Pharmacokinetic interaction between amprenavir and clarithromycin in healthy male volunteers

Recent Updates on Viral Oncogenesis: Available Preventive and Therapeutic Entities

Human viral oncogenesis is a complex phenomenon and a major contributor to the global cancer burden. Several recent findings revealed cellular and molecular pathways that promote the development and initiation of malignancy when viruses cause an infection. Even, antiviral treatment has become an approach to eliminate the viral infections and prevent the activation of oncogenesis. Therefore, for a better understanding, the molecular pathogenesis of various oncogenic viruses like, hepatitis virus, human immunodeficiency viral (HIV), human papillomavirus (HPV), herpes simplex virus (HSV), and Epstein-Barr virus (EBV), could be explored, especially, to expand many potent antivirals that may escalate the apoptosis of infected malignant cells while sparing normal and healthy ones. Moreover, contemporary therapies, such as engineered antibodies antiviral agents targeting signaling pathways and cell biomarkers, could inhibit viral oncogenesis. This review elaborates the recent advancements in both natural and synthetic antivirals to control viral oncogenesis. The study also highlights the challenges and future perspectives of using antivirals in viral oncogenesis.

Quantification of human hepatocyte cytochrome P450 enzymes and transporters induced by HIV protease inhibitors using newly validated LC-MS/MS cocktail assays and RT-PCR

Human immunodeficiency virus (HIV) protease inhibitors (PIs) produce profound and unpredictable drug-drug interactions (DDIs) that cannot be explained fully by their inhibition/inactivation of CYP3A enzymes. Delineating and quantifying the CYPs and transporters inducible by PIs are crucial in developing an integrative mechanistic understanding and prediction of PI-based DDIs. To do so, two LC-MS/MS cocktail assays were modified and validated simultaneously to quantify the CYP activity of CYP3A, 2B6, 2C8, 2C9, 2C19, 1A, 2E1, 2A6 and 2D6 enzymes. These new assays were applied to evaluate the induction potential of eight PIs in microsomes isolated from PI-treated human hepatocytes. The mRNA expression of these CYPs and transporters (OATP1B1, OATP1B3, OATP1A2, MDR1, MRP2 and MRP4) was also evaluated using relative RT-PCR. The majority of PIs were net inducers of CYP3As and 2B6 at both the mRNA and activity level (> 2-fold), while ritonavir, saquinavir, nelfinavir or lopinavir did not induce CYP3A activity (< 2-fold), presumably due to CYP3A inactivation. OATP1B1 and MDR1 were the only two hepatic transporters induced (> 2-fold) by the PIs. Amprenavir was the most potent net inducer. In conclusion, our validated cocktail assays can be implemented to comprehensively quantify CYP activities in human liver microsomes and hepatocyte studies. The results also provide the much needed data on the net induction potential of the PIs for hepatic CYPs and transporters. A qualitative agreement was observed between our results and published PI-based DDIs, suggesting that human hepatocytes are a useful platform for more extensive and quantitative in vitro-in vivo prediction of PI-based DDIs.

Effect of clarithromycin and fluconazole on the pharmacokinetics of montelukast in human volunteers

OBJECTIVE

Montelukast, a leukotriene receptor antagonist, is used in the treatment of asthma. The objective of the study reported here was to determine whether multiple doses of clarithromycin or fluconazole affect the pharmacokinetics of montelukast.

METHODS

This was a four-phase cross-over study with a washout period of 2 weeks between phases. In phase 1, 12 volunteers received a single oral dose of 10 mg montelukast. In phase 2, the volunteers received a single, oral dose of 1,000 mg clarithromycin once daily for 2 days, followed by, on day 3, a single oral dose of 10 mg montelukast co-administered with clarithromycin. In phase 3, a single oral dose of 50 mg fluconazole was given once daily for 6 days, followed by, on day 7, a single oral dose of 10 mg montelukast co-administered with 50 mg fluconazole. In the last phase (phase 4), a single oral dose of 150 mg fluconazole was given once daily for 6 days, followed by, on day 7, a single oral dose of 10 mg montelukast co-administered with 150 mg fluconazole. The plasma concentration of montelukast was measured by high performance liquid chromatography for 24 h.

