Comparative study of acute effects of single doses of fexofenadine, olopatadine, d-chlorpheniramine and placebo on psychomotor function in healthy volunteers

Why fexofenadine is considered as a truly non-sedating antihistamine with no brain penetration: a systematic review

OBJECTIVE

Fexofenadine is a second-generation inverse agonist of H1-receptor of histamine which is highly selective with proven efficacy in relieving symptoms associated with allergic conditions. It has an additional benefit of not penetrating the blood-brain barrier and therefore do not induce sedation and not impair the cognitive function/psychomotor performance. This review aimed at providing evidence based on available controlled studies to reinforce the non-sedative property of fexofenadine for treating patients with allergic rhinitis and urticaria.

METHODS

We performed an electronic literature search using keywords such as fexofenadine, drowsiness, somnolence, sedation, fatigue, cognitive, impairment, psychomotor, driving performances, sleep, rapid eye movement, alertness, clinical study, in vitro study, in vivo study, and pharmacodynamics in the Embase search engine. The review included randomized controlled trials, review articles, systematic reviews, and meta-analyses, together with post-marketing analysis conducted in healthy subjects and patients with allergy and were focused on comparing the antihistaminic potential or safety of fexofenadine with other antihistamines or placebo.

RESULTS

Positron emission tomography (PET) and proportional impairment ratio (PIR) data along with other objective tests from various studies confirmed the non-sedative property of fexofenadine. Results of brain H1-receptor occupancy (H1RO) obtained from PET showed no H1RO by fexofenadine, the receptor which is known to cause sedation of H1 antihistamines. Most studies calculating PIR value as 0 showed fexofenadine to be a non-impairing oral antihistamine regardless of dose. Clinical trials in adults and children showed fexofenadine to be well tolerated without sedative effect or impairment of cognitive/psychomotor function even at higher than recommended doses.

CONCLUSION

Published literature based on various parameters and clinical trials conducted for evaluating the effect of fexofenadine on sedation and central nervous system shows fexofenadine is both clinically effective and non-sedating.

Usefulness of a psychomotor function test as a cognitive function scale for patients with schizophrenia: A pilot study

As cognitive dysfunction due to schizophrenia is strongly associated with patients' social rehabilitation, cognitive functions have been examined as a therapeutic target. Although the Brief Assessment of Cognition in Schizophrenia (BACS) has been used to evaluate cognitive function, it is difficult to administer in routine clinical practice due to its time-consuming nature. Therefore, a novel tool is needed to facilitate the assessment of cognitive function. In the present study, we examined whether cognitive function can be assessed effectively by testing psychomotor function in patients with schizophrenia. Test batteries consisting of choice reaction time (CRT) and compensatory tracking task (CTT) and the BACS were examined in 20 schizophrenic patients to evaluate the correlation between the scales by Pearson correlation coefficient. Of the test batteries, the CRT was significantly correlated with attention functions, a subtest of the BACS (r = -0.506, p = 0.023), and the CTT was strongly correlated with attention functions (r = -0.716, p < 0.001) and working memory (r = -0.633, p = 0.003). A multiple regression analysis was performed to clarify the association between psychomotor function tests and the total BACS score, and peripheral awareness task, a component of CTT, was independently associated with the total BACS score (β = -0.59, p = 0.004) with an R2 of 0.37. Thus, of the psychomotor function tests, the CRT and the CTT are highly useful in assessing cognitive functions in schizophrenic patients. However, no having large sample size in this study is a limitation.

Antihistamine effects and safety of fexofenadine: a systematic review and Meta-analysis of randomized controlled trials

Background

As a new generation antihistamine, fexofenadine has been widely used in allergic diseases. However, there is still a lack of collective evidence regarding the antihistamine effects and safety profiles of fexofenadine relative to other antihistamine drugs and placebo. Therefore, we aimed to systematically evaluate the antihistamine effects and safety of fexofenadine.

Methods

An electronic literature search of randomized controlled trials (RCTs) was performed using Embase, Cochrane and PubMed from establishment to January 1st, 2018. RCTs comparing the antihistamine effects or safety (adverse events, sedative effects, and cognitive/psychomotor function) of fexofenadine with either other antihistamines or placebo for healthy subjects and patients with allergy were selected.

