Packed-column supercritical fluid chromatography of beta-blockers.

Packed-column subcritical and supercritical fluid chromatography (SFC) of a total of 10 beta-blocking drugs was investigated on four stationary phases using CO(2)-methanol based eluents. The stationary phases studied were all bonded silicas and included Diol, aminopropyl, cyanopropyl, and "C1". The SFC of some of these compounds was possible with simple CO(2)-methanol based mobile phases, but in general, it proved to be necessary to add triethylamine as a competing base in order to obtain acceptable peak shapes. The best chromatographic results were obtained on the aminopropyl bonded phase, with good results also seen on the Diol phase. Different selectivities were observed for the Diol and aminopropyl columns.

Disposition and pharmacology of propofol glucuronide administered intravenously to animals.

1. Propofol glucuronide (PG) is the major human metabolite of the i.v. anaesthetic propofol, 2,6-diisopropylphenol. 2. Bolus i.v. doses of 14C-PG (1 mg/kg) to rat and dog were eliminated in urine (40 and 66% respectively) and faeces (48 and 19%); 25 and 48% of the dose were excreted unchanged in urine. 3. In dog, PG was distributed from plasma (t 1/2 4 min) into a volume equivalent to extracellular water and eliminated with t 1/2 80 min. Total body clearance was 1.8 ml/min per kg, and renal clearance about 20% GFR. In rat, plasma 14C concentrations were about one-tenth those in dog, thus PG levels were not quantified. 4. Propofol was not detected in the plasma showing that PG is hydrolytically stable. Enterohepatic circulation of PG occurred in rat and to a lesser extent in dog. Metabolites, mainly side-chain hydroxylation products, were evident in both species from 4 h after dosing. 5. Bolus i.v. doses of PG (200 mg/kg) showed no hypnotic activity in mice.

Species differences in blood profiles, metabolism and excretion of 14C-propofol after intravenous dosing to rat, dog and rabbit.

1. Bolus i.v. doses of 14C-propofol (7-10 mg/kg) to rat, dog and rabbit, or an infusion dose (0.47 mg/kg per min for 6 h) to dog were eliminated primarily in urine (60-95% dose); faecal elimination (13-31%) occurred for rat and dog, but was minimal (less than 2%) for rabbit. 2. After bolus administration, blood 14C concentrations were maximal (8-30 micrograms equiv./ml) at 2-15 min; these declined rapidly during the 0-2 h period and thereafter more slowly. Propofol concentrations were maximal (4-16 micrograms/ml) at 2 min and the profiles were best fitted by a tri-exponential (rat and dog) or bi-exponential (rabbit) equation. Duration of sleep ranged from 5 to 8 min. 3. Infusion of 14C-propofol in dog gave a blood 14C concentration of 117 micrograms equiv./ml at the end of the 6 h infusion period; this declined at a similar rate to that after the bolus dose. Propofol concentration on termination of infusion was 13 micrograms/ml; thereafter, propofol concentrations declined less rapidly than after the bolus dose. Waking occurred about 44 min post-infusion. 4. Propofol was cleared by conjugation of the parent molecule or its quinol metabolite; hydroxylation of an isopropyl group also occurred in rat and rabbit. Biliary excretion leading to enterohepatic recirculation, and in turn increased sulphate conjugation, occurred in rat and dog, but not rabbit, resulting in a marked interspecies variation in drug clearance and metabolite profiles.

Distribution in female rats of an anaesthetic intravenous dose of 14C-propofol.

