A comparison of triprolidine and clemastine on histamine antagonism and performance tests in man: implications for the mechanism of drug induced drowsiness

Efficacy of Triprolidine in the Treatment of Temporary Sleep Disturbance

Triprolidine, a first-generation antihistamine for allergic rhinitis, has a shorter half-life and fewer persistent effects relative to other antihistamines and may be useful in the treatment of temporary sleep disturbance. Patients aged ≥18 years old were randomized 1:1:1 to receive either triprolidine 2.5 mg (n = 65), triprolidine 5 mg (n = 66), or placebo (n = 67) on 3 consecutive nights. Sleep disturbance index was monitored via wrist actimeter. Subjective measures were assessed via diary card. Triprolidine 2.5 mg had a significantly lower sleep disturbance index versus placebo on night 1 (P = .02); however, when adjusted for outliers, sleep disturbance index did not significantly differ between either dose of triprolidine versus placebo on night 1. Adjusted sleep disturbance index was significantly lower with triprolidine 2.5 and 5 mg versus placebo on night 3 (P = .0017 and P = .011, respectively) and for the mean of all 3 nights (P = .01 and P = .015, respectively). Sleep latency was significantly improved for triprolidine 2.5 mg versus placebo on nights 2 and 3 and for the mean of all 3 nights and for triprolidine 5 mg versus placebo for the mean of all 3 nights. Subjective measures showed those on both doses of triprolidine felt more refreshed on awakening versus placebo for the mean of all 3 nights, with no increase in daytime sleepiness. The frequency of adverse events was similar across groups. The optimum dose of triprolidine for treatment of temporary sleep disturbance was 2.5 mg. There were improvements in both objective and subjective measures of sleep quality versus placebo, with no safety concerns raised.

Sedation and memory: studies with a histamine H-1 receptor antagonist

The influence of sedation on the effect of an H-1 receptor antagonist on various cognitive functions, including memory, were evaluated. Diphenhydramine (50, 75 and 100 mg) and lorazepam (0.5 and 1.5 mg) were given on single occasions to 12 healthy volunteers (six males, six females) aged 20-33 (mean 23.4) years. Subjective assessments of sedation, sleep latencies, digit symbol substitution, choice reaction time, sustained attention and memory recall were studied 1.0 h before and 0.5, 2.0 and 3.5 h after drug ingestion. The study was double blind, placebo controlled and with a crossover design. With all doses of diphenhydramine there was subjective sedation, reduced sleep latencies and impairments in performance on the digit symbol substitution, choice reaction time and sustained attention tasks. No effects were observed with 0.5 mg lorazepam. With 1.5 mg lorazepam there was subjective sedation, fewer digit symbol substitutions, slowed choice reaction time, impaired attention and memory, but no effect on sleep latencies. Contrast analysis of data measured at all time points showed that although there was no difference in the effect of diphenhydramine (100 mg) and lorazepam (1.5 mg) on those tasks without a memory component, response times were slower with lorazepam on those tasks with a memory component. However, both 100 mg diphenhydramine and 1.5 mg lorazepam impaired prompted recall measured at 2 h post-ingestion only. It is considered that impaired memory is not necessarily associated with sedation, and that impairment of memory with drugs that lead to sedation may be effected through neuronal systems independent of those that affect arousal.

Central and peripheral evaluation of rupatadine, a new antihistamine/platelet-activating factor antagonist, at different doses in healthy volunteers

AIMS

To assess peripheral anti-H1 and central nervous system (CNS) activity of single increasing doses of rupatidine fumarate (RU), a new antihistamine/platelet-activating factor antagonist compound, in comparison with hydroxyzine and placebo.

METHODS

Eighteen healthy young subjects of both sexes took part in a crossover, randomised, double-blind, placebo-controlled study. Treatments tested were: RU 10, 20, 40 and 80 mg and hydroxyzine 25 mg, as a positive standard. Before and several times after drug intake, peripheral anti-H1 activity was appraised by the skin reactivity to intradermal injection of histamine. CNS effects were also obtained by objective tests of psychomotor performance and subjective mood scales.

