AIDS RESEARCH AND HUMAN RETROVIRUSES Volume 17, Number 2, 2001, pp. 93–98 Mary Ann Liebert, Inc.
Efficacy, Tolerance, and Pharmacokinetics of the Combination of Stavudine, Nevirapine, Nelfinavir, and Saquinavir as Salvage Regimen after Ritonavir or Indinavir Failure* JOSE L. CASADO, 1 FERNANDO DRONDA, 1 KURT HERTOGS,2 RAQUEL SABIDO,1 ANTONIO ANTELA,1 PALOMA MARTÍ-BELDA,1 PASCALE DEHERTOGH, 2 and SANTIAGO MORENO1 for the NELSANE STUDY
ABSTRACT The high rate of protease inhibitor treatment failure in clinical cohorts makes it necessary to define novel salvage therapies. In a prospective study of 31 HIV-infected patients included in a salvage regimen with stavudine, nevirapine, nelfinavir, and saquinavir, viral load decreased a median of 1.65 log10 and 1.95 log10 after 6 and 12 months of treatment, respectively, and 35 and 56% of patients had an HIV RNA level below 50 copies/ml at the same time points. At baseline, the mean number of mutations in the protease gene was 10 (2–19), and the V82A and L90M mutations were present in 54 and 21% of patients. The presence of the V82A mutation did not affect significantly the rate of response (36 vs. 38%), whereas the L90M mutation was associated with treatment failure (0 vs. 43%). Plasma trough levels of nelfinavir (NFV) and saquinavir (SQV), in a twice daily dosing regimen, were above the protein-corrected IC95 in most patients despite the addition of an enzymatic inducer such as nevirapine, and peak levels were 2- and 5-fold increased with respect to standard doses. However, pharmacokinetics of saquinavir-hard gel capsule (SQV-hgc) did not improve significantly in the three times daily dosing regimen. In conclusion, the combination of stavudine, nevirapine, nelfinavir, and saquinavir increased plasma drug levels and produced an adequate virological response in patients who had failed indinavir or ritonavir therapy. This degree of response is not significantly decreased in the presence of genotypic mutations associated with indinavir/ritonavir (IDV/RTV) resistance.
INTRODUCTION
T
the development of drug-resistant viral mutants.6 But there are more doubts about what this alternative regimen should be, especially in patients failing indinavir (IDV) or ritonavir (RTV) therapy. Virologic failure with these drugs is frequently associated with genotypic mutations and cross-resistance to other protease inhibitors.7 As a consequence it may be necessary to expose patients to new drug combinations for which there may be limited clinical data. In this setting, combination therapy with nelfinavir (NFV) plus saquinavir (SQV) could be a therapeutic option, taking into account the favorable pharmacokinetic interactions. The use of NFV increases 5-fold the plasma levels of SQV-hard gel capsules (SQV-hgc), avoiding the problems associated with the low bioavailability of this compound.8–10 Moreover, the addition of
of protease inhibitor (PI) therapy has had an impressive impact on the natural history of HIV infection.1 The use of these potent drugs has changed the approach to the clinical management of patients, and nowadays the goal of antiretroviral therapy is to reach and maintain the plasma viral load at as low a point as possible, ideally below the limit of detection of the most sensitive methods.2,3 However, data have shown a high rate of treatment failure in clinical cohorts, related to prior treatment, high plasma viral load, and nonadherence with therapy.4,5 As a general guideline, it is universally accepted that a change in therapy is indicated if the HIV RNA concentration is increasing, in order to prevent HE INTRODUCTION
1 Department
of Infectious Diseases, Ramon y Cajal Hospital, 28034 Madrid, Spain. 2800 Mechelen, Belgium. * Presented in part at the 7th European Conference on Clinical Aspects and Treatment of HIV Infection, October 23–27, 1999, Lisbon, Portugal. 2 Virco,
93
94
CASADO ET AL.
a nonnucleoside reverse transcriptase inhibitor (NNRTI) such as nevirapine is an attractive option in view of their nonoverlapping viral resistance profiles. Although nevirapine (NVP) produces a 28% decrease in plasma drug exposure to SQV,11 it does not modify the plasma levels of NFV12 and protease inhibitors do not influence NVP plasma levels.11–13 But how are drug levels affected in this combination? To answer this question, we analyzed patients who had failed an IDV- or RTV-containing regimen and who switched to the combination of NVP, NFV, and SQV, taking into account pharmacokinetic and resistance data.
