Does needle size matter?

Abstract

Hypodermic needles are in widespread use, but patients are unhappy with the pain, anxiety, and difficulty of using them. To increase patient acceptance, smaller needle diameters and lower insertion forces have been shown to reduce the frequency of painful injections. Guided by these observations, fine needles and microneedles have been developed to minimize pain and have found the greatest utility for delivery of vaccines and biopharmaceuticals such as insulin. However, pain reduction must be balanced against limitations of injection depth, volume, and formulations introduced by reduced needle dimensions. In some cases, needle-free delivery methods provide useful alternatives.

Keywords: drug delivery; hypodermic needle; insulin delivery methods; microneedle injection; needle gauge; needle length; pain from needle insertion.

Figures

Figure 1.

Size comparison among hypodermic needles and microneedles. Scanning electron micrographs of (a) 21-gauge, (b) 27-gauge, and (c) 31-gauge hypodermic needles (BD Technologies) and (d) tapered 33-gauge Terumo NanoPass hypodermic needle (image courtesy of Kyuzi Kamoi). Scanning electron micrographs of microneedles at the same magnification as hypodermic needles: (e) stainless steel microneedle with a total length of 1.5 mm (image courtesy of John Mikszta, BD Technologies), (f) nickel microneedle with a length of 500 μm, and (g) silicon microneedle with a length of 450 μm (image courtesy of NanoPass Technologies). Higher magnification scanning electron micrographs of (h) nickel microneedle and (i) silicon microneedle for the needles shown in f and g, respectively. (Note that although they have the same name, the NanoPass 33-gauge hypodermic needle by Terumo and the company NanoPass Technologies are unrelated.)

Figure 2.

Outer and inner diameters of conventional hypodermic needles as a function of needle gauge.