Non-cardiac adverse effects of antihistamines (H1-receptor antagonists)

A novel PEG–haloperidol conjugate with a non-degradable linker shows the feasibility of using polymer–drug conjugates in a non-prodrug fashion

A PEG–haloperidol conjugate was synthesised, which retains binding to the dopamine D₂receptor, showing the possibility of using polymer-drug conjugates as drugsper se' rather than as prodrugs.

Bezoar in a Pediatric Oncology Patient Treated with Coca-Cola

A bezoar is a mass of indigestible material. Bezoars can present with a gradual onset of non-specific gastrointestinal symptoms including abdominal pain, nausea and vomiting. However, bezoars can result in more serious conditions such as intestinal bleeding or obstruction. Without quick recognition, particularly in susceptible individuals, the diagnosis and treatment can be delayed. Currently resolution is achieved with enzymatic dissolution, endoscopic fragmentation or surgery. We describe, to our knowledge, the first pediatric patient with lymphoma to have had a bezoar treated with Coca-Cola.

Effects of antihistamines on the function of human α7-nicotinic acetylcholine receptors

Effects of the histamine H₁ receptor (H1R) antagonists (antihistamines), promethazine (PMZ), orphenadrine (ORP), chlorpheniramine (CLP), pyrilamine (PYR), diphenhydramine (DPH), citerizine (CTZ), and triprolidine (TRP) on the functional properties of the cloned α7 subunit of the human nicotinic acetylcholine receptor expressed in Xenopus oocytes were investigated. Antihistamines inhibited the α7-nicotinic acetylcholine receptor in the order PYR>CLP>TRP>PMZ>ORP≥DPH≥CTZ. Among the antihistamines, PYR showed the highest reversible inhibition of acetylcholine (100 µM)-induced responses with IC₅₀ of 6.2 µM. PYR-induced inhibition was independent of the membrane potential and could not be reversed by increasing the concentration of acetylcholine. Specific binding of [¹²⁵I] α-bungarotoxin, a selective antagonist for α7-nicotinic acetylcholine receptor, was not changed in the presence of PYR suggesting a non-competitive inhibition of nicotinic receptors. In line with functional experiments, docking studies indicated that PYR can potentially bind allosterically with the α7 transmembrane domain. Our results indicate that the H₂-H₄ receptor antagonists tested in this study (10 µM) showed negligible inhibition of α7-nicotinic acetylcholine receptors. On the other hand, H₁ receptor antagonists inhibited the function of human α7-nicotinic acetylcholine receptor, with varying potencies. These results emphasize the importance of α7-nicotinic acetylcholine receptor for future pharmacological/toxicological profiling.

Medications and impaired driving

OBJECTIVE

To describe the association of specific medication classes with driving outcomes and provide clinical recommendations.

DATA SOURCES

The MEDLINE and EMBASE databases were searched for articles published from January 1973 to June 2013 on classes of medications associated with driving impairment. The search included outcome terms such as automobile driving, motor vehicle crash, driving simulator, and road tests.

STUDY SELECTION AND DATA EXTRACTION

Only English-language articles that contained findings from observational or interventional designs with ≥ 10 participants were included in this review. Cross-sectional studies, case series, and case reports were excluded.

DATA SYNTHESIS

Driving is an important task and activity for the majority of adults. Some commonly prescribed medications have been associated with driving impairment measured by road performance, driving simulation, and/or motor vehicle crashes. This review of 30 studies identified findings with barbiturates, benzodiazepines, hypnotics, antidepressants, opioid and nonsteroidal analgesics, anticonvulsants, antipsychotics, antiparkinsonian agents, skeletal muscle relaxants, antihistamines, anticholinergic medications, and hypoglycemic agents. Additional studies of medication impact on sedation, sleep latency, and psychomotor function, as well as the role of alcohol, are also discussed.

CONCLUSIONS

Psychotropic agents and those with central nervous system side effects were associated with measures of impaired driving performance. It is difficult to determine if such associations are actually a result of medication use or the medical diagnosis itself. Regardless, clinicians should be aware of the increased risk of impaired driving with specific classes of medications, educate their patients, and/or consider safer alternatives.

