In this episode, I will discuss the organism Stenotrophomonas maltophilia.
Stenotrophomonas maltophilia is a gram-negative bacteria that typically has low virulence. It is usually found in soil, plants, animals, and water environments. It is frequently considered a colonizer rather than a pathogen. However, in many patients, especially those with compromised immune systems, Stenotrophomonas has the potential to be pathogenic.
Sources of infection may be nebulizers, dialysates, distilled water, or contaminated disinfectants.
If Stenotrophomonas is cultured from a sterile site in an at-risk patient, it can usually be considered pathogenic. Sterile sites include blood or pleural fluid.
However, because Stenotrophomonas is a colonizer, consideration must be made as to whether a positive culture in a non-sterile site represents an active infection. Non-sterile sites include airway secretions, skin, and urinary cultures.
For example, in a patient with Stenotrophomonas found in airway secretions, a diagnosis of pneumonia should be made before treating Stenotrophomonas as a pathogen. The risk factors that increase the likelihood of Stenotrophomonas being pathogenic are underlying malignancy, cystic fibrosis, corticosteroid or immunosuppressant therapy, the presence of an indwelling central venous catheter and exposure to broad-spectrum antibiotics.
Stenotrophomonas is intrinsically resistant to many antibiotics, including most beta-lactams and carbapenems, and it can quickly acquire resistance through horizontal gene transfer or mutation.
When it does cause an infection, Stenotrophomonas forms a biofilm and the duration of treatment usually is at least 14 days.
The preferred therapy to use when Stenotrophomonas is identified is sulfamethoxazole-trimethoprim. The dose, assuming normal renal function, is 15-20 mg/kg/day of trimethoprim component, divided into 3 doses.
In the event of a severe sulfa allergy, fluoroquinolones and minocycline are potential agents that can be used to treat Stenotrophomonas. When using minocycline, consider giving a loading dose of 200 mg before dropping down to 100 mg every 12 hours.
The biggest pitfall for taking care of a patient with a Stenotrophomonas infection is using an antibiotic that does not have sensitivity data. Because of the high risk of resistance the use of any other antibiotic therapy for Stenotrophomonas should be guided by sensitivity data. Other antibiotics that have the potential to be useful based on sensitivity data are:
- Doxycycline
- Ceftazidime
- Ceftriaxone
- Ampicillin/sulbactam
- Ticarcillin/clavulanate
- Tigecycline
In the case of multiple drug resistance, colistin with or without another agent should be used.
Asking questions about Stenotrophomonas is also a great test of whether your student or resident is on top of their game. So many students and residents seem to assume that since Stenotrophomonas rhymes with pseudomonas, it must be covered by similar antibiotics. As we just discussed, nothing could be further from the truth!
When a student or resident recognizes they are unfamiliar with Stenotrophomonas, I am looking to see whether they first take steps to close that knowledge gap before answering questions about which antibiotics to use.
Preceptors who belong to my Hospital Pharmacy Academy are now able to grant their students and residents 45-day complimentary access to the Academy content while they are on rotation.
With this feature, topic discussions have never been easier! Just assign your students and residents a Masterclass, then use that information to lead into a more advanced topic discussion, with no preparation on your part as a preceptor.
For example, I assign my students and residents the Vasopressor Masterclass. Then I ask the 7 topic discussion questions which accompany that Masterclass to lead a topic discussion, filling in the learner’s knowledge gaps as we progress through the questions.
To learn more about the Hospital Pharmacy Academy and join go to pharmacyjoe.com/academy.
If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.
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