Effect of an H1 Blocker, Chlorpheniramine, on Inhalation Tests with Histamine and Allergen in Allergic Asthma

Effect of an HI Blocker, Chlorpheniramine, on Inhalation Tests with Histamine and Allergen in Allergic Asthma* Valentin T. Papa, M.D., F.C.C.P.t In 15 asthmatic subjecfs, flow volume loops were recorded before ad after quantitative nebullDtloD of increasing concentration of his......, and . . . . ..., 1IIItD a FEVI > 10%) was obtained. threshold response (-~ Nine subjeds with reproducible threshold doses to these two agents were Included in the study. After pretreatment with 10 ... of Intravenously administered cillo... pheniramiDe, the threshold dose of his......, iDcreaed fourfold in eigbt subjects aDd e....tfold in one subject, wbereas the threshold doses to aDergen doubled Ia .ven and remained .....ected in two. One of these two subjects required 15 me chiorpheDiramiDe iatravenoUlly for comparable protection. In three subjects, tile threshold

I t is generally accepted that histamine is released in vioo when actively or passively sensitized fragments of lung, 1 tracheobronchial shipS,2 nasal polyps,3 or basophiIs4 are challenged with the apFor ecUtoriai comment see page 420

propriate allergen. In vivo, the blood level of histamine is increased during spontaneousl or allergeninduced6 attacks of asthma. Moreover, at least in vivo, the asthmatic bronchi are hyperreactive to exogenous histamine, 7 and thus, most likely to endogenous histamine as well. Yet, as repeatedly shown, the HI blockers are ineffective in this disease. 8,e

The negative reports with HI blockers in asthma are surprising for two main reasons. First of all, the immediate response to skin tests10 or the symptoms of hay fever or urticaria,8.11 many times due to an IgE mediated reaction, are decreased by HI blockers. Secondly, in the animal species in which histamine is an important mediator of anaphylaxis, experimental "asthma" can be decreased or prevented by pretreatment with appropriate doses of classic antihistamines. 12 One may explain the lack of activity of HI blockers in (allergic) asthma by the overriding activity of chemical mediators other than histamine or the use ·From the Pulmonary Division, Deparbnent of Medicine, Pritzker School of Medicine, University of Chicago. Presently at Pulmonary Division, Medical College of Ohio, Toledo. tchief, Pulmonary Division.

Manuscript received July 18; revision a~ October 4. Reprint requests: Dr. Popa, C.S. 10008, Medical College of Ohio, Toledo 43699

442 VALENnN T. POPA

w.

dose to inhaled acetylchoUne determiDed with a slmilar procedure aDd found reproducible. Pretreatment with 10 to 15 .... cblorpheDIramIDe increased this threshold dose two to four times, similarly to the etlect produced by 0.4 l1li of subcDbmeously administered atropine. However, 0.4 JIll atropine sc. did not alter the airway responses to aBe...n. The results mgest that Intravenously administered cblorpheDiramiDe provided It ... a dose ratio of at least four against iDbaIed histamine, C8D prevent aUacks of allergen-induced 88thma. The etlect Is probably mediated thro.... the HI rather thaD the acetylchoUne receptor.

of these competitive antagonists in insufficiently large doses. A review of the pertinent literature13 has disclosed that in the isolated studies claiming a beneficial effect of HI blockers in asthma, especially in the prevention of allergen-induced asthma,14-18 large doses of these drugs had been given either intravenously or by inhalation. In a recent controlled study,I3 cblorpheniramine maleate in a dose of 10 mg, intravenously, was shown to have mild bronchodilating effect in those asthmatic subjects with a moderate decrease in the ratio of forced expiratory volume in 1 sec/forced vital capacity (FEVI/FVC). Subsequently, other controlled studies confirmed that large aerosolized doses of chlorpheniramine17 or of another HI blocker, clemastine,18 are able to dilate the bronchi. The purpose of this study was to test the hypothesis that an HI blocker, used in appropriate doses, could prevent allergen-induced asthma. In preliminary experiments, we have found that 10 mg chlorpheniramine, administered intravenously, would increase the tolerance to inhaled histamine two to four times, depending on the endpoint used, -a FEVt ~ 20 percent or -a ~ 10 percent respectively. As histamine is only one of the chemical mediators of anaphylaxis, we reasoned that in studying the effect of HI blockers in antigen-induced asthma, we should resort to mild attacks of asthma, otherwise higher, potentially toxic intravenous doses of chlorpheniramine would have to be administered. Moreover, we thought that the design of our study should fulfill other requirements as CHEST, 78: 3, SEPTEMBER, 1980

well: physiologically, the bronchoconstrictor agents should be nebulized in quantitative fashion; only airway responses of similar magnitude, reproducible, and obtained at comparable baseline levels, should be used in the study. Pharmacologically, the agents used to modulate the bronchoconstrictor responses should not dilate the bronchi; the effect of HI blockers or any other modulating agents in drug or allergen-induced asthma should be expressed as a dose-ratio because this ratio allows a uniform, standardized assessment of the effect of the same agent against various types of bronchoconstrictor responses or of different agents with similar pharmacologic properties against the same bronchoconstrictor response. For this study, we choose chlorpheniramine as the HI blocker because milligram per milligram, it has less central, and possibly less anticholinergic, activity than diphenhydramine,19 the only other classic antihistamine available for intravenous use in the United States. MATERIAL AND METHODS

