In dermatology there are multiple successful precedents for dilution of products originally used for the face when repurposed for applications on the body. Injectable poly-Llactic acid and calcium hydroxyapatite, for example, required significantly more dilution to mitigate risks when transitioned to the body. Similarly, DCA, if diluted with lidocaine for example, could allow for treatment over larger areas with reduction in pain.3 To our knowledge, dilution beyond 0.3 cc lidocaine to 2 cc DCA has not been reported which may reflect concerns regarding the risk of altering the pH of the product due to a more acidic resultant solution. In anticipation of clinical studies, we demonstrate an experimental model for changes in pH with varying dilutions (Figure 1).
Using pH test strips, we tested different dilutions of DCA: with lidocaine, with lidocaine and epinephrine, and then both with sodium bicarbonate to mitigate injection pain and raise the pH of solution to closely approximate DCA (pH 8.3), as this basic pH is theoretically necessary to maintain the efficacy of the reaction.4 For comparison, DCA was also diluted with normal saline (Figure 2). Although the internal buffer in DCA, anhydrous disodium phosphate, is theoretically resistant to large pH changes, dilution of DCA with plain lidocaine should not go beyond a 2:1 ratio for risk of large pH shift (pH 6.5–7 in this case). Dilutions beyond this appear to overcome the internal buffer and significantly alter the pH. Adding epinephrine (pH 2.2–5) only furthers the pH drop. Addition of 8.4% sodium bicarbonate to 1% lidocaine with 1:100,000 epinephrine (approximately 1 mL:10 mL ratio), however, restored the target tissue pH around 7.5, which is close to the pH of DCA. Greater dilutions with saline may be possible given the pH effects were of less impact.
The addition of lidocaine with epinephrine may offer the added benefit of enhanced lipolysis, as catecholamines stimulate the lipolytic pathway via binding of beta adrenergic receptors on adipocytes.4 Therefore, we postulate that a mixture of DCA