Pediatric doxycycline-induced isolated APTT prolongation: a rare case with exploration of the vitamin K mechanism

Macrolide-resistant Mycoplasma pneumoniae (MRMP) is increasingly prevalent, and doxycycline is a first-line treatment. Although doxycycline is generally considered safe, clinically significant coagulation dysfunction has rarely been reported. This paper reports the first case of MRMP-associated doxycycline-induced coagulation dysfunction, highlighting a novel and potentially underrecognized serious adverse drug reaction. A patient with macrolide-resistant Mycoplasma pneumoniae infection developed significant coagulation dysfunction after five days of oral doxycycline treatment. The activated partial thromboplastin time was prolonged to more than twice the normal value. According to the World Health Organization causality assessment of adverse drug reactions, doxycycline was determined to be a likely cause of the coagulation dysfunction. Consequently, the patient’s hospital stay was prolonged, classifying this event as a serious adverse drug reaction. After a comprehensive literature review and in-depth discussion of the potential pathogenic mechanisms, we conclude that although doxycycline-related coagulation abnormalities have been rarely reported in the literature, their potential risk should not be overlooked. Clinicians should remain vigilant, especially in patients with underlying coagulation disorders or those receiving concurrent anticoagulants. Monitoring APTT is advised for early detection.