Itraconazole as an alternative for ritonavir liquid formulation when combined with saquinavir

A semi-mechanistic pharmacokinetic model of saquinavir combined with itraconazole in HIV-1-positive patients

The mechanism of drug-drug interaction between saquinavir, a protease inhibitor used effectively for HIV/AIDS treatment, and itraconazole, an azole antifungal agent, is hypothesized to involve competitive inhibition at CYP3A4 enzyme, an important drug metabolizing enzyme in humans. The resulting interaction between these CYP3A4 substrates can be utilized clinically as a pharmacokinetic booster for prolonging saquinavir dosing regimen and/or decreasing saquinavir dose requirement in HIV/AIDS patients. To quantitatively describe this specific drug-drug interaction, based on the existing data, we aimed to develop a mathematical model incorporated with the competitive inhibition phenomena. PlotDigitizer was used to extract data from literature. Advance Continuous Simulating Language Extreme (ACSLX), a FORTRAN-based computer program, was employed as our developing tool. Our computer model simulations could successfully describe concentration-time course of saquinavir from selected pharmacokinetic studies in HIV-1-positive patients. To extend the model's utility as an aid in saquinavir dosage regimens, the developed model may be applied to other HIV/AIDS patients in genuine clinical settings.

Clinically relevant drug-drug interactions between antiretrovirals and antifungals

INTRODUCTION

Complete delineation of the HIV-1 life cycle has resulted in the development of several antiretroviral drugs. Twenty-five therapeutic agents belonging to five different classes are currently available for the treatment of HIV-1 infections. Advent of triple combination antiretroviral therapy has significantly lowered the mortality rate in HIV patients. However, fungal infections still represent major opportunistic diseases in immunocompromised patients worldwide.

AREAS COVERED

Antiretroviral drugs that target enzymes and/or proteins indispensable for viral replication are discussed in this article. Fungal infections, causative organisms, epidemiology and preferred treatment modalities are also outlined. Finally, observed/predicted drug-drug interactions between antiretrovirals and antifungals are summarized along with clinical recommendations.

EXPERT OPINION

Concomitant use of amphotericin B and tenofovir must be closely monitored for renal functioning. Due to relatively weak interactive potential with the CYP450 system, fluconazole is the preferred antifungal drug. High itraconazole doses (> 200 mg/day) are not advised in patients receiving booster protease inhibitor (PI) regimen. Posaconazole is contraindicated in combination with either efavirenz or fosamprenavir. Moreover, voriconazole is contraindicated with high-dose ritonavir-boosted PI. Echinocandins may aid in overcoming the limitations of existing antifungal therapy. An increasing number of documented or predicted drug-drug interactions and therapeutic drug monitoring may aid in the management of HIV-associated opportunistic fungal infections.

Interactions between antifungal and antiretroviral agents

IMPORTANCE OF THE FIELD

Since the advent of combination antiretroviral therapy, the incidence of opportunistic infections has declined and the life expectancy of HIV-infected people has significantly increased. However, opportunistic infections, including fungal diseases, remain a leading cause of hospitalizations and mortality in HIV-infected people. With the availability of several new antiretroviral and antifungal agents, drug-drug interactions emerge as a potential safety concern.

AREAS COVERED IN THIS REVIEW

Relevant literature was identified using a Medline search of articles published up to March 2010 and a review of conference abstracts. Search terms included HIV, antifungal agents and drug interactions. Original papers and relevant citations were considered for this review.

WHAT THE READER WILL GAIN

Readers will gain an understanding of the pharmacokinetic properties of antiretroviral and antifungal agents, and insight into significant drug-drug interactions which may require dosage adjustments or a change in therapy.

TAKE HOME MESSAGE

Azole antifungal drugs, with the exception of fluconazole, pose the greatest risk of two-way interactions with antiretroviral drugs through CYP450 enzymes effects. Limited studies suggest the risk of interactions between antiretroviral drugs and echinocandins is much lower. The combination of tenofovir and amphotericin B should be used with caution and close monitoring of renal function is required.

Therapeutic drug monitoring in highly active antiretroviral therapy

IMPORTANCE OF THE FIELD

Despite the efficacy of combination antiretroviral therapy (ART), a large proportion of patients living with HIV/AIDS on ART does not achieve or maintain adequate virological suppression. Therapeutic drug monitoring (TDM) has been utilised to improve treatment outcomes of ART.

AREAS COVERED IN THE REVIEW

The potential incorporation of TDM into the clinical HIV management is supported by the existing relationship between drug exposure and efficacy/toxicity, the high inter-patient variability pharmacokinetics, and the accurate, specific and rapid method for drug level determination. The current status of TDM in ART is reviewed in this article with discussions on its feasibility, potential use and limitations.