RESULTS

Following clarithromycin co-administration, the area under the concentration-time curve from zero to infinity ( AUC(0-∞)) of montelukast increased by 144% [90% confidence interval (CI) 2.03-2.86]. The co-administration of a single oral dose of 150 and 50 mg fluconazole decreased the montelukast AUC(0-∞) by 30.7 (90% CI 0.53-0.81) and 38.8% (90% CI 0.57-0.69), respectively.

CONCLUSIONS

Clarithromycin increased the plasma concentrations of montelukast whereas fluconazole reduced the plasma concentrations of montelukast. The mechanism of the interaction is probably due to interference of the interacting drugs with transporters mediating the uptake of montelukast.

Pharmacokinetic drug interactions of antimicrobial drugs: a systematic review on oxazolidinones, rifamycines, macrolides, fluoroquinolones, and Beta-lactams

Like any other drug, antimicrobial drugs are prone to pharmacokinetic drug interactions. These drug interactions are a major concern in clinical practice as they may have an effect on efficacy and toxicity. This article provides an overview of all published pharmacokinetic studies on drug interactions of the commonly prescribed antimicrobial drugs oxazolidinones, rifamycines, macrolides, fluoroquinolones, and beta-lactams, focusing on systematic research. We describe drug-food and drug-drug interaction studies in humans, affecting antimicrobial drugs as well as concomitantly administered drugs. Since knowledge about mechanisms is of paramount importance for adequate management of drug interactions, the most plausible underlying mechanism of the drug interaction is provided when available. This overview can be used in daily practice to support the management of pharmacokinetic drug interactions of antimicrobial drugs.

Clarithromycin, a cytochrome P450 inhibitor, can reverse mefloquine resistance in Plasmodium yoelii nigeriensis- infected Swiss mice

During the last 2 decades there have been numerous reports of the emergence of mefloquine resistance in Southeast Asia and nearly 50% resistance is reported in Thailand. A World Health Organization report (2001) considers mefloquine as an important component of ACT (artesunate+mefloquine) which is the first line of treatment for the control of uncomplicated/multi-drug resistant (MDR) Plasmodium falciparum malaria. In view of the emergence of resistance towards this drug, it is proposed to develop new drug combinations to prolong the protective life of this drug. Prior studies have suggested that mefloquine resistance can be overcome by a variety of agents such as ketoconazole, cyproheptadine, penfluridol, Icajine and NP30. The present investigation reports that clarithromycin (CLTR), a new macrolide, being a potent inhibitor of Cyt. P450 3A4, can exert significant resistance reversal action against mefloquine resistance of plasmodia. Experiments were carried out to find out the curative dose of CLTR against multi-drug resistant P. yoelii nigeriensis. Mefloquine (MFQ) and clarithromycin (CLTR) combinations have been used for the treatment of this MDR parasite. Different dose combinations of these two drugs were given to the infected mice on day 0 (prophylactic) and day 1 with established infection (therapeutic) to see the combined effect of these combinations against the MDR malaria infection. With a dose of 32 mg/kg MFQ and 225 mg/kg CLTR, 100% cure was observed, while in single drug groups, treated with MFQ or CLTR, the cure was zero and 40% respectively. Therapeutically, MFQ and CLTR combinations 32+300 mg/kg doses cleared the established parasitaemia on day 10. Single treatment with MFQ or CLTR showed considerable suppression of parasitaemia on day 14 but neither was curative. Follow-up of therapeutically treated mice showed enhanced anti-malarial action as reflected by their 100% clearance of parasitaemia. The present study reveals that CLTR is a useful antibiotic to be used as companion drug with mefloquine in order to overcome mefloquine resistance in plasmodia.

