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[...]by adjusting the propulsive force, Zetajet can deliver to SQ, IM, and even to the intradermal space demonstrating the importance of propulsive force in determining delivery depth.4,5 Furthermore, there are a variety of different needle-free devices that generate propulsive force by the use of gas chambers, electromagnetic force, and shock waves.6 This clearly shows that fascia is penetrable even without the necessity of needle penetration below this surface, and that propulsive force is a crucial factor determining delivery depth even without the use of a needle. [...]the Duvauchelle et al study could also indicate that females may have different pharmacokinetic responses to epinephrine injection than males. [...]we feel that a role of compression in the depth of penetration cannot be excluded based on available data.