WHAT THE READER WILL GAIN

Mounting evidence from clinical trials has indicated the potential use of TDM in reducing the rates of treatment failure and adverse effect, avoiding the drug interactions, and special populations, such as children, pregnant women and patients with co-infections. TDM may play an important role even in resource-limited settings, to safeguard expanded use of bioequivalent generic antiretroviral drugs and avoid drug interactions with traditional Chinese medicines.

TAKE HOME MESSAGE

TDM is still in the centre of controversy in that several critical issues need to be addressed, such as limited adherence assessment, inappropriate response predictors, insufficient validation of target concentration windows and lack of the quality control of assay. The utility of TDM will remain experimental until more data are obtained from large clinical trials showing the benefit of TDM.

Antifungal therapy--state of the art at the beginning of the 21st century

The most relevant information on the present state of the art of antifungal chemotherapy is reviewed in this chapter. For dermatomycoses a variety of topical antifungals are available, and safe and efficacious systemic treatment, especially with the fungicidal drug terbinafine, is possible. The duration of treatment can be drastically reduced. Substantial progress in the armamentarium of drugs for invasive fungal infections has been made, and a new class of antifungals, echinocandins, is now in clinical use. The following drugs in oral and/or intravenous formulations are available: the broad spectrum polyene amphotericin B with its new "clothes"; the sterol biosynthesis inhibitors fluconazole, itraconazole, and voriconazole; the glucan synthase inhibitor caspofungin; and the combination partner flucytosine. New therapy schedules have been studied; combination therapy has found a significant place in the treatment of severely compromised patients, and the field of prevention and empiric therapy is fast moving. Guidelines exist nowadays for the treatment of various fungal diseases and maintenance therapy. New approaches interfering with host defenses or pathogenicity of fungal cells are being investigated, and molecular biologists are looking for new targets studying the genomics of pathogenic fungi.

Pharmacokinetics of Lower Doses of Saquinavir Soft-Gel Caps (800 and 1200 Mg Twice Daily) Boosted with Itraconazole in HIV-1-Positive Patients

Objective

The pharmacokinetics of 800 mg and 1200 mg of saquinavir soft-gel caps (SQV-SGC) twice daily plus 100 mg itraconazole once daily were compared to 1400 mg SQV-SGC twice daily without itraconazole.

Methods

The pharmacokinetics of SQV were determined in 17 randomly selected patients on 1400 mg twice daily SQV-SGC without itraconazole and after 2 weeks with lower SQV-SGC doses plus itraconazole. SQV plasma concentrations were determined by HPLC. Pharmacokinetic parameters were calculated by a non-compartmental model.

Results

Median (+IQR) area under plasma concentration-versus-time curve (AUC0–12h) were 3.33 (1.96–7.34), 4.29 (3.14–7.67) and 4.07 (2.76–4.49) mg/l.h for SQV 1400 mg without itraconazole, SQV 1200 mg with itraconazole and SQV 800 mg with itraconazole, respectively. These differences were not statistically significant. The median Cmin was above the proposed minimum effective concentration of 0.05 mg/l for all three regimens.

Conclusion

SQV-SGC 800 mg or 1200 mg twice daily boosted with 100 mg of itraconazole once daily resulted in adequate SQV pharmacokinetics not significantly different from SQV-SGC 1400 mg twice daily.

Therapeutic drug monitoring in HIV infection: current status and future directions

BACKGROUND

Highly active antiretroviral therapy (HAART) can suppress viral replication and prolong patient life substantially. However, HAART can fail for a number of reasons, including incomplete adherence, pharmacokinetic factors and the emergence of resistance. Because the number of possible antiretroviral combinations is limited, the use of existing treatment options must be optimized. Whether the application of therapeutic drug monitoring (TDM) in routine clinical practice may help with this purpose remains a subject of debate. However, TDM has been introduced in some centres despite the lack of guidelines for optimal use of this test.

OBJECTIVE

In October 2000, a panel of experts met in Perugia, Italy, to discuss the key issues surrounding the introduction of TDM into routine clinical practice. The purpose of the meeting was to achieve a consensus among panel members on the following issues: (i) validity of data suggesting the utility of TDM in HAART; (ii) patient categories and clinical settings in which TDM may be of most benefit; (iii) target levels of antiretroviral agents; (iv) influence of covariables on target levels of drugs; (v) blood sampling and dosage adjustment strategies; and (vi) future research steps needed to elucidate issues regarding the applicability of TDM in clinical practice.

