HIV prevention strategies + Drug interactions Flashcards
What is PrEP used in conjunction with other HIV prevention strategies? (3)
- Safer sex
- UTI screening and treatment
- Using sterile needles
What lab evaluation should be checked for PrEp
- HIV test
- Hep C (HCV) antibody (Q12 months)
- STIs: gonorrhea, chlamydia, syphilis
Clinical evaluation:
- HIV symptoms
- PrEP adherence
- indication for PrEP
- use of other prevention strategies, syndemic conditions (2+ diseases affecting each other)
Can PrEP be taken indefinitely?
Yes
- However, only dispense 3 month supply at a time to ensure they get testing q3months
What PrEP options do we have available (2)
Which is preferred
- TDF 300mg/ FTC 200mg daily:
- ODB covered
- TDF formulation is generally PREFERRED over TAF - TAF 25mg/ FTC 200mg daily:
- NOT covered by ODB
- Only approved for: MSM
- Trans-women
- Heterosexual men (biological men)
**Any bioloigcal women can’t take TAF
What is the on-demand PrEP dosing? Who is it for?
For MSM, Transgender women (off-label)
- 2-24 hours before sex: double dose
- 24 hours after 1st dose: 1 dose
- 48 hours after 1st dose: 1 dose
What is time to optimal drug concentration level for the following population on tenofovir
MSM
Non-pregnant women
Pregnant women
MSM
- 7 DAYS to reach max intracellular concentration of tenofovir in anal tissues
Non-pregnant women
- Up to 20 DAYS for tenofovir and/or FTC
Pregnant women
- At least 20 DAYS
* DHHS guidelines recommend continued use of condoms until PrEP is taken for 20+ days in pregnancy or post-partum
What is the likely cause for PrEP failure?
What is a good recommendation to make
When patient is exposed to a drug-resistant HIV strain
Thus, we recommend the use of condoms while on PrEP
Cabotegravir for PrEP
Superior/inferior to TDF/FTC?
Dosing?
In a non-inferiority study, Q2monthly Cabotegravir was shown to be SUPERIOR to DAILY TDF/FTC for prep
- Study was done in Cis-men and trans-women (who have sex with men)
Dose: Single-agent Cabotegravir (CAB) 3mL injection into gluteal region
- 1st injection, 2nd @1 month then Q2months onward
Lenacapavir for PrEP
Dosing?
Trial efficacy?
DOSING Lenacapavir (LEN) for PrEP:
Day 1: First injection + 2 PO tabs
Day 2: 2 PO tabs
Injections Q6months!!!
Trial:
- 0 HIV transmissions with Lenacapavir used for PrEP (in Cisgender women)
For PEP, what does the exposure significance and transmission risk depend on? (4)
- Type of body fluid involved
- Type of injury or exposure that occurred
- Size of the inoculum
- Attributes of the source + patient (i.e STI)
What is the % chance of getting HIV, Hep B, Hep C transmission from a needle stick injury
HIV: 0.23%
Hep B: 6-30%
Hep C: 3-10%
What baseline testing do you need to do for the individual source? (3)
HIV antigen/antibody (4th gen test)
Hep B (HBsAG)
Hep C (HCV Ab)
What baseline testing does the EXPOSED individual have to do? (6)
HIV antigen/antibody (4th gen test),
Hep B (HBsAg, anti-HBs, anti-HBc)
Hep C
- If starting on HIV PEP: CBC, SCr, ALT
- Pregnancy test
- If sexual exposure: STI testing
What is the cut-off start for PEP and duration of therapy
WHEN to start:
- within 72 hours of exposure
HOW LONG to be on PEP
- 4 weeks, if tolerated
What is the 1st line regimen for PEP for needle stick injury (occupational injury)
TDF 300mg / FTC 200mg + RALTEGRAVIR 400mg
What is the 1st line regimen for PEP for sexual assault exposure
TDF 300mg / FTC 200mg + DOLUTEGRAVIR 400mg
In the absence of any intervention, what is the risk of HIV transmission from mother to baby
25%
What choice of therapy is given to mother to prevent neonatal transmission
Dose?
When should be given?
When should you stop?
Give even if Resistance?
Zidovudine (NRTI)
Dose
- 2mg/kg IV loading dose 1 hour
- 1mg/kg/hr continuous infusion
When
- Give at the beginning of labour
- 3 hours before C-section
Stop
- when umbilical cord is clamped
Resistance
- still give medication
When should a women with HIV have a c-section (2)
- Women with high viral load (>1000 copies/mL)
- Unknown HIV VL during birth:
get C-section at 38 weeks (not the usual 39 weeks)
How long should newborn babies receive HIV medication for?
Should they breastfeed or get formula
2-6 weeks after birth
Formula
What is the rationale of giving IV Zidovudine regardless of Viral load count during labour
BC found that 9% of women with undetectable HIV VL had detectable HIV VL at delivery
When should the baby receive prophylaxis for HIV
Within 6 hours of delivery
Differentiate between low risk vs high risk of children getting HIV
Low
- Mother got ARV during pregnancy (antepartum) with sustained virologic suppression (<50 copies/mL) near delivery
- and no concerns with ARV adherence
High
- mother did not get ARV antepartum
- only got ARV intrapartum
- had detectable viral loads near delivery
- have acute/primary HIV infection
Treatment options for HIV prophylaxis for babies who are
Low risk
High risk
Low risk
- Zidovudine (NRTI) PO for 4 weeks
High risk
- Zidovudine PO + Lamivudine (3TC) + RalteGRAVIR (INSTI) or Nevirapine (NNRTI) PO for 6 weeks
What are ADRs and limitations of zidovudine
ADR
- ANEMIA (bone-marrow suppression)
- Lactic acidosis
- N/V
- headache
- insulin resistance
- Lipoatrophy
- Myopathy
Zidovudine monotherapy can have early HIV drug resistance
NRTI’s drug interactions
Typically no DDI except TDF/TAF
What are the substrates of TDF/TAF? (2)
BCRP and P-GP
- TDF and TAF are not treated the same
What drug interacts with TDF (2)
What to monitor?
Ledipasvir and velpatasvir (HCV drugs)
Monitor for tenofovir toxicity
What drugs interact with TAF (4)
What is the interaction?
Potent P-gp inducers
- rifampin
- rifabutin
- phenytoin
- carbamazepine
Decreases therapeutic effect
INSTIs interaction
Solution?
Interaction:
- Tend to interact with polyvalent cations (Ca, Mg, Al, Zn, Fe)
- Like iron supplements, cationic antacids
Solution
- Just separate (take INSTI in the morning and Polyvalent Cation at night - or vice versa)
Rilpivirine interaction?
Coadministration with PPIs can lead to loss of virologic response + resistance is possible
When using PI’s what is the safest use of steroid
Beclomethasone is the safest inhaled steroid (when using a CYP3A4 inhibitor)
Maraviroc interaction
Dosing depends on concurrent drug use: if administered with CYP3A4 inhibitor/inducer
Differentiate between enzyme inhibition and induction
Enzyme Inhibition interactions occur QUICKLY
- Lead to HIGH levels of the drug in the body and TOXIC effects
- This commonly occurs with PI Boosters (Ritonavir/Cobicistat) - inhibit CYP450 enzymes
- Enzyme inhibition can affect metabolism of inhaled and injectable drugs (like steroids), not just ORAL drugs
□ Ex. With inhaled steroid + Boosted PI (CYP3A4 inhibitor), Beclomethasone is the safest alternative
Enzyme Induction interactions occur SLOWLY
* Lead to compromised therapeutic goals
