The pharmacokinetics and pharmacodynamics of terfenadine in children

The pharmacokinetics and pharmacodynamics of terfenadine were studied in 13 children with allergic rhinitis, mean age 7.45 +/- 0.54 SEM years. Serum concentrations of the active carboxylic acid metabolite of terfenadine (terfenadine metabolite I) were measured before and hourly for 8 hours after administration of a single dose of terfenadine suspension. The mean maximum serum concentration of terfenadine metabolite I, 242 +/- 28 ng/ml, occurred at 2.3 +/- 0.2 hours; the mean serum half-life value was 2.0 +/- 0.1 hours. Wheals and flares after epicutaneous tests with histamine phosphate, 1.0 mg/ml and 0.2 mg/ml, were significantly suppressed from 1 to 8 hours after the terfenadine dose compared to predose values. Maximum wheal suppression occurred at from 3 to 6 hours. Itching was completely suppressed for 8 hours. No serious adverse effects occurred. Terfenadine in children appears to be well absorbed, and its carboxylic acid metabolite has a short serum elimination half-life. The duration of its suppressive effect on the histamine-induced wheal and flare greatly exceeds that expected from consideration of serum terfenadine metabolite I concentrations.     

Lack of subsensitivity to terfenadine during long-term terfenadine treatment

Eleven healthy male volunteers ingested terfenadine, 60 mg, every 12 hours for 56 days. Compliance was monitored strictly throughout the study. Before the first terfenadine dose on day 0, and 12 hours after the evening terfenadine dose every seventh day and on randomly selected "unscheduled" days, wheal-and-flare areas were measured after intradermal injections of 0.01 ml of histamine phosphate (1.0 mg/ml and 0.1 mg/ml). On days 0, 28, and 56, six volunteers had skin tests hourly for 12 hours after the morning terfenadine dose. On all study days, serum terfenadine metabolite I concentrations were measured each time histamine skin tests were performed. On days 7, 14, 21, 28, 35, 42, 49, and 56, the mean areas of the histamine-induced wheals did not differ significantly from each other but were significantly decreased compared to the mean wheal area on day 0 (p less than 0.01). On these days, the mean areas of the histamine-induced flares also did not differ significantly from each other but remained significantly suppressed compared to the mean flare areas on day 0 (p less than 0.01). Wheal-and-flare suppression was noted in all unscheduled histamine skin tests performed 12 hours after the evening terfenadine dose. In the subgroup of volunteers who had hourly tests, on day 0, the mean wheal-and-flare areas were significantly suppressed from 2 to 12 hours after the dose, with maximal wheal suppression occurring at 5 hours (p less than 0.05) and maximal flare suppression occurring from 3 to 9 hours (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

The pharmacokinetics and antihistaminic effects of brompheniramine

We studied the pharmacokinetics and antihistaminic effect of brompheniramine in seven normal adults. The mean peak serum brompheniramine concentration of 11.6 +/- 3.0 ng/ml occurred at a mean time of 3.1 +/- 1.1 hr. The mean serum half-life value was 24.9 +/- 9.3 hr, the mean clearance rate was 6.0 +/- 2.3 ml/min/kg, and the mean volume of distribution was 11.7 +/- 3.1 L/kg. The mean wheal size was significantly suppressed (p less than or equal to 0.1) at 3, 6, and 9 hr after the brompheniramine dose when mean concentrations ranged from 10.2 +/- 2.9 to 7.0 +/- 2.2 ng/ml. Significant suppression (p less than or equal to 0.05) of mean flare size was found from 3 to 48 hr after the brompheniramine dose, when mean concentrations ranged from 10.2 +/- 2.9 to 2.5 +/- 0.6 nl/ml. The mean pruritus score was significantly suppressed at 9 and 12 hr (p less than or equal to 0.1) and at 24 hr (p less than or equal to 0.05). Brompheniramine had a long half-life and large volume of distribution in normal adults. It also had a prolonged antihistaminic effect in the skin as evidenced by suppression of the wheal and flare response to histamine and by suppression of pruritus.     

