The safety profile and antiviral activity of the combination of stavudine, didanosine, and nelfinavir in patients with HIV infection

TDM: Therapeutic Drug Measuring or Therapeutic Drug Monitoring?

The third round of the International Interlaboratory Quality Control Program for Therapeutic Drug Monitoring in HIV infection (QC-program) consisted of the analysis not only of plasma samples but also of patient cases. The case was composed of different topics related to the therapeutic drug monitoring of antiretroviral drugs. The participants were asked to give recommendations concerning dose adjustments, changes to the regimen, and drug-drug interactions to observe whether the expert recommendations were comparable. Of the 30 participants of the QC-program, 16 returned their comments and recommendations with regard to the patient case. The drug level was easy to judge: approximately 90% were able to correctly do so. Almost half of the recommendations (44%) given were satisfactory. Levels of knowledge regarding HIV treatment appeared to be variable among the respondents and for this reason were partly incomparable.

Trimethoprim-Sulfamethoxazole (Tmp/Smx) Potentiates Indinavir Nephrotoxicity

Objectives

Indinavir is a widely prescribed protease inhibitor in the treatment of HIV infection. It has been associated with nephrolithiasis, crystalluria and tubulointerstitial nephritis. Nelfinavir is another protease inhibitor used successfully in AIDS treatment. The objective of this study was to evaluate the effect of both indinavir and nelfinavir individually, and in association with trimethoprim-sulfamethoxazole (TMP/SMX), on renal function in Wistar rats.

Methods

Doses of indinavir (80 mg/kg body weight [BW] daily), nelfinavir (75 mg/kg BW daily) and TMP/SMX (100 mg TMP/kg BW daily) were given by gavage for 15 days. Seven groups were studied: control, vehicle, TMP/SMX, indinavir, indinavir+TMP/SMX, nelfinavir, and nelfinavir+TMP/SMX.

Results

No changes were observed in body weight, urine volume and blood pressure. The vehicle group did not differ from the control group. TMP/SMX induced a small decrease in inulin clearance with no tubular alterations. Indinavir decreased inulin clearance (indinavir: 0.48 ±0.03 vs control: 0.93 ±0.08, P<0.001) and renal blood flow (indinavir: 6.2 ±0.2 vs control: 8.0 ±0.3, P<0.05). These effects were potentiated by TMP/SMX, which produced high vasoconstriction associated with alterations in tubular functions, characterised by increased fractional excretion of sodium (indinavir+TMP/SMX: 1.14 ±0.16 vs control: 0.39 ±0.07, P<0.01). Nelfinavir either alone or in combination with TMP/SMX did not change the renal function of the rats.

Conclusion

These results suggest that indinavir nephrotoxicity in rats is potentiated by TMP/SMX and that nelfinavir alone or in combination with TMP/SMX is not nephrotoxic.

Didanosine: an updated review of its use in HIV infection

Didanosine, like zidovudine, stavudine and lamivudine, is a nucleoside analogue reverse transcriptase inhibitor (NRTI). In the target cell for HIV, didanosine is converted to its active moiety, dideoxyadenosine-5'-triphosphate (ddATP), which inhibits HIV reverse transcriptase and terminates viral DNA growth. It is now well established that didanosine therapy produces beneficial effects on virological and immunological markers of HIV disease and improves clinical outcome in adults or children with HIV infection. In numerous clinical trials, pronounced and sustained decreases in plasma HIV RNA levels and increases in CD4+ cell counts occurred in previously untreated or antiretroviral therapy-experienced patients treated with didanosine in combination with at least 1 other antiretroviral drug; zidovudine, stavudine, lamivudine, nevirapine, nelfinavir and hydroxyurea (hydroxycarbamide) are among the drugs that have been given in combination with didanosine. Of note, HIV RNA levels decreased to below the limits of detection in some patients receiving triple or dual therapy with didanosine-containing regimens. In double-blind, placebo-controlled trials, triple therapy with didanosine, zidovudine and nevirapine was significantly more effective than dual therapy with various combinations of these agents in improving surrogate disease markers in treatment-naive patients and in delaying disease progression or death in treatment-experienced patients with advanced disease. Improvements in virological and immunological markers were greater with didanosine-containing triple regimens than with dual therapy or monotherapy in comparative trials. Triple therapy with didanosine, stavudine and indinavir showed efficacy similar to that of various other triple therapy regimens in nonblind comparative trials. Comparator regimens included combinations of stavudine, lamivudine plus indinavir, zidovudine, lamivudine plus indinavir and didanosine, stavudine and nevirapine. Combination therapy with didanosine plus hydroxyurea as dual therapy or with a third agent produced marked and sustained decreases in HIV RNA levels in the plasma and in lymph nodes. Combination therapy with didanosine and zidovudine delays disease progression and prolongs survival in patients with intermediate or advanced HIV infection. In large, randomised, double-blind, clinical trials, dual therapy with didanosine plus zidovudine was significantly more effective than zidovudine monotherapy in preventing disease progression and prolonging survival in previously untreated or antiretroviral therapy-experienced patients with intermediate or advanced HIV infection. Pancreatitis and peripheral neuropathy are serious adverse effects of didanosine. These effects are dose-related and usually reversible after discontinuation of treatment. Nausea, vomiting, diarrhoea and/or abdominal pain have been reported in patients receiving treatment with the drug.

