Drug-resistant TB | Infectious diseases | NCLEX-RN | Khan Academy
31
August

By Adem Lewis / in , , , , , , , , , , , , , , , , , , , /


Charles: This is Charles Prober. Morgan: And Morgan Theis. Charles: And for this video, we’re going to talk about
resistance among TB infections, so resistance, drug resistance, a very important topic because
it dramatically affects how we treat different patients. The timeline and the patient
that Morgan has drawn is going to help us
describe different scenarios about how to treat patients
who have different kinds of TB in terms of the resistance pattern. This little person we’ve
diagnosed as having a TB infection based upon their clinical presentation
and some of the laboratory tests we did, which we talked about in another video. And when the patient starts their therapy, especially if they’re in a
developing world, where the
Xpert RIF test is available – that’s that molecular test that
we described in another video that identifies that TB is present, it’s on a molecular assay, and that that particular TB
is resistant to rifampin. If that’s the case, then that’s going to immediately
modify how we treat this patient with their TB infection. But let’s assume that the
expert test is negative. Morgan: OK. Charles: And we have a TB
infection that we’ve diagnosed. We take cultures of the sputum, and we know that those cultures are
going to come back in 4 weeks or 6 weeks. It takes a bit of time. Those cultures are also
going to be tested. The bacteria are going to be tested for sensitivity to the
antituberculose agents, but we’re not going to have that
information out for about 6 weeks, because that’s how long
it takes the TB to grow. Morgan: OK, so here’s
my little culture plate that’s trying to grow out that sputum. Charles: Perfect. While we’re waiting for the
culture results and sensitivity
testing to come back, we need to start therapy
for this TB infection. The standard therapy is using
all of the first-line drugs that you’ve listed in
the top right-hand corner that we referred to before as RIPE: the rifampin, isoniazid,
pyrazinamide, and ethambutol. Morgan: OK. Charles: The rifampin
and isoniazid, or INH, are used for a full 6 months if this
turns out to be a sensitive TB bug. They’re both used for 6 months. The pyrazinamide and ethambutol
are used for the first 2 months of that 6-month interval. That’s the standard therapy. Now let’s consider we’ve got the
culture results that have come back from that sputum, and we’re
6 weeks into this treatment, and we discover from those culture
results that the organism, the TB, is resistant to one of our TB agents. The most common resistance
would be to INH, but they can be resistant to any
of the different first-line drugs. If the organism turns out
to be resistant to INH, we will stop the INH because
it won’t do much good, and we’ll either just continue the
three drugs for a longer period of time or we may add a fluoroquinolone. If the TB turns out to
be resistant to rifampin based upon that sensitivity testing, we’ll stop the rifampin and may
continue the other three drugs and maybe even add
something like streptomycin. Morgan: So the idea here is that if whatever drug this particular
TB organism is resistant to, you’re going to stop using it, and you’re going to continue
with the other ones. You may consider adding a secondary drug, and you might consider a longer treatment. Charles: All correct, yes. Charles: So if the bugs are resistant, the TB is resistant to
both INH and rifampin, the term that is used for
that resistance is MDR, which stands for multiple
drug-resistant TB. These are becoming increasingly
important around the world. It turns out that the countries
that have the most MDR isolates are five countries in the world, and those include China, India, Pakistan,
the Russian Federation countries, and South Africa. That’s only five countries, and they have the
largest amount of MDR-TB. The final type of resistant TB
that I would like to mention is called XDR-TB, which stands
for extreme drug resistant. XDR-TB is less common than
MDR-TB but more serious because it’s harder to treat because they’re resistant
to multiple drugs that are either first-line anti-TB drugs or second-line, which you’ve also put in
the right-hand corner of this picture. They’re more difficult to treat, and in fact, the mortality rate
for this XDR-TB is much higher. But let’s assume that we
do the sensitivity testing when the sputum comes back
positive at 6 weeks or so and they turn out to be sensitive, and we’re continuing on with
just a standard RIPE therapy. But then as we’re checking
the sputum cultures, as we want to do on a regular basis, when you get out to 3 months, it turns out the sputum
culture is still positive. It should not be still positive. You should have a negative sputum
culture by about 2 months or so, or even earlier. Morgan: Right, because
you’ve been treating the TB. Charles: Exactly. Morgan: OK. Charles: So if it’s still positive, there is one or two possibilities. One is the TB has developed resistance to one of the anti-tuberculose agents, in which case, you’ll
have to modify therapy. And you’ll know it’s resistant
because you tested sensitivity again. The other possibility is
it’s just a slow responder, that the patient continues
to have positive sputums even though the bugs are sensitive, are killed by the antibiotics
you’re using, and it’s just slow. Under either circumstance, therapy, you’ll have to
anticipate modifying therapy. If it’s resistant, you’ll change
the anti-tuberculose agents and treat the patient longer. If it’s sensitive, you’ll just anticipate treating the
patient longer than the standard 6 months. Then the final scenario
that I would like to mention is all goes well for
the 6 months of therapy. The patient’s chest X-ray gets better. They look well, and you believe you have
cured the infection. Morgan: OK, so here at 6 months … Charles: All is good. Morgan: … my patient is happy. Charles: Exactly. Morgan: And cured, supposedly. Charles: But the scenario
that I’ll now describe is several months or even years later, that happy patient becomes sad again because the patient has a
relapse of the infection. The signs and symptoms of TB reappear. Now, that may be because the
patient’s initial infection was never completely eradicated
and it just came back, or it may be that the patient acquired
a new TB infection from somebody else, so it’s a completely
different TB infection, so it’s not really relapse in that case. It’s re-infection, but nonetheless,
the symptoms have relapsed. Morgan: So how could
you tell the difference? If a patient who was treated
for their original TB then years later presented with TB again, how could you tell if it was a
relapse of their original bug or a new infection with a new bug? Charles: That’s a great question, and the only way you’d be
able to tell the difference is if you had both TB bugs in your
laboratory available to retest, and you can do molecular
testing on the two bugs and see if their DNA is
the same or different. If the DNA is the same,
then it’s a relapse because it’s the same bug. If the DNA is different,
then it’s a reinfection. Morgan: Oh, great. So you really can figure that out. Charles: Exactly.


6 thoughts on “Drug-resistant TB | Infectious diseases | NCLEX-RN | Khan Academy

  1. Charles Prober and Morgan Theese (sp?), 

    I want to thank you sincerely for your videos. The format is a nice change of pace from the exhausted format of powerpoint slides and lecturers. Also the scope seems just about right for preclinical medical education. Sometimes online videos can be a crap-shoot, but I hit gold wit your videos.   

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