Similar rapid onset of action and magnitude of effect of fexofenadine and cetirizine as assessed by inhibition of histamine-induced wheal-and-flare reaction.

BACKGROUND: Histamine-induced wheal-and-flare studies are useful, objective tests for determining differences in the peripheral H1-receptor blockade activities of antihistamines. OBJECTIVE: To evaluate the time of occurrence of 95% inhibition of histamine-induced wheal and flare after administration of fexofenadine hydrochloride, 180 mg, or cetirizine, 10 mg. METHODS: Forty-two volunteers (aged 18-60 years) were included in a randomized, double-blind, crossover study. Skin prick tests were undertaken using histamine (100 mg/mL) before treatment and 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 hours after treatment. Wheal and flare areas were evaluated, and the time to occurrence of 95% inhibition and the frequency of subjects exhibiting 95% inhibition before median time to 95% inhibition were calculated. RESULTS: Mean +/- SD time to 95% wheal inhibition was 2.46 +/- 0.71 hours with fexofenadine and 2.55 +/- 0.57 hours with cetirizine. The estimated mean difference between fexofenadine and cetirizine (-7 minutes in favor of fexofenadine; 2-sided 95% confidence interval, -21 to +7 minutes) was not statistically significant (P = .34). For wheal, 29% of subjects receiving fexofenadine and 24% receiving cetirizine achieved 95% inhibition before the median time of inhibition (2.5 hours). An exact permutation test yielded a P = .37. For flare, 26% of subjects receiving fexofenadine and 10% receiving cetirizine achieved 95% inhibition before the median time of inhibition (3 hours; P = .12 by exact permutation test). CONCLUSIONS: Fexofenadine and cetirizine have comparable onset of action times and similar frequencies of inhibition, as evaluated by the occurrence of 95% inhibition of histamine-induced wheal and flare.     

Pharmacokinetics and efficacy of chlorpheniramine in children

Chlorpheniramine is widely used, but there is very little information about its pharmacokinetics and efficacy in children. In 11 patients with allergic rhinitis, ages 6 to 16 yr, we found a mean serum chlorpheniramine half-life of 13.1 ± 6.3 hr, a mean volume of distribution of 7.0 ± 2.8 L/kg, and a mean clearance rate of 7.2 ± 3.2 ml/min/kg. Suppression of symptoms and signs of allergic rhinitis and suppression of the histamine-induced wheal and flare responses occurred when mean serum chlorpheniramine concentrations ranged from 2.3 to 12.1 and 4.1 to 10.0 ng/ml, respectively. This, combined with the large volume of distribution for the drug, suggests that tissue binding is an important aspect of chlorpheniramine pharmacokinetics.     

Relative potency of fexofenadine HCl 180 mg, loratadine 10 mg, and placebo using a skin test model of wheal-and-flare suppression.

BACKGROUND: H1-receptor antagonists differ in their ability to produce peripheral H1-blockade. Suppression of histamine-induced flares and wheals is a useful objective test for measuring these differences. OBJECTIVE: To evaluate the relative potency of fexofenadine HCI 180 mg, loratadine 10 mg, and placebo (PBO) in suppressing histamine-induced flares and wheals and compare the onset, duration, and maximum suppression of histamine achieved with each agent. METHODS: Thirty healthy volunteers were enrolled in this randomized, double-blind, single-dose, crossover study. Flares and wheals induced by skin-prick testing with histamine 1.8 mg/mL were measured before treatment, every 20 minutes during the first hour after dosing, and thereafter hourly between 2 and 12 hours and between 23 and 25 hours postdose. RESULTS: Fexofenadine was significantly more effective than loratadine in suppressing the histamine-induced flare response at hours 2 through 7 and 10 through 12 and produced greater flare suppression than did PBO at hours 2 through 25. Onset of flare suppression occurred 2 hours after dosing with fexofenadine and 4 hours after dosing with loratadine. Likewise, fexofenadine was superior to loratadine in suppressing the wheal response from hours 1 through 12 and was more effective than PBO at hours 1 through 12, 24, and 25. Throughout the 25-hour measurement interval, the magnitude of difference in both wheal and flare suppression consistently favored fexofenadine over loratadine. CONCLUSIONS: In a skin test model of wheal-and-flare suppression, fexofenadine showed rapid distribution into the skin compartment with faster onset of action and greater potency vs loratadine.     

