Administration-time differences in the pharmacokinetics of gentamicin intravenously delivered to human beings

Timing in drug absorption and disposition: The past, present, and future of chronopharmacokinetics

The importance of drug dosing time in pharmacokinetics, pharmacodynamics, and toxicity is receiving increasing attention from the scientific community. In spite of mounting evidence that circadian oscillations affect drug absorption, distribution, metabolism, and excretion (ADME), there remain many unanswered questions in this field and, occasionally, conflicting experimental results. Such data arise not only from translational difficulties caused by interspecies differences but also from variability in study design and a lack of understanding of how the circadian clock affects physiological factors that strongly influence ADME, namely, the expression and activity of drug transporters. Hence, the main goal of this review is to provide an updated analysis of the role of the circadian rhythm in drug absorption, distribution across blood-tissue barriers, metabolism in hepatic and extra-hepatic tissues, and hepatobiliary and renal excretion. It is expected that the research suggestions proposed here will contribute to a tissue-targeted and time-targeted pharmacotherapy.

Identifying 24 h variation in the pharmacokinetics of levofloxacin: a population pharmacokinetic approach

AIM

The objective of this study was to investigate whether the pharmacokinetics of orally administered levofloxacin show 24 h variation. Levofloxacin was used as a model compound for solubility and permeability independent absorption and passive renal elimination.

METHODS

In this single centre, crossover, open label study, 12 healthy subjects received an oral dose of 1000 mg levofloxacin at six different time points equally divided over the 24 h period. Population pharmacokinetic modelling was used to identify potential 24 h variation in the pharmacokinetic parameters of this drug.

RESULTS

The pharmacokinetics of levofloxacin could be described by a one compartment model with first order clearance and a transit compartment to describe drug absorption. The fit of the model was significantly improved when the absorption rate constant was described as a cosine function with a fixed period of 24 h, a relative amplitude of 47% and a peak around 08.00 h in the morning. Despite this variation in absorption rate constant, simulations of a once daily dosing regimen showed that tmax , Cmax and the area under the curve at steady-state were not affected by the time of drug administration.

CONCLUSION

The finding that the absorption rate constant showed considerable 24 h variation may be relevant for drugs with similar physicochemical properties as levofloxacin that have a narrower therapeutic index. Levofloxacin, however, can be dosed without taking into account the time of day, at least in terms of its pharmacokinetics.

The role of clock genes in pharmacology

The physiology of a wide variety of organisms is organized according to periodic environmental changes imposed by the earth's rotation. This way, a large number of physiological processes present diurnal rhythms regulated by an internal timing system called the circadian clock. As part of the rhythmicity in physiology, drug efficacy and toxicity can vary with time. Studies over the past four decades present diurnal oscillations in drug absorption, distribution, metabolism, and excretion. On the other hand, diurnal variations in the availability and sensitivity of drug targets have been correlated with time-dependent changes in drug effectiveness. In this review, we provide evidence supporting the regulation of drug kinetics and dynamics by the circadian clock. We also use the examples of hypertension and cancer to show current achievements and challenges in chronopharmacology.

Chronobiology and chronotoxicology of antibiotics and aminoglycosides

Few investigators have examined the circadian variation in the symptom intensity of infectious diseases. Seasonal patterns in a variety of infectious are well know. Less appreciated are the circadian patterns in the symptom expression of infections. Studies indicate that fever which accompanies the common cold peaks at 4 p.m., and this is in agreement with other studies indicating that the elevation of body temperature, fever, due to bacterial infections is higher in the evening while that due to viral infections is more likely in the morning. Animal and human studies reveal also administration-time-dependent differences in the pharmacokinetics and toxicity of antimicrobial agents. This is particularly true for the aminoglycosides, as their nephrotoxicity is greatest when administered during the resting period of laboratory animals and human beings. Food intake and low urinary pH has been found to be protective of the toxicity of aminoglycosides at this time of the day. Knowledge of the administration-time-dependence of aminoglycosides and the underlying mechanisms can be used to develop once-a-day formulations that are significantly less toxic, in particular to the kidney, in patients who require around-the-clock antimicrobial therapy.

