Response to Letter to the Editor regarding “Melanotan II injection resulting in systemic toxicity and rhabdomyolysis” in Clinical Toxicology 2012; 50(10):1169–73.

To the Editor:

We thank you for your interest in our brief communication and appreciate hearing your experience with a suspected Melanotan misuse. It is interesting that our patient took this substance with the purpose of enhancing a tan, where your patient took it as an aphrodisiac. In direct response to your questions, our patient did not exhibit any penile erections nor any back-arching behavior during his course in the emergency department or observed in the intensive care unit. He did, however, have diffuse muscle tremors and intense diaphoresis. Melanotan II has been described to cause “frequent stretching and yawning” in the Pilot Phase-I study by Dorr et al., as well as similar effects in rodent studies as you astutely note.¹ Your patient's symptoms may have been an exaggerated effect of this stretching-yawning phenomenon. This study also demonstrated spontaneous penile erections in 100% (n = 3) of subjects at a dose of 0.025 mg/kg that resolved in 1–5 h post injection.¹ Whether or not additional neurochemical effects are taking place is currently unknown. This would require further research as altering melanocortin pathways will likely become more prevalent with the addition of new pharmaceuticals (i.e., the new weight loss drug lorcaserin acts on serotonin and pro- opio-melanocortin pathways). We were not aware of such profound cases of priapism requiring intervention from melanocortin peptides as described in your case. However, the self-experimentation report of Mac Hadley did note an “unrelenting erection” of “about 8 h duration.”² If melanocortin peptides are used more frequently for treatment of erectile dysfunction (ED), we postulate that more cases of priapism may be observed (similar to other treatments for ED). Whether there is a dose-response effect or an idiosyncratic reaction has yet to be determined. Your patient is older and stated that he took a higher dose than in our case. Both of these factors may help explain some of the effects observed in your patient. Since your patient was using Melanotan as an aphrodisiac, did you explore the possibility of co-ingestants such as sildenafil, yohimbine, antipsychotics, or additional medications? Such history would be very helpful to establish a stronger causal link with Melanotan II and priapism. We sincerely appreciate your additional insights to the potential adverse effects with melanocortin peptides and encourage future reporting of such events.

Sincerely,

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.