Suppression of histamine-induced wheal response by loratadine (SCH 29851) over 28 days in man

Five groups of 12 healthy volunteers each received in double-blind, randomized fashion oral b.i.d. doses of 10, 20, or 40 mg loratadine, 12 mg chlorpheniramine maleate (CTM), or placebo for 28 days. Histamine and saline were injected intradermally into opposite arms at baseline and at specified times following treatment on days 1, 3, 7, 14, 21, and 28. Notable suppression of adjusted wheal formation (histamine-induced minus saline-induced) occurred within two hours after the first dose of each active treatment on day 1. In general, throughout the treatment period, suppression of adjusted wheal formation by all doses of loratadine was significantly greater than by placebo. Suppression by 10 mg loratadine was comparable to CTM, and 20 and 40 mg loratadine were significantly greater than CTM. Suppression of wheal formation by loratadine during the treatment period and during five days posttreatment were dose related. The continued effectiveness of loratadine throughout the 28 days suggests that tolerance to loratadine did not develop in this study. Sedation occurred in 8 of 12 subjects receiving CTM, 1 of 12 receiving 10 mg loratadine, and 1 of 12 receiving placebo.     

Levocetirizine: pharmacokinetics and pharmacodynamics in children age 6 to 11 years

BACKGROUND: The pharmacokinetics and pharmacodynamics of medications may differ between children and adults, necessitating different dose regimens for different age groups. Levocetirizine, the active enantiomer of cetirizine, is used in the treatment of allergic rhinitis and chronic urticaria in Europe. Its pharmacokinetics and pharmacodynamics have not yet been studied prospectively in school-age children. OBJECTIVES: This study was performed to investigate levocetirizine pharmacokinetic disposition and pharmacodynamics in relation to skin reactivity to histamine in children aged 6 to 11 years. METHODS: Blood samples were obtained at predose baseline and at defined intervals up to and including 28 hours after a 5-mg levocetirizine dose. Concurrently, epicutaneous tests with histamine phosphate, 1 mg/mL, were performed. Wheals and flares were traced at 10 minutes, and the areas were measured with a computerized digitizing system. RESULTS: In children aged 8.6 +/- 0.4 years (+/- SEM), the peak levocetirizine concentration was 450 +/- 37 ng/mL, and the time at which peak concentrations occurred was 1.2 +/- 0.2 hours. The terminal elimination half-life was 5.7 +/- 0.2 hours, the oral clearance was 0.82 +/- 0.05 mL/min/kg, and the volume of distribution was 0.4 +/- 0.02 L/kg. Compared with predose areas, the wheals and flares produced by histamine phosphate were significantly decreased from 1 to 28 hours, inclusive (P < .05). Mean maximum inhibition of wheals and flares occurred from 2 to 10 hours (97% +/- 1%) and from 2 to 24 hours (93% +/- 1%), respectively. CONCLUSIONS: Levocetirizine had an onset of action within 1 hour and provided significant peripheral antihistaminic activity for 28 hours after a single dose. Once-daily dosing may be optimal in children aged 6 to 11 years, as it is in adults.     

Twenty-four hours of activity of cetirizine and fexofenadine in the skin.