Impact of ATP-binding cassette transporters on human immunodeficiency virus therapy

Even though potent antiretrovirals are available against human immunodeficiency virus (HIV)-1 infection, therapy fails in a significant fraction of patients. Among the most relevant reasons for treatment failure are drug toxicity and side effects, but also the development of viral resistance towards the drugs applied. Efflux by ATP-binding cassette (ABC-) transporters represents one major mechanism influencing the pharmacokinetics of antiretroviral drugs and particularly their distribution, thus modifiying the concentration within the infected cells, that is, at the site of action. Moreover, drug-drug interactions may occur at the level of these transporters and modulate their activity or expression thus influencing the efficacy and toxicity of the substrate drugs. This review summarizes current knowledge on the interaction of antiretrovirals used for HIV-1 therapy with ABC-transporters and highlights the impact of ABC-transporters for cellular resistance and therapeutic success. Moreover, the suitability of different cell models for studying the interaction of antiretrovirals with ABC-transporters is discussed.

Drug interactions with new and investigational antiretrovirals

More than 20 individual and fixed-dose combinations of antiretrovirals are approved for the treatment of human immunodeficiency virus (HIV) infection. However, owing to the ongoing limitations of drug resistance and adverse effects, new treatment options are still required. A number of promising new agents in existing or new drug classes are in development or have recently been approved by the US FDA. Since these agents will be used in combination with other new and existing antiretrovirals, understanding the potential for drug interactions between these compounds is critical to their appropriate use. This article summarizes the drug interaction potential of new and investigational protease inhibitors (darunavir), non-nucleoside reverse transcriptase inhibitors (etravirine and rilpivirine), chemokine receptor antagonists (maraviroc, vicriviroc and INCB 9471), integrase inhibitors (raltegravir and elvitegravir) and maturation inhibitors (bevirimat).

Interaction studies of tipranavir-ritonavir with clarithromycin, fluconazole, and rifabutin in healthy volunteers

Three separate controlled, two-period studies with healthy volunteers assessed the pharmacokinetic interactions between tipranavir-ritonavir (TPV/r) in a 500/200-mg dose and 500 mg of clarithromycin (CLR), 100 mg of fluconazole (FCZ), or 150 mg of rifabutin (RFB). The CLR study was conducted with 24 subjects. The geometric mean ratios (GMR) and 90% confidence intervals (90% CI; given in parentheses) of the areas under the concentration-time curve (AUC), the maximum concentrations of the drugs in serum (C(max)), and the concentrations in serum at 12 h postdose (Cp12h) for multiple-dose TPV/r and multiple-dose CLR, indicating the effect of TPV/r on the CLR parameters, were 1.19 (1.04-1.37), 0.95 (0.83-1.09), and 1.68 (1.42-1.98), respectively. The formation of the metabolite 14-OH-CLR was decreased by 95% in the presence of TPV, and the TPV AUC increased 66% compared to that for human immunodeficiency virus (HIV)-negative historical controls. The FCZ study was conducted with 20 subjects. The GMR (and 90% CI) of the AUC, C(max), and Cp24h, indicating the effect of multiple-dose TPV/r on the multiple-dose FCZ parameters, were 0.92 (0.88-0.95), 0.94 (0.91-0.98), and 0.89 (0.85-0.92), respectively. The TPV AUC increased by 50% compared to that for HIV-negative historical controls. The RFB study was conducted with 24 subjects. The GMR (and 90% CI) of the AUC, C(max), and Cp12h for multiple-dose TPV/r and single-dose RFB, indicating the effect of TPV/r on the RFB parameters, were 2.90 (2.59-3.26), 1.70 (1.49-1.94), and 2.14 (1.90-2.41), respectively. The GMR (and 90% CI) of the AUC, C(max), and Cp12h of TPV/r and RFB with 25-O-desacetyl-RFB were 4.33 (3.86-4.86), 1.86 (1.63-2.12), and 2.76 (2.44-3.12), respectively. Coadministration of TPV with a single dose of RFB resulted in a 16% increase in the TPV Cp12h compared to that for TPV alone. In the general population, no dose adjustments are necessary for the combination of TPV/r and CLR or FCZ. Combining TPV/r with RFB should be done with caution, while toxicity and RFB drug levels should be monitored. Study medications were generally well-tolerated in these studies.