Keynote review: in vitro safety pharmacology profiling: an essential tool for successful drug development

Broad-scale in vitro pharmacology profiling of new chemical entities during early phases of drug discovery has recently become an essential tool to predict clinical adverse effects. Modern, relatively inexpensive assay technologies and rapidly expanding knowledge about G-protein coupled receptors, nuclear receptors, ion channels and enzymes have made it possible to implement a large number of assays addressing possible clinical liabilities. Together with other in vitro assays focusing on toxicology and bioavailability, they provide a powerful tool to aid drug development. In this article, we review the development of this tool for drug discovery, its appropriate use and predictive value.

Effects of first and second generation antihistamines on muscarinic induced mucus gland cell ion transport

Background

The first generation antihistamines, such as diphenhydramine, are fairly potent muscarinic antagonists in addition to being H1 selective antihistamines. The antimuscarinic action is often not desirable since it is in part responsible for the drying of secretions in the airways and the sedative effect. We therefore examined a number of antihistamines for antimuscarinic effects on ion transport by mucus gland cells isolated from the airways of swine. Enzymatically isolated airway mucus gland cells were purified utilizing density gradients and grown in culture on porous inserts (Millicell HA™) at an air interface. Cells grown in this manner maintain phenotype and polarity. Transport of ions, as short-circuit current measured under voltage-clamp, was measured in response to acetylcholine (ACh) or histamine applied to the serosal side of the gland cell layers. Concentration-response relationships for ACh or histamine were generated in the presence and absence of various drugs. The potencies against muscarinic receptor activation were estimated using the dose-ratio method of Schild.

Results

Three known muscarinic antagonists were used to validate the system. Atropine had a pA₂ of 9.4 ± 0.1 (n = 9). 4-DAMP and methoctramine had pA₂ values of 8.6 ± 0.1 and 5.6 ± 0.1, respectively (n = 12, 11) all consistent with inhibition of an M3 subtype muscarinic receptor. The rank order of potency of the antihistamines against the inhibition of M3 receptors was desloratadine = diphenhydramine > hydroxyzine (pA₂; 6.4, 6.2, 4.8, respectively). pA₂ values for fexofenadine, loratadine and cetirizine were not determined since they had no effect on the cholinergic response at the highest drug concentrations tested (10, 10 and 100 μM, respectively). The pA₂ values for the antihistamines against the histamine response could not be calculated, but the estimates of the rank order of potency were estimated to be desloratadine> cetirizine ≈ hydroxyzine > fexofenadine > loratadine > diphenhydramine.

Conclusion

The rank order of selectivity for histamine receptors over muscarinic receptors was estimated to be cetirizine ≈ fexofenadine > loratadine > desloratadine ≥ hydroxyzine ≥ diphenhydramine.

Optimising the management of allergic rhinitis: an Australian perspective

Allergic rhinitis (AR) is one of the most prevalent medical conditions. It has significant effects on quality of life and can have considerable socioeconomic effects. The traditional classification of perennial and seasonal rhinitis does not distinguish between provoking factors, nor does it indicate the most appropriate treatment. A more useful classification is based on symptoms, which may be intermittent or persistent, and vary widely in severity. The goal of management is to achieve optimal symptom control. Therapeutic options include allergen avoidance, pharmacotherapy and immunotherapy. Antihistamines and intranasal corticosteroids (INCS) have become the cornerstones of therapy. A variety of effective treatments are available for consumers to self-select, without the advice of a doctor or pharmacist. INCS are widely recognised as the most effective pharmacotherapy for AR, in both adults and children. The efficacy of various preparations is similar, but those with low systemic bioavailability are preferred for children and for patients who are also receiving inhaled, topical or systemic corticosteroids.

