We describe a 67-year-old man with medical history of focal post-stroke seizure and type 2 diabetes mellitus treated with carbamazepine, clobazam, gliclazide, insulin glargine, and omeprazole we visited for the onset in the last 7 days of asthenia, cough with mucus, breathing difficulty, chest pain, and weight loss. After clinical and laboratory tests, pulmonary tuberculosis was diagnosed, and a treatment with isoniazid, ethambutol, pyrazinamide rifampicin, and pyridoxine was started. Therapeutic drug monitoring of tuberculosis treatment documented that all drugs were in normal therapeutic range. Four days after the beginning of the treatment, we documented the improvement of fever, and three days later the patient showed sleepiness, visual disorder and asthenia. Clinical and pharmacological evaluation suggested a carbamazepine toxicity probably related to a drug interaction (Drug Interaction Probability Scale score = 6). The impossibility to switch carbamazepine for another antiepileptic drug, due to a resistant form of seizure, induced the discontinuation of tuberculosis treatment, resulting in the normalization of serum carbamazepine levels in one day (10 µg/ml) and in the worsening of fever, requiring a new clinical and pharmacological evaluation. The titration dosage of carbamazepine and its therapeutic drug monitoring allowed to continue the treatment with both antitubercular drugs and carbamazepine, without the development of adverse drug reactions. To date, tuberculosis treatment was stopped and clinical evaluation, radiology and microbiology assays documented the absence of tubercular infection and no seizures appeared (carbamazepine dosage 800 mg/bid; serum levels 9.5 µg/ml).
Therapeutic drug monitoring: how to improve drug dosage and patient safety in tuberculosis treatment