Where possible those antibiotics most associated with harm should be avoided in those most at risk. These include the 4C antibiotics which are most associated with C.diff infection. Older people are more likely to have had previous antibiotic exposure and therefore have an increased incidence of bacteria resistant to antimicrobials.

See: Prevention, diagnosis and management of CDI

The frail elderly are at increased risk of antimicrobial related adverse effects, healthcare associated infections, and infections due to resistant organisms. 

Things to think about when prescribing in frail elderly patients

1. When anticipatory/advanced care plans are in place or 'end of life care' initiated, carefully consider the relative clinical benefits and risks of antimicrobial therapy.
2. Review old microbiology results to assess the potential of a resistant organism – including MRSA and multi-drug resistant E.coli.
3. Follow the guidelines.
4. Check for potential drug interactions due to polypharmacy. Clarithromycin is a particular risk for cardiac adverse events.
5. Monitor response to antimicrobial therapy daily; identify resolution of infection by temperature normalisation, and increased energy, alertness, mobility and appetite.
6. A duration of 5 days is usually sufficient for most indications unless there is a clear indication for a longer duration.
7. Avoid long term use of prophylactic antimicrobials in patients with recurrent UTIs.