MATERIALS AND METHODS Study population This study was performed in the HIV Care Unit at Ramon y Cajal Hospital (Madrid, Spain). This unit provides primary and specialized care to HIV-infected adults in an urban area with a high prevalence of HIV infection. All patients receiving antiretroviral therapy were included in our antiretroviral cohort study, with clinical and analytical determinations every 3 months. Since the time that NVP and NFV became available in Spain, all patients who had experienced treatment failure with a protease inhibitor-containing regimen were subsequently administered a combination of stavudine, NVP, NFV, and SQV and have been monitored on a prospective basis (NELSANE [nelfinavir, saquinavir, nevirapine] study), including resistance and pharmacokinetic assays. The study was approved by our institutional review board, and all the patients gave written informed consent. For the purpose of this study, we selected those patients who had received only RTV, IDV, or both, before they were administered the combination described above, and who have completed 12 months of follow-up. NVP was started at a dose of 200 mg once daily for 15 days, and then 200 mg twice daily. SQV and NFV were used as standard doses (600 and 750 mg three times daily, respectively) or on a twice daily basis (1000 and 1250 mg twice daily). Only patients with two consecutive viral load determinations above 1000 copies/ml were included. Patients with prior SQV or NFV experience, or who had received prior NNRTI therapy, were excluded from this analysis.
Data collection Each patient was evaluated at baseline, at 6 weeks, at month 3, and every 3 months thereafter. Baseline data, including age, sex, prior antiretroviral therapy, adherence, and intolerance or toxicity history, were obtained at the time of the switch to the stavudine1NVP1NFV1SQV regimen. Adherence was quantified as the percentage of doses reportedly taken. CD41 cell count was determined by flow cytometry. Plasma viral load determination was performed by an ultrasensitive branched DNA assay (Chiron, Emeryville, CA), with a lower level of detection of 50 copies/ml. Adverse events were graded according to the toxicity rating scale developed by the World Health Organization (WHO).
Resistance analysis In all the patients, plasma was obtained prior to the switch in treatment and stored at 270°C. Genotypic analysis was performed by automated population-based full-sequence analysis (Applied Biosystems, Foster City, CA). Results of the genotypic analysis are reported as amino acid changes generated by codon changes at positions along the entire protease gene, compared with the wild-type (HXB2) reference sequence. Phenotypic resistance analysis was performed on nine randomly selected plasma samples by a recombinant virus assay (Antivirogram; Virco, Mechelen, Belgium) as described by Hertogs et al.14 Viral population was classified according to the increase in median inhibitory concentration (IC50) relative to a wild-type reference virus (susceptible, ,4-fold increase; resistant, .4fold increase). Patients and clinicians did not have the results of resistance analysis prior to use the therapy.
Pharmacokinetic analysis In 11 patients, plasma drug levels were measured after at least 14 days of therapy (mean, 47 days). After an overnight fasting, patients, under observation, ingested their antiretroviral therapy during breakfast. Blood samples were collected in heparinized tubes just before and 1, 2, and 4 hr after ingestion of the protease inhibitors. Plasma was isolated by centrifugation to 2000 rpm for 10 min on the same day, heated to 58°C for at least 30 min to inactivate HIV, and immediately stored at 270°C until analysis.8 SQV and NFV concentrations in plasma were measured by a validated high-performance liquid chromatographic (HPLC) assay. Briefly, plasma samples and standards were loaded onto Sep-Pak C18 columns (500 mg, 3 cm3; Waters, Milford, MA) and washed with a mixture of methanol and phosphate buffer (10 mM, pH 6) (1:1, v/v). The elution was done with methanol and evaporated to dryness. The extracts were redissolved in methanol–water (1:1, v/v) for direct injection into the HPLC. The separation was resolved on a Nova-Pak C18 column (4 mM; 150 3 3.9 mm; Waters) with a mobile phase of 10 mM phosphate buffer with 10 mM triethylamine (pH 5.5)–acetonitrile (42:58, v/v) at a flow rate of 1 ml/min. Absorbance was monitored at 220 nm. Peaks of interest, i.e., saquinavir (retention time, 3.2 min) and nelfinavir (retention time, 5.8 min), were quantified with a Kontron (Milan, Italy) chromatograph data acquisition system. The lower limit of quantification of the assay was 50 ng/ml for saquinavir and 100 ng/ml for nelfinavir. The intra- and interassay variability was less than 7% for both drugs. Trough and peak plasma values were determined for each patient, taking into account the dose of both protease inhibitors (twice daily for six patients, three times daily in five cases). Because NFV and SQV bind plasma proteins with high affinity (.98%), trough plasma values were compared with the protein-corrected IC95 against both protease inhibitors15 (Table 2).
