Drug interactions in patients infected with human immunodeficiency virus

Comparison of pharmacokinetics and safety of albuvirtide in healthy subjects after intravenous drip and bolus injection

Albuvirtide (ABT) is the first long-acting HIV fusion inhibitor developed in China, blocking the invasion of HIV-1 virus into target cells. This study aimed to compare the pharmacokinetics (PK), tolerability, and safety of ABT following a single intravenous (IV) bolus injection or intravenous drip in healthy Chinese subjects. A single-center, randomized, open-label, single-period, parallel phase I clinical trial was conducted. Thirty subjects were randomly divided into three groups in a ratio of 1:1:1. After an overnight fast, all subjects received a single dose of 320 mg ABT either by intravenous drip for 45 min (group A) or bolus injection for 0.5 min (group B), or bolus injection for 3 min (group C). ABT plasma concentrations were analyzed using a validated enzyme-linked immunosorbent assay (ELISA). Non-compartmental analysis was used to evaluate PK parameters. The median time to reach maximum concentration was 0.75 h in group A and 0.16 h in both groups B and C. Elimination half-life, mean residence time, apparent clearance, and apparent volume of distribution were similar among the three groups. The 90% confidence intervals (CI) of geometric mean ratios of PK parameters for groups B and C relative to group C were within 85-120%. All adverse events (AEs) reported in this study were mild, according to the CTCAE guidelines and the study investigator's judgement. ABT bolus injections for 0.5 min and 3 min are expected to be well tolerated and to exhibit similar PK characteristics as IV drip for 45 min, offering potential clinical benefits.

Innate Immune Response Against HIV-1

The innate immune system is comprised of both cellular and humoral players that recognise and eradicate invading pathogens. Therefore, the interplay between retroviruses and innate immunity has emerged as an important component of viral pathogenesis. HIV-1 infection in humans that results in hematologic abnormalities and immune suppression is well represented by changes in the CD4/CD8 T cell ratio and consequent cell death causing CD4 lymphopenia. The innate immune responses by mucosal barriers such as complement, DCs, macrophages, and NK cells as well as cytokine/chemokine profiles attain great importance in acute HIV-1 infection, and thus, prevent mucosal capture and transmission of HIV-1. Conversely, HIV-1 has evolved to overcome innate immune responses through RNA-mediated rapid mutations, pathogen-associated molecular patterns (PAMPs) modification, down-regulation of NK cell activity and complement receptors, resulting in increased secretion of inflammatory factors. Consequently, epithelial tissues lining up female reproductive tract express innate immune sensors including anti-microbial peptides responsible for forming primary barriers and have displayed an effective potent anti-HIV activity during phase I/II clinical trials.

Progress in the Consideration of Possible Sex Differences in Drug Interaction Studies

Background:

Anecdotal evidence suggests that there may be sex differences in Drug-drug Interactions (DDI) involving specific drugs. Regulators have provided general guidance for the inclusion of females in clinical studies. Some clinical studies have reported sex differences in the Pharmacokinetics (PK) of CYP3A4 substrates, suggesting that DDI involving CYP3A4 substrates could potentially show sex differences.

Objective:

The aim of this review was to investigate whether recent prospective DDI studies have included both sexes and whether there was evidence for the presence or absence of sex differences with the DDIs.

Methods:

The relevant details from 156 drug interaction studies within 124 papers were extracted and evaluated.

Results:

Only eight studies (five papers) compared the outcome of the DDI between males and females. The majority of the studies had only male volunteers. Five studies had females only while 60 had males only, with 7.7% of the studies having an equal proportion of both sexes. Surprisingly, four studies did not specify the sex of the subjects.

:

Based on the limited number of studies comparing males and females, no specific trends or conclusions were evident. Sex differences in the interaction were reported between ketoconazole and midazolam as well as clarithromycin and midazolam. However, no sex difference was observed with the interaction between clarithromycin and triazolam or erythromycin and triazolam. No sex-related PK differences were observed with the interaction between ketoconazole and domperidone, although sex-related differences in QT prolongation were observed.

Conclusion:

This review has shown that only limited progress had been made with the inclusion of both sexes in DDI studies.

Mail-order pharmacy experience of veterans living with AIDS/HIV

BACKGROUND

The VA system is the largest single provider of healthcare in the United States and to individuals infected with HIV specifically. High quality medication management is particularly important since HIV is a chronic infectious condition which requires taking multiple medications with strict requirements for adherence to medication regimens. Veterans Administration (VA) patients are required to obtain all chronic medications using the VA mail-order pharmacy system.

OBJECTIVE

Drawing on Donabedian's Quality Improvement framework, this study sought to examine experiences that Veterans with HIV have with the Veterans Administration medication mail-order system, and to explore opportunities for quality improvement.

METHODS

A sequential, explanatory mixed-methods design was used to interview Veterans receiving care at a Midwestern Veterans Administration Hospital using a mail-order experience survey followed by in-depth interviews. All 57 Veterans, out of 72, who were successfully contacted consented to participate.

RESULTS

Overall, Veterans evaluated the mail-order service positively and valued the accuracy (correct medication delivery). However, a notable problem emerged with respect to assuring access to HIV medications with about half (47%) indicating running out of HIV medication. Respondents identified structural issues with respect to days covered by mailed medications (90 versus current 30 days) and process issues with scheduling new refills. Veterans also indicated the information sheets were too long, complex and not helpful for their queries. Patients were open to pharmacists playing an active role during clinic visits and felt this would help manage their conditions better.

CONCLUSIONS

Veterans generally reported that the VA Mail-order service was of high quality. However, some findings indicate there are opportunities to improve this service to be more patient-centered particularly for vulnerable HIV patients.

Significant Drug Interactions in the HIV Patient

Current treatment guidelines advocate the use of triple combination antiretroviral therapy for the management of human immunodeficiency virus (HIV) infection with one protease inhibitor (PI) or nonnucleoside reverse transcriptase inhibitor (NNRTI) plus two nucleoside reverse transcriptase inhibitors (NRTIs). Additionally, patients often receive medications for prophylaxis and treatment of opportunistic infections and comorbid illnesses. Polypharmacy with potent medications places the patient with HIV at significant risk of drug interactions. The purpose of this review is to assist clinicians regarding awareness and management of clinically significant drug interactions frequently encountered in the HIV population.

Pharmacodynamic and pharmacokinetic interactions are discussed in depth with several tables of significant interactions encountered in the patient with HIV. Certain combinations of NRTIs have antagonistic antiretroviral action (e.g., zidovudine plus stavudine), and thus should be avoided. All of the currently available PIs and delavirdine are cytochrome (CYP) 450 inhibitors and can cause significant inhibition of concomitant drug metabolism. Nevirapine is a CYP 450 inducer and can cause induction of drug metabolism, whereas efavirenz may cause inhibition or induction. Drug-herbal interactions are reviewed, including the decreased concentrations of indinavir following the administration of St. John’s wort. Additionally, the pharmacist’s role as an integral member of the HIV patient care team is discussed.

