Circadian rhythms are cyclic changes that are crucial in plasma drug concentrations. Various standard circadian parameters, including core body temperature, heart rate, and other cardiovascular factors, directly impact disease states and the therapeutic response to drug therapy.

The time of drug administration is an important factor to consider, as it can influence the toxic dose of a drug. For example, a study conducted by Prins et al. in 1997 examined the effects of the timing of aminoglycoside administration on serum aminoglycoside levels and the incidence of nephrotoxicity in 221 patients. The study found no statistically significant differences in drug trough or peak drug levels for different drug administration periods. However, nephrotoxicity occurred significantly more frequently when the aminoglycosides were given during the rest period (12 am-7:30 am), suggesting that the administration time is an independent risk factor for nephrotoxicity.

Circadian changes also impact drug response in chronic obstructive pulmonary disease (COPD) patients. Changes in respiration during the sleep cycle can aggravate symptoms of hypoxemia in some COPD patients. Additionally, circadian variations have been observed in the incidence of acute myocardial infarction, sudden cardiac death, and stroke. Platelet aggregation favoring coagulation increases in the early morning hours, coinciding with the peak incidence of these cardiovascular events.

Time-dependent pharmacokinetics and physiologic functions are important in treating certain hypertensive subjects. Hypertensive individuals who experience an early-morning rise in blood pressure may face an increased risk of stroke or hypertensive crisis. Verapamil, a commonly used antihypertensive, has been studied for its effect on forearm vascular resistance (FVR) and early-morning blood pressure rise. The diurnal pattern of FVR differed between hypertensive and normotensive individuals, and verapamil appeared to minimize the diurnal variation in FVR in hypertensives. However, it did not significantly affect the early-morning rate of blood pressure rise.

Overall, understanding the influence of circadian rhythms on drug concentrations and therapeutic response is crucial in optimizing treatment strategies for various medical conditions. By considering time-dependent pharmacokinetics and physiological functions, healthcare professionals can make informed decisions to improve patient outcomes and minimize potential risks.