Issue link: https://www.e-digitaleditions.com/i/1463386
Inhalation April 2022 11 and the concept that the solenoid valve should open in less than 100 milliseconds. Other curiosities come up in reviewing the USP and Pharm. Eur. descriptions of DPI test- ing. The USP until recently named the ASCO 8030G13 solenoid valve as an adequate valve for the testing (https://www.emerson.com/en-us/ catalog/asco-sku-8030g013ac11060d) whereas the Pharm. Eur. Section 2.9.18 names the type 256-A08 valve by Bürkert GmbH (https://www. burkert-usa.com/en/products/solenoid-valves/ general-purpose-2-2-solenoids/145766). Additionally, the Pharm. Eur. description declares the inside diameter (ID) of the passageway through the seat of the solenoid valve to be ≥ 8 mm, saying "A 2-way, 2-port solenoid valve having a minimum airflow resistance orifice with ID ≥ 8 mm and an opening time ≤ 100 ms (e.g., type 256-A08, Burkert GmbH, D-74653 Ingelfingen), or equivalent." But the USP has dropped the 8-mm orifice dimen- sion from its description (Table 1). erefore, a seri- ous and reasonable user is certainly within his or her rights to ask "Why the differences and changes? Do these matter?" The pump is on and the solenoid valve starts to open—now what? A typical carbon vane vacuum pump suitable for this testing (e.g., Becker Seco SV 1025) rotates 30 times per second, with five or six carbon vanes, thereby moving small packets of air every five to six milli- seconds. Pressure waves travel at approximately 340 number of seconds at a target flow rate when it is attached to a good-quality cascade impactor (Figure 1). is figure calls out common test components described in USP Chapter <601> [5] and in Pharm. Eur. Section 2.9.18 [6]. Before running a test of a DPI with the components shown in Figure 1, the user has the additional chal- lenge of setting the flow rate so that the pressure drop across the inhaler is 4 kPa. Why that pressure drop? And further, why not simply measure the flow rate in real time at the exit of the impactor? Good questions. But hasn't the USP and Pharm. Eur. description changed over the years? Yes. is question is not news to many practitioners of the art. It is even considered a "normal" event, to be expected. After all, one might say the description should improve in a cautious and orderly way. In fact, the USP and equivalent organizations in other regions of the world convene expert panels to con- sider and adjust the published protocols. Further, the USP publishes proposed revisions to its protocols [7, 8] and invites public comment. It is instructive, then, to see a few aspects of the "evolution" of the USP depictions because it highlights some of the back- ground thinking of the leaders in the field (Table 1). ere are some components of Figure 1 that have not changed at all in 20 years—rightly or wrongly— namely the flow control valve (Parker Hannifin 8FV12LNSS; still available today), the location of the pressure tap on the dry powder total dose tube (integral to the determination of the test flow rate), Figure 1 Flow configuration for routine APSD testing of DPIs. Mouthpiece Adapter Inhaler Induction Port Pre-separator Flow-Control Valve Timer Connector Connector Vacuum Pump Two-Way Solenoid Valve Vacuum Tubing Vacuum Tubing Vacuum Tubing P2 P3