Albuterol extended-release products: effect of food on the pharmacokinetics of single oral doses of Volmax and Proventil Repetabs in healthy male volunteers

Simple and accurate quantitative analysis of seven prohibited threshold substances in human urine by liquid chromatography/tandem mass spectrometry in doping control

A simple and accurate liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the quantitative determination of ephedrine, pseudoephedrine, methylephedrine, cathine, salbutamol, morphine and epitestosterone in human urine. Urine samples were spiked with internal standard and diluted with acetonitrile. After centrifugation, the supernatants were directly analyzed by LC/MS/MS using the selected reaction monitoring (SRM) mode. The linearity, intra- and inter-day precision, accuracy, limit of detection (LOD) and limit of quantification (LOQ) were evaluated and the method was found to be accurate and reproducible for the quantitation of threshold substances. When the method was applied to the analysis of blind urine samples for the proficiency test, the results were close to the nominal concentrations, within 87.7-106.6% of nominal values, suggesting that the developed methods can be successfully applied to routine doping analyses.

Predicting effect of food on extent of drug absorption based on physicochemical properties

PURPOSE

To develop a statistical model for predicting effect of food on the extent of absorption (area under the curve of time-plasma concentration profile, AUC) of drugs based on physicochemical properties.

MATERIALS AND METHODS

Logistic regression was applied to establish the relationship between the effect of food (positive, negative or no effect) on AUC of 92 entries and physicochemical parameters, including clinical doses used in the food effect study, solubility (pH 7), dose number (dose/solubility at pH 7), calculated Log D (pH 7), polar surface area, total surface area, percent polar surface area, number of hydrogen bond donor, number of hydrogen bond acceptors, and maximum absorbable dose (MAD).

RESULTS

For compounds with MAD >or= clinical dose, the food effect can be predicted from the dose number category and Log D category, while for compounds with MAD < clinical dose, the food effect can be predicted from the dose number category alone. With cross validation, 74 out of 92 entries (80%) were predicted into the correct category. The correct predictions were 97, 79 and 68% for compounds with positive, negative and no food effect, respectively.

CONCLUSIONS

A logistic regression model based on dose, solubility, and permeability of compounds is developed to predict the food effect on AUC. Statistically, solubilization effect of food primarily accounted for the positive food effect on absorption while interference of food with absorption caused negative effect on absorption of compounds that are highly hydrophilic and probably with narrow window of absorption.

Relative biologic availability and pharmacokinetics of albuterol preparations in healthy Chinese

The authors' goal was to study the biologic availability and pharmacokinetics of two different formulations of controlled-release (CR) tablets of albuterol. A two-way, cross-over biologic availability study was performed with 20 healthy male volunteers to evaluate the relative biologic availability of two CR tablets of albuterol versus two different formulations of immediate-release (IR) albuterol tablets. Albuterol concentrations in plasma were measured using an HPLC procedure. Each patient subject received a 4.8-mg CR tablet every 12 hours for 6 days and a 4.8-mg IR tablet every 8 hours for 6 days. Tests of single doses and steady state were assayed for CR and IR albuterol tablets. The mean Cmax and tmax for two CR tablets given after a single dose were 7.3+/-1.5, 7.9+/-1.4 microg x L(-1) and 4.6+/-0.8, 4.8+/-0.5 hours, respectively. The Cmax and tmax for two IR tablets given after a single dose were 12.5-/+1.3, 15.3 +/-2.3 microg x L(-1) and 1.3+/-0.4, 1.6+/-0.4 hours, respectively. The relative biologic availability of two CR albuterol tablets were 106.0+/-6.2% and 109.8+/-9.0%, respectively. Administration of CR albuterol twice a day provides an alternative to administration of IR albuterol three or four times a day.