BACKGROUND: Cetirizine and fexofenadine, the active metabolite of terfenadine, are powerful and well-tolerated H1 receptor antagonists effective in the treatment of skin and nose atopic diseases. OBJECTIVE: We have compared the pharmacodynamic activity of the two antihistamines at therapeutic dosages, cetirizine at 10 mg and fexofenadine at 120 mg and 180 mg, on histamine-induced skin reactivity during a 24-hour period after single intake. METHODS: Twenty-six healthy volunteers participated in a randomized, double-blind, crossover, placebo-controlled study. The areas of wheal and flare induced by histamine (100 mg/mL) administered by prick test were measured at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, and 24 hours postdose. Statistical analysis of the areas under the time-response curves was performed by a Friedman's ANOVA followed by a Wilcoxon test and Bonferroni's correction. RESULTS: The three active treatments clearly inhibited the wheal and flare areas throughout the 24-hour period compared with placebo. Maximal inhibition occurred at 4 hours postdose. Between 4 and 24 hours postdose, the time course of inhibition by cetirizine differed significantly (P < 0.001) from that by fexofenadine at either dose, which did not differ from each other. At 24 hours, fexofenadine inhibited <40% of the skin reaction, whereas cetirizine reduced 60% of the wheal. The duration of effect, considered as the time for wheal to be inhibited by at least 70%, also significantly favored cetirizine (19 hours) compared with fexofenadine (9.3 and 8.5 hours for 180 and 120 mg, respectively; P < 0.001). Consistency of activity was evaluated by the frequency of total inhibition of the wheal (> or =95%). Consistency was observed in 26 of 26 participants for cetirizine, 21 of 26 for fexofenadine, 180 mg, and 10 of 26 for fexofenadine, 120 mg (P < 0.001), suggesting better consistency for cetirizine. There was no serious adverse event. CONCLUSIONS: Our study clearly shows better duration of action and consistency of the antihistaminic activity of cetirizine compared with fexofenadine (120 and 180 mg) in the histamine-induced skin reaction during a 24-hour period.     

Double-blind comparison of terfenadine, chlorpheniramine, and placebo in the treatment of chronic idiopathic urticaria

The efficacy of terfenadine, a nonsedating H1 antihistamine, in the management of chronic idiopathic urticaria was compared with chlorpheniramine and placebo in a parallel multicenter trial. Subjects with symptoms of hives for 3 days per week for at least 6 weeks were initially screened and admitted if no identifiable cause for symptoms could be determined. Patients entered a single-blind placebo period, and if hives of moderate severity were present for at least 3 days during the week, they were randomly assigned in a double-blind fashion to take terfenadine, 60 mg twice daily, chlorpheniramine, 4 mg three times a day, or placebo for 6 weeks. Data were analyzed for 122 patients. Those patients receiving both active treatments noted significant improvement in symptoms: pruritus, redness, number of hives, and waking hours during which hives were present, at the end of the first day of therapy. Symptom control by terfenadine was statistically superior to placebo during all 6 weeks, as rated by both patients and investigators. However, statistical significance was not achieved for chlorpheniramine at all observation points. Diphenhydramine was permitted as a relief medication for refractory symptoms and was taken by 52% of subjects receiving placebo, 26% taking chlorpheniramine, and only 9% of patients who were receiving terfenadine. In addition to providing superior symptom control, terfenadine caused less drowsiness and fatigue than chlorpheniramine. Terfenadine is a useful therapeutic agent for primary management of chronic idiopathic urticaria.     

Central nervous system effects of H1-receptor antagonists in the elderly.

