Pharmacokinetics and safety of amprenavir and ritonavir following multiple-dose, co-administration to healthy volunteers

Pathophysiology and Clinical Management of Dyslipidemia in People Living with HIV: Sailing through Rough Seas

Infections with human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS) represent one of the greatest health burdens worldwide. The complex pathophysiological pathways that link highly active antiretroviral therapy (HAART) and HIV infection per se with dyslipidemia make the management of lipid disorders and the subsequent increase in cardiovascular risk essential for the treatment of people living with HIV (PLHIV). Amongst HAART regimens, darunavir and atazanavir, tenofovir disoproxil fumarate, nevirapine, rilpivirine, and especially integrase inhibitors have demonstrated the most favorable lipid profile, emerging as sustainable options in HAART substitution. To this day, statins remain the cornerstone pharmacotherapy for dyslipidemia in PLHIV, although important drug-drug interactions with different HAART agents should be taken into account upon treatment initiation. For those intolerant or not meeting therapeutic goals, the addition of ezetimibe, PCSK9, bempedoic acid, fibrates, or fish oils should also be considered. This review summarizes the current literature on the multifactorial etiology and intricate pathophysiology of hyperlipidemia in PLHIV, with an emphasis on the role of different HAART agents, while also providing valuable insights into potential switching strategies and therapeutic options.

Pharmacokinetics, safety and antiviral activity of fosamprenavir/ritonavir-containing regimens in HIV-infected children aged 4 weeks to 2 years-48-week study data

BACKGROUND

Pharmacokinetics, safety and antiviral activity of fosamprenavir (FPV) with ritonavir (RTV) twice daily were evaluated in HIV-1-infected infants and children 4 weeks to <2 years over 48 weeks.

METHODS

Results from intensive pharmacokinetic sampling of subjects enrolled in single dose visits was used to determine individualized dosing for the first 6-10 subjects in each of 2 cohorts (4 weeks to <6 months, 6 months to <2 years); steady state pharmacokinetic data were then used to select the dosage regimen for the remaining subjects recruited to the cohort. Intensive pharmacokinetic sampling was performed at week 2 or 8; predose samples were collected every 4-12 weeks thereafter. Safety and plasma HIV-1 RNA were monitored every 4-12 weeks.

RESULTS

Fifty-nine subjects received study medication. FPV 45 mg/kg boosted with RTV 7 to 10 mg/kg BID achieved average plasma amprenavir area under curve(0-τ) values 26% to 28% lower and Cmax similar to historical adult data for FPV/RTV 700/100 mg BID; amprenavir Cτ values were lower in the subjects <6 months of age. At week 48, 35 of 54 (65%) subjects had achieved plasma HIV-1 RNA <400 copies/mL and 33 of 54 (61%) had plasma HIV-1 RNA values <50 copies/mL. The most common adverse events were diarrhea, upper respiratory tract infection, gastroenteritis and otitis media.

CONCLUSIONS

Final FPV/RTV dosing regimens achieved plasma amprenavir exposures comparable with those from regimens approved in adults, with the exception of trough exposures in the <6-month-old infants. The FPV/RTV regimens led to viral suppression in 61% of patients and were generally well tolerated.

Population pharmacokinetic modeling and simulation of amprenavir following fosamprenavir/ritonavir administration for dose optimization in HIV infected pediatric patients

Fosamprenavir (FPV) is the phosphate ester prodrug of the HIV-1 protease inhibitor amprenavir (APV). A pediatric population pharmacokinetic model for APV was developed and simulation was used to identify dosing regimens for pediatric patients receiving FPV in combination with ritonavir (RTV) which resulted in concentrations similar to those in adults receiving FPV/RTV 700/100 mg BID. Pharmacokinetic data was obtained from HIV infected subjects aged 2 months to 18 years receiving either FPV or FPV/RTV. A two-compartment model with first order absorption and elimination was an appropriate structural model. Significant covariates in the model included RTV coadministration on clearance, fed status on bioavailability for the oral suspension, body weight on clearance and volume terms, black race on clearance, and age on clearance. The following FPV/RTV twice daily dosing regimens in pediatric patients delivered plasma APV exposure similar to adults: 45/7 mg/kg in patients weighing <11 kg, 30/3 mg/kg in patients weighing 11 to <15 kg, 23/3 mg/kg in patients weighing 15 to <20 kg, and 18/3 mg/kg in patients weighting ≥20 kg. Additionally children weighing ≥39 kg can receive the adult regimen.

NIMROD: a program for inference via a normal approximation of the posterior in models with random effects based on ordinary differential equations

Models based on ordinary differential equations (ODE) are widespread tools for describing dynamical systems. In biomedical sciences, data from each subject can be sparse making difficult to precisely estimate individual parameters by standard non-linear regression but information can often be gained from between-subjects variability. This makes natural the use of mixed-effects models to estimate population parameters. Although the maximum likelihood approach is a valuable option, identifiability issues favour Bayesian approaches which can incorporate prior knowledge in a flexible way. However, the combination of difficulties coming from the ODE system and from the presence of random effects raises a major numerical challenge. Computations can be simplified by making a normal approximation of the posterior to find the maximum of the posterior distribution (MAP). Here we present the NIMROD program (normal approximation inference in models with random effects based on ordinary differential equations) devoted to the MAP estimation in ODE models. We describe the specific implemented features such as convergence criteria and an approximation of the leave-one-out cross-validation to assess the model quality of fit. In pharmacokinetics models, first, we evaluate the properties of this algorithm and compare it with FOCE and MCMC algorithms in simulations. Then, we illustrate NIMROD use on Amprenavir pharmacokinetics data from the PUZZLE clinical trial in HIV infected patients.

Intestinal first-pass metabolism by cytochrome p450 and not p-glycoprotein is the major barrier to amprenavir absorption

Recent studies showed that P-glycoprotein (P-gp) increases the portal bioavailability (FG) of loperamide by sparing its intestinal first-pass metabolism. Loperamide is a drug whose oral absorption is strongly attenuated by intestinal P-gp-mediated efflux and first-pass metabolism by cytochrome P450 3A (CYP3A). Here the effect of the interplay of P-gp and Cyp3a in modulating intestinal first-pass metabolism and absorption was investigated for another Cyp3a/P-gp dual substrate amprenavir, which is less efficiently effluxed by P-gp than loperamide. After oral administration of amprenavir, the portal concentrations and FG of amprenavir were approximately equal in P-gp competent and P-gp deficient mice. Mechanistic studies on the effect of P-gp on Cyp3a-mediated metabolism of amprenavir using intestinal tissue from P-gp competent and P-gp deficient mice (Ussing-type diffusion chamber) revealed that P-gp-mediated efflux caused only a slight reduction of oxidative metabolism of amprenavir. Studies in which portal concentrations and FG were measured in P-gp competent and P-gp deficient mice whose cytochrome P450 (P450) enzymes were either intact or inactivated showed that intestinal first-pass metabolism attenuates the oral absorption of amprenavir by approximately 10-fold, whereas P-gp efflux has a relatively small effect (approximately 2-fold) in attenuating the intestinal absorption. Cumulatively, these studies demonstrate that P-gp has little influence on the intestinal first-pass metabolism and FG of amprenavir and that intestinal P450-mediated metabolism plays the dominant role in attenuating the oral absorption of this drug.

Clinical outcomes and management of mechanism-based inhibition of cytochrome P450 3A4

Mechanism-based inhibition of cytochrome P450 (CYP) 3A4 is characterized by NADPH-, time-, and concentration-dependent enzyme inactivation, occurring when some drugs are converted by CYPs to reactive metabolites. Such inhibition of CYP3A4 can be due to the chemical modification of the heme, the protein, or both as a result of covalent binding of modified heme to the protein. The inactivation of CYP3A4 by drugs has important clinical significance as it metabolizes approximately 60% of therapeutic drugs, and its inhibition frequently causes unfavorable drug–drug interactions and toxicity. The clinical outcomes due to CYP3A4 inactivation depend on many factors associated with the enzyme, drugs, and patients. Clinical professionals should adopt proper approaches when using drugs that are mechanism-based CYP3A4 inhibitors. These include early identification of drugs behaving as CYP3A4 inactivators, rational use of such drugs (eg, safe drug combination regimen, dose adjustment, or discontinuation of therapy when toxic drug interactions occur), therapeutic drug monitoring, and predicting the risks for potential drug–drug interactions. A good understanding of CYP3A4 inactivation and proper clinical management are needed by clinical professionals when these drugs are used.

