Effect of efavirenz on the pharmacokinetics of ketoconazole in HIV-infected patients

The Influence of Different Triazole Antifungal Agents on the Pharmacokinetics of Cyclophosphamide

Background: Cyclophosphamide is one of the most important chemotherapeutic drugs. Known as a widely accepted treatment strategy, chemotherapy may damage the immune function of cancer patients; as a result, invasive fungal infections (IFIs) occur. Triazole antifungal agents are the most acceptable drugs for IFI treatment, especially those infections caused by chemotherapy. Objective: We aimed to investigate the effects of different triazole antifungal drugs, including fluconazole, itraconazole, and ketoconazole, on the pharmacokinetics (PK) of cyclophosphamide. In addition, we also characterize the potential drug-drug interactions (DDIs) between cyclophosphamide and various triazole antifungal drugs. Methods: The necessary pharmacokinetic parameters and physicochemical data were obtained from published studies. Physiologically based pharmacokinetic (PBPK) models were developed and validated in virtual subjects using Simcyp software. The validated PBPK models were used to evaluate potential DDIs between cyclophosphamide and different triazole antifungal agents in cancer patients. Triazole antifungal agents were simulated by oral administration, whereas cyclophosphamide was simulated by intravenous administration. Results: Simulated plasma concentration-time curves of fluconazole, itraconazole, ketoconazole, and cyclophosphamide were in good consistency with the observed profiles. Our results suggested that the pharmacokinetic parameters of cyclophosphamide were increased by various extents when coadministered with different triazole antifungals. The area under the plasma concentration-time curve of cyclophosphamide was increased when combined with fluconazole, itraconazole, or ketoconazole. Conclusions and Relevance: Ketoconazole had the greatest effect on the PK of cyclophosphamide among the 3 triazole antifungals. Our study provides clues that the toxicity and adverse drug reactions that are associated with cyclophosphamide should be closely monitored when coadministered with ketoconazole.

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.

Antiretroviral drug interactions: overview of interactions involving new and investigational agents and the role of therapeutic drug monitoring for management

Antiretrovirals are prone to drug-drug and drug-food interactions that can result in subtherapeutic or supratherapeutic concentrations. Interactions between antiretrovirals and medications for other diseases are common due to shared metabolism through cytochrome P450 (CYP450) and uridine diphosphate glucuronosyltransferase (UGT) enzymes and transport by membrane proteins (e.g., p-glycoprotein, organic anion-transporting polypeptide). The clinical significance of antiretroviral drug interactions is reviewed, with a focus on new and investigational agents. An overview of the mechanistic basis for drug interactions and the effect of individual antiretrovirals on CYP450 and UGT isoforms are provided. Interactions between antiretrovirals and medications for other co-morbidities are summarized. The role of therapeutic drug monitoring in the detection and management of antiretroviral drug interactions is also briefly discussed.

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.

A phase I clinical study of high dose ketoconazole plus weekly docetaxel for metastatic castration resistant prostate cancer

PURPOSE

This phase I study of high dose ketoconazole and docetaxel was designed against castration resistant prostate cancer to determine the maximum tolerated doses, side effects, and pharmacokinetic interaction of co-administered docetaxel and ketoconazole.

MATERIALS AND METHODS

Patients with metastatic castration resistant prostate cancer received weekly docetaxel for 3 of every 4 weeks plus daily ketoconazole. Pharmacokinetic studies were performed on day 1 (docetaxel alone) and day 16 (after ketoconazole).

RESULTS

The study enrolled 42 patients at 9 different dose levels. The combination regimens investigated included docetaxel weekly, increasing from 5 to 43 mg/m(2), with starting doses of 600, 800 or 1,200 mg ketoconazole daily. Decreases in prostate specific antigen of 50% or greater were seen in 62% of patients. Of 25 patients with soft tissue disease 7 (28%) had a partial response. Median overall survival was 22.8 months and was significantly greater in docetaxel naïve patients than in patients pretreated with docetaxel (36.8 vs 10.3 months, p = 0.0001). The most frequently observed adverse events were anemia, edema, fatigue, diarrhea, nausea, sensory neuropathy and elevated liver function tests. The fractional change in docetaxel clearance correlated significantly with ketoconazole exposure (p <0.01). Concomitant ketoconazole increased docetaxel exposure 2.6-fold with 1,200 mg daily, 1.6-fold with 800 mg daily and approximately 1.3 to 1.5-fold with 600 mg daily.

CONCLUSIONS

Combination regimens using 600 mg ketoconazole daily were fairly well tolerated and the maximum tolerated dose of docetaxel was 32 mg/m(2). Results suggest that the combination has significant antitumor activity in castration resistant prostate cancer. The long survival in the docetaxel naïve cohort warrants additional, larger trials of docetaxel with ketoconazole or possibly CYP17A1 inhibitors such as abiraterone.

Effects of oral posaconazole on the pharmacokinetics of atazanavir alone and with ritonavir or with efavirenz in healthy adult volunteers

BACKGROUND

Patients with HIV/AIDS are at increased risk for opportunistic fungal infections. These patients may require concomitant treatment with antiretrovirals and azole antifungals, and interactions between these classes of drugs should be anticipated.

METHODS

A phase 1, open-label, randomized, crossover, drug interaction study was conducted to assess the pharmacokinetic effects of coadministration of posaconazole (400 mg twice daily), with atazanavir (ATV) (300 mg/d alone) and with ritonavir (100 mg/d) or with efavirenz (400 mg/d) in healthy volunteers.