Comparative anticholinergic activities of 10 histamine H1 receptor antagonists in two functional models

We determined the relative rank orders of anticholinergic potencies of 10 antihistamines in two functional bioassays: (1) an in vitro assay measuring inhibition of carbachol-induced contractions of isolated guinea pig trachealis muscle, (2) an in vivo bioassay comparing systemic hypotensive responses to bolus i.v. injections of acetylcholine before and after infusions of an antihistamine in anaesthetized rats. In vitro, the rank order of anticholinergic potencies of the antihistamines was cyproheptadine>promethazine>desloratadine>diphenhydramine>loratadine>chlorpheniramine>hydroxyzine>pyrilamine. The pA2 values ranged from 8.2+/-0.4 for cyproheptadine to 4.8+/-0.4 for pyrilamine. Fexofenadine and cetirizine (up to 3 x 10(-4) M) were inactive. In vivo, five antihistamines showed anticholinergic activity: cyproheptadine>promethazine>desloratadine>loratadine>diphenhydramine. The remaining antihistamines had no significant effect at i.v. infusion doses up to 50 imol/kg. Cetirizine and fexofenadine did not antagonize cholinergic responses in either model.

Levocetirizine better protects than desloratadine in a nasal provocation with allergen

BACKGROUND

Direct comparisons of antihistamines are rare but very much needed. Newly available antihistamine preparations, levocetirizine, the R-enantiomer of racemate cetirizine, and desloratadine, an active metabolite of loratadine, have been recently released for allergic rhinitis.

OBJECTIVE

We sought to compare levocetirizine and desloratadine in a nasal provocation test (NPT) with grass pollen.

METHODS

Twenty-four volunteers with grass pollen allergy and a history of rhinitis were enrolled in a double-blind, placebo-controlled, crossover study. Three NPTs were performed in a dose-escalating manner during the out-of-season period 4 hours after a single dose of levocetirizine (5 mg), desloratadine (5 mg), or placebo.

RESULTS

CONCLUSIONS

This study demonstrates a better overall protection of a single dose of levocetirizine compared with desloratadine in an NPT with grass pollen allergen. In contrast to late-phase inflammatory markers, which were unaffected, extravascular leakage of the early-phase marker albumin was significantly limited by levocetirizine.

H1-Antihistamines: more relevant than ever in the treatment of allergic disorders

Histamine is an important chemical mediator of inflammation, vasodilation, increased vascular permeability, decreased peripheral resistance, airway smooth muscle contraction, and sensory nerve stimulation causing itching. It also plays a significant role in neurotransmission and in cardiac function. In allergic rhinoconjunctivitis and urticaria, there is strong evidence for the role of H(1)-antihistamine treatment. In asthma, additional dose-response studies, including higher doses of antihistamines than those used in allergic rhinitis, are needed to determine the role of antihistamines. In atopic dermatitis, the itch-relieving topical glucocorticoid-sparing effects of H(1)-antihistamines also require further documentation. The potential benefits of each H(1)-antihistamine should be weighed against the potential risks, and second-generation H(1)-antihistamines with excellent, well-documented safety records should be used in preference to older, less safe H(1)-antihistamines. Second-generation H(1)-antihistamines are more relevant than ever in the treatment of allergic disorders.

The effects of acute doses of fexofenadine, promethazine, and placebo on cognitive and psychomotor function in healthy Japanese volunteers

BACKGROUND

Genetic variations in cross-cultural metabolic capability may attenuate the lack of central nervous system effects of fexofenadine.

OBJECTIVE

To compare the pharmacodynamics of fexofenadine and promethazine versus placebo in Japanese volunteers.

METHODS

In this randomized, crossover, double-blind study, 24 subjects received single doses of fexofenadine 60 mg and 120 mg, promethazine 25 mg, and placebo, with a 6-day washout period between treatments. Objective measures included critical flicker fusion, choice reaction time, and a compensatory tracking task. A line analog rating scale evaluated self-rated sedation. A rapid visual information-processing task evaluated vigilance at baseline and at 2 hours.