Fifteen subjects with bronchial asthma20 were initially enrolled in the study, and selected according to the following criteria: age between 20 and 30, in an asthma-free interval, (ie, no attack of asthma in the last four weeks), clear cut history of attacks of asthma biggered by a well defined environmental allergen, and positive skin (prick) and radioallergosorbent (RAST) tests to that allergen. Because 10 mg of intravenously administered chlorpheniramine dilates the bronchi only if FEV1 is low,13 the FEV1 of our subjects had to be higher than 60 percent of the predicted21 if a bronchodilating effect of such an intravenous dose was to be avoided· the variability (ie, range/mean) of the three highest FYC and FEV1 had to be less than 5 percent within the day and less than 10 percent from day to day. Nine out of these 15 subjects were finally included in the study: these nine all showed reproducible responses to both inhaled histamine and allergen. In these nine subjects, an identical dose of drug or allergen produced airway responses of comparable magnitude (-4 FEV1 between 10 and 18 percent). Histamine dihydrochloride (Calbiochem, Los Angeles) , allergens (Hollister-Stier, SpokaneO), and in three subjects, acetylcholine chloride (Calbiochem, Los Angeles) as well, were aerosolized in saline solution through a disposable manifold nebulizer (Bard-Parker, Rutherford, N.J.). The mouth piece was removed, and the subject was asked to breathe directly from the nebulizer with lips tightened around the exit port. The particle size distribution of a saline aerosol ranged between 0.8p. and 6.0p. for 80 percent of the particles (information provided by manufacturer and double-checked by Dr. Peter Lee from the Pulmonary Seetion of the Abraham Lincoln School of Medicine, University of Illinois, Chicago). The nebulizer was connected in line with a volume ventilator (Monaghan 225, Littleton, °For each allergen, small aliquots of allergens were dispensed in plastic tubes which were stored at -20°C. Twenty-four hours before the allergen challenge a tube with the appropriate allergen was used to prepa:e the various dilutions These dilutions were kept at 4°C and were used over a maxi: mum of six days.

CHEST, 78: 3, SEPTEMBER, 1980

Colo). The tidal volume was set at 500 ml and the plateau flow at 2 L/second. The nebulizer was activated in inspiration only. The airflow powering the nebulizer was 6 L/minute. The Huid (saline) output was 0.10 mVI0 breaths. We calibrated the flow, volume, and duration of air delivered by the ventilator with a 13 L Collins spirometer and a computerized system with flow as primary signaL 22 With the ventilator in assist mode, histamine, acetylcholine, and allergen were inhaled during a sequence of ten breaths. The dose delivered was expressed in milligrams base for drugs or in protein nitrogen units (PNU) for allegens. Chlorpheniramine maleate in a dose of 10 mg, was injected slowly intravenously after test doses of 8 mg orally and 5 mg intravenously administered on separate days had failed to produce drowsiness, sleepiness, dryness of nasal or buccal mucosa, or accommodation changes. This screening procedure was prompted by the severe drowsiness experienced by one subject after intravenous administration of 10 mg. This subject was not included in the study. In the three subjects receiving atropine, we planned to use progressively increasing doses, starting with 0.4 mg given subcutaneously. The ECG was monitored for one hour after the administration of chlorpheniramine or atropine. Flow volume curves were recorded with a computerized system using flow as primary signal.22 Mean FYC, FEV l' peak expiratory flow (FEFmax) and forced expiratory flow at 50 percent, 75 percent, between 25 percent and 75 percent of the vital capacity (FEF5OI, FEF751 and FEF25-751 respectively) were obtained from the three flow volume loops with the highest FEV1.18 A typical nebulization session consisted of the recording of flow volume curves before and after increasing concentrations of histamine, acetylcholine, or allergen until the mean FEV 1 decreased with at least 10 percent (threshold response), and the subjects complained of chest tightness, shortness of breath, or wheezing. Thus, all threshold responses in this study were characterized by a change in FEV1 of twice its spontaneous variability and by symptoms and signs consistent with acute airway constrietion. 23 All the mean 4 FEVt preceding the threshold response were less than 5 percent of the baseline value. Two main reasons have influenced the selection in our inhalation tests of an endpoint characterized by -4 FEV1 ~ 101 rather than the more popular -4 FEV1 ~ 20 percent: 24 (a) The design of the study required the use of mild attacks of drug- or allergen-induced asthma. Histamine is only one of the mediators of IgE-induced allergic manifestations, and therefore, the dose ratio of chlorpheniramine against allergen should be smaller than the dose ratio of this HI blocker against histamine. It follows that in a study concerned with the possible effects of chlorpheniramine against allergen-induced asthma, the administered dose of this drug should increase the tolerance to inhaled histamine at least fourfold. A ratio of chlorpheniramine against histamine lower than 4, eg, 2, might not reveal the protective effect of this HI blocker against allergen induced asthma. For attacks of asthma with a higher physiologic endpoint, eg -4 FEV1 ~ 201, doses of chlorpheniramine higher than 10 mg intravenously would have been indicated in order to achieve a dose ratio of 4 against histamine. Such doses are potentially toxic18 and potentially bronchodilator. It is not clear why a certain dose of chIorpheniramine, eg, 10 mg intravenously, dilates the bronchi only if these are moderately or severely constricted.13 One explanation, tempting but not proven, is that moderately or severely constricted bronchi are surrounded by more histamine than the normal or mildly consbicted ones. 18 The bronchodilator effect would have made