Darunavir/ritonavir pharmacokinetics following coadministration with clarithromycin in healthy volunteers

This study investigated the steady-state pharmacokinetic interaction between the HIV protease inhibitor, darunavir (TMC114), administered with low-dose ritonavir (darunavir/ritonavir), and clarithromycin in HIV-negative healthy volunteers. In a 3-way crossover study, 18 individuals received darunavir/ritonavir 400/100 mg bid, clarithromycin 500 mg bid, and darunavir/ritonavir 400/100 mg bid plus clarithromycin 500 mg bid in 3 separate sessions for 7 days, with a washout period of at least 7 days between treatments. Pharmacokinetic assessment was performed on day 7. Safety and tolerability of the study medication were monitored throughout. Coadministration of darunavir/ritonavir with clarithromycin resulted in a reduction in darunavir maximum plasma concentration (Cmax) and area under the curve from administration until 12 hours postdose (AUC12 h) of 17% and 13%, respectively. Ritonavir Cmax and AUC12 h were unchanged. During coadministration with darunavir/ritonavir, clarithromycin Cmax and AUC12 h increased by 26% and 57%, respectively; 14-hydroxy-clarithromycin plasma concentrations were reduced to below the lower limit of quantification (<50 ng/mL). The study medication was generally well tolerated. Based on these pharmacokinetic findings, neither clarithromycin nor darunavir/ritonavir dose adjustments are necessary when clarithromycin is coadministered with darunavir/ritonavir.

Fosamprenavir calcium plus ritonavir for HIV infection

Fosamprenavir is a protease inhibitor (PI) approved for the treatment of HIV-1 infection. Fosamprenavir is a prodrug of amprenavir developed to reduce the pill burden yet maintain the unique resistance pattern and efficacy associated with amprenavir. In a head-to-head, noninferiority trial in antiretroviral treatment-naive HIV-infected patients, the antiviral efficacy and tolerability of ritonavir-boosted fosamprenavir was not inferior to ritonavir-boosted lopinavir, when the PIs were combined with two other nucleoside reverse transcriptase inhibitors. There are fewer studies published about fosamprenavir use in antiretroviral treatment-experienced HIV-infected patients. The high genetic barrier to the development of resistance to fosamprenavir and the low level of cross-resistance between ritonavir-boosted fosamprenavir and other PI regimens are notable. As with amprenavir, gastrointestinal disturbance and rash are the most frequent short-term treatment-limiting events with fosamprenavir. Treatment with ritonavir-boosted fosamprenavir can produce a durable response. To date, fosamprenavir is one of the recommended preferred PI components for the treatment of antiretroviral-naive HIV-infected patients.

Emerging drugs to replace current leaders in first-line therapy for breast cancer

Increasing knowledge of drug resistance and side effects of currently approved agents, and of the biology of breast cancer, has given way to new treatment options that improve on previously available agents, or medications that target specific kinases and proteins associated with an oncogenic phenotype. This paper discusses new agents, including improved formulations of paclitaxel and epothilones, and molecularly targeted agents such as bevacizumab, sunitinib malate, pertuzumab, lapatinib, the mTOR inhibitors and farnesyl transferase inhibitors. Although endocrine therapy is a targeted therapy, it is not covered in this paper. These agents have increased excitement in the treatment of breast cancer and stand on the forefront of a potential improvement in quality of life and treatment options for patients afflicted with this deadly disease.

