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CP-036 Drug interactions involving antibiotics: do they care?
  1. D Briegas Morera,
  2. C Bonilla Galán,
  3. C Meneses Mangas,
  4. LM Bravo García-Cuevas,
  5. S Martín Clavo,
  6. JF Rangel Mayoral,
  7. R Medina Comas,
  8. L Romero Soria
  1. Hospital Infanta Cristina, Hospital Pharmacy Service, Badajoz, Spain


Background Drugs interact when the effect of a drug is modified by another co-administered drug, food or herb. According to a number of studies, almost half the prescriptions are accompanied by interactions (8–43%, depending on the ward), but few (12–25%) are clinically relevant. Antibiotics are a wide group of drugs used a great deal in our environment (in 49.8% of inpatients), and are associated with important interactions. Pharmacists help doctors to manage them by writing an intervention on the patient history, after evaluating patient clinical status.

Purpose To describe quantitative and qualitative antibiotic-drug interactions among our patients, assessing their expected clinical impact and intervening if they are relevant; to see how doctors modify prescriptions.

Material and methods We searched interactions involving antibiotics in all available prescriptions of every ward at the time of screening. We used Medscape app as screening tool, adopting their rating system (minor, significant, serious or contraindicated), considering intervention only in the relevant ones. SPSS20 was used for data coding and statistical processing. To improve intervention quality, additional data were reviewed in trusted sources like Stockley or Lex Interact.

Results Antibiotics were found in 156 prescriptions, mostly penicillins (45 prescriptions), quinolones (35) and carbapenems (34). A total of 1,415 interactions were detected (average per patient 9.07 ± 9.39), only 271 (19.2%) involving antibiotics. Among those, 76 minor, 116 significant, 78 serious and one contraindicated interaction were found. We intervened in only 16 cases (mostly about nephro/ototoxicity, serotonergic syndrome involving linezolid and monoamine-oxidase inhibitors, and proarrhythmic combinations). Only four prescriptions were modified after the interaction had been reported.

Conclusion Antibiotics play an important role in interactions; despite this few are dangerous, and must be filtered before choosing to intervene. Despite their relevance, doctors seem to underestimate the associated risks, ignoring the advice given. To improve their knowledge and respect for this topic, our Service will soon be teaching a course for healthcare professionals.

References and/or Acknowledgements (NONE)

No conflict of interest.

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