INHALATION TESTS IN ALLERGIC ASTHMA 443

the protective effect of chlorpheniramine difficult to interpret. ( b) During our preliminary tests with a different endpoint, PD 20,24 two subjects challenged with inhaled allergen according to the recommended protocol developed biphasic attacks of asthma with the late component lasting several days. In our previous experience with approximately 1,500 inhalation tests with allergen, such an incident occurred only four other times. In spite of its rarity, considering the basic needs of the experimental protocol, the validity of -~ FEV1 ~ 10 percent (see below) and the fact that these two incidents occurred within one year at the same institution, we elected to measure only small, "threshold" airway response. The use in inhalation tests of an endpoint characterized by -~ FEV1 ~ 10 percent was considered to be physiologically valid for the following reasons: 1. As shown in Figure 1, in six asthmatic subjects we have obtained reproducible threshold doses using as physiologic endpoint -~ FEV1 ~ 10 percent. This is not at all surprising since Tiffeneau,25 with an identical endpoint, has repeatedly reported that the inhalation tests with histamine, acetylcholine, and allergen were reproducible in most subjects. 2. In antigen challenge tests, characterized by mild comparable airway responses and presence of wheezing, an increase in the concentration of allergen leads to an increase in the airway responses.28 3. Our arbitrary threshold response is not at variance with PD20, characterized by -~ FEV1 20 percent. PD20 is calculated by the interpolation of two doses, one producing a FEV 1 response larger than -10 percent, but smaller than -20 percent and the other just above -20 percent. It seems a reasonable assumption that if PD 20 is valid, so are the lower (our threshold dose) and the higher -~ FEV1 used for its calculation. Then, a -~ FEV1 20 percent may not necessarily represent a larger airway response than -~ FEV1 10 percent if the variability of the former response is 10

percent and the variability of the latter response is only 5 percent. This is consistent with a fundamental principle of statistical analysis: the significance of a change depends on both the magnitude of change and its variability.21 4. A physiologic endpoint similar to that adopted by us for this study has been extensively used by others.25 ,28,31 Tiffeneau's findings in particular have been repeatedly confirmed by others, including the authors using PD 20.32,3a Incidentally, the provocation dose 35( -~ Gaw/VL > 35 percent) proposed by Chai et aI,24 and interchangeably used with PD20 , is definitely lower than the latter34 and very likely similar to our threshold dose. 5. In our protocol for inhalation tests, besides the physiologic endpoint, we have also included a clinical criterionthe presence of mild wheezing in '''positive'' inhalation tests. Although mild symptoms of asthma may not always be associated with mild wheezing, the presence of the latter gives more weight to the significance of a physiologic change which, whatever its magnitude, is essentially arbitrary. Others have previously shown that during inhalation tests with bronchoconstrictor agents, the first chest complaints appear when -~ FEV1 is ~10 percent or slightly higher. 23 ,35,38 When this degree of physiologic impairment is associated with wheezing, as it was in our study, other physiologic changes suggesting the presence of bronchoconstriction are also present, eg, an increase in the alveolar slope of the single breath N2 washout,31 increase in the work of breathing and dynamic lung oompliance38 and increase in the airway or pulmonary resistance.39,40 6. Acute 41 ,42 or chronic decreases 43 in FEV1 of around 10 percent occurring in groups of subjects were found to be statistically significant. 7. Recently, others have also used relatively mild attacks of asthma when such small airway responses were appropriate to the design of their study..Jl,42

>

>

>

o--!!.-o First test 100 ..-

o o ~

II

CD

.2 co > CD

.5 CD

6 __

OA

OA

~

!.b... A Second test 1

Patient number

90 .....-----------..-'O--""'r"'Ilr-----P-lIlr--..... ~--~r_------\ \

A,

,

80

o

en

co

..c

-> w

70

u. <]

* 0.04

0.08

0.16

0.32

0.64

1.28

2.56

5.12

Histamine Base mg/ml nebulized 1. Dose response curves to inhaled histamine in six asthmatic subjects. Horizontal line (90 percent baseline FEV1) marks minimum decrease in FEV1 required for positive test. Note reproducibility of histamine dose as determined with an endpoint characterized by -A FEV1 ~ lOS.

FxCUBB

444 VALENnN T. POPA

CHEST, 78: 3, SEPTBMBER, 1980

through (c) lasted 15 to 21 days, and the following steps lasted an additional 12 to 18 days. The subjects remained asymptomatic during this period of time.

Nebulization was started with 0.005 mg histamine, 1 PNU allergen, and 0.025 mg acetylcholine [threshold doses (TD) of acetylcholine are frequently higher than TD of histamine].28 The doses were doubled every 15 minutes (for drugs) or 30 minutes (for allergen). When chlorpheniramine or atropine were used to assess their influence on TDs, the drug or allergen challenge test proceeded as usual except that chlorpheniramine was injected 90 minutes, and atropine 30 minutes, before ·the expected therapeutic response (ie, immediately after nebulization of 1/64th of TD of histamine or acetylcholine and Ith of TD of allergen for chIorpheniramine; and immediately after the nebulization of ~th of TO of histamine or acetylcholine and ~ of TO of allergen for atropine). The design of study included the following steps: ( a) determination on separate days of TO of inhaled histamine and allergen; (b) repetition of the same protocol mentioned above in order to assess the reproducibility of these TDs. (This step led to the inclusion in the study of only nine out of the 15 initial subjects); (c) determination of TO of histamine and allergen after pretreabnent with 10 mg chlorpheniramine administered intravenously. If chlotpheniramine administered intravenously would protect against mild allergen-induced asthma, the study should attempt to determine whether this action is due to the antihistaminic or anticholinergic properties of this drug. For this purpose, in three subjects, the threshold response to inhaled acetylcholine was determined and checked for reproducibility. Then the TDs of acetylcholine were determined after pretreabnent with chIorpheniramine, and on separate days, atropine suHate subcutaneously. Atropine was used in a dose which had a dose ratio against acetylcholine identical with that of the previously used dose of chlotpheniramine. The TD of allergen was again determined, this time in the presence of atropine. In order to determine the stability of TDs of allergen, in two subjects, after completion of allergen-stropine test, the TD of allergen was again assessed, without any drug pretreabnent. The challenge tests with drugs and allergens were performed two or three days apart, respectively. Steps ( a) Table

