Original Article | Published:

Oral magnesium supplementation in asthmatic children: a double-blind randomized placebo-controlled trial

European Journal of Clinical Nutrition volume 61, pages 5460 (2007) | Download Citation

Guarantors: C Gontijo-Amaral and JD Ribeiro.

Contributors: CG-A conceived the idea and was responsible for study design, execution, data analysis and preparation of the paper. JDR coordinated and supervised the clinical trial. AC-N assisted with preparation of the paper and data analysis. LSCG assisted with preparation of the paper. MAGOR helped to perform pulmonary function tests.

Subjects

Abstract

Objective:

To investigate the long-term effect of oral magnesium supplementation on clinical symptoms, bronchial reactivity, lung function and allergen-induced skin responses in children and adolescents with moderate persistent asthma.

Design:

A double-blind randomized parallel placebo-controlled study.

Setting and subjects:

The patients were recruited from the Pediatric Outpatient Clinic, Division of Pulmonology, Allergy and Immunology, and followed at the Center for Investigation in Pediatrics at State University of Campinas Hospital, Brazil. Thirty-seven out of 72 patients met the study criteria. There were no dropouts.

Intervention:

The 37 patients (aged 7–19 years, 19 males) were randomized in two groups: magnesium (n=18, 300 mg/day) and placebo (n=19), during 2 months. Both patient groups received inhaled fluticasone (250 μg twice a day) and salbutamol as needed. The primary outcome was bronchial reactivity evaluated with methacholine challenge test (PC20).

Results:

After a follow-up of 2 months, the methacholine PC20 for testing bronchial reactivity has augmented significantly in the magnesium group only. The skin responses to recognized antigens have also decreased in patients treated with magnesium. The forced vital capacity (FVC), the forced expiratory volume at first second (FEV1), the forced expiratory flow at 25–75 and the FEV1/FVC ratio were similar in both groups. The magnesium group presented fewer asthma exacerbations and used less salbutamol compared to the placebo group.

Conclusions:

Oral magnesium supplementation helped to reduce bronchial reactivity to methacholine, to diminish their allergen-induced skin responses and to provide better symptom control in pediatric patients with moderate persistent asthma treated with inhaled fluticasone.

Introduction

Magnesium is naturally obtained from whole seeds, grains, nuts and vegetables. However, it is mostly lost after food processing (National Research Council (US), 1989). Recent reports show that before industrialization, magnesium intake was estimated in 475–500 mg/day (Altura and Altura, 1991–92). However, it has declined substantially during the last century. Current dietary surveys show that the average magnesium intake in Western countries is often below the Recommended Drug Allowance (280 and 350 mg/day, respectively, for female and male adults) (National Research Council (US), 1989; USDA, 1990). Asthma prevalence has increased dramatically over the last 50 years (Chadwick and Cardew, 1997). Epidemiological evidence indicates that low magnesium intake is associated with airway hyper-reactivity and self-reported wheezing (Britton et al., 1994; Soutar et al., 1997).

Trendelenburg first recognized the potential bronchodilator effect of magnesium in 1912, when he observed bronchial smooth-muscle relaxation in cows, after magnesium administration. Rosello and Pla originally demonstrated, in 1936, a bronchodilator effect of magnesium in asthmatic patients. In vitro studies showed the relaxant effect of magnesium on vascular (Altura et al., 1984) and bronchial (Spivey et al., 1990) tones.

The mechanism for a beneficial effect of magnesium on pulmonary function is not completely clear. It is apparently brought by competition with calcium entry through voltage- and receptor-operated calcium channels, as well as by inhibition of intracellular calcium release (Saris et al., 2000). However, inhibition of cholinergic transmission (Del Castillo and Engbaek, 1954), stimulation of nitric oxide (Kemp et al., 1994) and prostacyclin (Nadler et al., 1987) synthesis, and stabilization of mast cells and T-lymphocytes (Bois, 1963) can also contribute, at least in part, for the beneficial effect of magnesium in asthma.