2,4,5-Trisubstituted thiazole derivatives: a novel and potent class of non-nucleoside inhibitors of wild type and mutant HIV-1 reverse transcriptase

Novel 2,4,5-trisubstituted thiazole derivatives (TSTs) were designed and synthesized as HIV-1 non-nucleoside reverse transcriptase inhibitors (NNRTIs). Among the thirty-eight synthesized target compounds, thirty TSTs showed potent inhibition against HIV-1 replication in wild type HIV-1 at submicromolar concentrations (from 0.046 to 9.59 μM). Compounds 21, 23 and 24 were also tested on seven NNRTI-resistant HIV-1 strains, and all exhibited inhibitory effects with fold changes in IC50 ranging from 2.6 to 111, which were better than those of nevirapine (15.6-fold-371-fold). Docking simulations of compound 24 revealed a reasonable mechanism for the binding mode, and three-dimensional quantitative structure activity relationship (3-DQSAR) studies on this novel series of TST further elucidated the structure-activity relationship (SAR). The results suggested the great potential of TSTs as a novel class of NNRTIs with antiviral efficacy and a good resistance profile.

A cooperative mechanism of clotrimazoles in P450 revealed by the dissociation picture of clotrimazole from P450

The dissociation processes of clotrimazole (CLT) in several models are comparatively investigated by molecular dynamics simulations to explore the cooperative mechanism of clotrimazoles in P450. Our results suggest that when P450 only accommodates the active CLT (CLT1), CLT1 continually diffuses away from heme, and the partial BC loop (residues 73-88) and the extended FG loop (residues 173-186) first close and then open. When the enzyme binds to two CLT molecules, CLT1 basically keeps close to heme, and the partial BC loop and the extended FG loop move close to each other. Clearly, the effector CLT (CLT2) plays a cooperative role in the inhibition of CLT1 on P450. CLT2 restrains the dissociation of CLT1 first through direct π-π stacking interactions and then through the rearranged binding site induced by CLT2. The presence of CLT1 can help to stabilize the protein structure around CLT2 by interacting with M86, Q173, and M174.

Invasive pulmonary aspergillosis

In susceptible patients, invasive aspergillosis has a high incidence and a mortality of up to 80%. The diagnosis of this condition is difficult, especially in the early stages of the disease and, as a consequence, antifungal therapy, despite its expense and toxicity, is often initiated empirically. Until recently, there were very few effective antifungal agents for established invasive aspergillosis, but the introduction of two new drugs, voriconazole and caspofungin, has increased the treatment options. These newer antifungal therapies, combined with improved early diagnosis due to the introduction of newer microbiologic techniques, offer the hope that there will be a significant improvement in the substantial morbidity and mortality associated with invasive aspergillosis over the next 5 years.

The effect of ritonavir on human CYP2B6 catalytic activity: heme modification contributes to the mechanism-based inactivation of CYP2B6 and CYP3A4 by ritonavir

The mechanism-based inactivation of human CYP2B6 by ritonavir (RTV) in a reconstituted system was investigated. The inactivation is time, concentration, and NADPH dependent and exhibits a K(I) of 0.9 μM, a k(inact) of 0.05 min⁻¹, and a partition ratio of approximately 3. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed that the protonated molecular ion of RTV exhibits an m/z at 721 and its two major metabolites are an oxidation product with MH⁺ at m/z 737 and a deacylated product with MH⁺ at m/z 580. Inactivation of CYP2B6 by incubation with 10 μM RTV for 10 min resulted in an approximately 50% loss of catalytic activity and native heme, but no modification of the apoprotein was observed. RTV was found to be a potent mixed-type reversible inhibitor (K(i) = 0.33 μM) and a type II ligand (spectral dissociation constant-K(s) = 0.85 μM) of CYP2B6. Although previous studies have demonstrated that RTV is a potent mechanism-based inactivator of CYP3A4, the molecular mechanism responsible for the inactivation has not been determined. Here, we provide evidence that RTV inactivation of CYP3A4 is due to heme destruction with the formation of a heme-protein adduct. Similar to CYP2B6, there is no significant modification of the apoprotein. Furthermore, LC-MS/MS analysis revealed that both CYP3A4 and human liver microsomes form an RTV-glutathione conjugate having a MH⁺ at m/z 858 during metabolism of RTV, suggesting the formation of an isocyanate intermediate leading to formation of the conjugate.

Antibiotics-related adverse events in the infectious diseases department of a French teaching hospital: a prospective study

Antibiotics are a significant cause of adverse events (AE), but few studies have focused on prescriptions in hospitalized patients. In infectious diseases departments, the high frequency and diversity of antibiotics prescribed makes AE post-marketing monitoring easier. The aim of our study was to assess the incidence and type of AE in the infectious diseases department of a French teaching tertiary-care hospital. The main characteristics of each hospitalization, including all antibiotics prescribed and any significant AE were recorded prospectively in the medical dashboard of the department. We included all patients having suffered an AE due to systemic antibiotics between January 2008 and March 2011. Among the 3963 hospitalized patients, 2682 (68%) received an antibiotic and 151/2682 (5.6%) suffered an AE. Fifty-two (34%) AE were gastrointestinal disorders, 32 (21%) dermatological, 20 (13%) hepatobiliary, 16 (11%) renal and urinary disorders, 13 (9%) neurological and 11 (7%) blood disorders. Rifampin, fosfomycin, cotrimoxazole and linezolid were the leading causes of AE. Sixty-two percent of the antibiotics causing an AE were stopped and 38% were continued (including 11% with a dose modification). Patients suffering from AE had an increased length of stay (18 vs 10 days, P < 0.001). Our data could help choosing the safest antibiotic when several options are possible.

The significance of antiretroviral-associated acute kidney injury in a cohort of ambulatory human immunodeficiency virus-infected patients

BACKGROUND

To determine the incidence and significance of acute kidney injury (AKI) after initiating highly active antiretroviral therapy (HAART).

METHODS

A prospective cohort study of 271 consecutively treated HIV-infected patients, initiating first (75) or sequential HAART (196) from January 2008 to June 2011. AKI was diagnosed according to the Risk, Injury, Failure, Loss of kidney function, End-stage renal disease (RIFLE)/Acute Kidney Injury Network (AKIN) criteria, and the risk of progression to chronic kidney disease (CKD) was evaluated.

RESULTS

A greater estimated glomerular filtration rate (eGFR) decrease after 1 year was observed for patients initiating a tenofovir disoproxil fumarate (TDF)-based regimen (-6.45 versus +0.98 mL/min/1.73 m(2) when compared with patients without TDF; P < 0.01), both in the case of the first (-8.5 versus -2.27; P = 0.04) or successive regimens (-5.3 versus + 1.18 mL/min/1.73 m(2); P < 0.01). AKI, as defined, was observed in 10% (28 cases, 6.98 episodes/100 patients-year), mostly stage I (27 cases), in a median time of 6 (3-16.5) months. Four cases (14%), having a worse baseline renal function progressed to CKD, whereas four recovered completely. In the multivariate analysis, AKI was associated with the concomitant use of cotrimoxazole prophylaxis and to low CD4+ count. CKD was diagnosed in 2% (six cases) of patients. Therefore, the overall rate of HAART-associated renal disorders was 11% (30 cases, 7.46 episodes/100 patients-year (95% confidence interval, 6.09-8.83).