Results

Fifty-one studies of 14,551 participants met the inclusion criteria. When compared with the first-generation antihistamines, fexofenadine produced significantly lower adverse events frequency (OR = 0.446; 95% CI: 0.214 to 0.929, P = 0.031), significantly lower sedative effects frequency (OR = 0.265; 95% CI: 0.072 to 0.976, P = 0.046) and significantly less change of all cognitive/psychomotor function. When compared with the second-generation antihistamines, fexofenadine produced significantly marginal sedative effects (OR = 0.59; 95% CI, 0.38 to 0.93; P = 0.02) and significantly less change of most of the cognitive/psychomotor function. When compared with placebo, fexofenadine produced more significant antihistamine effects.

Conclusions

Fexofenadine has a positive antihistamine effect, which is probably no worse than the second-generation antihistamines. Fexofenadine probably has a favorable safety profile, which is more likely better than that of the first-generation antihistamines. There is lack of data to support that fexofenadine has a better overall safety profile compared to the second-generation antihistamines, however, some presently available evidence on sedative effects and certain aspects of cognitive/psychomotor function favors fexofenadine. Therefore, fexofenadine may be worthy of recommendation for safety related workers.

Urticaria: A comprehensive review: Treatment of chronic urticaria, special populations, and disease outcomes

Second-generation antihistamines are considered first-line agents in the treatment of chronic urticaria because of their safety and efficacy profile. Some patients require higher doses of H₁ antihistamines alone or in combination with other classes of medications, including H₂ antihistamines, leukotriene receptor antagonists, or first-generation H₁ antihistamines. One major therapeutic advance has been omalizumab, a humanized monoclonal anti-immunoglobulin E that was recently approved by the US Food and Drug Administration for the treatment of chronic urticaria that is unresponsive to H₁ antagonists. In addition, the second article in this continuing medical education series outlines several evidence-based alternative treatments for urticaria and the differences in recommendations between 2 major consensus groups (the European Academy of Allergy and Clinical Immunology/World Allergy Organization and the American Academy of Allergy, Asthma and Immunology/American College of Allergy, Asthma and Immunology Joint Task Force).

A simulated car-driving study on the effects of acute administration of levocetirizine, fexofenadine, and diphenhydramine in healthy Japanese volunteers

OBJECTIVE

Antihistamines are often used for treating allergic rhinitis. However, many older antihistamines cause sedative side effects. The sedative effects of antihistamines on car-driving have been investigated. This has not been investigated for levocetirizine, a new-generation antihistamine, in Asian populations, and so we evaluated its sedative effects in healthy Japanese subjects.

METHODS

In this double-blind, placebo-controlled, four-way crossover study, healthy volunteers received single doses of levocetirizine 5 mg, fexofenadine 60 mg, diphenhydramine 50 mg, and placebo at intervals of at least 6 days. Simple brake reaction time and choice brake reaction time task (CBRT), a lateral tracking (LT) task, and a multiple task, a mixture of CBRT and LT task, were used to compare driving performance between the four drugs. Subjective sedation was also assessed.

RESULTS

The simple brake reaction time and CBRT, and the CBRT component of the multiple task, did not show any significant differences between the drugs. In contrast, the LT, both as a single parameter and as a component of the multiple task, showed significant differences between diphenhydramine and the newer-generation antihistamines in a manner that corresponds with subjective sedation.

CONCLUSIONS

Levocetirizine and fexofenadine did not impair psychomotor performance in subjects performing simulated car-driving tasks, while diphenhydramine did impair psychomotor performance in the subjects. Copyright © 2016 John Wiley & Sons, Ltd.

Central nervous system effects of the second-generation antihistamines marketed in Japan--review of inter-drug differences using the proportional impairment ratio (PIR)-

Background

Second-generation antihistamines (AHs) have, in general, fewer sedative effects than the first-generation. However, important inter-drug differences remain in the degree of cognitive and/or psychomotor impairment. The extent to which a particular compound causes disruption can be conveniently compared, to all other AHs, using the Proportional Impairment Ratio (PIR). Although the PIR can differentiate the relative impairment caused by individual drugs, there is no indication of the reliability of the ratios obtained.

Objective

To calculate the PIRs –together with 95% confidence intervals (CIs), as an index of reliability– and compare AHs currently, or soon to be, available in Japan, with respect to their intrinsic capacity to cause impairment.

