Utilization of Anti-asthma Medications in Two Quebec Populations of Anti-asthma Medication Users: A Prescription Database Analysis

Utilization of Anti-asthma Medications in Two Quebec Populations of Anti-asthma Medication Users: A Prescription Database Analysis

Claudine Laurier, Wendy Kennedy, Line Gariépy, André Archambault and André-Pierre Contandriopoulos

Abstract

This study describes the utilization of anti-asthma medications in two groups of users of such medications in the province of Quebec, Canada, during the year from June 1, 1990, to May 31, 1991. It is based on a secondary analysis of existing data banks recording the medications reimbursed by two government-funded ambulatory drug reimbursement programs that cover individuals aged 65 and over (seniors) and income security (welfare) recipients (ISRs). The study analyzed the use of the anti-asthma medications included in the list of medications eligible for reimbursement for program beneficiaries. Use was studied in two random samples of individuals who had at least one prescription filled for an anti-asthma medication (2566 seniors and 3695 ISRs). The most commonly used medication in both groups was inhaled salbutamol 100 mcg. Various forms of theophylline tablets were also used by a high proportion of the sample studied. Over 75% of the seniors and 68% of the ISR group used at least one form of theophylline during the course of the year. Inhaled corticosteroids were used by 43% of the seniors and by 36% of the ISR group, and sympathomimetics (ß2-agonists), by 63% of seniors and 68% of ISRs.

Key words: Asthma; drug therapy; drug utilization; pharmacoepidemiology; Quebec

Introduction

Anti-asthma medications, mainly bronchodilators, anti-inflammatory medications and theophylline, are used in the treatment of individuals with chronic bronchitis or emphysema (also referred to as chronic obstructive pulmonary disease or COPD) as well as those with asthma. For reasons including disease classification and the difficulty of accurate diagnosis (particularly in older persons), there are problems in measuring the prevalence of these diseases.^1-4 However, some estimates are available.

Asthma prevalence estimates of between 5% and 10% have often been used,^5,6 and it has been estimated that COPD is seen in 1-3% of females and in 4-6% of males.³The 1987 Santé Québec population survey measured the self-reported prevalence of asthma, bronchitis and emphysema (as one comprehensive category) as 3.9% in the general Quebec population.⁷

With these relatively high rates of disease, there is an accompanying high use of the medications to treat them. In 1985, more than 3% of the prescriptions filled in community pharmacies in the US were for medications with an indication in the treatment of asthma or COPD. The increase in the number of prescriptions for these medications from 1972 to 1985 was in the order of 200%, in contrast to an increase of just 7% for all other types of medication.⁸ In Canada, the increase in prescriptions for all airway medications was 38% from 1985 to 1990. ⁹ A recent study in Saskatchewan found that the number of persons using anti-asthma drugs rose from an average of 33 per 1000 in 1989 to 47 per 1000 in 1993.¹⁰

A cross-sectional study (one day per month) of airway drug prescriptions recorded in 1990 by a random sample of Canadian physicians showed that 18% of the patients had been prescribed an inhaled corticosteroid; 49%, an inhaled ß2-agonist; and 24%, a theophylline product.⁹ This study, however, did not follow the patients' utilization of medications over time.

The objective of the current study was to examine the use of medications by a selected sample of airway drug users over a relatively extended time period, and this article reports the patterns of use for a 12-month period, from June 1, 1990, to May 31, 1991.

Methods

Source of Information

An analysis of the use of prescribed anti-asthmatic medications was performed using information from the medications database of the Régie de l'assurance-maladie du Québec (RAMQ). In essence, this database contains the pharmacy billing information for the prescribed drugs and pharmaceutical services provided for the two groups covered by the Quebec ambulatory drug reimbursement programs: individuals aged 65 years and older (seniors) and income security (welfare) recipients (ISRs).

Identification of Sample

The study considered individuals who were eligible for the drug plans over the entire study period (June 1, 1988 to May 31, 1992) and who received at least one prescription between June 1 and October 30, 1990, for any of the anti-asthma medications reimbursed at that time. Because they are not specific for asthma or COPD, oral corticosteroids were not used as inclusion criteria. The medications studied and the manner in which they were grouped for the various analyses are illustrated in Figure 1.

Among seniors,^a 51,327 met the inclusion criteria, and a random 5% sampling resulted in a sample size of 2566. A random 20% sample from the 18,475 eligible ISRs identified produced a sample of 3695 individuals.

