MRCPath Part1
Congratulations!
For those of you who found out that you passed Part 1 or Part 2 of the FRCPath last week, Congractulations!
Beta-lactamases
- Clavulanic acid, ceftazidime, cefoxitin, cefotetan and imipenem are all strong inducers or selectors of Class C β-lactamases in many nosocomial gram negative organisms and have the potential to increase the development of resistant organisms in individual patients and in the hospital flora. Therefore, these agents should be used only when necessary.
Virology resources
Here are two useful resources:
AMH.
How to pass FRCPath Part 1
I thought that I would share with you my tips for passing Part 1 in Medical Microbiology & Virology. Here are my ten top tips.
Antifungal Drugs [overview]
This review on antifungal drugs and their mechanisms of action, can be found HERE.
AMH.
Boosted PI
The boosting of PIs is a therapeutic strategy wherein a small dose of ritonavir is given concurrently with another PI to pharmacologically enhance exposure to the latter PI through the inhibition of the enzyme cytochrome p450. For many of the PIs, ritonavir boosting results in improved drug levels that can increase efficacy, decrease pill burden, add flexibility to the dosing schedule, and remove fasting restrictions. However, with increased drug exposure, there is the potential for increased toxicity, which has manifested in greater gastrointestinal intolerance (lopinavir/ritonavir), nephrolithiasis (indinavir), hyperbilirubinemia (indinavir, atazanavir), and hyperlipidemia (many PIs). Boosting can also result in significant drug interactions with other compounds metabolized by the cytochrome p450 pathway. Whether boosting increases lipodystrophy remains unclear.
At this point in time, most PIs -- including lopinavir, saquinavir, indinavir, and amprenavir -- are given in the boosted form. Whether atazanavir should be administered without boosting to antiretroviral-naive patients remains an issue of debate, but it is generally boosted when prescribed for treatment-experienced patients and must be boosted when used in tandem with an NNRTI or tenofovir. Nelfinavir, which is naturally boosted by food, remains the only PI for which boosting with ritonavir is not recommended.
AMH.
Yersinia spp.
- Y. enterocolitica and Y. pseudotuberculosis are pleomorphic gram-negative bacilli in the family Enterobacteriaceae.
- They are non-lactose-fermenting, urease-positive organisms that grow at a wide range of temperature; they are motile at 25° C but not at 37° C.
- Y. enterocolitica colonies give a “bulls-eye” appearance on CIN (cefsulodin, Irgasan, novobiocin) medium. Y. pseudotuberculosis colonies on CIN medium are smaller with a deep-red centre with a sharp border surrounded by a translucent zone. Yersinia species are facultative anaerobes, oxidase-negative and ferment glucose with little or no gas production. They are non-motile at 37°C, but, with the exception of Y. pestis, are motile at 22 - 29°C. Phenotypic characteristics are often temperature dependent and more are expressed by cultures at 22– 29°C rather than 35 - 37°C.
- Both grow on BHI, MacConkey, and SS agars at room temperature and at 37° C, and in buffered saline at 4° C. Colonies are difficult to detect after incubation for 24 hours but are readily apparent at 48 hours.
- They can be distinguished from other enteric pathogens and from Y. pestis by biochemical profiles; however, rapid tests may be a cause of misidentification if not properly coded.
- More than 60 serotypes and six biotypes of Y. enterocolitica have been described. Most strains from patients belong to serotypes O:3, O:5.27, O:8, and O:9 and to biotypes 2, 3, and 4. There is a separate system for serotyping Y. pseudotuberculosis, also based on somatic antigens. Six serotypes (I through VI) and four subtypes of Y. pseudotuberculosis have been identified, with O-group I accounting for approximately 80% of human cases.
HBV Mutants
Chronic Immune Active HBV (Precore and Core Promoter Mutants)
Some individuals with chronic hepatitis B are infected with a mutant HBV variant that results in HBeAg negative chronic hepatitis. In such patients, viral mutations in the precore or core promoter regions prevent HBeAg production in an otherwise normally replicating HBV. Thus, these patients typically have high serum HBV DNA levels, but negative HBeAg titers. The prevalence of precore or core promoter mutations is highest among persons from Southern Europe and Asia, with prevalence estimates of 60-70%. Chronic HBeAg-negative hepatitis B is diagnosed in a patient with the following laboratory profile:
- HBsAg positive longer than 6 months
- HBeAg negative, anti-HBe positive
- Serum HBV DNA greater than 104 copies/ml
- Persistently elevated or intermittently normal hepatic aminotransferase levels