Intravenous (Noppen et al., 1990; Ciarallo et al., 1996; Silverman et al., 2002) or inhaled magnesium (Plaisance et al., 1994) has been shown to be beneficial for the control of acute asthma in adults and children. There are two studies about oral magnesium supplementation in adult patients. The first of them, performed by Hill et al. in 1997, shows that short-term change in dietary magnesium improves the clinical symptoms but not the lung function tests in adult with asthma. The second study, published in 2003 by Fogarty et al. showed that magnesium had no effect in adults with asthma. To date, the effect of oral magnesium in children with chronic persistent asthma has not been evaluated yet.

The aim of this study was to investigate the effect of magnesium given as oral supplementation on the control of asthma symptoms, bronchial reactivity, lung function and allergen-induced skin responses in children and adolescents with moderate persistent asthma treated with inhaled fluticasone. We hypothesized that magnesium given as oral supplementation can help to control chronic persistent asthma in children.

Materials and methods

Subjects and study design

Thirty-seven children and adolescents (19 males, 18 females; 35 Caucasians, 2 Blacks; age 7–19 years; height 117–173 cm; and weight 20–60 kg) were included. The patients were recruited from Pediatric Outpatient Clinic, Division of Pulmonology, Allergy and Immunology, and followed at the Center for Investigation in Pediatrics at State University of Campinas Hospital, Brazil. The inclusion criteria were as follows: patients with clinical history of recurrent and reversible symptoms of airway obstruction, high serum IgE levels, positive skin tests to at least one of the tested recognized allergens and family history of allergy. All of them had persistent moderate atopic asthma, diagnosed in accordance to the current Global Initiative for Asthma (GINA) criteria. (NIH Publication No. 02-3659) (National Institutes of Health, 2002).

None of the patients had received systemic steroids, theophylline, leukotriene modifiers or oral beta2-adrenergic agents, for at least 1 month before the study. None was taking any treatment likely to affect magnesium absorption or excretion, including diuretics, digoxine or calcium-containing medications. Smokers and patients with infections or chronic diseases were not included.

All children were using inhaled steroid as a usual procedure in moderate cases of asthma. There was a run-in period of 1 week. At this period, the patients could use inhaled salbutamol (100 μg/dose) if necessary and the inhaled steroid was switched to fluticasone (250 μg twice a day, Flixotide Diskus), before starting the protocol. We have used medications at this period owing to the ethically responsible procedures in those cases and in accordance with the current GINA criteria for moderated persistent asthma.

A double-blind randomized parallel placebo-controlled study was performed between January 2001 and December 2002. Patients were randomized into two groups: magnesium-glycine (MG, n=18) given per oral, 300 mg/day during 2 months, and placebo-control (PC, n=19). Glycine was used as placebo, so the difference between the two groups was only the presence or absence of magnesium. Both patient groups received inhaled fluticasone (250 μg twice a day). During the study period, patients used pressured metered dose inhaler containing salbutamol (100 μg/dose), if necessary.

The patients' compliance was checked fortnightly and included the revision of a diary containing information about the number of days using inhaled salbutamol and the number of days with asthma exacerbation episodes. Asthma exacerbation episodes were defined as at least one of the following clinical symptoms: wheezing, chest tightness and coughing.

The randomization, drug manipulation and dispensing were blind and carried out independently from the recruitment and assessment of participants. A pharmacist prepared capsules containing either placebo (glycine) or MG, and randomly dispensed the capsules with variations A and B. The magnesium or glycine powder presented a similar appearance. The randomization code was broken at the end of the study (Peto et al., 1976). If the patients used less than 80% of the doses/month of fluticasone or magnesium/placebo, they would be excluded.

The experimental protocol included clinical evaluation, serum dosage of magnesium, skin response to recognized antigens, lung function tests and assessment of bronchial responsiveness by methacholine challenge test. All of them performed at the beginning and after 60 days of magnesium or placebo administration. The primary outcome was bronchial reactivity evaluated with methacholine challenge test (PC20) and the secondary outcomes were asthma symptoms, lung function and allergen-induced skin responses.