_{(^a Since seniors had to be 65 or older in 1988 to
be eligible for the study, the analysis is based on individuals aged
67 or more in 1990/91.)}

For both groups, we analyzed use of the selected prescribed drugs during the period from June 1, 1990, to May 31, 1991.

To ensure that the analysis was not overly biased by the inclusion of persons whose medication use was cut short because of their departure from the province during the study year, we eliminated from the sample individuals who received no prescription (of any type, not just anti-asthmatic medication) during the last four months of the year. This criterion also eliminated very occasional users of prescribed medications. The resulting final sample consisted of 2363 seniors and 3266 ISRs.

Analysis

The analysis examined the proportion of persons (users) receiving prescriptions for various anti-asthma medications during the one-year period and the average number of prescriptions per user. Individual medications were grouped into classes (see Figure 1), and the proportion of users was analyzed according to age, sex and geographic region of residence. In addition, users of certain combinations of medications were analyzed. The relationship between demographic variables and the proportion of users was examined using the Pearson chi-squared test, and results were deemed significant at a level of p < 0.05.

We estimated the proportion of ambulatory users of anti-asthma medications in the population aged 67 and older by comparing the number of seniors identified in the database who received an anti-asthma medication to the population of Quebec aged 67 and older in 1990. b This can only be a rough estimate since the calendar year and the fiscal year of the Régie are not the same and because some individuals were institutionalized and thus did not consume their medications on an ambulatory basis.

_{( ^b Population statistics used were those individuals
in Quebec who were eligible for the health programs in 1990, published
by five-year age groups. To arrive at age groups of 67-76 and 77 and
over, the age and sex proportions of the 1991 Census data for Quebec
were applied (Statistics Canada, Cat 93-310).)}

