Reversible atrioventricular block associated with transdermal fentanyl use: a paediatric case with non-Hodgkin lymphoma

Pain is a common and significant clinical problem in childhood cancers, arising both from the disease itself and from administered treatments. Although pain control is primarily achieved with routine analgesics, this may be insufficient in chronic or progressive stages of the disease. In such cases, treatment with potent analgesics, such as opioid derivatives, comes into play. Transdermal fentanyl is widely preferred in paediatric oncology practice due to its ease of administration and effective analgesic properties. The most common adverse effects of opioids include tolerance, nausea, vomiting, and constipation. Drugs known to cause atrioventricular block include beta-blockers, digoxin, calcium channel blockers, certain immunosuppressive agents, and many antiarrhythmic drugs. Drug-induced atrioventricular block is generally reversible and resolves after discontinuation of the offending agent. In this report, we present a paediatric patient with common variable immunodeficiency and non-Hodgkin lymphoma who developed first-degree atrioventricular block along with second-degree type I (Wenckebach) and type II atrioventricular block during transdermal fentanyl therapy. Given the rarity of this adverse effect, we believe this case contributes to the literature by highlighting a potential conduction system complication associated with opioid use.