CONCLUSIONS

The initiation of a tenofovir-based regimen is followed by a significant decline in eGFR, although it could be misinterpreted by the concomitant use of cotrimoxazole. A substantial proportion of patients develop AKI, but only a minority progress to CKD. Patients initiating HAART and developing AKI should be carefully monitored for progression of renal disease.

The Effect of Ravuconazole on the Pharmacokinetics of Nelfinavir in Healthy Male Volunteers

An open-label, nonrandomized study was conducted to assess the effect of ravuconazole on the pharmacokinetics of concomitantly administered nelfinavir. Healthy volunteers received 750 mg nelfinavir on day 1, 750 mg nelfinavir and 400 mg ravuconazole on day 2, 400 mg ravuconazole on days 3 to 28, and 750 mg nelfinavir and 400 mg ravuconazole on day 29. The geometric means of C(max) and area under the curve of nelfinavir coadministered with ravuconazole were 30.7% and 31.9% higher on day 2 and 7.9% and 16.2% lower on day 29, respectively, compared to the corresponding values on day 1. These findings are consistent with the potential for ravuconazole to both inhibit and induce CYP3A isozymes. The alterations in the systemic exposure to nelfinavir were within the range defined by the 90% confidence interval. The study data indicate that coadministration of ravuconazole did not result in a clinically significant change in the plasma levels of nelfinavir.

Safety and effectiveness of HAART in tuberculosis-HIV co-infected patients in Brazil

BACKGROUND

Antiretroviral therapy (ART) significantly reduces tuberculosis (TB) incidence among persons with human immunodeficiency virus (HIV), but the safety and effectiveness of concomitant treatment for both diseases remain unclear.

OBJECTIVE

To evaluate the impact of ART and anti-tuberculosis treatment on survival and risk of adverse events (AE) among co-infected individuals.

METHODS

In a retrospective cohort study, clinical data were collected from 618 TB-HIV patients treated with rifampin, isoniazid and pyrazinamide ± ethambutol between 1 January 1995 and 31 December 2003. Patients were categorized into two groups: highly active ART (HAART) or no ART. Different HAART regimens were evaluated. Bivariate analysis, multivariate logistic regression and survival analysis using Cox proportional hazards regression were used.

RESULTS

One-year mortality was lower for patients receiving HAART (adjusted hazard ratio [aHR] 0.17, 95%CI 0.09-0.31) compared to no ART. HAART increased the risk of AE (aHR 2.08, 95%CI 1.29-3.36). The odds of AE when receiving a ritonavir + saquinavir HAART regimen was eight-fold higher compared to no ART (OR 8.31, 95%CI 3.04-22.69), while efavirenz-based HAART was not associated with a significantly increased risk of AE (OR 1.42, 95%CI 0.76-2.65).

CONCLUSION

HIV patients with TB have significantly better survival if they receive HAART during anti-tuberculosis treatment. Efavirenz-based HAART is associated with fewer AEs than protease inhibitor-based HAART.

Identification of the potential regions of Epap-1 that interacts with V3 loop of HIV-1 gp120

Early pregnancy associated protein-1 (Epap-1), a 90kDa glycoprotein present in first trimester placental tissue, inhibits HIV-1 entry through interaction with HIV-1 gp120 at V3 and C5 regions. In the present study, we have identified the specific 32 mer region of Epap-1 that can interact with V3 loop. This was achieved by docking between Epap-1 molecular model and gp120 and studying the interaction of peptides with gp120 in vitro. Out of four peptides analyzed, two peptides (P-2 and P-3) showed significant interaction with V3 domain (N=8; N=7) of gp120. In the studies conducted using soluble gp120 and virus, peptide P-2 has shown conserved interaction at V3 loop regions recognized by 257D and F425 antibodies and higher anti-viral activity. Also, P-2 inhibited cell fusion mediated dye transfer between gp120 expressing HL2/3 and CD4 expressing Sup T1 cells suggesting its inhibition of viral entry, which is further confirmed by its action on HIV infection mediated by Tat activated beta gal expression in TZM-bl cells. Further optimization of P-2 peptide showed that the anti-viral activity and gp120 interaction residues lie in the N-terminal region of the peptide. These results together suggest that P-2 inhibits viral entry through specific interaction at V3 loop region.

Anti-AIDS agents 90. novel C-28 modified bevirimat analogues as potent HIV maturation inhibitors

In a continuing study of bevirimat (2), the anti-HIV-maturation clinical trials agent, 28 new betulinic acid (BA, 1) derivatives were designed and synthesized. Among these compounds, 17, with a C-28 MEM ester moiety, and 22, with a C-28 ethyl hexanoate, increased the anti-HIV replication activity compared with 2 by 2-fold while compounds 40, 41, 48, and 49, with C-28 piperazine or piperidine amide substitutions, increased the activity by 3- to 15-fold. The best new compound, 41, exhibited an anti-HIV IC(50) of 0.0059 μM compared with 0.087 μM for 2. All of the active compounds showed only antimaturation effects, as confirmed by TZM-bl assay, in blocking the HIV replication. The results suggest that proper C-28 substitutions can further enhance the antimaturation activity of 2 without any antientry effects. Thus, 41 may serve as a promising new lead for development of anti-AIDS clinical trial candidates.

The mysteries and demands of HIV care: qualitative analyses of HIV specialists’ views on their expertise

To deepen our understanding of the mysteries and demands associated with HIV care and to inform the debate about HIV specialization, we conducted in-depth interviews with a purposive sample of 20 identified HIV specialists in the San Francisco Bay Area. Participants were from several medical specialties and reported a median of 50% of their time spent in HIV patient care. Through constant comparison, a template of open codes was constructed to identify themes that emerged from the data. Data were analyzed according to the conventions of qualitative research and revealed six interrelated themes: (1) coping with uncertainty and rapid change: being 'comfortable with mystery'; (2) the powerful role of experience; (3) the dual faces of knowledge: 'knowing the patient' and 'knowing the facts'; (4) the dual faces of passion: challenge and calling; (5) stress and burnout; and (6) the relationship between academia and 'the trenches'. The themes underscore the dual dimensions of HIV care: providers must interweave the 'half-baked' science about drug therapies, side effects and drug interactions with the psychosocial and lifestyle factors of the patient. They also provide insight into quantitative findings linking greater HIV experience with better patient outcomes and suggest that providers need skills associated with generalist and specialist training, a phenomenon that argues for a 'special' specialty for HIV care.