RESULTS

All active treatments showed a significant reduction of the wheal and flare reaction in relation to placebo, RU displaying a potent dose-dependent inhibition pattern. The global nonparametric Friedman test to changes from placebo in 15 objective variables from psychomotor performance showed a significant impairment of similar magnitude after hydroxyzine 25 mg (p = 0.01) and RU 80 mg (p = 0.02), but this was slower in development and recovery after the latter. After RU 40 mg, a smaller impairment was also obtained (p = 0.04). Activity (p = 0.01) and drowsiness (p = 0.02) scales showed significant changes, the subjects feeling less active and more drowsy after all active treatments.

CONCLUSION

RU presents a potent dose-dependent peripheral anti-H1 activity, displaying psychomotor impairment activity only at the highest dose (80 mg), while therapeutically relevant lower doses (10 and 20 mg) were similar to placebo.

Low dose clemastine inhibits sneezing and rhinorrhea during the early nasal allergic reaction

BACKGROUND

Clemastine (1 mg) is currently available over-the-counter for the treatment of allergic rhinitis.

OBJECTIVE

To evaluate the efficacy of half the standard dose of clemastine (0.5 mg) in inhibiting the nasal response to allergen and the cutaneous response to histamine.

METHODS

Double-blind, placebo-controlled, crossover study of 20 allergic subjects out of season. The subjects received placebo or clemastine administered one, four, and six hours before the challenges. Filter paper discs were used both to challenge the nasal mucosa with diluent and allergen and collect generated secretions. Sneezes, secretion weights, nasal and ocular symptoms, and albumin levels in nasal secretions were monitored for the nasal challenge. Intradermal skin testing was performed with diluent followed by histamine and the wheal and flare reactions were measured.

RESULTS

There was a significant reduction in the number of sneezes after clemastine administered one, four, and six hours prior to challenge compared with placebo (P < .01). Clemastine administered four and six hours before challenge reduced sneezing significantly more than clemastine administered one hour before challenge (P < .05). Antigen-induced increases in secretion weights and symptoms of rhinorrhea were significantly reduced compared with placebo only when clemastine was administered four and six hours prior to challenge (P < .05). Pretreatment with clemastine had no significant inhibitory effects on other nasal symptoms or on albumin levels in nasal secretions, an objective index of increased vascular permeability. Pretreatment with clemastine did not inhibit the histamine-induced wheal skin reaction but showed a tendency, when administered six hours prior to the intradermal challenge, to reduce the flare reaction induced by the lowest dose of histamine (P = .05).

CONCLUSIONS

The data show that clemastine, given at half the usual dose four and six hours prior to allergen challenge, provides relief for sneezing and rhinorrhea and suggests that this dose might be useful in the treatment of allergic rhinitis.

The pharmacokinetics and bioavailability of clemastine and phenylpropanolamine in single-component and combination formulations

Studies were conducted in healthy male volunteers (n = 171; age range, 19-49 years; 22-27 subjects per study) to examine the following: pharmacokinetics and dose proportionality of the antihistamine clemastine; the effect of coadministration of phenylpropanolamine and clemastine on the pharmacokinetics of the two drugs; and the bioavailability of clemastine tablets and combination tablets of clemastine and sustained-release phenyl-propanolamine under fasted and fed conditions after single-dose administration and at steady state. All studies used crossover designs, with randomized drug treatments separated by a 7-day washout period for the single-dose studies, and with administration every 6 or 12 hours for 7 days per treatment for the steady-state studies. After single oral doses of clemastine solution (1,2, and 4 mg), the area under the concentration-time curve (AUC) and maximum concentration (Cmax) were dose proportional. Clemastine showed a first-pass reduction in the extent of absorption, with oral bioavailability calculated as 39.2 +/- 12.4%. Extravascular distribution of drug was suggested by the high volume of distribution (799 +/- 315 L) and low Cmax (0.577 +/- 0.252 ng/mL/mg) observed at 4.77 +/- 2.26 hours after administration, and by the biphasic decline in plasma concentration. The terminal elimination half-life (t1/2) of clemastine was 21.3 +/- 11.6 hours. Steady-state concentrations of clemastine were consistent with linear pharmacokinetic processes, and clearance was unaffected by age in the range studied, or by race. Clemastine solution and tablets were bioequivalent, and food had no significant effect on rate and extent of absorption of clemastine. The 1- and 2-mg clemastine tablets showed proportional bioavailability. Coadministration of clemastine with phenylpropanolamine did not significantly influence the pharmacokinetics of clemastine or the AUC and elimination t1/2 of phenylpropanolamine, but reduced the rate of absorption of phenylpropanolamine. Combination tablets containing 1 mg or 2 mg of immediate-release clemastine plus 75 mg of sustained-release phenylpropanolamine for twice daily administration were bioequivalent to the separate components and showed no significant interaction with food.

