Oral or IV antibiotics?

There are many self-perpetuating myths when it comes to antibiotic use in children. A few that seem intuitive, and come up almost daily, include the idea that intravenous antibiotics are ‘better’, that children require lower doses than adults, and ‘longer is better’ when it comes to treatment duration.

A few key concepts can be helpful to understand why certain routes and doses of antibiotics are required:

• Pharmacokinetics: the effect of the body on the drug – how the body absorbs, distributes, metabolizes and excretes the antibiotic
• Pharmacodynamics: the effect of the drug on the body – how the antibiotic effects bacteria in the body 
• Bioavailability: the amount of the antibiotic which is effectively absorbed when given orally and reaches the bloodstream

Here are some points to consider next time you need to chart antibiotics for a child.

When are intravenous antibiotics absolutely required?

1. Speed – if there is a life (think sepsis, meningitis) or limb-threatening (eg. necrotising fasciitis) intravenous antibiotics are required as they reach peak plasma levels in seconds/minutes, rather than hours
2. Absorption – for children with poor or unreliable oral absorption (eg. inflammatory bowel disease, short gut) intravenous antibiotics will likely be required
3. Neonates – in general neonates are considered to have poor oral absorption, therefore antibiotics are usually given intravenously
4. No oral options – in some cases there may be no oral option available; this is particularly relevant for highly resistant organisms such as extended-spectrum beta-lactamase producing organisms
5. High dose – if a very high dose of an antibiotic is required the volume of liquid required for a child to consume may be excessive, in these cases intravenous antibiotics may be required
6. Nil per os – in children who are not able to take any oral medications (eg. bowel obstruction) intravenous antibiotics may be required; remember insertion of a nasogastric tube and NG medications may be an option particularly for younger children
7. Worsening infection on oral antibiotics – this one can be a little tricky as factors such as wrong dose (antibiotics are commonly under-dosed in the community), wrong antibiotic, and poor compliance need to be considered, but sometimes children may require admission for intravenous antibiotics

When can you change to oral antibiotics?

There are four general principles guiding the change from intravenous to oral antibiotics (McMullen et al.)

• Clinical condition – note that fever alone does not need to prevent switch
• Ability to absorb oral antibiotics
• Availability of an appropriate oral antibiotic
• Practical issues

The above reference gives a thorough discussion on the evidence of when to switch to oral antibiotics for a range of common paediatric infections (skin and soft tissue, urinary tract infections etc).

What are other factors need to be taken into account?

Bioavailability – some drugs have excellent oral absorption, therefore there it is almost criminal to give them IV if the child can swallow them! Think metronidazole, rifampicin, doxycycline, ciprofloxacin and clindamycin (which all have good tissue penetration)

“Help – my child refuses to take oral antibiotics!” – this is a tricky one and the use of an experienced paediatric pharmacist is invaluable as there are many aids that can be used to help resilient toddlers take their medications

Why is this important?

The implications of shortening the course of intravenous antibiotics and antibiotics overall are numerous…

• Shorter courses of antibiotics may affect antimicrobial resistance
• Shorter inpatient stays (required unless outpatient antimicrobial therapy available through a hospital in the home service) associated with improved quality of life in children and their families, and money-saving for the hospital system
• Intravenous antibiotics may be associated with line complications, pain and traumatic experiences for children

Selected references

McMullan BJ, Andresen D, Blyth CC, Avent ML, Bowen AC, Britton PN, Clark JE, Cooper CM, Curtis N, Goeman E, Hazelton B. Antibiotic duration and timing of the switch from intravenous to oral route for bacterial infections in children: systematic review and guidelines. The Lancet Infectious Diseases. 2016 Aug 1;16(8):e139-52.