OUTCOME

This report, which has been updated to include data published or presented at conferences up to the end of August 2001, summarizes the data presented and issues discussed at the meeting. This article will guide the reader through the data and discussions that have allowed the panel to formulate a series of position statements regarding the current status and future applications of TDM in antiretroviral therapy. These statements have been formulated to provide suggestions for the design of future TDM clinical trials, as well as to provide useful points of reflection for centres in which TDM is already in use.

Pharmacokinetics of intravenous itraconazole followed by itraconazole oral solution in patients with human immunodeficiency virus infection

This randomized, open-label, comparative study assessed the pharmacokinetics and safety of intravenous and oral hydroxypropyl-beta-cyclodextrin (HP-beta-CD) solutions of itraconazole in patients with advanced human immunodeficiency virus (HIV) infection. All patients received 1-hour intravenous infusions of itraconazole 200 mg twice dailyfor 2 days, then once dailyfor 5 days. Patients were then randomized to receive itraconazole oral solution, 200 mg twice daily or 200 mg once daily, for a further 28 days. Itraconazole was solubilized by HP-beta-CD in both intravenous and oral solutions, so HP-beta-CD concentration in plasma was measured. Thirty-two patients were enrolled and analyzed (n = 32 for intravenous treatment, 32 completed; n = 16 for oral once daily, 15 completed; n = 16 for oral twice daily, 12 completed). Steady-state plasma concentrations of itraconazole and hydroxyitraconazole were reached by days 3 and 6, respectively. After intravenous dosing, mean trough plasma concentrations of itraconazole and hydroxyitraconazole were 906 ng/ml and 1,690 ng/ml, respectively. During oral dosing, mean trough plasma concentrations of itraconazole and hydroxyitraconazole were maintained or increased in the 200 mg twice-dailygroup but fell with the 200 mg once-daily oral dose. Itraconazole was generally well tolerated and had a favorable safetyprofile; minor changes in hematology variables were noted during the intravenous phase, and HP-beta-CD was cleared rapidly, mostly in urine. Twenty-eight patients (88%) experienced at least one adverse event; no adverse event was severe, and only seven were definitely related to itraconazole. In conclusion, itraconazole 200 mg given intravenously twice daily for 2 days, then once daily for 5 days, rapidly achieves amean steady-state trough concentration of itraconazole of over 250 ng/ml, which is associated with clinic outcome and is effectively maintained with itraconazole oral solution 200 mg twice daily in patients with advanced HIV infection.

The effect of fluconazole on ritonavir and saquinavir pharmacokinetics in HIV-1-infected individuals

AIMS

To study the effect of fluconazole on the steady-state pharmacokinetics of the protease inhibitors ritonavir and saquinavir in HIV-1-infected patients.

METHODS

Five subjects treated with saquinavir and three with ritonavir received the protease inhibitor alone (saquinavir 1200 mg three times daily, ritonavir 600 mg twice daily) on day 1, and the same protease inhibitor in combination with fluconazole (400 mg on day 2 and 200 mg on days 3 to 8). Pharmacokinetic parameters were determined on days 1 and 8.

RESULTS

In the saquinavir group, the median increase in the area under the plasma concentration vs time curve was 50% from 1800 microg l(-1) h to 2700 microg l(-1) h (P = 0.04, median increase: 900 microg l(-1) h; 2.5 and 97.5 percentile: 500-1300), and 56% for the peak concentration in plasma (from 550 to 870 microg l(-1), P = 0.04; median increase: 320 microg l(-1) h, 2.5 and 97.5 percentile: 60-450 microg l(-1)). In the ritonavir group, there were no detectable changes in the pharmacokinetic parameters on addition of fluconazole.

CONCLUSIONS

Because of the favourable safety profile of saquinavir, dose adjustments are probably not necessary with concomitant use of fluconazole, as is the case for ritonavir.

Current management of fungal infections

The management of superficial fungal infections differs significantly from the management of systemic fungal infections. Most superficial infections are treated with topical antifungal agents, the choice of agent being determined by the site and extent of the infection and by the causative organism, which is usually readily identifiable. One exception is onychomycosis, which usually requires treatment with systemically available antifungals; the accumulation of terbinafine and itraconazole in keratinous tissues makes them ideal agents for the treatment of onychomycosis. Oral candidiasis in immunocompromised patients also requires systemic treatment; oral fluconazole and itraconazole oral solution are highly effective in this setting. Systemic fungal infections are difficult to diagnose and are usually managed with prophylaxis or empirical therapy. Fluconazole and itraconazole are widely used in chemoprophylaxis because of their favourable oral bioavailability and safety profiles. In empirical therapy, lipid-associated formulations of amphotericin-B and intravenous itraconazole are safer than, and at least as effective as, conventional amphotericin-B (the former gold standard). The high acquisition costs of the lipid-associated formulations of amphotericin-B have limited their use.