CONCLUSIONS

Didanosine is an effective and generally well tolerated drug in previously untreated and antiretroviral therapy-experienced patients with HIV infection. Given once or twice daily, it has an important role as a component of triple combination regimens for the treatment of patients with symptomatic or asymptomatic HIV infection.

Nelfinavir. A review of its therapeutic efficacy in HIV infection

Nelfinavir is a selective inhibitor of HIV protease, the enzyme responsible for post-translational processing of HIV propeptides. In the presence of the drug, immature, noninfectious virus particles are produced. Nelfinavir in combination with nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors and/or other protease inhibitors profoundly suppresses viral replication. Plasma HIV RNA levels (viral loan) rapidly fall below the limit of detection (LOD; usually 400 or 500 copies/ml in the majority of patients. When used in combination with NRTIs, nelfinavir 1250mg twice daily produced similar results to 3-times-daily nelfinavir at a range of total daily dosages. In an ongoing study > 70% of adults receiving a nelfinavir based combination regimen had plasma HIV RNA levels below the LOD (< 400 copies/ml) after 84 weeks. In addition, 73% of paediatric patients receiving nelfinavir plus at least 1 new NRTI had viral loads below the LOD (< 400 copies/ml) after 34 weeks. Furthermore, CD4+ cell counts generally increased in conjunction with reductions in viral load. Combination therapy with nelfinavir and saquinavir results in higher saquinavir plasma concentrations, make twice-daily administration of saquinavir feasible and may delay the emergence of resistant viral strains. A unique mutation at codon 30 (D30N) of the protease gene confers resistance to nelfinavir, but HIV with D30N mutation remains fully susceptible to indinavir, ritonavir and saquinavir in vitro. Nonetheless, in clinical use, significant cross-resistance is seen with all currently available protease inhibitors. Diarrhoea is the most frequently reported adverse event in patients receiving nelfinavir-based combination therapy and has been reported in up to 32% of nelfinavir recipients in randomised trials. Diarrhoea is generally of mild to moderate severity and does not result in weight loss. Rash, nausea, headache and asthenia were each reported in < or = 5% of patients. Approximately 5% of patients enrolled in an expanded access programme in the US discontinued nelfinavir because of adverse events. Nelfinavir is metabolised by the cytochrome P450 system. Several clinically significant pharmacokinetic drug interactions between nelfinavir and other drugs (i.e. ketoconazole, rifabutin, rifabutin, rifampicin), including other protease inhibitors (i.e. indinavir, ritonavir, saquinavir) have been documented. As with other available protease inhibitors, hyperglycaemia, hyperlipidaemia and abnormal fat distribution have been reported, albeit infrequently, in association with nelfinavir.

CONCLUSION

Nelfinavir-based combination regimens are well tolerated and produce profound and prolonged suppression of HIV replication in adult and paediatric patients. Hence, nelfinavir is suitable for inclusion in antiretroviral regimens for initial therapy for HIV infection and, alternatively, in regimens for patients unable to tolerate other protease inhibitors.