BACKGROUND: The potential adverse central nervous system effects of H1-receptor antagonists have not been optimally studied in the elderly. OBJECTIVE: We hypothesized that newer H1-receptor antagonists such as cetirizine and loratadine would cause less central nervous system dysfunction than the older H1-receptor antagonists diphenhydramine and chlorpheniramine in this population, as they do in younger subjects. METHODS: We performed a randomized, double-blind, single-dose, placebo-controlled, 5-way crossover study in 15 healthy elderly subjects (mean age 71 +/- SD 5 years). On study days at least 1 week apart, they received cetirizine 10 mg, loratadine 10 mg, diphenhydramine 50 mg, chlorpheniramine 8 mg, or placebo. Outcome measures, recorded before and 2 to 2.5 hours after dosing were latency of the P300 event-related potential in which increased latency reflects a decreased rate of cognitive processing, visual analogue scale for subjective somnolence, and histamine skin tests for measurement of peripheral H1-blockade. RESULTS: The changes in P300 following each treatment yielded variances that were not equal (P > .05), precluding usual statistical analysis of the means. These variances were ranked: chlorpheniramine > diphenhydramine > loratadine > placebo > cetirizine. The rank of mean differences in the visual analogue scale increase from pre-dose baseline was: diphenhydramine > chlorpheniramine > cetirizine > loratadine > placebo. All H1-receptor antagonists suppressed the histamine-induced wheal and flare significantly compared to baseline. CONCLUSION: In the elderly, the new H1-receptor antagonists cetirizine and loratadine are less likely to cause adverse central nervous system effects than the old H1-antagonists chlorpheniramine or diphenhydramine, but this requires confirmation using additional objective tests of central nervous system function.     

Comparison of the effects of levocetirizine and loratadine on histamine-induced wheal, flare, and itch in human skin

BACKGROUND: This randomized, double-blind, crossover study compared the effects of the R-enantiomer of cetirizine, levocetirizine, with those of loratadine on the wheal, flare, and itch response to histamine in human skin. METHODS: Levocetirizine (5 mg), loratadine (10 mg), or placebo was taken orally 4 h before the intradermal injection of histamine (20 microl, 100 microM) or the control vehicle into the forearm skin of healthy volunteers. Flare areas were assessed by scanning laser Doppler imaging before and at 30-s intervals for a period of 9 min. Wheal areas were measured by planimetry at 10 min. Itch was scored every 30 s with a visual analogue scale. RESULTS: After placebo administration, the mean peak flare area was 23.01+/-1.94 cm(2), the wheal area 248+/-27 mm(2), and the cumulative itch score 28.8+/-4.6% (mean+/-SEM). Levocetirizine reduced the flare, wheal, and itch by 60%, 68%, and 91%, respectively (all P<0.001, Student's t-test for paired data). The effects of loratadine were variable and not statistically significant. CONCLUSION: Levocetirizine (5 mg) is a potent inhibitor of the effects of histamine in human skin with an efficacy that exceeded that of loratadine (10 mg) when single doses of the drugs were administered 4 h before the test.     

A double‐blind, single‐dose, crossover comparison of cetirizine, ebastine, epinastine, fexofenadine, terfenadine, and loratadine versus placebo: suppression of histamine‐induced wheal and flare response for 24 h in healthy male subjects

BACKGROUND: New H1-antagonists have become available, but there has been no comparison of their potency for inhibiting histamine in the skin. METHODS: Cetirizine 10 mg, ebastine 10 mg, epinastine 20 mg, fexofenadine 60 mg, terfenadine 60 mg, loratadine 10 mg, or placebo was given to 14 healthy male volunteers in a double-blind, crossover randomized manner. Inhibition of the wheal and flare response to epicutaneous histamine phosphate (100 mg/ml) challenge was measured at 0, 0.5, 1, 2, 4, 6, 8, 10, 12, and 24 h after doses. RESULTS: Epinastine inhibited the wheal and flare after 30 min. Cetirizine commenced acting at 1 h and was superior to other treatments. Ebastine was no better than placebo until 4 h, but was efficacious thereafter until 24 h. Terfenadine induced potent inhibition after 1 h and was superior to its metabolite fexofenadine. Loratadine was the least potent inhibitor. Inhibition of the flare response paralleled the patterns seen for wheals. The rank order for area under the curve (0-24 h) was cetirizine, epinastine, terfenadine, ebastine, fexofenadine, loratadine, and placebo. CONCLUSIONS: The inhibition of histamine effects in the skin may be useful in predicting the clinical utility of newly introduced antihistamines in treating allergic disorders.     

Objective antihistamine side effects are mitigated by evening dosing of hydroxyzine.

