SFC-MS/MS as an orthogonal technique for improved screening of polar analytes in anti-doping control.

HPLC is considered the method of choice for the separation of various classes of drugs. However, some analytes are still challenging as HPLC shows limited resolution capabilities for highly polar analytes as they interact insufficiently on conventional reversed-phase (RP) columns. Especially in combination with mass spectrometric detection, limitations apply for alterations of stationary phases. Some highly polar sympathomimetic drugs and their metabolites showed almost no retention on different RP columns. Their retention remains poor even on phenylhexyl phases that show different selectivity due to π-π interactions. Supercritical fluid chromatography (SFC) as an orthogonal separation technique to HPLC may help to overcome these issues. Selected polar drugs and metabolites were analyzed utilizing SFC separation. All compounds showed sharp peaks and good retention even for the very polar analytes, such as sulfoconjugates. Retention times and elution orders in SFC are different to both RP and HILIC separations as a result of the orthogonality. Short cycle times could be realized. As temperature and pressure strongly influence the polarity of supercritical fluids, precise regulation of temperature and backpressure is required for the stability of the retention times. As CO2 is the main constituent of the mobile phase in SFC, solvent consumption and solvent waste are considerably reduced. Graphical Abstract SFC-MS/MS vs. LC-MS/MS.

Electrically assisted liquid-phase microextraction combined with capillary electrophoresis for quantification of propranolol enantiomers in human body fluids.

In this study, electromembrane extraction (EME) combined with cyclodextrin (CD)-modified capillary electrophoresis (CE) was applied for the extraction, separation, and quantification of propranolol (PRO) enantiomers from biological samples. The PRO enantiomers were extracted from aqueous donor solutions, through a supported liquid membrane (SLM) consisting of 2-nitrophenyl octyl ether (NPOE) impregnated on the wall of the hollow fiber, and into a 20-µL acidic aqueous acceptor solution into the lumen of hollow fiber. Important parameters affecting EME efficiency such as extraction voltage, extraction time, pH of the donor and acceptor solutions were optimized using a Box-Behnken design (BBD). Then, under these optimized conditions, the acceptor solution was analyzed using an optimized CD-modified CE. Several types of CD were evaluated and best results were obtained using a fused-silica capillary with ammonium acetate (80 mM, pH 2.5) containing 8 mM hydroxypropyl-ß-CD as a chiral selector, applied voltage of 18 kV, and temperature of 20°C. The relative recoveries were obtained in the range of 78-95%. Finally, the performance of the present method was evaluated for the extraction and determination of PRO enantiomers in real biological samples.

HPLC column-switching technique for sample preparation and fluorescence determination of propranolol in urine using fused-core columns in both dimensions.

A new and fast high-performance liquid chromatography (HPLC) column-switching method using fused-core columns in both dimensions for sample preconcentration and determination of propranolol in human urine has been developed. On-line sample pretreatment and propranolol preconcentration were performed on an Ascentis Express RP-C-18 guard column (5 × 4.6 mm), particle size, 2.7 µm, with mobile phase acetonitrile/water (5:95, v/v) at a flow rate of 2.0 mL min(-1) and at a temperature of 50 °C. Valve switch from pretreatment column to analytical column was set at 4.0 min in a back-flush mode. Separation of propranolol from other endogenous urine compounds was achieved on the fused-core column Ascentis Express RP-Amide (100 × 4.6 mm), particle size, 2.7 µm, with mobile phase acetonitrile/water solution of 0.5% triethylamine, pH adjusted to 4.5 by means of glacial acetic acid (25:75, v/v), at a flow rate of 1.0 mL min(-1) and at a temperature of 50 °C. Fluorescence excitation/emission detection wavelengths were set at 229/338 nm. A volume of 1,500 µL of filtered urine sample solution was injected directly into the column-switching HPLC system. The total analysis time including on-line sample pretreatment was less than 8 min. The experimentally determined limit of detection of the method was found to be 0.015 ng mL(-1).