Statistical analysis Those patients with an HIV RNA level below 50 copies/ml provided the primary measure of antiretroviral response during the study period, specifically after 6 and 12 months of therapy. Data were analyzed by an intent-to-treat approach (with miss-
d4T1 NVP1 NFV1 SQV AS SALVAGE REGIMEN
95
ing data equal to failure), and were repeated as an on-treatment analysis. The association between activity and baseline variables (plasma viral load, CD41 cell count, duration of PI therapy, number of PIs used, number of mutations, mutation pattern, phenotypic resistance, and plasma PI levels) was determined by a Mann–Whitney or x2 test, with the Fisher exact test used when necessary. All p values were two-tailed, and a value of less than 0.05 was considered significant.
RESULTS Patients A total of 1432 patients started protease inhibitor therapy between March 1996 and December 1998 at the HIV Care Unit (Ramon y Cajal Hospital). Of them, 93 patients have been included in a rescue regimen with stavudine (d4T), NVP, NFV, and SQV. During the study period, a total of 31 patients met our inclusion/exclusion criteria. The reasons for excluding the remaining patients were prior SQV or NNRTI therapy. Baseline characteristics at the time of switch to a d4T1NVP1NFV1SQV regimen are summarized in Table 1. Of note, 57% of patients had received sequentially both RTV and IDV, median time on protease inhibitor therapy was 76 weeks, and mean self-reported adherence during RTV/IDV treatment was 87%. Concerning treatment failure, 14 patients (44%) related any degree of intolerance or toxicity with indinavir or ritonavir. All the patients have received extense NRTI therapy prior to and during protease inhibitor therapy, but all the patients continued to take stavudine because it was considered the best NRTI option for these severely pretreated patients.
TABLE 1.
Outcome As inclusion criteria, all patients had at least 1 year of follow-up with the stavudine1NVP1NFV1SQV-containing regimen. A grade 3–4 toxicity was observed in six patients (19%), mainly rash (four cases, 13%) and diarrhea (two cases), leading to discontinuation of therapy in a median time of 16 days. A lower degree of intolerance to therapy (mainly mild diarrhea) was observed in four additional patients, although it was possible to continue therapy. During the study, five patients developed an HIV-related infection in a median time of 121 days (two herpes zoster, two esophageal candidiasis, one disseminated cytomegalovirus), but no patient died during the study period. Using an intent-to-treat analysis, in which all patients who discontinued therapy for any reason were treated as virologic failures, 25% of patients at month 6 and 31% at month 12 reached a plasma viral load of ,50 copies/ml. Furthermore, plasma viral load decreased to a median of 1.64 log10 (range, 0.2–3.5 log10) after 6 months and to a median of 1.95 log10 (range, 0.8–3.5 log10) after 12 months of therapy. CD41 cell count increased from 183 3 106/liter at baseline to 259 3 106/liter at month 6, and to 290 3 106/liter at month 12. In an on-treatment analysis, the proportion of patients with plasma viral load below 50 copies/ml increased to 35% (8 of 23) at month 6 and to 56% (10 of 18) at month 12. During the 12 months of the study period, mean self-reported adherence was 94%.