In vitro characterization of a controlled-release chlorpheniramine maleate delivery system prepared by the air-suspension technique

Non-pareil cores were spray-coated with a chlorpheniramine maleate (an alkylamine antihistamine) layer and a Eudragit NE30D overcoat in a Wurster air-suspension apparatus. In vitro dissolution studies demonstrated that drug release was a function of polymer membrane thickness. Polyethylene glycol 6000, as a hydrophillic additive, increased the in vitro release of chlorpheniramine maleate from the pellets. Pellets coated with 8.30% Eudragit NE30D, 0.50% talc and 1.00% polyethylene glycol 6000 were found to display desirable controlled release characteristics for chlorpheniramine maleate over the 8-h testing period, which were also comparable with that of Dykatuss capsules. The controlled release pellets exhibited first-order release characteristics for chlorpheniramine maleate. Reproducibility of the manufacturing conditions employed in the study were confirmed thus ensuring reproducibility of drug release characteristics between batches of chlorpheniramine maleate pellets. Drug release from the pellets was shown to be independent of the dissolution method and medium used. Pellets displayed no significant change in drug release characteristics relative to the initial drug release data when stored for 12 weeks at room temperature (20 +/- 2 degrees C) and for 8 weeks at a low temperature (5 +/- 1 degrees C). However, pellets stored at 37 degrees C with 80% relative humidity and at 40 +/- 2 degrees C showed a slower in vitro drug release after 8-week storage and therefore failed to maintain their initial drug release profile.

Microencapsulated Eudragit RS30D-coated controlled-release pellets: the influence of dissolution variables and topographical evaluation

The air suspension technique was employed to prepare Eudragit RS30D-coated controlled-release pellets of salbutamol. Drug release in dissolution studies can be dependent on the dissolution method and medium used. Thus, the aim of this study was to investigate the influence of various dissolution methods and dissolution medium pH values on drug release from a batch of pellets which displayed controlled drug-release characteristics over an 8-h period in deionized water using the rotating basket method. In vitro testing using the official USP XXII (rotating basket and rotating paddle) and non-official (rotating bottle) methods showed drug release to be independent of the method used. The prepared pellets displayed pH-dependent drug-release characteristics when tested in hydrochloric acid (pH 1.5), phosphate buffer (pH 6.8) and deionized water (pH 7.2). Also, in vitro testing, which exposed the pellets to a changing pH gradient that simulated the gastrointestinal pH conditions following oral administration, was used to confirm the drug-release characteristics. The results showed controlled-release characteristics to be maintained, with the drug being released over an 8-h period. Scanning electron microscopic evaluation proved useful in the elucidation of the physical characteristics of the controlled-release pellets as well as in the identification of a possible mode of drug transfer into the dissolution medium.

Enantioselective disposition of albuterol in humans

The study of enantioselective disposition of chiral drugs is important to provide a rationale of plasma concentration-effect relationships, which are often misleading when based on total drug concentration. It is also important when considering new dosage routes or formulations in order to optimize therapeutic plasma concentrations of the active enantiomer. Improvements in the sensitivity and selectivity of biological assays coupled with the developments in chiral analysis have made it possible to study the enantioselective disposition of drugs. Although valuable pharmacokinetic data were obtained for the beta 2-agonists by nonenantioselective methodology, more recent chiral studies have revealed the existence of extensive enantioselectivity in the disposition of these agents. The most significant features of the enantioselective disposition of albuterol are the relatively rapid plasma clearance and low bioavailability of the eutomer. Although this in itself does not necessarily justify the development of a single enantiomer formulation, the implications of the high levels of distomer after i.v. and oral dosing await clarification. Similarly, more work is required to elucidate the consequences of the major difference in disposition between albuterol and terbutaline in humans through both in vivo and in vitro studies of the mechanisms giving rise to this phenomenon. The enantioselective disposition of the other clinically used beta 2-agonists, such as fenoterol, formoterol, and salmeterol also needs to be characterized. The metabolism of the majority of beta 2-agonists is generally by conjugation to give one major metabolite. The situation is therefore uncomplicated by multiple metabolic pathways, which may differ in the extent and direction of their enantioselectivity. Many beta 2-agonists are excreted largely unchanged in the urine making studies of urinary excretion accessible without the requirement for very sensitive assays. The realization that the enantiomers of beta 2-agonists previously thought of as "inactive" may be associated with toxic effects is a further compelling reason to study the enantioselective pharmacokinetics of this class of drugs. In addition, the role of enantiomers in producing side effects, such as tremor and reduction in renal function, needs to be reassessed. The beta 2-agonists can be looked on as textbook examples of the inherent danger of ignoring chirality in the study of pharmacokinetics and pharmacodynamics. The growing body of information on the enantioselective disposition of beta 2-agonists in humans will enhance the rational use of these drugs in the future management of patients.