Methods

Results from studies of cetirizine, desloratadine, ebastine, fexofenadine, levocetirizine, loratadine, mequitazine, and olopatadine were included in the PIR calculations. All data utilised came from crossover studies in healthy volunteers which were randomised and placebo and positive-internal controlled. Existing databases from studies reporting the sedative effects of AHs on objective (speed, accuracy, memory) and subjective (feeling) psychometrics were augmented, via results from suitable studies published after the previous reviews. The null value for a PIR was one.

Results

A total of 45 studies were finally included for this review. Of the AHs assessed, fexofenadine, ebastine, and levocetirizine showed a PIR for objective tests of 0. However, only fexofenadine (PIR = 0.49) had an upper limit of the 95% CI of less than 1. Fexofenadine, levocetirizine, desloratadine, olopatadine, loratadine, and mequitazine all had a PIR for subjective ratings of 0, but the upper limits of the 95% CIs were all in excess of 1, although fexofenadine (PIR = 2.57) was the lowest.

Conclusions

The results show that there are differences between second-generation AHs in the extent of sedation produced. However, subjective ratings indicate that patients may not necessarily be aware of this.

Maintenance of remission with low-dose olopatadine hydrochloride for itch in well-controlled chronic urticaria

Background:

The long-term follow-up of chronic urticaria (CU) is important to ensure the adequate treatment of patients. Olopatadine hydrochloride is one of the second-generation nonsedating antihistamines.

Methods:

This study was designed to assess the optimal dose of olopatadine to suppress symptoms of chronic urticarial itch in well-controlled patients. After CU patients were treated with 10 mg olopatadine, patients having a visual analog scale (VAS) itch score of less than 20 were randomly allocated into one of three groups: 10 mg/day (n = 35), 5 mg/day (n = 30), or no medication (n = 32).

Results:

The suppressive effects of both the 5 mg and 10 mg olopatadine treatments on the VAS itch score were more significant and longer lasting over a period of 4 weeks than the no-medication treatment. Both the 5-mg group and the 10-mg group showed improved urticarial symptoms and maintained their VAS itch score within normal limits compared to the no-medication group. The differences between the 5-mg and 10-mg groups were not significant.

Conclusion:

These results demonstrate that treatment with olopatadine at a dose of 5 mg once daily is effective and safe for the management and prevention of CU symptoms for itch in well-controlled patients.

Effects of single therapeutic doses of promethazine, fexofenadine and olopatadine on psychomotor function and histamine-induced wheal- and flare-responses: a randomized double-blind, placebo-controlled study in healthy volunteers

Since most first-generation antihistamines have undesirable sedative effects on the central nervous systems (CNS), newer (second-generation) antihistamines have been developed to improve patients’ quality of life. However, there are few reports that directly compare the antihistaminic efficacy and impairment of psychomotor functions. We designed a double-blind, placebo controlled, crossover study to concurrently compare the clinical effectiveness of promethazine, a first-generation antihistamine, and fexofenadine and olopatadine, second-generation antihistamines, by measuring their potency as peripheral inhibitors of histamine-induced wheal and flare. Further, we investigated their sedative effects on the CNS using a battery of psychomotor tests. When single therapeutic doses of fexofenadine (60 mg), olopatadine (5 mg) and promethazine (25 mg) were given in a double-blind manner to 24 healthy volunteers, all antihistamines produced a significant reduction in the wheal and flare responses induced by histamine. In the comparison among antihistamines, olopatadine showed a rapid inhibitory effect compared with fexofenadine and promethazine, and had a potent effect compared with promethazine. In a battery of psychomotor assessments using critical flicker fusion, choice reaction time, compensatory tracking, rapid visual information processing and a line analogue rating scale as a subjective assessment of sedation, promethazine significantly impaired psychomotor function. Fexofenadine and olopatadine had no significant effect in any of the psychomotor tests. Promethazine, fexofenadine and olopatadine did not affect behavioral activity, as measured by wrist actigraphy. These results suggest that olopatadine at a therapeutic dose has greater antihistaminergic activity than promethazine, and olopatadine and fexofenadine did not cause cognitive or psychomotor impairment.