Placebo controlled comparison of acute effects of ebastine and clemastine on performance and EEG

The effects of single oral doses of 10 and 20 mg ebastine were compared with placebo and 2 mg clemastine in a double-blind cross-over study in 16 healthy male volunteers. Clemastine produced the known pattern of changes, namely impairment of psychomotor performance, drowsiness, and a selective effect on cognitive processes. Earlier encoding in a perceptual stage was slowed whereas abstract classification processes were not affected. Electrophysiological measures of vigilance showed a general decrease in vigilance especially 2.5 and 4.5 h after dosing. In contrast at no time was any effect of ebastine different from that of the placebo. Ebastine 10 and 20 mg differed positively from clemastine in its effect on pursuit tracking, subjective rating of drowsiness and general discomfort. Ebastine 10 mg also differed positively from clemastine in the EEG features of vigilance. It is concluded that 10 and 20 mg ebastine were free from sedative adverse effects.

Sedation and histamine H1-receptor antagonism: studies in man with the enantiomers of chlorpheniramine and dimethindene

1. The effects of 10 mg (+)- and (-)-chlorpheniramine and 5 mg (+)- and (-)-dimethindene on daytime sleep latencies, digit symbol substitution and subjective assessments of mood and well-being were studied in 6 healthy young adult humans. Each subject also took 5 mg triprolidine hydrochloride as an active control and two placebos. 2. Daytime sleep latencies were reduced with triprolidine, (+)-chlorpheniramine and (-)-dimethindene, and subjects also reported that they felt more sleepy after (+)-chlorpheniramine and (-)-dimethindene. Performance on digit symbol substitution was impaired with (+)-chlorpheniramine. 3. Changes in measures with (-)-chlorpheniramine and (+)-dimethindene were not different from changes with placebo. 4. In the present study, changes in measures of drowsiness and performance were limited to the enantiomers with high affinity for the histamine H1-receptor. These findings strongly suggest that sedation can arise from H1-receptor antagonism alone, and provide further support for the belief that the histaminergic system is concerned with the regulation of alertness in man.

A comparative study of cyproheptadine and DL carnitine on psychomotor performance and memory in healthy volunteers

This study was performed in order to investigate the extent and severity of cyproheptadine effects on psychomotor performance, mood and memory functions and to compare them to the effects of DL carnitine, another appetite stimulant. Twelve healthy volunteers received 2 doses (at 800 am and 1200 am) of 6 mg cyproheptadine, 1600 mg DL carnitine and placebo on separate days at a weekly intervals. The study followed a double-blind, latin-square design. Assessment of dependent variables was performed 1 h after the first and 1 h and 5 h after the second administration of the drug. On each of these occasions, the following measurements were performed: choice reaction time (CRT), critical flicker fusion (CFF), digit symbol substitution test (DSST), short-term memory (paired words association test), long-term memory (picture test) and 100 mm visual analogue scales of subjective ratings (VAS). Cyproheptadine significantly impaired objective measures (CFF) and subjective ratings both at 1 h and 5 h after the second dosage. Compared with cyproheptadine, DL carnitine induced a slight improvement in psychomotor performance as assessed by CRT. None of the drugs had any effect on memory and on appetite at the doses studied. In conclusion, cyproheptadine at usual doses had a sedative effect, the intensity and duration of which implied a certain risk in performing daytime functions eg when driving, or manipulating machines. DL carnitine had no effect on vigilance.