The effect of ciprofloxacin and clarithromycin on sildenafil oral bioavailability in human volunteers

Sildenafil is the first oral therapeutic agent for the management of male erectile dysfunction. Its oral bioavailability is only 40% due to extensive presystemic elimination, mainly by CYP3A4. This study examined the effect of coadministration of ciprofloxacin or clarithromycin, which inhibit CYP3A4, on the bioavailability and pharmacokinetics of sildenafil. Twelve healthy male volunteers received sildenafil alone or after pretreatment with the inhibitors in a balanced three-way crossover design. The pharmacokinetic analysis showed that ciprofloxacin coadministration with sildenafil significantly increased the AUC from 1407 +/- 380 to 2986 +/- 917 microg h/l (90% confidence interval 119%-159%) and the Cmax from 287 +/- 67 to 623 +/- 192 microg/l (90% confidence interval 127%-152%). Similarly, clarithromycin coadministration increased sildenafil AUC from 1407 +/- 380 to 3209 +/- 762 microg h/l (90% confidence interval 127%-161%) and Cmax from 287 +/- 67 to 694 +/- 259 microg/l (90% confidence interval 132%-157%). Ciprofloxacin coadministration and clarithromycin coadministration with sildenafil did not affect the rate of sildenafil absorption significantly. These results indicate that coadministration of ciprofloxacin and clarithromycin significantly increased sildenafil bioavailability which can be attributed to the inhibitory effect of ciprofloxacin and clarithromycin on CYP3A4. Dose adjustment of sildenafil is thus necessary when administered with such drugs.

Fosamprenavir

Fosamprenavir is one of the most recently approved HIV-1 protease inhibitors (PIs) and offers reductions in pill number and pill size, and omits the need for food and fluid requirements associated with the earlier-approved HIV-1 PIs. Three fosamprenavir dosage regimens are approved by the US FDA for the treatment of HIV-1 PI-naive patients, including fosamprenavir 1,400 mg twice daily, fosamprenavir 1,400 mg once daily plus ritonavir 200mg once daily, and fosamprenavir 700 mg twice daily plus ritonavir 100mg twice daily. Coadministration of fosamprenavir with ritonavir significantly increases plasma amprenavir exposure. The fosamprenavir 700 mg twice daily plus ritonavir 100mg twice daily regimen maintains the highest plasma amprenavir concentrations throughout the dosing interval; this is the only approved regimen for the treatment of HIV-1 PI-experienced patients and is the only regimen approved in the European Union. Fosamprenavir is the phosphate ester prodrug of the HIV-1 PI amprenavir, and is rapidly and extensively converted to amprenavir after oral administration. Plasma amprenavir concentrations are quantifiable within 15 minutes of dosing and peak at 1.5-2 hours after fosamprenavir dosing. Food does not affect the absorption of amprenavir following administration of the fosamprenavir tablet formulation; therefore, fosamprenavir tablets may be administered without regard to food intake. Amprenavir has a large volume of distribution, is 90% bound to plasma proteins and is a substrate of P-glycoprotein. With <1% of a dose excreted in urine, the renal route is not an important elimination pathway, while the principal route of amprenavir elimination is hepatic metabolism by cytochrome P450 (CYP) 3A4. Amprenavir is also an inhibitor and inducer of CYP3A4. Furthermore, fosamprenavir is commonly administered in combination with low-dose ritonavir, which is also extensively metabolised by CYP3A4, and is a more potent CYP3A4 inhibitor than amprenavir. This potent CYP3A4 inhibition contraindicates the coadministration of certain CYP3A4 substrates and requires others to be co-administered with caution. However, fosamprenavir can be co-administered with many other antiretroviral agents, including drugs of the nucleoside/nucleotide reverse transcriptase inhibitor, non-nucleoside reverse transcriptase inhibitor and HIV entry inhibitor classes. Coadministration with other HIV-1 PIs continues to be studied.The extensive fosamprenavir and amprenavir clinical drug interaction information provides guidance on how to co-administer fosamprenavir and fosamprenavir plus ritonavir with many other commonly co-prescribed medications, such as gastric acid suppressants, HMG-CoA reductase inhibitors, antibacterials and antifungal agents.

Pharmacokinetics and Pharmacodynamics of Methadone Enantiomers After Coadministration with Amprenavir in Opioid-Dependent Subjects

STUDY OBJECTIVE

To investigate the steady-state pharmacokinetics of methadone enantiomers when coadministered with amprenavir.