Two dimensional chromatography mass spectrometry: Quantitation of chiral shifts in metabolism of propranolol in bioanalysis.

In this study a heart-cutting 2D-LC method was successfully developed and optimized in order to discriminate and quantitate (S)-propranolol, (R)-propranolol, and its hydroxy metabolites, namely the isomeric (S)-4'­hydroxy propranolol, (R)-4'­hydroxy propranolol, (S)-5'­hydroxy propranolol, (R)-5'­hydroxy propranolol, (S)-7'-hydroxy propranolol, and (R)-7'­hydroxy propranolol in one chromatographic run. Thereby, experiments investigating chiral discrimination in ring hydroxylation of propranolol were made feasible. Analysis of human urine samples after administration of a single oral dose of 40 mg of propranolol clearly revealed considerable chiral shifts in propranolol and its 4'-, 5'-, and 7'-hydroxy metabolites. Furthermore, the excretion rates of the individual (S)- and (R)-enantiomers were continuously monitored over 24 h post administration. Studies were performed utilizing a 2D-LC system hyphenated to a triple quadrupole mass spectrometer. The chromatographic system was endued with a reversed phase column (phenyl-hexyl) in first dimension and a teicoplanin based chiral column in second dimension. The method was basically validated and successfully evaluated as robust. Calibration was performed achieving accuracy between 80% and 120%. Maximal excretion rates of (S)-propranolol, (R)-propranolol, (S)-4'­hydroxy propranolol, (R)-4'­hydroxy propranolol, (S)-5'­hydroxy propranolol, (R)-5'­hydroxy propranolol, and (R)-7'­hydroxy propranolol were 237 ng/min, 281 ng/min, 4 ng/min, 4 ng/min, 1 ng/min, 9 ng/min, and 3 ng/min, respectively.

High-throughput quantitative analysis by desorption electrospray ionization mass spectrometry.

A newly developed high-throughput desorption electrospray ionization (DESI) source was characterized in terms of its performance in quantitative analysis. A 96-sample array, containing pharmaceuticals in various matrices, was analyzed in a single run with a total analysis time of 3 min. These solution-phase samples were examined from a hydrophobic PTFE ink printed on glass. The quantitative accuracy, precision, and limit of detection (LOD) were characterized. Chemical background-free samples of propranolol (PRN) with PRN-d(7) as internal standard (IS) and carbamazepine (CBZ) with CBZ-d(10) as IS were examined. So were two other sample sets consisting of PRN/PRN-d(7) at varying concentration in a biological milieu of 10% urine or porcine brain total lipid extract, total lipid concentration 250 ng/microL. The background-free samples, examined in a total analysis time of 1.5 s/sample, showed good quantitative accuracy and precision, with a relative error (RE) and relative standard deviation (RSD) generally less than 3% and 5%, respectively. The samples in urine and the lipid extract required a longer analysis time (2.5 s/sample) and showed RSD values of around 10% for the samples in urine and 4% for the lipid extract samples and RE values of less than 3% for both sets. The LOD for PRN and CBZ when analyzed without chemical background was 10 and 30 fmol, respectively. The LOD of PRN increased to 400 fmol analyzed in 10% urine, and 200 fmol when analyzed in the brain lipid extract.

Preparation and evaluation of propranolol molecularly imprinted solid-phase microextraction fiber for trace analysis of beta-blockers in urine and plasma samples.

An improved multiple co-polymerization technique was developed to prepare a novel molecularly imprinted polymer (MIP)-coated solid-phase microextraction (SPME) fiber with propranolol as template. Investigation was performed for the characteristics and application of the fibers. The MIP coating was highly crosslinked and porous with the average thickness of only 25.0 microm. Consequently, the adsorption and desorption of beta-blockers within the MIP coating could be achieved quickly. The specific selectivity was discovered with the MIP-coated fibers to propranolol and its structural analogues such as atenolol, pindolol, and alprenolol. In contrast, only non-specific adsorption could be shown with the non-imprinted polymer (NIP)-coated fibers, and the extraction efficiencies of propranolol and pindolol with the MIP-coated fibers were higher markedly than that with the commercial SPME fibers. A MIP-coated SPME coupled with high-performance liquid chromatography (HPLC) method for propranolol and pindolol determination was developed under the optimized extraction conditions. Linear ranges for propranolol and pindolol were 20-1000 microg L(-1) and detection limits were 3.8 and 6.9 microg L(-1), respectively. Propranolol and pindolol in the spiked human urine and plasma samples, extracted with organic solvent firstly, could be simultaneous monitored with satisfactory recoveries through this method.