Anti-AIDS agents 81. Design, synthesis, and structure-activity relationship study of betulinic acid and moronic acid derivatives as potent HIV maturation inhibitors

In our continuing study of triterpene derivatives as potent anti-HIV agents, different C-3 conformationally restricted betulinic acid (BA, 1) derivatives were designed and synthesized in order to explore the conformational space of the C-3 pharmacophore. 3-O-Monomethylsuccinyl-betulinic acid (MSB) analogues were also designed to better understand the contribution of the C-3' dimethyl group of bevirimat (2), the first-in-class HIV maturation inhibitor, which is currently in phase IIb clinical trials. In addition, another triterpene skeleton, moronic acid (MA, 3), was also employed to study the influence of the backbone and the C-3 modification toward the anti-HIV activity of this compound class. This study enabled us to better understand the structure-activity relationships (SAR) of triterpene-derived anti-HIV agents and led to the design and synthesis of compound 12 (EC(50): 0.0006 microM), which displayed slightly better activity than 2 as a HIV-1 maturation inhibitor.

Management of oropharyngeal and esophageal candidiasis in patients with HIV infection

Mucocutaneous candidiasis is frequently one of the first signs of HIV infection. Over 90% of patients with AIDS will develop oropharyngeal candidiasis at some time during their illness. Although numerous antifungal agents have been developed, azoles, both topical (clotrimazole) and systemic (fluconazole, itraconazole, voriconazole and posaconazole), have replaced older topical antifungals (gentian violet and nystatin) in the management of oropharyngeal candidiasis in these patients. The systemic azoles are generally safe and effective agents in HIV-infected patients with oropharyngeal candidiasis. A constant concern in these patients are relapses, which depend on the degree of immunosuppression and are commonly encountered after topical therapy rather than with systemic azole therapy. In patients with fluconazole-refractory mucosal candidiasis, treatment options now include itraconazole solution, voriconazole, posaconazole and the newer echinocandins (caspofungin, micafungin and anidulafungin). The objective of this article is to review the epidemiology, diagnosis and newer management modalities of oropharyngeal and esophageal candidiasis in HIV-infected individuals.

Optimal management of oropharyngeal and esophageal candidiasis in patients living with HIV infection

Mucocutaneous candidiasis is frequently one of the first signs of human immunodeficiency virus (HIV) infection. Over 90% of patients with AIDS will develop oropharyngeal candidiasis (OPC) at some time during their illness. Although numerous antifungal agents are available, azoles, both topical (clotrimazole) and systemic (fluconazole, itraconazole, voriconazole, posaconazole) have replaced older topical antifungals (gentian violet and nystatin) in the management of oropharyngeal candidiasis in these patients. The systemic azoles, are generally safe and effective agents in HIV-infected patients with oropharyngeal candidiasis. A constant concern in these patients is relapse, which is dependent on the degree of immunosuppression commonly seen after topical therapy, rather than with systemic azole therapy. Candida esophagitis (CE) is also an important concern since it occurs in more than 10% of patients with AIDS and can lead to a decrease in oral intake and associated weight loss. Fluconazole has become the most widely used antifungal in the management of mucosal candidiasis. However, itraconazole and posaconazole have similar clinical response rates as fluconazole and are also effective alternative agents. In patients with fluconazole-refractory mucosal candidiasis, treatment options now include itraconazole solution, voriconazole, posaconazole, and the newer echinocandins (caspofungin, micafungin, and anidulafungin).

Entry inhibitors in the treatment of HIV-1 infection

Infection of target cells by HIV is a complex, multi-stage process involving attachment to host cells and CD4 binding, coreceptor binding, and membrane fusion. Drugs that block HIV entry are collectively known as entry inhibitors, but comprise a complex group of drugs with multiple mechanisms of action depending on the stage of the entry process at which they act. Two entry inhibitors, maraviroc and enfuvirtide, have been approved for the treatment of HIV-1 infection, and a number of agents are in development. This review covers the entry inhibitors and their use in the management of HIV-1 infection. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

Anti-AIDS agents. 78. Design, synthesis, metabolic stability assessment, and antiviral evaluation of novel betulinic acid derivatives as potent anti-human immunodeficiency virus (HIV) agents

In a continuing study of potent anti-HIV agents, seventeen 28,30-disubstituted betulinic acid (BA, 1) derivatives and seven novel 3,28-disubstituted BA analogues were designed, synthesized, and evaluated for in vitro antiviral activity. Among them, compound 21 showed an improved solubility and equal anti-HIV potency (EC(50) = 0.09 microM) when compared to HIV entry inhibitors 3b (IC9564, (3R,4S)-N'-[N-[3beta-hydroxy-lup-20(29)-en-28-oyl]-8-aminooctanoyl]-4-amino-3-hydroxy-6-methylheptanoic acid) and 4 (A43-D, [[N-[3beta-O-(3',3'-dimethylsuccinyl)-lup-20(29)-en-28-oyl]-7-aminoheptyl]carbamoyl]methane). Using a cyclic secondary amine to form the C-28 amide bond increased the metabolic stability of the derivatives significantly in pooled human liver microsomes. The most potent compounds 47 and 48 displayed potent anti-HIV activity with EC(50) values of 0.007 and 0.006 microM, respectively. These results are slightly better than that of bevirimat (2, 3',3'-dimethylsuccinylbetulinic acid), which is currently in phase IIb clinical trials. Compounds 47 and 48 should serve as attractive promising leads to develop next generation, metabolically stable, 3,28-disubstituted bifunctional HIV-1 inhibitors as clinical trials candidates.

HIV entry inhibitors and their potential in HIV therapy

This review discusses recent progress in the development of anti-HIV agents targeting the viral entry process. The three main classes (attachment inhibitors, co-receptor binding inhibitors, and fusion inhibitors) are further broken down by specific mechanism of action and structure. Many of these inhibitors are in advanced clinical trials, including the HIV maturation inhibitor bevirimat, from the authors' laboratories. In addition, the CCR5 inhibitor maraviroc has recently been FDA-approved. Possible roles for these agents in anti-HIV therapy, including treatment of virus resistant to current drugs, are also discussed.

Anti-AIDS agents 73: structure-activity relationship study and asymmetric synthesis of 3-O-monomethylsuccinyl-betulinic acid derivatives

3-O-3'(or 2')-Methylsuccinyl-betulinic acid (MSB) derivatives were separated by using recycle HPLC. The structures of four isomers were assigned by NMR and asymmetric synthesis. 3-O-3'S-Methylsuccinyl-betulinic acid (3'S-MSB, 4) exhibited potent anti-HIV activity with an EC(50) value of 0.0087microM and a TI value of 6.3x10(3), which is comparable to the data for bevirimat (DSB, PA-457), a current clinical trials drug that was also derived from betulinic acid. The anti-HIV potency of 4 was slightly better than that of AZT.

