A Call for a Consortium for Optimal Management of Drug-Drug Interactions in Patient Care

Assessment of drug-drug interaction in an elderly human immunodeficiency virus population: Comparison of 3 expert databases

AIMS

Polypharmacy increase the risk of drug-drug interactions (DDIs) in the elderly population living with human immunodeficiency virus (HIV). Several expert databases can be used to evaluate DDIs. The aim of the study was to describe actual DDIs between antiretroviral drugs and comedications in an elderly population and to compare grading of the DDIs in 3 databases.

METHODS

All treatments of HIV-infected subjects aged 65 years and older were collected in 6 French HIV centres. Summary of Product Characteristic (SPC), French DDI Thesaurus (THES), and Liverpool HIV DDI website (LIV) were used to define each DDI and specific grade. DDIs were classified in yellow flag interaction (undefined grade in SPC and THES or potential weak interaction in LIV), amber flag interaction (to be considered/precaution of use in SPC and THES and potential interaction in LIV) and red flag interaction (not recommended/contraindication in SPC and THES and do not administer/contraindication in LIV).

RESULTS

Among 239 subjects included, 60 (25.1%) had at least 1 DDI for a total of 126 DDIs: 23/126 red flag DDIs were identified in 17 patients. All these 23 DDIs were identified in LIV. THES and SPC missed 6 and 1 red flag DDIs, respectively. Seven of 23 red flag DDIs were identified in the 3 databases concomitantly.

CONCLUSION

Polypharmacy is frequent in this elderly HIV population leading to DDI in a quarter of the subjects. The discrepancies between databases can be explained by differences in analysis methods. A consensus between databases would be helpful for clinicians.

Differential pharmacokinetic drug-drug interaction potential of eletriptan between oral and subcutaneous routes

1. Pharmacokinetic drug-drug interaction (DDI) data is important from a label claim either in combination drug usage or in polypharmacy situation. 2. Eletriptan undergoes first pass related metabolism through CYP3A4 enzyme to form pharmacologically active N-desmethyl metabolite. 3. Differential DDI interaction of the concomitant oral dosing of ketoconazole (20.1 mg/kg), a CYP3A4 inhibitor, with oral (4.2 mg/kg) or subcutaneous dose (2.1 mg/kg) of eletriptan was evaluated in male Sprague Dawley rats. Serial pharmacokinetic samples were collected and simultaneously analysed for eletriptan/N-desmethyl eletriptan using validated assay. Non-compartmentally derived pharmacokinetic parameters for various treatments were analysed statistically. 4. After oral eletriptan in presence of ketoconazole, C_max (40 vs. 32 ng/mL alone) and AUC_inf (81 vs. 24 ng.h/mL alone) of eletriptan increased; the formation of N-desmethyl eletriptan decreased (C_max=1.1 ng/mL, 3.9%) with ketoconazole as compared to without treatment (C_max=3.7 ng/mL, 11.2%). After subcutaneous eletriptan in presence of ketoconazole, there was no change in C_max (153 vs.152 ng/mL) or AUC_inf (267 vs. 266 ng.h/mL) of eletriptan. Formation of N-desmethyl eletriptan after the subcutaneous dose was determined at few intermittent time points with/without ketoconazole. 5. Preclinical data support differential DDI of eletriptan when dosed oral vs. subcutaneous, which need to be evaluated in a clinical setting.

Drug-drug interaction potential in men treated with enzalutamide: Mind the gap

AIMS

Metastatic castration-resistant prostate cancer (mCRPC) patients are generally older patients with several co-morbidities and are therefore at increased risk of complications due to drug-drug interactions (DDIs). We assessed the prevalence of potential DDIs in a cohort of mCRPC patients treated with enzalutamide.

METHODS

We conducted a retrospective review of pharmacy records to retrieve individual drug histories of mCRPC patients who started enzalutamide therapy in a tertiary care setting. Potential DDIs were analysed using two international drug interaction compendia: Lexicomp^® and Micromedex^® , and the Dutch drug database. Two potential pharmacodynamic DDIs were analysed.

RESULTS

A total of 105 records were evaluated for potential DDIs with enzalutamide. Of 205 different co-medications, 56 were flagged by at least one of the three compendia: Lexicomp, Micromedex and the Dutch drug database flagged for potential DDIs in 85%, 54% and 32%, respectively. Eighty-five per cent of DDIs were classified as major. The median number of co-medications per patient was 11 (range 1-26). The median (range) number of interactions per patient was 4 (0-10), 1 (0-5) and 0 (0-2) for Lexicomp, Micromedex and the Dutch drug database, respectively. In 23% and 45% of all patients, a potential DDI was found with PPIs and CNS depressants, respectively.

CONCLUSIONS

A high prevalence of potential DDIs was found. The inclusion and grading of potential DDIs was highly variable between the three drug interaction compendia. Physicians, nurses and pharmacists should be aware of this potential problem, which might require intensive monitoring or alternative treatment strategies to prevent suboptimal treatment of the co-morbidities in patients treated with enzalutamide.