GS-8374, a novel HIV protease inhibitor, does not alter glucose homeostasis in cultured adipocytes or in a healthy-rodent model system

Adverse effects induced by HIV protease inhibitors (PIs) are a significant factor in limiting their clinical success. PIs directly contribute to peripheral insulin resistance and alterations in lipid metabolism. GS-8374 is a novel PI with potent antiretroviral activity and a favorable resistance profile. Here we report on the potential of GS-8374 to adversely affect glucose and lipid homeostasis. Acute effects of GS-8374 and control PIs on glucose uptake and lipid accumulation were assessed in vitro in mouse OP9 and primary human adipocytes, respectively. GS-8374 and atazanavir showed no effect on insulin-stimulated deoxyglucose uptake, whereas ritonavir and lopinavir caused significant reductions. Similarly, in vitro lipid accumulation was not significantly affected in adipocytes treated with either GS-8374 or atazanavir. In euglycemic-hyperinsulinemic clamp experiments performed in rats during acute infusion of therapeutic levels of PIs, sustained serum GS-8374 levels of 8 μM had no effect on peripheral glucose disposal (similar to the findings for atazanavir). Comparable serum levels of lopinavir and ritonavir produced acute 19% and 53% reductions in in vivo glucose disposal, respectively. In conclusion, similar to atazanavir, but unlike ritonavir and lopinavir, GS-8374 neither affects insulin-stimulated glucose uptake in adipocytes in culture nor acutely alters peripheral glucose disposal in a rodent model system. These results dissociate the antiretroviral activity of GS-8374 from adverse effects on insulin sensitivity observed with some of the first-generation PIs and provide further support for the use of these experimental systems in the preclinical evaluation of novel PIs.

How much ritonavir is needed to boost protease inhibitors? Systematic review of 17 dose-ranging pharmacokinetic trials

BACKGROUND

Ritonavir has been evaluated at boosting doses of 50–800 mg daily with seven protease inhibitors: amprenavir, atazanavir, darunavir, indinavir, lopinavir,saquinavir and tipranavir. Minimizing the boosting dose of ritonavir could improve tolerability and lower costs.

METHODS

A MEDLINE search identified 17 phamacokinetic trials using different ritonavir doses with protease inhibitors. The dose of ritonavir used was correlated with plasma levels of each boosted protease inhibitor. For the five pharmacokinetic trials of lopinavir/ritonavir, a meta-analysis was used to estimate the effects of lopinavir dose versus ritonavir dose on lopinavir pharmacokinetics.

RESULTS

Saquinavir, fosamprenavir and darunavir were boosted equally well by lower(50–100 mg) versus higher doses of ritonavir. Indinavir, tipranavir and lopinavir were boosted more by higher ritonavir doses. Data on atazanavir were inconclusive. The ritonavir dose-dependence of boosting effects did not correlate with their bioavailability or their effects on ritonavir plasma levels. Atazanavir and indinavir raised plasma ritonavir levels by 69–72%, whereas saquinavir had no effects on ritonavir. Darunavir,lopinavir, tipranavir and fosamprenavir all lowered ritonavir plasma levels. For the meta-analysis of lopinavir/ritonavir trials, the 200/150 mg twice daily (b.i.d.) dose of lopinavir/ritonavir (one Meltrex 200/50mg tablet and one ritonavir 100mg b.i.d.)showed lopinavir area under the curve and minimum concentration similar to the standard 400/100mg b.i.d. dose.

CONCLUSION

It may be possible to use three protease inhibitors (saquinavir, amprenavir and darunavir) with lower doses of ritonavir. A 200/150 mg b.i.d. dose of lopinavir/ritonavir could lower costs while maintaining very similar lopinavir plasma levels to the standard dose. New pharmaco enhancer drugs may need to be used at different doses to boost different antiretrovirals.

Drug/Drug interaction between lopinavir/ritonavir and rosuvastatin in healthy volunteers

OBJECTIVES

This open-label, single-arm, pharmacokinetic (PK) study in HIV-seronegative volunteers evaluated the bioequivalence of rosuvastatin and lopinavir/ritonavir when administered alone and in combination. Tolerability and lipid changes were also assessed.

METHODS

Subjects took 20 mg of rosuvastatin alone for 7 days, then lopinavir/ritonavir alone for 10 days, and then the combination for 7 days. Intensive PK sampling was performed on days 7, 17, and 24.

RESULTS

Twenty subjects enrolled, and PK data were available for 15 subjects. Geometric mean (+/-SD) rosuvastatin area under the concentration time curve (AUC)[0,tau] and maximum concentration (Cmax) were 47.6 ng.h/mL (+/-15.3) and 4.34 ng/mL (+/-1.8), respectively, when given alone versus 98.8 ng.h/mL (+/-65.5) and 20.2 ng/mL (+/-16.9) when combined with lopinavir/ritonavir (P < 0.0001). The geometric mean ratio was 2.1 (90% confidence interval [CI]: 1.7 to 2.6) for rosuvastatin AUC[0,tau] and 4.7 (90% CI: 3.4 to 6.4) for rosuvastatin Cmax with lopinavir/ritonavir versus rosuvastatin alone (P < 0.0001). There was 1 asymptomatic creatine phosphokinase elevation 17 times the upper limit of normal (ULN) and 1 liver function test elevation between 1.1 and 2.5 times the ULN with the combination.

CONCLUSIONS

Rosuvastatin low-density lipoprotein reduction was attenuated with lopinavir/ritonavir. Rosuvastatin AUC and Cmax were unexpectedly increased 2.1- and 4.7-fold in combination with lopinavir/ritonavir. Rosuvastatin and lopinavir/ritonavir should be used with caution until the safety, efficacy, and appropriate dosing of this combination have been demonstrated in larger populations.

Effects of ritonavir and amprenavir on insulin sensitivity in healthy volunteers

BACKGROUND

Some HIV protease inhibitors (PIs) have been shown to induce insulin resistance in vitro but the degree to which specific PIs affect insulin sensitivity in humans is less well understood.

METHODS

In two separate double-blind, randomized, cross-over studies, we assessed the effects of a single dose of ritonavir (800 mg) and amprenavir (1200 mg) on insulin sensitivity (euglycemic hyperglycemic clamp) in healthy normal volunteers.

RESULTS

Ritonavir decreased insulin sensitivity (-15%; P = 0.008 versus placebo) and non-oxidative glucose disposal (-30%; P = 0.0004), whereas neither were affected by amprenavir administration.

CONCLUSION

Compared to previously performed studies of identical design using single doses of indinavir and lopinavir/ritonavir, a hierarchy of insulin resistance was observed with the greatest effect seen with indinavir followed by ritonavir and lopinavir/ritonavir, with little effect of amprenavir.

Induction of P-glycoprotein expression and activity by ritonavir in bovine brain microvessel endothelial cells

Extended treatment with human immunodeficiency virus (HIV) protease inhibitors (HPIs) is standard in HIV/AIDS therapy. While these drugs have helped decrease the overall incidence of AIDS defining illnesses, the relative prevalence of HIV/AIDS dementia has increased. HPIs may cause induction of blood-brain barrier (BBB) drug transporters (P-glycoprotein; P-gp) and thereby limit entry of HPIs into brain tissue, increasing the probability that the brain could become an HIV sanctuary site. Using bovine brain microvessel endothelial cells (BMEC) as an in-vitro model of the BBB, the potential for the HIV protease inhibitor ritonavir to cause induction of P-gp activity and expression was examined. BMEC were isolated from fresh cow brain by enzymatic digest and density centrifugation. Primary culture BMEC were co-incubated with ritonavir or vehicle control for 120 h. Quantitative drug accumulation of rhodamine 123 (Rh123) and fluorescence microscopy were used as measures of P-gp activity. P-gp expression was assessed using quantitative Western blotting. Ritonavir decreased Rh123 cell accumulation and increased P-gp immunoreactive protein in a concentration-dependent manner. Fluorescent microscopy mirrored Rh123 quantitative studies. In BMEC pretreated with 30 microM ritonavir, Rh123 accumulation was decreased 40% and immunoreactive P-gp protein increased 2-fold. Collectively, a strong correlation between decreased Rh123 BMEC accumulation and increased P-gp immunoreactive protein was observed (Spearman r2 = 0.77, P < 0.0001). Thus extended exposure of BMEC to ritonavir caused a concentration-dependent increase in P-gp activity and expression. Similar findings may occur at the clinical level with prolonged HIV protease inhibitor use, giving insight into the central nervous system as an HIV sanctuary site and eventual development of HIV dementia.

