Application of microdialysis for the determination of muscle and subcutaneous tissue concentrations after oral and topical ibuprofen administration.

BACKGROUND: The topical administration of non-steroidal antiinflammatory drugs (NSAIDs) is widely used for the treatment of soft tissue pain. However, it is not known whether effective tissue concentrations are reached with the topical route. OBJECTIVE: To evaluate and compare unbound muscle and subcutaneous tissue ibuprofen concentrations with use of microdialysis after topical and oral administration. METHODS: In a 2-way crossover design, 11 healthy volunteers received either 800 mg oral ibuprofen or 16 g of 5% ibuprofen gel applied onto the skin of the thigh (defined area, 17 x 19 cm). Microdialysis catheters were inserted into the medial vastus muscle (25 to 30 mm) and into the subcutaneous adipose layer of the thigh (4 to 5 mm). Dialysate was collected in 20-minute intervals up to 5 hours. RESULTS: Essentially all of the orally administered dose was recovered in urine as ibuprofen or metabolites during 24 hours, but only about 0.55% of the topically administered dose was recovered. The relative systemic bioavailability of ibuprofen gel, based on urine recovery data, was (mean +/- SD) 0.57%+/-0.30%. Mean values of the dialysate areas under the drug concentration-time curves after topical and oral administration were 731.2+/-605.0 and 176.6+/-122.9 ng x h x mL(-1) for subcutaneous tissue and 63.5+/-90.3 and 213.4+/-117.2 ng x h x mL(-1) for muscle, respectively. Muscle dialysate concentrations after topical administration varied considerably among the subjects. CONCLUSION: These results suggest that, if target tissue concentrations correlate directly with the degree of pain relief, patients with pain caused by dermal or subcutaneous tissue damage will have greater pain relief after topical administration of ibuprofen accompanied with less systemic side effects. In addition, a proportion of patients with muscle pain may also experience pain relief from topical ibuprofen.

Interaction of pefloxacin and enoxacin with the human cytochrome P450 enzyme CYP1A2.

BACKGROUND AND OBJECTIVES: Pefloxacin is reported to cause clinically relevant inhibition of theophylline metabolism in vivo, but in vitro pefloxacin was only a weak inhibitor of the cytochrome P450 CYP1A2, mediating main theophylline biotransformation. We therefore further characterized the interaction between pefloxacin and CYP1A2. METHODS: A randomized 3-period change-over study was conducted in 12 healthy young volunteers on the steady-state interactions between pefloxacin or enoxacin (400 mg twice a day) with caffeine (183 mg once daily), a validated marker of CYP1A2. Caffeine pharmacokinetics were estimated after its fifth dose. Studies in human liver microsomes were carried out to measure the effect of pefloxacin and norfloxacin on caffeine 3-demethylation, an in vitro CYP1A2 probe, and to identify the enzyme(s) that mediate pefloxacin N-4'-demethylation with selective inhibitors. RESULTS: For the in vivo study, ANOVA-based point estimates (90% confidence intervals [CI]) for the ratios of caffeine pharmacokinetics with and without pefloxacin coadministration were 1.11 for maximal steadystate plasma concentrations (Cmax,ss; 90% CI, 0.99 to 1.26), 0.53 for total clearance (CLt,ss; 90% CI, 0.49 to 0.58), and 1.04 for the beta-phase distribution volume (Vdbeta; 90% CI, 0.96 to 1.13). The values for enoxacin were 1.99 for Cmax,ss (90% CI, 1.77 to 2.23), 0.17 for CLt,ss (90% CI, 0.16 to 0.19), and 1.01 for Vdbeta (90% CI, 0.90 to 1.13). Thus pefloxacin caused a 2-fold decrease in caffeine clearance, and enoxacin caused a 6-fold decrease in caffeine clearance. In vitro, norfloxacin and pefloxacin competitively inhibited CYP1A2, with inhibition constant (Ki) values of 0.1 and 1 mmol/L, respectively, and CYP1A2 was the only enzyme with a relevant contribution (approximately 50%) to pefloxacin N-4'-demethylation. CONCLUSIONS: Enoxacin and to a lesser extent pefloxacin may cause clinically relevant interactions with further CYP1A2 substrates. The data suggest that the pefloxacin interaction is partly mediated by its major metabolite norfloxacin.

Lack of bioequivalence of a generic mefloquine tablet with the standard product.