Cognitive domains affected by histamine H(1)-antagonism in humans: a literature review

The neurotransmitter histamine has been suggested to be involved in cognitive functioning. Generally, studies in animals have shown a decrease in performance after decreasing histamine neurotransmission and improved performance after increasing histamine neurotransmission. It is unclear, however, what role histamine plays in cognition in humans. Up until now, most data are derived from studies and reviews that aimed to assess the sedative potential of H(1)-antagonists and not the effects on cognition in particular. The objective of this paper is specifically to review which cognitive domains are affected by H(1)-antagonists. Taken together, 90 experimental studies on the performance effects of sedative H(1)-antagonists published between 1973 and 2009 were reviewed. Results showed that psychomotor skills and attention are most frequently impaired and memory the least. Tasks assessing memory that were affected usually required rapid responses. It was concluded that both the complexity of the task as well as the demand for information processing speed determines the sensitivity to the effects of central H(1)-antagonism. The importance of the sensitive cognitive domains to histaminergic dysfunction, as well as the relation between histamine related decrease in arousal and task performance deserve further research.

Cerebral histamine H1 receptor binding potential measured with PET under a test dose of olopatadine, an antihistamine, is reduced after repeated administration of olopatadine

Some antihistamine drugs that are used for rhinitis and pollinosis have a sedative effect as they enter the brain and block the H(1) receptor, potentially causing serious accidents. Receptor occupancy has been measured with PET under single-dose administration in humans to classify antihistamines as more sedating or as less sedating (or nonsedating). In this study, the effect of repeated administration of olopatadine, an antihistamine, on the cerebral H(1) receptor was measured with PET.

METHODS

A total of 17 young men with rhinitis underwent dynamic brain PET with (11)C-doxepin at baseline, under an initial single dose of 5 mg of olopatadine (acute scan), and under another 5-mg dose after repeated administration of olopatadine at 10 mg/d for 4 wk (chronic scan). The H(1) receptor binding potential was estimated using Logan graphical analysis with cerebellum as reference region input.

RESULTS

The acute scan showed a slight decrease in H(1) receptor binding potential across the cerebral cortex (by 15% in the frontal cortex), but the chronic scan showed a marked decrease (by 45% from the acute scan in the frontal cortex). Behavioral data before and after the PET scans did not reveal any sedative effect.

CONCLUSION

The results may be interpreted as either intracerebral accumulation of olopatadine or H(1) receptor downregulation due to repeated administration. The study shows feasibility and potential value for PET in evaluating the pharmacologic effect of a drug not only after a single dose but also after repeated administration.

Sedation and antihistamines: an update. Review of inter-drug differences using proportional impairment ratios

BACKGROUND

The use of antihistamines (AHs) has been associated with cognitive and psychomotor impairments, largely caused by the sedative properties of many of these drugs. Due to the ambulant nature of the population using AHs, it is important to evaluate these effects using standardised methodology and psychometric tests. A previous extensive review of the literature collated the results of studies of H(1) receptor antagonists to determine the extent to which a particular AH produced impairments on a battery of psychometric tests by calculating a proportional impairment ratio for each AH.

OBJECTIVE

In light of a number of major studies published following the previous review, and the development of the second and new-generation AHs, the present review aims to add to the database and update the review, using the same methodology.

RESULTS AND CONCLUSION

The newer generation AHs appear to be the least impairing, and the first generation, as expected, appear to be the most impairing. There are also differences within the AH drug generations. The review highlights the necessity to consider the sedating potential of AHs, along with other factors such as efficacy, when prescribing AHs to ambulant patients.

Fexofenadine hydrochloride in the treatment of allergic disease: a review

Fexofenadine is a selective, non-sedating H1 receptor antagonist, marketed in the United States since 2000. The FDA approved an oral suspension in 2006, for the treatment of seasonal allergic rhinitis and chronic idiopathic urticaria in children. The tablet, capsule, and oral suspension are bioequivalent. Although fexofenadine does not use P450 CYP 3A4 it does interact with a number of drugs at P-glycoprotein and organic anion transporter polypeptides. The risk of toxicity from other drugs may increase with the administration of fexofenadine. Orange and grapefruit juices reduce the bioavailability of fexofenadine. Fexofenadine has been shown to have an impact on inflammatory mediators, other than histamine, such as decreasing the production of LTC₄, LTD₄, LTE₄, PGE₂, and PGF_2α; inhibiting cyclo-oxygenase 2, thromboxane; limiting iNOS generation of NO; decreasing cytokine levels (ICAM-1, ELAM-1, VCAM-1, RANTES, I-TAC, MDC, TARC, MMP-2, MMP-9, tryptase); and diminishing eosinophil adherence, chemotaxis, and opsonization of particles. These effects may provide benefit to some of the inflammatory responses of an acute allergic reaction and provide a basis for future development of H1 antagonists with stronger anti-inflammatory effects. These studies also support the contention that fexofenadine is effective for the treatment of allergic rhinits and chronic idiopathic urticaria.