First-generation antihistamines have potency, pharmacokinetic, and cost advantages compared with nonsedating second-generation antihistamines. Bedtime dosing of hydroxyzine was investigated as a dosing strategy to minimize reaction time degradation and adverse subjective symptoms previously documented for hydroxyzine in divided doses. Hydroxyzine, 50 mg qhs, was compared with terfenadine, 60 mg bid, in this double-blind, placebo-controlled crossover study of 15 healthy, asymptomatic adults. Computer-based eye-hand reaction time tests of simple reaction time (SRT) and choice reaction time (CRT) were not statistically different among the three drugs. Drowsiness, dry mouth, and irritability were significant for hydroxyzine (P = .0001, .001 and .02, respectively) compared with terfenadine or placebo, but less than seen in a previous study of hydroxyzine, 25 mg bid. Symptom scores with terfenadine were comparable to placebo. Histamine skin test wheal and flare were both significantly and comparably suppressed by hydroxyzine and terfenadine (P = .0001). While wheal suppression by hydroxyzine was universal, four of the 15 subjects showed little or no suppression with terfenadine (P = .03). Although bedtime dosing of hydroxyzine did not eliminate subjective symptoms, it maintained skin H1-receptor antagonism the following morning and alleviated the prolongation of reaction times previously reported with hydroxyzine in divided doses. The significant adverse subjective symptoms and psychomotor performance degradations caused by first-generation antihistamines can be mitigated by creative dosing schedules.     

The effects of butterbur on the histamine and allergen cutaneous response.

BACKGROUND: Butterbur or Petasites hybridus is an herbal remedy that exhibits antihistamine and antileukotriene activity and has been shown to attenuate the response to adenosine monophosphate challenge in patients with allergic rhinitis and asthma. However, no data are available regarding its effects on the histamine and allergen cutaneous response. OBJECTIVE: To evaluate the effects of butterbur compared with fexofenadine and montelukast on the histamine and allergen wheal and flare cutaneous responses. METHODS: Atopic patients were randomized into a double-blind, double-dummy, crossover study to receive for 1 week butterbur, 50 mg twice daily (8 AM and 10 PM); fexofenadine, 180 mg once daily (10 PM), and placebo once daily (8 AM); montelukast, 10 mg once daily (10 PM), and placebo once daily (8 AM); or placebo twice daily (8 AM and 10 PM). Patients attended the department at 10 AM and had measurements of the cutaneous wheal and flare responses to histamine, allergen, and saline control at 10-minute intervals for 60 minutes. RESULTS: Twenty patients completed the study. The mean +/- SE histamine wheal and flare responses, respectively, were significantly attenuated (P < .05) by fexofenadine (9.4 +/- 1.8 mm2 and 13.5 +/- 3.2 mm2) compared with placebo (15.5 +/- 3.3 mm2 and 179.8 +/- 74.3 mm2) but not by butterbur (16.4 +/- 2.1 mm2 and 297.7 +/- 121.2 mm2) or montelukast (19 +/- 1.9 mm2 and 240.2 +/- 66.6 mm2). The allergen wheal and flare responses, respectively, were also significantly attenuated (P < .05) by fexofenadine (31.1 +/- 6.3 mm2 and 256.9 +/- 86.5 mm2) compared with placebo (65.4 +/- 15.2 mm2 and 1,014.5 +/- 250.0 mm2) but not by butterbur (50.4 +/- 9.2 mm2 and 1,110.3 +/- 256.1 mm2) or montelukast (58.8 +/- 9.1 mm2 and 1,463.6 +/- 295.6 mm2). CONCLUSIONS: Butterbur did not produce any significant effects on the histamine and allergen cutaneous response compared with placebo, whereas mediator antagonism with fexofenadine but not montelukast produced significant attenuation. This finding would suggest that butterbur may not be effective in allergic skin disease.     