Genotypic and phenotypic resistance Frozen plasma for sequencing of the HIV protease gene was available from the 31 patients. The mean number of mutations
BASELINE CHARACTERISTICS OF 31 PATIENTS INCLUDED IN A STAVUDINE 1NEVIRAPINE 1NELFINAVIR 1SAQUINAVIR CONTAINING REGIMEN AFTER INDINAVIR OR RITONAVIR FAILURE
Characteristic
Value
Sex male Mean age Previous NRTI therapy Mean number of NRTIs Prior PI therapy RTV/IDV/both (%) CD41 cell count HIV RNA level Adherence (self-reported) Median time on therapy At entry on d4T1NVP1NFV1SQV CD41 cell count HIV RNA level
81% 42 years (range, 28–66 years) 33 months 2.62 8/35/57% 46 3 106/liter (range, 3–351 3 106/liter) 5.04 log10 copies/ml (range, 2.69–6 log10 copies/ml) 87% (range, 60–100%) 19 months (range, 5–31 months) 174 3 106/liter (range, 7–660 3 106/liter) 4.4 log10 copies/ml (range, 2.6–5.9 log10 copies/ml) V82A
Phenotype and major mutations in nine patients IDV RTV NFV SQV
L90M
Resistance
R
S
R
S
5/9 5/9 5/9 1/8
4/5 4/5 3/5 1/1
1/4 1/4 2/4 4/8
1/5 1/5 1/5 1/1
0/4 0/4 0/4 0/8
Abbreviations: NRTI, nucleoside reverse transcriptase inhibitor; IDV, indinavir; RTV, ritonavir; NVP, nevirapine; NFV, nelfinavir; SQV, saquinavir; R, resistant; S, susceptible.
96
CASADO ET AL.
FIG. 1. Frequency of major mutations in the protease gene as determined by virologic response at month 12 in 31 patients who had failed in an indinavir and/or ritonavir-containing regimen: rate of mutations (open columns), percentage of viral suppression (shaded columns), and detectable HIV load (solid columns).
was 10 (range, 2–19) and, specifically, 21% had the L90M mutation and 54% had the V82A mutation, which is consistent with IDV and RTV resistance (Fig. 1). Both mutations were present simultaneously in four patients, and mutations at positions 46 and 84 were observed in 37 and 21% of patients, respectively. Other frequent mutations were observed at positions 63 (88%), 71 (49%), and 37 (57%). In the reverse transcriptase (RT) gene, the mean number of mutations was 4 (1–20), predominantly at positions 215 (75%) and 184 (67%). No patient presented changes at position 69, 75, 151, 103, or 181 of the RT gene (associated with stavudine resistance, multiresistance, or nevirapine resistance). Phenotypic assays of nine isolates revealed a high rate of baseline resistance to protease inhibitors (Table 1). Strikingly, highlevel resistance to NFV was observed in 56% of patients (five of nine), due to cross-resistance. Also, 13% (one of eight) showed phenotypic resistance to SQV. Overall, the presence of the V82A mutation was predominant in those strains with phenotypic resistance of IDV or RTV (Table 1). In contrast, most isolates were susceptible to d4T (89%; eight of nine) and to nevirapine (78%; seven of nine). Two of these strains with increased IC50 values for nevirapine (5.5- and 6-fold resistance) did not show any major mutations, a fact attributed to prior NRTI therapy, which does not compromise virological response.16
Pharmacokinetics of the combination Plasma drug levels were determined in 11 patients (Table 2). Despite a great interindividual variability, NFV trough levels
were above the protein-corrected IC95 of the virus in 100% of patients (mean, 4253 ng/ml; range, 890–11540 ng/ml), and the mean peak level was 2-fold higher than that found with the standard doses of NFV (mean, 6127 ng/ml; range, 1280–12,450 ng/ml). SQV trough levels were above the protein-corrected saquinavir IC95 in 55% of patients (mean, 479 ng/ml; range, 50–1350 ng/ml), and the increase in the mean peak level was 3-fold with respect to the use of saquinavir-hard gel capsule (SQV-hgc) as the only PI (mean, 753 ng/ml; range, 80–2110 ng/ml). Of note, two patients had SQV levels below the protein-corrected IC95 in all the pharmacokinetic determinations. With this combination of drugs, we found higher plasma drug levels for patients receiving both PIs twice daily (Table 2). Thus, only one of six patients receiving SQV twice daily had a trough plasma level below the IC95, in comparison with four of five receiving it as a three times daily regimen.