Volume 18, No.1 -1997 [Table of Contents]		Utilization of Anti-asthma Medications in Two Quebec Populations of Anti-asthma Medication Users: A Prescription Database Analysis Claudine Laurier, Wendy Kennedy, Line Gariépy, André Archambault and André-Pierre Contandriopoulos Abstract This study describes the utilization of anti-asthma medications in two groups of users of such medications in the province of Quebec, Canada, during the year from June 1, 1990, to May 31, 1991. It is based on a secondary analysis of existing data banks recording the medications reimbursed by two government-funded ambulatory drug reimbursement programs that cover individuals aged 65 and over (seniors) and income security (welfare) recipients (ISRs). The study analyzed the use of the anti-asthma medications included in the list of medications eligible for reimbursement for program beneficiaries. Use was studied in two random samples of individuals who had at least one prescription filled for an anti-asthma medication (2566 seniors and 3695 ISRs). The most commonly used medication in both groups was inhaled salbutamol 100 mcg. Various forms of theophylline tablets were also used by a high proportion of the sample studied. Over 75% of the seniors and 68% of the ISR group used at least one form of theophylline during the course of the year. Inhaled corticosteroids were used by 43% of the seniors and by 36% of the ISR group, and sympathomimetics (ß2-agonists), by 63% of seniors and 68% of ISRs. Key words: Asthma; drug therapy; drug utilization; pharmacoepidemiology; Quebec Introduction Anti-asthma medications, mainly bronchodilators, anti-inflammatory medications and theophylline, are used in the treatment of individuals with chronic bronchitis or emphysema (also referred to as chronic obstructive pulmonary disease or COPD) as well as those with asthma. For reasons including disease classification and the difficulty of accurate diagnosis (particularly in older persons), there are problems in measuring the prevalence of these diseases.^1-4 However, some estimates are available. Asthma prevalence estimates of between 5% and 10% have often been used,^5,6 and it has been estimated that COPD is seen in 1-3% of females and in 4-6% of males.³The 1987 Santé Québec population survey measured the self-reported prevalence of asthma, bronchitis and emphysema (as one comprehensive category) as 3.9% in the general Quebec population.⁷ With these relatively high rates of disease, there is an accompanying high use of the medications to treat them. In 1985, more than 3% of the prescriptions filled in community pharmacies in the US were for medications with an indication in the treatment of asthma or COPD. The increase in the number of prescriptions for these medications from 1972 to 1985 was in the order of 200%, in contrast to an increase of just 7% for all other types of medication.⁸ In Canada, the increase in prescriptions for all airway medications was 38% from 1985 to 1990. ⁹ A recent study in Saskatchewan found that the number of persons using anti-asthma drugs rose from an average of 33 per 1000 in 1989 to 47 per 1000 in 1993.¹⁰ A cross-sectional study (one day per month) of airway drug prescriptions recorded in 1990 by a random sample of Canadian physicians showed that 18% of the patients had been prescribed an inhaled corticosteroid; 49%, an inhaled ß2-agonist; and 24%, a theophylline product.⁹ This study, however, did not follow the patients' utilization of medications over time. The objective of the current study was to examine the use of medications by a selected sample of airway drug users over a relatively extended time period, and this article reports the patterns of use for a 12-month period, from June 1, 1990, to May 31, 1991. Methods Source of Information An analysis of the use of prescribed anti-asthmatic medications was performed using information from the medications database of the Régie de l'assurance-maladie du Québec (RAMQ). In essence, this database contains the pharmacy billing information for the prescribed drugs and pharmaceutical services provided for the two groups covered by the Quebec ambulatory drug reimbursement programs: individuals aged 65 years and older (seniors) and income security (welfare) recipients (ISRs). Identification of Sample The study considered individuals who were eligible for the drug plans over the entire study period (June 1, 1988 to May 31, 1992) and who received at least one prescription between June 1 and October 30, 1990, for any of the anti-asthma medications reimbursed at that time. Because they are not specific for asthma or COPD, oral corticosteroids were not used as inclusion criteria. The medications studied and the manner in which they were grouped for the various analyses are illustrated in Figure 1. Among seniors,^a 51,327 met the inclusion criteria, and a random 5% sampling resulted in a sample size of 2566. A random 20% sample from the 18,475 eligible ISRs identified produced a sample of 3695 individuals. _{(^a Since seniors had to be 65 or older in 1988 to be eligible for the study, the analysis is based on individuals aged 67 or more in 1990/91.)} For both groups, we analyzed use of the selected prescribed drugs during the period from June 1, 1990, to May 31, 1991. To ensure that the analysis was not overly biased by the inclusion of persons whose medication use was cut short because of their departure from the province during the study year, we eliminated from the sample individuals who received no prescription (of any type, not just anti-asthmatic medication) during the last four months of the year. This criterion also eliminated very occasional users of prescribed medications. The resulting final sample consisted of 2363 seniors and 3266 ISRs. Analysis The analysis examined the proportion of persons (users) receiving prescriptions for various anti-asthma medications during the one-year period and the average number of prescriptions per user. Individual medications were grouped into classes (see Figure 1), and the proportion of users was analyzed according to age, sex and geographic region of residence. In addition, users of certain combinations of medications were analyzed. The relationship between demographic variables and the proportion of users was examined using the Pearson chi-squared test, and results were deemed significant at a level of p < 0.05. We estimated the proportion of ambulatory users of anti-asthma medications in the population aged 67 and older by comparing the number of seniors identified in the database who received an anti-asthma medication to the population of Quebec aged 67 and older in 1990. b This can only be a rough estimate since the calendar year and the fiscal year of the Régie are not the same and because some individuals were institutionalized and thus did not consume their medications on an ambulatory basis. _{( ^b Population statistics used were those individuals in Quebec who were eligible for the health programs in 1990, published by five-year age groups. To arrive at age groups of 67-76 and 77 and over, the age and sex proportions of the 1991 Census data for Quebec were applied (Statistics Canada, Cat 93-310).)}