Treatment of nocturnal asthma by addition of oral slow-release albuterol to standard treatment in stable asthma patients

Nocturnal and early-morning complaints in asthma patients are sometimes difficult to treat. We investigated the efficacy of an oral osmotically controlled release (OR) formulation of albuterol 8 mg in 35 patients with stable asthma and nocturnal complaints and/or morning dipping of the peak expiratory flow (PEF). The mean age was 45 years (range 22-70), the FEV(1) was 61 +/- 20% of predicted, and inhaled steroids were used by 32 patients. Albuterol OR was added to their usual treatment. The use of theophyllines and oral adrenergics was not allowed. Twice-daily (b.i.d.) dosing was compared to one dose at night and to placebo. The three-period crossover study was double-blind placebo-controlled with treatment periods of 2 weeks. Responses have been analyzed by means of multiple regression analysis at a significance level of 5%. There was no significant difference of the FEV(1) or the weekly means of PEFs between the periods. During the b.i.d. treatment, the daytime and nocturnal symptom scores, used rescue medication, subjective sleep quality, and nocturnal waking tended to be better. Mental fitness was improved, but significantly only in the morning. We concluded that additional treatment with albuterol 8 mg OR once or twice daily did not lead to an overall clinical improvement in this group of patients with nocturnal asthma during standard treatment. In view of the tendency to improvement, it may be worth trying this treatment in individual patients.

Enantioselective disposition of salbutamol in man following oral and intravenous administration

1 Salbutamol is a beta 2-adrenoceptor stimulant used clinically as a racemate where the activity resides predominantly in the (-)R enantiomer with little or no activity attributed to the (+)S enantiomer. Salbutamol undergoes extensive pre-systemic metabolism and active renal excretion. 2 The pharmacokinetics of the enantiomers of salbutamol have been investigated after intravenous (1.6 mg) and oral (4 mg) dosing with racemic drug to seven normal male volunteers. Plasma and urine samples were analysed by chiral h.p.l.c. after solid phase extraction. 3 The ratio of (-)R/(+)S salbutamol in plasma and urine following intravenous administration ranged from near unity soon after dosing to about 0.66 after 8 h. The ratio remained at about 0.3 in both plasma and urine over the 8 h following an oral dose. 4 The following pharmacokinetic parameters for (+)S and (-)R salbutamol were found to be significantly different (P < 0.05) after intravenous administration (clearance 0.39 +/- 0.12 vs 0.62 +/- 0.18 1 h-1 kg-1, terminal phase half-life 2.85 +/- 0.83 vs 2.00 +/- 0.49 h, amount excreted unchanged in urine 55 +/- 11 vs 46 +/- 8%) and following oral administration (amount excreted unchanged in urine 32 +/- 11 vs 8 +/- 4% and bioavailability 0.71 +/- 0.09 vs 0.30 +/- 0.07). 5 The active (-)R enantiomer of salbutamol undergoes significantly faster metabolism in man than the inactive (+)S enantiomer resulting in considerably lower bioavailability of the active enantiomer following oral administration.