Background and ObjectivesThe effects of age and sex on apixaban pharmacokinetics and pharmacodynamics were studied.MethodsThis was an open-label, single-dose, 2 × 2 factorial study. Healthy young (aged 18–40 years) and elderly (aged ≥65 years) male and female subjects received a single oral 20 mg dose of apixaban. Blood and urine samples were collected for pharmacokinetic and pharmacodynamic (blood only) analyses. Subjects were monitored for adverse events throughout the study.ResultsSeventy-nine subjects were enrolled into four groups: young males (n = 20), elderly males (n = 20), young females (n = 20) and elderly females (n = 19). Age did not affect the maximum observed plasma concentration (Cmax). The mean area under the concentration–time curve from time zero extrapolated to infinite time (AUC∞) was 32 % greater in elderly subjects than in young subjects. The mean Cmax and AUC∞ values were 18 and 15 % higher, respectively, in females than in males. The time course of the mean international normalized ratio (INR), modified prothrombin time (mPT) and anti-Xa activity tracked the apixaban concentration–time curve. All three pharmacodynamic measures exhibited a positive linear correlation with the plasma apixaban concentration. Differences in the mean INR, mPT and anti-Xa activity between age and sex groups were small (<15 % at the maximum mean values) and were generally related to pharmacokinetic differences. However, anti-Xa activity demonstrated less variability than the INR or mPT, and may have utility as a bioassay for apixaban. Apixaban was well tolerated, with no serious adverse events.ConclusionThere were no clinically meaningful age- or sex-related differences in the pharmacokinetics and pharmacodynamics of apixaban that would require dose modification on the basis of age or sex alone.
Aims
To determine whether repeated once daily administration of grapefruit juice altered the pharmacokinetics or pharmacodynamics of the calcium antagonist amlodipine.
Methods
The effects of grapefruit juice on the pharmacokinetics and pharmacodynamics of oral and intravenous amlodipine were assessed in 20 healthy men in a placebo‐controlled, open, randomized, four‐way crossover study using single doses of amlodipine 10 mg. For 9 days beginning with the day of administration of amlodipine, grapefruit juice (or water control) was given once daily, and blood samples, blood pressure and heart rate measures were obtained. Plasma concentrations of amlodipine and its enantiomers were determined in separate assays by GC‐ECD.
Results
Oral amlodipine had high systemic availability (grapefruit juice: 88%; water: 81%). Pharmacokinetic parameters of racemic amlodipine (AUC, Cmax, tmax, and kel) were not markedly changed with grapefruit juice coadministration. Total plasma clearance and volume of distribution, calculated after intravenous amlodipine, were essentially unchanged by grapefruit juice (CL 6.65 ml min−1 kg−1, juice vs 6.93 ml min−1 kg−1, water; Vdss 22.7 l kg−1, juice vs 21.0 l kg−1, water). Grapefruit juice coadministration did not greatly alter the stereoselectivity in amlodipine oral or intravenous kinetics. The sum of S(–) and R(+) enantiomer concentrations correlated well with total racemic amlodipine concentration (r2 = 0.957; P = 0.0001). Coadministration of grapefruit juice with either route of amlodipine administration did not significantly alter blood pressure changes vs control.
Conclusions
Grapefruit juice has no appreciable effect on amlodipine pharmacodynamics or pharmacokinetics, including its stereoselective kinetics. Bioavailability enhancement by grapefruit juice, noted with other dihydropyridine calcium antagonists, does not occur with amlodipine. Once daily grapefruit juice administration with usual oral doses of amlodipine is unlikely to alter the profile of response in clinical practice.
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