		Results Table 1 reports the age and sex breakdown of the samples studied. We estimated that 8.0% (51,537/641,345) of the 1990 Quebec population aged 67 and over received an anti-asthma medication in an ambulatory setting during the index period. This estimated proportion does not vary for the two age subgroups of seniors (67-76 and 77+); however, it is higher among senior men (11.0%) than senior women (6.1%). We were unable to make the same estimate using the ISR population because we did not have information on the number of persons in the population who were income security recipients for the whole period of four years. Table 2 presents results for those medications used by at least 5% of the sample of users, together with the mean number of prescriptions per user. The most frequently used medications were very similar among the two groups. Among the seniors, the most commonly used medication was salbutamol 100 mcg, used by 46% in 1990/91. There was also a high proportion (over 10%) of users of various forms of long-acting theophylline tablets: 300 mg (27%) and 200 mg (23%); one form of theophylline liquid: 80 mg/15 ml (13%); two forms of beclomethasone: 0.05 mg (24%) and 0.25 mg (16%); and ipratropium 0.02 mg (18%). Among the ISR group, salbutamol 100 mcg was also the most commonly used medication (40%). There was high usage of the 0.05 mg form of beclomethasone (20%) as well as the 0.25 mg form (11%); orciprenaline 2 mg/ml liquid (11%); two of the long-acting forms of theophylline: 200 mg (12%) and 300 mg (25%); and one of the liquid forms of theophylline: 80 mg/15 ml (14%). About 30% of the seniors and 25% of the ISRs received three or more prescriptions of inhaled salbutamol 100 mcg. Since a canister holds 200 doses, these patients probably were taking at least 600 doses during the year, enough for daily use. Results of the analysis of the use of classes of medications appear in Table 3 along with results of the Pearson chi-squared test on the variable of sex. Over three quarters of the seniors and over two thirds of the ISR group used at least one form of theophylline during the 1990/91 study period. Inhaled corticosteroids were used by 43% of the seniors and by 36% of the ISRs; inhaled sympathomimetics (ß2-agonists), 60% of seniors and 58% of ISRs; oral sympathomimetics, 7% of seniors and 17% of ISRs; ipratropium, 19% of seniors and 10% of ISRs; and cromoglycate, less than 1% of seniors and 3% of ISRs. Percentage of use varied significantly according to the user's sex in both sample groups, but not for the same medication groups nor in the same way. Proportionately more male than female seniors used ipratroprium and theophyllines, and more senior women than men used inhaled sympathomimetics. In the ISR group, proportionately more women than men used inhaled corticosteroids, and a smaller proportion of the women than of the men used cromoglycate and oral sympathomimetics.



		Table 4 summarizes the results of the analysis of the distribution of use within classes of medications for different age groups. Proportional use in the seniors group does not vary significantly according to age with one exception. In the case of theophyllines, the proportion of younger senior users was somewhat lower (74%) than the proportion of older seniors (78%). Proportional use of all classes of anti-asthma medications in the ISR group varies significantly according to age. Region of residence^c (not shown) was not found to be significant for the percentage of senior users in any of the medication classes and only for theophyllines among ISR users, who used them less often in the Quebec region (66%) than in the Montreal (70%) and other (72%) regions. However, among ISRs, the influence of region on use of cromoglycate and inhaled corticosteroids approached the significance level at ^p = 0.06 and ^p = 0.08, respectively. The Quebec region again showed lower use (2%) of cromoglycate than did the other two regions (4% and 5%, respectively), but higher use of inhaled corticosteroids (38% in contrast to 35% and 33%). _{( ^c Regions were regrouped according to the following: Quebec region (Bas St Laurent, Îles-de-la-Madeleine, Saguenay, Lac St-Jean, Nord du Québec, Trois-Rivières, Québec, Chaudière-Appalaches), Montreal region (Montréal-Centre, Laval, Laurentides, Lanaudiere, Montérégie) and other regions (Estrie, Outaouais, Abitibi-Temiscamingue, Côte-Nord, Nouveau-Québec).)} The proportions of users of selected combinations of medications are provided in Table 5 according to the user's sex. Variation between sexes was significant in seniors for those receiving at least one prescription each of an inhaled sympathomimetic, an inhaled corticosteroid of low strength and a long-acting form of theophylline, and for those receiving at least one prescription each of an inhaled sympathomimetic, an inhaled corticosteroid, a long-acting form of theophylline and an ipratropium. In both cases, the percentage of users was higher for men (14.9% and 9.9%, respectively) than for women (11.4% and 5.7%). In the ISR group, more women (37.6%) than men (27.9%) received at least one prescription each of an inhaled sympathomimetic and any strength of inhaled corticosteroid, and more women (18.3%) than men (14.3%) had at least one prescription each of an inhaled sympathomimetic and a high-strength inhaled corticosteroid. Table 6 presents the difference in proportions of users for combinations of medications according to age group. Among seniors, there was only one combination in which a significant variation by age group was found: persons receiving at least one prescription each of an inhaled sympathomimetic and any strength of an inhaled corticosteroid. The percentages of users of all the selected anti-asthma medication combinations in the ISR group varied significantly according to age. Combinations tended to be less frequent among younger children. Region of residence (not shown) had a significant influence on seniors' use of the combination of an inhaled sympathomimetic, an inhaled high-strength corticosteroid and a long-acting form of theophylline, with higher use in the Montreal region (15.0%) than in the Quebec (11.6%) or other (10.0%) regions. Region also significantly influenced ISRs' combined use of an inhaled sympathomimetic and an inhaled corticosteroid, both high-strength and any strength. For these combinations, the Quebec region (19.5% and 33.1%, respectively) showed higher use thanthe Montreal (15.5% and 28.3%) or other (15.6% and 31.8%) regions.