Ebastine: the effect of a new antihistamine on psychomotor performance and autonomic responses in healthy subjects

1. Ebastine, through its carboxylic acid metabolite has antihistamine (H1-receptor) activity in man. 2. We have examined in a single blind placebo controlled study the effects of 10 mg and 50 mg of ebastine on cardiovascular, autonomic and psychomotor function in healthy subjects. 3. Ebastine had no effect on blood pressure or heart rate and there was no evidence of any anticholinergic activity on circulatory reflexes or salivation. 4. Ebastine did not impair psychomotor performance as assessed by critical flicker fusion at either dose. 5. Ebastine 10 mg had no effect on sedation measured by visual analogue scale or direct questioning, however ebastine 50 mg did cause a modest increase in indices of sedation. 6. Ebastine did not have detectable sedative properties at the 10 mg dose where long-lasting antihistamine effects can be demonstrated.

Acrivastine in seasonal allergic rhinitis: two randomized crossover studies to evaluate efficacy and safety

In two randomized crossover studies, the antihistamine, acrivastine, was evaluated for the treatment of seasonal allergic rhinitis. One study on 31 patients found both 4 and 8 mg acrivastine given three times daily to be significantly better than placebo for alleviating hay fever. There were no significant differences in symptom scores between the two doses, although more patients (63%) favoured 8 mg acrivastine over the 4 mg dose (46%) or placebo (35%). The other study found the higher dosage regimen to be similar in efficacy to 1 mg clemastine given three times daily. Both dosages were significantly better than placebo for reducing symptom scores in all 18 evaluable patients. The incidence of adverse experiences was low in both studies; there being no dose-related effects of acrivastine. In the second study, drowsiness, probably or possibly treatment related, occurred on seven occasions during clemastine treatment and once with acrivastine. These studies indicate that 8 mg acrivastine given three times daily is both well tolerated and of equal efficacy to clemastine for the treatment of seasonal allergic rhinitis.

The pharmacokinetics, antihistamine and concentration-effect relationship of ebastine in healthy subjects

1. The kinetics and effects of ebastine 10 and 50 mg were studied after oral dosing in healthy subjects. 2. The parent drug was extensively metabolised during the first pass to its carboxylic acid derivative, carebastine. 3. The pharmacokinetics of carebastine were linear over the dose range studied and the terminal elimination half-life was 10.6 +/- 2.6 and 12.5 +/- 1.9 h respectively after 10 and 50 mg of ebastine. 4. Antihistamine (H1-receptor) activity was examined with intradermal histamine (2 micrograms). Oral ebastine reduced the histamine wheal area for up to 24 h and also reduced subjective local pain. 5. Antihistamine activity correlated well with plasma levels of carebastine in individual subjects. 6. Ebastine appears to have potential as an antihistamine for once a day dosing.

Behavioural effects of histamine and its antagonists: a review

This review focuses on the behavioural effects of histamine and drugs which affect histaminergic function, particularly the H1- and H2-receptors antagonists. Research in this area has assumed considerable importance with increasing interest in the role of brain histamine, the clinical use of both H1 and H2 antagonists and evidence of nonmedical use of H1 antagonists. Results from a number of studies show that H1 and H2 antagonists have clear, but distinct subjective effects and that H1 antagonists have discriminative effects in animals. While H1 antagonists are reinforcers in certain conditions, histamine itself is a punisher. Moderate doses of H1 antagonists affect psychomotor performance in some situations, but the results are variable. The exceptions are terfenadine and astemizole, which do not seem to penetrate the blood-brain barrier readily. In studies of schedule-controlled behaviour, marked changes in response rate have been observed following administration of H1 antagonists, with the magnitude and direction dependent on the dose and the baseline behaviour. Histamine reduces avoidance responding, an effect mediated via H1-receptors. Changes in drinking and aggressive behaviour have also been observed following histamine administration and distinct roles for H1- and H2-receptors have been delineated. Separate H1- and H2-receptor mechanisms have also been suggested to account for changes in activity level. While the H2 antagonists do not always have strong behavioural effects when administered peripherally, there is evidence that cimetidine has a depressant effect on sexual function. These and other findings reveal an important role for histaminergic systems in a wide range of behaviour.

