TMP-SMX is used to treat a wide range of infections, though it is known to cause ADRs in 40–80% of HIV infected individuals, which can impact the management of opportunistic infection in advanced HIV.1 Typically, in non-infected patients, ADRs to TMP-SMX only occur in 3–5% of cases. The authors propose two mechanisms for the increase in sulfa hypersensitivity reactions in patients with HIV. The first being that HIV-induced changes to immune function caused by a decrease in CD4 cells may be to blame.  The second theory is more infection-related and has to do with HIV-specific factors related to increasing viral load. The risk of ADRs generally increases as CD4 counts decrease and viral loads increase; most reactions occur in patients with CD4 count <100 cell/μL.2  In this patient, CD4 count was only slightly reduced at 407cell/μL while viral load was elevated at 9,645,190 copies/μL. While the link between ADRs and latent HIV infection has been well established, if viral load is a significant factor, then ADRs should occur not only in the late phase of HIV but also during primary HIV, such as in this case.

Conclusion

This case suggests how asymptomatic acute HIV infection may be identified by an adverse reaction to TMP-SMX. Also demonstrated is clinical evidence to support the correlation between viral load and ADRs to TMP-SMX without a severely diminished CD4 count. The authors stress that the limitations of one study cannot show causality, and therefore call for further research into whether viral proteins themselves are the root cause of HIV-related sulfa reactions.

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References:

1.     Arp J, Rieder MJ, Urquhart B, Freeman D, Tucker MJ, Krizova A, Lehmann D, Dekaban GA. Hypersensitivity of HIV-1-infected cells to reactive sulfonamide metabolites correlated to expression of the HIV-1 viral protein tat. J Pharmacol Exp Ther. 2005 Sep; 314(3):1218-25.

2.     Rieder MJ, Krause R, Bird IA, Dekaban GA. Toxicity of sulfonamide-reactive metabolites in HIV-infected, HTLV-infected, and noninfected cells. J Acquir Immune Defic Syndr Hum Retrovirol. 1995 Feb 1; 8(2):134-40.