The liver’s production of cholesterol is greatest after midnight, with production dropping to its lowest in the morning and early afternoon. This happens because of a rhythmic change in the activity of an enzyme in the liver involved in cholesterol synthesis. What does this mean for cholesterol-lowering medications? Simvastatin (Zocor) is metabolized relatively quickly, and most studies show greater lowering of LDL cholesterol when it is taken in the evening. But that’s not true for other statins, such as atorvastatin (Lipitor) and rosuvastatin (Crestor). They metabolize more slowly, so it does not matter when they are taken.
Stomach acid production peaks in the evening and at night. But the best time to take two of the most commonly prescribed drugs to treat heartburn appears to vary. For instance, the H2 blocker cimetidine (Tagamet) may work better when taken in the early evening, as may the proton pump inhibitor, or PPI, rabeprazole (brand name AcipHex). But the PPI pantoprazole (Protonix) has been shown to improve the pH (a measure of acidity) of the stomach more effectively when taken in the morning.
People with asthma experience significantly more symptoms at night. That’s because the lungs are more sensitive to histamines—pro-inflammatory chemicals that affect the airways—and allergens that can constrict the airway at night. Some asthma drugs therefore have optimal dosing times. For example, taking bambuterol (Singulair) late in the day was found to have a better effect at opening the airways in the early morning vs taking it in the morning. Taking theophylline in the evening also leads to higher blood levels that are maintained through the night and morning, when the lungs need them most.
Blood pressure tends to peak during the day and fall at night. But that's not the case in some older people, in whom blood pressure may remain elevated at night. They are often advised to take certain blood pressure-lowering medications, such as ACE inhibitors and beta blockers, at bedtime. Why these drugs work better at night may have to do with a variation in kidney function as well as differences in drug metabolism by the liver. In contrast, hydrochlorothiazide (HCTZ) should be taken in the morning since it acts as a diuretic, which could impede sleep.
Scientists have found rhythmic changes in the body’s synthesis of genetic material (DNA and RNA) throughout the day that may affect the susceptibility of tumor cells to drugs. Specifically, these cancerous cells appear to have different cell-division cycles (by which the cells reproduce and proliferate) than normal cells. By timing certain chemotherapy drugs to the right time of day, doctors might be able to use a smaller and therefore less toxic dose to achieve the same benefit with fewer side effects. Some research suggests that more than two dozen different chemotherapy drugs’ toxicity is influenced by circadian rhythm.
People with rheumatoid arthritis often experience morning pain and stiffness. Researchers have found that levels of pro-inflammatory compounds in the blood, such as C-reactive protein (CRP) and interleukin-6 (IL-6), increase at night. So taking corticosteroids at night should lead to a reduction in morning pain and stiffness in these people.In contrast, people with osteoarthritis generally have the least pain during the morning. Thus taking non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, earlier in the day—before joint pain peaks—may provide more efficient relief.