Histamine H1-receptor blockade in humans affects psychomotor performance but not memory

Results from recent animal studies suggest an important role for histamine in memory functioning. Histaminergic drugs might prove beneficial for people suffering from memory impairment. To determine if histamine is involved in memory functioning this study evaluates the effects of histaminergic dysfunction on memory performance by administrating a H1-antagonist to humans. The study was conducted according to a 4-way, double-blind, crossover design in 20 healthy female volunteers, aged 18-45 years. On each test day subjects completed three test sessions: before and around 2 and 4 h after administration of single oral doses of dexchlorpheniramine 2 mg or 4 mg, scopolamine 1 mg or placebo. Drug effects were assessed using tests of memory, psychomotor and attention performance, and subjective alertness. Results showed that dexchlorpheniramine impaired performance in tests of spatial learning, reaction time, tracking and divided attention but showed no effects on working memory, visual memory, word learning or memory scanning. Scopolamine induced a similar pattern of effects. In addition, both drugs decreased subjective alertness. In conclusion results show that dexchlorpheniramine and scopolamine clearly impaired performance on psychomotor and attention tasks but do not suggest a specific role of the histaminergic system in learning and memory in humans.

Repeated-dose effects of mequitazine, cetirizine and dexchlorpheniramine on driving and psychomotor performance

AIMS

Previous studies have demonstrated that the antihistamines mequitazine, cetirizine and dexchlorpheniramine produce mild sedation after single doses. It is unknown, however, whether acute sedation persists after repeated dosing. Therefore, this study assessed the effects of repeated dosing of these antihistamines on driving and psychomotor performance.

METHODS

Sixteen healthy volunteers were treated with mequitazine 10 mg q.a.m., cetirizine 10 mg q.a.m., dexchlorpheniramine Repetab 6 mg b.i.d. and placebo for four separate 8-day periods. Drug effects were assessed on days 1 and 8 using on-the-road driving tests (highway driving and car following), psychomotor tests (tracking and divided attention) and subjective questionnaires.

RESULTS

Dexchlorpheniramine and mequitazine significantly impaired driving performance on the highway driving test on the first day; dexchlorpheniramine increased Standard Deviation of Lateral Position by 2 cm [95% confidence interval (CI) 0.5, 3.8] and mequitazine by 2.5 cm (CI 1.0, 4.3). These effects on driving performance disappeared after 8 days of treatment. No effect of treatment was found on car following, tracking and divided attention. Although subjective ratings confirmed that subjects knew their driving had been impaired in the mequitazine and dexchlorpheniramine condition after completion of the highway driving test on day 1, they did not expect their driving to be affected before the start of the test. Cetirizine did not impair performance on any of the tests.

CONCLUSIONS

Single doses of mequitazine 10 mg and dexchlorpheniramine Repetab 6 mg cause mild driving impairment. However, when taken over several days, the impairing effect wears off, possibly as a result of tolerance.

Brain histamine H receptor occupancy of orally administered antihistamines measured by positron emission tomography with (11)C-doxepin in a placebo-controlled crossover study design in healthy subjects: a comparison of olopatadine and ketotifen

AIMS

The strength of sedation due to antihistamines can be evaluated by using positron emission tomography (PET). The purpose of the present study is to measure histamine H(1) receptor (H(1)R) occupancy due to olopatadine, a new second-generation antihistamine and to compare it with that of ketotifen.

METHODS

Eight healthy males (mean age 23.5 years-old) were studied following single oral administration of olopatadine 5 mg or ketotifen 1 mg using PET with (11)C-doxepin in a placebo-controlled crossover study design. Binding potential ratio and H(1)R occupancy were calculated and were compared between olopatadine and ketotifen in the medial prefrontal (MPFC), dorsolateral prefrontal (DLPFC), anterior cingulate (ACC), insular (IC), temporal (TC), parietal (PC), occipital cortices (OC). Plasma drug concentration was measured, and correlation of AUC to H(1)R occupancy was examined.