DESIGN

Prospective, open-label, within-subject pharmacokinetic study.

SETTING

University research center.

SUBJECTS

Nineteen opioid-dependent, methadone-maintained, healthy individuals were enrolled.

INTERVENTION

On study day 1, subjects received their usual once-daily dose of methadone alone. On study days 2-11, they received the same once-daily methadone dose plus amprenavir 1200 mg twice/day. Serial blood samples were collected over 24 hours on study days 1 and 11 for measurement of plasma R- and S-methadone, and over 12 hours on day 11 for serum amprenavir concentrations.

MEASUREMENTS AND MAIN RESULTS

Standard pharmacokinetic parameters were determined from the concentrations and compared between the two treatments (methadone alone vs methadone with amprenavir). Subjects served as their own control for methadone comparisons, and amprenavir comparisons were made by using a historic control group (38 healthy men). Opioid-effect measures were assessed throughout the study. Coadministration of amprenavir with methadone resulted in a 3-4-hour delay in plasma R- and S-methadone enantiomer peak concentrations at steady state (Cmax-ss). The active R-methadone enantiomer area under the plasma concentration-time curve during a dosing interval (AUCt-ss, Cmax-ss, and the minimum plasma concentration at steady state (Cmin-ss) were decreased by 13%, 25%, and 21%, respectively, after coadministration of methadone and amprenavir. The inactive S-enantiomer AUCt-ss, Cmax-ss, and Cmin-ss were decreased by 40%, 48%, and 52%, respectively. No clinically significant changes were noted in opioid pharmacodynamic effects, and there was no evidence of opioid withdrawal. No methadone dosage was changed in any subject.

CONCLUSION

No a priori adjustment in methadone dosage is required during coadministration with amprenavir as there is only a small effect on R-methadone exposure and no evidence of opioid withdrawal.

A phase I trial of pharmacokinetic modulation of carboxyamidotriazole (CAI) with ketoconazole in patients with advanced cancer

PURPOSE

Carboxyamidotriazole (CAI) is a novel antineoplastic agent in clinical development with limited oral bioavailability. In vitro, ketoconazole has been demonstrated to inhibit CYP3A4-mediated metabolism of CAI. We performed this phase I trial to determine if ketoconazole-mediated CYP3A4 inhibition would lead to favorable alteration of CAI pharmacokinetics, and to evaluate the safety, toxicity and tolerability of the proposed combination.

DESIGN

Forty-seven patients were treated using a standard three patients per cohort CAI dose-escalation scheme. In cycle 1, CAI was administered alone on day-6 followed by a single dose of ketoconazole (200 mg) on day 0. CAI and ketoconazole (200 mg/day) were subsequently coadministered on days 1 and 3-28. Plasma samples for pharmacokinetic analysis were obtained following the doses on days-6 and 1. All subsequent cycles were of 28-day duration, and consisted of daily CAI and ketoconazole coadministration.

RESULTS

Pharmacokinetic analysis was performed on samples from 44 patients. In most patients administration of ketoconazole produced an increase in CAI AUC and Cmax with a decrease in CAI clearance. Seven patients experienced stable disease for up to 12 months. Gastrointestinal and constitutional toxicities were the most common toxicities.

CONCLUSIONS

Coadministration of CAI with ketoconazole increased CAI exposure in most of the patients without altering the toxicity profile of CAI. The highest CAI dose administered on the trial was 300 mg/day. The clinical utility of such a modulation strategy might be explored in future clinical trials of CAI.

