Cotrimoxazole-associated atrioventricular block in lupus nephritis: Is there a new elephant in the room?

BackgroundCotrimoxazole (trimethoprim-sulfamethoxazole) is widely used for infection prophylaxis in immunocompromised patients, including those with lupus nephritis. Although generally well tolerated, rare cardiovascular adverse effects may occur and are not well recognized.Case presentationWe report the case of a 43-year-old man with newly diagnosed class IV lupus nephritis who developed a high-grade atrioventricular block (AVB) shortly after initiation of cotrimoxazole prophylaxis. The patient had no previous cardiac disease, normal renal function, and normal serum potassium levels at presentation. Cotrimoxazole was discontinued immediately, leading to complete recovery of atrioventricular conduction within 7 days. No recurrence occurred during follow-up.DiscussionWhile AVB has been associated with cotrimoxazole in the context of acute kidney injury or hyperkalemia, this case demonstrates a potential direct drug-induced nodal toxicity, as no metabolic or structural abnormalities were identified. The temporal relationship, absence of alternative explanations, and reversibility after drug withdrawal support a probable causal association between cotrimoxazole and AVB.ConclusionThis case highlights the importance of considering cotrimoxazole as a potential, reversible cause of atrioventricular conduction disturbances, even in patients with normal renal and electrolyte profiles. Clinicians should be aware of this possible complication and monitor electrocardiographic changes when prescribing cotrimoxazole, particularly in patients receiving immunosuppressive therapy.