Outpatient parenteral antimicrobial therapy

What is OPAT?

OPAT is the administration of intravenous antimicrobial therapy to patients in an outpatient setting or in their own home. It can be used for patients with severe or deep seated infections who require parenteral treatment but are otherwise stable and well enough not to be in hospital; these patients may be discharged early to an OPAT service or may avoid hospital admission altogether.

What type of infections can be treated?

Which patients are suitable?

Patients referred for outpatient treatment need to be clinically stable, both in terms of their general condition and their infection. Thus they should have stable vital signs and be at low risk of their infection progressing or developing serious complications.2 3 24 Patients with a diagnosis of cellulitis, for example, need to be assessed by a healthcare practitioner competent to exclude other more serious conditions that could potentially be confused with cellulitis, such as septic arthritis or necrotising fasciitis. Patients with endocarditis are more likely to develop potentially life threatening complications in the first two weeks of therapy, and outpatient administration is therefore not recommended until after this period.16 Determination of suitability will generally require a medical review, unless a protocol is in place for assessment by another trained healthcare practitioner.11

Other health and social issues also need to be explored. OPAT requires the patient to engage actively and reliably with therapy, and thus patients with substance misuse or serious mental health problems may not be suitable. In addition, there must be no other barrier to discharge from hospital. For example, although diabetic foot infections may be suitable for OPAT, many patients will require other care that has to be provided in hospital, including adjustment of diabetic control, vascular assessment, and surgical intervention.25 Finally, home based care must be suitable from a social perspective—for example, an acceptable home environment, access to a telephone, adequate transport, and support from family or carers, In general the OPAT nurse, in collaboration with other professional teams, is best placed to assess these additional factors, and current OPAT guidelines recommend that patients should be assessed by both a doctor and nurse before being accepted for outpatient administration.2 3 24

How is OPAT delivered?

Three service models can be used to deliver OPAT, all of which have been shown to be effective: an ambulatory care centre, a nurse attending the patient’s home, or self administration. The approach used varies among countries—for example, infusion centres have been the dominant model in the US whereas services in Australia tend to follow the “hospital in the home” visiting nurse model. However, it is becoming increasingly common for individual OPAT services to offer all three models, allowing treatment to be tailored to each patient’s circumstances.2 Most OPAT services described in the literature are based in acute hospitals, predominantly in specialist infectious diseases units.4 5 13 18 Services may also be established by other inpatient specialist teams or in frontline emergency or acute medicine units9: in the UK, the Society of Acute Medicine has recently established a working group to promote the development of OPAT in this setting.

In the ambulatory care centre model, the patient attends a healthcare facility daily, or as required, with antibiotics administered by a healthcare practitioner. Treatment in the patient’s home may be administered by community nurses, outreach nurses from the acute hospital, or nurses provided through a private healthcare company. In the third model patients (or carers) are taught to administer therapy; this has the advantages of engaging patients in their care, allowing more flexibility of dose frequency and timing, and reducing staffing costs. Despite theoretical concerns about line infections, two large retrospective studies have shown that self administration is as safe as administration by a healthcare worker in the community.14 26

The model of OPAT used largely determines the type of intravenous access. Options include temporary “butterfly” needles that are inserted and removed for each dose, short term peripheral cannulas, or, for longer antibiotic courses, peripherally inserted central cannulas or tunnelled central lines. Bolus injections or infusions may be used, depending on the choice of antimicrobial agent(s). Infusions allow higher doses to be administered but require additional administration time and training.27 Novel delivery devices allow patients greater freedom to continue normal daily activities. For example, portable elastomeric infusion devices can be carried in the patient’s pocket or a carrying pouch and deliver continuous infusions over 24 hours.3

What are the benefits?

The clinical effectiveness of OPAT has been established for a wide range of infections through numerous retrospective case series, as outlined above. However, there have been few randomised controlled trials comparing OPAT with inpatient care. Furthermore, there are no published data on clinical efficacy of OPAT services based entirely in a community setting, although there are descriptions of collaborative services across primary and secondary care sectors.9

OPAT has been shown to be cost effective in many healthcare contexts. One retrospective study from a UK service compared the actual costs of OPAT over two years with the theoretical costs of inpatient care for the same patient cohort and found that OPAT cost 47% of equivalent inpatient national average costs.4 However, in reality there is a wide range of funding arrangements for OPAT in operation across the UK, and in some instances OPAT may offer little cost advantage to commissioners over inpatient care. A national tariff for OPAT would allow consistency and equity and support wider use.