Posaconazole for the management of mucosal candidiasis

Mucocutaneous candidiasis (MC) is one of the first signs of HIV infection. In the pre-highly active antiretroviral therapy (HAART) era, more than 90% of patients with HIV infection eventually developed some form of oral candidiasis during their illness, and an additional 10% developed esophageal candidiasis (EC). Although several antifungal agents are available, systemic azoles (e.g., fluconazole and itraconazole) have replaced older topical antifungals (e.g., gentian violet and nystatin) in the management of MC in these patients. Overall, the azoles are safe and effective agents in HIV-infected patients with MC. However, clinical relapses are extremely common in HIV patients not on HAART or who are noncompliant. The relapses are dependent on the degree of immunosuppression and are more common following treatment with clotrimazole or ketoconazole than with fluconazole or itraconazole. Posaconazole is a new extended-spectrum triazole recently approved for the management of oropharyngeal candidiasis (OPC). In vitro, posaconazole possesses potent activity against Candida species, including strains that are resistant to fluconazole. Recent clinical trials demonstrate that posaconazole is as efficacious as fluconazole in producing a successful clinical response in HIV-infected patients with OPC/EC. In addition, posaconazole has been demonstrated to be well tolerated and more effective in sustaining clinical success after treatment was discontinued. Posaconazole appears to be an effective alternative in the management of MC in these difficult-to-treat infections.

Anesthesia in HIV-infected children

In 2005, it was estimated that 2.3 million children below 15 years of age were living with human immunodeficiency virus (HIV)/AIDS and 570,000 children below 15 years died. Maternal-infant or vertical transmission is the most common mode of HIV infection in children. As transplacental passage of maternal anti-HIV antibodies, diagnosis of HIV infection in young infants relies on virologic assays. Infants older than 18 months of age can be diagnosed by serology alone. Pediatric HIV infections are classified according to Center for Disease Control and Prevention 1994 revised classification system. The understanding of viral pathogenesis, the development of highly active antiretroviral therapy, and the ability to quantitate viral burden have led to significant reduction in disease progression and morbidity in HIV-infected children. As survival improves, these children will require anesthesia care and pain treatment during the course of their illness. Considerations for the anesthesiologist include: possible involvement of multiple organ systems, adverse reactions and drug interactions of antiretroviral agents and adequate infection control to prevent HIV transmission in hospital and other infections to the immunocompromised patients. Finally, care should be taken not to violate confidentiality.

Interactions Between Antiretrovirals and Antineoplastic Drug Therapy

Despite the established impact of highly active antiretroviral therapy (HAART) in reducing HIV-related morbidity and mortality, malignancy remains an important cause of death. Patients who receive the combination of cancer chemotherapy and HAART may achieve better response rates and higher rates of survival than patients who receive antineoplastic therapy alone. However, the likelihood of drug interactions with combined therapy is high, since protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) are substrates and potent inhibitors or inducers of the cytochrome P450 (CYP) system. Since many antineoplastic drugs are also metabolised by the CYP system, coadministration with HAART could result in either drug accumulation and possible toxicity, or decreased efficacy of one or both classes of drugs. Although formal, prospective pharmacokinetic interaction studies are not available in most instances, it is possible to infer the nature of drug interactions based on the metabolic fates of these agents. Paclitaxel and docetaxel are both metabolised by the CYP system, although differences exist in the nature of the isoenzymes involved. Case reports describing adverse consequences of concomitant taxane-antiretroviral therapy exist. Although other confounding factors may have been present, these cases serve as reminders of the vigilant monitoring necessary when taxanes and HAART are coadministered. Similarly, vinca alkaloids are substrates of CYP3A4 and are, thus, vulnerable to PI- or NNRTI-mediated changes in their pharmacokinetics. Interactions with the alkylating agents cyclophosphamide and ifosfamide are complicated as a result of the involvement of the CYP3A4 and CYP2B6 isoenzymes in both the metabolic activation of these drugs and the generation of potentially neurotoxic metabolites. Existing data regarding the metabolic fate of the anthracyclines doxorubicin and daunorubicin suggest that clinically detrimental interactions would not be expected with coadministered HAART. Commonly used endocrine therapies are largely substrates of the CYP system and may, therefore, be amenable to modulation by concomitant HAART. In addition, tamoxifen itself has been associated with reduced concentrations of both anastrozole and letrozole, raising the concern that similar inducing properties may adversely affect the outcome of PI- or NNRTI-based therapy. Similarly, dexamethasone is both a substrate and concentration-dependent inducer of CYP3A4; enhanced corticosteroid pharmacodynamics may result with CYP3A4 inhibitors, while the efficacy of concomitant HAART may be compromised with prolonged dexamethasone coadministration. Since PIs and NNRTIs may also induce or inhibit the expression of P-glycoprotein, the potential for additional interactions to arise via modulation of this transporter also exists. Further research delineating the combined safety and pharmacokinetics of antiretrovirals and antineoplastic therapy is necessary.

RXR-induced TNF-alpha suppression is reversed by morphine in activated U937 cells

Deficiency in vitamin A has been associated with adverse clinical outcomes in drug users with HIV-1 infection. Retinoids have been demonstrated to suppress proinflammatory cytokine production by immune cells in vitro. These effects are induced by ligand-mediated activation of the retinoid receptors--retinoic acid receptor (RAR) and retinoid X receptor (RXR). In these studies, the effects of all-trans-retinoid acid (ATRA, a RAR agonist), 9-cis-retinoic acid (9cis RA; RAR and RXR agonist), LG101305 (RXR agonist), LG100815 (RAR antagonist) and LG101208 (RXR antagonist) on TNF-alpha production by phytohemagglutanin-activated U937 cells and the modulation of these effects by morphine were examined. TNF-alpha production was suppressed in all cultures exposed to retinoid agonist and antagonist agents. For cells exposed to RXR agonists or RAR antagonist, incubation with morphine resulted in the reversal of TNF-alpha suppression and this effect was inhibited by naloxone. These data suggest that interactions between RXR and morphine are involved in the immune effects of retinoids on TNF-alpha production by activated U937 cells. Such information may be important for understanding interactions between drugs of abuse and immune function in individuals with chronic proinflammatory states such as HIV-1 infection.

Potential drug interaction with paclitaxel and highly active antiretroviral therapy in two patients with AIDS-associated Kaposi sarcoma

Highly active antiretroviral therapy (HAART) consisting of multiple combinations of antiretroviral agents that inhibit HIV (HIV) replication has been associated with improvements in CD4+ T-lymphocyte cell counts, suppression of HIV replication, and regression of HIV-associated Kaposi's sarcoma (KS). Several of these agents have complex drug-drug interactions and have the potential to aggravate paclitaxel-associated toxicities. Herein two patients with KS are described who received paclitaxel while on HAART and who developed life-threatening toxicities. These cases are presented to alert clinicians to potentially serious drug interactions that can occur between various components of HAART and paclitaxel. Clinicians contemplating taxane-based chemotherapy for HIV-associated KS should carefully monitor patients for adverse events and, depending on their patient's HAART regimen, consider reducing the taxane dose.

Interactions between recreational drugs and antiretroviral agents

OBJECTIVE

To summarize existing data regarding potential interactions between recreational drugs and drugs commonly used in the management of HIV-positive patients.

DATA SOURCES

Information was obtained via a MEDLINE search (1966-August 2002) using the MeSH headings human immunodeficiency virus, drug interactions, cytochrome P450, medication names commonly prescribed for the management of HIV and related opportunistic infections, and names of commonly used recreational drugs. Abstracts of national and international conferences, review articles, textbooks, and references of all articles were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

Literature on pharmacokinetic interactions was considered for inclusion. Pertinent information was selected and summarized for discussion. In the absence of specific data, prediction of potential clinically significant interactions was based on pharmacokinetic and pharmacodynamic properties.

