What is chronotherapy, or how to take your medication at the right moment?

What is chronotherapy? 

Almost all of our body's functions are subject to the circadian rhythm, i.e. a 24-hour cycle dominated by the alternation of day and night, whether it be blood pressure, heart rate, hormone production, etc.

During the day, our cells adapt their activity according to our internal clock, located in our brain.

The rhythm of our organs' functioning, our heart rate, variations in hormone secretions, our temperature or blood pressure, not to mention the periods of wakefulness and sleep, are all dictated by the time of day. This is called "chronobiology".

And it can also have consequences on certain treatments. Indeed, these circadian oscillations can modify the sensitivity of our cells to certain therapeutic molecules. It is in fact a question of administering the right medicine to patients at a certain time of day when this medicine is best tolerated and therefore more effective, causing fewer side effects.

Where can chronotherapy be used?

Chronotherapy has especially been used in cancerology in order to optimize chemotherapy.

Indeed, chemotherapy treatments aim to attack cancerous cells but are at the same time harmful or even toxic for healthy cells and can, therefore, lead to very significant adverse effects.

Researchers have wondered whether there is a period of time when healthy cells are less sensitive to anti-tumor chemotherapy molecules. By administering treatments during this particular period of time, it is possible to minimize the side effects and increase treatment's effectiveness. And thus, as the side effects can be reduced, chemotherapy doses can be increased in order to eliminate cancer cells even more quickly and effectively. 

In order to determine the ideal time to administer a drug, the circadian rhythms of the area targeted by this drug must be first studied. This area can be the part of the body affected by the tumor or, for example, the intestine, since many cancer patients suffer from severe diarrhea after administration of chemotherapy drugs.

Unfortunately, it is difficult to apply chronotherapy in cancer treatment because the best time for chemotherapy administration varies widely depending on many criteria such as the patient's gender (men and women react very differently to chemotherapy) or their genome.

Nevertheless, chronotherapy is being used in many other fields, such as cardiology, or in the treatment of inflammatory diseases.

Chronotherapy for rheumatoid diseases

Chronotherapy has been proven to be effective in the administration of anti-inflammatory drugs for rheumatoid diseases such as osteoarthritis.

In order to be most effective, anti-inflammatory drugs must be active in the early morning, when patients experience the most significant pain. 

Drugs have therefore been developed that can be taken late in the evening and release their active ingredients during the night to ease the pain that appears upon waking up.

Chronotherapy for cardiovascular diseases

The Lille University Hospital (Lille, France) has successfully demonstrated that adverse events after heart surgery, involving disconnection and reconnection of the heart, were greater when the operation took place in the morning, rather than in the afternoon (15% of complication cases compared to 8%). 

A key element to consider here is the patient's chronotype. Indeed, there are "morning chronotypes", whose biological clock is shorter than the earth clock, and "evening chronotypes", whose internal clock exceeds 24 hours.

The chronotype actually shifts the metabolic rhythms and thus the optimal rules of treatment administration. 

In order to measure a patient's circadian rhythm at an individual level, it is necessary to equip the patient with a sensor (via a connected watch, for example) that will be able to measure the patient's activity, temperature and heart rate, among other things. 

This is a major challenge that could enable the development of new techniques and the prediction of optimal periods of time for each patient to take their treatments or for surgical procedures!