Written informed consent was obtained from all patient's parents and healthy individuals before the study. The Medical School Ethics Committee approved the experimental protocol in accordance with the Brazilian Ministry of Health, Resolution 196/96.

Lung function and methacholine tests

Pulmonary function tests included the following parameters: forced vital capacity (FVC), forced expiratory volume at first second (FEV1), mid-expiratory flow at 25–75% of vital capacity (FEF25–75) and FEV1/FVC ratio. Nasal clamp was used in all patients, the parameters were recorded as the best of three blows and the room temperature was controlled at 23–25°C. Patients had not presented respiratory infections during the previous 15 days. The pulmonary function values of FVC, FEV1 and FEF25–75 were described and analyzed as percent predicted values for the study subjects. The predicted values were based on the Polgar–Promadah normal values (Polgar and Promadhat, 1971).

Methacholine challenge test was adapted and performed according to the American Thoracic Society criteria, with the provocative concentration causing a 20% fall in FEV1 (PC20) as a measure of airway responsiveness (Crapo et al., 2000). Briefly, FEV1 was measured using a dry bellows spirometer after 15 min rest in the seated position, and taking the best of three flows (CPFS/D MedGraphics; BREEZE PF Version 3.8 B for Windows 95/98/NT software). Methacholine aerosols (Sigma, code A2251, St Louis, MI, USA) were delivered from a series of De Vilbiss handheld nebulizers (646 model). Subjects inhaled doubling doses of methacholine (from 0.125 to 40 mg/ml) during rapid inspiration from functional residual capacity to total lung capacity. Subjects were asked to hold their breath for 3 s after inhalation, and then to exhale slowly for 3 s. FEV1 was measured 1 min after each inhalation. A 5-min interval was observed between inhalation of different methacholine concentrations. The challenge was interrupted when the FEV1 had fallen by 20% or more from the baseline value. PC20FEV1 was calculated by linear interpolation on a log dose–response plot. Reversion of PC20FEV1 was accomplished by inhaled salbutamol (two doses of 200 μg). FEV1 was recorded after 10 min, as the best of three blows. Methacholine challenge testing was not carried out on any subject who had an FEV1 of <70% of that predicted.

Serum dosage of magnesium

Serum dosage of magnesium was collected in all patients, before and after the study period. To dosage serum magnesium, it was used an atomic absorption method, with equipment Variant Spectra AA 250-plus.

Allergy skin tests

Allergen skin sensitivity to the most relevant antigens for southeast Brazil – Dermatophagoides pteronyssinus, Dermatophagoides farinae and Blomia tropicalis – with histamine and saline controls (IPI/ASAC, SãoPaulo, Brasil) was estimated by standard allergen skin-prick test methods, measuring the response to each allergen as the mean of two right-angled diameters, one of which was the largest measurable diameter of weal. The skin test response was recorded after 15 min and considered positive if the mean diameter of the weal was at least 3 mm, corrected for the mean diameter of negative control weal if necessary (Demoly et al., 1998). The patients were regarded as being atopic if they had one or more positive skin-prick tests. The same physician performed the prick tests between 0800 and 2400 hours, before and after the study period, using the same lot of antigens. There is no significant seasonal variation regarding inhaled antigens in this region of Brazil.

Statistical analysis

The sample size of 16 patients for each group was determined before starting the study, considering appropriate calculations for randomized clinical trials and the possibility of a type II error. The primary outcome used in designing the study was PC20FEV1 methacholine, log transformed. A mean log 10 PC20FEV1 value of 0.16 was chosen based on a study performed by Hill et al. (1997), considering a standard deviation (s.d.) of 0.57 base units and a sample error of 0.57 base units, we calculated that 16 subjects in each group would be required for 80% power at the 5% level of significance (Montgomery, 1991). Descriptive statistics was performed. The results were represented as bar graphs and tables showing the mean and s.d.

