Design Innovation

Mechanical Performance of Generic and Proprietary Enema Bottles

[+] Author and Article Information
Donna L. Walsh2

 Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993donna.walsh@fda.hhs.gov

R. Jason Schroeder

 Center for Devices and Radiological Health, Office of Surveillance and Biometrics, Food and Drug Administration, 1350 Piccard Drive, Rockville, MD 20850

Sandy F. Stewart

 Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993


Corresponding author.

J. Med. Devices 2(2), 025001 (May 30, 2008) (7 pages) doi:10.1115/1.2902856 History: Received October 25, 2007; Revised February 12, 2008; Published May 30, 2008

Enemas containing the anti-inflammatory drug mesalamine are an effective treatment for a distal form of inflammatory bowel disease (IBD). An IBD patient discovered that a generic mesalamine enema was more difficult and painful to use than the proprietary version. A study was initiated to determine whether these differences were measurable in the laboratory using conventional mechanical test equipment. Differences among three bottle types (the proprietary brand and two generic versions) were quantified by mechanical testing. The compressive force required to squeeze the drug from each bottle was measured, tensile testing was performed on the bottle wall, and stiffness of the nozzle tips was studied via bend testing. The thickness of the bottle walls and the inner diameter (ID) of the nozzles were also recorded. The work required to expel the drug from the generic versions during bottle compression was significantly greater than for the proprietary (p<0.01). This was likely due to the wall thickness being greater in the generics; the elastic moduli of the three bottles were similar. The ID of the nozzles was smaller for the generic bottles, suggesting additional resistance to flow. Increased flow resistance was also observed for bottles in which lubricant obstructed the nozzle opening. The work required to bend the nozzle was greater in the generics than in the proprietary (p<0.01). These differences between the generic and proprietary bottles are consistent with the patient’s subjective experience. Poor bottle performance may adversely affect patient compliance with this treatment. Improved bottle design (such as tighter tolerances for wall thickness, nozzle ID, and nozzle stiffness) and manufacturing controls (e.g., preventing the nozzle lubricant from impeding delivery of the drug) could be achieved through the development of a standard specification for enema bottles. An optimal bottle design is suggested.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Bottle compression test: (A) testing machine crosshead, (B) 100N load cell, (C) Delrin® compression bars, (D) test bottle, (E) base of testing machine, and (F) beaker for catching bottle contents

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Figure 2

Approximate dimensions of modified ISO 37 Type 3 die: A=66mm, B=8.5mm, C=14mm, D=4mm, radius E=8mm, and radius F=10mm

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Figure 3

Diagram of bottle cross section before and during compression: r1=original radius, ϕ1=original angle, t=wall thickness (assumed to remain constant), a1=arclength along the midline of the wall thickness, b1=arclength of the uncompressed outer surface, r2=compressed radius, ϕ2=compressed angle, a2=arclength along the midline of the wall thickness, and b2=arclength of the deformed outer surface

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Figure 4

Nozzle bend test: (A) testing machine crosshead, (B) 100-N load cell, (C) Delrin® compression bar, (D) test bottle, (E) base of testing machine, (F) nozzle holding jig, and (G) distance between fillet on compression bar and end of nozzle=12mm

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Figure 5

Bottle compression test: observed compressive load versus distance for each bottle within each run

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Figure 6

Work for each bottle type in each run of the bottle compression test

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Figure 7

Multiple compression testing: (a) load versus distance for the multiple (six) compressions of a single bottle for each bottle type and (b) compressive work for each bottle type over the multiple compression runs.

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Figure 8

Tensile test: (a) load versus extension for bottle wall in tension and (b) stress versus strain for bottle wall in tension

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Figure 9

Nozzle bend test: load versus tip deflection for nozzle tips




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