Pharmacokinetics of oral theophylline in Thai asthmatic children.

Pharmacokinetic studies of theophylline were carried out in 12 Thai asthmatic children after oral administration of Elixir Quibron and Tablet Aminophylline. No significant differences in any of the pharmacokinetic parameters between these two dosage forms were observed. Peak serum concentrations of theophylline were reached in an average time of 3.16 hours (range 1.71-7.71). It was shown that the elimination half-life of theophylline in Thai asthmatic children (average 7.21 hours) was longer than that observed for subjects in western countries. Variations in elimination half-lives ranging from 4.44 to 14.34 hours were intersubject variations. Due to the slow elimination of theophylline in Thai patients, a dosage regimen of 5 mg/kg every 8 hours was recommended as more suitable than 5 mg/kg every 6 hours. Using data from this study, the predicted maximum and minimum serum theophylline concentrations at steady state were calculated to be 16.53 micrograms/ml and 9.96 micrograms/ml, respectively. This dosage regimen should be suitable not only for Thai people but also for Asian people of similar races and under similar environmental conditions.

Relationship between theophylline concentration in serum and saliva in Thai asthmatic children.

The relationship of theophylline concentration in serum and saliva was studied in 10 Thai asthmatic children receiving “Elixir Quibron” and Tablet Aminophylline orally in a cross over design. There was an excellent linear relationship between theophylline concentration in serum and saliva regardless of dosage forms. Proportionality factor that relates saliva to serum concentration obtained in this study was 1.60. Serum Theophylline concentration can be estimated by analysis of saliva concentration multiplied by 1.60. These observations suggest that determination of theophylline concentration in saliva is an effective, convenient, noninvasive, and painless method for routine indirect monitoring of serum theophylline concentration in Thai asthmatic children.

Antihistaminic effect of ''plai'' (zingiber cassummunar roxb.) on histamine skin test in asthmatic children.

The rhizome of “Plai” (Zingiber cassummunar Roxb.) has been used as antiasthmatic drug in Thai traditional medicine for a long time. Compound “D” in hexane fraction of “Plai” extract has been shown to inhibit smooth muscle contraction nonspecifically in guinea pig. It also antagonized the action of histamine on bronchial smooth muscle both in vivo and in vitro. Clinical trials of “Plai” have been shown to be effective in asthmatic patients. The purpose of this study is to determine whether usual dose of “Plai” has any antihistamine effect on skin testing. The study was carried out in 24 asthmatic children who had no any medication for 24 hours. There were 13 males and 11 females, age ranged between 8-16 years. Twelve subjects were tested for effect of “Plai” by using intracutaneous test with 0.02 ml of 1 : 100 histamine solution before and 1ฝ hours after taking 500 mg of “Plai” orally. Diameter of wheal reactions were measured in millimeter. Comparison of wheal size before and after “Plai” was made by statistical analysis and the patients were carefully observed for any side effect. Similar procedures were done in another 12 subjects before and at 1ฝ hours after taking chlorpheniramine (0.1 mg/kg) by month. Comparison in any change of wheal was observed and compared. The results of study revealed that 500 mg. of “Plai” had antihistamine effect. The size of wheal reactions before and after “Plai” had statistical significant difference (P < .005). The size of wheal reactions before and after chlorpheniramine also had statistical significant difference (P < .0005), and reduction of wheal size by “Plai” was lesser than by chlorpheniramine (P < .05). No any adverse reaction was observed during the study.