Interpretation of genotype and pharmacokinetics for resistance to fosamprenavir-ritonavir-based regimens in antiretroviral-experienced patients

In this study, named the Zephir study (Telzir-pharmacokinetics), 121 antiretroviral-experienced human immunodeficiency virus (HIV) patients failing on highly active antiretroviral therapy (HAART) were included in a prospective cohort and received a fosamprenavir-ritonavir (700 mg/100 mg twice a day)-based regimen. The impact of baseline HIV type 1 (HIV-1) mutations, pharmacokinetic (PK) parameters, and genotype inhibitory quotient (GIQ) on the virological response at week 12 (W12) was assessed. HIV reverse transcriptase and protease were sequenced at W0. The response at W12 was defined as<2.3 log10 HIV-1 RNA copies/ml or a virus load decrease of>or=1 log10 copies/ml. W4 amprenavir PK were determined by high-performance liquid chromatography. Patients had a median of nine previous treatments over 8 years. Median W0 values were as follows: 295 CD4+/microl, 4.4 log10 HIV-1 RNA copies/ml, and 6 protease- and 5 nucleotide reverse transcription inhibitor-related mutations. Respective values for minimum concentration of drug in serum (Cmin) and area under the concentration-time curve (AUC) from 0 to 24 h were 1,400 ng/ml and 35 mg.h/ml. At W12, 52% of the patients were successes, with a median decrease of -0.7 log10 HIV-1 RNA copies/ml. The Zephir mutation score included 12 IAS protease mutations associated with poorer virological response: L10I/F/R/V, L33F, M36I, M46I/L, I54L/M/T/V, I62V, L63P, A71I/L/V/T, G73A/C/F/T, V82A/F/S/T, I84V, L90M, and polymorphism mutations I13V, L19I, K55R, and L89M. Comparing<4 versus>or=4 mutations, HIV-1 RNA decreases were -2.3 log10 copies/ml versus -0.1 log10 copies/ml (P<10(-4)) with 93% versus 19% successes (P<10(-4)), respectively. This score predicted W12 failure with 94% sensitivity, versus 31% for the ANRS 2005 algorithm. Cmin (<1,600 ng/ml), AUC (<40 mg.h/ml), and GIQ (<300) values were associated with failure (all P values were <10(-4)). The need to test genotype-based algorithms using different patient databases before their implementation in clinical practice is highlighted. Specific mutations, PK and GIQ, provide relevant information for monitoring fosamprenavir-ritonavir-based HAART.

Pharmacokinetic and safety evaluation of high-dose combinations of fosamprenavir and ritonavir

High-dose combinations of fosamprenavir (FPV) and ritonavir (RTV) were evaluated in healthy adult subjects in order to select doses for further study in multiple protease inhibitor (PI)-experienced patients infected with human immunodeficiency virus type 1. Two high-dose regimens, FPV 1,400 mg twice a day (BID) plus RTV 100 mg BID and FPV 1,400 mg BID plus RTV 200 mg BID, were planned to be compared to the approved regimen, FPV 700 mg BID plus RTV 100 mg BID, in a randomized three-period crossover study. Forty-two healthy adult subjects were enrolled, and 39 subjects completed period 1. Due to marked hepatic transaminase elevations, predominantly with FPV 1,400 mg BID plus RTV 200 mg BID, the study was terminated prematurely. For FPV 1,400 mg BID plus RTV 100 mg BID, the values for plasma amprenavir (APV) area under the concentration-time profile over the dosing interval (tau) at steady state [AUC(0-tau)], maximum concentration of drug in plasma (C(max)), and plasma concentration at the end of tau at steady state (C(tau)) were 54, 81, and 26% higher, respectively, and the values for plasma RTV AUC(0-tau), C(max), and C(tau) were 49% higher, 71% higher, and 11% lower, respectively, than those for FPV 700 mg BID plus RTV 100 mg BID. For FPV 1,400 mg BID plus RTV 200 mg BID, the values for plasma APV AUC(0-tau), C(max), and C(tau) were 26, 48, and 32% higher, respectively, and the values for plasma RTV AUC(0-tau), C(max), and C(tau) increased 4.15-fold, 4.17-fold, and 3.99-fold, respectively, compared to those for FPV 700 mg BID plus RTV 100 mg BID. FPV 1,400 mg BID plus RTV 200 mg BID is not recommended due to an increased rate of marked hepatic transaminase elevations and lack of pharmacokinetic advantage. FPV 1,400 mg BID plus RTV 100 mg BID is currently under clinical evaluation in multiple PI-experienced patients.

Metabolic Abnormalities Associated with the Use of Protease Inhibitors and Non-nucleoside Reverse Transcriptase Inhibitors

The use of protease inhibitors and non-nucleoside reverse transcriptase inhibitors for the treatment of HIV infection and AIDS has been associated with multiple abnormalities in glucose and lipid metabolism. Specifically, these abnormalities include insulin resistance, increased triglycerides and increased LDL cholesterol levels. The metabolic disturbances are due to a combination of factors, including the direct effect of medications, restoration to health and HIV disease, as well as individual genetic predisposition. Of the available anti-retroviral medications, indinavir has been associated with causing the most insulin resistance and ritonavir with causing the most hypertriglyceridemia.

What a Cardiologist Needs to Know About Patients With Human Immunodeficiency Virus Infection

Patient case: A 48-year-old man with human immunodeficiency virus (HIV) infection developed chronic chest pain that started after a bout of pneumonia. He has hypertension and has smoked cigarettes in the past. His current medications include Kaletra and Combivir. His total cholesterol was 331 mg/L, his HDL cholesterol was 27 mg/L, his triglycerides were 935 mg/L, and his LDL cholesterol could not be calculated. How should this patient be evaluated and managed?

Amprenavir and efavirenz pharmacokinetics before and after the addition of nelfinavir, indinavir, ritonavir, or saquinavir in seronegative individuals

Adult AIDS Clinical Trials Group 5043 examined pharmacokinetic (PK) interactions between amprenavir (APV) and efavirenz (EFV) both by themselves and when nelfinavir (NFV), indinavir (IDV), ritonavir (RTV), or saquinavir (SQV) is added. A PK study was conducted after the administration of single doses of APV (day 0). Subjects (n = 56) received 600 mg of EFV every 24 h (q24h) for 10 days and restarted APV with EFV for days 11 to 13 with a PK study on day 14. A second protease inhibitor (PI) (NFV, 1,250 mg, q12h; IDV, 1,200 mg, q12h; RTV, 100 mg, q12h; or SQV, 1,600 mg, q12h) was added to APV and EFV on day 15, and a PK study was conducted on day 21. Controls continued APV and EFV without a second PI. Among subjects, the APV areas under the curve (AUCs) on days 0, 14, and 21 were compared using the Wilcoxon signed-rank test. Ninety-percent confidence intervals around the geometric mean ratios (GMR) were calculated. APV AUCs were 46% to 61% lower (median percentage of AUC) with EFV (day 14 versus day 0; P values of <0.05). In the NFV, IDV, and RTV groups, day 21 APV AUCs with EFV were higher than AUCs for EFV alone. Ninety-percent confidence intervals around the GMR were 3.5 to 5.3 for NFV (P < 0.001), 2.8 to 4.5 for IDV (P < 0.001), and 7.8 to 11.5 for RTV (P = 0.004). Saquinavir modestly increased the APV AUCs (GMR, 1.0 to 1.4; P = 0.106). Control group AUCs were lower on day 21 compared to those on day 14 (GMR, 0.7 to 1.0; P = 0.042). African-American non-Hispanics had higher day 14 efavirenz AUCs than white non-Hispanics. We conclude that EFV lowered APV AUCs, but nelfinavir, indinavir, or ritonavir compensated for EFV induction.

