Therapeutic drug monitoring uncovering incorrect antiretroviral drug intake in a patient with swallowing difficulties.

A woman living with HIV reported swallowing difficulties that interfered with oral antiretroviral therapy. Treatment with darunavir/cobicistat/emtricitabine/tenofovir alafenamide (Symtuza®) was initiated, with the patient choosing to chew the tablet before swallowing because of her swallowing difficulties. Therapeutic drug monitoring, performed because of this non-standard administration, revealed unexpectedly low darunavir trough concentrations despite reported adherence and maintained virological suppression. A structured pharmacological assessment revealed that the patient had been consistently taking the medication in the fasting state, despite initial counselling to take it with food. After correction of the drug intake conditions, darunavir exposure increased to therapeutic levels. This case highlights the clinical value of therapeutic drug monitoring in identifying medication intake errors and optimising antiretroviral therapy in patients with swallowing difficulties.