Nonlinear accumulation of propranolol enantiomers

Pharmacokinetic Variability of Drugs Used for Prophylactic Treatment of Migraine

In this review, we evaluate the variability in the pharmacokinetics of 11 drugs with established prophylactic effects in migraine to facilitate 'personalized medicine' with these drugs. PubMed was searched for 'single-dose' and 'steady-state' pharmacokinetic studies of these 11 drugs. The maximum plasma concentration was reported in 248 single-dose and 115 steady-state pharmacokinetic studies, and the area under the plasma concentration-time curve was reported in 299 single-dose studies and 112 steady-state pharmacokinetic studies. For each study, the coefficient of variation was calculated for maximum plasma concentration and area under the plasma concentration-time curve, and we divided the drug variability into two categories; high variability, coefficient of variation >40%, or low or moderate variability, coefficient of variation <40%. Based on the area under the plasma concentration-time curve in steady-state studies, the following drugs have high pharmacokinetic variability: propranolol in 92% (33/36), metoprolol in 85% (33/39), and amitriptyline in 60% (3/5) of studies. The following drugs have low or moderate variability: atenolol in 100% (2/2), valproate in 100% (15/15), topiramate in 88% (7/8), and naproxen and candesartan in 100% (2/2) of studies. For drugs with low or moderate pharmacokinetic variability, treatment can start without initial titration of doses, whereas titration is used to possibly enhance tolerability of topiramate and amitriptyline. The very high pharmacokinetic variability of metoprolol and propranolol can result in very high plasma concentrations in a small minority of patients, and those drugs should therefore be titrated up from a low initial dose, depending mainly on the occurrence of adverse events.

Dispersive liquid–liquid microextraction of propranolol enantiomers from human plasma based on the solidification of a floating organic droplet

Background: A dispersive liquid–liquid microextraction based on the solidification of a floating organic droplet was developed and validated for the extraction of propranolol enantiomers from human plasma. The studied enantiomers were extracted from diluted and alkalized plasma samples using 1-undecanol as the extracting solvent. HPLC–fluorescence detection analyses were carried out on a chiral column, using n-hexane–ethanol (80:20, v/v) plus 0.2% triethylamine as the mobile phase, at a flow rate of 0.8 ml/min. The significant factors in the microextraction procedure, including extracting and disperser solvents volume, solution pH and salt contents were optimized by using a central composite design and the response surface methodology. Results: Under optimized conditions, the mean recoveries were approximately 14% with linear responses over the 0.5–100 ng/ml concentration range for both enantiomers. The LOQ was 0.5 ng/ml (S/N = 10). Intra-day (n = 5) and inter-day (n = 3) assay precision (1 and 50 ng/ml) showed RSD lower than 8 and 9.5% for studied enantiomers, respectively. Finally, the method was successfully used for the determination of propranolol enantiomers in plasma samples obtained after single drug administration of racemic propranolol tablet to three healthy volunteers. The plasmatic concentrations of (-)-(S)-PROP were higher than those of (+)-(R)-PROP in all times after oral administration of the racemic drug. Conclusion: The obtained results proved that the proposed method is a powerful technique for sample preparation, providing suitable recoveries, efficient cleanup, high selectivity and sensitivity and low consumption of organic solvent for determination of the studied enantiomers in plasma samples after oral administration of the racemic drug to volunteers.

Pharmacokinetics of pirmenol enantiomers and pharmacodynamics of pirmenol racemate in patients with premature ventricular contractions

The pharmacokinetics and pharmacodynamics of pirmenol were investigated in 12 patients with premature ventricular contractions (PVCs) after oral administration of racemic pirmenol, 100 mg and 200 mg every 12 hours. Holter monitoring was performed and serial blood samples were collected after the seventh doses. Plasma concentrations of pirmenol enantiomer were determined using a stereospecific liquid chromatographic assay. Clearance of total (-)-pirmenol was 20% higher than that of total (+)-pirmenol, and the difference in unbound clearance was 45% between enantiomers. Total pirmenol showed a smaller difference because of stereoselective protein binding, with 25% (100-mg dose) or 27% (200-mg dose) higher fraction unbound for (+)-pirmenol than for (-)-pirmenol. Distribution volume was similar for both enantiomers. Dose-dependent clearance was observed for unbound pirmenol enantiomers, as both enantiomers showed 20% lower unbound clearance at the higher dose. Antiarrhythmic effect (% reduction in PVCs from baseline) was correlated with plasma concentrations of pirmenol using a sigmoid maximum drug effect model, and patients showed a large variability in their antiarrhythmic response to plasma concentrations of pirmenol. The median value for minimum effective plasma concentration of racemic pirmenol was 1.5 micrograms/mL.

