Background Drug interactions are prevalent among HIV-infected patients, potentially resulting in drug toxicity, therapeutic failure and/ or viral resistance. HIV-infected patients are at higher risk of drug interactions given the multiple ARV agents required for treatment and the potential for co-morbidities. Previous research has shown interaction incidence with ARVs (antiretrovirals) to be high, with the majority of interactions occurring between ARVs and co-medication (non-ARV medication).

Purpose The aim of this research was to ascertain the rate of co-medication omissions from patients’ medical charts and to determine the significance of drug interactions between ARV agents and co-medications in an ID (infectious diseases) clinic.

Material and methods This mixed methods study incorporated face to face patient interviews and was conducted in an outpatient ID clinic. All patients over 18 and on at least one ARV (for HIV) attending the clinic over an eight week period were eligible for inclusion. 92 participants were interviewed and co-medications analysed for potential interactions with concurrent ARVs. Co-medication omissions were determined by analysing participants’ medical charts. Data was analysed using descriptive and non-parametric statistics in SPSS (vs 21). Mann-Whitney U (p < 0.05), Spearman’s (p < 0.05) and Kruskal Wallis test (p < 0.05) were used to determine the number of omissions, interactions and severity.

Results 179 omissions and 114 interactions were identified. 72.5% of co-medications were omitted (only 7.1% of ARVs were omitted). Interaction incidence was 46.2% with 41.2% of interactions considered high risk (contraindicated, major or moderate). 41.9% of co-medication omissions led to an interaction and 16.8% led to a high risk interaction. 49.4% of co-medications were prescribed by GPs while ID doctors accounted for only 8.1% of prescriptions. Number of co-medications was a significant factor for omissions and interactions.^* Age influenced interactions^** but not independently.^***

*(Spearman’s: p < 0.01);**(Spearman’s: p < 0.01);***(Multiple Regression: p > 0.1).

Conclusion Rates of co-medication omissions and interactions was alarming, but comparable with other studies. High risk interactions being overlooked may have serious consequences for patients. Ageing HIV populations suggest increased medicines use and hence risk for interactions. Polypharmacy and communication improvement were issues identified for reducing interaction rates. Recommendations to reduce omissions included pharmacist led medicine reconciliation and prescriber education.

References and/or Acknowledgements n/a

No conflict of interest.