OBJECTIVE: To assess the bioequivalence between a generic tablet of mefloquine (Mephaquin = M1) with the reference tablet (Lariam = M2) in healthy volunteers. METHODS: This open label, randomized two-way crossover study was performed in a single centre. Following an overnight fast, eighteen healthy volunteers received a single oral dose of 750 mg mefloquine either in the form of three M1 lactabs or three M2 tablets. Serial blood samples were collected up to 8 weeks after drug administration. Plasma samples were analysed for mefloquine and its carboxylic acid metabolite using liquid chromatography and subsequent tandem mass spectrometry (LC-MS/MS). The pharmacokinetic parameters of mefloquine and its metabolite were estimated by non-compartmental methods. RESULTS: The pharmacokinetics of mefloquine after administration of M1 and M2 tablets were significantly different as reflected by the respective mean values of maximum plasma concentration (Cmax 656 vs 1018 ng x ml(-1)), time to reach maximum concentration (tmax 46 vs 13 h) and area under the plasma concentration-time curve (AUC0-->infinity 338 vs 432 microg x h x ml(-1)). No significant differences existed between the elimination half-lives of the two formulations (394 vs 396 h). The relative bioavailability (M1 vs M2) was 0.78 and ranged from 0.38 to 1.37. Bioequivalence could not be demonstrated for log-transformed data of AUC0-->infinity or AUC0-->last within a predefined range of 80-125% and for Cmax within a range of 70-143%. CONCLUSIONS: The observed differences in Cmax, tmax and AUC are consistent with a slower rate and lower extent of mefloquine absorption after administration of M1. Statistical evaluation of these kinetic data showed that the M1 tablet is not bioequivalent to the M2 tablet. Clinical consequences of this finding cannot be excluded.

Differential effects of EGF receptor signalling on neuroblast lineages along the dorsoventral axis of the Drosophila CNS.

The Drosophila ventral nerve cord derives from a stereotype population of about 30 neural stem cells, the neuroblasts, per hemineuromere. Previous experiments provided indications for inductive signals at ventral sites of the neuroectoderm that confer neuroblast identities. Using cell lineage analysis, molecular markers and cell transplantation, we show here that EGF receptor signalling plays an instructive role in CNS patterning and exerts differential effects on dorsoventral subpopulations of neuroblasts. The Drosophila EGF receptor (DER) is capable of cell autonomously specifiying medial and intermediate neuroblast cell fates. DER signalling appears to be most critical for proper development of intermediate neuroblasts and less important for medial neuroblasts. It is not required for lateral neuroblast lineages or for cells to adopt CNS midline cell fate. Thus, dorsoventral patterning of the CNS involves both DER-dependent and -independent regulatory pathways. Furthermore, we discuss the possibility that different phases of DER activation exist during neuroectodermal patterning with an early phase independent of midline-derived signals.

Defluorinated sparfloxacin as a new photoproduct identified by liquid chromatography coupled with UV detection and tandem mass spectrometry.

Photodegradation of sparfloxacin was observed by means of high-pressure liquid chromatography with UV detection and liquid chromatography coupled with UV detection and tandem mass spectrometry (LC-MS/MS). Three products were detected. Comparison with an independently synthesized derivative of sparfloxacin revealed the structure of one product which is believed to be 8-desfluorosparfloxacin. The second product is likely to be formed by the splitting off of a fluorine and a cyclopropyl ring. Thus, photodefluorination of quinolone antibacterial agents is found and proved for the first time by LC-MS/MS.

The light-stimulated cytosolic calcium transient in Limulus ventral nerve photoreceptors: two components in the rising phase.

1. Light-evoked electrical responses were measured in Limulus ventral nerve photoreceptors simultaneously with changes in the cytosolic free calcium concentration, by means of arsenazo III. 2. It has been shown here for the first time that the rise of the arsenazo signal consists of two phases. Only the slow phase in the rise of the signal depends on the membrane voltage. The reversal potential of the amplitude of this slow rising phase was about +196 mV. After removal of external calcium the reversal potential was about +20 mV. 3. When Na+ in the superfusate was replaced by Li+, the amplitude of the fast rising phase was reduced on the average to 50%, while the slow rising phase was not affected. 4. We conclude that the fast rising phase is caused by release of calcium from internal stores while the slow increase in [Ca2+]i is due to influx across the plasma membrane, possibly through light-activated ion channels.