Table 3.

Literature Data on the Required Minimum Inspiratory Flow Rates to Use Several Dry Powder Inhalers⁽⁶⁴⁾

Device	Resistance	“Minimum” effective		Drug	In vitro observation
	R (kPa1/2/L/min)	Q (L/min)	ΔP (kPa)
In vitroa
Twisthaler	0.044	20 < Q < 28	1.1	Mometasone	Lower limit of acceptable in vitro performance
HandiHaler	0.051	23 < Q < 33	1.2	Tiotropium	Lower limit of in vitro performance
HandiHaler	0.051	28	1.2	Tiotropium	Fine particle dose reduced by 30% compared to medium flow rates (40 L/min)
In vivob
Diskus	0.026	30	0.6	Salmeterol	FEV1 shown to be equivalent at 30 L/min to that at 60 L/min
Turbuhaler	0.036	31	1.2	Terbutaline	Maximal FEV1 at 1 hour postdose shown to be reduced at flow rates below 31 L/min
Turbuhaler	0.034	36	1.4	Budesonide	Scintigraphically determined lung dose showed a 50% reduction when inhaled flow rate was decreased from 58 to 36 L/min
Easyhaler	0.041	30	1.4	Budesonide/formoterol	AUC (area under the curve) of budesonide and formoterol reduced by 25% and 5%, respectively, when inhaled flow rate is reduced from maximal effort flow rate (82 L/min)

^aData obtained in bench in vitro experiments.

^bData obtained in clinical studies.

FEV₁, forced expiratory volume in 1 second.