Latent tuberculosis infection (LTBI) is infection with bacteria from Mycobacterium tuberculosis complex group with no clinical signs and symptoms. Due to the possibility of disease progression to an active state, individuals with high-risk factors should be treated for LTBI. In Slovenia a combination of rifampicin and isoniazid is usually used. These drugs affect metabolism of concomitant drug therapy and can cause drug-drug interactions.
The aim of the study was to determine the incidence of potential and actual drug-drug interactions in out-patients with LTBI, to identify predictors of actual drug interactions and to determine a time frame of actual interaction manifestation.
The study included out-patients who were treated for LTBI at the University Clinic of Respiratory and Allergic Diseases Golnik between 1. 1. 2013 and 31. 12. 2015 and were receiving concomitant systemic therapy. We examined patients’ medical documentation and collected their demographic data, data of their LTBI treatment and data on clinical manifestation of interactions. We identified potential drug interactions using Lexicomp®. In case of actual drug interactions, we calculated time in which they clinically manifested.
Potential drug interactions were present in 84.3 % (118/140) of patients and were clinically manifested in 18.6 % (22/118) of patients with potential drug interactions. All actual drug interactions were due to rifampicin activity. Anti-inflammatory and analgesic drugs, antihypertensive drugs, and proton pump inhibitors were involved in actual drug interactions with rifampicin. Most of actual drug interactions included methylprednisolone (7), methotrexate (6), and paracetamol (4). Patients’ age and sex, duration of LTBI treatment, the number of concomitant diagnosis and the number of concomitant drugs did not statistically affect the prevalence of actual drug interactions. Among patients with actual drug interactions 72.7 % had a diagnosis of chronic inflammatory disease. Median time for clinical onset of actual drug interaction was 19.5 days.
In out-patients with LTBI potential drug interactions are common, but were clinically manifested only in 18.6 % of patients. For patients treated for LTBI and at the same time receiving drugs for chronic inflammatory diseases, such as rheumatoid arthritis, ankylosing spondilitis, psoriasis, arthropathy and ulcerative colitis, a pharmacotherapy review at a clinical pharmacist would be recommended to prevent clinical consequences of drug-drug interactions.