		Discussion The data reflect the acquisition, delivery and reimbursement of anti-asthma medications for the beneficiaries of two public ambulatory drug plans. These data can be assumed to be relatively complete because full reimbursement (there was no copayment provision at this time) was an incentive for the beneficiaries to obtain all their prescription medications through the drug plans. Although no conclusions can be drawn with respect to the actual use of the medications, reimbursed prescriptions serve as an indicator of use and certainly as a measure of dispensing. Therefore, although our analysis discusses the proportions of users of different medications, we cannot infer actual consumption behaviour. Because this study looked at percentage of use over a one-year period, the results are higher than those of a cross-sectional sample of anti-asthmatic medication users in Canada in 1990 that found inhaled ß2-agonist use was 49% and inhaled corticosteroid use was 18%.⁹ It is to be expected that the age of the user would be related to differences in proportions of users in the ISR group (which includes children and younger and middle-aged adults), whereas it is less important in the seniors group. This variation in use associated with age has been observed in previous studies.^11,12 Studies of use of health resources^12,13 and of asthma incidence or prevalence^11,14 have also shown differences in medication use associated with sex. In our study, sex often had a significant influence on the observed utilization, whether within classes of medications or combinations of medications; this occurred in both the seniors and the ISR groups. The variation by sex in proportionate use of inhaled corticosteroids continued to appear among the ISRs when the use of these drugs was examined in combination with use of inhaled sympathomimetics; this seems to be explained mainly by those individuals using higher-strength inhaled corticosteroids. Even though the groups studied here include patients with COPD as well as those with asthma, it may be useful to compare the use patterns here with guidelines for the treatment of asthma, particularly among ISRs, which would tend to exclude COPD sufferers (especially those under age 42). The combinations of medications may illustrate what proportion of these individuals are treated with the anti-asthma medication regimens recommended by guidelines developed in 1989 by a Canadian consensus group and more recently rediscussed.¹⁵ These guidelines involve four levels of asthma severity. Level 1: Inhaled ß2-agonist as needed +/- cromoglycate Level 2: Level 1 + maintenance treatment with cromoglycate or low-dose levels of inhaled corticosteroid Level 3: Level 1 + maintenance treatment with higher-dose inhaled corticosteroid +/- trial with a long-acting theophylline or a long-acting ß2-agonist as adjunct treatment +/- inhaled ipratropium Level 4: Level 3 + oral prednisone This study did not examine the use of oral corticosteroids, but we can see that the combination of inhaled sympathomimetic and low-strength corticosteroid could correspond with the second level of asthma severity, and the use of inhaled sympathomimetic and high-strength inhaled corticosteroid with or without theophylline compares with Level 3. Based on this, we estimate that 18% of the ISRs were treated in accordance with Level 2 severity. However, a proportion of those were treated more in accordance with a Level 3 severity regimen because a large proportion of them (60%) received an additional long-acting theophylline. This may mean that instead of increasing the strength of the inhaled corticosteroid, doses of the same strength of the medication were increased or else long-acting theophylline was added in preference to increasing corticosteroid dose. This could also reflect the anterior use of a theophylline to which corticosteroids were added, or for which they were substituted during the year. Seventeen percent of the ISRs appeared to be treated in accordance with Level 3 (of inhaled ß2-agonist and high-strength corticosteroid), of which a portion received the additional treatment of a long-acting theophylline, resulting in use by 10% of the ISRs. About 27% of the ISRs seem to have used inhaled sympathomimetics without receiving inhaled corticosteroids in the same year. Some of the data on combinations of use may not reflect use at any one time, as the data cover a period of 12 months. Therefore, the combinations of different medications used may reflect the evolution of or change in treatment patterns occurring during this time. In particular, the use of inhaled sympathomimetics