Patient cases

Case #2

A 29-year-old male with a history of (herpes simplex virus) HSV and syphilis has been newly diagnosed with HIV, low CD4 (<200 cells/mm3), and high viral load.

  • Negative screening result for HLA-B*5701
  • Initiated abacavir, lamivudine and lopinavir/r
  • Concomitant medications:
    • Valacyclovir (chronic medication) initiated before antiretroviral therapy
    • Co-trimoxazole initiated with antiretrovirals

Day 8
Patient noted myalgias and low-grade fever peaking at 37.8°C.

Day 9
Patient noted faint rash with low-grade fever peaking at 39°C approximately 9 hours after morning dose.

Day 10
Patient experienced same symptoms at the same time after morning dose, but fever peaked at 38°C with fewer myalgias.

Day 11
Patient was evaluated in clinic:

  • Temperature 37°C
  • Generalised fine urticarial rash
  • Asymptomatic

Course of action:

  • Symptoms appear to have been resolving each day despite continued abacavir dosing over several days
  • Symptom resolution and the patient’s negative HLA-B*5701 screening status suggest another aetiology
  • Continue abacavir dosing with close monitoring and discontinue co-trimoxazole


  • Co-trimoxazole is stopped on day 11; subject is seen in the clinic on days 12 and 13, and symptoms continue to decline in severity
  • Patient is given topical steroids and antihistamines for the rash
  • By day 15, rash and myalgias have resolved and patient remains afebrile on abacavir, lamivudine, and lopinavir/r

Conclusion: Hypersensitivity to Co-trimoxazole

Case #2 – alternative scenario

Patient is seen on days 12 and 13; symptoms continue but do not increase or decrease in severity.

Patient is given topical steroids and antihistamines for the rash.

By day 15, rash is resolving but myalgias continue; patient complains of malaise.

Course of action:

Permanently discontinue abacavir if no other cause of the patient’s symptoms is identified; in this case, abacavir hypersensitivity cannot be definitively ruled out.

Case #2 summary

  • Consider other causes for rash and fever when patient is taking concurrent medications known to be associated with these symptoms or with allergies, particularly if screening suggests a low risk of abacavir hypersensitivity
  • However, a negative HLA-B*5701 screen does not definitively rule out the possibility of a hypersensitivity reaction
    • If a diagnosis of abacavir hypersensitivity cannot be excluded, then abacavir must be permanently discontinued, regardless of the results of any test