Drug interactions between antiretroviral drugs and comedicated agents

HIV-infected individuals usually receive a wide variety of drugs in addition to their antiretroviral drug regimen. Since both non-nucleoside reverse transcriptase inhibitors and protease inhibitors are extensively metabolised by the cytochrome P450 system, there is a considerable potential for pharmacokinetic drug interactions when they are administered concomitantly with other drugs metabolised via the same pathway. In addition, protease inhibitors are substrates as well as inhibitors of the drug transporter P-glycoprotein, which also can result in pharmacokinetic drug interactions. The nucleoside reverse transcriptase inhibitors are predominantly excreted by the renal system and may also give rise to interactions. This review will discuss the pharmacokinetics of the different classes of antiretroviral drugs and the mechanisms by which drug interactions can occur. Furthermore, a literature overview of drug interactions is given, including the following items when available: coadministered agent and dosage, type of study that is performed to study the drug interaction, the subjects involved and, if specified, the type of subjects (healthy volunteers, HIV-infected individuals, sex), antiretroviral drug(s) and dosage, interaction mechanism, the effect and if possible the magnitude of interaction, comments, advice on what to do when the interaction occurs or how to avoid it, and references. This discussion of the different mechanisms of drug interactions, and the accompanying overview of data, will assist in providing optimal care to HIV-infected patients.

Drug-induced rhabdomyolysis after concomitant use of clarithromycin, atorvastatin, and lopinavir/ritonavir in a patient with HIV

A case report of drug-induced rhabdomyolysis in a 34-year-old HIV-infected male with a history of liver disease and concomitant use of clarithromycin, atorvastatin, and lopinavir/ritonavir is presented.

Cytochrome P450 3A4 activity after surgical stress

OBJECTIVE

To evaluate the relationship between the acute inflammatory response after surgical trauma and changes in hepatic cytochrome P450 3A4 activity, compare changes in cytochrome P450 3A4 activity after procedures with varying degrees of surgical stress, and to explore the time course of any potential drug-cytokine interaction after surgery.

DESIGN

Prospective, open-label study with each patient serving as his or her own control.

SETTING

University-affiliated, acute care, general hospital.

PATIENTS

A total of 16 patients scheduled for elective repair of an abdominal aortic aneurysm (n = 5), complete or partial colectomy (n = 6), or peripheral vascular surgery with graft (n = 5).

INTERVENTIONS

Cytochrome P450 3A4 activity was estimated using the carbon-14 [14C]erythromycin breath test (ERMBT) before surgery and 24, 48, and 72 hrs after surgery. Abdominal aortic aneurysm and colectomy patients also had an ERMBT performed at discharge. Blood samples were obtained before surgery, immediately after surgery, and 6, 24, 32, 48, and 72 hrs after surgery for determination of plasma concentrations of interleukin-6, interleukin-1beta, and tumor necrosis factor-alpha. Clinical markers of surgical stress that were collected included duration of surgery, estimated blood loss, and volume of fluids administered in the operating room.

MEASUREMENTS AND MAIN RESULTS

ERMBT results significantly declined in all three surgical groups, with the lowest value at the time of the 72-hr study in all three groups. There was a trend toward differences in ERMBT results among groups that did not reach statistical significance (p =.06). The nadir ERMBT result was significantly and negatively correlated with both peak interleukin-6 concentration (r(s) = -.541, p =.03) and log interleukin-6 area under the curve from 0 to 72 hrs (r(s) = -.597, p =.014). Subjects with a peak interleukin-6 of >100 pg/mL had a significantly lower nadir ERMBT compared with subjects with a peak interleukin-6 of <100 pg/mL (35.5% +/- 5.2% vs. 74.7% +/- 5.1%, p <.001).

CONCLUSIONS

Acute inflammation after elective surgery was associated with a significant decline in cytochrome P450 3A4 activity, which is predictive of clinically important changes in the metabolism of commonly used drugs that are substrates for this enzyme.

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.

Effects of metronidazole on hepatic CYP3A4 activity

STUDY OBJECTIVE

To evaluate the effect of a short course of oral metronidazole, commonly used for bowel-preparation regimens, on hepatic cytochrome P450 (CYP) 3A4 activity, as measured by the [14C N-methyl]-erythromycin breath test (ERMBT) in healthy volunteers.

DESIGN

Prospective, nonrandomized, interventional study

SETTING

University-affiliated, community, teaching hospital.

SUBJECTS

Five healthy male volunteers.