Circadian variations in the pharmacokinetics, tissue distribution and urinary excretion of nifedipine after a single oral administration to rats

Circadian variations in the pharmacokinetics, tissue distribution and urinary excretion of nifedipine were examined in fasted rats after administering a single oral dose at three different dosing times (08:00 am, 16:00 pm, 00:00 am). The plasma concentrations, the areas under the plasma concentration-time curve from zero to 6 h (AUC(0-6 h)) and the peak plasma concentration (C(max)) were significantly higher in the rats dosed at 08:00 am (immediately inactive), and was lower at 16:00 pm (most inactive) and 00:00 am (most active). The time to reach the C(max) (T(max)) was the shortest in the rats dosed at 08:00 am. It was very interesting to observe the double peak phenomena in the plasma concentration profiles, showing a larger peak followed by a smaller peak. There was a dosing time dependency on the tissue distribution 30 min after administration, showing a similar tendency to the pharmacokinetic behavior. However, there was no distinct dosing time dependency observed at 2 h after administration due to the extensive disposition. The cumulative urine excretion of nifedipine in the rats dosed at 08:00 am was significantly higher (about two-fold) than in those dosed at 16:00 pm and 00:00 am. The pharmacokinetics of nifedipine in the rats was consistent with that observed in human subjects in terms of the day-night clock time but the biological time was the opposite, as marked by the rest-activity cycles. These results may help to explain the circadian time-dependency of nifedipine pharmacokinetics.

Absence of circadian variation in the pharmacokinetics of lopinavir/ritonavir given as a once daily dosing regimen in HIV-1-infected patients

AIMS

To compare the pharmacokinetics of lopinavir/ritonavir (LPV/r) 800/200 mg administered once daily in the morning compared with the evening.

METHODS

This was a randomized, two-way, cross-over study in HIV+ subjects. In each subject the pharmacokinetics of each drug were characterized after 2 weeks of LPV/r 800/200 mg administered once daily at 08.00 h and 19.00 h. On study days, LPV/r was taken with a standardized meal (800 kCal, 25% from fat) after fasting for at least 5 h. LPV/r concentrations were measured by LC-MS/MS, and the data were analyzed by noncompartmental pharmacokinetic analysis.

RESULTS

Fourteen subjects completed the study (all men, mean age/weight 44 year/81 kg). The median (interquartile range) LPV AUC(0,24 h), maximum plasma concentration (C(max)) and concentration at the end of the dosing interval (C(24 h)) after am and pm dosing was, respectively, 143 (116-214) mg l(-1) h, 12.8 (10.3-17.2) mg l(-1), 1.34 (0.58-3.25) mg l(-1), and 171 (120-232) mg l(-1) h, 12.9 (8.22-16.3) mg l(-1), 1.15 (0.59-1.98) mg l(-1). The geometric mean ratio (GMR, am : pm) and 95% CI of the LPV AUC(0,24 h), C(max), and C(24 h) was 0.91 (0.79, 1.06), 1.11 (0.94, 1.32), and 1.19 (0.72, 1.96), respectively. The median ritonavir C(max) after am and pm dosing was 1.05 and 0.90 mg l(-1), respectively. The GMR (95% CI) of the RTV AUC(0,24 h), C(max), and C(24 h) was 0.93 (0.80, 1.08), 1.27 (1.00, 1.63), and 1.04 (0.68, 1.60), respectively. Administration of LPV/r in a once-daily regimen was generally well tolerated.

CONCLUSIONS

No differences were observed in the pharmacokinetics of LPV/r after am or pm dosing with food, which suggests that this once daily combination, can be taken in the morning or evening. Such flexibility in dosing may improve adherence.

Aminoglycoside nephrotoxicity: do time and frequency of administration matter?

Aminoglycosides remains the mainstay in the treatment of gram-negative infections despite their potential oto-and nephrotoxicity although alternatives with equal or better efficacy are available. Several approaches were investigated to decrease aminoglycosides nephrotoxicity. Among them, only the once-daily dosing of aminoglycosides has been brought to the clinic and physicians are now increasingly adopting this approach to reduce the toxicity of these agents. The incidence of aminoglycoside nephrotoxicity can be further reduced in view of the recent data on the circadian variations of their nephrotoxicity. In fact, it has been clearly demonstrated in both experimental animals and humans that the toxicity is maximal when the drug is injected during the rest period compared with the activity period. Thus, injecting aminoglycosides once-daily at the time of the lowest toxicity is actually the most interesting and clinically applicable approach to reduce aminoglycosides toxicity.

Circadian changes in pharmacokinetics of sulfamethoxazole administered orally to rabbits

Circadian variations of sulfamethoxazole pharmacokinetics were studied after a single oral administration of sulfamethoxazole, 50 mg/kg, to rabbits at 09:00 (a.m.) and 22:00 (p.m.). The profiles of plasma sulfamethoxazole concentration showed from 6 h to 24 h significant statistical difference (p<0.05) between 09:00 and 22:00. The half-life (t(1/2)) was significantly shorter in the morning (11.2 +/- 3.2 h) when compared to the nighttime (15.4 +/- 3.5 h) (p< 0.05). The AUC was significantly decreased in the morning (1325 +/- 264 microg/ml x h) than that in the nighttime (2059 +/- 379 microg/ml x h) (p<0.05). Total body clearance (CLt) was significantly higher when sulfamethoxazole was given in the morning (6.65 +/- 0.23 ml/min) versus in the nighttime (4.28 +/- 0.20 ml/min) (p<0.05).