Background:  The use of HIV protease inhibitors (PI) in infected pregnant women is increasing, with the dual purposes of maintaining maternal health and preventing mother-to-child HIV-transmission. At our outpatient clinic, nelfinavir (NFV)-based combination therapy is routinely used as first-line regimen in these patients. Whether or not the trough concentration (C_min) threshold is achieved in these patients is controversial.

Methods:  Drugs plasma levels were routinely assayed 2 weeks following treatment start or during the second or third trimester of pregnancy in women who were under treatment before pregnancy. NFV was measured by reverse-phase HPLC with a detection limit of 0.05 ng/mL. CD4 cell count and HIV plasma viral load were measured before NFV-based treatment start and at the time of NFV trough level measurement.

Results:  At least 1 NFV plasma trough concentration (C_min) was available in 40 women (35 black, 3 white, 2 Asian; median age 30 years, median weight 73 kg). NFV dosing regimen was either 1250 mg twice daily (n = 36) or 750 mg thrice daily (n = 4). Average NFV C_min was 1.27±0.86 ng/mL and below the recommended trough level (i.e., 1 ng/mL) in 18 patients (45%). Simultaneously, the median HIV viral load decreased from 4.12 log₁₀ to 2.02 log₁₀, after a median of 15 days upon treatment start. Despite increasing the NFV dosing regimen for 8 of the 18 women, whose C_min <1 ng/mL, to 1500 mg twice daily, trough level remained <1 ng/mL in 2 of these 8 women. Of the 37 women with HIV plasma viral load at the time of delivery, 25 had undetectable HIV plasma viral load (<50 copies/mL), and 5 had plasma viral load >500 copies/mL. No vertical transmission occurred. Women with NFV C_min <1 ng/mL were compared with those with C_min >1 ng/mL. No significant difference was observed between these 2 groups regarding age, CD4 cell count, HIV viral load, or trimester of pregnancy. A trend toward lower decline in HIV plasma viral load was observed in women with low trough level (–1.49 vs –1.85 log₁₀, p 0.08).

Conclusions:  The recommended NFV C_min threshold was not achieved in almost half of our pregnant women treated with this PI, with a trend toward lower decline in viral load in these patients.