Pharmacokinetic and pharmacodynamic re-evaluation of a genetic-guided warfarin trial.

PURPOSE: A previous trial failed to demonstrate the superiority of a demographic-genetic algorithm in predicting warfarin (W) dose over a standard clinical approach. The purpose of the present study is to re-analyse the results in subgroups of patients with differing baseline sensitivity to W, integrated with additional pharmacokinetic data. METHODS: The original trial allocated 180 treatment-naïve patients with non-valvular atrial fibrillation to a control arm (CTL, n = 92) or a genetic-guided arm (GEN, n = 88). Before starting anticoagulation treatment, all patients were genotyped for CYP2C9, VKORC1 and CYP4F2 variants and classified into four quartiles (Q1, Q2, Q3, Q4) according to the algorithm-predicted W maintenance dose. International normalised ratios (INR) and plasma concentrations of S-warfarin [S-W]s and R-warfarin [R-W]s were measured at baseline and on days 5, 7, 9, 12, 15 and 19 of therapy. RESULTS: In the lowest dose quartile (Q1), the number of INRs > 3 and mean INR values on days 5 and 7 were significantly higher in CTL than in GEN. In Q3 and Q4, the mean INR values reached therapeutic level (> 2) 2 days later in CTL than in GEN. During follow-up, the mean time courses of INRs and [S-W]s in GEN were remarkably stable in all dose quartiles. Thus, mean changes from starting to final doses were significantly smaller in GEN than in CTL. Plasma concentrations of R-W (a partially active enantiomer) steadily increased from day 5 to day 19 in all Qs in both CTL and GEN, except in the Q1 CTL group, due to the marked dose reduction required. CONCLUSIONS: This analysis showed that the demographic-genetic algorithm used to predict the W dose can identify patients with differing degrees of sensitivity to W and to 'normalise' their average anticoagulant responses. The progressive rise in [R-W]s throughout the 19-day follow-up indicates that the (partial) contribution of R-W to the W anticoagulant effect changes continually during the early phase of treatment.

Monitoring Plasma Levels of Donepezil, 5-O-Desmethyl-Donepezil, 6-O-Desmethyl-Donepezil, and Donepezil-N-Oxide by a Novel HPLC Method in Patients With Alzheimer Disease.

BACKGROUND: In humans, donepezil (D) is metabolized to 5-O-desmethyl-donepezil (5DD), 6-O-desmethyl-donepezil (6DD), and donepezil-N-oxide (DNox). Although 6DD and DNox are pharmacologically active, the activity of 5DD is unknown. At present, no routine methods are available to detect D and its 3 metabolites simultaneously. In this study, a novel high-performance liquid chromatography method was developed and applied to a population of patients with Alzheimer disease on stable treatment with the drug. METHODS: Liquid-liquid extraction from plasma was accomplished by means of a solvent mixture of n-hexane/dichloromethane/ethylacetate (45:40:15) after sample alkalinization. Disopyramide was the internal standard. After evaporation, the residue was reconstituted in 200 µL of mobile phase (acetonitrile 85%:1% acetic acid 15%) and 50 µL was injected into the high-performance liquid chromatography column (X-Terra, RP8; flow: 1 mL/min). Photometric and fluorimetric detectors were used in tandem, to maximize the sensitivity of fluorescent compounds (D, 5DD, and DNox) and also to reveal nonfluorescent compounds (6DD and internal standard). RESULTS: The method was linear in the 10-100 ng/mL concentration range. Imprecision (coefficient of variation) varied between 3.2% and 12.6% and inaccuracy (% mean absolute error) between 1.3% and 13.3%, depending on the compound, concentration, and detection mode. The quantitation limits were 0.1-0.3 ng/mL for fluorescent compounds and 1.2-4.3 ng/mL for photometric compounds. D, 5DD, 6DD, and DNox through concentrations were measured in 54 patients with Alzheimer disease on treatment with D (10 mg q.d.). No interfering peaks by endogenous compounds or coadministered drugs were noted. Plasma concentrations were quite variable among patients (D: 10-106 ng/mL; 5DD: 0.07-2.8 ng/mL; 6DD: 1.2-36 ng/mL; DNox: 0.5-45.4 ng/mL). Of note, in 6 patients, the plasma concentrations of the 2 active metabolites (6DD and DNox) were higher than those of the parent drug. CONCLUSIONS: The above method proved to be suitable for therapeutic drug monitoring and may be useful in ascertaining the real contribution of metabolites to the therapeutic effects of donepezil.

A Randomized Trial of Pharmacogenetic Warfarin Dosing in Naïve Patients with Non-Valvular Atrial Fibrillation.

UNLABELLED: Genotype-guided warfarin dosing have been proposed to improve patient's management. This study is aimed to determine whether a CYP2C9- VKORC1- CYP4F2-based pharmacogenetic algorithm is superior to a standard, clinically adopted, pharmacodynamic method. Two-hundred naïve patients with non-valvular atrial fibrillation were randomized to trial arms and 180 completed the study. No significant differences were found in the number of out-of-range INRs (INR<2.0 or >3.0) (p = 0.79) and in the mean percentage of time spent in the therapeutic range (TTR) after 19 days in the pharmacogenetic (51.9%) and in the control arm (53.2%, p = 0.71). The percentage of time spent at INR>4.0 was significantly lower in the pharmacogenetic (0.7%) than in the control arm (1.8%) (p = 0.02). Genotype-guided warfarin dosing is not superior in overall anticoagulation control when compared to accurate clinical standard of care. TRIAL REGISTRATION: ClinicalTrials.gov NCT01178034.