Effects of triprolidine and dipipanone in the cold induced pain test, and the central nervous system of healthy volunteers

1 Twelve healthy volunteers took part in a study of the interaction between the antihistamine triprolidine and the opioid dipipanone in the cold induced pain (CP) test and tests of sedation. They received placebo, triprolidine 2.5 mg, dipipanone 8 mg or the combination of the two active treatments according to a double-blind, randomised, balanced, crossover design. 2 Antihistamine activity was demonstrated by triprolidine reducing the size of wheals and flares produced by intradermal histamine 1.6 micrograms. However, triprolidine produced no analgesia in the CP test, nor did it enhance the analgesia produced by dipipanone alone. 3 Neither treatment alone produced statistically significant sedation, assessed by visual analogue scales (VAS), side effect check list, body sway and reaction times. However, the combination did cause significant sedation. 4 Dipipanone reduced pupil size, depressed respiration, and decreased salivation. Triprolidine had no effects on pupil size and respiration, but reduced salivation slightly. It was concluded that histaminergic (H1) mechanisms are unlikely to be involved in pain produced by cold.

Pharmacologic evaluation of loratadine (SCH 29851), chlorpheniramine and placebo

The antihistaminic effect of loratadine (160 mg) was compared in twenty-four normal male volunteers to chlorpheniramine maleate (4 mg) and placebo in a double blinded 3-way cross-over study of latin square design. After receiving single oral doses of each medication, the wheal response to serial 0.1 ml intradermal histamine (2 micrograms) and saline (control) injections were recorded over a 24-h period. The calculated wheal areas were compared to base-line measurements. The results were analyzed by analysis of variance. Loratadine exhibited a more pronounced inhibition of histamine wheal formation than placebo or chlorpheniramine maleate (p less than 0.003). In contrast to chlorpheniramine maleate which had a duration of action of only 3 h, loratadine inhibited the response for the entire observation period between 1 and 24 h post-dose. Although sedation was observed less frequently with loratadine (Placebo, n = 2; chlorpheniramine, n = 3; and loratadine, n = 1), the relative incidence were not statistically significant.

Acute and subacute actions on human performance and interactions with diazepam of temelastine (SK&F93944) and diphenhydramine

Thirteen healthy subjects participated in a combined acute and subacute double-blind, cross-over trial of two H1-antihistamines diphenhydramine (DPH) and temelastine (SKF) against placebo. The doses were DPH 50 mg b.d. and SKF 100 mg b.d. Objective (digit symbol substitution, flicker fusion, Maddox wing, attention, tracking, choice reaction) and subjective (visual analogue scales, side-effects on questionnaire) tests were done on Days 1, 4 and 5, on each occasion before drug intake and after 90 min and 3 h. On Day 1 DPH caused clear sedation of unpleasant character and impaired flicker fusion, attention and digit symbol substitution. SKF shifted the VAS assessment "drowsy/alert" towards drowsiness at 90 min, without objective impairment. On Day 4 DPH reduced exophoria and impaired flicker fusion without subjective sedation. On Day 5, diazepam 0.3 mg/kg (DZ) given with the other drugs caused subjective sedation of pleasant character and impaired various functions in the objective tests. Neither SKF nor DPH increased the effects of DZ; DPH slightly counteracted the effect of DZ on exophoria. At home, SKF did not differ from placebo while DPH proved sedative. DPH did not improve sleep but caused dry mouth and blurred vision. Measurement of plasma levels of antihistamines on each test day revealed the development of tolerance to antihistamine-induced sedation. The concentration of DZ measured by bioassay was somewhat elevated in the presence of DPH. Since the majority of the performance tests were not influenced by temelastine, it appears to be an acceptable, novel H1-antihistamine for the treatment of allergic disorders.

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.

Pharmacodynamic and pharmacokinetics of BW 825C: a new antihistamine

The new H1-receptor antagonist BW 825C and triprolidine (2.5 and 5 mg) were administered to 12 healthy male volunteers in a double blind placebo controlled, balanced, crossover design. Histamine antagonism was measured by assessment of flare and weal areas after intradermal injection of histamine. The 2 compounds were approximately equipotent in blocking the flare and weal response to intradermal histamine and had a similar duration of action. Triprolidine impaired performance of vigilance and reaction time (p less than 0.05) compared with placebo while BW 825C did not. Drowsiness measured using visual analogue scales followed both triprolidine treatments, but not BW 825C. BW 825C had a plasma half-life (t1/2) of 1.7 +/- 0.2 h and triprolidine of 4.6 +/- 4.3 h. The peak plasma level of BW 825C was approximately 6 times that of triprolidine. It was concluded that BW 825C might be a clinically active H1-antagonist with reduced sedative side-effects.

