Effects of a mu-opioid receptor agonist (codeine phosphate) on visuo-motor coordination and dynamic visual acuity in man

Effects of codeine (30, 60 and 90 mg) on visuo-motor coordination and dynamic visual acuity, together with critical flicker fusion, digit symbol substitution, complex reaction time and subjective assessments of mood, were studied from 0.75-2.0 h after ingestion by six healthy female adults. The study was double-blind and placebo controlled, and triprolidine (10 mg) was used as the active control. The effect on visuo-motor coordination was limited and was dose related and linear, and performance was altered on visuo-motor coordination with 60 and 90 mg codeine, and on dynamic visual acuity with 90 mg codeine (P less than 0.05). No other effect of codeine was detected. Modulated neuromuscular function is likely to be the common denominator of the changes in performance with codeine, though nausea, but not sedation, may be a contributory factor. It is possible that altered performance with codeine may involve interactions with different receptors than those which lead to sedation.

5-Hydroxytryptamine and noradrenaline uptake inhibition: studies on sleep in man

Effects of an inhibitor of the uptake of noradrenaline (maprotiline, 75 and 150 mg) and two inhibitors of the uptake of 5-hydroxytryptamine (zimelidine, 100 and 200 mg; indalpine, 25 and 50 mg) on sleep were studied in healthy man. Maprotiline reduced the duration of rapid eye movement (REM) sleep and increased the duration of stage 2 sleep, and there was evidence of sedation the next day. Zimelidine and indalpine reduced the duration of REM sleep, but also reduced the total sleep time and increased wakefulness and stage 1 (drowsy) sleep. It is suggested that in acute studies, the effects of inhibition of uptake on sleep are likely to arise from presynaptic inhibition of release of transmitter, although other mechanisms cannot be excluded. Suppression of REM sleep is believed to be due to the balance between cholinergic and monoaminergic influences being disturbed rather than a specific effect arising from the modulation of a particular transmitter.

Transient insomnia and rapidly eliminated hypnotics

The effects of an ultra-rapidly eliminated hypnotic (midazolam 7.5-15.0 mg; mean elimination half-life approximately 2 h) and a rapidly eliminated hypnotic (brotizolam 0.125-0.25 mg; mean elimination half-life approximately 5 h) were studied on transient insomnia induced by sleeping in a reclining seat. Rest in the seat did not lead to delay in sleep onset, but there was increased wakefulness and drowsy sleep and less REM sleep. There were no differences in wakefulness or drowsiness between sleep with drugs in the seat and with placebo in bed, but with midazolam, though not with brotizolam, there was a reduction in REM sleep less than or equal to 300 min after sleep onset. Ultra-rapidly and rapidly eliminated compounds used in the management of transient insomnia should be given in doses that are as free as possible from central nervous system depression as indicated by suppression of REM sleep during the early part of the night. Low doses of ultra-rapidly eliminated drugs are indicated for sleep-onset insomnia and for short periods of sleep, while rapidly eliminated hypnotics with elimination half-lives of approximately 5 h have the potential to sustain sleep free of residual effects.

Modulation of delta activity by hypnotics in middle-aged subjects: studies with a benzodiazepine (flurazepam) and a cyclopyrrolone (zopiclone)

Period crossing analysis was used to study the effects of flurazepam (30 mg) and zopiclone (5, 7.5, and 10 mg) on delta wave activity (0.5-2.0 Hz) during the first 4 h of sleep in middle-aged subjects. The drugs do not affect the visual scoring of slow wave sleep in middle age, but modification of delta activity does occur. Mean amplitude of delta wave activity over the 4-h period was reduced by both drugs, while the total number of delta waves and their mean period increased. The number of high-amplitude delta waves (greater than 60 microV) was decreased by the drugs, and those of low amplitude (10-60 microV) increased. Power in the frequency band 1.2-2.0 Hz was reduced.