The inhibitory effect of terfenadine and flurbiprofen on early and late-phase bronchoconstriction following allergen challenge in atopic asthma

We have studied the effect of cyclo-oxygenase inhibition and H1-receptor antagonism on the early and late bronchoconstrictor responses to inhaled allergen in mild atopic asthmatics. In the first phase of the study histamine inhalation challenge tests were performed in seven mild, atopic asthmatics 2 h after treatment with placebo or flurbiprofen (50, 100 or 150 mg). Flurbiprofen in these single doses had no effect on histamine reactivity. Ten atopic asthmatics participated in the second phase of the study in which the time course of the bronchoconstrictor response to inhalation of allergen was observed on four separate occasions after treatment with (a) placebo, (b) flurbiprofen, 150 mg, (c) terfenadine 180 mg, and (d) the combination of flurbiprofen and terfenadine. On each occasion subjects inhaled a concentration of allergen (Dermatagaphoides pteronyssinus, grass pollen) that had previously been shown to produce a 30% fall in FEV1 (PC30 allergen). The mean maximum fall in FEV1 during the early reaction was 33.2 +/- 3.3% from the post-saline baseline value following placebo and this was reduced to 27.5 +/- 5.3% after flurbiprofen (n.s.), 20.3 +/- 3.2% after terfenadine (P less than 0.05), and 23.1 +/- 2.3 after the treatment combination (P less than 0.05). Seven subjects developed late asthmatic reactions (LAR) after placebo and in these subjects the mean maximum fall in PEFR during the LAR was reduced from 22.6 +/- 3.1% after placebo to 16.7 +/- 3.2% after flurbiprofen (P less than 0.05), 15.2 +/- 2.3% after terfenadine (P less than 0.05) and 11.5 +/- 3.1% after the treatment combination (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of loratadine (SCH 29851) in suppression of histamine-induced skin wheals

The efficacy and safety of single oral doses (10, 20, 40, and 80 mg) of loratadine (SCH 29851) in suppressing formation of histamine-induced wheals were assessed in a crossover study in 29 healthy male subjects. One hour prior to dosing and 1, 2, 3, 4, 6, 8, 12, 16, 24, 28, 32, 36, 40, and 48 hours after dosing, histamine and saline were injected intradermally into opposite arms. Measurements of resulting wheal areas showed loratadine suppressed wheal formation significantly better than placebo; suppression was dose related. The mean suppression over 48 hours was 16% in placebo-treated subjects and 35%, 45%, 51%, and 67% in the 10, 20, 40, and 80 mg loratadine-treated subjects, respectively. The onset of action occurred within the first hour. Duration of suppression was dose related, ranging from 12 hours with the lowest dose (10 mg) to 48 hours with the higher doses (40 and 80 mg). Incidence of sedation and other side effects were comparable among all doses of loratadine and placebo.     

Suppressive effects of histamine skin reactivity by a nonsedating antihistamine-mequitazine.

The suppressive activity of mequitazine (MQZ) on histamine skin reactivity was evaluated in 29 healthy subjects (age 22-25 years) in a single-blind study. Fifteen subjects received MQZ, at a dosage of 5 mg BID, for 7 days while 14 served as controls. A prick skin test with saline or histamine hydrochloride (1 mg/ml and 10 mg/ml) was performed in duplicate, on both forearms, starting from the baseline day and continuing for 4 days after medication had been discontinued (total of 11 days). The skin-test subject and the reader was unaware of the randomization process. Mean diameters of wheal and flare as well as the skin index scores (after Voorhost) were used in the analysis. Maximal flare suppression (as compared to the baseline values) was observed on day 6 (97% suppression for 1 mg/ml and 54% suppression for 10 mg/ml, p less than 0.01). Suppression of wheal size was significant (19% for 1 mg/ml and 28% for 10 mg/ml) but was not clinically relevant. Suppression of skin index scores was maximal on day 6 (71% for 1 mg/ml and 43% for 10 mg/ml, p less than 0.01). After MQZ had been discontinued, all measurements gradually returned to baseline values and were not different therefrom within 3 days. However, final measurements of wheal and flare were smaller than baseline values (60-94% of baselines). We conclude that MQZ, at the manufacturers's recommended dose of 5 mg BID, significantly suppressed flare size of histamine skin tests and recommend that MQZ be discontinued for at least 3 days prior to performing allergy skin tests.     

