Theodor W. Guentert

Convenient and sensitive high-performance liquid chromatography assay for ketoprofen, naproxen and other allied drugs in plasma or urine.

A new high-performance liquid chromatography technique enables convenient and rapid assay of ketoprofen and naproxen in biological samples at a sensitivity (10 and 2 ng/ml, respectively in plasma; 20 and 50 ng/ml in urine) far greater than previously available. Superior sensitivity is attributable to the buffered neutral eluent employed, which yields improved separation from material of biological origin. There is no interference from the major ketoprofen and naproxen metabolites tested and excellent reproducibility and accuracy can be maintained. Moreover, the same system can be used to assay probenecid and also shows promise of applicability to ibuprofen, fenoprofen and other members of the aryl-alkanoic acid class of non-steroidal anti-inflammatory agents.

Effect of saturable binding on the pharmacokinetics of drugs: a simulation

The time‐courses of both total and unbound drug concentrations with time were simulated under conditions of saturable binding to either plasma proteins or tissues, or both, following a single intravenous dose. The curves were either linear, convex, or concave, depending upon the extent of distribution and the intrinsic ability of an eliminating organ to remove drug from the body. Saturable binding should therefore be considered whenever data showing nonlinear semilogarithmic decline are to be interpreted.

Determination of quinidine and its major metabolites by high-performance liquid chromatography.

A specific and precise assay, capable of quantitating in human plasma simultaneously but separately quinidine, dihydroquinidine and the quinidine metabolites 2-quinidinone, 3-OH-quinidine and a third metabolite found--tentatively identified as the product formed by rearrangement of quinidine-N-oxide-is reported. The assay uses a normal phase high-performance liquid chromatographic (HPLC) system with a variable-wavelength UV detector at 235 nm and has a limit of sensitivity at approximately 20 ng/ml. The mobile phase consists of hexanes-ethanol-ethanolamine (91.5:8.47:0.03). A 2-ml plasma sample is worked up by adding primaquine base as an internal standard and extracting with ether-dichlormethane-isopropanol (6:4:1). The organic extract is evaporated and the residue reconstituted in 100-600 micron1 of mobile phase and an aliquot injected onto the column. Comparison of this procedure with the Edgar and Sokolow (dichloroethane) extraction--fluorescence procedure and with the Cramer and Isaksson (benzene) double extraction--fluorescence assay indicates that both fluorescence procedures give quinidine concentrations up to 2.3 times those determined by HPLC. These discrepancies were shown to be due to carry-over of metabolites and some extraneous background fluorescence.

Ketoprofen Pharmacokinetics and Bioavailability Based on an Improved Sensitive and Specific Assay

SummaryA commercial capsule containing 50 mg of ketoprofen (Orudis), a simple capsule containing 50 mg of ketoprofen alone and 50 mg of ketoprofen in an aqueous solution were given as separate doses in a randomized sequence to 12 normal adult males. The areas under the resulting plasma concentration-time curves (AUC) were remarkably consistent for each volunteer. The bioavailability from the commerical capsule relative to that from the solution was 99.7%±10.5% and that from the simple capsule was 102%±10%. After 6 of the volunteers had taken the commercial capsule 6 hourly for thirteen doses, their AUC extrapolated to infinity was significantly higher (by 22%) than that after the single dose indicating, contrary to previous reports, accumulation upon multiple dosing. The interdose AUC after the thirteenth dose was, however, statistically indistinguishable from the AUC-to-infinity after the single dose as might be expected from linear kinetics. The ketoprofen solution generated peak plasma concentrations in only one-third the time (21±7 min) required for the capsules (commercial, 72±45; simple, 61±39 min). Despite plasma concentrations being tracked over a 200-fold range, log linearity was not established within 12 h in any of the 42 profiles obtained. A two-compartment open model was fitted to the solution data giving excellent prediction of the time-to-peak and clearance (Cl/F=5.2±1.1 l/h) as determined by eye and by log-trapezoidal rule, respectively.

Determination of quinidine and metabolites in urine by reverse-phase high-pressure liquid chromatography

A new reverse-phase high-pressure liquid chromatography assay allowing simultaneous but separate quantitation of urinary levels of quinidine and its major metabolites, 2-quinidinone, 3-OH-quinidine and a newly detected N-oxide, is described. The compounds were separated on a alkyl phenyl column using 0.05 M phosphate buffer pH 4.5/acetonitrile/tetrahydrofuran (80 : 15 : 5, v/v) as mobile phase and were detected by UV at lambda = 230 nm. The assay procedure includes extraction of the compounds from urine samples into a mixture of dichloromethane/isopropanol (4 : 1, v/v), evaporation of the organic extracts to dryness and reconstitution of the residue in acetonitrile. The new assay was compared to a modification of the Cramer and Isaksson fluorescence assay which has recently been recommended for analysis of quinidine in urine. The consistently higher quinidine levels observed in the fluorescence assay could be accounted for by the quinidine levels and metabolite carry-over as determined by HPLC.

Evaluation of a modified high-performance liquid chromatography assay for acebutolol and its major metabolite.

Extensive modification of an existing high-performance liquid chromatography assay for acebutolol and its major metabolite has markedly improved chromatographic stability eliminating the previous need for frequent adjustment of the eluent composition to accommodate continuous loss of column retention. The eluents now used and avoidance of the requirement for elevated column temperature may be significant factors in the ability to maintain column life over 8 months of continuous use with little decrease in retention. As a result of the improved chromatographic stability full advantage can now be taken of automatic injection devices for the unattended processing of large numbers of samples. A significant modification of the work-up of blood samples has improved precision of the assay in whole blood. Nevertheless, it is recommended that plasma samples rather than whole blood be analyzed, since the plasma assay is faster and still more precise.

Pharmacokinetics and pharmacodynamics of quinidine and its metabolite, quinidine-N-oxide, in beagle dogs

SummaryQuinidine and one of its major metabolites, quinidine-N-oxide, were given by separate i.v. infusions to each of three beagle dogs. Plasma and urine samples were analysed for pharmacokinetic comparison of the drug and its metabolite. Quinidine apparently distributed into two major compartments, while the N-oxide distributed into three compartments. The compartment-independent pharmacokinetic parameters (mean ± SD) were for quinidine Vdss 4.78±1.1 l/kg, clearance 0.074±0.047 l/min, terminal half-life 720±343 min and for quinidine-N-oxide Vdss 1.03±0.21 l/kg, clearance 0.065±0.012 l/min, terminal half-life 316±69 min. Only 29% of quinidine was recovered in the urine as unchanged drug while 77% of the N-oxide was excreted unchanged via the kidney. Non-linear renal elimination of the N-oxide was observed in two out of three dogs with a Michaelis-Menten constant, KM of about 7 μg/ml (21 μM).Prolongation of the QT-interval in the ECG response was used for comparing pharmacodynamic effects. Quinidine was about three to four fold more active than the N-oxide at similar plasma concentrations. Quinidine-N-oxide concentrations in plasma after quinidine administration were very low and would not contribute significantly to the quinidine effect.