Determination of selected beta-receptor antagonists in biological samples by solid-phase extraction with cholesterolic phase and LC/MS.

A new method is presented for the determination of five selected beta-receptor antagonists by HPLC, which emphasizes sample preparation via retention on a new type of silica gel sorbent used for solid-phase extraction (SPE). Sorbents of this type were obtained by the chemical modification of silica gels of various porosities by cholesterol ligands. The cholesterol-based packing material was investigated by spectroscopic methods and elemental analysis. The recoveries obtained with the extraction procedure were optimum over a relatively broad sample pH range (3.08-7.50). Analytical factors such as the sample loading, the washing step and elution conditions, the concentration of beta-receptor antagonists to be extracted, and the type of sorbent were found to play significant roles in the sample preparation procedure and would therefore need to be controlled to achieve optimum recoveries of the analytes. Under optimum conditions, the recoveries of nadolol, acebutolol, esmolol, oxprenolol and propranolol from spiked buffers, blood and urine were reproducible and dependent on the polarity or hydrophilicity of the compounds. The above analytes were determined by reverse-phase high-performance liquid chromatography (HPLC) with UV and ESI-ion trap mass spectrometry (MS) detection. The described method was found to be suitable for the routine measurement of compounds that are both polar and basic, and can be applied for the analysis of biological samples such as urine and blood in clinical, toxicological or forensic laboratories. The recovery measurements were performed on spiked human urine and serum, and on real samples of mouse blood serum.

Evaluation of the use of UPLC-TOFMS with simultaneous [14C]-radioflow detection for drug metabolite profiling: application to propranolol metabolites in rat urine.

The non-selective beta-adrenergic receptor antagonist propranolol [1-(isopropylamino)-3-(1-naphthoxy)-2-propanol] is metabolised extensively in vivo. Enumerating and identifying the many metabolites that result from multiple biotransformations provides a considerable analytical challenge, greatly aided by efficient chromatography coupled to sensitive mass spectrometric detection. Here the use of the newly introduced high-resolution technique of "ultra performance liquid chromatography" (UPLC) linked to quadrupole time-of-flight mass spectrometry (TOFMS) with simultaneous [(14)C]-radioflow detection was applied to rapid metabolite profiling. [14C]-propranolol, dosed intraperitoneally to rat at 25 mg kg(-1) and 200 microCi kg(-1) was used as a model compound for this evaluation. Some 14 metabolites were detected in the urine by this technique including a number of conjugated metabolites such as sulphates, several isobaric glucuronides and two novel di-glucuronides.

Magnetic multi-walled carbon nanotube poly(styrene-co-divinylbenzene) for propranolol extraction and separation by capillary electrophoresis.

AIM: The preparation of magnetic multi-walled carbon nanotube poly(styrene-co-divinylbenzene) for propranolol magnetic solid-phase extraction is described. MATERIALS & METHODS: A study comparing propranolol adsorption and desorption was performed with only magnetic multi-walled carbon nanotubes, and different poly(styrene-co-divinylbenzene) with and without magnetic multi-walled carbon nanotubes. Enantiomeric separation of propranolol took place by cyclodextrin-modified capillary electrophoresis and the method was validated in spiked human urine samples. RESULTS: Recovery values raised when styrene/divinylbenzene millimoles ratio was 19.57:15.80. Enrichment factors increased up to approximately 100, detection limits were 13.8 and 10.5 ng ml-1 for R- and S-propranolol respectively, quantitation limits were 46.0 and 34.8 ng ml-1 for R- and S-propranolol respectively, recoveries from spiked samples ranged from 90.9 to 109.0%, and relative standard deviations were <6.3%. CONCLUSION: This methodology was proven to be more effective than classical solid-phase extraction strategies and may be applied to other kind of biological samples.