Relationship between baseline variables and response A lower baseline HIV load (3.65 vs. 4.53 log10; p 5 0.01) and prior exposure to IDV or RTV but not to both (p 5 0.005) were associated with an undetectable HIV RNA level after 6 and 12 months of therapy. Sex, age, or time on protease inhibitor therapy (514 vs. 575 days, p 5 0.35) were not significantly different in patients reaching viral suppression. In the genotypic resistance assay, the mean number of mutations in the protease gene showed a trend to significance (6 vs. 11, p 5 0.16), and the presence of the L90M mutation was strongly associated with treatment failure, with no patient with this point
d4T1 NVP1 NFV1 SQV AS SALVAGE REGIMEN TABLE 2. AFTER
PHARMACOKINETIC PARAMETERS FOR NELFINAVIR AND SAQUINAVIR -HARD GEL CAPSULES ADMINISTRATION TWICE D AILY OR THREE TIMES DAILY , TOGETHER WITH NEVIRAPINE a Dose (mg)
Cmin (ng/ml)
Cmax (ng/ml)
Protein-corrected IC95 (ng/ml)
1250 3 2 1 1000 3 2 750 3 3 1 600 3 3 600 3 3 1200 3 3 750 3 3
6670–860 2310–170 25 250 1500
8850–1250 3940–350 247 2100 3500
278
Protease inhibitor(s) Nelfinavir 1 saquinavir Saquinavir-hgc Saquinavir-sgc Nelfinavir
97
567
Abbreviations: Cmin, trough levels; Cmax , peak levels; hgc, hard gel capsule; sgc, soft gel capsule. a Data are expressed as median values. For comparison, data on each drug when used as a single PI, and the proteincorrected IC95, are included. mutation reaching an undetectable HIV load, albeit it was not significant (0 vs. 43%, p 5 0.09). At the same time, the presence of the V82A mutation decreased slightly the rate of virological response (36 vs. 38%, p 5 0.9). In the phenotypic analysis, three of four patients with isolates susceptible to NFV, and five of seven susceptible to SQV, showed viral suppression after 12 months of therapy, whereas only one of five patients with resistance to NFV achieved an undetectable HIV load.
DISCUSSION Our study shows the rate of virologic response and pharmacokinetic interactions obtained with the use of a novel quadruple antiretroviral regimen composed of stavudine, NVP, NFV, and SQV-hgc. One-third of our patients, largely pretreated with NRTIs and PIs, maintained HIV loads below 50 copies/ml after 12 months of therapy in the most stringent analysis. Also, this salvage regimen was well tolerated and produced a marked immunological benefit. Results from the Viradapt study confirm the importance of maintaining therapeutic concentrations,17 a fact potentially critical when using complex four-drug regimens including dual PIs and an enzymatic inducer such as nevirapine. All the patients in our study had NFV trough plasma concentrations above the plasma-protein binding corrected IC95, as occurred with most patients receiving SQV-hgc twice daily. Moreover, mean peak levels of NFV and SQV-hgc achieved with this combination in a twice daily regimen exceeded 2- and 5-fold those obtained with NFV and SQV monotherapy, respectively. These data are not surprising, as pharmacokinetic data support twice daily administration of NFV because of higher trough, peak, and area under the curve (AUC) values.18,19 However, at a three times daily dosing, the combination of nevirapine, NFV, and SQVhgc showed little benefit in the pharmacokinetics of SQV. Previous drug interactions studies have shown a 5-fold increase in SQV area under the curve after the administration of SQV-soft gel capsules (SQV-sgc) with NFV three times daily,20 and probably the better pharmacokinetic profile observed with this new preparation of SQV makes it more recommendable. A short exposure to IDV or RTV and a lower viral load were found to be among the factors associated with virological response. They probably indicate that the switch in therapy should be performed before higher increases in plasma viral load could lead to accumulation of more mutations producing high-level
resistance.21 Other studies have noted the close association between baseline resistance and poor outcome. In a retrospective study, Zolopa et al. found a strong relation between the number of major mutations in the protease gene and the virologic response to RTV1SQV therapy, and the use of genotypic data provides prognostic information not available through standard clinical evaluation.22 In our study, the presence of the L90M mutation at baseline was associated with treatment failure. It is known that the presence of L90M is an essential exchange in the protease gene that determines loss of sensitivity to SQV,23 and prior studies of RTV1SQV as rescue regimen have suggested a role for the L90M mutation in predicting the failure of therapy.24 Moreover, this mutation has been correlated with resistance to NFV.25 In contrast, viral suppression was observed in