Peripheral antihistamine and central sedative effects of three H1-receptor antagonists

The effects of single oral doses of three antihistamine compounds on histamine-induced itch and flare reactions were studied in 24 healthy volunteers by a double-blind balanced design. Central sedative effects were concurrently analyzed using a set of computerized neuropsychological tests and analogue ratings. Hydroxyzine 20 mg had a more pronounced inhibitory effect on the cutaneous response than 3 mg clemastine or 3 mg azatadine. Clemastine tended to cause more sedation than the other two drugs. A compound score, reflecting the balance between peripheral and CNS effects, showed hydroxyzine to have relatively more peripheral antihistamine effect and less sedative effect than the other two drugs. The independence of peripheral and CNS antihistamine effects was also suggested by correlation analysis. Subjects displayed individual sensitivity to the peripheral antihistamine effect of the three drugs; a marked antihistamine effect of one drug predicted a marked effect of the other two drugs. This was not the case for CNS sedation. The independence of peripheral and CNS effects should encourage development of new and more specific antihistamine compounds.

A comparison of methods for assessing the sedative effects of diphenhydramine on skills related to car driving

A double blind cross-over study was performed to compare the sensitivity of "oof road" driving with that of laboratory tests of driving-related skills to drug induced sedation. Twelve experienced drivers (6 M, 6 F) received single oral doses of the H1-antagonist diphenhydramine 25, 50 and 100 mg and placebo. Each treatment was administered on 2 separate occasions, once in the driving school when real driving skills were assessed and again in the laboratory when performance of an adaptive tracking task, body sway and visual reaction were measured. On all occasions subjects assessed their own performance and alertness/sedation using visual analogue scales. Data were subjected to analysis of variance and differences assessed by Newman Keul's test. Diphenhydramine failed to impair driving performance at any dose while all doses produced significant changes in each of the 3 laboratory tests. Subjects rated themselves sedated after all 3 doses of active drug in the laboratory but only after the 100 mg dose in the driving school. Tests performed in the psychopharmacology laboratory appear to be more sensitive to the sedative effects of diphenhydramine than tests of "off road" driving. The implications are discussed.

Antihistamines and visual function: studies on dynamic acuity and the pupillary response to light

1 Effects of three antihistamines, triprolidine (10 mg) in a sustained release form, astemizole (10 mg) and terfenadine (60 mg), have been studied on dynamic visual acuity and on the response of the pupil to light, together with critical flicker fusion, digit symbol substitution and cancellation, and subjective assessment of mood. The study was double-blind and effects were observed from 0.5-4.0 h after ingestion. 2 Triprolidine impaired dynamic acuity and reduced the threshold for subjective fusion of a flickering light, but there were no changes with astemizole or terfenadine. The diameter of the pupil and its response to light were not changed by the drugs. 3 Performance on digit symbol substitution and cancellation was not altered by the drugs. 4 Astemizole and terfenadine are promising antihistamines for those involved in skilled activity.

A comparison of triprolidine and cyclizine on histamine (H1) antagonism, subjective effects and performance tests in man

1 The effects of triprolidine and cyclizine on the histamine skin response, performance tests and subjective effects were examined in a controlled, double-blind study in eight healthy volunteers. 2 Triprolidine was considerably more potent that cyclizine in inhibiting the skin response to histamine. Significant inhibition of flare size occurred at 1, 2 an 4 h after triprolidine 2.5 mg. A smaller but significant reduction occurred at 2 and 4 h after cyclizine 100 mg but not after the 50 mg dose. 3 Cyclizine 100 mg produced a significant increase in reaction time at 4.5 h compared with lactose. Smaller though non significant increases followed triprolidine and cyclizine 50 mg. 4 Subjective effects were seen only after cyclizine 100 mg when subjects were significantly more drowsy, feeble, muzzy, lethargic and dreamy than after lactose dummy. No significant changes followed triprolidine 2.5 mg or cyclizine 50 mg. 5 It was concluded that while cyclizine has antihistamine properties, these are weak compared with triprolidine, and are not seen with doses sufficiently low to avoid central nervous system impairment.

