Endocrine Abstracts

Introduction: Doxycycline is a broad-spectrum antibiotic that is used to treat gram negative, gram positive and atypical bacterial infections. It is a member of the second-generation tetracycline class of antibiotics.

Case: We describe a case of a (non-diabetic) male patient who developed hypoglycaemia following treatment with doxycycline. A 73-year-old male presented to the emergency department following a witnessed collapse at 9am on the 4^thof September 2021. He was found to have a blood glucose level of 2.6 mmol/l with the London Ambulance Service. He had a past medical history of asthma, prostatic cancer, GORD and spondylosis. He had recently been prescribed doxycycline by his GP for treatment of a possible lower respiratory tract infection. He took an initial dose of 200 mg of doxycycline followed by 100 mg once daily for 11 days. It was on day 11 that he collapsed. During admission he received a Computed Tomography (CT) Head scan due to head injury which was reported as normal. His cortisol levels were normal at 346 nmol/l and he did not have any further episodes of hypoglycaemia after stopping doxycycline. Following discharge, he was reviewed at an endocrine clinic and endocrine causes of hypoglycaemia were investigated with a prolonged fasting glucose (15 hours) showed normal glucose and a repeat hormonal profile for IGF-1, IGF-2 and cortisol all of which were normal.

Discussion: Medications can frequently cause hypoglycaemia especially in the elderly. Anti-diabetic medications are usually the culprit however many other non-diabetic medications used routinely can also cause hypoglycaemia and the list of these medications is expanding. Doxycycline has a number of side effects. Commonly known side effects include gastrointestinal irritation such as vomiting, diarrhoea and oesophageal ulceration. It is also known to cause photosensitivity and photo-onycholysis. A rare side effect of doxycycline that is not well known is hypoglycaemia A Study of the FDA Adverse Event Reporting System (FAERS) on hypoglycaemia associated with antibiotics alone and in combination with sulfonylureas and meglitinides showed that many patients developed hypoglycaemia while on antibiotics with or with sulfonylureas and meglitinides.

Conclsion: Hypoglycaemia due to doxycycline is rare. The mechanism for doxycycline-induced hypoglycaemia is still unclear but it may be related to augmented insulin sensitivity, direct hepatotoxicity, inhibition of insulin degradation in the liver as well as inhibition of glycogenolysis. Paying attention to this potential adverse event is important as this medication is commonly prescribed antibiotic, especially in outpatient setting.