patients with a high number of mutations and in the presence of the V82A mutation, the mutation most frequently found after the use of RTV or IDV, suggesting that this salvage regimen may be an effective alternative treatment for patients failing on IDV or RTV therapy. In our patients, the presence of a phenotypically susceptible isolate was associated with an improved rate of response. However, our study is not potent enough to analyze the role of phenotype in predicting response. This was not a comparative study. Thus, although previous studies with the combination of RTV1SQV as rescue regimen have shown different virologic responses, ranging from 15% to more than 50% of patients with HIV loads below detectable limits,24 we cannot establish which is the best rescue regimen after IDV or RTV failure. Furthermore, the different characteristics of the patients included make it difficult to generalize these results. In a similar study, Deeks et al.26 reported a viral load below 50 copies/ml in five of nine patients after 24 weeks of salvage therapy with abacavir, nevirapine, nelfinavir, and saquinavir, although they have not analyzed the role of genotype or pharmacokinetic interactions. Also, Piketty et al. analyzed the combination of efavirenz, ritonavir, and saquinavir in patients who had failed with a previous PI.27 They found a similar rate of response, with 45% of patients maintaining an HIV load below 50 copies/ml after 24 weeks, and the levels of SQV were above the non-protein-corrected IC90 in 97% of patients. In summary, we have presented a prospective study about a triple-class regimen with the combination of an NRTI (stavudine), an NNRTI (NVP), and dual protease inhibitor therapy (NFV plus SQV) in patients who had failed with RTV or IDV
98
CASADO ET AL.
therapy. Our data show that this regimen is well tolerated, increases plasma drug levels of NFV and SQV-hgc when used in a twice daily regimen, and produces an adequate virological response after 12 months in a large proportion of patients. The presence of the V82A mutation does not reduce significantly the rate of response, suggesting that this combination could play a role as first salvage regimen after IDV or RTV failure.
15.
16.
17.
ACKNOWLEDGMENT Supported, in part, by grants from Roche and BoehringerIngelheim Laboratories.
18.
19.
REFERENCES 1. Palella FJ Jr, Delaney K, Moorman A, et al.: Declining morbidity and mortality among patients with advanced human immunodeficiency virus infection. N Engl J Med 1998;338:853–860. 2. Havlir DV and Richman DD: Viral dynamics of HIV: Implications for drug development and therapeutic strategies. Ann Intern Med 1996;124:984–994. 3. Raboud JM, Montaner JSG, Conway B, et al.: Suppression of plasma viral load below 20 copies/ml is required to achieve a longterm response to therapy. AIDS 1998;12:1619–1624. 4. Fatkenheuer G, Theisen A, Rockstroh J, et al.: Virological treatment failure of protease inhibitor therapy in an unselected cohort of HIV-infected patients. AIDS 1997;11:F101–F105. 5. Casado JL, Perez-Elias MJ, Antela A, et al.: Predictors of longterm response to protease inhibitor therapy in a cohort of HIV-infected patients. AIDS 1998;12:F75–F79. 6. Carpenter CCJ, Cooper DA, Fischl MA, et al.: Antiretroviral therapy in adults. Updated recommendations of the International AIDS Society—USA Panel. JAMA 2000;283:381–390. 7. Condra JH, Schleif WA, Blahy OM, et al.: In vivo emergence of HIV-1 variants resistant to multiple protease inhibitors. Nature 1995;374:569–571. 8. Merry C, Barry MG, Mulcahy F, Halifax KL, and Back DJ: Saquinavir pharmacokinetics alone and in combination with nelfinavir in HIV-infected patients. AIDS 1997;11:F117–F120. 9. Schapiro JM, Winters MA, Stewart F, et al.: The effect of high dose saquinavir on viral load and CD4 cell counts in HIV-infected patients. Ann Intern Med 1996;124:1039–1050. 10. Barry M, Gibbons S, Back D, and Mulcahy F: Protease inhibitors in patients with HIV disease. Clinically important pharmacokinetic considerations. Clin Pharmacokinet 1997;32:194–209. 11. Sahai J, Cameron W, Salgo M, et al.: Drug interaction study between saquinavir and nevirapine. In: IVth Conference on Retroviruses and Opportunistic Infections, Washington DC, 1997. [Abstract 614] 12. Skowron G, Leoung G, Kerr B, et al.: Lack of pharmacokinetic interaction between nelfinavir and nevirapine. AIDS 1998;12:1243– 1244. 13. Merry C, Barry MG, Mulcahy F, et al.: The pharmacokinetics of combination therapy with nelfinavir plus nevirapine. AIDS 1998; 12:1163–1167. 14. Hertogs K, de Bethune M, and Miller V: A rapid method for simultaneous detection of phenotypic resistance to inhibitors of protease and reverse transcriptase in recombinant human immuno-
20.