1. Bolus i.v. doses of 14C-propofol (9 mg/kg) were administered to female rats for measurement of tissue levels of total 14C and propofol from 2 min to 24 h post-dose; whole-body autoradiography was studied at 6 min, 2 h and 24 h post-dose, and also involved 15-day pregnant rats. 2. The blood propofol concentration-time profile was fitted by a tri-exponential function corresponding to a three-compartment open model. Data show rapid distribution during the mixing period into highly perfused tissues and muscle, comprising the central compartment, and slower uptake into less well-perfused skin and adipose tissues comprising the deeper compartments. 3. The initial decline in blood propofol concentration was associated with redistribution (t1/2 4 min), the second decline (15-240 min post-dose) was associated with metabolism (t1/2 33 min) and the third decline reflected slow depletion of drug from deep tissue compartments (t1/2 6.4 h). 4. Blood and brain propofol concentrations on waking (at 7 min post-dose) were 4 micrograms/ml and 9 micrograms/g respectively; the model shows that, at this time, 30% of the dose was lost from the central compartment by redistribution and a similar amount by metabolism. 5. Tissue profiles of total 14C and propofol diverged for highly perfused tissues (other than brain) because of slow clearance of metabolites, accentuated by enterohepatic recirculation.

The use of graphitized carbon black in solid phase extraction: comparison with C18 bonded silica gel.

Preliminary studies on the properties of a commercially available graphitized carbon black for the solid-phase (or liquid-solid) extraction of drugs and metabolites from biological fluids such as urine and plasma are described. A variety of basic drugs, all of the beta-blocker type, were efficiently extracted from dog plasma and subsequently recovered from the adsorbent using chloroform-methanol mixtures. Similarly metabolites of the non-steroidal anti-flammatory drug ibuprofen also were efficiently extracted from human urine. The proportions of methanol and chloroform used for elution were found to be critical to ensure complete recoveries of adsorbed material. Proton NMR studies of the column eluates from both carbon and C18 bonded silica gel extraction cartridges revealed differences in capacity and selectivity following the application of ibuprofen containing metabolite samples.

Ion-pair reversed-phase thin-layer chromatography of basic drugs using sulphonic acids.

The use of sulphonic acid ion-pair reagents in the thin-layer chromatography of four basic drugs (all secondary amines) on C18-bonded silica gel, paraffin coated silica gel and silica gel itself has been investigated. Effects of the ion-pair reagents were only obtained on C18-bonded silica gel, and only then when the reagents were pre-coated onto the stationary phase. In general the largest reductions in the RF values of the test compounds occurred when sodium dodecylsulphate was coated onto the plates.

The effect of bromazepam (Lexotan) administration on antipyrine pharmacokinetics in humans.

Six healthy volunteers were given a standard regimen of bromazepam (Lexotan) (6 mg t.d.s.) for five days. Compliance with the study protocol was demonstrated by measuring drug concentrations at steady state. Steady-state levels of 3-hydroxybromazepam were also determined. These were found to be much lower than the concentrations of bromazepam. Since the metabolite is known to be less active than the parent drug, it is likely that the metabolic will contribute little to the pharmacological effects of the drug in humans. Antipyrine pharmacokinetics were studied immediately before bromazepam administration was started, after the dosing schedule had been completed and one week after dosing had been discontinued. There were no significant changes in the disposition of antipyrine on any occasion. Therefore, although previous studies have demonstrated enzyme induction in laboratory animals given high doses of bromazepam, similar effects are unlikely to occur in humans being treated with therapeutic doses of the compound.

Species variation in the metabolism of a substituted cinnamate ester anti-inflammatory pro-drug.

1. The metabolic fate of the substituted cinnamic acid ester, Ro 03-6037, has been examined in rat, mouse, baboon, dog, marmoset, rabbit and man. 2. All species are capable of reducing the cinnamate double bond, but the subsequent one-carbon fragment loss can be carried out only by rat, dog, rabbit and marmoset. 3. The inability of man, as well as baboon and mouse, to perform this terminal metabolic step, which results in formation of the active anti-inflammatory agent, renders the compound unsuitable as a drug for humans. 4. Reduction of the double bond is not carried out by gut flora. 5. An h.p.l.c. analytical method is described for estimation of the metabolites in biological fluids.

Some aspects of the metabolism of misonidazole.

The metabolism of the 2-nitroimidazole hypoxic cell radiosensitizer, misonidazole, has been studied in patients receiving radiotherapy. Results are presented which show that the compound reaches adequate levels in tumour tissue and that, in animal systems, reduction products of the nitro group may also be present. Ah h.p.l.c method is described which has been used to quantify unchanged misonidazole and its nitroimidazole metabolites.