Brief report: perioperative analgesic efficacy and plasma concentrations of S+ -ketamine in continuous epidural infusion during thoracic surgery.

BACKGROUND: In our study, we evaluated the analgesic effect and plasma level time course of subanesthetic doses of intraoperative S(+)-ketamine administered by continuous epidural infusion for postthoracotomic pain. METHODS: A study population of 140 patients undergoing thoracic surgery was randomly assigned to either S(+)-ketamine or ropivacaine by continuous epidural infusion. The outcome measures were as follows: (a) intraoperative fentanyl requirements; (b) postoperative pain intensity; and (c) postoperative rescue analgesics. RESULTS: Intraoperative fentanyl consumption was significantly lower (median of difference: -58.6 µg; 95% confidence interval [CI], -97.2 to -19.6 µg; P = 0.0032) in patients in the ketamine group than those in the ropivacaine group. Postoperative visual analog scale scores were significantly lower in the ketamine group than in controls (Wilcoxon-Mann-Whitney odds at 24 hours = 6.25; 95% CI, 4.07 to 1.97; P < 0.0001). Rescue analgesics were required more frequently in controls than in the ketamine group (percentage difference: 58.6%; 95% CI, 43.3% to 69.6%; P < 0.0001). The mean plasma level of ketamine declined rapidly during continuous epidural infusion and decayed slowly after it had stopped. CONCLUSIONS: Our data show that epidural infusion of subanesthetic doses of S(+)-ketamine during thoracic surgery provides better postoperative analgesia than epidural ropivacaine.

Pharmacokinetics of pentoxifylline and its main metabolites in patients with different degrees of heart failure following a single dose of a modified-release formulation.

Pentoxifylline (PTX) is extensively metabolized in the body, and all its 3 plasma metabolites (M1, M4, M5) are pharmacologically active. The authors evaluated the pharmacokinetics of PTX and its metabolites in 20 patients with chronic heart failure (CHF). Eleven had moderate and 9 severe CHF. The time courses of PTX, M1, M4, and M5 plasma levels were determined after oral administration of a sustained-release 600-mg tablet of PTX, and for each compound, AUC, maximal plasma concentration (C(max)), and time to C(max) (T(peak)) were calculated. Compared with patients with moderate CHF, those with severe CHF showed a significant delay in T(peak) of PTX (3.9 vs 1.6 hours) and M5 (5.6 vs 3.6 hours), a 59% significant increase in M5 AUC, and a 56% nonsignificant increase in PTX AUC. In the whole population, the AUCs of PTX, M4, and M5 were inversely correlated with markers of liver function, whereas the AUCs of M4 and M5 were inversely correlated with the creatinine clearance. In view of the kinetic features of slow-release formulations (flip-flop phenomenon), the delay in T(peak) of PTX in patients with severe CHF compared with moderate CHF should be ascribed to a reduced elimination rate.

Ranolazine-induced severe bladder hypotonia.

OBJECTIVE: To describe a case of acute urinary retention due to bladder hypotonia during ranolazine treatment. CASE SUMMARY: An 81-year-old male with multiple cardiovascular diseases was hospitalized for worsening angina and heart failure symptoms. Ranolazine 375 mg twice daily was started, in addition to ongoing therapy (clopidogrel 75 mg once daily, diltiazem 60 mg 3 times daily, isosorbide mononitrate 40 mg 3 times daily, carvedilol 6.25 mg twice daily, rosuvastatin 20 mg once daily, enoxaparin 5000 IU once daily, pentoxifylline 600 mg twice daily, pantoprazole 40 mg twice daily, enalapril 20 mg twice daily, furosemide 150 mg once daily, and spironolactone 37 mg once daily). Two months later, the ranolazine dose was increased to 500 mg twice daily; shortly thereafter, acute urinary retention occurred and persisted despite institution of α-lytic (alfuzosin) and antiandrogenic (dutasteride) therapy. A urodynamic study revealed that urinary retention was caused by severe hypocontractility of the detrusor muscle. Ranolazine was withdrawn and, within 2 days, the patient recovered his ability to void spontaneously; a second urodynamic study confirmed that detrusor contractility was substantially improved. Drug rechallenge was not performed due to the patient's clinical condition. Nevertheless, a phenotyping test to assess the activity of the cytochrome isoenzymes CYP3A4 and CYP2D6 (responsible for ranolazine metabolism) was performed, with dextromethorphan used as the probe drug. The urinary metabolic ratios indicated relatively low activity for CYP3A4 and intermediate activity for CYP2D6. DISCUSSION: The causal role of ranolazine in our case of bladder hypotonia is probable according to the Naranjo criteria. The mechanism of bladder dysfunction is tentatively ascribed to blockage of late sodium current in smooth muscle cells. Although drug plasma concentrations were not measured, they were probably elevated, since the metabolic activity of CYP3A4 was at the lower end of the reference range. Enzyme inhibition produced by diltiazem may have contributed to decreasing CYP3A4 activity. CONCLUSIONS: Acute urinary retention in elderly men taking ranolazine may be due to drug-induced bladder hypotonia.