Immediate effect of caffeine on sympathetic nerve activity: why coffee is safe? A single-centre crossover study.

PURPOSES: Habitual coffee drinking is ubiquitous and generally considered to be safe despite its transient hypertensive effect. Our purpose was to determine the role of the sympathetic nervous system in the hypertensive response. METHODS: In a single-centre crossover study, medical caregivers were studied after consumption of standard coffee (espresso), water and decaffeinated coffee (decaff) given in random order at least 1 month apart. Plasma caffeine levels, mean arterial pressure, heart rate, total peripheral resistance and muscle sympathetic activity were recorded. Baroreflex activity was assessed using burst incidence and RR interval changes to spontaneous blood pressure fluctuations. RESULTS: A total of 16 subjects (mean [± standard error] age 34.4 ± 2 years; 44% female) were recruited to the study. Three agents were studied in ten subjects, and two agents were studied in six subjects. Over a 120-min period following the consumption of standard coffee, mean (± SE) plasma caffeine levels increased from 2.4 ± 0.8 to 21.0 ± 4 µmol/L and arterial pressure increased to 103 ± 1 mmHg compared to water (101 ± 1 mmHg; p = 0.066) and decaff (100 ± 1 mmHg; p = 0.016). Peripheral resistance in the same period following coffee increased to 120 ± 4% of the baseline level compared to water (107 ± 4; p = 0.01) and decaff (109 ± 4; p = 0.02). Heart rate was lower after both coffee and decaff consumption: 62 ± 1 bpm compared to water (64 bpm; p = 0.01 and p = 0.02, respectively). Cardio-vagal baroreflex activity remained stable after coffee, but sympathetic activity decreased, with burst frequency of 96 ± 3% versus water (106 ± 3%; p = 0.04) and decaff (112 ± 3%; p = 0.001) despite a fall in baroreflex activity from - 2.2 ± 0.1 to - 1.8 ± 0.1 bursts/100 beats/mmHg, compared to water (p = 0.009) and decaff (p = 0.004). CONCLUSION: The hypertensive response to coffee is secondary to peripheral vasoconstriction but this is not mediated by increased sympathetic nerve activity. These results may explain why habitual coffee drinking is safe.

A 1 g dose of intravenous iron is sufficient to treat iron deficiency anaemia.

One hundred and ninety-four patient episodes were audited for response to a standardised 1 g intravenous iron infusion for medical outpatients with iron deficiency anaemia. Patients received either ferric carboxymaltose or iron polymaltose. At 5-7 weeks after infusion, mean increase in Hb was 26.7 g/L and ferritin was 161 mcg/L, and only one patient had Hb <100 g/L. This reassures that 1 g dose of intravenous iron is sufficient for most patients, with benefits for treatment costs and patient convenience.

Electronic structure of the water oxidation catalyst cis,cis-[(bpy)2(H2O)Ru(III)ORu(III)(OH2)(bpy)2]4+, the blue dimer.

The first designed molecular catalyst for water oxidation is the "blue dimer", cis,cis-[(bpy)(2)(H(2)O)Ru(III)ORu(III)(OH(2))(bpy)(2)](4+). Although there is experimental evidence for extensive electronic coupling across the µ-oxo bridge, results of earlier DFT and CASSCF calculations provide a model with magnetic interactions of weak to moderately coupled Ru(III) ions across the µ-oxo bridge. We present the results of a comprehensive experimental investigation, combined with DFT calculations. The experiments demonstrate both that there is strong electronic coupling in the blue dimer and that its effects are profound. Experimental evidence has been obtained from molecular structures and key bond distances by XRD, electrochemically measured comproportionation constants for mixed-valence equilibria, temperature-dependent magnetism, chemical properties (solvent exchange, redox potentials, and pK(a) values), XPS binding energies, analysis of excitation-dependent resonance Raman profiles, and DFT analysis of electronic absorption spectra. The spectrum can be assigned based on a singlet ground state with specific hydrogen-bonding interactions with solvent molecules included. The results are in good agreement with available experimental data. The DFT analysis provides assignments for characteristic absorption bands in the near-IR and visible regions. Bridge-based dπ → dπ* and interconfiguration transitions at Ru(III) appear in the near-IR and MLCT and LMCT transitions in the visible. Reasonable values are also provided by DFT analysis for experimentally observed bond distances and redox potentials. The observed temperature-dependent magnetism of the blue dimer is consistent with a delocalized, diamagnetic singlet state (dπ(1)*)(2) with a low-lying, paramagnetic triplet state (dπ(1)*)(1)(dπ(2)*)(1). Systematic structural-magnetic-IR correlations are observed between ν(sym)(RuORu) and ν(asym)(RuORu) vibrational energies and magnetic properties in a series of ruthenium-based, µ-oxo-bridged complexes. Consistent with the DFT electronic structure model, bending along the Ru-O-Ru axis arises from a Jahn-Teller distortion with ∠Ru-O-Ru dictated by the distortion and electron-electron repulsion.

Free drug metabolic clearance in elderly people.

The question of whether metabolic drug clearance is decreased in elderly people has been the subject of considerable debate and is very important because clearance is a determinant of dosing. Drug clearance has been shown to be consistently impaired for flow-limited (high-clearance) drugs, but there have been conflicting results for capacity-limited (low-clearance) drugs. A limitation of the studies of capacity-limited drugs is that most have estimated clearance based on total drug concentrations (protein-bound plus free). Total drug clearance reflects both the intrinsic clearance of free drug and the extent of protein binding. Total clearance is a valid measure for capacity-limited drugs with low protein binding and appears to be consistently impaired in elderly subjects. For phenazone [antipyrine] (fraction unbound [f(u)] >0.9), seven studies have demonstrated statistical reductions in clearance of 20-52%. For theophylline (f(u) 0.6), five studies have demonstrated reductions in clearance of 22-35%. For paracetamol [acetaminophen] (f(u) 0.8), the clearance of which has been quoted as unchanged, four studies have demonstrated reductions in clearance of 19-35%. For highly protein-bound drugs, total clearance is not the appropriate parameter. Free drug clearance is more appropriate since it is independent of changes in protein binding. The literature was reviewed to test the hypothesis that in elderly people, capacity-limited drugs with high protein binding will show decreased free clearance even in the absence of a decrease in total clearance. For these drugs, data for free drug clearance based on measurement of actual free drug concentrations are limited, but suggest that the intrinsic metabolic clearance is impaired in elderly subjects. Four studies of naproxen (f(u) <0.01) have shown reduced free drug clearance of 50% or more. Two studies of valproic acid (f(u) 0.1-0.2) have shown reduced free clearance of 39% and 65%. Two studies of ibuprofen (f(u) <0.01) have shown reduced free clearance of S-ibuprofen of 21% and 28%. There is some indirect evidence for reduced clearance of the highly protein-bound drugs oxaprozin, temazepam, lorazepam, diazepam, phenytoin and warfarin, although studies measuring free concentrations are lacking. Together, the above studies support the hypothesis that the intrinsic metabolic drug clearance is impaired in elderly subjects, in the order of 20-60%, and that this effect is masked if highly protein-bound drugs are assessed using total drug clearance. If the findings are confirmed in future well-designed studies of free drug clearance, there are profound and beneficial implications for dosing of drugs in elderly people. Lower doses are likely to achieve appropriate concentrations, allowing full efficacy but decreased dose-related adverse effects.