Therapeutic Drug Monitoring: Role for a Pharmacist in Multidisciplinary Antiretroviral Management

The current treatment guidelines for HIV pharmacotherapy recommend combinations of antiretrovirals (ARVs) to achieve optimal suppression of HIV replication. However, the initiation and long-term management of ARV therapy in a patient is often complicated by variable medication adherence, complex medication use with multiple drug interactions, the occurrence of drug toxicity, and drug therapy for comorbid conditions that require additional patient education and laboratory monitoring. For these reasons, the inclusion of a well-trained pharmacist in multidisciplinary health system management strategies has been increasing. Furthermore, the use of fixed-dose ARVs is accompanied by considerable interpatient variation in pharmacokinetics yielding a range of drug exposures from any given ARV dose. One approach to overcoming this variable drug exposure is to use plasma concentration monitoring (eg, therapeutic drug monitoring [TDM]) as a clinical tool to adjust doses to achieve targeted concentration ranges, often in conjunction with HIV resistance tests. While data in support of TDM are emerging, the development of programs that include an HIV pharmaceutical care specialist and an adherence program with an integrated clinical pharmacology resource that can provide reliable TDM assays has been reported and provides the rationale for including pharmacists in the implementation of ARV TDM programs.

Mechanism-based inhibition of cytochrome P450 3A4 by therapeutic drugs

Consistent with its highest abundance in humans, cytochrome P450 (CYP) 3A is responsible for the metabolism of about 60% of currently known drugs. However, this unusual low substrate specificity also makes CYP3A4 susceptible to reversible or irreversible inhibition by a variety of drugs. Mechanism-based inhibition of CYP3A4 is characterised by nicotinamide adenine dinucleotide phosphate hydrogen (NADPH)-, time- and concentration-dependent enzyme inactivation, occurring when some drugs are converted by CYP isoenzymes to reactive metabolites capable of irreversibly binding covalently to CYP3A4. Approaches using in vitro, in silico and in vivo models can be used to study CYP3A4 inactivation by drugs. Human liver microsomes are always used to estimate inactivation kinetic parameters including the concentration required for half-maximal inactivation (K(I)) and the maximal rate of inactivation at saturation (k(inact)). Clinically important mechanism-based CYP3A4 inhibitors include antibacterials (e.g. clarithromycin, erythromycin and isoniazid), anticancer agents (e.g. tamoxifen and irinotecan), anti-HIV agents (e.g. ritonavir and delavirdine), antihypertensives (e.g. dihydralazine, verapamil and diltiazem), sex steroids and their receptor modulators (e.g. gestodene and raloxifene), and several herbal constituents (e.g. bergamottin and glabridin). Drugs inactivating CYP3A4 often possess several common moieties such as a tertiary amine function, furan ring, and acetylene function. It appears that the chemical properties of a drug critical to CYP3A4 inactivation include formation of reactive metabolites by CYP isoenzymes, preponderance of CYP inducers and P-glycoprotein (P-gp) substrate, and occurrence of clinically significant pharmacokinetic interactions with coadministered drugs. Compared with reversible inhibition of CYP3A4, mechanism-based inhibition of CYP3A4 more frequently cause pharmacokinetic-pharmacodynamic drug-drug interactions, as the inactivated CYP3A4 has to be replaced by newly synthesised CYP3A4 protein. The resultant drug interactions may lead to adverse drug effects, including some fatal events. For example, when aforementioned CYP3A4 inhibitors are coadministered with terfenadine, cisapride or astemizole (all CYP3A4 substrates), torsades de pointes (a life-threatening ventricular arrhythmia associated with QT prolongation) may occur.However, predicting drug-drug interactions involving CYP3A4 inactivation is difficult, since the clinical outcomes depend on a number of factors that are associated with drugs and patients. The apparent pharmacokinetic effect of a mechanism-based inhibitor of CYP3A4 would be a function of its K(I), k(inact) and partition ratio and the zero-order synthesis rate of new or replacement enzyme. The inactivators for CYP3A4 can be inducers and P-gp substrates/inhibitors, confounding in vitro-in vivo extrapolation. The clinical significance of CYP3A inhibition for drug safety and efficacy warrants closer understanding of the mechanisms for each inhibitor. Furthermore, such inactivation may be exploited for therapeutic gain in certain circumstances.

Protease inhibitor-based HAART, HDL, and CHD-risk in HIV-infected patients

OBJECTIVE

To study the effects of HIV-infection and protease inhibitor (PI)-based highly active anti-retroviral therapy (HAART) on the lipid and high-density lipoprotein (HDL) subpopulation profile and to relate the changes to coronary heart disease (CHD)-risk.

METHODS AND DESIGN

The lipid and HDL subpopulation profiles of HIV-positive subjects (n = 48) were studied prospectively by comparing pre- and post-PI-HAART data as well as cross-section by comparing the profiles to HIV-negative subjects with (n = 96) and without CHD (n = 96).

RESULTS

HIV-infected HAART-naïve subjects had lower concentrations of low-density lipoprotein cholesterol (LDL-C) and HDL-C and higher concentration of triglycerides (TG) than healthy controls. After receiving PI-based HAART, LDL-C and TG concentrations increased, while HDL-C concentrations remained unchanged. The HDL subpopulation profiles of HAART-naïve HIV-positive patients were significantly different from those of healthy controls and were similar to those with CHD. Moreover, the HDL subpopulation profile changed unfavorably after PI-based HAART, marked with increased concentrations of the small, lipid-poor pre-beta-1 HDL (32% or 3.9 mg/dl; p < 0.001), and decreased concentration of the large, cholesterol-rich alpha-1 HDL (9% or 1 mg/dl ns).

CONCLUSION

An already unfavorable lipid and HDL subpopulation profile of HIV-positive HAART-naïve subjects further deteriorated after receiving PI-based treatment, which may cause increased CHD-risk in these subjects.

Drug interactions in the management of HIV infection

The availability of antiretroviral therapy has significantly reduced the morbidity and mortality of HIV infection. In addition, improved treatment of opportunistic infections and comorbidities common to patients with HIV is further prolonging the lives of patients. Improvement in the treatment of HIV has led to a significant increase in the number of medications which caregivers are able to utilise to manage HIV/AIDS. Antiretroviral medications, as well as many of the drugs used in the management of opportunistic infections and primary care (e.g., macrolide antibiotics, azole antifungals, cholesterol-lowering medications), are particularly prone to drug interactions. The interpretation of clinically significant interactions is complicated by the rate at which new information on drug metabolism and transport is becoming available. Management of drug interactions in HIV is further confounded by conflicting study results and differences between documented and theoretical inter-actions. The mechanisms and significance of interactions involving antiretrovirals, drugs used for opportunistic infections, and other medications commonly used in HIV patients will be reviewed.

Boosted saquinavir hard gel formulation exposure in HIV-infected subjects: ritonavir 100 mg once daily versus twice daily

OBJECTIVES

The amount of ritonavir needed to enhance saquinavir hard gel (hg) plasma concentrations is unclear. Reduced ritonavir dosing may help to reduce ritonavir-related side effects and costs. This study examined the pharmacokinetics of twice-daily saquinavir-hg (1000 mg) in the presence of ritonavir 100 mg, dosed twice-daily and once-daily on one single occasion.

METHODS

Eighteen HIV-infected adults taking saquinavir/ritonavir 1000/100 mg twice-daily underwent pharmacokinetic (PK) assessment of saquinavir/ritonavir on day 1 following a morning saquinavir/ritonavir dose. On day 2, PK assessment was repeated when subjects took saquinavir without ritonavir. Drug intake (with a standard meal containing 20 g of fat) was timed on days -1, 1 and 2. Geometric mean ratios (GMR) and 95% confidence intervals (CI) were calculated to assess changes in saquinavir PK parameters.

RESULTS

Geometric mean saquinavir AUC(0-12), C(trough), C(max) and elimination half-life on days 1 and 2 were 14 389 and 9590 ng.h/mL, 331 and 234 ng/mL, 2503 and 1893 ng/mL and 2.80 and 2.82 h, respectively. The GMR (95% CI) for these parameters were 0.67 (0.53-0.84), 0.71 (0.48-1.04), 0.76 (0.58-0.98) and 1.01 (0.86-1.18), respectively.

CONCLUSIONS

Withholding a ritonavir dose significantly reduces overall saquinavir exposure and C(max), but had no impact on the elimination half-life. These data establish the need to administer saquinavir and ritonavir simultaneously.

The effects of HIV protease inhibitors on carbohydrate and lipid metabolism

Since the introduction of HIV protease inhibitors (PIs), disorders of glucose and lipid metabolism have emerged. In dissecting out the direct effect on lipid and glucose metabolism, it has become apparent that individual PIs have different effects on metabolism. Some PIs such as indinavir acutely induce insulin resistance. PIs have also been shown to cause other disorders of glucose metabolism, including impairment of insulin secretion and increased endogenous glucose production. Individual PIs also have different effects on lipid metabolism. Ritonavir predominantly increases triglyceride and very low-density lipoprotein cholesterol levels. Limited studies in HIV-negative volunteers suggest that several of the PIs do not increase low-density lipoprotein cholesterol levels. This review examines the direct effects of PIs on glucose and lipid metabolism by assessing prospective studies of HIV-infected and healthy normal volunteers, and in vitro studies.