Performance studies with the H1-histamine receptor antagonists, astemizole and terfenadine

1 Effects of the antihistamines, terfenadine (60 mg) and astemizole (10 and 20 mg), on performance (visuo-motor coordination, arithmetical ability and digit symbol substitution) and on mood were studied in six healthy adult females. The study was double-blind, placebo controlled and included an antihistamine with known central effects (triprolidine 10 mg in sustained release form). 2 There were no changes in performance after terfenadine (60 mg) and astemizole (10 and 20 mg). Triprolidine (10 mg) caused a decrement in visuo-motor coordination (P less than 0.01) 0.5 h after ingestion which lasted until 3.5 h (P less than 0.001). The subject assessed their performance as impaired from 1.5-3.5 h (P less than 0.05) with triprolidine (10 mg), and their mood assessments were also altered. 3 Terfenadine (60 mg) and astemizole (10 and 20 mg) are likely to prove useful antihistamines for those involved in skilled activity.

Single and repeated dose comparison of three antihistamines and phenylpropanolamine: psychomotor performance and subjective appraisals of sleep

1 In a double-blind cross-over study, nine healthy male students received placebo, brompheniramine 12 mg), carbinoxamine (12 mg), clemastine (1 mg), and phenylpropanolamine (50 mg) orally. Three doses of each drug were given: at 08.30 h and 21.00 h on the first day of treatment and at 08.30 h on the following day. 2 Psychomotor skills and subjective feelings were recorded before and 2, 6 and 12 h after the first dose on day 1 as well as before and 2 and 6 h after the third dose on day 2. Subjective appraisals of sleep were requested on the morning of day 2. 3 All antihistamines tended to cause subjective drowsiness on the first day of treatment. Drowsiness was felt for a maximum of 2 h after carbinoxamine, 6 h after brompheniramine, and 12 h after clemastine. In contrast to antihistamines, phenylpropanolamine made subjects more alert and quick witted. Tolerance to the antihistamine-induced drowsiness developed on the second day. 4 Divided attention, tracking, speed anticipation and sleep were not affected by any drug. Carbinoxamine slowed reactions 2 h after the first dose, but no impairment was measured in objective tests after brompheniramine or clemastine. 5 Phenylpropanolamine improved reaction speed and reaction accuracy and enhanced flicker recognition throughout the study. Phenylpropanolamine plasma levels and improvement in flicker fusion test results correlated with each other on day 2. 6 The results suggest that phenylpropanolamine and the antihistamines studied are comparatively harmless to psychomotor performance and driving skills.

The effects upon vigilance and reaction speed of the addition of ephedrine hydrochloride to chlorpheniramine maleate

The addition of stimulant, ephedrine hydrochloride (15 mg), to the antihistamine, chlorpheniramine maleate (10 mg) is shown significantly to reduce the adverse drowsy effects of the latter upon various components of human performance. Auditory vigilance--a test of long-term attentiveness--is shown particularly to benefit from the addition of ephedrine. Whilst ephedrine does not aid simple reaction speed, it does reduce the pausing in serial-choice performance, indicative of a drowsy state, which otherwise occurs under chlorpheniramine alone.

Effect of the antihistamines, brompheniramine maleate and triprolidine hydrochloride, on performance in man

1 Effects of brompheniramine maleate (4 and 12 mg) and triprolidine hydrochloride (2.5 and 10 mg) on visuo-motor coordination, and on subjective assessments of performance, well-being and sleep were each studied in six subjects at 0.5, 1.5, 3.0, 5.0 and 7.0 h after ingestion. The doses refer to immediate and sustained release preparations respectively. 2. Triprolidine hydrochloride (2.5 mg) had an immediate effect on performance which persisted to 3.0 h, and the sustained release preparation (10 mg) impaired performance from 1.5 to 5.0 h. Brompheniramine maleate (4 mg) impaired performance from 1.5 to 3.0 h, and the sustained release preparation (12 mg) impaired performance at 1.5 h. There were no consistent changes in the subjective assessments of performance, or of well-being and sleep. 3. The studies emphasize the variable effects of antihistamines on performance, and suggest that effects on performance of sustained release preparations may be similar to those of the usual form. Sustained release preparations may provide an advantage in clinical practice if the antihistaminic activity is prolonged.