The Student's t-test was used to compare age, height, weight and body index mass. χ2 and Fisher's exact tests were used to analyze respectively sex and race. The Mann–Whitney U-test was used to compare asthma exacerbation episodes and the number of days of inhaled salbutamol use. Analysis of variance (ANOVA for repeated measures) followed by Tukey and profile tests were used to analyze pulmonary function, skin-prick test, serum dosage of magnesium and methacoline challenge test data. Methacoline challenge test, FEV1 and FVC was log transformed. P-values lower than 0.05 were considered significant (Milliken and Johnson, 1984).

Results

Thirty-seven out of 72 patients screened to participate in this study met the study criteria. There were no dropouts. No adverse effects were reported from patients in either group.

Randomization resulted in an equivalent distribution of patients regarding age, sex, race, weight, height and body mass index (BMI). These results are shown in Table 1. Both groups presented appropriate compliance.

Table 1: Demographic characteristics of asthmatic patients

Figure 1 shows that patients who received magnesium presented fewer asthma exacerbation episodes, and used less inhaled salbutamol (P<0.05 in both circumstances, Mann–Whitney test), which was not observed in the PC group.

Figure 1
Figure 1

Clinical evaluation. Asthmatic children and adolescents who received oral magnesium supplementation (MG) during 2 months presented fewer days of asthma exacerbation episodes and inhaled salbutamol compared to placebo control group (PC). (*P<0.05, Mann–Whitney test).

Table 2 presents lung function test values for both groups. After 2 months of oral magnesium supplementation or placebo, the analysis of the interaction of groups versus time data (ANOVA for repeated measure) have not shown significant changes in FVC (P=0.2383), FEV1 (P=0.1207), FEF25–75% (P=0.1267) and FEV1/FVC ratio (P=0.0857). In the analyses between groups, both presented similar FVC, FEV1, FEF25–75%, and FEV1/FVC ratio values (in all situations, Tukey's test). The comparison within groups (effect of time) showed that after 2 months of oral magnesium supplementation, the FVC, FEV1, FEF25–75% and FEV1/FVC ratio values have increased significantly in MG group patients (in all situations, profile test). In the placebo group, only the FEV1 and FEF25-75% values increased significantly during the study period (in both situations, profile test).

Table 2: Lung function tests data of patients from the MG or placebo control group during the study period: mean, s.d. and P-values of the within- (Profile test) and between- (Tukey's test) group comparisons

Figure 2 shows the methacoline test data. After 2 months of oral magnesium supplementation or placebo, a higher dose of methacoline was necessary to induce a 20% fall in the FEV1 in patients of the MG group compared to the PC group (P<0.05, Tukey's test).

Figure 2
Figure 2

Methacholine-induced bronchial challenge. After 2 months of magnesium supplementation, the dose of methacholine necessary to induce a 20% fall in the FEV1 was significantly higher in the magnesium group (MG) compared to the placebo control group (PC) (*P<0.05, Tukey's test).

At the beginning of the study, all the patients were within the normal range of magnesium. At that time, the mean serum magnesium concentration was 2.10±0.18 mg/dl in the magnesium group and 2.11±0.18 mg/dl in the placebo control group (the reference range in our laboratory is 1.58–2.55 mg/dl). After the 2 months of supplementation with magnesium or placebo, the mean serum magnesium concentration was 2.13±0.16 mg/dl in the magnesium group and 2.08±0.14 mg/dl in the placebo control group. There were no statistically significant differences in the analyses of variance (ANOVA for repeated measures) between the two groups with respect to serum magnesium levels (P=0.128).