Resistance profiles observed in virological failures after 24 weeks of amprenavir/ritonavir containing regimen in protease inhibitor experienced patients

Amprenavir (APV) is an HIV protease inhibitor (PI) used for the treatment of either naive or PI-experienced HIV-infected patients. Several genotypic resistance pathways in protease gene have been described to be associated to unboosted APV failure (I50V, V32I + I47V, I54L/M, or less commonly I84V, which may be accompanied by one ore more accessory mutations such as L10F, L33F, M46I/L). The aims of this study were to investigate the efficacy up to week 24 of an APV plus ritonavir containing regimen in PI experienced patients and to determine the genotypic resistance profiles emerging in patients failing to this therapy. Forty-nine, PI experienced but APV naïve patients were treated with APV (600 mg bid) plus ritonavir (100 mg bid). By intent-to-treat analysis, the median decrease in viral load (VL) was -1.32 log10 (min +0.6; max -2.8) and -1.46 log10 (min +0.5; max -2.8) 12 and 24 weeks after initiating APV plus ritonavir regimen, respectively. Twelve patients harboured a VL >200 copies/ml at week 24. Among these patients, the selection of mutations previously described with the use of APV as first PI (V32I, L33F, M46I/L, I50V, 54M/L, and I84V) was observed. However, in some cases, mutations classically described after the use of other PIs (V82F and L90M) were selected but always with APV-specific mutations. There was no relation between the resistance pathways selected with either APV or ritonavir plasma minimal concentration, but higher APV plasma minimal concentration were associated with a lower rate of resistance mutations selection.

Steady-State Pharmacokinetics of Saquinavir Hard-Gel/Ritonavir/Fosamprenavir in HIV-1???Infected Patients

BACKGROUND

In vitro synergy and complementary resistance profiles provide a strong rationale for combining fosamprenavir with saquinavir as part of a potent double-boosted protease inhibitor regimen. This study evaluated the steady-state pharmacokinetics of saquinavir 1000 mg twice daily (bid) and fosamprenavir 700 mg bid administered with 2 different doses of ritonavir (100 and 200 mg bid) in HIV-1-infected subjects.

METHODS

On day 1, 12-hour pharmacokinetic profiles for saquinavir/ritonavir (1000/100 mg bid) were obtained for 18 subjects. All subjects were receiving ongoing treatment with a saquinavir/ritonavir-containing regimen. Fosamprenavir 700 mg bid was then added to the regimen, and pharmacokinetic sampling was repeated for all 3 agents at day 11. The ritonavir daily dose was then increased to 200 mg bid, and a 3rd pharmacokinetic profile was obtained at day 22.

RESULTS

The coadministration of fosamprenavir 700 mg bid with saquinavir/ritonavir 1000/100 mg bid resulted in a statistically nonsignificant decrease in saquinavir concentrations (by 14, 9, and 24%, for saquinavir area under the concentration-time curve [AUC]0-12, C(max), and C(trough), respectively). This was compensated for by an increased ritonavir dose of 200 mg bid, which resulted in a statistically nonsignificant increase in saquinavir exposure compared with baseline. Amprenavir levels did not appear to be significantly influenced by coadministration of saquinavir with fosamprenavir. Fosamprenavir significantly reduced ritonavir exposure, but the increased ritonavir dose compensated for this interaction.

CONCLUSIONS

Our findings showed that saquinavir/ritonavir/fosamprenavir was well tolerated over the study period. Saquinavir plasma concentrations were slightly lowered by the addition of fosamprenavir to the regimen. However, the addition of a further 100 mg ritonavir bid restored the small and insignificant decrease.

The effects of HIV protease inhibitors on carbohydrate and lipid metabolism

Since the introduction of HIV protease inhibitors (PIs), disorders of glucose and lipid metabolism have emerged. In dissecting out the direct effect on lipid and glucose metabolism, it has become apparent that individual PIs have different effects on metabolism. Some PIs such as indinavir acutely induce insulin resistance. PIs have also been shown to cause other disorders of glucose metabolism, including impairment of insulin secretion and increased endogenous glucose production. Individual PIs also have different effects on lipid metabolism. Ritonavir predominantly increases triglyceride and very low-density lipoprotein cholesterol levels. Limited studies in HIV-negative volunteers suggest that several of the PIs do not increase low-density lipoprotein cholesterol levels. This review examines the direct effects of PIs on glucose and lipid metabolism by assessing prospective studies of HIV-infected and healthy normal volunteers, and in vitro studies.

SOLO: 48-week efficacy and safety comparison of once-daily fosamprenavir /ritonavir versus twice-daily nelfinavir in naive HIV-1-infected patients

OBJECTIVE

To compare the magnitude and durability of the antiviral response to fosamprenavir (FPV) plus ritonavir (RTV) once-daily (FPV/r QD) with nelfinavir twice-daily (NFV BID), each administered with abacavir and lamivudine twice-daily.

METHODS

An international, phase III, randomized, open-label study in antiretroviral therapy-naive, HIV-infected adults.

RESULTS

Patients with advanced HIV disease received FPV/r QD (n = 322) or NFV BID (n = 327). At week 48, 69% of patients in the FPV/r QD group and 68% in the NFV BID group had plasma HIV-1 RNA (vRNA) < 400 copies/ml, whereas 55% of patients in the FPV/r QD group and 53% in the NFV BID group had vRNA < 50 copies/ml (intent to treat, rebound/discontinuation = failure). More patients in the NFV BID group (17%) experienced virological failure than in the FPV/r QD group (7%). Efficacy of FPV/r QD was maintained in patients with CD4+ cell counts < 50 x 10 cells/l or vRNA >/= 100 000 copies/ml at entry. At week 48, median CD4+ cell counts were increased to 203 x 10 cells/l (FPV/r QD group) and 207 x 10 cells/l (NFV BID group). Both regimens were generally well tolerated. Diarrhea was more common on NFV BID than on FPV/r QD (16 versus 9%; P = 0.008). Fasting lipid profile results were generally favorable in both treatment arms. FPV/r QD maintained plasma amprenavir (APV) trough concentrations above the mean phenotypic drug-susceptibility (IC50) for wild-type virus for APV.

CONCLUSION

As a first choice protease inhibitor with a low daily pill burden, FPV/r QD was well tolerated and provided potent, durable antiviral suppression.

In vitro-in vivo model for evaluating the antiviral activity of amprenavir in combination with ritonavir administered at 600 and 100 milligrams, respectively, every 12 hours

The study objective was to evaluate the pharmacodynamics of amprenavir in an in vitro system, develop an exposure target for maximal viral suppression, and determine the likelihood of target attainment based on the pharmacokinetics of amprenavir and ritonavir in human immunodeficiency virus (HIV)-infected patients. Population pharmacokinetic data were obtained from 13 HIV-infected patients receiving amprenavir and ritonavir in doses of 600 and 100 mg, respectively, every 12 h. A 2,500-subject Monte Carlo simulation was performed. Target attainment was also estimated for a target derived from clinical data. Maximal viral suppression (in vitro) was achieved when amprenavir free-drug concentrations remained greater than four times the 50% effective concentration (EC(50)) for 80% of the dosing interval. At an amprenavir EC(50) of 0.03 microM, the likelihood of target attainment is 97.4%. For reduced-susceptibility isolates for which the EC(50)s are 0.05 and 0.08 microM, target attainment is 91.0 and 75.8%, respectively. For the clinical target of a trough concentration/EC(50) ratio of 5, the target attainment rates were similar. Treatment with amprenavir and ritonavir at doses of 600 and 100 mg, respectively, twice a day provides excellent suppression of wild-type isolates and reduced-susceptibility isolates up to an EC(50) of 0.05 micro M. Even at 0.12 microM, target attainment likelihood exceeds 50%, making this an option for patients with extensive exposure to protease inhibitors when this treatment is used with additional active antiretroviral agents.

Efficacy, safety and predictive factors of virological success of a boosted amprenavir-based salvage regimen in heavily antiretroviral-experienced HIV-1-infected patients

BACKGROUND

Amprenavir (APV) has been shown to be effective in naive or treatment-experienced HIV-1 infected patients. However, the safety and efficacy of the APV 600 mg/ritonavir (RTV) 100 mg twice a day (bid) combination, the usually recommended dosage for boosted APV, have been less well studied. We assessed the predictive factors associated with virological success of APV/RTV-based regimens.