Drowsiness, impaired performance and tricyclic antidepressants drugs

1. The effects of amitriptyline, protriptyline, protriptyline, and a chemically related potential antidepressant, BW247, on performance tests and subjective ratings were studied. 2. Two groups of twelve healthy subjects received drugs and lactose dummy in identical capsules at weekly intervals according to a balanced design, under double-blind conditions, and with standarized tests and environment. 3. Amitriptyline produced the most marked effects, with significant (P less than 0.05) impairment in auditory vigilance after 6.25 mg. Auditory reaction time, tapping rate, arithmetic, and digit symbol substitutions were impaired by amitriptyline 12.5 and 25 mg and all doses produced increased ratings of mental sedation. The effects began 1.5 h after drug and lasted approximately 5 h. 4. Nortriptyline produced fewer effects which were later in onset. Tapping at 1.8 h and auditory vigilance at 3.5 to 4.5 h were impaired by nortriptyline 25 mg whereas reaction time was prolonged by both doses at 5 h. No change in rating of mental sedation occurred. 5. No significant change in performance or subjective ratings followed protriptyline 10 mg or BW247, 12.5 and 25 mg. 6. The findings are discussed in relation to the presence of secondary and tertiary amines on the side chain of the compounds, and their relative abilities to block neuronal uptake of noradrenaline and 5-hydroxytryptamine.

Performance studies with antihistamines

1 Effect of four antihistamines, chlorpheniramine (4 mg), clemastine (1 mg), promethazine (10 mg) and terfenadine (60 mg), on visuo-motor coordination and on subjective assessments of performance and well-being were compared with placebo in six healthy females from 0.5--7.0 h after morning ingestion of each drug. The study was double-blind, and the doses used were believed to be equally potent in their antihistaminic activity. 2 There was impaired performance 1.5 h (P less than 0.01) after chlorpheniramine, 3.0 h (P less than 0.05) and 5.0 h (P less than 0.01) after clemastine, and 3.0 h (P less than 0.01) and 5.0 h (P less than 0.001) after promethazine. It was not possible to establish effects on performance after ingestion of terfenadine. Subjective assessments of performance were not altered. 3 The subjects as a group reported improved alertness (P less than 0.05) and improved wakefulness (P less than 0.05) 0.5 h and 3.5 h respectively after ingestion of terfenadine, and were less energetic (P less than 0.05) 7.0 h after ingestion of chlorpheniramine. There were not other consistent changes in assessments of well-being.

The effect of diphenhydramine alone and in combination with ethanol on histamine skin response and mental performance

The effects of diphenhydramine and diphenhydramine plus ethanol on response to intradermal histamine and on mental performance were assessed in twelve male volunteers. A significant impairment of histamine skin response was found with diphenhydramine. This response was unaffected by ethanol. Ethanol improved performance with a tracking test compared with diphenhydramine alone, the effect was not potentiated by the combination. None of the treatments had a significant effect on a digit symbol substitution test. Co-administration of ethanol and diphenhydramine caused greater impairment of performance in a serial seven subtraction test than diphenhydramine alone. There was no correlation between central and peripheral effects of the antihistamine.

Inhibitory activity of terfenadine on histamine-induced skin wheals in man

The inhibitory effect of orally administered terfenadine on the area of histamine-induced skin wheals was studied by single dose and multiple dose trials in 12 normal male volunteers. Single doses of 20, 60 and 200 mg of terfenadine produced dose-dependent decreases in histamine wheal area that reached a maximum by the fourth hour after dosing. The 60 and 200 mg doses blocked almost 90% of histamine whealing, and significant reduction of the wheal area persisted for 8 h. During the multiple dose trial histamine whealing was markedly inhibited after the fifth and sixth dose of terfenadine 20, 40 or 60 mg every 8 h and of 60 mg every 12 h. On the last three dosage schedules inhibition persisted for at least 12 h after the final dose. Inhibition of histamine-induced skin whealing appears to be a quantitative index of the time course of histamine H1-receptor antagonist action.