Patient No./Bex/ Height, Age, yr em

l-~ntlaropometrie

Statistical Analysis. Student~ s t-test for paired observations,21 the test applied by others" for the analysis of dose responses based on arbitrary physiologic criteria, was used in this study to assess the significance of changes in threshold doses produced by chIorpheniramine and atropine. The study has been approved by the Committee on Human Investigation of the University of Chicago. Infonned consent was obtained from each subject.

REsuLTS

The anthropometric and respiratory measurements

of the subjects participating in this study are shown in Table 1. The same table shows the TDs of al-

lergen, histamine, and when determined, acetycholine. The range of TDs of histamine was sixteenfold, between 0.08 and 1.28 mg. The average change at the threshold level varied with the measurement: 3.0 to 8.0 percent for FVC, 11.3 to 18.6 percent for FEVl, and 16.0 to 21.9 percent for FEF25-75S. The percent changes in FEFmax, (4.1 to 9.1) were comparable to the percent changes in FVC, and the percent changes in FEF50S, (15.8-22.6) and FEF75~ (14.6-23.2) were quite similar to the percent changes in FEF25-75%. In eight subjects, the administration of 10 mg chlorpheniramine intravenously increased the TD of histamine four times (the ratio of TD histamine + chlorpheniramine/TD histamine was four), whereas in one subject, the same amount of chlorpheniramine exhibited a dose-ratio of 8 (Fig 2). In seven subjects, 10 mg of this HI blocker increased the TD

Data, Rupiratory Mea_remem. and Tlare.laold Doae To ~Uer.en, Hutamine and ~eet"lelaoline·

FEF FVC FEV1 FEV1/FVC FEFmax 25-75% FEF50% FEF75%

Allergen

TDA

TDH TDAC

l/F /25

165

88

83

77

102

47

57

49

cat hair

250

0.08

2/F /26

168

88

73

68

108

33

35

29

cat hair

250

0.08

3/M/27

178

77

72

77

99

33

34

28

ragweed

10

0.08

4/M/27

183

110

92

67

104

47

47

43

dog hair

100

0.16

5/F /27

171

86

71

71

89

34

35

34

ragweed

10

0.16

6/M/20

185

96

60

54

96

31

32

32

ragweed

100

0.32

7/M/29

175

105

94

62

125

61

62

49

ragweed

20

0.32

8/F /24

168

94

94

82

94

49

58

50

ragweed

250

1.28

9/F /24

160

113

88

65

92

67

83

64

horse hair

200

1.28

0.4 0.2 0.2

*TDA indicates threshold dose of allergen, expressed in PNU delivered; TDH, threshold dose of histamine, expressed in mg delivered; and TDAC, threshold dose of acetylcholine, expressed in mg delivered. For abbreviations of respiratory measurements see Method. Elipses indicates not determined. The table presents the average basal values of all the days of experiments expressed as percent of predicted21 except for FEVt/FVC which is represented by the observed percent ratio.

CHEST, 78: 3, SEPTEMBER, 1980

INHALATION TESTS IN ALLERGIC ASTHMA 445

....,

ra '...., Q) Q)

2.56

C. Q..

1.28

'-

U .r::. ....,

..

0.64

~ :J:

0.32

'+-

0

0.16

I-

0.08

c

••

5.12

~

, ,,

,

, ,,

(15mg) 0

.:

,

, ,,

,,

• • , ,,

~

DIscuSSION

,,

0.32

,

, ,,

,/

1.28

0.16 0.64 TOofH WITHOUT CP PRETREAT. FIcmm 2. Influence of chlorpheniramine injected intravenouslyon threshold dose of inhaled histamine. Threshold dose of histamine is expressed in milligrams of histamine base delivered to patient. Abbreviations: pretreat indicates pretreatment; TD, threshold dose; H, histamine, and CP, chlorpheniramine. Closed circles indicate changes in TD of H produced by 10 mg chlorpheniramine given intravenously. Open circle indicates changes in TO of H produced by 15 mg chIorpheniramine given intravenously. One of subjects with 'ID of H of 0.16 mg, was tested first with chlorpheniramine, 10 mg, and his TO of H increased to 0.64 mg-one of the closed circles at this dose level-and then with 15 mg chIorpheniramine.

of allergen twice (Fig 3). In one of these two subjects, 15 mg chlorpheniramine intravenously increased the TD to allergen twice (Fig 3) and the