The effect of dosage release formulations on the pharmacokinetics of propranolol stereoisomers in humans

Recent studies in dogs have suggested that the disposition of S- and R-propranolol may depend on the input rate of drug delivered to the liver. Therefore, this study was designed to determine whether differences in the disposition of S- and R-propranolol occur in humans when altering the input rate of propranolol by giving different dosage forms of the drug. Twelve healthy subjects were enrolled in a single-dose, 4-way crossover pharmacokinetic study in which racemic propranolol was given according to 1 of 4 treatments: one 80-mg immediate-release (IR) tablet, phase A; two 80-mg IR tablets, phase B; a 160-mg controlled-release capsule, phase C; or a 10-mg IV bolus, phase D. The results showed no significant differences in the ratios of S/R-propranolol for AUC, clearance, or overall mean concentration among the oral dosage groups. Significant differences in these parameters including Cmax S/R ratio were seen between the oral phases and the IV phase. These differences appear to be related more to the route of administration than to the low input rate. However, at high concentrations there may be input-rate alteration in S/R ratios. Specifically, for phase B, which had the highest Cmax concentrations, the Cmax S/R ratio was significantly lower than the other oral dosage groups A and C (Cmax S/R ratios: 1.44 versus 1.54 and 1.54, respectively; P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Enantioselective bioanalysis of beta-blocking agents: focus on atenolol, betaxolol, carvedilol, metoprolol, pindolol, propranolol and sotalol

The recent developments in enantioselective HPLC-separation techniques are impressive and are driven by industrial and academic interests; thus there is for instance a high demand for developing stereoselective assays for chiral drugs in biological fluids. The beta-blocking agents, which possess an amino-propanol- or -ethanol side chain with at least one chiral centre, represent one of the most intensively investigated groups of more than 40 drugs introduced world wide. Seven of the most popular beta-blockers were chosen as representatives: atenolol; betaxolol; carvedilol; metoprolol; pindolol; propranolol; and sotalol, these span the whole range of lipophilicity to hydrophilicity (polarity). Enantioselective HPLC bioassays for these beta-blockers published so far, including techniques based on chiral derivatizing agents (CDAs), chiral stationary phases (CSPs) and chiral mobile phase additives (CMPAs) have been reviewed and documented in the light of general aspects together with pharmacokinetic and pharmacodynamic considerations.

Selective effect of adjuvant arthritis on the disposition of propranolol enantiomers in rats detected using a stereospecific HPLC assay

Nonstereospecific studies have indicated that the pharmacokinetics of propranolol (PR) are altered in inflammatory conditions such as arthritis. However, as the kinetics and dynamics of PR are stereoselective, we examined the effect of adjuvant arthritis (AA) on the disposition of the individual enantiomers. A novel normal-phase stereospecific HPLC assay for PR was developed involving chiral derivatization with S-(naphthyl)ethyl isocyanate and fluorescence detection. Oral and iv doses of racemic PR were administered to control and AA rats (n = 6). AA had no significant effect on either clearance or S:R ratio after iv doses. On the other hand, after oral doses, clearance was significantly decreased in AA. Although significant for both enantiomers, this effect was more pronounced on the less active R-enantiomer. The AUC R:S ratio was, therefore, significantly altered (AA, 14 +/- 3.0; control, 4.3 +/- 1.2). Increased total (S+R) plasma concentrations of PR in AA, possibly due to a reduced intrinsic clearance, therefore, reflect mainly increased concentrations of the less active R-enantiomer.

Liquid chromatographic analysis of propranolol enantiomers in human blood using precolumn derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate

A method for the determination of the R-(+) and S-(-) enantiomers of propranolol in blood was developed. After extraction with heptane-isopentanol and derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate, excess reagent was removed using solid-phase extraction. The enantiomers were separated on an achiral, reversed-phase, radially compressed column, and detected by fluorescence with excitation and emission wavelengths of 260 and 340 nm, respectively. The limit of quantification was 0.5 ng/ml. This method was used for pharmacokinetic analysis of propranolol enantiomers after administration of immediate-release (80 mg) or sustained-release (160 mg) racemic propranolol.