Why is it necessary to check for syphilis, kidney function, and hepatitis in individuals on Pre-Exposure Prophylaxis (PrEP)?

Why Regular Monitoring for Syphilis, Kidney Function, and Hepatitis is Essential for PrEP Users

Regular testing for syphilis, kidney function, and hepatitis in individuals on PrEP is mandatory because these conditions directly impact morbidity and mortality, and early detection allows for timely intervention to prevent serious complications.

Kidney Function Monitoring

Why Monitor Kidney Function

• PrEP medications (particularly tenofovir disoproxil fumarate) are primarily eliminated by the kidneys and can cause renal impairment 1
• Glomerular dysfunction with decreased creatinine clearance may occur in PrEP users 2

Monitoring Schedule

• Baseline creatinine clearance assessment is mandatory before starting PrEP 2
• At the first quarterly follow-up visit, estimated creatinine clearance should be calculated 2
• Annual creatinine clearance evaluation for standard-risk patients 2
• More frequent monitoring (every 3-6 months) for high-risk patients:
  • Age >50 years
  • Prior creatinine clearance <90 mL/min
  • Comorbidities like diabetes or hypertension 2

Clinical Implications

• PrEP is not recommended for those with creatinine clearance <60 mL/min 2, 1
• Kidney dysfunction is usually reversible upon discontinuation of PrEP 2

Syphilis Screening

Why Monitor for Syphilis

• High incidence of syphilis among PrEP users (19.1 cases per 100 person-years in some cohorts) 3
• Risk factors for acquiring syphilis while on PrEP include:
  • Being homosexual, gay, or lesbian (aOR 2.7)
  • History of syphilis in the six months before PrEP (aOR 2.2)
  • Irregular condom use (aOR 1.7)
  • Recreational drug use (aOR 1.5) 3

Monitoring Schedule

• Baseline syphilis serology before starting PrEP 2
• Quarterly syphilis serology testing (every 3 months) 2

Clinical Implications

• Studies show increased rates of STIs after PrEP initiation compared to before 4, 5
• Regular screening allows for early detection and treatment, preventing complications like neurosyphilis and cardiovascular syphilis

Hepatitis Monitoring

Why Monitor for Hepatitis

• Severe acute exacerbations of hepatitis B can occur when PrEP is discontinued in patients with chronic HBV 6
• PrEP contains medications active against HBV (tenofovir/emtricitabine), which can mask HBV infection 2
• Hepatitis C can be sexually transmitted, particularly in high-risk populations 7

Monitoring Schedule

• Baseline hepatitis B surface antigen (HBsAg) testing is mandatory before starting PrEP 2, 1
• Annual hepatitis C virus antibody testing for standard-risk patients 2
• More frequent hepatitis C testing (every 3-6 months) for:
  • People who inject drugs
  • MSM who engage in sex while using drugs 2

Clinical Implications

• PrEP should be used with caution in those with HBV coinfection due to risk of hepatitis flares or hepatic decompensation upon discontinuation 2
• Close monitoring of hepatic function with both clinical and laboratory follow-up for several months is required when discontinuing PrEP in HBV-infected individuals 6

Comprehensive Monitoring Algorithm

1. Before Starting PrEP:

   • HIV testing (combination antigen-antibody assay)
   • Serum creatinine with calculated clearance
   • Hepatitis B serology (HBsAg, HBsAb, anti-HBc)
   • Syphilis serology
   • Other STI screening (gonorrhea, chlamydia)

2. One Month After Starting PrEP:

   • HIV testing

3. Every 3 Months:

   • HIV testing
   • Syphilis serology
   • Other STI screening

4. Every 6-12 Months:

   • Creatinine clearance assessment (more frequent for high-risk patients)
   • Hepatitis C antibody testing (more frequent for high-risk patients)

Common Pitfalls to Avoid

• Missing follow-up tests: Studies show high rates of missed syphilis tests (33.4% at 30 days, 38.8% during follow-up) 3
• Extending prescription refills without testing: PrEP prescriptions should not exceed 90 days without interval HIV testing 1
• Ignoring risk behavior changes: Risk compensation may occur, with decreased condom use leading to increased STI risk 5
• Overlooking renal monitoring in high-risk patients: Those with baseline kidney issues or risk factors need more frequent monitoring 2
• Failing to screen for hepatitis B before discontinuation: Abrupt discontinuation without monitoring can lead to severe hepatitis flares 6

By adhering to this comprehensive monitoring schedule, healthcare providers can ensure the safe and effective use of PrEP while minimizing potential complications related to syphilis, kidney dysfunction, and hepatitis.