Solid-phase microextraction coupled with capillary electrophoresis for the determination of propranolol enantiomers in urine using a sol-gel derived calix[4]arene fiber.

A new type of diglycidyloxy-calix[4]arene coated fiber made by sol-gel method was initially prepared for capillary electrophoresis (CE) sample pretreatment. By using headspace solid-phase microextraction (SPME) combined with a novel back-extraction facility coupled off-line to capillary zone electrophoresis (CZE), the simultaneous determination of propranolol enantiomers in human urine was achieved. The clean up effect and preconcentration effect were realized for the first time without derivatization during the SPME process in terms of these strong polarity and thermal stable compounds. Ultrasonic back-extraction and field amplified sample injection (FASI) technologies were employed. Extraction and back-extraction parameters were optimized. Preconcentration of the sample by calix[4]arene fiber based SPME and FASI increased the sensitivity, yielding a limit of detection (LOD) of 0.01microg/ml by CZE-diode array detection (DAD). Method repeatability (RSD<6.5%) and fiber reusability (>150 extraction procedures) were observed over a linear range (0.05-10microg/ml) in urine samples. Based on the superior thermal stability, high alkali- and solvent-resistant ability, marvelous repeatability and long lifetime of the novel fiber, this SPME-FASI-CZE procedure could meet the demand of minimum required performance limit (MRPL) set by the World Anti-doping Agency (WADA) for the detection of propranolol in urine samples.

Water-compatible graphene oxide/molecularly imprinted polymer coated stir bar sorptive extraction of propranolol from urine samples followed by high performance liquid chromatography-ultraviolet detection.

Due to the high selectivity and stability, molecularly imprinted polymers (MIPs) have been successfully applied in stir bar sorptive extraction (SBSE) as a special coating to improve the selective extraction capability for target analytes. However, traditional MIPs usually suffer from incompatibility in aqueous media and low adsorption capacity, which limit the application of MIP coated stir bar in aqueous samples. To solve these problems, a water-compatible graphene oxides (GO)/MIP composite coated stir bar was prepared in this work by in situ polymerization. The prepared water-compatible GO/MIP coated stir bar presented good mechanical strength and chemical stability, and its recognition ability in aqueous samples was improved due to the polymerization of MIP in water environment, the adsorption capacity for target analytes was also increased by the addition of GO in MIP pre-polymer solution. Based on it, a method of water-compatible GO/MIP coated stir bar sorptive extraction combined with high performance liquid chromatography-ultraviolet detector (HPLV-UV) was proposed for the analysis of propranolol (PRO) in aqueous solution. The influencing factors of SBSE, such as sample pH, salt effect, stirring rate, extraction time, desorption solvent and desorption time, were optimized, and the analytical performance of the developed SBSE-HPLC-UV method was evaluated under the optimized conditions. The limit of detection (LOD) of the proposed method for PRO was about 0.37 µg L(-1), and the enrichment factor (EF) was 59.7-fold (theoretical EF was 100-fold). The reproducibility was also investigated at concentrations of 5 µg L(-1) and the relative standard deviation (RSD) was found to be 7.3% (n=7). The proposed method of GO/MIP coating-SBSE-HPLC-UV was successfully applied for the assay of the interested PRO drug in urine samples, and further extended to the investigation of the excretion of the drugs by monitoring the variation of the concentration of PRO in urine within 10h after drug-taking.

Vortex-assisted liquid-liquid extraction combined with field-amplified sample injection and sweeping micellar electrokinetic chromatography for improved determination of ß-blockers in human urine.