Modulation of catecholamine transmission and sleep in man

The effect of modulation of catecholamine transmission on sleep in man was studied using mianserin (20 and 40 mg) and nomifensine (50 and 100 mg). It is suggested that reduced wakefulness induced by mianserin during sleep is primarily related to postsynaptic antagonism of alpha adrenoceptors, though a possible synergistic effect with antagonism of histamine H1 receptors cannot be excluded, while increased wakefulness with nomifensine is related to inhibition of the uptake of catecholamines and/or direct or indirect dopaminergic activity. The reduction in rapid eye movement (REM) sleep with both drugs is believed to be a non-specific effect which arises from a disturbance of the balance between monoaminergic and cholinergic influences.

Performance overnight in shiftworkers operating a day-night schedule

Performance was measured during the day (0800-1700 hours) and during the night (1700-0800 hours) of a day-night schedule, and the effect of caffeine (300 mg) was studied during the overnight periods of work. The sleep electroencephalogram was recorded together with oral temperature and urinary electrolyte excretion. Impairment of performance within 9 h after the beginning of the daytime work period was minimal, and was limited to a test of continuous performance, but impairment of performance within 9 h after the beginning of the overnight work period was more pronounced and included lowered vigilance. Impaired performance overnight was related to time on task and circadian rhythmicity, and was alleviated to some extent by the use of caffeine.

Hypnotic activity of an imidazo-pyridine (zolpidem)

Effects of an imidazo-pyridine (zolpidem: 10, 20 and 30 mg) on overnight sleep and on performance the next day were studied in young adults and in middle aged individuals. The young adults were used particularly as an homogenous group to establish any possible adverse effects of the drug on sleep and on performance the next day, and the middle aged subjects with their less restful sleep were used to study efficacy. In the young adults zolpidem led to a marked increase in slow wave sleep with a reduction in stage 2 sleep. There were no significant changes in REM sleep, though there was a tendency for REM sleep to be delayed. In the middle aged there was a reduction in awake activity and drowsy sleep with an increase in stage 2 sleep. The latency to REM sleep was increased but the duration of REM sleep over the whole night was not reduced. Digit symbol substitution and a complex reaction time task were used to study performance, but there were no residual effects with zolpidem (9 h after ingestion). Zolpidem is likely to prove useful in the management of transient and short-term insomnia in healthy middle aged individuals when impaired performance the next day is to be avoided.

Hypnotics. Their place in therapeutics

Sleep disturbance has become a subject of serious study only over the past few years, but even so there is already an increasing awareness of the nature of insomnia and a greater understanding of the role which hypnotics should play in clinical medicine. An hypnotic may be used to shorten sleep onset when there is difficulty in falling asleep, to reduce nocturnal wakefulness, or to provide an anxiolytic effect during the next day when insomnia is accompanied by a marked element of anxiety. The purpose of an hypnotic is to meet one or more of these clinical problems; to ensure that the patient is given the most useful medication, consideration must be given to duration of activity. This depends on the absorption, distribution and elimination characteristics of the drug. It is now appreciated that the most appropriate use of hypnotics is in the individual with insomnia of recent origin. An hypnotic with the most relevant pharmacokinetic profile should be used for the shortest period of time and then only as required, while low doses will ensure freedom from adverse effects. The place of hypnotics in chronic insomnia remains less certain. Their careful use may well be of benefit, though it must be part of a well defined clinical strategy. Assessment of the patient is essential to identify any specific conditions which would impair sleep.

Antihistamines: impaired performance and the tendency to sleep

The central effects of various antihistamines were studied using a variety of tests of performance, including visuo-motor co-ordination and dynamic visual acuity, as well as paper and pencil tests and critical flicker fusion. The possible relationship between performance and sedation was also studied using digit symbol substitution and latencies to drowsy sleep. There was high degree of correlation between drowsiness, as indicated by the relative ease with which individuals fell asleep over the day, and impaired performance, but it was not possible to establish the relationship for each time of the day. These findings lend some support to the suggestion that impaired performance with antihistamines may be a non-specific effect of sedation.

Behavioural responses to diazepam of drug-naive and experienced monkeys (Macaca mulatta)

Effects of 5 mg/kg diazepam given once a week for several weeks to drug-naive and drug-experienced monkeys were studied on a spatial delayed-alternation task. In both groups response latency was increased and the number of correct responses was reduced. The effects were consistent over weeks in the experienced monkeys, but in the naive monkeys there were greater initial effects on response latency and on repeat errors, and these lessened over 2-3 weeks. Thereafter, effects resembled those observed in the experienced group. Results are discussed in terms of the possible factors involved in the development and persistence of tolerance to benzodiazepines.

