Validation of the use of zebrafish larvae in visual safety assessment.

INTRODUCTION: 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.

Relationships between preclinical cardiac electrophysiology, clinical QT interval prolongation and torsade de pointes for a broad range of drugs: evidence for a provisional safety margin in drug development.

OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Head injuries in three Scottish neurosurgical units. Scottish head injury management study.

The organisation of care for patients with head injuries in Scotland was investigated by studying retrospectively 785 patients admitted in 1974 and 1975 to neurosurgical units in Glasgow, Aberdeen, and Dundee. The reasons for the injuries and the patients' clinical conditions were similar in each unit. The referral practices at the hospitals containing the units were compared and found to be different from that of the unit in Edinburgh. It is concluded that patients in the Glasgow, Aberdeen, and Dundee units, which operate a similar policy for head-injured patients, are in general similar. Transferring to a neurosurgical unit only selected patients rather than all patients with head injuries is safe practice only if policies are agreed with primary surgeons and patients can be transferred without delay.

Head injuries in accident and emergency departments at Scottish hospitals.

The features of 3500 patients with head injury who attended accident and emergency departments in Scotland during 1974 are described. These represented 10 per cent of all attenders at these departments. Recent alcohol consumption was noted in 25 per cent of adult males; this was commonest amongst those who were victims of assault or pedestrians involved in traffic accidents. Forty-one per cent of patients had scalp wounds; 58 per cent had radiographs of the skull taken and of these 2.7 per cent had fractures of the skull. Although 20 per cent of patients had altered consciousness at some time, only 5 per cent showed any evidence of impaired consciousness when seen at hospital. Twenty-three per cent of those attending were admitted to hospital. Criteria which are important when assessing whether a head-injured patient should be admitted to hospital are listed.

Patients in acute surgical wards: a survey in Glasgow.

A survey was made of all patients in general surgical, urological, and orthopaedic and accident wards in Glasgow on one day in June 1975. Its purpose was to define features of acute surgical practice of relevance to the future planning of resources, particularly bed numbers. Over 40% of the patients in both surgical and orthopaedic wards were over 65 years. Most patients had serious conditions and could not have been treated other than by admission to an acute surgical ward. But a substantial minority no longer needed such facilities and could have been transferred to second-line beds, although many still required skilled nursing care. Delay in the discharge of elderly patients from acute surgical wards as a consequence of non-surgical (often medical or social) problems results in a proportion of acute surgical beds fulfilling a second-line function. Unless arrangements for the earlier discharge of these patients are made any reduction in acute surgical beds is likely to restrict elective surgery, especially in orthopaedics.