RESULTS

H(1)R occupancy after olopatadine treatment was significantly lower than that after ketotifen treatment in the all cortical regions (P < 0.001). Mean H(1)R occupancies for olopatadine and ketotifen were, respectively: MPFC, 16.7 vs. 77.7; DLPFC, 14.1 vs. 85.9; ACC, 14.7 vs. 76.1; IC, 12.8 vs. 69.7; TC, 12.5 vs. 66.5; PC, 13.9 vs. 65.8; and OC, 19.5 vs. 60.6. Overall cortical mean H(1)R occupancy of olopatadine and ketotifen were 15% and 72%, respectively. H(1)R occupancy of both drugs correlated well with their respective drug plasma concentrations (P < 0.001).

CONCLUSION

It is suggested that 5 mg oral olopatadine, with its low H(1)R occupancy and thus minimal sedation, could safely be used an antiallergic treatment for various allergic disorders. Abbreviations histamine H(1) receptor (H(1)R), histamine H(1) receptor occupancy (H(1)RO), dopamine D(2) receptor (D(2)R), positron emission tomography (PET), blood-brain barrier (BBB), binding potential ratio (BPR), distribution volume (DV).

Effects of fexofenadine and hydroxyzine on brake reaction time during car-driving with cellular phone use

Antihistamines are a mainstay treatment for allergic rhinitis; however, many older agents cause adverse events, including sedation and central nervous system (CNS) impairment. Research has shown sedating effects of antihistamines on driving; currently, no known study has examined whether cellular phone usage while driving further compounds impairment in individuals administered antihistamines. The aim of this study was to examine this endpoint. In a randomized, double-blind, placebo-controlled, three-way crossover study, healthy volunteers received fexofenadine HCl 120 mg, hydroxyzine HCl 30 mg and placebo. Brake reaction time (BRT) was used to examine driving performance across four conditions: driving only; driving while completing simple calculations; complex calculations; and conversing on a cellular phone. Subjective sedation assessments were also conducted. Brake reaction time with and without cellular phone usage in fexofenadine-treated subjects did not differ significantly from placebo in any condition. In contrast, hydroxyzine-treated subjects were significantly more sedated and had slower BRTs, suggesting slower hazard recognition and brake application, compared with the fexofenadine and placebo groups in all conditions. Importantly, cellular phone operation was an additive factor, increasing BRTs in hydroxyzine-treated volunteers. Fexofenadine did not impair CNS function in subjects involved in a divided attention task of driving and cellular phone operation.

Ocular allergy treatment comparisons: azelastine and olopatadine

Azelastine hydrochloride 0.05% and olopatadine hydrochloride 0.1% are topical ocular allergy treatments that have demonstrated multiple pharmacologic actions, including antihistamine, mast cell stabilization, and inhibition of proinflammatory mediators. In this article, the mechanisms of action, efficacy, and tolerability of these two agents on ocular signs and symptoms are examined. By studying the various target sites of drug action, an enhanced clinical response algorithm of these topical ocular agents can be implemented to maximize the response for patients suffering from ocular allergy.

Second-Generation Antihistamines

Antihistamines are useful medications for the treatment of a variety of allergic disorders. Second-generation antihistamines avidly and selectively bind to peripheral histamine H1 receptors and, consequently, provide gratifying relief of histamine-mediated symptoms in a majority of atopic patients. This tight receptor specificity additionally leads to few effects on other neuronal or hormonal systems, with the result that adverse effects associated with these medications, with the exception of noticeable sedation in about 10% of cetirizine-treated patients, resemble those of placebo overall. Similarly, serious adverse drug reactions and interactions are uncommon with these medicines. Therapeutic interchange to one of the available second-generation antihistamines is a reasonable approach to limiting an institutional formulary, and adoption of such a policy has proven capable of creating substantial cost savings. Differences in overall efficacy and safety between available second-generation antihistamines, when administered in equivalent dosages, are not large. However, among the antihistamines presently available, fexofenadine may offer the best overall balance of effectiveness and safety, and this agent is an appropriate selection for initial or switch therapy for most patients with mild or moderate allergic symptoms. Cetirizine is the most potent antihistamine available and has been subjected to more clinical study than any other. This agent is appropriate for patients proven unresponsive to other antihistamines and for those with the most severe symptoms who might benefit from antihistamine treatment of the highest potency that can be dose-titrated up to maximal intensity.