Central effects during the continuous osmotic infusion of a benzodiazepine (triazolam)

The effects of relatively constant plasma levels of a rapidly eliminated benzodiazepine (triazolam) were studied in young healthy males to determine whether tolerance to certain effects may develop over a relatively short period of time. The drug was given over a period of 30 h (2 days and 1 night) at zero-order rate using a rectal osmotic pump. Performance was measured at 2 hourly intervals during the day and was continuously impaired during the infusion, though there was a rapid recovery when the infusion ceased. All tasks were affected, in particular mental arithmetic and letter cancellation, but there was some improvement in performance during the second day. The normal circadian improvement in performance may have contributed to this effect, but some degree of tolerance to the effect of the drug cannot be excluded. Overnight there was a marked reduction in wakefulness, suppression of slow wave sleep, and delay to the onset and reduction in the duration of rapid eye movement sleep. During the night after infusion there was less slow wave sleep and increased wakefulness. The experimental design may prove useful in the study of tolerance to drugs.

Studies on the possible central and peripheral effects in man of a cholinesterase inhibitor (pyridostigmine)

The effect of a reversible cholinesterase inhibitor (pyridostigmine: 30 mg, 8-hourly for 3 days) on psychomotor performance and visual function and on the electrical activity of the brain was studied in healthy man. It was not possible to detect any change during the six individual experimental sessions over the 3 days, but with pooling of the data there was a drug effect. The threshold for detection of a flickering light was increased and less responses were missed on a dynamic visual-acuity task. Visuo-motor coordination was impaired. The observations were consistent with the known activity of the drug and suggest an increase in central arousal and minimal alteration in motor coordination.

Hypnotics and aircrew

The management of sleep difficulties which arise during air operations must be related, at least initially, to the cause, but the aeromedical specialist is frequently faced with the possible use of hypnotics. There are no simple guidelines, but an understanding of various issues will help toward the effective use of these drugs in those who have to cope with irregularity of rest and carry out skilled work. Some knowledge of the pharmacokinetics of the drugs concerned is useful as persistence of effect and the potential for accumulation with repeated ingestion are important factors, while efficacy in relation to sleep of different durations and at unusual times must also be considered.

Central effects of H1 and H2 antihistamines

H1-antihistamines are usually associated with impairment of central nervous functions, but unacceptable decrements in performance may not be an inevitable sequel of their use. Effects are dependent on the ability of a particular drug to cross the blood brain barrier, and so compounds which cross so slowly that tolerance of the central nervous system can develop gradually without any immediate changes in performance are of interest. However, sustained release formulations and compounds which have a selective affinity for the peripheral receptor may also have their part to play in the management of allergic states in those involved in skilled activity. As far as H2-antagonists are concerned, it is likely that as they are less liposoluble they would be free of central effects. Studies on the central effects of H1 and H2 antagonists are reviewed, and tentative recommendations are made in respect of these findings concerning the possible use of these drugs in aircrew.

Histaminergic systems and sleep. Studies in man with H1 and H2 antagonists

Effects of H1 (mepyramine, mequitazine, triprolidine and brompheniramine) and H2 (cimetidine and ranitidine) antagonists on sleep were studied in healthy man. There were no effects of mepyramine (50 and 100 mg), and the only effect of mequitazine (5 and 10 mg) was a reduction in the number of awakenings. Triprolidine (10 and 20 mg) and brompheniramine (4 and 8 mg) did not alter wakefulness during sleep or the total sleep time, but rapid eye movement sleep was reduced. There were no effects of ranitidine (150 and 300 mg), but slow wave sleep was increased by cimetidine (200 and 400 mg). It is tentatively suggested that the histaminergic system is concerned with the mechanisms which favour vigilance during the wakeful state, and the balance between wakefulness and slow wave activity during sleep. Effects of some H1 antihistamines on rapid eye movement sleep are believed to be due to their monoaminergic rather than their histaminergic activity.