METHODS

Patients in the PharmAdapt study receiving an APV/RTV-containing regimen were included in the study. The predictivity of covariates on virological response at 4 months was analysed according to the data analysis plan. We processed logistic regression using bootstrapping to allow several covariates in the models.

RESULTS

Forty patients received an APV/RTV-containing regimen, 38 of whom were male (95%). Risk factors were heterosexual contacts (four patients; 10%), homosexual contacts (31 patients; 78%), and intravenous drug use (four patients; 10%). Twenty-seven per cent of patients were Centers for Disease Control and Prevention Classification System (CDC) stage A, 38% were stage B and 35% were stage C. The median baseline CD4 count was 313 cells/microL [interquartile range (IQR) 211, 414], and the median baseline viral load was 4.4 log(10) HIV-1 RNA copies/mL (IQR 3.7, 4.9). Patients were exposed to a median number of 7.5 (IQR 6, 9) drugs for a median number of 3.8 (IQR 3.3, 4.3) years. The baseline number of resistance mutations was 4 [IQR 3, 5 for nucleoside reverse transcriptase inhibitors (NRTIs), 1 (IQR 0, 2)] for non-nucleoside reverse transcriptase inhibitors (NNRTIs) and 6 [IQR 5, 8 for protease inhibitors (PIs)]. At month 4, median viral load decreased to 1.2 log(10) copies/mL (IQR 0.3, 1.6); 50% of patients had a viral load<200 copies/mL by intention-to-treat analysis. The number of APV resistance mutations was associated with viral load changes. Median APV concentration was 1750 ng/mL (IQR 1130, 2520). At month 4, using several cut-offs, neither APV concentration nor the genotypic inhibitory quotient was predictive of viral load changes. Baseline viral load and the number of protease mutations were associated with outcome.

CONCLUSIONS

Efficacious APV concentrations need to be determined for antiretroviral-experienced patients. Baseline viral load and the number of mutations on the protease coding region (PRO) were associated with the virological outcome of APV/RTV-based regimens.

Drug interactions with antiretrovirals

The recent development of new antiretroviral drugs, along with the evolution in clinical practice guidelines that include the recommendation of the use of three- to four-drug combination regimens for achieving optimal suppression of viral replication, has focused clinicians on the relevance of drug-drug interactions in the chronic care of HIV-infected individuals. However, the routine clinical management of drug interactions is complicated by our expanding knowledge of the physiologic mechanisms underlying pharmacokinetic interactions, particularly as they relate to drug transport and tissue distribution (eg, P-glycoprotein) and biotransformation (hepatic cytochrome p450 mono-oxygenase induction and inhibition). This review provides an updated summary of key drug interactions that have been reported since its initial publication.

Salvage Therapy with Amprenavir, Lopinavir and Ritonavir 200 Mg/D or 400 Mg/D in HIV-Infected Patients in Virological Failure

Objectives

To compare the antiviral efficacy of a salvage therapy combining lopinavir and amprenavir with 200 mg/d or 400 mg/d ritonavir, together with nucleoside reverse transcriptase inhibitors, over a 26-week period in HIV-infected patients in whom multiple anti-retroviral regimens had failed.

Design

Phase IIb, randomized, open-label, multicentre trial. Patients were eligible if they had <500 CD4+ cells/mm3 and >4 log10 copies/ml HIV-RNA after treatment with at least two protease inhibitors (PIs) and one non-nucleoside reverse transcriptase inhibitor.

Results

At baseline ( n=37), the median CD4+ cell count was 207/mm3 and the median plasma HIV-1 RNA level was 4.7 log10 copies/ml; the median number of PI mutations was seven and the median decrease in phenotypic susceptibility to lopinavir and amprenavir was 9.7 and 2.6, respectively. The mean number of antiretrovirals received prior to randomization was 7.7. The fall in the median HIV-1 RNA level at week 26 was -1.4 log10 copies/ml in the 200 mg/d ritonavir group and -2.5 log10 copies/ml in the 400 mg/d group ( P=0.02). Viral load fell below 50 copies/ml in 32% and 61% of patients, respectively ( P=0.07). After adjustment for the ritonavir dose, a smaller number of PI mutations was the only baseline characteristic associated with a better virological response at week 26. Amprenavir concentrations were significantly lower in presence of lopinavir. The lopinavir inhibitory quotient at week 6 correlated weakly with the change in the HIV-RNA level at week 26.

Conclusion

Combination of amprenavir, lopinavir and 400 mg/d ritonavir shows significant virological efficacy without increased toxicity in HIV-infected patients in whom multiple antiretroviral regimens have failed.

Deep Salvage With Amprenavir and Lopinavir/Ritonavir

The safety, efficacy, and mutual interactions of combination amprenavir with lopinavir/ritonavir as deep salvage treatment were investigated in a prospective 24-week pilot study. HIV-infected patients (n = 22) with virologic failure to nucleoside reverse transcriptase inhibitors (NRTIs), non-NRTIs, and at least 2 protease inhibitors received 400/100 mg of lopinavir/ritonavir with 600 mg of amprenavir every 12 hours combined with NRTIs. Patients receiving the same doses of lopinavir/ritonavir (n = 10) or amprenavir with ritonavir (n = 8) were chosen as controls for pharmacokinetic analyses. Mean changes from baseline HIV RNA levels and CD4 counts after 24 weeks were -1.13 log10 copies/mL and +88 x 10 cells/L, respectively. The mean plasma trough concentration (Cmin)and peak concentration (Cmax) of amprenavir were 104% and 228% lower and the Cmin of lopinavir was 46% lower in patients in whom the drugs were coadministered than in controls. There were 4 permanent drug discontinuations because of toxicity. An inhibitory quotient (IQ) of amprenavir higher than 0.8 was the best predictor of virologic outcome at 24 weeks, even after adjusting for amprenavir Cmin or phenotypic susceptibility. Deep salvage therapy using lopinavir/ritonavir with amprenavir is sufficiently safe and shows partial efficacy. When these drugs are coadministered, therapeutic drug monitoring should be employed and the IQ can be used to determine target drug levels.

The metabolic effects of lopinavir/ritonavir in HIV-negative men

BACKGROUND

Therapy with HIV protease inhibitors (PI) has been shown to worsen glucose and lipid metabolism, but whether these changes are caused by direct drug effects, changes in disease status, or body composition is unclear. Therefore, we tested the effects of the PI combination lopinavir and ritonavir on glucose and lipid metabolism in HIV-negative subjects.

METHODS

A dose of 400 mg lopinavir/100 mg ritonavir was given twice a day to 10 HIV-negative men. Fasting glucose and insulin, lipid and lipoprotein profiles, oral glucose tolerance, insulin sensitivity by euglycemic hyperinsulinemic clamp, and body composition were determined before and after lopinavir/ritonavir treatment for 4 weeks.

RESULTS

On lopinavir/ritonavir, there was an increase in fasting triglyceride (0.89 +/- 0.15 versus 1.63 +/- 0.36 mmol/l; P = 0.007), free fatty acid (FFA; 0.33 +/- 0.04 versus 0.43 +/- 0.06 mmol/l; P = 0.001), and VLDL cholesterol (15.1 +/- 2.6 versus 20 +/- 3.3 mg/dl; P = 0.05) levels. There were no changes in fasting LDL, HDL, IDL, lipoprotein (a), or total cholesterol levels. Fasting glucose, insulin, and insulin-mediated glucose disposal were unchanged, but on a 2 h oral glucose tolerance test glucose and insulin increased. There were no changes in weight, body fat, or abdominal adipose tissue by computed tomography.

CONCLUSION

Treatment with 4 weeks of lopinavir/ritonavir in HIV-negative men causes an increase in triglyceride levels, VLDL cholesterol, and FFA levels. Lopinavir/ritonavir leads to a deterioration in glucose tolerance at 2 h, but there is no significant change in insulin-mediated glucose disposal rate by euglycemic hyperinsulinemic clamp.

Saquinavir drug exposure is not impaired by the boosted double protease inhibitor combination of lopinavir/ritonavir

OBJECTIVE

To assess the pharmacokinetic interaction of saquinavir and lopinavir/ritonavir.

