To attempt to determine the relative value of preclinical cardiac electrophysiology data (in vitro and in vivo) for predicting risk of torsade de pointes (TdP) in clinical use.
Published data on hERG ...(or I(Kr)) activity, cardiac action potential duration (at 90% repolarisation; APD(90)), and QT prolongation in dogs were compared against QT effects and reports of TdP in humans for 100 drugs. These data were set against the free plasma concentrations attained during clinical use (effective therapeutic plasma concentrations; ETPC(unbound)). The drugs were divided into five categories: (1) Class Ia and III antiarrhythmics; (2) Withdrawn from market due to TdP; (3) Measurable incidence/numerous reports of TdP in humans; (4) Isolated reports of TdP in humans; (5) No reports of TdP in humans.
Data from hERG (or I(Kr)) assays in addition to ETPC(unbound) data were available for 52 drugs. For Category 1 drugs, data for hERG/I(Kr) IC(50), APD(90), QTc in animals and QTc in humans were generally close to or superimposed on the ETPC(unbound) values. This relationship was uncoupled in the other categories, with more complex relationships between the data. In Category 1 (except amiodarone), the ratios between hERG/I(Kr) IC(50) and ETPC(unbound) (max) ranged from 0.1- to 31-fold. Similar ranges were obtained for drugs in Category 2 (0.31- to 13-fold) and Category 3 (0.03- to 35-fold). A large spread was found for Category 4 drugs (0.13- to 35700-fold); this category embraced an assortment of mechanisms ranging from drugs which may well be affecting I(Kr) currents in clinical use (e.g. sparfloxacin) to others such as nifedipine (35700-fold) where channel block is not involved. Finally, for the majority of Category 5 drugs there was a >30-fold separation between hERG/I(Kr) activity and ETPC(unbound) values, with the notable exception of verapamil (1.7-fold), which is free from QT prolongation in man; this is probably explained by its multiple interactions with cardiac ion channels.
The dataset confirms the widely-held belief that most drugs associated with TdP in humans are also associated with hERG K(+) channel block at concentrations close to or superimposed upon the free plasma concentrations found in clinical use. A 30-fold margin between C(max) and hERG IC(50) may suffice for drugs currently undergoing clinical evaluation, but for future drug discovery programmes, pharmaceutical companies should consider increasing this margin, particularly for drugs aimed at non-debilitating diseases. However, interactions with multiple cardiac ion channels can either mitigate or exacerbate the prolongation of APD and QT that would ensue from block of I(Kr) currents alone, and delay of repolarisation per se is not necessarily torsadogenic. Clearly, an integrated assessment of in vitro and in vivo data is required in order to predict the torsadogenic risk of a new candidate drug in humans.
The use of zebrafish (
Danio rerio) larvae was investigated to predict adverse visual effects and to establish the potential application of this organism in early drug safety assessment.
Methods ...Following a comparison of the effects of 4 compounds in TL and WIK strains of zebrafish larvae, a blinded validation set of 27 compounds was tested on WIK strain of larval zebrafish in the optomotor response (OMR) assay. Selected compounds were also tested in the optokinetic response (OKR) and locomotor assays. Larvae were exposed from 3–8 days post-fertilisation (d.p.f.) by immersion in embryo culture media (E3) containing the compound in 1% DMSO (v/v). At 8 d.p.f. toxicity was assessed and the OMR or OKR assays were undertaken at non-toxic treatment levels. Compounds were then rated as ‘red’, ‘amber’ or ‘green’ according to their effects on visual function prior to unblinding of the identities of the test compounds.
Results Overall, the OMR assay revealed a good concordance between the effects of compounds in WIK strain zebrafish with the data available from other
in vivo and
in vitro models or the clinic: thirteen out of nineteen positive compounds produced the expected effect while six of the eight negative compounds were correctly predicted. This gave an overall predictivity of 70% with a sensitivity of 68% and a specificity of 75%. The two false positive compounds were further tested in locomotor and optokinetic response assays and it was shown that a motility defect, rather than an effect on vision, had given rise to the positive result in the OMR assays. Therefore, the OMR assay would best be employed with other techniques to identify false positives. Further studies on two of the false negatives at higher concentrations suggested that the initial concentrations tested were too low. Therefore, it should be ensured that the maximum tolerated concentration is tested in the OMR assay. A comparison of four standard compounds in the OMR assay in WIK and TL zebrafish wild type strains revealed no difference in sensitivity between the strains.
