Oral and enteral route of administration for antimicrobials
For most infections, oral antimicrobial therapy is appropriate. Parenteral (eg intravenous, intramuscular) therapy may be required under specific circumstances – see Parenteral route of administration for antimicrobials.
Advantages of oral therapy over parenteral therapy may include the absence of intravenous catheter–associated infection risk or thrombophlebitis, lower drug cost, and reduced hospital costs (eg staff, equipment). Oral therapy may facilitate early discharge from the hospital or emergency departmentMcCarthy, 2020.
If oral therapy is used, ensure that:
- the patient can tolerate the antimicrobial and has reliable oral absorption
- the selected antimicrobial:
- is appropriate for the indication
- has adequate tissue penetration at the infection site
- has good bioavailability (see Examples of antimicrobials with good oral bioavailability in adults).
[NB1]
The following examples are antimicrobials that have oral bioavailability over 90% at standard oral dosing:
- ciprofloxacin [NB2]
- doxycyclineLandersdorfer, 2023
- fluconazoleLandersdorfer, 2023
- itraconazole
- linezolidLandersdorfer, 2023
- metronidazole
- moxifloxacin
- posaconazole modified-release tablets
- rifampicin
- trimethoprim+sulfamethoxazole
- voriconazole.
The following examples are antimicrobials that have oral bioavailability between 50 and 90% [NB3]Béïque, 2015:
- amoxicillin
- amoxicillin+clavulanate
- cefalexin
- clindamycinLandersdorfer, 2023
- flucloxacillin.
The following is an example of an antimicrobial that is extensively distributed and achieves high intracellular concentrations; as a result, it is effective even though its oral bioavailability is low:
- azithromycin.
NB1: This figure should not be extrapolated to children as bioavailability of antimicrobials in children differ from adults.
NB2: Lower oral bioavailability is compensated by increased oral dosing.
NB3: These antimicrobials may be given orally rather than parenterally; however, intravenous therapy is still required in patients with severe infection or where the chosen antimicrobial does not have adequate tissue penetration at the infection site.
For children unable to swallow tablets, the availability of a suitable drug formulation can affect antimicrobial choice. The Australian Medicines Handbook Children’s Dosing Companion1 includes information about the administration of medicines to children (including information about palatability).
To enable administration in children, it may be possible to crush or disperse oral solid-dose formulations of antimicrobial. Considerations include:
- the suitability of the oral solid-dose formulation for crushing or dispersing – see the Don’t Rush to Crush Handbook2 for detailed advice
- the ability of carers to perform preparation steps
- patient acceptability (eg taste)
- practicality of dosing, consider:
- rounding the dose to capsules, whole tablets or tablet portions (for scored tablets) – this may enable more accurate dosing
- the volume of liquid formulation required to administer the dose – it may be possible to use a more concentrated liquid formulation to enable a smaller volume to be administered.
If the oral route is unsuitable, the enteral route (eg nasogastric [NG], nasoenteric, percutaneous endoscopic gastrostomy [PEG]) may be used.