TO to histamine 8 times (Fig 2). The changes in histamine and allergen threshold doses produced by chlorpheniramine were significant at P
44& VALENTIN T. POPA

forced expiratory Hows. SpeciBcally, mean FEV1 remained within 5 percent of its basal value.

sum-

The main finding of this study was that a ciendy high dose of chlorpheniramine administered intravenously can protect against mild attacks of allergen-induced asthma on the basis of its HI blocking properties. A second and quite unexpected finding was that regardless of the degree of bronchial reactivity to histamine, a fixed dose of chlorpheniramine given intravenously produced a comparable rate of protection against histamine-induced bronchoconstriction. The implication of the first finding is that in asthma, endogenous histamine plays a role not only in the resting bronchial tonus, 13 but also in the acute bronchial changes induced by allergen challenge. The implication of the second finding is that the bronchial hyperreactivity to histamine is probably unrelated to the degree of association of chlorpheniramine, and most likely histamine, with the HI receptor of the bronchial smooth muscle. In any immunopharmacologic study of the human airways, the most difficult problem is to demonstrate that the changes in bronchial caliber occurring after the administration of a drug represent neither spontaneous variation nor the activity of another agent. Five lines of evidence indicate that in our study, the

.....

co

400

.....

200

••,,,,

Q) ~

Q)

c. c..

100

.....

40

«

~

20

0

10

~

u ~

\t-

C I-

•• ,,,

o.,,,

(lSmg)

~

~

~

, ,•

~

, ,,

,

.'

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,,

~

10 20 40 100 200 400

TO of A WITHOUT CP PRETREAT. FIGURE 3. InJluence of chlorpheniramine injected intravenouslyon threshold dose of inhaled allergen. Threshold dose of allergen is expressed in protein nitrogen units delivered to patient. As in the case of histamine threshold doses, dose delivered was ten times less concentration of agent used for nebulization (see Methods). For abbreviations and symbols, see Fig 2. One of the two subjects who did not increase his TO of A after 10 mg chlorpheniramine was retested with 15 mg chlorpheniramine (open circle).

CHEST, 78: 3, SEPTEMBER, 1980

..,;

..,;

co

co

Q)

e. 115mg)

• , ,, , , • , ,, , ,

10°·8

0

L:

~0.4

,

~

00.2

C

FIGURE 4. Effect on threshold dose of allergen of dose of atropine having an antiQ) cholinergic activity similar to anticholiner, gic activity of 10 or 15 mg chIorphenira, , 0)40 iO.8 , mine given intravenously. Left panel: ,, +oJ ,, .c ,, influence of intravenously given chlor, co 20 , , ~0.4 , , pheniramine on threshold dose of acetyl, choline. Middle panel: influence of 0.4 mg ,, ' 010 ,, ~0.2 atropine given subcutaneously on threshold ,/ , , C , dose of acetylcholine. Right panel: influ,, ,, tence of 0.4 mg atropine given subcutane0.8 10 20 40 ously on threshold dose of allergen. Abbreviations: ACh indicates acetylcholine; 0.4 AT, atropine; and remaining abbreviations TOof ACh are noted in legend for Figure 2. TO of A (15mg)

+oJ

~ 1.6

1.6

+oJ

I-

l+oJ

e. I-

Q.. Q)

CD

Q)

I-

I-

co

I+oJ

CD

U

...,;

Q)

I+oJ

,,

, ,, , ,

0.4 TO of ACh

0

• •

~

Q) I-

0.80 +oJ

« ~

« ~

....

airway responses have been reasonably well-controlled. First of all, in contrast with previous studies with HI blockers in allergen-induced asthma,9,14-18 the nebulization of drugs and allergen has been conducted in a uniform fashion, with the How, volume, and duration of aerosolization being controlled. The use of a volume ventilator has avoided the variability in breathing patterns, and hence, as just reported, the variability in the deposition of particles and airway response. 45 The size of aerosol particles has also been double-checked In essence, the delivery of drug or allergen has probably been controlled in greater detail than currently suggested by Chai et al. 24 Second, in opposition to previous studies with HI blockers,9,14-18 the intraindividual variability of airway responses has been checked by relying only on reproducible responses obtained over a short period of time, in free interval, at comparable baseline level. Third, in this study, the antagonists have not affected the basal physiologic measurements as has been the case in some of the previously mentioned studies with HI blockers. I4-16 A larger dose of atropine (0.6 mg subcutaneously) is usually needed to dilate the bronchi of subjects with ~ FEV1/FVC comparable or even smaller than that of our subjectS.48 As expected13 we found that at high FEVI and S FEVI/FVC, 10 mg chlorpheniramine given intravenously has no bronchodilating activity. Therefore, in this study, a concomitant change in baseline values of forced expiratory Hows has not adulterated the antihistamine, anticholinergic, and antiallergic eHects of chlorpheniramine and atropine. Fourth, the magnitude of drug or allergen bronchoconstriction has been adjusted to the specific needs of the study, and ethical considerations. The use of an endpoint - a FEV1 > lOS, appropriate for this study and physiologically valid if associated CHEST, 78: 3, SEPTEMBER, 1980

.. .'

