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HY points about each drug followed by a quiz at the end
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Hepatitis B
- Many drugs used for hepatitis B. USMLE does not expect you to memorize all of them.
- Questions on the USMLE will be more focused on understanding hepatitis B serology.
BEATT → Hepatitis B, Entecavir, Adefovir, Telbivudine, Tenofovir
Entecavir, Telbivudine
MOA of entecavir and telbivudine?
- Competitively inhibit HepB DNA polymerase.
- Nucleoside analogues.
Adefovir, Tenofovir
MOA of adefovir and tenofovir?
- Inhibit reverse transcriptase.
- Adenosine nucleotide analogues.
- Tenofovir is also used for HIV as part of HAART therapy.
Interferon-alpha
MOA of interferon-alpha as antiviral therapy?
- Causes degradation of viral mRNA, thereby inhibiting protein synthesis.
- Different formulations, including pegylated-interferon-alpha, which can be used for both HepB and C.
Adverse effects of interferon-alpha?
- Neutropenia (mouth ulcers, sore throat, fever).
- Depression.
What do I need to know about the microbiology for hepatitis B?
- USMLE specifically wants you to know that it is DNA, enveloped, and circular (yes, they ask this).
What do I need to know about HepB serology?
- HBs – surface antibody
- A marker of immunity.
- Positive if immune; negative if not immune.
- This should pretty much be the first marker you look at when interpreting HBV lab results. You can immediately just say, “Okay, the patient is immune.” Or, “Ok, he/she is not immune.”
- HBsAg – surface antigen
- A marker of infectivity.
- If positive, indicates current infection, either acute or chronic.
- If (+), means the patient cannot be immune because he or she clearly has a current infection.
- HBeAg – “e” antigen
- Marker of robust infectivity.
- Correlates with a high level of viral replication.
- If positive, means person with HepB can easily transmit virus to a non-immune individual.
- Helps guide clinical management.
- HBcAb – core antibody
- Marker of acute, chronic, or resolved HBV infection.
- If positive, means person has had the actual disease before, either now or in the past.
- Cannot be positive if the patient has never been infected.
- Negative if vaccinated.
- HBcAb IgM
- Subclass of HBcAb.
- Positivity indicates recent infection with HBV (<6 mos).
- Positive during the window period.
- HBcAb IgG
- Subclass of HBcAb.
- Marker of past or current infection.
- If HBsAg is also positive (and HBcAb IgM is negative), indicates chronic HepB infection.
As the patient begins to develop immunity to HepB, he or she will start producing HBsAb. At the same time, as he or she begins to clear the virus, HBsAg will decrease.
The short time period between when HBsAg has been reduced to undetectable levels, while simultaneously, HBsAb has not yet risen to detectable levels, denotes the window period.
If the USMLE asks you which serum marker is most reliable during the window period, the answer is HBcAb IgM because it’s the only one that’s positive.
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