Stanford resistance mutation sheet

Frequently updated, the Stanford HIV database posts lists of clinically relevant mutations on its website that can be downloaded. The link is:

http://hivdb.stanford.edu/pages/download/resistanceMutations_handout.pdf

- Christopher Hurt

Viral decay curve

Once you start someone on ARVs, there's a predictable decline in viral load associated with it. This article from Nature Medicine has a nice figure, showing that different cell populations actually give rise to different portions of the decay curve, and as each replication within each "compartment" of cell type gets shut off by ARVs, that population's contribution to the viral load trails off, leading to the curve. (Hopefully it'll make better sense when you look at the figure!)

http://www.nature.com/nm/journal/v9/n7/fig_tab/nm0703-853_F2.html
from (http://www.nature.com/nm/journal/v9/n7/full/nm0703-853.html)

- Christopher Hurt

Sexual Assaults and PEP

There is a protocol that can be obtained from Lynda Bell in clinic regarding the care of survivors of sexual assaults. We will sometimes be called to weigh in on HIV PEP alone, as they have a protocol they follow for everything else. However, if you are ever called about what should be done, particularly if a SANE nurse is not available, here are some basics from the protocol.

Baseline laboratory tests should include:

• HIV Antibody testing
• CBC with differential
• LFTs
• BUN/Creatinine
• STD Screen (gonorrhea, chlamydia, syphilis)
• Hepatitis B serology
• Hepatitis C serology
• Pregnancy test

Prophylaxis against the most frequently diagnosed STDs among sexually assaulted women should be administered:

• Ceftriaxone 125mg IM in a single dose [Gonorrhea]
• Metronidazole 2gms orally in a single dose [BV, Trichomoniasis]
• Azithromycin 1gm orally in a single dose OR Doxycycline 100mg orally twice daily for seven days [Chlamydia]

HIV post-exposure prophylaxis is offered within 72 hours of the assault. If the perpetrator's HIV medical history is unknown, the two preferred regimens are:

• NNRTI-based: Efavirenz plus (Lamivudine or Emtricitabine) plus (Zidovudine or Tenofovir)...usually as Sustiva plus Combivir, or Sustiva plus Truvada.
• PI-based: Lopinavir/Ritonavir (Kaletra), plus Zidovudine or Tenofovir...usually as Kaletra plus Combivir, or Kaletra plus Truvada.

I've been advised typically to use the PI-based regimen unless there is another reason they should be avoided. Keep in mind that if the source patient (in the case of needlesticks) is one of OUR HIV clinic patients, we have access to their genotype and med history, and can formulate an appropriate PEP for the victim based on this information (i.e. you wouldn't want to start someone on PEP that their virus would be resistant to).

All sexual assault cases should follow up with a mid-level provider in the ID Clinic, regardless of whether or not they accept PEP. We usually just send a phone message to Lynda Bell with the patient's general information, and she contacts them to set up a follow up within 48 hours or so.

Risk Assessment

Sometimes, you are asked to comment on the risk, given different exposures (assault, blood splashes in the eye, needlestick, etc.). The risk for HIV acquisition per various acts can be found in the MMWR, January 21, 2005). It is also estimated in the Sanford Guide for the treatment of HIV.

Vaccinations in PEP

Hepatitis B: Patients who are unvaccinated prior to the assault should receive the initial Hep B vaccine, and follow up to complete the series. Unless the offender is known to have Acute Hep B, HBIG is not required. Remember, all patients should have serologies drawn.

Tetanus: If the patient has skin abrasions or other wounds and immunization status is greater than 5 years, give Tetanus Toxoid 0.5ml IM. If the patient has never been immunized, also give Hyper-Tetanus 250mcg IM.

Yvonne Carter, MD

Antiretrovirals and Resistance

So this is a big topic, and I had put together a PowerPoint (with the "script" in the notes section beneath each slide) for a School of Pharmacy class in 2008 on antiretroviral resistance testing. It's at a level that I think is good for people getting acquainted with the principles of resistance tests:

http://www.unc.edu/~churt/downloads/ARV_Resistance_Hurt.ppt

This covers the basics of:

• why HIV mutates so readily
• principles of the techniques involved for resistance testing
• who needs to get a test (by the 2007/08 DHHS guidelines)
• what happens to your patient's blood sample once you order a test
• the differences among phenotypic, genotypic, and "virtual phenotype" testing
• a tangent on why certain positions (like K103N or M184V) are so significant, but other positions aren't (the answer is tertiary protein structure)

I'd welcome any questions or comments on this. The top 5 gurus for ARV resistance here (in order of who you should talk to if you have a significant, burning question) are:

1. Joe Eron
2. Joe Eron
3. Joe Eron
4. David Margolis
5. David Wohl

The thumbnail version
Basically, HIV mutates so quickly because it's crappy at proofreading itself. The reverse transcriptase (RT) has poor (but present) proofreading activity, so if it mismatches a nucleotide base-pair, it can't stop, back up, and excise the mismatch. Instead it blows through the copy, generating many, many point-mutations in the sequence of each copy. Poor fidelity in the copying process means more mutations, some of which are fatal to the protein/enzyme, rendering it useless - but others are fortuitous and confer resistance to a medication. The selection pressure of the ARVs drives natural selection in a beautifully Darwinian way. This is an important point, because without the selection pressure, the most "fit" (able to copy itself readily) version (aka "quasispecies") of HIV in the body will overgrow all others. This is usually referred to as "wild-type," meaning there's no native resistance. However, keep in mind that if a patient is infected with resistant virus at the outset (transmitted drug resistance), then that is their wild-type. Some mutations will revert back towards wild-type over time, through back-mutations, but others may persist for months-t0-years after acute infection. This is the underpinning for why the DHHS recommends now that all patients newly entering HIV care have some baseline assessment of antiretroviral resistance.

At UNC, our test of choice is the "virtual phenotype" or VIRCOtype, provided by Virco, a company with an office in the RTP but whose main offices (and labs) are in Belgium. This test combines a repository of straight-up nucleotide sequence data with one of phenotypic resistance information as lab-cultured viruses are exposed to drugs and their replication measured. Although it has some warts, it's pretty good at predicting what meds will work and which won't. It can't predict synergy, however, and that's a significant drawback.

The mutations are alphabet soup and will be for a while. Don't freak out, it's supposed to be that way – and I never feel bad about looking at one of the IAS-USA resistance cards in the clinic, since even people like Joe Eron and Amanda Corbett refer to them routinely. Realistically, you don't need to memorize any mutations. The ones that make a difference will be repeat customers and you'll come to know them by repetition. Others are less important and you have other stuff to fill your brain up with as things get going for you here. (Plus as each new med comes out of the pipeline, a new set of mutations will become apparent as more and more people get on them.)

– Christopher Hurt