In addition to reducing direct costs, OPAT frees inpatient capacity, which can then be used either to admit further patients or as part of a planned reduction in bed capacity. More detailed modelling of these downstream benefits has not been undertaken but might provide added evidence of OPAT’s cost effectiveness.

Finally, there is increasing evidence that OPAT is associated with a very low rate of healthcare associated infection. Despite theoretical concerns about the use of broad spectrum agents such as ceftriaxone, the risk of Clostridium difficile infection seems to be low: a meta-analysis of three large UK OPAT cohorts found the rate of C difficile infection to be 0.1%,10 although there are no published prospective data.

What are the risks?

Despite these benefits, OPAT is associated with increased clinical risk compared with inpatient care because of the reduced level of supervision. At least 25% of patients having OPAT experience an adverse reaction of some type, ranging from mild antibiotic associated diarrhoea to severe line infections.24 The treatment pathway—from patient selection, determination of the therapeutic regimen and intravenous access device to communication with other teams and ongoing monitoring during therapy—provides numerous opportunities for error.28 In addition, as OPAT is used increasingly for more complex infections in patients with serious comorbidities, the likelihood of adverse events unrelated to the infection increases. A retrospective survey of US physicians involved in OPAT found that 68% had seen at least one major adverse event in their patients in the preceding year,29 highlighting the importance of a formal governance structure. The adverse events included unexpected death, line related bacteraemia, air embolism, drug hypersensitivity, and drug induced blood dyscrasia.

About 10% of patients will require readmission, with higher rates for patients with more complex infections.4 5 14 18 19 In addition, many patients require further unplanned input during therapy: one study found that 12% of OPAT patients needed urgent advice or an unscheduled home visit.30 Thus it is essential that the service has an established system for 24 hour access to clinical support and a formal (re)admission pathway to secondary care.

One further potential risk is overuse of intravenous antimicrobial therapy as an alternative to oral agents purely because an OPAT service exists. Similarly, there is also a risk that a broad spectrum once daily parenteral antimicrobial agent could be chosen in preference to a potentially more efficacious agent requiring multiple daily doses for reasons of convenience alone. OPAT should therefore operate within the context of an antibiotic stewardship programme, and it is essential that a microbiologist or infectious diseases physician is involved in both the initial design of antibiotic protocols and ongoing patient care. Several studies have found that assessment of referred patients by an infection specialist results in reduced use of intravenous therapy, improved clinical care, and substantial cost savings.31 32 33

How can the risks be reduced?

It is clear that OPAT delivered through a formal service structure is safer than when delivered through ad hoc arrangements. Several bodies have published recommendations on delivery of OPAT2 3 34 and the aim of these is to ensure that the risks associated with OPAT are minimised. In the UK a consensus statement on the use of OPAT was recently published as a joint initiative between the British Society for Antimicrobial Chemotherapy and the British Infection Association.24 It covers service structure, patient selection criteria, antimicrobial selection and delivery, frequency and type of clinical and blood test monitoring, monitoring of outcomes, and clinical governance. It recommends the core OPAT team should comprise, as a minimum, an OPAT specialist nurse, doctor, infection specialist (either an infectious diseases physician or a microbiologist), and a pharmacist. A doctor with suitable training and experience (who may also be the infection specialist, when he or she delivers hands-on clinical care) should take responsibility for management decisions for each patient, in collaboration with the team. Although patients on prolonged courses of antimicrobials can be reviewed weekly, or less frequently if stable, those receiving treatment for cellulitis should be reviewed daily to allow switching from intravenous to oral therapy as soon as clinically appropriate.

What is the future of OPAT in the UK?

OPAT offers a rare opportunity not only to improve patient choice while maintaining service quality but also to reduce healthcare costs and improve service efficiency. Use of OPAT is likely to continue to expand in the UK, as in many other countries, driven by enthusiasm for increasing care delivery in the community as well as by cost pressures and patient choice. OPAT was recently cited as one of five antimicrobial prescribing decision options in Department of Health guidance on antibiotic stewardship.35 Services will continue to be developed both in primary and secondary care, and it is likely that integrated services across sectors will be established in order to combine primary care’s capacity and expertise in home treatment with the specialist knowledge and back-up of secondary care.