Establishing whether it is safe to switch
The principles of, and criteria for, switching from OPAT to oral therapy are similar to those applied to inpatients switching from IV to oral antibiotics.
The following should be considered:
Physiological stability – although patients should be physiologically stable before commencing OPAT, all OPAT patients have their basic observations checked on each attendance (i.e. pulse, blood pressure, respiratory rate, temperature and oxygen saturations).
Any clinically important change in these observations merits patient review. All parameters should be checked and be within normal ranges (or be normal for that patient) before switching to oral therapy.
If physiological parameters are not within normal ranges, an explanation should be sought and patient safety ensured before switching to oral therapy.
Establishing the patient is clinically improving – assuming the patient’s basic observations are satisfactory, other criteria are reviewed. These include:
The patient’s history (i.e. are they feeling better, is pain improving, are other symptoms improving, etc.) and examination as appropriate.
Blood markers of infection and inflammation (e.g. WCC and CRP; procalcitonin if used) should be reviewed.
In case 1 the patient’s observations are normal and their blood tests have improved, but on examination there is local deterioration and what appears to be an abscess has evolved. If available, the patient requires an ultrasound scan to confirm this and, if confirmed, will require incision and drainage.
Although it is possible oral therapy will suffice at this point in time, most clinicians will continue OPAT (or if readmitted to hospital, IV therapy) until surgery and then consider an early switch to oral antibiotics depending on clinical progress thereafter and microbiological cultures from operation (e.g. highly resistant bacteria may mandate ongoing IV therapy).
In general, once relatively small soft tissue abscesses are incised and drained, only relatively short courses of antibiotics are required and for small uncomplicated abscesses (<5cm diameter), perhaps none at all.
Is the oral route or gastrointestinal tract (absorption) compromised – this is not a problem in most OPAT patients, but sometimes patients with malabsorption or a short bowel may require IV therapy throughout or therapeutic drug monitoring (TDM) after switching to oral therapy.
Does the patient have a ‘red-flag’ diagnosis that mandates a certain length of IV therapy, such as meningitis? Increasingly, the evidence-base for an earlier switch to oral antibiotics is emerging; for example, in the management of bone and joint infections and endocarditis (e.g. OVIVA and POET trials, respectively, as discussed in step 1.5).
Is there an evidence-base or national guideline about when to switch to oral therapy for the infection being treated by OPAT? In endocarditis, for example, current national and international guidelines suggest IV therapy throughout (please find resources in see also and downloads below), although the recent POET trial (see step 1.5) challenges this guidance for selected patients.
Is clinically effective and safe oral therapy achievable accounting for the following factors:
- Antimicrobial susceptibility of isolated pathogens – ideally, the narrowest spectrum effective and safest agent should be used accounting for other considerations.
- Oral and tissue bioavailability (at the site of infection) of potential oral agents.
- Antibiotic intolerances and allergies.
- The potential for drug-drug interactions.
- Patient comorbidities including obesity.
- Predicted patient adherence.
- Pregnancy (including likelihood of occurring on therapy), breast-feeding and impact on contraception.
A 2016 paper Alkhoufi et al said the objective of their study was:
to develop a set of measurable conditions that should be met in adult hospitalised patients for a safe IV-to-oral switch.
Table 1 on page 545 of their paper lists their suggestions.