or hydroxychloroquine are currently recommended for treatment of hospitalized patients in several countries.” A recently reported death of a man self-medicating with chloroquine phosphate, an aquarium cleaning additive, reiterates the potential toxicity of these compounds5. The FDA issued an Emergency Use Authorization to facilitate the availability of chloroquine phosphate and hydroxychloroquine sulfate during the COVID-19 pandemic to treat patients for whom a clinical trial is not available, or participation is not feasible. Hydroxychloroquine remains under investigation in the United States and internationally to assess the efficacy and safety for pre-exposure or post-exposure prophylaxis of SARS-COV-2, and treatment of patients with COVID-19.

How does Therapeutic Drug Monitoring apply to Hydroxychloroquine and Chloroquine?

Therapeutic drug monitoring (TDM) may be performed to inform physicians seeking to optimize dosage regimens based on measurements of drug concentrations at designated intervals. The feedback from TDM can help doctors maintain a therapeutic concentration in an individual patient’s bloodstream while minimizing potential side effects. The United States Food and Drug Administration (FDA) outlines potential risk factors for patients using hydroxychloroquine and chloroquine, including:

  • Cardiac Effects, including Cardiomyopathy and QT prolongation which may lead to cardiac arrhythmias
  • Irreversible Retinal Damage
  • Worsening of psoriasis and porphyria
  • Proximal myopathy and neuropathy
  • Neuropsychiatric events
  • Hypoglycemia
  • Chloroquine should be avoided during pregnancy
  • Reduced antibody response to rabies vaccine

Hydroxychloroquine has a very long elimination half-life of 40 to 50 days, which can add to the complexity of dosing. Additional pharmacokinetic interactions make it difficult to predict blood concentrations from a given dose. The following drugs can significantly affect blood concentrations of chloroquine or hydroxychloroquine:

  • Antacids and kaolin reduce absorption of chloroquine when taken together
  • Cimetidine causes increased chloroquine concentrations

Hydroxychloroquine is concentrated in red blood cells and has a pronounced and highly variable blood-to-plasma ratio of approximately 76.

Partner with NMS Labs for Therapeutic Drug Analysis and Monitoring

Healthcare providers depend on laboratory testing to aid in monitoring the amount of the drug found in the bloodstream so he or she can ensure that the drug level is within an effective range. NMS Labs proudly offers healthcare providers and Clinical Research Organizations therapeutic drug monitoring tests. Physicians trust our assays to assist them in assessing and adjusting individual patient medication doses to improve patient care.

Accredited by the College of American Pathologists (CAP) ISO 15189 and Clinical Laboratory Improvement Amendments (CLIA)


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Hydroxychloroquine and Chloroquine Testing

Information and insights obtained from Hydroxychloroquine and Chloroquine testing can be used to help minimize the risk of toxicity for a patient and shorten the time needed to establish and maintain an optimal dosing regimen.

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Chloroquine Testing

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1. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury [Internet]. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases; 2012-. Hydroxychloroquine. [Updated 2018 Mar 25]. Available from:
2. Wang M, Cao R, Zhang L, Yang X, Liu J, Xu M, Shi Z, Hu Z, Zhong W, Xiao G. Remdesivir and chloroquine effectively inhibit the recently emerged novel coronavirus (2019-nCoV) in vitro. Cell Res. 2020 Mar;30(3):269-271. Available from:
3. Colson P, Rolain JM, Lagier JC, Brouqui P, Raoult D. Chloroquine and hydroxychloroquine as available weapons to fight COVID-19. Int J Antimicrob Agents. 2020 Mar 4:105932. doi: 10.1016/j.ijantimicag.2020.105932. [Epub ahead of print]. Available from:
4. Yao X, Ye F, Zhang M, Cui C, Huang B, Niu P, Liu X, Zhao L, Dong E, Song C, Zhan S, Lu R, Li H, Tan W, Liu D. In Vitro Antiviral Activity and Projection of Optimized Dosing Design of Hydroxychloroquine for the Treatment of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Clin Infect Dis. 2020 Mar 9. pii: ciaa237. doi: 10.1093/cid/ciaa237. [Epub ahead of print]. Available from
5. Waldrop, Theresa, and Dave Alsup. “Arizona Man Dies after Self-Medicating with Chloroquine to Treat Coronavirus.” CNN, Cable News Network, 24 Mar. 2020
6. S Tett, D Cutler, R Day, K Brown, A dose-ranging study of the pharmacokinetics of hdyroxychloroquine following intravenous administration to healthy volunteers. Br J clin Pharm 1988. 26:303-313.