With antibiotic-impregnated catheters (AICs), the antibiotics act in the area of the critical surgical wounds and directly on the surface of the implant. This is therefore a local application of antibiotics in which antibiotics are delivered to the surrounding tissue via the catheters for a certain period of time. Instead of an antimicrobial coating on the catheter surface, as it is sometimes done in other implants, “impregnation” means that the antibiotics are embedded in the silicone matrix of the catheter. The manufacture of such "impregnated" catheters utilizes the fact, that certain organic solvents are absorbed by the silicone, like water by a sponge. During drying, i.e. when the solvent escapes again from the silicone, the dissolved antibiotics remain in the catheter. From there, they are slowly released into the CSF and surrounding tissue over at least the critical first four weeks after implantation. This antibiotics-dispensing time can be determined through the production process. Compared to a single dose of antibiotics during surgery, this delivery over a certain critical period of time naturally represents a decisive advantage. A further advantage is that the antibiotic not only acts externally towards the surrounding tissue, but also into the inside catheter lumen filled with CSF.

However, Rifampicin is unfortunately also known for its rapid development of resistance [51]. Therefore, it was combined with a second antibiotic (Clindamycin Hydrochloride), which has a different mode of action and thus makes the development of resistance unlikely. Another advantage of combining two different antibiotics is that individual concentrations can be lower and thus locally toxic concentrations can be avoided [52]

Since the first clinical study in 2003, Bactiseal has been used and described very often [53; 54]. In 2011, Medtronic additionally launched the ARES-catheter that conforms to the same specifications concerning the type and amount of antimicrobial agents used (510(k)-Nr.:K110560). Many study-data on the use of these products are available, which prove the safety and effectiveness of such AICs in the field of hydrocephalus therapy. Today, in Western countries, AICs are used as part of prophylactic protocols in a clear majority of cases. In their world-wide survey, Behbabani at el. analyzed 118 complete responses. The evaluation revealed that AICs are available in about 80% of the American and European institutions. Many other neurosurgical centers disclose that they routinely use AIC for all shunt or EVD procedures [25; 55; 56]. Data from two large multi-center studies also indicate the widespread use of AICs for pediatric patients in USA: the reported usage rates were over 50% within 2,007 cases, reported by Lakomkin et al. [57], and over 80% in 4,913 cases, as reported by Chu et al. [24].

As mentioned above, strictly speaking there is a lack of clinical evidence for many individual prophylactic measures in a hygiene protocol, with exception of AICS. This is because in 2019, the efficacy of AICs was demonstrated for the first time and with a very high level of evidence in the BASICS study [5; 6]. The BASICS study is one of the few randomized, prospective, controlled trials (RCTs) with an excellent study design and valid case number planning. It is initially surprising that this evidence was only provided so late, i.e. only recently, as catheters of this type have been on the market for over two decades and a large number of studies on their use are available. However, this fact underlines how time-consuming, cost-intensive and difficult it is to conduct a proper, well-designed RCT. All previous studies, including prospective randomized studies, had too small a number of cases to prove efficacy.

The BASICS study, on the other hand, must be regarded as an outstanding first-class RCT, which is elaborate and proper in terms of design, implementation and evaluation. In particular, the final case number of 1,605 patients, which is very high compared to other studies, corresponds to a sufficient study power of at least 80%. It compares three treatment groups with each other, which is why it is also referred to as a 3-arm study: standard catheters, silver-impregnated catheters and AICs. Silver-impregnated catheters (SICs) theoretically have a similar mechanism of action to AICs, but use silver as an anti-microbial agent. As with AICs, the silver is located in the silicone matrix and is released into the surrounding tissue when implanted. SICs are described much less frequently than AICs in the literature and their effectiveness is controversial.

A total of 1,605 patients of all ages and hydrocephalus etiologies were studied in 21 UK and Irish hospitals between 2013 and 2017, i.e. more than 530 cases per group. Only patients who received a ventriculoperitoneal shunt (from any manufacturer) for the first time were included. Patients with subsequent shunts were excluded, as these are known to carry an increased risk of infection and therefore cannot be fairly compared with first-time shunts. After implantation, all patients were followed up for a minimum of 6 months and a maximum of 2 years.