INTERVENTION

Subjects underwent a baseline ERMBT in the morning before receiving three oral doses of metronidazole 500 mg administered at 3 P.M., 7 P.M., and 11 P.M. Repeat ERMBTs were performed at 24, 72, and 96 hours after the initial ERMBT. Changes in ERMBT values were compared with baseline results using Freidman's repeated-measures analysis of variance on ranks.

MEASUREMENTS AND MAIN RESULTS

The ERMBT values did not change significantly compared with baseline (p=0.82). Median (range) ERMBT values expressed as a percentage of baseline at 24, 72, and 96 hours were 110.3 (96.2-136.9), 101.3 (99.3-115.0), and 101.8 (95.5-116.3), respectively

CONCLUSION

A short course of oral metronidazole does not result in a significant change in hepatic CYP3A4 activity as measured by the ERMBT.

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.

Drug-Drug interactions of clinical significance in the treatment of patients with Mycobacterium avium complex disease

Therapeutic and prophylactic regimens directed specifically against Mycobacterium avium complex (MAC) are increasingly being used in patients infected with the human immunodeficiency virus (HIV). Several of the drugs used in the management of MAC have been associated with significant drug interactions involving the cytochrome P450 (CYP) enzyme system. This enzyme system is also highly influenced by other drugs used in the management of patients with HIV, particularly the protease inhibitors, non-nucleoside reverse transcriptase inhibitors (NNRTIs) and azole antifungals. This article reviews the published concentrations or subtherapeutic concentrations of other drugs have been described. In particular, concurrent use of rifabutin with clarithromycin or fluconazole has resulted in increased concentrations of rifabutin and an accompanying increase in the incidence of rifabutin toxicities, including uveitis and leucopenia. Similar results have been seen when rifabutin is combined with protease inhibitors or delavirdine. The macrolides, clarithromycin and azithromycin, have also been associated with significant drug interactions. Clarithromycin has a higher affinity for CYP than azithromycin and, thus, is more frequently associated with clinically significant drug interactions. Clarithromycin is an inhibitor of CYP and may result in toxic concentrations of other drugs metabolised by this enzyme system. Such interactions have been described with rifabutin and the statin lipid-lowering agents. In addition, nevirapine and efavirenz have been shown to significantly reduce clarithromycin concentrations, whereas the protease inhibitors and delavirdine may increase clarithromycin concentrations. Other drugs used in the management of patients with MAC are not metabolised by CYP and thus have a lower incidence of interactions, although the absorption of ciprofloxacin may be impaired when it is given with products containing multivalent cations, such as didanosine. However, clinicians must remain vigilant for drug interactions when reviewing a patient's medication profile, keeping in mind both interactions that have been described in the literature and those that may be predicted based upon known pharmacokinetic profiles.

Variability in activity of hepatic CYP3A4 in patients infected with HIV

STUDY OBJECTIVES

To evaluate hepatic cytochrome P450 (CYP) 3A4 activity in patients infected with the human immunodeficiency virus (HIV) using the erythromycin breath test (ERMBT), and to examine the relationship of the ERMBT to plasma concentrations of indinavir and nelfinavir.

DESIGN

Prospective observational study.

SETTING

University infectious diseases clinic.

SUBJECTS

Thirty-nine HIV-positive patients and 47 healthy controls.

INTERVENTION

After the ERMBT in patients and controls, 25 patients received indinavir or nelfinavir.

MEASUREMENTS AND MAIN RESULTS

Compared with controls, ERMBT variability was significantly greater in HIV-positive patients, including a subset of 19 patients receiving no concurrent drugs reported to alter CYP3A4 activity. Correlation between the ERMBT and first-dose plasma indinavir concentrations nearly reached statistical significance (p=0.07).

CONCLUSION

Variability in hepatic activity of CYP3A4 in HIV-positive patients may be greater than in controls and may explain some between-subject variability in plasma concentrations of indinavir. However, clearance mechanisms for protease inhibitors are complex, and if it is important to assess systemic exposure, the ERMBT is not a substitute for direct measurement of plasma concentrations.