with wheezing is not proposed here as an alternative to the endpoint - a FEV1 > 2OS. The latter is an excellent endpoint for routine assessment of bronchial hyperreactivity. 24 Fifth, the magnitude of airway responses at the threshold level in the same individual and across subjects was quite similar. Thus, it seems justifiable to use dose-ratios in comparing the effect of chlorpheniramine or atropine on drug or allergen-induced bronchoconstriction. In this study, 10 mg chlorpheniramine given intravenously could protect seven out of the nine subjects against mild immediate attacks of allergen-induced asthma. In all the previous studies in which this class of drugs has protected against immediate allergen-induced asthma, there were subjects who were less protected than the others. I4-18 In our study, one of the two subjects unprotected by the standard dose of 10 mg chlorpheniramine was protected in the usual fashion (ie, doubling of the threshold dose) by 15 mg of chlorpheniramine. This observation suggests that the use of a single dose of HI blocker may not uncover the antiallergic effect of this drug. This error may be compounded by using as physiologic criterion, an airway response too large for the dose of HI blocker used, eg, provocation dose 20 percent. It was interesting that in spite of a half life of 28 hours,47 chlorpheniramine could not protect against the late asthmatic attacks. Similar observations were reported by Nakazawa et al I8 with another drug displaying both HI blocking and anticholinergic activity. The low dose-ratio against allergen (2: 1) shown by the relatively large dose of chlorpheniramine intravenously administered in these experiments suggests that if HI blockers will ever find a place in the therapy of asthma, they would have to be administered by inhalation. In principle, this route should INHALATION TESTS IN ALLERGIC ASTHMA 447

allow the topical administration of high doses with minimum systemic toxicity. The timing of allergen or drug nebulization in relation to administration of cblorpheniramine and atropine was predicted on the haH life of these two latter drugs, (28 hours for the HI blocker"7 and 1.3-2.0 hours for atropine48 ), and the moment when their target (bronchodilating) effect, due to the displacement of the corresponding agonist, was at its peak (60 to 120 minutes for 10 mg chlorpheniramine intravenously13 and probably 30 minutes for 0.6 mg atropine subcutaneously"). From our data, it is now easy to understand why Schiller and Lowell9 could not detect any protection against allergen-induced bronchoconstriction after pretreatment with 0.6 to 1.2 mg tripelennamine intravenously. This drug is less potent than cblorpheniramine: compare for instance the dose/tablet of these drugs, 4 mg for chlorpheniramine, versus 25 or 50 mg for tripelennamine. These authors have injected doses of tripelennamine which simply could not achieve the blood levels needed to protect against allergen-induced asthma. In experiments, apparently not controlled for their reproducibility, the same drug has successfully prevented allergeninduced asthma 15 when administered in higher doses. Although our inhalation tests with allergen were well controlled and reproducible, we feel that a dose ratio of chlorpheniramine against allergen of only 2:1 requires further confirmation with other methods and design, eg, use of high doses of inhaled HI blocker, determination of protective effect against larger allergen-induced airway responses, etc. Thus, our study should not be construed as a plea for immediate use of HI blockers in the therapy of asthma. The dose-ratio of chIorpheniramine against histamine was found to be 4:1 in eight subjects and 8:1 in one subject (Fig 2). The protective effect of HI blockers against histamine-induced asthma has been repeatedly reported,9,15,49.50 but to the best of our knowledge, it has never been expressed in terms of dose-ratio. One may speculate that the dose-ratio of chIorpheniramine against histamine might be smaller for the bronchial smooth muscle than for other tissues, eg, peripheral vascular muscle. For instance, the dose of chlorpheniramine which protects against skin responses to histamine or allergen was found to be 4 mg three times daily,IO comparable to the dose of chIorpheniramine currently used in the treatment of urticaria or hay fever. From a pharmakolcinetic study with chlorpheniramine (Peets et al),41 one may infer that the blood level produced by 12 mg chIorpheniramine administered orally as a single dose (ie, much more than the usual oral dose), is

448 VALENTIN T. POPA

smaller than the blood level of 10 mg of the same drug administered intravenously. H this is true, the lower affinity of chIorpheniramine for the HI receptor of the bronchial smooth muscle than for the HI receptor of vascular smooth muscle might explain why in the doses currently used, only the vascular effects of histamine are antagonized by HI blockers. However, alternate explanations for the efficacy of chlorpheniramine in extrabronchial allergic reactions should also be considered because the affinity constant of HI blockers for HI receptors tends to be very similar across organs and across species.51 The higher dose-ratio of cblorpheniramine against histamine (4: 1) than against allergen (2: 1) (Fig 3 ) may be attributed to the fact that histamine is only one of the chemical mediators of allergen-IgE antibody reactions. In three subjects, the anticholinergic activity of 10 mg chlorpheniramine intravenously and 0.4 mg atropine subcutaneously were found to be very similar (Fig 4). In vitro, in guinea pigs, the anticholinergic activity of chlorpheniramine is much smaller. II,52 This is probably an illustration of the well known discrepancy between in vivo and in vitro responses to bronchoconstrictor agents153 and underscores the need for human experiments in the pharmacology of airways. Our findings of a smaller dose-ratio of chIorpheniramine against acetylcholine than against histamine are consistent with other data obtained in humans49,50 and animals. 51 We found that a dose of atropine (0.4 mg subcutaneously administered), with the anticholinergic effect of 10 or 15 mg chlorpheniramine, intravenously, failed to prevent mild attacks of asthma (Fig 4). This was not unexpected because larger doses of atropine also failed to protect against allergen-induced asthma."·M Our observation suggests that the protective effect of chlorpheniramine in mild attacks of asthma is due to its HI blocking activity and not to its anticholinergic activity. A most intriguing finding in the present study was that 10 mg chlorpheniramine, administered intravenously, regardless of the degree of bronchial reactivity to histamine, had an almost constant dose-ratio against histamine: 4:1 in eight subjects and 8:1 in one subject. Thus, the subjects who reacted to lesser amounts of inhaled histamine showed a comparable rate of protection with the subjects who reacted to higher amounts of the same agonist. Interestingly, Douglas et al55 have reported that, in vivo, the guinea pigs have a similar dose ratio of atropine against acetylcholine, regardless of their widely different acetylcholine responsiveness. Consider now the generally accepted equation of