As a result, a significant difference was found between the infection rate of 6% in the standard group and that of 2% in the AIC group. The easily overlooked but important statement that this reduction was "significant" means that this difference was almost certainly not due to chance - "due to normal unavoidable variability" – but was actually due to the effectiveness of the AICs. As an important result of the BASICS study, it should be emphasized here that the group with the silver catheters had the same infection rate as the standard group (6%), so that it cannot be assumed that the SICs are effective.

The extensive BASICS data was also thoroughly analyzed in terms of the costs incurred. The result was that the use of AICs leads to an effective cost saving (in the UK healthcare system) of £135,753 (approx. $171,000, approx. €158,000) per infection avoided. This figure corresponds well with the results of previous comprehensive cost/benefit analyses. In 2015, Parker et al. analyzed data from 287 US hospitals from 10,819 adult and 1,770 pediatric patients [59]. They estimate the total additional costs per infection at approx. 45,000-95,000$ for adults and approx. 56,000-121,000$ for children.

„In analysis of this large, nationwide database, AICs were found to be associated with a significant reduction in infection incidence, resulting in tremendous cost savings. AICs were associated with a cost savings of $42,125 and $230,390 per 100 de novo shunts placed in adult and pediatric patients, respectively.“

Also in 2015, Edwards et al. [34] presented a comprehensive literature analysis, which came to the following conclusion:

“The rate of decrease in infection with AIC shunts was shown to have the greatest impact on the cost savings realized with use of AIC shunts.”

In terms of the cost-benefit analysis, the BASICS study has therefore fully confirmed the earlier analyses and, despite the higher initial costs, a relevant cost saving through the use of AICs can now be considered certain.

The decrease in the likelihood of infection with age was also confirmed, whereby the effectiveness of AICs is most evident in children and those with high infection rates.

However, BASICS also came to an unexpected conclusion: the cumulative overall revision rates, which include all possible complications or shunt failures, remained just as high for AICs as for standard catheters (and silver catheters). In other words, the mean lifetime of the shunt did not increase with AICs despite a reduction in the risk of infection. In the AIC study group, other complications instead of infections occurred more frequently, so that the relative number of all revisions remained unchanged. In particular, blockages of the ventricular catheter and valves increased. Mallucci et al. hypothesized that the AICs convert an infection into a low-grade infection in which the original pathogens with low virulence are confined to a biofilm in the (non-impregnated) valve body. This could then lead to mechanical failure. The authors write:

“However, changes in CSF composition and flow (such as debris or high protein) might block the intricate valve mechanism. Our study was not powered or designed to answer this question directly,[...] Nevertheless, from the patient’s perspective, although mechanical shunt revision still requires surgery which could impact on quality of life, the hospital admission is short, prolonged antibiotics are not required, and patients recover faster with fewer long-term neurological sequelae than if their shunts become infected.”

Clearly, a revision due to an infection is a worse complication than a revision caused by other reasons, as these infections are more difficult to treat and increase the risk of subsequent infections. Long antibiotic treatments and reoperations are not only devastating for the patient but also present a great burden to the healthcare system due to costs of the treatment (antibiotics, multiple reoperations) and prolonged hospital stays.

If the occurrence of increased revision rates for non-infectious reasons when using AICs is indeed confirmed, the underlying cause must be clarified in the future.

We end our overview with a quote from another recent meta-analysis, which also takes a critical look at the results of the BASICS study, the study by Goda et al. [60]. This work should not go unmentioned here because of the application of various, rather rarely used complex methods (“Cochrane risk of bias assessment tool”, “trial sequential analysis”, “network meta-analysis”) to clarify the evidence question:

 “…antibiotic medicated ventriculoperitoneal shunts had the highest probability of being the best option in terms of the relative infection rates.”

To date, the available evidence, thus, points to the effectiveness and cost-efficiency of antibiotic-impregnated catheters, giving surgeons a well-studied option to address infection risks in shunt surgery.