in combination with inhaled corticosteroids of any strength was estimated to be 37% among seniors and 30% among ISRs. If one adds the proportionate use of a combination of sympathomimetic and either strength of inhaled corticosteroid, the sum is 43% for seniors and 35% for ISRs, respectively reflecting 6% and 5% use of more than one strength of inhaled corticosteroid. There could be patients receiving more than one corticosteroid at any one time, but the more likely explanation is a change over the period analyzed. The nature of the populations studied limits the generalizability of this study, in that the use patterns do not necessarily reflect what is currently being used by the younger or working populations in Quebec. However, this study of use of anti-asthma medications could be seen as relatively representative of the Quebec population aged 65 and older who have been diagnosed as asthmatic and/or suffering from COPD and who received a medication for their condition. The individuals who are either undiagnosed or need very little treatment would not be included. The income security recipients are less likely to be representative of the overall population under 65 years of age, as this group is more likely to suffer from illnesses than the overall population. Moreover, only ISRs who were eligible for an entire four-year period were considered, which would further restrict their representativeness. Acknowledgements We would like to thank Glaxo Canada, who partly funded the project, and Mrs M Paré, for her invaluable assistance. _{Author References Claudine Laurier, Faculté de pharmacie, Université de Montréal, CP 6128, succ. Centre-ville, Montréal (Québec) H3C 3T4; and Groupe de recherche interdisciplinaire en santé, Université de Montréal Wendy Kennedy, Faculté de pharmacie, Université de Montréal; and Groupe de recherche interdisciplinaire en santé, Université de Montréal; and Centre québécois d'excellence en santé respiratoire, Hôpital du Sacré-Coeur, Montreal, Quebec Line Gariépy, Faculté de pharmacie, Université de Montréal; and Conseil d'Évaluation de Technologie de Santé de Québec, Montreal, Quebec André Archambault, Faculté de Pharmacie, Université de Montréal André-Pierre Contandriopoulos, Groupe de recherche interdisciplinaire en santé; and Département d'administration de santé, Université de Montréal} References 1. Bates DV. Respiratory function in disease. 3rd ed. Montreal: WB Saunders Co, 1989. 2. Society AT. Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease (COPD) and asthma. Am Rev Respir Dis 1987;136:225-44. 3. Society AT. Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1995;152:S77-S120. 4. Woolcock AJ. Worldwide trends in asthma morbidity and mortality. Explanation of trends. Bull Int Union Tuberc Lung Dis 1991;66(2-3):85-9. 5. MacKenzie CA, Tsanakas J, Tabachnik E, et al. An open study to assess the long-term safety of fluticasone propionate in asthmatic children. International Study Group. Br J Clin Pract 1994;48(1):15-8. 6. Jenkins MA, Hurley SF, Bowes G, McNeil JJ. Use of antiasthmatic drugs in Australia. Med J Aust 1990;153:323-8. 7. Émond A, Guyon L, Camirand F, Chenard L, Pineault R, Robitaille Y. Et la santé, ça va? Tome 1, Rapport de l'enquête Santé Québec 1987. Quebec: Publications du Québec, 1988. 8. Bosco LA, Knapp DE, Gerstman B, CF G. Asthma drug therapy trends in the United States, 1972 to 1985. J Allergy Clin Immunol 1987;80:398-402. 9. Kesten S, Rebuck AS, Chapman KR. Trends in asthma and chronic obstructive pulmonary disease therapy in Canada, 1985 to 1990. J Allergy Clin Immunol 1993;92(4):499-506. 10. Habbick B, Baker MJ, McNutt M, Cockcroft DW. Recent trends in the use of inhaled B2-adrenergic agonists and inhaled corticosteroids in Saskatchewan. Can Med Assoc J 1995;153(10):1437-43. 11. Gerstman BB, Bosco LA, Tomita DK, Gross TP, Shaw MM. Prevalence and treatment of asthma in the Michigan Medicaid population younger than 45 years, 1980-1986. J Allergy Clin Immunol 1989;83:1032-9. 12. Bosco LA, Gerstman BB, Tomita OK. Variations in the use of medication for the treatment of childhood asthma in the Michigan Medicaid population, 1980 to 1986. Chest 1993;104(6):1727-32. 13. Leufkens HG, Urquhart J. Variability in patterns of drug usage. J Pharm Pharmacol 1994;46 Suppl 1:433-7. 14. Svenson LW, Woodhead SE, Platt GH. Estimating the prevalence of asthma in Alberta: a study using provincial health care records. Chronic Dis Can 1993;14(2)28-33. 15. Clark T. Mise à jour sur les recommandations du consensus. Le clinicien 1994 nov; Suppl:7-11. [Previous][Table of Contents] [Next]


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