RESULTS

All protease inhibitors (PIs) and nonnucleoside reverse transcriptase inhibitors are substrates and potent inhibitors or inducers of the cytochrome P450 system. Many classes of recreational drugs, including benzodiazepines, amphetamines, and opioids, are also metabolized by the liver and can potentially interact with antiretrovirals. Controlled interaction studies are often not available, but clinically significant interactions have been observed in a number of case reports. Overdoses secondary to interactions between the "rave" drugs methylenedioxymethamphetamine (MDMA) or gamma-hydroxybutyrate (GHB) and PIs have been reported. PIs, particularly ritonavir, may also inhibit metabolism of amphetamines, ketamine, lysergic acid diethylmide (LSD), and phencyclidine (PCP). Case series and pharmacokinetic studies suggest that nevirapine and efavirenz induce methadone metabolism, which may lead to symptoms of opiate withdrawal. A similar interaction may exist between methadone and the PIs ritonavir and nelfinavir, although the data are less consistent. Opiate metabolism can be inhibited or induced by concomitant PIs, and patients should be monitored for signs of toxicity and/or loss of analgesia. PIs should not be coadministered with midazolam and triazolam, since prolonged sedation may occur.

CONCLUSIONS

Interactions between agents commonly prescribed for patients with HIV and recreational drugs can occur, and may be associated with serious clinical consequences. Clinicians should encourage open dialog with their patients on this topic, to avoid compromising antiretroviral efficacy and increasing the risk of drug toxicity.

The role of protease inhibitor therapy in children with HIV infection

In comparison with HIV infection in adults, higher HIV RNA levels in children with perinatal HIV infection, differences in the natural history of HIV disease progression, and the presence of a relatively immature immune system contribute to the more complex and problematic nature of pediatric antiretroviral therapy. Current US treatment guidelines for pediatric HIV infection advocate aggressive therapy with potent combination antiretroviral regimens, to achieve profound and durable suppression of viral replication and preservation of immune function. The combination of a protease inhibitor (PI) and dual nucleoside reverse transcriptase inhibitors (NRTIs) is the most commonly recommended form of highly active antiretroviral treatment (HAART). However, use of PI therapy in pediatrics has been constrained by the lack of suitable drug formulations, a paucity of pharmacokinetic and safety data, and drug intolerance. Pharmacokinetic studies of PIs demonstrate frequent differences between children and adults, and greater variability among children, which has led to subtherapeutic dosage regimens and the development of viral resistance. The optimal dosage of many PIs in younger children is not yet known. A therapeutically important drug interaction associated with PIs is that occurring between the various PIs themselves, which allows lower doses of PI at less frequent intervals. Dual PI regimens will probably become more common, as they permit a simpler antiretroviral regimen, lower pill/medication burden, fewer adverse effects and improved adherence. Poor adherence to antiretroviral therapy remains the greatest barrier to overall success in the treatment of HIV-infected children. The key to improving adherence in HIV-infected children is to find treatment regimens that are better suited to their normal life. With improvements in existing PIs and the development of newer ones, simplification of current antiretroviral therapy to once-daily regimens without loss of potency should be achievable. PI-containing HAART has transformed HIV infection into a chronic illness, and HIV-infected children now live longer.

Pseudo-Parkinson disease secondary to ritonavir-buspirone interaction

OBJECTIVE

To report a case of Parkinson-like symptoms appearing in a patient after introduction of ritonavir to buspirone therapy.

CASE SUMMARY

A 54-year-old HIV-positive white man presented to the clinic with a 2-week history of ataxia, shuffling gait, cogwheel rigidity, resting tremor, and sad affect with masked features. This patient had been receiving high-dose buspirone (40 mg every morning and 30 mg every evening) for 2 years prior to the introduction of ritonavir/indinavir combination therapy (400 mg/400 mg twice daily) 6 weeks prior to initiation of the above symptoms. Buspirone was decreased to 15 mg 3 times daily, ritonavir/indinavir was discontinued, and amprenavir 1200 mg twice daily was added. The patient's symptoms began to subside after 1 week, with complete resolution after about 2 weeks. The patient continued to receive buspirone for an additional 12 months without recurrence of symptoms.

DISCUSSION

This is the first reported interaction of buspirone and antiretrovirals. Buspirone, extensively metabolized by CYP3A4, was likely at supratherapeutic levels due to the inhibitory effect of ritonavir and, secondarily, indinavir. The Parkinson-like symptoms developed rapidly and severely, impacted this patient's quality of life, and necessitated significant clinic expenditures to identify this drug-drug interaction.

CONCLUSIONS

This case demonstrates a severe drug-drug interaction between buspirone and ritonavir and further demonstrates the need for awareness of the metabolic profile for all agents an HIV-infected patient is receiving.

Synthesis and in vitro antibacterial activity of novel 5'-O-analog derivatives of zidovudine as potential prodrugs

An efficient, short synthesis of four potential prodrugs of 3'-azido-3'-deoxythymidine (AZT) and their antibacterial activity are reported. The 5'-OH group of AZT was functionalized with oxalyl chloride obtaining an acyl chloride derivative (AZT-Ox), which by further transformation with leucine, isoleucine and valine amino acids led to the corresponding AZT analogs, namely AZT-Leu, AZT-iLeu and AZT-Val. A carboxyl acid derivative (AZT-Ac) was also obtained by hydrolysis of AZT-Ox. These compounds, which exhibit anti HIV activity, have killed collection and clinical strains of some opportunistic infectious agents in AIDS-related complex. Thus, the clinical strains, K. oxytoca, S. typhi and K. pneumoniae, and collection strain K. pneumoniae ATCC 10031 showed sensitivity to antibiotics. The activity order for the studied compounds against the most sensitive strain (K. pneumoniae ATCC 10031) was AZT-Leu > AZT-iLeu > AZT-Val > AZT-Ac > AZT. On the other hand, the activity order for the second most sensitive strain (K. oxytoca) was AZT-Leu > AZT-Val = AZT-Ac > AZT-iLeu > AZT. The most effective antibacterial drug AZT-Leu, M.I.C.=0.125 microgmL(-1)) was 16 times more active than AZT (AZT, M.I.C.=2 microg mL(-1)) against K.