Sustained performance with short evening and morning sleeps

The effect which early evening sleep may have on overnight and subsequent daytime performance, and the effect which morning sleep may have on daytime performance after overnight sleep deprivation has been studied in six healthy male volunteers. It would appear that relatively short periods of natural and drug induced (brotizolam 0.125 mg) sleep have a beneficial effect on subsequent performance even in the absence of preceding sleep debt. In the event of disturbed sleep in shiftwork an hypnotic may be helpful, and in this context, one which is rapidly eliminated and sustains sleep is appropriate.

Sleep of shiftworkers within the arctic circle

The sleep of shiftworkers in the Arctic has been investigated using electroencephalography. The subjects were studied four times a year over a 2-year period. There was a trend toward less restful sleep during the autumn and winter months, but otherwise sleep at various times of the day was similar to that of individuals elsewhere. This would suggest that sleep disturbance in polar shiftworkers can be managed in a similar way to that of shiftworkers in temperate regions.

Pharmacodynamic correlates of modified absorption: studies with lormetazepam

The bioavailability, pharmacokinetics, and effects on performance of lormetazepam (1 mg) have been compared using soft gelatin capsule and tablet formulations. Lormetazepam was more rapidly absorbed from the soft gelatin capsule (tmax = 1.0 +/- 0.2 h) than from the tablet (tmax = 2.4 +/- 0.4 h), and the plasma concentration-time curve for the capsule was shifted to the left. Bioavailability and elimination kinetics did not differ between the formulations. The number of substitutions in the digit symbol test was reduced between 0.5 and 1.5 h for both formulations (P less than 0.001), but the degree of impairment at 0.5 h was greater after the capsule than after the tablet (P less than 0.01). Visuo-motor co-ordination was impaired from 0.5 to 1.5 h after the tablet and the capsule (P less than 0.01), and extended to 5.5 h after the tablet (P less than 0.05). These observations reflect the differences in the plasma concentration-time curves.

Biological studies with continuous-wave radiofrequency (28 MHz) radiation

Effects of high-frequency (28 MHz) continuous-wave radiation have been studied in the rat and monkey. No histopathological (rat-125 mW cm-2 for 28 days) or hematological (monkey-25 mW cm-2 for 24 days) changes could be attributed to the radiation. In the monkey (125 mW cm-2 for 11 days) there was an increase in urinary calcium concentration which was most likely due to restricted movement. In the rat (220 mW cm-2 for 13 days) there was reduced uptake of iodine by the thyroid, lower levels of plasma thyroid-stimulating hormone, and reduced ratio of protein bound to nonprotein bound iodine. Food consumption was also decreased. The changes are likely to have arisen as a compensatory response to an induced heat load. A nonthermal effect of continuous-wave high-frequency radiation has not been shown in this study. The effects were likely to be associated with either physiological compensation for induced heating or restriction of movement.

Activity of the chloro- and triazolo-benzodiazepines. Behavioural studies in the monkey (Macaca mulatta)

The effects of 1,4-benzodiazepines with various heterocyclic ring structures (triazolo, triazino and imidazo), and of 1,4-benzodiazepines with chlorine substitution in the phenyl ring (4'- chlorodiazepam , 2'- chlorodiazepam and 2'- chloronordiazepam ) were studied on spatial-delayed alternation and delayed matching-to-sample tasks in the monkey. Within the dose range 0.25-0.75 mg kg-1, the triazolo compounds had marked activity, decreasing the number of correct responses and increasing total response time. The triazino was less potent and the imidazo compounds were the least likely to disrupt performance. Smaller doses (0.005, 0.01 and 0.05 mg kg-1) of triazolam did not impair performance on the tasks, and larger doses of imidazo (1.0, 3.0 and 7.5 mg kg-1) were without effect on delayed alternation. Within the dose range 1.0-10.0 mg kg-1, 4'- chlorodiazepam was without effect and only the largest dose of diazepam and 2'- chlorodiazepam impaired performance. 2'- Chloronordiazepam decreased the number of correct responses at all doses (1.0, 3.0 and 10.0 mg kg-1) and with the largest dose, the total response time was increased. The studies suggest that the effects of a drug on higher nervous function in the monkey cannot easily be predicted from standard pharmacological tests in other animals or other species of monkey.