A new micellar electrokinetic chromatography (MEKC) method was developed and validated for the analysis of carvedilol and propranolol in human urine samples. In this study, vortex-assisted liquid-liquid extraction (VALLE) coupled with field-amplified sample injection and sweeping was employed for biological sample clean-up and sensitivity enhancement in MEKC. After VALLE, the urine samples were analyzed by MEKC. Tris-phosphate buffer (60mmolL(-1), pH 2.0) containing 40% (v/v) methanol was first filled into an uncoated fused-silica capillary (56cm, 50µm i.d.). The pretreated urine sample was loaded by electrokinetic injection (10kV, 250s). The stacking and separation were performed using Tris-phosphate buffer (30mmolL(-1), pH 3.0) containing 30% (v/v) methanol and 50mmolL(-1) sodium dodecyl sulfate (SDS) at -25kV. Detection was carried out at 195 and 214nm for carvedilol and propranolol, respectively. The suggested method is linear (r(2)≥0.997) over a dynamic range of 0.005-1µgmL(-1) in urine. The intra- and inter-day relative standard deviation and relative error values of the method were below 20%, which shows good precision and accuracy. Finally, this method was successfully applied to the analysis of real urine samples.

Determination of propranolol and carvedilol in urine samples using a magnetic polyamide composite and LC-MS/MS.

AIM: ß-blockers are compounds that bind with adrenoreceptors hindering their interaction with adrenalin and noradrenalin. They are clinically relevant and they are also used in some sport as doping agents. RESULTS: A new method based on the combination of dispersive micro-solid phase extraction and LC-MS/MS has been developed to determine propranolol and carvedilol in urine samples. For this purpose a magnetic-polyamide composite is synthesized and used as sorbent. Working under the optimum conditions, the method provides limits of detection and quantification in the range of 0.1-0.15 µg/l and 0.3-0.5 µg/l, for carvedilol and propranolol, respectively. The precision, expressed as RSD, was better than 9.6% and the relative recoveries varied between 73.7 and 81.3%. CONCLUSION: The methodology is appropriate for the determination of ß-blockers in urine samples at the low microgram per liter range for therapeutic purposes.

Carbon nanotubes as adsorbent of solid-phase extraction and matrix for laser desorption/ionization mass spectrometry.

A method with carbon nanotubes functioning both as the adsorbent of solid-phase extraction (SPE) and the matrix for matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) to analyze small molecules in solution has been developed. In this method, 10 microL suspensions of carbon nanotubes in 50% (vol/vol) methanol were added to the sample solution to extract analytes onto surface of carbon nanotubes because of their dramatic hydrophobicity. Carbon nanotubes in solution are deposited onto the bottom of tube with centrifugation. After removing the supernatant fluid, carbon nanotubes are suspended again with dispersant and pipetted directly onto the sample target of the MALDI-MS to perform a mass spectrometric analysis. It was demonstrated by analysis of a variety of small molecules that the resolution of peaks and the efficiency of desorption/ionization on the carbon nanotubes are better than those on the activated carbon. It is found that with the addition of glycerol and sucrose to the dispersant, the intensity, the ratio of signal to noise (S/N), and the resolution of peaks for analytes by mass spectrometry increased greatly. Compared with the previously reported method by depositing sample solution onto thin layer of carbon nanotubes, it is observed that the detection limit for analytes can be enhanced about 10 to 100 times due to solid-phase extraction of analytes in solution by carbon nanotubes. An acceptable result of simultaneously quantitative analysis of three analytes in solution has been achieved. The application in determining drugs spiked into urine has also been realized.

Stereoselective urinary excretion of S-(-)- and R-(+)-propranolol glucuronide following oral administration of RS-propranolol in Chinese Han subjects.