Table 3 shows skin-prick test data (papules diameter). After 2 months of oral magnesium supplementation or placebo, the analysis of the interaction of groups versus time data (ANOVA for repeated measures) have shown significant changes in tests performed with D. peronyssinus (P=0.0012), D. farinae (P=0.0002), Blomia (P=0.0091), but not with the negative control saline (P=0.3850). In the analyses between groups, the MG group showed smaller papule diameter values (D. peronyssinus and D. farinae) compared to PC group (P<0.05 in both situations, Tukey's test). The comparison within groups (profile test) showed that after 2 months of oral magnesium supplementation, the papule diameter values for D. peronyssinus (P=0.004), D. farinae (P=0.001) and Blomia (P=0.013) values have decreased significantly in MG group patients, but not in the PC group patients.

Table 3: Skin-prick tests data for D. pteronyssinus, D. farinae and B. tropicalis with histamine (positive control) and saline (negative control) of patients from the magnesium group or placebo control group during the study period (mean and standard deviation)

Discussion

Our results showed that after 2 months, children and adolescents with moderate persistent asthma who were treated on regular basis with inhaled fluticasone and received oral magnesium supplementation presented a significant improvement in bronchial responsiveness, as assessed by the methacholine test. They presented a significant clinical improvement, as shown by a fewer number of asthma exacerbation episodes and less use of inhaled salbutamol, as well. The skin responses to recognized antigens such as D. farinae and D. pteronyssinus have also decreased in patients supplemented with magnesium.

The literature shows only two studies investigating the effect of oral magnesium, both in adults and showing conflicting results (Hill et al., 1997; Fogarty et al., 2003). To date, these two important studies about the use of oral magnesium in asthmatic patients are very different in the number of participants and duration of intervention. In the study performed by Hill et al. (1997), 17 asthmatic subjects adhered to a low magnesium diet for two periods of 3 weeks, preceded and separated by a 1-week run-in/wash-out, in which the patients took either magnesium (400 mg/day) or placebo tablet supplementation. A high magnesium intake was associated with improvement in symptom scores, although not in objective measures of airway reactivity. Taken together, the authors suggested that a more extended study period of the effect of a high magnesium intake, sustained over a longer period, was necessary to investigate the beneficial role of magnesium in asthma control in adult patients. Besides, in the study performed by Fogarty et al. (2003), 100 asthmatic patients received supplementation with magnesium (450 mg/day) during 16 weeks. There was no evidence of any beneficial effect of magnesium supplementation in these patients. The authors suggested that the most likely explanation for their findings was that their participants were already well controlled on conventional asthma medications, and under that circumstances nutrient supplementation had nothing to add.

Our study was the first performed in children and adolescents, aiming to investigate the effects of oral magnesium given on a regular basis. Up to the time of the study outline, there was no available data in children, which could be used as parameter for an improved planning, considering effective doses of magnesium, length of the treatment period and possible side or beneficial effects. Some of these aspects were, however, based on studies performed in adult patients (Britton et al., 1994; Hill et al., 1997); others were obtained on updates revision of physiological, clinical and analytical aspects of the use of magnesium in different diseases (Saris et al., 2000).

Assessment of age, weight, height, race and sex indicated that our population was homogeneous, and moreover that it presented characteristics similar to those of other studies performed in asthmatic children. Even after being randomized, all the two groups remained with similar demographic characteristics without statistically significant differences.

It is interesting to point out that only those patients who received oral magnesium presented fewer asthma exacerbation episodes and required less inhaled salbutamol. If magnesium modulates the late-phase allergic response or chronic inflammation also remains to be determined. Analyzing the clinical data, the children spent 20–25% of the study time with exacerbations. We do not believe that it must be occurred a sub-optimal treatment, once all the patients received free pressured metered dose inhaler fluticasone (Flixotide Diskus, GlaxoSmithKline, Ware, Hertfordshire, England) and the usage was checked by the physician fortnightly. Besides, another explanation was an overestimate of the asthma exacerbations, in view of the simplicity of our diary, once it would be used to the same patient and family.