DESIGN

Patients from the Frankfurt HIV cohort with limited reverse transcriptase inhibitor (RTI) options received the protease inhibitor (PI) combination of saquinavir (soft-gel capsules, 1000 mg twice a day) plus lopinavir/ritonavir (400/100 mg twice a day), without RTI (LOPSAQ group). A control group received the same doses of saquinavir and ritonavir plus two to three RTI (RITSAQ group). A steady-state 12 h pharmacokinetic assessment was performed.

METHODS

Plasma levels of saquinavir, ritonavir and lopinavir were determined by liquid chromatography-tandem mass spectrophotometry. Minimum and maximum plasma concentrations (Cmin and Cmax), the clearance (Cltot) and the area under the concentration time curve (AUC) were calculated.

RESULTS

Data were collected from 45 patients (LOPSAQ) and 32 patients (RITSAQ). There was no significant difference between the groups for median saquinavir Cmin, Cmax, Cltot and AUC (LOPSAQ: 543 ng/ml, 2300 ng/ml, 1020 ml/min and 16 977 ng*h/ml; RITSAQ: 427 ng/ml, 2410 ng/ml, 1105 ml/min and 15 130 ng*h/ml). Median ritonavir Cmin, Cmax and AUC were lower, the Cltot was higher in the LOPSAQ group (78 ng/ml, 428 ng/ml and 2972 ng*h/ml, 551 ml/min) compared with RITSAQ (194 ng/ml, 683 ng/ml and 6506 ng*h/ml, 266 ml/min; P < 0.001). Lopinavir levels were similar to historical data.

CONCLUSION

Effective plasma levels of both saquinavir and lopinavir can be achieved by the co-administration of saquinavir soft-gel capsules and lopinavir/ritonavir. This boosted double PI combination could be an effective option for patients with limited RTI options.

Pharmacodynamics and clinical use of anti-HIV drugs

Antiretroviral drug exposure has been linked to both antiviral efficacy and the development of toxicity and further research in this area is ongoing and necessary. Use of these data may have important implications for TDM of HAART regimens in clinical practice. TDM, in conjunction with an assessment of the patient's viral resistance in the form of an IQ, needs to be examined and validated in large clinical trials.

Impact of drug levels and baseline genotype and phenotype on the virologic response to amprenavir/ritonavir-based salvage regimens

Coadministration of amprenavir (APV) with small doses of ritonavir (RTV) results in a significant increase in APV plasma concentrations. Viruses showing resistance to other protease inhibitors (PI) may remain susceptible to APV, supporting a role for this drug in salvage therapy. We enrolled 35 patients who began a rescue intervention based on APV/RTV 600/100 mg twice daily. Their median viral load before beginning APV/RTV was 4.15 logs and their median CD4 count was 247 cells per microliter. The median prior PI exposure was of 43 months. At baseline, the median number of PI resistance mutations was 7. A significant virologic response (VR) (>1 log drop in plasma HIV-RNA and/or to <50 copies per milliliter) was recorded in 21.7% (5/23) of treated patients at week 48 (14.3% in the intent-to-treat analysis). The VR was significantly more frequent among subjects with less than 5 PI resistance mutations (66.6% vs. 5.8%; p = 0.008). Patients with prior exposure to lopinavir showed VR significantly less frequently than those not exposed to that drug (11% versus 60%; p < 0.05). The mean APV plasma trough concentration at week 12 was 1.3 microg/mL, and did not differ significantly comparing subjects having or not having VR. A trend toward a higher VR rate at week 48 was noticed among subjects with high genotypic inhibitory quotients (GIQ). In summary, HIV genotyping but not drug levels might be helpful to predict which patients would benefit from a rescue intervention based on APV/RTV 600/100 twice daily.

Outcomes of Dual–Protease Inhibitor Salvage Therapy in Human Immunodeficiency Virus–Infected Patients Referred to a Telephone Consultation Service

OBJECTIVE

To determine the clinical outcomes of dual-protease inhibitor salvage therapy in heavily experienced patients after their providers consulted the National HIV Telephone Consultation Service (Warmline, 800-933-3413).

DESIGN

Observational survey study.

SETTING

Consultation service for United States health care providers.

PATIENTS

Thirty-one human immunodeficiency virus (HIV)-infected patients who had received previous treatment with at least two protease inhibitor--or nonnucleoside reverse transcriptase inhibitor--based regimens and had a viral load of at least 1000 copies/ml.

INTERVENTION

Patients whose providers consulted Warmline regarding antiretroviral salvage regimens were identified through a review of telephone calls from January-July 2001. Virologic and immunologic outcomes were determined for patients who had received a regimen containing either ritonavir and indinavir or ritonavir and amprenavir.

MEASUREMENTS AND MAIN RESULTS

Primary outcomes were percentages of patients with a viral load less than 500 copies/ml at 3 and 6 months and changes in log10 viral load and CD4+ cell count at 3 and 6 months compared with baseline values. By using intent-to-treat analysis, a viral load less than 500 copies/ml was achieved in 35% of the 31 patients at 3 months and in 32% of them at 6 months. By using as-treated analysis, this outcome was achieved in 48% of 23 patients who continued therapy at 3 months and in 59% of 17 patients who continued therapy at 6 months. At 3 months (23 patients) and 6 months (17 patients), respectively, changes in viral load were -1.7 log10 copies/ml (p<0.001) and -1.4 log10 copies/ml (p<0.001), and changes in CD4+ cell count were +99 cells/mm3 (p<0.001) and +95 mm3 (p=0.012), compared with baseline.

CONCLUSION

Significant improvements in virologic and immunologic markers occurred in patients heavily experienced with antiretroviral therapy after starting dual-protease inhibitor treatment regimens. Salvage therapy guided by Warmline consultation appears to be beneficial for this patient population with limited treatment options.

Effects of didanosine formulations on the pharmacokinetics of amprenavir

STUDY OBJECTIVES

To determine the effects of concurrent, single doses of didanosine (both buffered and encapsulated enteric-coated bead formulations) on amprenavir steady-state pharmacokinetics, and to determine the effect of staggered dosing of the buffered formulation.

DESIGN

Two-period, single-sequence, prospective, open-label drug interaction study with a 10-day washout interval.

SETTING

Clinical research unit.

SUBJECTS

Sixteen healthy volunteers without human immunodeficiency virus infection.

INTERVENTION

Amprenavir 600 mg twice/day was given for the first 4 days of each treatment period, with 12-hour pharmacokinetic evaluations conducted on the last 2 days of each period. Amprenavir was administered according to the following sequential treatments (all fasting): amprenavir alone, concurrent with buffered didanosine, 1 hour before buffered didanosine, and concurrent with the encapsulated enteric-coated bead formulation of didanosine.

MEASUREMENTS AND MAIN RESULTS

Plasma was collected 0, 1, 2, 3, 4, 6, 8, and 12 hours after dosing and assayed for amprenavir by using high-performance liquid chromatography. Noncompartmental pharmacokinetic parameters were determined. Geometric mean ratios for each treatment relative to amprenavir alone were determined and reported with 90% confidence intervals (CIs). No significant trends were noted in predose concentrations measured during either period. Area under the concentration-time curve during one 12-hour dosing interval (AUC12) was found to be bioequivalent for all treatments. Peak drug concentration (Cmax) was reduced by 15% on average with concurrent administration of buffered didanosine, and bioequivalence was not demonstrated for this parameter. For concurrent enteric-coated didanosine, geometric mean ratios for Cmax and AUC12 were 0.93 and 0.94, respectively. For buffered didanosine given 1 hour after amprenavir, geometric mean ratios were 1.06 and 1.10 for the same parameters, respectively. No differences were observed in 12-hour concentration (C12) with concurrent administration of buffered or enteric-coated didanosine.

CONCLUSION

Amprenavir AUC12 and C12 are not significantly affected by concurrent administration of the buffered or enteric-coated formulations of didanosine. Therefore, amprenavir may be administered concurrently with either the buffered or the encapsulated enteric-coated bead formulation of didanosine in the fasting state.

A review of low-dose ritonavir in protease inhibitor combination therapy

The pharmacokinetics of protease inhibitors center around the microsomal enzyme cytochrome P-450 3A4. As a potent inhibitor of this enzyme, ritonavir can increase the bioavailability and half-life of coadministered protease inhibitors. Evidence suggests that increased exposure to protease inhibitors is clinically relevant. Antiretroviral treatment with low-dose ritonavir-boosted lopinavir, indinavir, and saquinavir has durable virological activity and shows impressive immune reconstitution. Although tolerable in most cases, gastrointestinal side effects, hepatotoxicity, and blood lipid abnormalities remain relevant issues. Additional study will elucidate the advantages and disadvantages of twice-daily, low-dose ritonavir-boosted regimens and determine whether once-daily regimens based on this principle will have a lasting role in clinical practice.

