{
  "abstract": "Background Rifampicin plays a vital bactericidal role in the treatment of Tuberculosis (TB). Achieving the WHO recommended dose of 10 mg/kg can be limited by fixed-dose preparations, which carry the risk of underdosing. Several studies have revealed low rifampicin concentrations at the site of pulmonary infection when 10 mg/kg dosing is used (van Ingen et al., 2011). Although low serum rifampicin levels are associated with treatment failure, relapse, and acquired drug resistance, rifampicin levels are not monitored routinely during TB treatment (Holden et al., 2022).Objectives To explore if patients who are initially smear positive with low rifampicin (<8 mg/L) are as likely to remain smear positive after 2 weeks of treatment, as those with therapeutic rifampicin levels (>8 mg/L)The final dose (mg/kg) of rifampicin required to achieve therapeutic rifampicin levels (8 mg/L or more).Method We conducted a retrospective review of all adult patients who initiated treatment for Pulmonary Tuberculosis between October 2021 and March 2025, identifying 118 patients. 20 patients who were not able to complete treatment were excluded. Patients‘ weights, smear results, initial and final rifampicin doses, and dose adjustments were collected from patient records. Rifampicin levels (2 hours post-dose) were checked two weeks after treatment initiation and after any dose adjustment. Levels below 8 mg/L were considered subtherapeutic.Results 47 (out of 98) patients were smear-positive at treatment initiation, and 14 patients stayed smear-positive at two weeks of treatment. Of note, 12 patients who were smear positive at 2 weeks, had subtherapeutic (<8 mg/L) rifampicin levels. The mean rifampicin dose (mg/kg) required to achieve therapeutic levels of rifampicin in this cohort was 14.47 mg/kg.About one-third (27%) of patients with subtherapeutic rifampicin levels were on a dosage of 450 mg or below.Rifampicin levels 4.0–8.0 mg/L were accepted in two patients due to age and patient concerns.Interestingly, monitoring rifampicin levels identified two patients who were non-compliant with treatment and directly-observed therapy brought rifampicin levels in range.Conclusion While fixed-dose preparations aid in treatment compliance, the WHO-recommended dose is limited by the fixed-dose preparations. 86% of patients who stayed smear-positive at two weeks after treatment initiation had subtherapeutic (<8 mg/L) rifampicin levels.References van Ingen J, Aarnoutse RE, Donald PR, Diacon AH, Dawson R, Plemper van Balen G, Gillespie SH, Boeree MJ. Why do we use 600 mg of rifampicin in tuberculosis treatment? Clinical Infectious Diseases 2011;52(9):e194–e199. doi:HYPERLINK \"https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1093%2Fcid%2Fcir184&data=05%7C02%7CAbstracts%40brit-thoracic.org.uk%7C4118d6a78e744d122afe08ddf048cf2f%7Cdd0ce28c0d1a4210a53096dba109cdba%7C0%7C0%7C638930917711016223%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=ohRVJEaHOCaRJEHkmvkbLMAcTotTWShSkvT95fDRiRQ%3D&reserved=0\"https://doi.org/10.1093/cid/cir184Holden A, Dhadda S, Obisi N, French K, Thickett K, Carter R. P149 Routine monitoring of rifampicin levels reveals subtherapeutic levels in 76% of patients with fully sensitive TB. ‘Die Hard II’ – Antibiotic Resistance and Challenges in TB [online] 2022;A162.2–A163. doi:HYPERLINK \"https://gbr01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1136%2Fthorax-2022-btsabstracts.284&data=05%7C02%7CAbstracts%40brit-thoracic.org.uk%7C4118d6a78e744d122afe08ddf048cf2f%7Cdd0ce28c0d1a4210a53096dba109cdba%7C0%7C0%7C638930917711050999%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=SGGIY3UEpCv3YHrIPUNttWZxAQRhAAudyRhXMO5huUw%3D&reserved=0\"https://doi.org/10.1136/thorax-2022-btsabstracts.284",
  "authors": [
    {
      "affiliations": [
        "New Cross Hospital, Wolverhampton, UK"
      ],
      "name": "R Haider"
    },
    {
      "affiliations": [
        "New Cross Hospital, Wolverhampton, UK"
      ],
      "name": "A Idzik"
    },
    {
      "affiliations": [
        "New Cross Hospital, Wolverhampton, UK"
      ],
      "name": "E Roddy"
    },
    {
      "affiliations": [
        "New Cross Hospital, Wolverhampton, UK"
      ],
      "name": "K Thickett"
    },
    {
      "affiliations": [
        "New Cross Hospital, Wolverhampton, UK"
      ],
      "name": "R Carter"
    }
  ],
  "title": "M45 Persistently positive sputum smears with sub-therapeutic rifampicin levels in pulmonary tuberculosis – a call for change?",
  "uid": "ceda51f8-9501-5762-ade3-cdcdd74e205a"
}