Discussion Overall, these results suggest that the OMR assay in zebrafish could be useful in predicting the adverse effects of drugs on visual function in man and would support its potential as a screen for ‘frontloading’ safety pharmacology assessment of this endpoint
in vivo.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Background: Tuberculous pericarditis is common in Transkei (Eastern Cape). Two randomized trials showed benefits at two years for prednisolone in patients with constrictive pericarditis, and open ...drainage plus prednisolone in patients with pericardial effusion. Aim: To see whether the advantages of prednisolone and open drainage were maintained up to 10 years. Design: Follow-up of randomized, double-blind, placebo-controlled trials. Methods: All 383 patients (143 constriction, 240 effusion) received the same anti-tuberculosis chemotherapy. They were randomized to prednisolone or placebo for the first 11 weeks, and were followed-up over 10 years. Among the 240 with effusion, 122 were also randomized to immediate open surgical drainage of pericardial fluid versus pericardiocentesis as required. Adverse outcomes were: death from pericarditis, pericardiectomy, repeat pericardiocentesis, and subsequent open drainage. Results: The 10-year follow-up rate was 96%. In constriction patients, adverse outcomes occurred in 19/70 (27%) prednisolone vs. 28/73 (38%) placebo (p = 0.15), deaths from pericarditis being 2 (3%) vs. 8 (11%), respectively (p = 0.098, Fisher's exact test). In effusion patients, adverse outcomes occurred in 14/27 (52%) with neither drainage nor prednisolone, vs. 4/29 (14%) drainage and prednisolone, 4/35 (11%) drainage and placebo, and 6/31 (19%) prednisolone and no drainage (p = 0.08 for interaction). Drainage eliminated the need for repeat pericardiocentesis. In the 176 with effusion and no drainage, adverse outcomes occurred in 17/88 (19%) prednisolone vs. 35/88 (40%) placebo patients (p = 0.003), with repeat pericardiocentesis 20 (23%) placebo vs. 9 (10%) prednisolone (p = 0.025). In a multivariate survival analysis (stratified by type of pericarditis), prednisolone reduced the overall death rate after adjusting for age and sex (p = 0.044), and substantially reduced the risk of death from pericarditis (p = 0.004). At 10 years, the great majority of surviving patients in all treatment groups were either fully active or out and about, even if activity was restricted. Discussion: In the absence of a clear contraindication, a corticosteroid should be used in addition to antituberculosis chemotherapy in the management of patients with tuberculous pericarditis.
Summary
The laryngeal mask airway was inserted in 10 cadavers. At postmortem the chest was opened and an infusion set primed with a dilute barium solution was inserted into the oesophagus and ligated ...in place. A cricoid force of 43 N was then applied and the infusion set was positioned so that when the clamp was opened it generated a pressure of 7.8 kPa within the oesophagus. The cricoid pressure was able to stop the flow of fluid into the oesophagus. This demonstrates that cricoid pressure is effective in preventing reflux at intragastric pressures which are encountered clinically and the presence of the laryngeal mask airway does not compromise this.
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BFBNIB, FZAB, GIS, IJS, KILJ, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Where antiretroviral drugs are available, interaction of protease inhibitors and rifampicin must be considered and guidelines for this have been issued by the Centers for Disease Control and ...Prevention. 14 Coexistence of epidemic tuberculosis and HIV infection, interested clinicians, and good basic laboratory services in Zimbabwe and South Africa provide an appropriate environment for further work on TB pericarditis and adjunctive prednisolone. ...the resurgence of all types of tuberculosis should alert general physicians and cardiologists in the developed world to the possibility of TB pericarditis.
Peripheral aromatic amino acid decarboxylase (AADC) inhibitors, such as benserazide, are routinely used to potentiate the effects of L-3, 4-dihydroxyphenylalanine (L-DOPA) in Parkinson's disease (PD) ...and in experimental models of PD. However, there is little information available on the optimal dose or the timing of administration relative to L-DOPA treatment. We now assess the effect of dose, timing, and supplemental administration of benserazide on the rotational response induced by L-DOPA in unilateral 6-hydroxydopamine-lesioned rats. L-DOPA (12.5 mg/kg, p.o.) concomitant with benserazide (3.125-15 mg/kg, p.o.) produced a dose-dependent increase in contraversive rotation compared with the effects of L-DOPA alone. The optimal L-DOPA response was achieved with 10 mg/kg of benserazide and this dose was used in subsequent experiments. When L-DOPA treatment was delayed for 1, 2, or 3 h after benserazide, the rotational response declined suggesting loss of AADC inhibition. Unexpectedly, there was also a progressive decline in response when benserazide and L-DOPA were given together but at increasingly later time points of 08.00, 09.00, 10.00, and 11.00 h. To assess supplemental administration of benserazide, an additional dose was given 2 h after the initial benserazide/L-DOPA treatment. This produced a further increase in the number of contralateral rotations indicating that the effect of benserazide declines while plasma levels of L-DOPA are maintained. Therefore, optimization of the dose and timing of benserazide administration is essential to achieve a consistent L-DOPA response in 6-hydroxydopamine-lesioned rats. These findings may have implications for the way in which peripheral AADC inhibitors are used in the treatment of PD.
In the light of the recent Calman Report and the Royal College of Anaesthetists document 'Specialist training in anaesthesia, supervision and assessment', there is currently much debate concerning ...the future of anaesthesia training in the UK. We present a description of anaesthesia training in the US for discussion and comparison. US residency training is short and seamless. It is highly structured, but retains a capacity for specialisation. It may offer ideas for the future direction of training in the UK.
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