Safety, pharmacokinetics, and pharmacodynamics of cyclodextrin itraconazole in pediatric patients with oropharyngeal candidiasis

The safety, pharmacokinetics, and pharmacodynamics of cyclodextrin itraconazole (CD-ITRA) oral suspension were investigated in an open sequential dose escalation study with 26 human immunodeficiency virus (HIV)-infected children and adolescents (5 to 18 years old; mean CD4(+)-cell count, 128/microl) with oropharyngeal candidiasis (OPC). Patients received CD-ITRA at either 2.5 mg/kg of body weight once a day (QD) or 2.5 mg/kg twice a day (BID) for a total of 15 days. Pharmacokinetic sampling was performed after the first dose and for up to 120 h after the last dose, and antifungal efficacy was evaluated by standardized scoring of the oropharynx. Apart from mild to moderate gastrointestinal disturbances in three patients (11.5%), CD-ITRA was well tolerated. Two patients (7.6%) discontinued treatment prematurely due to study drug-related adverse events. After 15 days of treatment, the peak concentration of drug in plasma (C(max)), the area under the plasma concentration-time curve (AUC) from 0 to 24 h (AUC(0-24)), the concentration in plasma at the end of the dosing interval (predose) (C(min)), and the terminal half-life of itraconazole (ITRA) were (means and standard deviations) 0.604 +/- 0.53 microg/ml, 6.80 +/- 7.4 microg. h/ml, 0.192 +/- 0.06 microg/ml, and 56.48 +/- 44 h, respectively, for the QD regimen and 1.340 +/- 0.75 microg/ml, 23.04 +/- 14.5 microg. h/ml, 0.782 +/- 0.19 microg/ml, and 104.22 +/- 94 h, respectively, for the BID regimen. The mean AUC-based accumulation factors for ITRA on day 15 were 4.14 +/- 0.9 and 3.53 +/- 0.6, respectively. A comparison of the dose-normalized median AUC of the two dosage regimens revealed a trend toward nonlinear drug disposition (P = 0.05). The mean metabolic ratios (AUC of hydroxyitraconazole/AUC of ITRA) at day 15 were 1.96 +/- 0.1 for the QD regimen and 1.29 +/- 0.2 for the BID regimen, respectively (P < 0.05). The OPC score (range, 0 to 13) for all 26 patients decreased from a mean of 7.46 +/- 0.8 at baseline to 2.8 +/- 0.7 at the end of therapy (P < 0.001), demonstrating antifungal efficacy in this setting. The relationships among C(max), C(min), AUC(0-12), C(max)/MIC, C(min)/MIC, AUC(0-12)/MIC, time during the dosing interval when the plasma drug concentrations were above the MIC for the infecting isolate, and the residual OPC score at day 15 for the entire study population fit inhibitory effect pharmacodynamic models (r, 0.595 to 0.421; P, <0.01 to <0.05). All patients with fluconazole-resistant isolates responded to treatment with CD-ITRA; however, there was no clear correlation between the MIC of ITRA and response to therapy. In conclusion, CD-ITRA was well tolerated and efficacious for the treatment of OPC in HIV-infected pediatric patients. Pharmacodynamic modeling revealed significant correlations between plasma drug concentrations and antifungal efficacy. Based on this documented safety and efficacy, a dosage of 2.5 mg/kg BID can be recommended for the treatment of OPC in pediatric patients > or =5 years old.

Alcohol use and HIV pharmacotherapy

Alcohol consumption by individuals infected with HIV is an important medical management issue with significant implications for the effectiveness of antiretroviral therapy as well as an important evolving field of HIV research. Alcohol consumption is a risk factor for poor medication adherence and can modify liver drug metabolism, both of which can lead to the emergence of drug-resistant virus. Research indicates that alcohol consumption greater than 50 g/day (four or five drinks) is a risk factor for liver disease progression among patients with HIV/HCV coinfection. In addition, alcohol-induced cirrhosis can result in changes in drug metabolism in the liver through compromised liver function. More research studies are needed to elucidate the biological and molecular basis of the clinical changes induced by alcohol consumption in HIV-infected individuals and on the relationship of these changes to the effectiveness of HIV pharmacotherapy. Specifically, research areas that are of particular importance are (1) determining alcohol consumption levels and patterns and its impact on antiretroviral medication adherence, efficacy, and physician prescribing practices; (2) identifying behavioral interventions to enhance adherence to HIV medications and reduce alcohol consumption; (3) clarifying the relationships and interactions among alcohol metabolism, HIV drug metabolism, and pharmacogenetics; (4) elucidating the extent of liver toxicity due to antiretroviral therapy and drug-drug interactions in individuals who consume alcohol; and (5) delineating the contribution of alcohol consumption to end-stage organ damage, particularly in HIV/HCV coinfection.

Severe interaction between ritonavir and acenocoumarol

OBJECTIVE

To report a clinically severe interaction between ritonavir (RTV) and acenocoumarol resulting in a decrease in the anticoagulant effect severe enough to eventually preclude RTV administration.

CASE SUMMARY

An asymptomatic, HIV-infected, 46-year-old man with mitraortic prosthetic valves receiving acenocoumarol therapy started stavudine, lamivudine, and RTV 600 mg twice daily. His international normalized ratio (INR) decreased dramatically (the opposite of what should be expected). Although the acenocoumarol dose was progressively increased to 3 times the original dose, it was impossible to achieve the previous INR and RTV was withdrawn.

DISCUSSION

RTV is an inducer of the hepatic isoenzymes CYP1A2, CYP1A4, and CYP2C9/19 and leads to extensive metabolism of acenocoumarol that cannot be balanced by dose increases. This effect is the opposite of what was expected to occur, considering that RTV is also a strong inhibitor of most hepatic isoenzymes.

CONCLUSIONS

RTV severely decreases the anticoagulant effect of acenocoumarol. It must be added to the list of drugs that affect the action of oral anticoagulants, and it probably should be avoided in patients receiving acenocoumarol.

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.

Acute liver failure associated with antiretroviral treatment for HIV: a report of six cases

BACKGROUND/AIMS

Severe hepatotoxicity is a rare but potentially fatal side effect of all antiretrovirals. We report a series of six human immunodeficiency virus (HIV)-infected patients admitted with acute liver failure (ALF) over a 25-month period, of whom five died. All had been treated with a range of antiretroviral therapy and only two had had acquired immune deficiency syndrome (AIDS) defining illnesses.

RESULTS

Median duration of antiretroviral therapy was 12.5 months (range 1-23). Median time from the introduction of new antiretroviral therapy to the onset of ALF was 8 weeks (range 2-12). The development of ALF was unrelated to duration of HIV treatment or type of antiretroviral therapy, and was not predicted by close out-patient supervision and monitoring of liver function. Biochemical investigations were variable but revealed a predominantly hepatocellular pattern. Liver biopsy revealed typical features of mitochondrial toxicity in only one case, with confluent hepatocellular necrosis, inflammation and cholestasis seen in the others.

CONCLUSIONS

There is a need to increase awareness of the potential hepatotoxicity of antiretroviral therapy and to develop means of predicting its development. With increasing usage of antiretroviral therapy, severe hepatotoxicity and ALF may arise more frequently, and the outcome is poor despite intensive supportive therapy.

Clinical pharmacology and pharmacokinetics of amprenavir

OBJECTIVE

To review the pharmacokinetics, pharmacodynamics, drug interactions, and dosage and administration information of amprenavir.

DATA SOURCE

An extensive review of the literature (MEDLINE search from 1994 to April 2001) relating to the clinical pharmacology of the HIV protease inhibitors was conducted. Meeting abstracts or full presentations and data submitted to the Food and Drug Administration were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

The data on pharmacokinetics, pharmacodynamics, drug interactions, and drug resistance were obtained from in vitro studies and open-label and controlled clinical trials.