AIM: To study the stereoselectivity of phase II glucuronidation metabolism of side-chain propranolol in Chinese Han population. METHODS: Sixteen adult Chinese Han volunteers with an average age of 20 years were given a single oral dose of 20 mg racemic propranolol. Human urine at indicated time after administration was collected and S-(-)-propranolol glucuronide and R-(+)-propranolol glucuronide were determined simultaneously by using RP-HPLC. RESULTS: The mean values of k were 0.19+/-0.04 h(-1) and 0.28+/-0.06 h(-1), of t(1/2) 3.56+/-0.73 h and 2.45+/-0.50 h, of T(max) 2.21+/-0.45 and 1.75+/-0.33 h, and of Xu(0-24) 5.65+/-0.98 and 2.95+/-0.62 micromoL for S-(-)- and R-(+)-propranolol glucuronide, respectively. The cumulative excretion percentages in urine of doses were 14.7+/-2.46% and 7.68+/-1.60% for S-(-)- and R-(+)-propranolol glucuronide, respectively. The results showed the elimination rate constant k of S-(-)-propranolol glucuronide was less than that of R-(+)-propranolol glucuronide; and the elimination half-life (t(1/2)), T(max) and the cumulative excretion amount(Xu(0-24)) of R-(+)-propranolol glucuronide were significantly less than that of S-(-)-propranolol glucuronide. CONCLUSION: The propranolol glucuronidation of the side-chain undergoes stereoselective excretion in Chinese Han population after an oral administration of racemic propranolol.

Gas chromatographic-mass spectrometric differentiation of atenolol, metoprolol, propranolol, and an interfering metabolite product of metoprolol.

Over a 10-year period, 1993-2002, Federal Aviation Administration identified 50 pilot fatalities involving atenolol, metoprolol, and propranolol, which is consistent with the fact that these drugs have been in the lists of the top 200 drugs prescribed in the U.S. In a few of the 50 pilot fatality cases, initial analysis suggested the presence of atenolol and metoprolol. However, there was no medical history with these cases supporting the use of both drugs. Therefore, atenolol, metoprolol, and/or propranolol, with their possible metabolite(s), were re-extracted from the selected case specimens, derivatized with pentafluoropropionic anhydride (PFPA), and analyzed by gas chromatography-mass spectrometry (GC-MS). The MS spectra of these three antihypertensives and a metoprolol metabolite are nearly identical. All of the PFPA derivatives had baseline GC separation, with the exception of a metoprolol metabolite product, which co-eluted with atenolol. There were four primary mass fragments (m/z 408, 366, 202, and 176) found with all of the PFPA-beta-blockers and with the interfering metabolite product. However, atenolol has three unique fragments (m/z 244, 172, and 132), metoprolol has two unique fragments (m/z 559 and 107), propranolol has four unique fragments (m/z 551, 183, 144, and 127), and the metoprolol metabolite product has two unique fragments (m/z 557 and 149). These distinctive fragments were further validated by using a computer program that predicts logical mass fragments and performing GC-MS of deuterated PFPA-atenolol and PFPA-propranolol and of the PFPA-alpha-hydroxy metabolite of metoprolol. By using the unique mass fragments, none of the pilot fatality cases were found to contain more than one beta-blocker. Therefore, these mass ions can be used for differentiating and simultaneously analyzing these structurally similar beta-blockers in biological samples.

Effects of (R)- and (S)-propranolol hydrochloride enantiomers on the resonance Rayleigh scattering spectra with erythrosine B as probe and their analytical applications.

Propranolol, a chiral drug with two configurations, i.e., (R)-propranolol hydrochloride (RPH) and (S)-propranolol hydrochloride (SPH), has racemes that can be used in clinical diagnosis due to their synergistic effects. SPH has a ß-receptor blocking effect, and RPH has an antiarrhythmic effect. In pH 4.6 Britton-Robinson (BR) buffer solution, both RPH and SPH can react with erythrosine B to form 1:1 ion-association complexes. In the SPH-Ery B reaction system, a remarkable enhancement of the resonance Rayleigh scattering (RRS) signal located at 338 nm was observed. However, a similar phenomenon was not obvious and was unstable in the RPH-Ery B reaction system. Based on this result, a simple, novel and sensitive method for the determination of SPH was proposed based on the RRS technique. The linear range and limit of detection were 0.0680~4.0 µg mL(-1) and 20.6 ng mL(-1), respectively. Additionally, the spectroscopic approaches of frequency doubling scattering (FDS) and second-order scattering (SOS) were also proposed for SPH detection in this article. The interaction information regarding the mechanism of the reaction, suitable reaction conditions, influencing factors and the effects of mixed solutions were our investigation aims. The method had been applied to the determination of SPH in fresh serum and urine samples of healthy human subjects with satisfactory results.