RESULTS

Fexofenadine was not significantly different from placebo on any test at any timepoint. In contrast, promethazine impaired critical flicker fusion thresholds (F[3,63] = 5.37, P = 0.0023); increased recognition reaction time (F[3,63] = 13.63, P < 0.0001) and total reaction time (F[3,63] = 12.23, P < 0.0001) components of the choice reaction time test; reduced tracking accuracy (F[3,63] = 14.25, P < 0.0001) and increased reaction times to peripheral stimuli (F[3,63] = 9.29, P < 0.0001) in the compensatory tracking task; reduced the number of valid responses (F[3,63] = 14.86, P < 0.0001) and impaired reaction times (F[3,63] = 12.02, P < 0.0001) in the rapid visual information-processing task test; and impaired subjective ratings of sedation (F[3,63] = 7.55, P = 0.0002), compared with placebo.

CONCLUSIONS

A battery of tests sensitive to impairment by promethazine failed to show any negative cognitive or psychomotor effects with fexofenadine 60 and 120 mg. Fexofenadine is an intrinsically non-impairing antihistamine in Japanese subjects.

An evaluation of the effects of high-dose fexofenadine on the central nervous system: a double-blind, placebo-controlled study in healthy volunteers

BACKGROUND

As regards central nervous system (CNS) effects there are three types of antihistamines. Those that cross the blood-brain barrier and cause widespread impairment of cognitive and psychomotor function; those that cross into the brain and, although without much impairment at low clinical doses, have a dose-related relationship to impairment; and those that do not cross into the brain and therefore possess no intrinsic potential for impairing CNS function.

OBJECTIVE

[corrected] To investigate the acute effects of fexofenadine (360 mg) on various aspects of cognitive and psychomotor function in comparison to placebo and promethazine (positive internal control), an antihistamine known to produce psychomotor and cognitive impairment.

METHODS

Fifteen healthy volunteers received fexofenadine 360 mg, promethazine 30 mg and placebo in a 3-way cross-over, double-blind study. For each treatment condition, subjects were required to perform a series of tests of cognitive function and psychomotor performance at baseline and 1, 3, 5 and 7 h post-dose. The test battery consisted of critical flicker fusion (CFF), choice reaction time (CRT), compensatory tracking task (CTT) and a subjective assessment of sedation (LARS).

RESULTS

Fexofenadine was not distinguishable from placebo in any of the objective and subjective tests for up to seven hours following drug administration. However, all measures were significantly impaired following the administration of promethazine, which confirms the sensitivity of the test battery for sedation. The effects of fexofenadine and placebo were not significantly different from one another, whereas promethazine caused an overall reduction in CFF thresholds when compared to placebo (P < 0.05). There was an overall significant increase (impairment) in recognition, motor and total reaction time (P < 0.05), and both the tracking accuracy and reaction time aspects of CTT were significantly impaired (P < 0.05) following the administration of promethazine. In contrast, the effects of fexofenadine could not be distinguished from the placebo condition. Subjective ratings of sedation were significantly higher with promethazine when compared to placebo (P < 0.05) and fexofenadine (P< 0.05).

CONCLUSIONS

Fexofenadine at a dose of 360mg is demonstrably free from disruptive effects on aspects of psychomotor and cognitive function in a study where the psychometric assessments have been shown to be sensitive to impairment, as evidenced by the effects of the verum control promethazine 30 mg. The identification of an antihistamine (fexofenadine) devoid of central effects even at supraclinical doses separates it from currently available first and second generation drugs with no objective evidence of CNS side-effects on cognition and psychomotor function, and highlights the need for the introduction of a third generation of non-sedative antihistamines.

Effect of cetirizine, levocetirizine, and dextrocetirizine on histamine-induced nasal response in healthy adult volunteers

BACKGROUND

Cetirizine, an effective H1-receptor antagonist, is a racemate mixture of two enantiomers: levocetirizine (R enantiomer) and dextrocetirizine (S enantiomer).

METHODS

To investigate the pharmacologic activity of the two enantiomers of cetirizine, we conducted a randomized, double-blind, four-way, crossover study to assess the effect of treatment with 5 mg levocetirizine, 5 mg dextrocetirizine, and 10 mg cetirizine and matched placebo, on histamine-induced changes in the nasal airways of 24 healthy volunteers. Four hours after a single oral intake, all subjects were challenged by nasal aerosol application with increasing doubling concentrations (from 0.25 to 32 mg/ml) of histamine in both nostrils. Nasal resistance was measured by passive anterior rhinomanometry (PAR), and changes in histamine threshold were calculated together with the absolute number of sneezes after each challenge.