RESULTS

Posaconazole increased maximum observed plasma concentration (Cmax) and area under the plasma concentration-time curve (AUC) of ATV by 2.6-fold and 3.7-fold, respectively. Posaconazole increased ATV Cmax and AUC when administered with ritonavir by 1.5-fold and 2.5-fold, respectively. Most subjects who received ATV (with and without ritonavir) and posaconazole experienced clinically relevant increases in total bilirubin. Coadministration of posaconazole and efavirenz resulted in clinically relevant decreases of posaconazole Cmax and AUC of approximately 45% and 50%, respectively.

CONCLUSIONS

Frequent monitoring of adverse events and toxicity related to antiviral exposure is recommended in the event of coadministration of posaconazole and ATV with or without ritonavir. In addition, because of decreased posaconazole exposure, coadministration with efavirenz should be avoided unless the benefit to patients outweighs the risk.

Pharmacokinetic interaction between efavirenz and ketoconazole in rats

1. It is well known that efavirenz and ketoconazole act as an inducer and inhibitor of CYP3A4, respectively. As a result of these actions, co-administration of these drugs may result in changes in the pharmacokinetic parameters of one or both of them. 2. Duodenum-cannulated rats have been used to compare the effect of intraduodenal (KC(i.d.)) and intravenous administration of ketoconazole (KC(i.v.)) on the pharmacokinetics of efavirenz after intraduodenal administration, as well as the potential effect of efavirenz as a CYP450 inducer on ketoconazole pharmacokinetic profile. 3. While KC(i.v.) did not show any significant effect on efavirenz pharmacokinetic profile, KC(i.d.) increased significantly (p < 0.05) the peak concentration (C(max)) and the area under the plasma concentration-time curve (AUC) of efavirenz by 25.5% and 44.5%, respectively. In addition, the time necessary to reach peak concentration (T(max)) increased markedly by 71%. However, the mean total clearance (CL/F) of efavirenz was significantly decreased by 45%. Efavirenz did not produce any alteration in ketoconazole pharmacokinetics. 4. These findings suggest that when the treatment starts with enteral administration of ketoconazole, the inhibitor effect on CYP450 prevails over the inducer effect of efavirenz.

Clinical Evidence of Interaction Between Itraconazole and Nonnucleoside Reverse Transcriptase Inhibitors in HIV-Infected Patients with Disseminated Histoplasmosis

Background

Itraconazole is the preferred drug for chronic maintenance therapy in HIV-infected patients with disseminated histoplasmosis. Unfortunately, few clinical data exist confirming a presumed interaction between itraconazole and nonnucleoside reverse transcriptase inhibitors (NNRTIs).

Objective

To determine whether serum itraconazole concentrations are affected by the type of antiretroviral therapy (NNRTI or protease inhibitor [PI]) being taken concomitantly.

Methods

This retrospective cohort identified patients on antiretroviral therapy and itraconazole for disseminated histoplasmosis between January 2003 and December 2006 at a large HIV clinic in Houston, TX. Available laboratory values were abstracted from medical records.

Results

Thirteen itraconazole concentrations from 10 patients were avaitable for analysis: 7 patients were on concomitant Pls, 4 on concomitant NNRTIs, and 2 on antiretroviral regimens containing both Pls and NNRTIs. Six of the itraconazole concentrations during concomitant PI treatment were therapeutic (>1.0 μg/mL). in contrast with none in patients taking an NNRTI. All patients taking concomitant NNRTIs had undetectable serum itraconazole concentrations (<0.05 μg/mL). Two patients switched from NNRTI-based to PI-based antiretroviral regimens and subsequently reached therapeutic itraconazole concentrations. Although limited by small sample size, this study provides the largest clinical data among HIV-infected patients demonstrating that coadministration of an NNRTI and itraconazole results in significant decreases in itraconazole blood concentrations, likely by inducing the CYP3A4 enzyme system.

Conclusions

Itraconazole concentrations should be monitored in patients taking concomitant NNRTIs. PI-based highly active antiretroviral therapy (HAART) may be preferred over NNRTI-based HAART when itraconazole is used to treat HIV-infected patients with disseminated histoplasmosis.

Influence of antiretroviral drugs on the pharmacokinetics of prednisolone in HIV-infected individuals

BACKGROUND

Corticosteroids are cytochrome P450 3A4 substrates, which have been associated with toxicities in patients receiving cytochrome P450 3A4 inhibitors such as human immunodeficiency virus protease inhibitors. In a study in healthy volunteers, ritonavir significantly increased prednisolone exposure.

METHODS

We investigated the influence of antiretroviral (ARV) medications on prednisolone pharmacokinetics in 3 groups of 10 human immunodeficiency virus-infected subjects. One group received lopinavir/ritonavir, and another efavirenz, as part of their ARV regimen; a third group did not receive ARV medications. Each subject received a single 20-mg prednisone dose followed by serial blood sampling for prednisolone. Prednisolone pharmacokinetics were compared among the groups.

RESULTS

Area under the concentration-time curve was significantly lower in efavirenz recipients versus subjects receiving lopinavir/ritonavir (geometric mean ratio = 0.60, P = 0.01). Average prednisolone area under the concentration-time curve was higher in subjects taking lopinavir/ritonavir versus subjects not on ARVs; however, this difference was not significant (P > 0.05).

CONCLUSIONS

These data indicate that prednisolone concentrations may fluctuate widely when human immunodeficiency virus-positive individuals established on efavirenz therapy change to lopinavir/ritonavir or vice versa.