Mechanism by which hydralazine increases propranolol bioavailability.

Five healthy subjects were given oral 14C-propranolol (10 microCi, 40 mg) alone and in combination with hydralazine, 25 and 50 mg. Hydralazine increased propranolol peak concentrations from 25 +/- 7 ng/ml to 61 +/- 10 and 85 +/- 11 ng/ml, reduced time to peak concentrations from 2.2 +/- 0.2 hr to 0.7 +/- 0.1 and 0.8 +/- 0.1 hr, and increased area under the propranolol concentration: time curves from 153 +/- 38 ng X ml-1 X hr to 246 +/- 64 and 324 ng X ml-1 X hr (in all cases P less than 0.05). Hydralazine did not change the fraction of the 14C-propranolol dose recovered in the urine as basic, acidic, and polar metabolites: 0.28 +/- 0.2, 0.27 +/- 0.03, and 0.44 +/- 0.03. The urinary excretion rate of radioactive metabolites of propranolol in acid, basic, and residue fractions increased in the 0 = to = 2-hr time interval after hydralazine but there was no change in the relative proportion of each metabolite fraction at any time. Similar results were obtained by HPLC. Studies with radioactive propranolol indicate that a major acid and basic metabolite remains to be defined in addition to unextracted polar metabolites. Our data indicate that hydralazine increases propranolol bioavailability by its hemodynamic actions rather than by inhibition of its metabolism.

Urine and plasma propranolol.

Eight hypertensive patients who had been followed in an outpatient clinic during long-term therapy with propranolol (40 to 160 mg twice daily) were studied during a 24-hr stay in the ward. The usual oral dose was given and the total and free plasma concentrations were determined during the 24 hr and the urinary excretion of unchanged drug was measured. Average free plasma concentration of propranolol (y free) was calculated from: y free = Excreted propranolol (ng/24 hr)/Creatinine clearance (ml/24 hr). There was a significant relationship between log y free and average free plasma concentration (means free) determined from the directly measured plasma concentration curve: log y free = 0.0743 means free - 0.0466 (r = 0.98, P less than 0.001). In another group of propranolol-treated hypertensive patients there was a significant positive relationship between orosomucoid concentration and reciprocal of the free propranolol fraction in plasma. From this relationship the average total drug concentration (y total) was calculated from y free; there was a significant correlation with directly measured total plasma level: log y total = 0.0038 . means total + 1.0895 (r = 0.91, P less than 0.001). It is suggested that individually determined values of y free below 30 ng/ml and y total below 400 ng/ml (the concentration range studied) can be used to calculate the average mean 24-hr free and total plasma concentrations.

Influence of debrisoquin phenotype on the inducibility of propranolol metabolism.

The effects of rifampin (600 mg) once daily for 22 days on the total and fractional metabolic clearances of propranolol were determined in a group of six genetically extensive (EM) and six poor metabolizers (PM) of debrisoquin. The impaired ability of PMs to metabolize propranolol to the ring-oxidized metabolite 4-hydroxypropranolol was confirmed. The total oral clearance of propranolol increased about fourfold in both phenotypes from 219.2 +/- 52.8 to 976.7 L/hr in the EMs and from 75.0 +/- 12.6 to 289.8 +/- 78.2 L/hr in the PMs. The extent of induction of glucuronidation was similar in the two groups. 4-Hydroxylation was induced in both phenotypes but the increase was fifteenfold greater in EMs than in PMs. This would imply that the cytochrome P-450 determined by the debrisoquin allele or some coinherited 4-hydroxylase(s) was induced to a greater extent in EMs than PMs.