CHEST, 78: 3, SEPTEMBER, 1980

4 o -to-J

co ~

3

I

Q)

(/)

.g 2

"-'

1 0.47

7

8

9

10

11

-Log concentration of chlorpheniramine (blood level) 5. Plot of-log concentration of antagonist versus log ( dose-ratio-l ). K i v represents association constant of antagonist as determined from assumed blood levels of chlorpheniramine and log (dose-ratio-l). Figure is only used to illustrate the point that in eight subjects with similar dose ratio of chlorpheniramine against histamine (4: 1 ), their K t v might have been identical. Real Ka was obtained in mtra and was 9.3 for human bronchi, 9.1 for guinea pig trachea, and 9.4 for perfused guinea pig lung. 51 FIGURE

competitive antagonism: S1 ,S8 log (dose-ratio-l) = log concentration antagonist - log affinity constant of this antagonist for the receptor. The relationship between log ( dose-ratio-l) and - log concentration antagonist is linear; this line has a slope of - I and its intersection with the x axis marks the log affinity constant (Fig 5). In eight subjects, a single dose of 10 mg chlorpheniramine, given intravenously, (presumed blood level around 30 mp.gl ml ) 41 produced a unique dose-ratio against histamine of 4:1. As chlorpheniramine is the competitive antagonist of histamine and both bind on the same HI receptor, the slope of the plot log (dose-ratio-l) versus-log concentration antagonist should be equal to - I. Thus, each of our individual data points would be located on a line with a slope of - I. Our data points were identical in eight subjects (dose-ratio 4:1), and their slope as well as their intersection of the x axis would also be identical. It results that these subjects, regardless of their degree of reactivity to inhaled histamine, have a similar association constant for cblorpheniramine or histamine. Stated differently, in our subjects the diHerences in histamine hyperreactivity were not related to diHerences in the binding of chlorpheniramine, and most likely histamine, to bronchial HI receptor (Fig 5). Interestingly, the

CHEST, 78: 3, SEPTEMBER, 1980

highest threshold to inhaled histamine (1.28 mg) was also the lowest histamine threshold in a group of normal subjects. One might then argue that the binding of chlorpheniramine (and histamine) by the bronchial HI receptor of our asthmatic subjects is grossly within normal limits. H this is troe, the hyperreactivity to histamine in these asthmatic subjects was related either to an increased number of "normal" HI receptors and!or to an usual number of "normal" receptors but one or more lesions along the path leading from the recognition component of the receptor to muscular contraction. Although we think that this reasoning is consistent with our present understanding of agonist-antagonist interaction, we must also take into account the limitations of our data: data have been obtained in vivo and cannot have the accuracy of the in vitro experiments; the slope relating log (dose-ratio-l) to log concentration antagonist has been drawn through a single point; the behavior of receptors on tissues hyperreactive to the corresponding agonist has not been analyzed theoretically and experimentally. Furthermore, it would be dangerous to extend to the whole population of asthmatic subjects conclusions based on the pharmacologic behavior of the airways of eight subjects because the pharmacologic abnormality of asthmatic bronchi may not be uniform. For instance our ninth subject had a diHerent dose ratio of chlorpheniramine against histamine, 8: 1 instead of 4:1. Studies specifically designed to determine the behavior of bronchial receptors in asthma are urgently needed. Our present data suggest that with the limitations imposed by human experiments, such a study is feasible. ACKNOWLEDGMENT: We gratefully acknowledge the help with statistical analysis given by Mohan Garg and L. Johnson. Dr. M. Spangenberg, Schering Corporation, kindly provided the chlorpheniramine maleate (Chlortrimeton) ·

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INHALATION TESTS IN ALLERGIC ASTHMA 449

