Calcium sulphate as a local antibiotic carrier in the treatment of bone infections and deep wounds

Why use local antibiotic therapy?

Chronic osteomyelitis, fracture-related infection and infection around orthopaedic implants share a common feature: microorganisms live in poorly perfused or necrotic tissue and in biofilms. Systemically administered antibiotics reach these areas at low concentrations, whereas activity against bacteria in biofilms requires concentrations many times higher than the usual minimum inhibitory concentration (MIC).

A local antibiotic carrier is placed in the cavity created by surgical removal of necrotic bone and infected tissue. The aim is to achieve a high local drug concentration precisely where the risk of recolonisation is greatest, with low systemic exposure. The carrier also fills dead space, which would otherwise fill with haematoma and provide a favourable environment for recurrent infection.

What is calcium sulphate as a carrier?

High-purity synthetic calcium sulphate, rather than natural gypsum, is used for this indication. The powder is mixed with liquid and the selected antibiotic, then formed into beads or a paste, or injected into the defect. After setting, the carrier gradually dissolves in the tissue over several weeks, releasing the antibiotic as it does so.

Properties relevant to clinical practice

• Resorption: the carrier breaks down in the tissue, so a second procedure for its removal is generally unnecessary.
• Release profile: most of the antibiotic is released in the first few days, with lower release over the following weeks; the exact kinetics depend on the drug, the form of the carrier and local conditions.
• Osteoconductivity: the carrier can act as a temporary scaffold for bone ingrowth, but complete filling of the defect with bone tissue is not the rule.
• Antibiotic compatibility: heat generation during setting is considerably lower than with bone cement, allowing heat-sensitive drugs to be used.

In laboratory models, antibiotic-loaded calcium sulphate beads prevented colonisation and biofilm formation on implant surfaces and were also active against established biofilms. These findings explain the mechanism but do not demonstrate clinical outcomes.

Comparison with non-resorbable carriers

The conventional local carrier consists of antibiotic-loaded polymethylmethacrylate beads or spacers. These are well established and mechanically stable, but they do not degrade and are usually removed in a second procedure. Once the antibiotic has been released, their surfaces can provide a substrate for biofilm formation.

In a small randomised study of chronic osteomyelitis and infected nonunion, both carriers achieved similar infection eradication rates, while the resorbable carrier group underwent fewer repeat operations. The study included 30 patients and should therefore be interpreted as preliminary evidence.

When is use considered?

• Chronic osteomyelitis after surgical removal of necrotic bone.
• Fracture-related infection and infected nonunion, as part of staged treatment.
• Periprosthetic joint infection, during revision surgery and as an adjunct to other measures.
• Selected cases of diabetic foot osteomyelitis after surgery, following a multidisciplinary decision.
• Deep soft-tissue cavities after debridement of infected tissue, when dead space needs to be filled.

Debridement is a prerequisite

A local carrier does not treat infection that the surgeon has not removed. The outcome depends primarily on complete removal of necrotic bone, sequestra and infected foreign bodies, bone stability and the ability to cover the defect with healthy, well-perfused soft tissue. In chronic limb ischaemia, the feasibility of revascularisation should be assessed first, because without a blood supply neither a local nor a systemic approach can achieve healing.

Bone and deep-tissue samples for microbiological and histopathological analysis are taken before the carrier is placed. The results guide systemic antibiotic therapy and allow assessment of whether the chosen local antibiotic was appropriate.

Antibiotic selection

Vancomycin, gentamicin and tobramycin are the most commonly used antibiotics, alone or in combination, because together they cover a large proportion of Gram-positive and Gram-negative pathogens. The drug must be suitable for mixing with the carrier and must not adversely alter its setting time. Some antibiotics delay or prevent setting, so the combination and dose are selected according to the carrier's instructions and verified compatibility data.

Selection should take account of the known or expected pathogen, previous microbiological findings, the patient's drug hypersensitivity and renal function. Local administration does not remove the need for culture-directed systemic therapy.

Monitoring and adverse effects

Wound discharge

As the carrier dissolves in the tissue, fluid forms and may drain through the surgical wound, particularly when a large volume of carrier has been used or the soft-tissue layer is thin. In a large series of chronic osteomyelitis cases, prolonged discharge lasting more than two weeks was recorded in 15.4% of cases and was not associated with recurrent infection. In a systematic review and meta-analysis, wound complications were recorded in 17% of patients treated for osteomyelitis.

The discharge may be clear or whitish and milky because of the dissolved carrier. It should be distinguished from purulent discharge, spreading erythema, increasing pain and fever, which indicate infection. For wound care, this means more frequent assessment, an absorbent dressing appropriate to the volume of exudate and protection of the periwound skin from maceration.

Systemic effects

• Transient hypercalcaemia has been reported, particularly with larger carrier volumes; serum calcium levels are monitored in patients at risk.
• Renal function is monitored when aminoglycosides or vancomycin are used, particularly in patients with pre-existing chronic kidney disease, older people and those receiving other nephrotoxic drugs.
• Heterotopic ossification and soft-tissue irritation have rarely been reported, mainly when the carrier has not remained confined to the bone defect.

Razina dokaza·Low to moderate · Pedrazzini et al., systematic review and meta-analysis, 2026.Included 41 studies, with no randomised controlled trials.

What does the evidence show, and what are its limitations?

A 2026 systematic review and meta-analysis included 41 studies and found no randomised controlled trials. The pooled infection eradication rate was 88% for osteomyelitis and also 88% for periprosthetic joint infection, with substantial heterogeneity between studies. These results reflect the overall treatment rather than the effect of the carrier alone, as patients also underwent surgery and received systemic antibiotics.

Data on diabetic foot osteomyelitis are sparse and inconsistent. In a retrospective cohort of 45 patients, 29% were ulcer-free at six months, osteomyelitis recurred in 42%, wound discharge was recorded in 62% and acute kidney injury in 9%. The authors recommended caution pending randomised studies.

In their joint 2023 guidelines, the International Working Group on the Diabetic Foot (IWGDF) and the Infectious Diseases Society of America (IDSA) suggest not using local antibiotics as an adjunct to systemic therapy for soft-tissue and bone infections of the diabetic foot. This is because the certainty of the evidence is low: available studies have a high risk of bias and inconsistent results, and the safety of routine use has not been clearly established. The use of a local carrier in this population is therefore an individual decision for an experienced team, rather than standard practice.

Role in wound care

For the wound-care team, most of the work begins after surgery. It is important to know that a resorbable carrier has been placed in the wound, what discharge to expect and which signs indicate infection or compromised wound closure.

• Document the type of carrier, the added antibiotic, the date of placement and the anatomical site.
• At each dressing change, describe the amount, colour and odour of the discharge and the condition of the wound edges and periwound skin.
• Select a dressing according to the volume of exudate and protect the periwound skin; for heavy discharge, consider more frequent dressing changes or a more absorbent dressing system.
• Do not irrigate the wound under pressure or remove white material appearing in the wound without consulting the operating surgeon.
• Monitor laboratory results requested by the operating surgeon, such as renal function and calcium levels.
• Notify the operating surgeon without delay if there is purulent discharge, spreading erythema, increasing pain, fever or separation of the wound edges.

Frequently asked questions