Erectile dysfunction as rare side effect in the simultaneous intrathecal application of morphine and clonidine

We report on the case of a 52-year-old man who presented with a history of chronic neuropathic pain treated with intrathecal application of morphine for many years. In spite of significant dose escalation, considerable pain relief had not been achieved. Ziconotide had been tried but not only did it not provide pain relief, but it also caused severe side effects in this patient. A combination of morphine and clonidine was delivered by a programmable pump, slowly increasing the clonidine rate over several weeks. For ease of transition and minimization of hospitalization, which was a special concern to this patient, combining clonidine and morphine was chosen over monotherapy with hydromorphone, with both possibilities being described as equal alternatives in the literature. Considerable pain relief was achieved during week 2 at a clonidine dose of 0.040 mg/d, thereby decreasing the visual analog score (VAS) from 10 to 4. Yet, after developing erectile dysfunction and relative hypotension soon after beginning clonidine treatment, the patient decided not to continue with the combined application of morphine and clonidine. Treatment was therefore switched back to the former monotherapy with morphine. Thereafter, erectile dysfunction disappeared and blood pressure returned to habitual high levels. Although common in systemic application, erectile dysfunction caused by the intrathecal application of clonidine has not been described yet in the literature. In this patient, this rare side effect decisively impaired life quality, subjectively outweighing the considerable pain relief which could be achieved after formerly inefficacious treatment. Further and prospective investigation might be needed to estimate the connection of erectile dysfunction to intrathecal application of clonidine.