The versatility of the brute force orientation of polar asymmetric top molecules in a molecular beam has been investigated. In symmetric top molecules the electric field only mixes free rotor basis functions with different J but equal K and M values, but in asymmetric top molecules the mixing includes K, because of the asymmetry, in addition to field-induced J-mixing. This distinction is important with respect to the orientation behavior. For asymmetric top molecules all Stark curves for different J-states and different K-values, but equal M, in the corresponding symmetric eigenbasis, feature avoided crossings. Dependent on the velocity with which the molecules pass through the orientation field, these avoided crossings will be traversed adiabatically or nonadiabatically. For near-symmetric top molecules, such as iodobenzene, the crossings will in general be nonadiabatic, and, as expected, the behavior is similar to that of the corresponding symmetric top. If the crossings are adiabatic, the orientation behavior can be drastically different from the behavior of the corresponding symmetric top molecule. A strong asymmetry need not always be prohibitive in attaining a perceptible degree of orientation, as is demonstrated by the case of water.
To characterize the potential of ciprofloxacin penetration into human soft tissues following intravenous (i.v.) and oral (p.o.) administration, we measured the free ciprofloxacin concentrations in interstitial space fluid of skeletal muscle and subcutaneous adipose tissue by microdialysis. In addition, ciprofloxacin concentrations were measured in cantharis-induced skin blisters, saliva, and capillary plasma and were compared to the total concentrations in venous plasma. The concentrations in saliva and capillary blood were similar to the corresponding total levels in plasma. In vitro both in vivo ciprofloxacin concentration-time profiles were equally effective against select bacterial strains. In conclusion, single-dose administration of two bioequivalent dosage forms of ciprofloxacin might lead to differences in target site pharmacokinetics. These differences, however, are not related to a difference in target site pharmacodynamics.
The bioequivalence of thiamin in 2 therapeutically used preparations was tested in 10 healthy young men. Thiamin was orally administered either as lipophilic benfotiamine or as water-soluble thiamin mononitrate. Biokinetic data, measured as area under the curve and maximal concentration in plasma and hemolysate after ingestion, demonstrated a significantly improved bioavailability from the lipophilic derivative despite an ingested dose of only 40% as compared with the water-soluble salt. A superior cellular efficacy of benfotiamine was also concluded from the short-term stimulation of the thiamin-dependent transketolase activity in erythrocytes.
Br J Clin Pharmacol AimsTo evaluate the extent to which enterohepatic recycling circulation contributes to moxifloxacin bioavailability in healthy, males by administration of activated charcoal and to evaluate the efficacy of activated charcoal administration in decreasing systemic concentrations of moxifloxacin in the event of overdose. MethodsNine healthy males, mean age 34 years (range 23-45 years) participated in a single centre, randomized, nonplacebo-controlled, three way crossover study. The pharmacokinetics of moxifloxacin in plasma and urine were determined for up to 96 h following a 400 mg single dose randomly administered on three separate occasions with a minimum washout phase of 1 week. Treatment A was 400 mg moxifloxacin IV as a 1 h infusion, treatment B was 400 mg moxifloxacin IV as a 1 h infusion with oral activated charcoal (5 g directly before the start of the infusion, 5 g immediately after the end of the infusion, and 10 g at 2, 4 and 8 h after the start of the infusion), treatment C was 400 mg oral moxifloxacin with activated charcoal (10 g 15 min before and at 2, 4 and 8 h after drug administration). The subjects underwent a series of clinical and laboratory tests. ResultsSingle 400 mg doses of moxifloxacin (PO and/or IV) were safe and well tolerated. The bioavailability of moxifloxacin was significantly decreased when given with charcoal (AUC = 35.5 (IV reference) vs 5.40 (PO) vs 28.5 (IV) mg l -1 h). Concurrently peak concentrations were lowered C max = 3.38 (IV reference) vs 0.62(PO) vs 2.97 (IV) mg l -1 ) by approximately 85% ( P < 0.05) following oral administration and by 20% after IV treatment ( P < 0.05). Bioavailability amounted to 15.4% (95% confidence interval 9.6, 25.0%) for treatment B while it was 80.4% (95% confidence interval 76.3.6, 84.6%) for treatment C. Terminal half-lives were not affected. The kinetics of urinary excretion corroborated these findings. ConclusionsThe results of this study show that moxifloxacin undergoes pronounced enteric recycling after systemic uptake. In addition, these findings confirm that activated charcoal may be useful in treating moxifloxacin overdose by preventing its absorption. Moxifloxacin charcoal interactionBr J Clin Pharmacol 59 :5 537
In a crossed molecular beam experiment, we have measured angular and time-of-flight (TOF) distributions of products formed in the reaction K + C 6 H 5 I f KI + C 6 H 5 at a collision energy of E tr ) 1.9 eV. From these data we have extracted the double-differential reaction cross section in the center-of-mass frame. The brute force technique has been applied to orient for the first time an asymmetric top, namely the reagent molecule C 6 H 5 I. The effect of molecular orientation on the angular distribution of products has been investigated. We determined the difference of product intensity for (a) preferred encounters with the I end and the phenyl end (parallel steric effect) and (b) side-on attacks with the axis pointing in two opposite directions (perpendicular steric effect). We find (i) preferred sideways scattering of KI with a mean recoil energy of 31.6% of the totally available energy; (ii) an additional reaction channel with a branching ratio of 0.65% by which a flux of slow products, most likely KI, is formed; (iii) the transformation of the data to a more adapted coordinate frame reveals that backward rather than sideways scattering reflects the dynamics of the reaction; (iv) a tight correlation between the direction of the product flux and the orientation of the molecular axis; (v) the experimental results can be rationalized by the direct interaction with product repulsion (DIPR) model; (vi) the ratio of product yield for attacks of the K atoms to the I end (head) and the phenyl end (tail) amounts to ≈28:1; (vii) the full apex angle of the cone-of-acceptance amounts to ≈110°; (viii) the harpooning mechanism and simple molecular orbital arguments rationalize the impulsive reaction mechanism implicit to the DIPR model and offer an explanation for the existence of a channel for slow KI products.
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