Flashcards in Treatment of TB Deck (58):
1st line drugs for TB
Pyridoxine can be added adjectively to TB treatments. Why?
TO prevent drug-induced neuropathy
What are the majors organs affected by TB?
-nodes, pleura, bones, and joints
How is TB spread?
inhalation of infectious droplet nuclei aerosolized by pulmonary TB
What is MDR TB?
resistant to isoniazid and rifampin.
What is XDR TB?
resistant to isoniazid and rifampin plus a fluoroquinolone and one of the three second line drugs
Describe the mycobacterial cell wall
The mycobacterial cell wall consists of an inner layer and an
outer layer that surround the plasma membrane
How is the inner layer of the mycobacterial wall constructed?
The inner compartment consists of peptidoglycan (PG), arabinogalactan (AG), and mycolic acids (MA) covalently linked
together to form a complex known as the MA-AG-PG complex that extends from the
plasma membrane outward in layers, starting with PG and ending with MAs
complex is insoluble and referred to as the essential core of the mycobacterial cell
While multidrug resistance has recently grabbed headlines, mycobacteria are
inherently resistant to numerous antibiotics. Why?
Mycobacteria have unusually impermeable cell walls that are thought to be advantageous in stressful conditions of osmotic shock or desiccation as well as
contributing to their considerable resistance to many drugs.
T or F. Lipophilic drugs, such as fluoroquinolones or rifamycins, pass more easily through the lipid-rich cell wall and
thus are more active.
What is another reason for resistance to antibiotics in Mycoplasma TB?
TB forms caseous granulomas, which is composed of macrophages (where the TB resides), neutrophils, and a cuff of lymphocytes
Poor penetrative ability of the drugs into the granuloma, coupled with the hypoxic centre and fibrotic ring can all impact drug
Other possible resistance mechanisms to drugs?
efflux pumps, antibiotic-modifying or -degrading enzymes such as β-lactamase, target-modifying
enzymes, and decoys that mimic the drug target.
What is the most common cause of TB treatment failure?
poor adherence (leads to resistance!)
T or F. TB infection can be latent or active
Are those with latent infection likely to spread TB?
No, with a latent infection, the patient is
initially asymptomatic (this may progress, as shown) and is not a public health risk.
How could you ID a latent TB infection?
chest X-ray would appear normal, however, a TB skin test would yield a positive
T or F. The majority of patients who become infected do not go on to experience
T; their immune systems can intervene. However, the risk of active disease
development is clearly greater in immunocompromised patients.
What are the symptoms of active TB?
-cough (progressing to productive), chest pain, SOB
-flu like symptoms, fever
-weight loss, fatigue
Before beginning immuosuppressants like TNF-alpha inhibitors, a TB test should be performed to avoid allowing latent TB to become active. What should be done if the assay shows a positive result?
Anti-tubercular drug treatment should
be initiated. What is not resolved is whether or not this prolonged treatment regimen needs to be completed before the immunosuppressive drugs can be initiated.
Rules for reading a TB test
-measure rxn within 48-72hrs
-measure induration, not erythema
-record rxn in millimeters, NOT positive/negative
What is the preferred drug regimen for HIV patients, children 2-11 yoa, pregnant women with pyridoxine/vitamin B6 supplementation with LATENT TB?
Isoniazid 1x daily for 9 months
What is the preferred drug regimen for persons over 12 yoa with LATENT TB?
Isoniazid + Rifapentine 1x weekly for 3 months
When is Isoniazid + Rifapentine 1x weekly for 12 weeks contraindicated?
-Under 2 yoa
-With concurrent anti-retrovirals
-Women expecting to be pregnant
How to manage patients that miss treatment?
Extend or re-start treatment and use DOT
What is the preferred drug regimen for ACTIVE TB initial phase?
Daily INH, RIF, PZA, and EMB for 56 doses
What is the preferred drug regimen for ACTIVE TB continuation phase?
Daily INH and RIF for 126 doses (18 weeks) or twice-weekly INH and RIF for 36 doses (18 weeks)
What is the purpose of the initiation phase of TB treatment?
Kill most of the bacilli (but some can survive longer)
T or F. The initial phase of TB treatment determines the ultimate effectiveness of the regimen
What is the purpose of the continuation phase of TB treatment?
finishes killing TB
How is the treatment of active TB in HIV patients different?
Initial phase is the same and the continuation phase consists of INH and a rifamycin for 4 months
What is dose intensity based on for TB in HUV patients?
CD4 counts, 2x/week for greater than 100CD4/ul and daily or 3x/week for less than 100CD4/ul
What is something to be cautious of in Active TB HIV patients?
DD interactions with some PIs and NNRTIs
How is isoniazid changed one inside the body?
it is a pro-drug that acetylated by NAT2 isoforms to its principal metabolite,
How is N-acetyl isoniazid excreted?
How is N-acetyl isoniazid activated?
diffuses into mycoplasma and is activated by KatG (oxidase/peroxidase) to the nicrotinoyl radial, which reacts with NAD+ or NADP+ to produce adducts that inhibit cell-wall (enoyl-acyl carrier reductase) and nucleus acid synthesis
Specifically, how does isoniazid inhibit nucleic acid synthesis?
dihydrofolate reductase inhibitor
What is the significance of isoniazid in drug dosing?
humans vary in their acetylating capacity (called 'status')
What ethnicities are typically fast acetylators?
Asians (may require higher doses)
What is a risk for slow acetylators?
drug accumulation giving rise to lupus-like AEs
What endogenous molecule does isonazid deplete?
vitamin B6 (so pyridoxine supplements are often given)
How does isoniazid deplete vitamin B6?
CYP2E1 products bind and inactivate pyridoxine species and inhibits pyridoxine phosphokinase
What are some possible toxicities isoniazid?
-Peripheral neuropathy (Give vitamin B6)
-Seizures in epileptic patients (reduction of GABA)
Hemolysis is a possible AE of isoniazid in ____ patients
Isoniazid inhibits which CYP?
DD interactions of Isoniazid?
What are the member of the rifamycin family of drugs?
How do rifamycin drugs work?
They inhibit bacterial RNA synthesis by forming a stable complex with DNA-dependent RNA polymerase (rpoB)
How are rifamycins metabolized?
via deacetylation and CYP3A hydrolysis
What is one thing to remember about Rifamycins?
they are CYP1A2 2C9, 2C19, and 3A4 INDUCERS (Rifampin the most) by promoting protein synthesis in the liver
AEs of rifamycins?
-discoloration of contact lens
How does Pyrazinamide enter mycobacteria?
processed by initial
deamination within the mycobacterium and is effluxed, only to re-enter the bacillus
by simple diffusion in an acidic environment.
How does pyrazinamide kill TB?
1) Inhibition of fatty acid synthase type 1 inhibiting mycelia acid synthesis
2) reduction of intracellular pH
3) disruption of membrane transport by HPOA
Toxicities of Pyrazinamide?
-Inhibition of urate excretion, causing hyperuricemia in nearly all patients
-May cause gout
T or F. Pyrazinamide is allowed during pregnancy
How does Ethambutol work?
The final one of the principal drugs to consider is ethambutol. Activity is limited to
mycobacteria where it seems to work by inhibiting mycobacterial cell wall production
by inhibiting arabinosyl transferase enzyme activity.
AEs of Ethambutol?
-dose-related optic neuropathy (change in acuity or red-green blindness)
-hyperuricemia and elevated LFTs
2nd line options for TB