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Experimental Ebola Treatment Being Used

Eric Toner, MD, August 14, 2014

It has been reported that 3 foreign aid workers infected by Ebola virus in west Africa (2 American healthcare workers and a Spanish priest) were treated with the experimental drug ZMappTM. The 2 Americans have survived, but the Spaniard has died. There are now reports that the drug is being made available to some infected Liberian physicians as well. The question has been raised in the media whether the drug should be made more widely available to infected people in Africa.1 The answer depends on a number of clinical issues, such as whether the drug is safe and effective; ethical issues, such as whether adequate informed consent can be obtained and how patients should be prioritized; regulatory issues, if used in the US or elsewhere; and logistical issues, such as how much is available, how quickly could manufacturing be ramped up, and whether the drug can be practically delivered to patients in Africa. In this brief report, we summarize what has been published so far about this drug.

What Is ZMappTM?

ZMappTM is a cocktail of 3 monoclonal antibodies that target 3 distinct glycoproteins on the Ebola virus. The 3 monoclonal antibodies are produced by genetically modified tobacco plants into which human-mouse hybrid anti-Ebolavirus genes have been inserted. The plant then produces the antibodies, which can be extracted. 2,3  Next-generation monoclonal antibodies such as these are being developed as therapy for a variety of infectious diseases.4

Safety and Efficacy in Humans Have Not Been Established

The drug has shown promise in nonhuman primate studies for both treatment of illness and postexposure prophylaxis but has not yet entered human trials. Therefore, neither safety nor efficacy has been established. The 3 Ebola patients treated recently are the first 3 humans to receive this drug. Whether the drug has had an impact on their clinical course is unclear because the patients also received other treatments, including convalescent serum in at least one case, and up to a third of Ebola patients recover with just good supportive care. No human dosing studies have been conducted, so the optimal dosage has not been determined. It is also not clear at what point in the clinical course the drug is effective. Furthermore, assuming that the drug has some efficacy in humans, it is not known whether it will affect the clinical course in patients who may not have access to basic supportive care. It will take much larger formal clinical trials to know if the drug is helpful or not.

Informed Consent

Informed consent is crucial in clinical trials, especially when safety has not yet been established. Consent is even more fraught when the patient is seriously ill with a potentially deadly disease. It might be reasonable to assume that physicians and other healthcare workers would be better able than patients to understand the complexities of informed consent for use of an untested drug.

Regulatory Issues

There is a clear process in the US for compassionate use of an experimental drug in an extreme circumstance such as this. The process is different in other countries, and the process, if it exists, in the Ebola-affected countries is unknown.

Manufacturing Issues

Because the drug has not yet entered human trials, the amount of drug that has been produced is quite small. The producer of the drug reports that its supply is now exhausted. How long it would take to manufacture hundreds or thousands of additional doses is not clear.

Delivery Issues

Most drugs require a reliable delivery chain. Potency is often affected by extreme heat. Whether proper conditions can be maintained throughout the delivery chain in the affected regions is unknown.

Other Drugs and Vaccines

Several other drugs that use entirely different mechanisms of action are also in early development as are Ebola vaccines. All of these countermeasures involve the same difficult issues as ZMappTM when being considered for use in this crisis.

Conclusion

Desperate times may indeed call for desperate action, and in this extreme circumstance it is not unreasonable to consider the use of an untested countermeasure. But to the extent that the many issues outlined above can be minimized, the less difficult the decision becomes. Given the very limited information available and many unanswered questions, clinicians and authorities are right to be very cautious about using these drugs at this time.

References

  1. Associated Press. Experimental Ebola drug: Questions and answers about ZMapp. CBS News website, August 12, 2014. http://www.cbsnews.com/news/experimental-ebola-drug-questions-and-answers-about-zmapp/. Accessed August 13, 2014.
  2. Pettitt J, Zeitlin L, Kim do H, et al. Therapeutic intervention of Ebola virus infection in rhesus macaques with the MB-003 monoclonal antibody cocktail. Sci Transl Med 2013;5(199):199ra113.
  3. ZMapp information sheet. Mapp Biopharmaceutical website. Undated. http://www.mappbio.com/zmapinfo.pdf. Accessed August 13, 2014.
  4. Gronvall G, Rambhia K, Adalja A, et al. Next-Generation Monoclonal Antibodies: Challenges and Opportunities. Report by the UPMC Center for Health Security. February 2013. http://www.upmchealthsecurity.org/our-work/pubs_archive/pubs-pdfs/2013/2013-02-04-next-gen-monoclonal-antibodies.pdf. Accessed August 13, 2014.