21.
22.
23.
24.
25.
26.
27.
deficiency virus type 1 isolates from patients treated with antiretroviral drugs. Antimicrob Agents Chemother 1998;42:269–276. Condra JH, Petropoulos CJ, Ziermann R, et al.: Resistance to HIV1 protease inhibitors and predicted responses to therapy. Antiviral Ther 2000;5:2. Casado JL, Hertogs K, Moreno A, et al.: Factors influencing decreased susceptibility to nevirapine in NNRTI-naive patients. Antiviral Ther 2000;5:25. Durant J, Clevenbergh P, Garraffo R, et al.: Importance of protease inhibitors plasma levels in HIV-infected patients treated with genotypic-guided therapy: Pharmacological data from the Viradapt study. AIDS 2000;14:1333–1339. Schuster T, Linde R, Wintergerst U, et al.: Nelfinavir pharmacokinetics in HIV-infected children: A comparison of twice daily and three times daily dosing. AIDS 2000;14:1467–1468. Johnson M, Petersen A, Winslade J, and Clendeninn N: Comparison of BID and TID dosing Viracept (Nelfinavir, NFV) in combination with stavudine (d4T) and lamivudine (3TC). In: Vth Conference on Retroviruses and Opportunistic Infections, Chicago, February 1998. [Abstract 373]. Kravcik S, Sahai J, Kerr B, et al.: Nelfinavir mesylate increases saquinavir-soft gel capsule exposure in HIV1 patients. In: IVth Conference on Retroviruses and Opportunistic Infections, Washington DC, January 1997. [Abstract 389]. Molla A, Korneyeva M, Gao Q, et al.: Ordered accumulation of mutations in HIV protease confers resistance to ritonavir. Nat Med 1996;2:760–766. Zolopa AR, Shafer RW, Warford A, et al.: HIV-1 genotypic resistance patterns predict response to saquinavir-ritonavir therapy in patients in whom previous protease inhibitor therapy had failed. Ann Intern Med 1999;131:813–821. Jacobsen H, Hanggi M, Ott M, et al.: In vivo resistance to a human immunodeficiency virus type 1 proteinase inhibitor: mutations, kinetics, and frequencies. J Infect Dis 1996;173:1379–1387. Deeks SG, Grant RM, Beatty GW, Horton C, Detmer J, and Eastman S: Activity of a ritonavir plus saquinavir-containing regimen in patients with virologic evidence of indinavir or ritonavir failure. AIDS 1998;12:F97–F102. Dronda F, Casado JL, Moreno S, et al.: Cross-resistance to nelfinavir can be predicted in the absence of the D30N mutation. In: VIIth Conference on Retroviruses and Opportunistic Infections, San Francisco, 2000. [Abstract 756] Deeks SG, Hellmann NS, Grant RM, et al.: Novel four-drug salvage treatment regimens after failure of a human immunodeficiency virus type 1 protease inhibitor-containing regimen: antiviral activity and correlation of baseline phenotypic drug susceptibility with virological outcome. J Infect Dis 1999;179:1375–1381. Piketty C, Race E, Castiel P, et al.: Efficacy of a five-drug combination including ritonavir, saquinavir and efavirenz in patients who failed on a conventional triple-drug regimen: Phenotypic resistance to protease inhibitors predicts outcome of therapy. AIDS 1999;13:F71–F77.
Address reprint requests to: Jose L. Casado Infectious Diseases Unit Ramon y Cajal Hospital Cra. Colmenar, km 9.1 28034 Madrid, Spain E-mail:
[email protected]