RESULTS

Both levocetirizine and cetirizine significantly attenuated the histamine-induced increase in nasal airway resistance by nearly 50% (from a median resistance of 2.51 Pa per cm3/s to 1.29 and 1.31 Pa per cm3/s, respectively) at the maximal concentration, and they concomitantly increased the histamine threshold by fourfold (from 8 to 32 mg/ml), compared with placebo. Sneezing was also attenuated by both levocetirizine and cetirizine. However, these antihistaminic effects were not seen with dextrocetirizine.

CONCLUSIONS

This study shows a similar activity of levocetirizine and cetirizine on the inhibition of histamine-induced increase in nasal resistance, indicating that the antihistaminic properties of cetirizine are probably attributable to levocetirizine.

A randomized, double-blind, crossover comparison among cetirizine, levocetirizine, and ucb 28557 on histamine-induced cutaneous responses in healthy adult volunteers

BACKGROUND

Cetirizine is a highly efficacious and long-acting second-generation H1-receptor antagonist for the treatment of allergic diseases, such as allergic rhinitis and chronic idiopathic urticaria, in adults and children. Pharmacologic studies have demonstrated that cetirizine, a racemate mixture composed of equal amounts of two enantiomers, does not undergo hepatic metabolism to any significant level. The enantiomers are excreted mainly unchanged, predominantly in the urine and to a lesser extent in the faeces.

METHODS

The pharmacologic activity and potency of the two enantiomers of cetirizine in the management of allergic skin conditions were investigated by studying the effect of treatment with 5.0 mg cetirizine; 2.5 mg levocetirizine, the (R)-enantiomer; and 2.5 mg ucb 28557, the (S)-enantiomer, on histamine-induced wheal and flare response in 18 healthy volunteers. Each treatment was administered as a single oral dose in randomized, double-blind, and crossover manner, and the efficacy of treatment was assessed over a period of 32 h, as per cent inhibition of the histamine-induced wheal and flare areas before treatment. Blood and urine samples were collected in a time-dependent manner and analyzed for the total amounts of each study drug, to elucidate their pharmacokinetic profiles.

RESULTS

Both cetirizine and levocetirizine caused a marked inhibition of histamine-induced wheal and flare, whereas ucb 28557 was inactive in this model. Inhibition of the wheal response observed for cetirizine and levocetirizine was apparent by 1 h after dosage and lasted for mean durations of 24.4 and 28.4 h, respectively. In addition, the response for cetirizine and levocetirizine became maximal by 6 h after treatment, rising to 79.5% and 83.8%. Similarly, cetirizine and levocetirizine also markedly inhibited the histamine-induced flare response. This effect was evident for both drugs by 1 h after dosage and lasted over a mean period of 28.4 and 26.0 h, respectively, for cetirizine and levocetirizine. The inhibitory effect of these compounds on histamine-induced flare response was also maximal by approximately 6 h after dosage, peaking at 88.5%) and 83.6%, respectively. Statistical evaluation showed that cetirizine and levocetirizine were equivalent for maximum inhibition of histamine-induced wheal and flare. However, levocetirizine was found to be superior to cetirizine when area under the curve was compared. In contrast, ucb 28557 was not found to inhibit histamine-induced wheal and flare responses at any time during the study period. Plasma concentrations of levocetirizine were found to be approximately double those of ucb 28557 at 4 and 8 h after dosing, and 50-60% of the drugs were excreted unchanged in urine over a period of 32 h.

CONCLUSIONS

The finding that, in this model, levocetirizine 2.5 mg has comparable antihistaminic activity to cetirizine 5 mg, whereas its other enantiomer ucb 28557 has no pharmacodynamic effect, suggests that the antihistaminic properties of cetirizine observed in the management of allergic skin conditions are likely to be attributable to levocetirizine.