Comparative activity of cetirizine and desloratadine on histamine-induced wheal-and-flare responses during 24 hours.

BACKGROUND: Cetirizine and desloratadine are antihistamines active in the treatment of symptoms associated with seasonal allergic rhinitis and chronic urticaria. OBJECTIVE: To compare the antihistamine activity of desloratadine, the active metabolite of loratadine, with that of cetirizine in the skin wheal-and-flare responses during 24 hours. METHODS: This was a double-blind, randomized, placebo-controlled, single oral dose, crossover study. Skin reaction to histamine (100 mg/mL), administered by prick tests, was measured by the wheal and flare surface areas for 24 hours (before treatment and at 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours). Eighteen healthy volunteers (mean age, 33.9 years; 13 women) participated in this study. The areas under the curves of the wheal-and-flare responses as a function of time (primary efficacy variables) were compared using analysis of variance. RESULTS: A highly significant overall treatment effect (P < .001) was detected for wheal and flare inhibition, with the activity of cetirizine and desloratadine significantly superior to that of placebo (P < .001). In addition, the activity of cetirizine was significantly superior to that of desloratadine (P < .001). With desloratadine, only 3 of the 18 subjects achieved a wheal inhibition of at least 70%, occurring between 2 and 4 hours, whereas all subjects using cetirizine reached a wheal inhibition of at least 70% between 0.5 and 3 hours (median time, 1.7 hours). The difference between the 2 active drugs was highly significant (P < .001). The median duration of wheal inhibition of at least 70% was zero with placebo and desloratadine and was 21.9 hours with cetirizine (P < .001). No serious adverse events were reported, and no subject withdrew from the study due to an adverse event. CONCLUSION: Cetirizine was associated with significantly greater suppression of skin reactivity to histamine compared with desloratadine during 24 hours after a single dose, with a consistent duration of action for cetirizine, as previously reported.     

Ketotifen inhibits the cutaneous but not the airway responses to platelet-activating factor in man

We studied the effect of ketotifen, an oral antiallergic and antihistaminic drug, on the airway and cutaneous responses to platelet-activating factor (PAF) in a double-blind, randomized, and crossover study in six normal subjects. Ketotifen (three doses of 2 mg taken during a 14-hour period before PAF) did not alter PAF-induced bronchoconstriction and did not prevent the accompanying flushing and coughing. The transient neutropenia (74.5 +/- 4.8% fall; p less than 0.001) and rebound neutrophilia (104 +/- 55% rise) induced by PAF were not affected by ketotifen. On the day placebo was received, airway responsiveness to methacholine increased after PAF exposure with the concentration needed to cause a 40% fall in baseline partial expiratory flow rate (PC40), decreasing from 69.2 mg/ml (geometric standard error of the mean, 2.69) to 23.3 mg/ml (2.34) on day 3 (p less than 0.001). Ketotifen had no effect, because on the day ketotifen was administered, mean PC40 also decreased from 52.7 mg/ml (2.5) to 21.5 mg/ml (2.14) (p less than 0.01). In the skin, ketotifen reduced the flare area (from 8.05 +/- 3.60 to 1.14 +/- 0.29 cm2; p less than 0.05) and the wheal volume (from 0.068 +/- 0.010 to 0.045 +/- 0.008 cc; p = 0.02) induced by intradermal PAF (200 ng). Cutaneous responses to histamine (1 microgram) were significantly inhibited. Thus, the bronchoconstriction and bronchial hyperresponsiveness induced by PAF are not inhibited by ketotifen. Ketotifen inhibits PAF-induced wheal and flare in the skin, which is probably histamine dependent. The airway effects of PAF are unlikely to be mediated by histamine release.