chial asthma. J Allerg Coo ImmunoI1977; 60:312-316 6 Bhat KN, Arroyave CM, Marney SR, et al: Plasma histamine changes during provoked bronchospasm in asthmatic patients. J Allerg Clin Immunol 1976; 58:647656 7 Curry JJ: The effect of antihistamine substances and other drugs on histamine bronchoconstriction in asthmatic subjects. J Clin Invest 1946; 25:792-799 8 Feinberg SM, Malkiel S, Feinberg AR: The antihistamines: their clinical application. Chicago: Year Book Medical Publishers Inc, 1950 9 Schiller IW, Lowell FC: The effect of drugs in modifying the response of asthmatic subjects to inhalation of pollen extracts determined by vital capacity measurements. Ann Allerg 1947; 5:564-569 10 Collins J, Dundas E, Edgar H, et al: Graded response of experimental skin wheal and its suppression by chlorpromazine and antihistamines. J Allergy 1960; 31:387394 11 Cirillo VJ, Tempero KF: Pharmacology and therapeutic use of antihistamines. Am J Hosp Pharmacol 1976; 33: 1200-1207 12 Herxheimer H: Bronchoconstrictor agents and their antagonists in the intact guinea pig. Arch Intern Pharmacodyn 1956; 106:371-380 13 Popa V: Bronchodilating activity of an blocker, chIorpheniramine. J Allerg Clin Immunoll977; 59:54-63 14 Booij-Noord H, Orie NGM, Berg W, et al: Protection tests on bronchial allergen challenge with disodium cromoglycate and thiazinamium. J Allerg 1970; 46:111120 15 Herxheimer H: Antihistamines in bronchial asthma. Br Med J 1949; 4:901-905 16 Nakazawa T, Toyoda T, Furukawa M, et at: Inhibitory effects of various drugs on dual asthmatic responses in wheat Bour-sensitive subjects. J Allerg Clin Immunol 1976; 58:1-9 17 Woenne K, Rattan M, Orange RP, et at: Bronchial hyperreactivity to histamine and methacholine in asthmatic children after inhalation of SCH 1000 and chlorpheniramine maleate. J Anergy Clin ImmunoI1978; 62:110-124 18 Nogrady SG, Hartley JPR, Handslip POJ, et al: Bronchodilation following inhalation of the antihistamine clemastine. Thorax 1978; 3S:479-482 19 Pandit PR, Kulkarni SO, Jogleker AY: Study on the relationship between antihistamine, anticholinergic and central depressant properties of various antihistamines. Indian J Mel Sci 1973; 27 :920-929 20 Ciba Guest Symposium Report: Terminology, definitions, and classmcation of chronic pulmonary emphysema and related conditions. Thorax 1959; 14:286-294 21 Knudson RJ, Lebowitz f"C, Burrows B: The maximal expiratory Bow-volume curve. Am Rev Respir Dis 1975; 113:587-595 22 Domizi DB, Earle RH: On line pulmonary function analysis: Program design. OECUS Proceedings, 1970; Fall: 19-23 23 Popa V, Teculescu 0, Stanescu 0, et al: The value of inhalation tests in the etiological diagnosis of perennial bronchial asthma. J Allergy 1968; 42:130-132 24 Chai H, Farr RS, Froelich LA, et at: Standardization of bronchial inhalation challenge procedures. J Allergy Clin Lrrununol 1975; 56:323-327 25 TiHeneau, R: Pharmacodynamie du poumon asthmatique. Sem Hop (Pathologie et Biologie) 1957; 33:59-71 26 Popa V: Deux difficulte des tests de provocation bron-

"1

450 VALENTIN T. PUPA

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preferential deposition of histamine in the human airway. Am Rev Respir Dis 1978; 117:485-492 Crompton GK: A comparison of responses to bronchodilator drugs in chronic bronchitis and chronic $8thma. Thorax 1968; 23:46-51 ', Peets EA, Jackson M, Symchowicz S: Metabolism of chlorpheniramine maleate in man. J Pharmacol Exp Ther 1972; 180:464-474 KaIser SC: The fate of atropine in man. Ann NY Acad Sci 1971; 179:667~ Altounyan REC: Variation of drug action of airway obstruction in man. Thorax 1964; 16:406-410 Casterline CL, Evans R: Further studies on the mechanism of human histamine-induced asthma. J ABerg Clin lrrununoI1977;59:420-424 Arunlakshana 0, Schild HO: Some quantitative uses of

drug antagonists. Br J Pharmacol 1959; 14:48-63 52 Tozzi S, Roth EE, Tabachnik ITA: The pharmacology of azatadine, a potential antiallergy drug. Agents and Actions 1974; 14:264-270 53 Douglas JS, Ridgway P, Brink C: Airway responses of the guinea pig in vivo and in vitro. J Pharmacal Exp Ther 1977;202:116-124 54 Rosenthal RR, Norman PS, Summer WR, et al: The role of parasympathetic system in antigen-induced bronchospasm. J Appl Physioll977; 42:600-608 55 Douglas JS, Dennis MW, Ridgway P, et al: Airway constriction in guinea-pigs: interaction of histamine with autonomic drugs. J Pharmacol Exp Ther 1973; 184:169179 56 Waud DR: Pharmacological receptors. Pharmacol Rev 1968; 20:49-88

Harvard Medical School Courses The Department of Radiology, Peter Bent Brigham Hospital, Harvard Medical School,

will present the course "Chest Disease, 1980: An Interdisciplinary Approach with Em-

phasis on Radiology," at the Hyatt Regency Hotel, Cambridge, October 20-24. Contact: Peter G. Herman, M.D., Department of Radiology, Harvard Medical School, 25 Shattuck Street, Boston 02115. The Department of Radiology, The Children's Hospital Medical Center, Harvard Medical School, will present the course, "Pediatric Radiology" November 3-5 at the Hyatt Regency Hotel, Cambridge. Contact: Robert L. Lebowitz, M.D., Department of Radiology, Children's Hospital Medical Center, 300 Longwood Avenue, Boston 02115.

University of Miami School of Medicine Courses The University of Miami School of Medicine, Department of Medicine, Division of General Medicine, will present the following courses: "Emergencies in Internal Medicine,n November 2-7, Sheraton Bal Harbour Hotel, Miami Beach; and cCAdvanced Cardiac Life Support" November 7-10, as a Nassau cruise. For information: Division of Continuing Education D23-3, PO Box 016960, Miami, Florida 33101.

CHEST, 78: 3, SEPTEMBER, 1980

INHALATION TESTS IN ALLERGIC ASTHMA 451