In this study, we provide evidence that oral supplementation of magnesium potentially modulates the early phase allergic reaction as long as it decreases skin reactivity to recognized inhaled allergens, such as D. farinae and D. pteronyssinus. These are important allergens in southeast Brazil. To date, some reports show that magnesium inhibits mast cell activation in vitro, under specific circumstances (Bois, 1963). Future studies are necessary to test bronchial immediate response to inhaled allergens in patients who received oral magnesium supplementation. In addition, the potential use of magnesium in the treatment of atopic dermatitis and asthma remains to be determined. Particularly, magnesium has a strong relation with the immune system, in both nonspecific and specific immune response, also known as innate and acquired immune response (Tam et al., 2003).

Although the assessment of serum magnesium concentrations is not an accurate reflection of the magnesium status of muscle, bone and other tissue, it is commonly used in clinical practice. However, there is a poor correlation between serum and intracellular magnesium concentrations, most probably because only 1% of total body magnesium reserves can be found in the whole blood (Quame, 1993). This way, our results is in accordance with recent studies of serum dosage of magnesium in asthmatic patients (Fantidis et al., 1995; Zervas et al., 2000). Intracellular ionized magnesium concentration in erythrocytes, polymorphonuclear and mononuclear leukocytes have been described recently and reflect more closely skeletal, cardiac and smooth muscle magnesium concentrations (Fantidis et al., 1995; Saris et al., 2000; Zervas et al., 2000). These techniques, however, are expensive and time consuming. Because of this, it was not suitable for use in our study.

In the analyses of lung function tests, our findings were similar to those reported among adults (Hill et al., 1997), because at the end, we observed a small but not significant improvement in FEV1, FVC, FEF25–75% and FEV1/FVC ratio. A possible explanation was that both group patients were using a considerable dose of fluticasone (250 μg twice a day) and so the differences between the groups were not so evident. The analyses within groups lend some support to this interpretation. Besides, the increase in the FEV1 and FEF25–75% values, during the course of the study, for both magnesium and placebo groups, were probably because of the effect of the treatment with fluticasone. Future studies with another type of protocol are now indicated.

In this paper, we report on the decrease of bronchial reactivity to methacholine after 2 months of oral magnesium supplementation. The mechanism for this inhibitory effect of magnesium on bronchial reactivity also remains to be determined. It can be explained by possible direct effects of magnesium blocking muscharinic receptors (Del Castillo and Engbaek, 1954) or by its indirect effects, that is, the decrease of bronchial reactivity to methacholine owing to the modulation of the allergic reaction by magnesium, as evidenced in this paper by the decrease of skin reactivity of allergic patients to recognized antigens. To date, magnesium blocks calcium channels, activates sodium and calcium pumps, inhibits the calcium's interaction with myosin and diminish calcium release from sarcoplasmatic reticulum, altogether promoting a bronchial relaxant effect (Altura et al., 1984; Britton et al., 1994).

Our double-blind randomized study shows that children and adolescents with moderate persistent asthma who received inhaled fluticasone in combination with oral magnesium supplementation presented better clinical results and a decrease in both bronchial reactivity and skin reaction to recognized antigens, showing a potential and important beneficial effect of magnesium, a low-cost mineral, for the control of asthma. Future large-scale studies are necessary to assess definitely the potential role of magnesium in the general treatment of asthma in children.

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Acknowledgements

We thank the statistical advice of Helymar Machado and Cleide M Silva, Albion Laboratory for providing magnesium, GlaxoSmitKline for providing fluticasone and salbutamol and Ao-Pharmacêutico for drug manipulation. C Gontijo-Amaral was supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES. Ministry of Education, Brazil.

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  1. Department of Pediatrics and Center for Investigation in Pediatrics, State University of Campinas Medical School, Unicamp, Campinas, SP, Brazil

    • C Gontijo-Amaral
    • , M A G O Ribeiro
    • , L S C Gontijo
    • , A Condino-Neto
    •  & J D Ribeiro
  2. Department of Immunology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP, Brazil

    • A Condino-Neto

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https://doi.org/10.1038/sj.ejcn.1602475

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