DATA SYNTHESIS

Like all HIV protease inhibitors, amprenavir interrupts the maturation phase of the HIV replicative cycle by forming an inhibitor-enzyme complex, which prevents HIV protease from binding with its normal substrates (biologically inactive viral polyproteins). Amprenavir has an enzyme inhibition constant (Ki = 0.6 nM) that falls within the Ki range of the other protease inhibitors. Amprenavir's in vitro 50% inhibitory concentration (IC50) against wild-type clinical HIV isolates is 14.6 +/- 12.5 ng/mL (mean +/- SD). Pharmacodynamic modeling indicates that, as is the case with other protease inhibitors, the concentration-response curve for amprenavir plateaus at amprenavir trough values above the IC50 for these isolates. This exposure-activity relationship, plus such favorable pharmacokinetic parameters as a long terminal elimination half-life (7-10 h), makes amprenavir an attractive drug of choice when considering potent antiretrovirals. The higher trough exposure obtained with amprenavir coadministered with ritonavir may allow effective treatment of patients with decreased susceptibility viral isolates and once-daily dosing. Amprenavir has been approved for adults and children; the recommended capsule doses are 1200 mg twice daily for adults and 20 mg/kg twice daily or 15 mg/kg 3 times daily for children < 13 years of age or adolescents < 50 kg. The recommended dose for amprenavir oral solution is 1.5 mL/kg twice daily or 1.1 mL/kg 3 times daily.

CONCLUSIONS

The clinical pharmacology, exposure-activity relationship, and drug resistance profile of amprenavir support the use of this potent HIV protease inhibitor in combination antiretroviral regimens, especially for persons who have experienced virologic failure while on protease inhibitor-containing regimens.

Serotonin syndrome in HIV-infected individuals receiving antiretroviral therapy and fluoxetine

OBJECTIVE

To describe HIV-infected individuals taking antidepressants who developed the serotonin syndrome due to drug--drug or drug--food interactions.

DESIGN AND SETTING

Case studies carried out at the HIV Outpatient Clinic, Atlanta Veterans Affairs Medical Center.

PARTICIPANTS AND INTERVENTIONS

HIV-positive patients who were receiving antiretroviral and antidepressant therapies and presented with symptoms consistent with the serotonin syndrome. Their antidepressants were discontinued or the doses reduced in order to resolve the symptoms.

RESULTS

Five cases of serotonin syndrome developed after patients who were taking antidepressants ingested P450 inhibitors.

CONCLUSIONS

Serotonin syndrome should be suspected in patients on serotonergic medications who present with mental status change, autonomic dysfunction, and neuromuscular abnormalities. Suspicion should be heightened in those who are ingesting substances known to inhibit P450 enzymes, such as protease inhibitors, non-nucleoside reverse transcriptase inhibitors, and grapefruit juice.

Effect of indinavir on the pharmacokinetics of rifampicin in HIV-infected patients

Indinavir, an antiretroviral agent, has an influence on the pharmacokinetics of other drugs by acting as an inhibitor of cytochrome P450-mediated drug metabolism. The incidence of tuberculosis has increased dramatically in the past decade because of an epidemic of HIV infection. Rifampicin is still one of the most valuable drugs for the standard treatment of tuberculosis. The objective of this study was to investigate the effects of indinavir on the pharmacokinetics of rifampicin in man. Our study was conducted in eleven HIV-infected patients. All patients received a 600-mg single dose of oral rifampicin on day 1 and 15- and 800-mg oral indinavir three times a day from day 2 to day 15. Rifampicin pharmacokinetic studies were carried out on day 1 and day 15. The results showed that rifampicin concentrations were higher when it was administered with indinavir than when it was administered alone. With concomitant indinavir medication, the mean AUC0-24 of rifampicin was increased by 73%. Therefore, we conclude that indinavir has an inhibitory effect on the metabolism of rifampicin.

Pharmacokinetic Interaction between amprenavir and rifabutin or rifampin in healthy males

The objective of this study was to determine if there is a pharmacokinetic interaction when amprenavir is given with rifabutin or rifampin and to determine the effects of these drugs on the erythromycin breath test (ERMBT). Twenty-four healthy male subjects were randomized to one of two cohorts. All subjects received amprenavir (1,200 mg twice a day) for 4 days, followed by a 7-day washout period, followed by either rifabutin (300 mg once a day [QD]) (cohort 1) or rifampin (600 mg QD) (cohort 2) for 14 days. Cohort 1 then received amprenavir plus rifabutin for 10 days, and cohort 2 received amprenavir plus rifampin for 4 days. Serial plasma and urine samples for measurement of amprenavir, rifabutin, and rifampin and their 25-O-desacetyl metabolites, were measured by high-performance liquid chromatography. Rifabutin did not significantly affect amprenavir's pharmacokinetics. Amprenavir significantly increased the area under the curve at steady state (AUC(ss)) of rifabutin by 2.93-fold and the AUC(ss) of 25-O-desacetylrifabutin by 13.3-fold. Rifampin significantly decreased the AUC(ss) of amprenavir by 82%, but amprenavir had no effect on rifampin pharmacokinetics. Amprenavir decreased the results of the ERMBT by 83%. The results of the ERMBT after 2 weeks of rifabutin and rifampin therapy were increased 187 and 156%, respectively. Amprenavir plus rifampin was well tolerated. Amprenavir plus rifabutin was poorly tolerated, and 5 of 11 subjects discontinued therapy. Rifampin markedly increases the metabolic clearance of amprenavir, and coadministration is contraindicated. Amprenavir significantly decreases clearance of rifabutin and 25-O-desacetylrifabutin, and the combination is poorly tolerated. Amprenavir inhibits the ERMBT, and rifampin and rifabutin are equipotent inducers of the ERMBT.

Dual protease inhibitor therapy in the management of the HIV-1

Throughout the first 20 years of the HIV-1 epidemic, there have been tremendous advances in the development of antiretroviral therapy (ART). In 1995, the availability of protease inhibitors (PI) as part of triple drug regimens resulted in durable viral suppression with an associated decline in HIV-1-related morbidity and mortality. Despite this early success, limitations of therapy have become apparent. In particular, the need for highly potent antiviral regimens, the importance of outstanding adherence to therapy, drug-related toxicity and the increasing problem of drug-drug and drug-food interactions. Dual PI therapy has been investigated with the hope of overcoming these problems. Select PI combinations may result in synergistic antiviral activity with enhanced viral suppression. Moreover, the ability of select agents to inhibit the cytochrome P450 (CYP450) system results in pharmacologic enhancement that allows for dosing with fewer pills on a less frequent basis, both of which can enhance drug adherence. Furthermore, these pharmacologic interactions can overcome drug-drug and drug-food interactions. Finally, the ability to increase drug levels using certain PI combinations may allow for drug concentrations to exceed those needed to inhibit resistant strains of HIV-1. The rationale for using dual PI therapy, along with the results of clinical trials using various PI combinations in treatment-naïve and experienced patients, is reviewed in this article.