A new method for investigating bioequivalence of inhaled formulations: A pilot study on salbutamol

Purpose: An efficient, cost-effective and non-invasive test is required to overcome the challenges faced in the process of bioequivalence (BE) studies of various orally inhaled drug formulations. Two different types of pressurized meter dose inhalers (MDI-1 and MDI-2) were used in this study to test the practical applicability of a previously proposed hypothesis on the BE of inhaled salbutamol formulations. Methods: Salbutamol concentration profiles of the exhaled breath condensate (EBC) samples collected from volunteers receiving two inhaled formulations were compared employing BE criteria. In addition, the aerodynamic particle size distribution of the inhalers was determined by employing next generation impactor. Salbutamol concentrations in the samples were determined using liquid and gas chromatographic methods. Results: The MDI-1 inhaler induced slightly higher EBC concentrations of salbutamol when compared with MDI-2. The geometric MDI-2/MDI-1 mean ratios (confidence intervals) were 0.937 (0.721-1.22) for maximum concentration and 0.841 (0.592-1.20) for area under the EBC-time profile, indicating a lack of BE between the two formulations. In agreement with the in vivo data, the in vitro data indicated that the fine particle dose (FPD) of MDI-1 was slightly higher than that for the MDI-2 formulation. However, the FPD differences between the two formulations were not statistically significant. Conclusion: EBC data of the present work may be considered as a reliable source for assessment of the BE studies of orally inhaled drug formulations. However, more detailed investigations employing larger sample sizes and more formulations are required to provide more evidence for the proposed method of BE assay.

Improved laboratory test methods for orally inhaled products

Existing pharmacopeial methods for the in vitro testing of orally inhaled products (OIPs) are simplified representations of clinical reality, as their objective is to provide metrics that are discriminating of product quality. Attempts to correlate measures such as fine particle fraction <5 µm aerodynamic diameter with in vivo measures of lung deposition have therefore been notoriously difficult to achieve. Although particle imaging-based techniques may be helpful to link in vitro to in vivo data as surrogates for clinical responses, a reappraisal of the purposes for laboratory-based testing of OIPs is required. This article provides guidance on approaches that may be helpful to develop clinically appropriate methods to assess OIP performance in the laboratory, with the ultimate goal of developing robust in vitro–in vivo relationships for the major inhaled drug classes.

Structure and function of the tuberculous lung: considerations for inhaled therapies

Inhaled therapies for pulmonary tuberculosis are in development and appear promising at first look. A fundamental premise of such therapy is efficient delivery of drug at high concentrations to the active disease site, while minimizing systemic delivery. This assumes that inhaled drug will actually reach the diseased lung, which while intuitive for healthy lungs, may be untrue for diseased lungs with abnormal structure or function. This review discusses the structural and functional aspects of respiratory physiology that are likely to impact local drug delivery and presents the available evidence on how this pertains to tuberculous lungs.

The effect of parental smoking on lung function and development during infancy

While the adverse effects of parental smoking on respiratory health during childhood are well recognized, its potential impact on early lung development is less clear. This review summarizes current evidence on the effect of parental smoking on lung function during infancy. It is difficult to separate the effects of pre- and postnatal exposure, since the majority of mothers who smoke in pregnancy (currently around 30% worldwide) continue to do so thereafter. Nevertheless, measurements undertaken prior to any postnatal exposure have consistently demonstrated significant changes in tidal flow patterns in infants whose mothers smoked in pregnancy. While there is, as yet, no convincing evidence from studies in human infants that smoking during pregnancy is associated with increased airway responsiveness at birth, many studies have demonstrated a reduction in forced expiratory flows (on average by 20%) in infants exposed to parental smoking. While maternal smoking during pregnancy remains the most significant source of such exposure and is likely to be responsible for diminished airway function in early life, continuing postnatal tobacco smoke exposure will increase the risk of respiratory infections, the combination of both being responsible for the two- to fourfold increased risk of wheezing illnesses observed during the first year of life in infants whose parents smoke. These findings emphasize the need to keep infants in a smoke-free environment both before and after birth, not least because of growing awareness that airway function in later life is largely determined by that during foetal development and early infancy.