Twice-daily amprenavir 1200 mg versus amprenavir 600 mg/ritonavir 100 mg, in combination with at least 2 other antiretroviral drugs, in HIV-1-infected patients

BACKGROUND

Low-dose ritonavir (RTV) boosts plasma amprenavir (APV) exposure. Little has been published on the efficacy, tolerability, and safety of APV 600 mg/RTV 100 mg (APV600/RTV) twice daily (BID) compared to APV 1200 mg BID (APV1200).

METHODS

ESS40011 was a 24-week, multicenter, open-label, clinical trial in which antiretroviral therapy-naïve and -experienced HIV-1-infected adults were randomized 3:1 to receive either APV600/RTV BID or APV1200 BID, in combination with > or = 2 non-protease inhibitor antiretroviral drugs. Non-inferiority of the APV600/RTV regimen to the APV1200 regimen was established if the 95% lower confidence limit for the difference in proportion of patients achieving HIV-1 RNA <200 copies/mL at week 24 with APV 600/RTV minus APV1200 was > or =-0.12. Late in the conduct of the trial, patients not yet completing 24 weeks of therapy were given the option of continuing treatment for an additional 24-week period.

RESULTS

211 patients were randomized, 158 to APV600/RTV and 53 to APV1200. At week 24, APV600/RTV was similar to or better than APV1200 (HIV-1 RNA <200 copies/mL in 62% [73/118] vs 53% [20/38] of patients; intent-to-treat: observed analysis). In the APV600/RTV arm, significantly more patients achieved HIV-1 RNA <50 copies/mL (48% [57/118] vs 29% [11/38] with APV1200, P = 0.04), and greater mean reduction from baseline in HIV-1 RNA was observed (-2.21 vs -1.59 log10 copies/mL, P = 0.028). The two treatment arms were similar with respect to mean overall change from baseline in CD4+ count, frequency of drug-related grade 1-4 adverse events, and frequency of discontinuing treatment due to adverse events (most commonly nausea, diarrhea, vomiting or fatigue; 7% vs 8%), although a lower proportion of patients in the APV600/RTV arm experienced drug-related oral/perioral paresthesia (2% vs 8%). Eleven (73%) of 15 patients who had HIV-1 RNA <200 copies/mL at week 24 and chose to continue study treatment maintained this level of virologic suppression at follow-up 24 weeks later.

CONCLUSIONS

APV600 RTV BID was similar to or better than APV1200 BID in virologic response. Virologic results in a small number of patients who continued treatment for 24 weeks post-study suggest that virologic suppression with APV600 RTV BID is durable.

Genotypic inhibitory quotient as predictor of virological response to ritonavir-amprenavir in human immunodeficiency virus type 1 protease inhibitor-experienced patients

Forty-nine protease inhibitor (PI)-experienced but amprenavir (APV)-naïve patients experiencing virological failure were treated with ritonavir (RTV) (100 mg twice a day [b.i.d.]) plus APV (600 mg b.i.d.). Patients responded to therapy with a median viral load decrease of -1.32 log(10) by week 12. The addition of low-dose RTV enhanced the minimal APV concentration in plasma (APV C(min)) up to 10-fold compared with that obtained with APV (1,200 mg b.i.d.) without RTV. Baseline PI resistance mutations (L10F/I/V, K20M/R, E35D, R41K, I54V, L63P, V82A/F/T/S, I84V) identified by univariate analysis and included in a genotypic score and APV C(min) at week 8 were predictive of the virological response at week 12. The response to APV plus RTV was significantly reduced in patients with six or more of the resistance mutations among the ones defined above. The genotypic inhibitory quotient, calculated as the ratio of the APV C(min) to the number of human immunodeficiency virus type 1 protease mutations, was a better predictor than the virological or pharmacological variables used alone. This genotypic inhibitory quotient could be used in therapeutic drug monitoring to define the concentrations in plasma needed to control replication of viruses with different levels of PI resistance, as measured by the number of PI resistance mutations.

Steady-state pharmacokinetics of amprenavir coadministered with ritonavir in human immunodeficiency virus type 1-infected patients

The protease inhibitor (PI) ritonavir is used as a strong inhibitor of cytochrome P450 3A4, which boosts the activities of coadministered PIs, resulting in augmented plasma PI levels, simplification of the dosage regimen, and better efficacy against resistant viruses. The objectives of the present open-label, multiple-dose study were to determine the steady-state pharmacokinetics of amprenavir administered at 600 mg twice daily (BID) and ritonavir administered at 100 mg BID in human immunodeficiency virus type 1 (HIV-1)-infected adults treated with different antiretroviral combinations including or not including a nonnucleoside reverse transcriptase inhibitor (NNRTI). Nineteen patients completed the study. The steady-state mean minimum plasma amprenavir concentration (C(min,ss)) was 1.92 microg/ml for patients who received amprenavir and ritonavir without an NNRTI and 1.36 microg/ml for patients who received amprenavir and ritonavir plus efavirenz. For patients who received amprenavir-ritonavir without an NNRTI, the steady-state mean peak plasma amprenavir concentration (C(max,ss)) was 7.12 microg/ml, the area under the concentration-time curve from 0 to 10 h (AUC(0-10)) was 32.06 microg. h/ml, and the area under the concentration-time curve over a dosing interval (12 h) at steady-state (AUC(ss)) was 35.74 microg. h/ml. Decreases in the mean values of C(min,ss) (29%), C(max,ss) (42%), AUC(0-10) (42%), and AUC(ss) (40%) for amprenavir occurred when efavirenz was coadministered with amprenavir-ritonavir. No unexpected side effects were observed. As expected, coadministration of amprenavir with ritonavir resulted in an amprenavir C(min,ss) markedly higher than those previously reported for the marketed dose of amprenavir. When amprenavir-ritonavir was coadministered with efavirenz, amprenavir-ritonavir maintained a mean amprenavir C(min,ss) above the mean 50% inhibitory concentration of amprenavir previously determined for both wild-type HIV-1 isolates and HIV-1 strains isolated from PI-experienced patients. These data support the use of low-dose ritonavir to enhance the level of exposure to amprenavir and increase the efficacy of amprenavir.

Pharmacokinetic interaction between amprenavir and delavirdine after multiple-dose administration in healthy volunteers

AIMS

To evaluate the safety and the pharmacokinetic interaction between amprenavir and delavirdine after multiple dose administration in healthy volunteers.

METHODS

This was a prospective, open-label, randomized, controlled, two-sequence, two-period multiple dose study with 18 healthy subjects. Volunteers were randomly assigned to amprenavir, 600 mg twice a day, or delavirdine, 600 mg twice a day, for 10 days, followed by both drugs for another 10 days with pharmacokinetic evaluation on day 10 and day 20. Adverse events were recorded throughout the study.

RESULTS

Amprenavir decreased all the delavirdine pharmacokinetic parameters apart from tmax. Delavirdine C12h dropped from 7,916 to 933 ng ml-1 (median decrease 5,930 ng ml-1, 95% CI 3,013, 8,955 ng ml-1). A decrease in amprenavir t(1/2) was also seen leading to almost identical median amprenavir C24h values. No serious clinical adverse events were observed during the study. The most frequently reported effects were gastrointestinal symptoms, headache, fatigue and rash.

CONCLUSIONS

Amprenavir is an effective inducer of delavirdine metabolism, probably through its effect on hepatic CYP3A4. This could have consequences in other drug-drug interaction situations. Delavirdine is an inhibitor of amprenavir metabolism. The regimen of amprenavir 600 mg and delavirdine 600 mg twice a day is not recommended when an antiretroviral effect from delavirdine is required.

Effects of formulation and dosing strategy on amprenavir concentrations in the seminal plasma of human immunodeficiency virus type 1-infected men

We compared seminal plasma pharmacokinetic data for the investigational amprenavir prodrug GW433908 with those for amprenavir and an amprenavir-ritonavir combination regimen. All 3 regimens resulted in detectable blood plasma and seminal plasma concentrations of amprenavir. The majority of these concentrations were greater than the plasma protein-corrected 50% inhibitory concentration for wild-type human immunodeficiency virus type 1.

Low-dose ritonavir for protease inhibitor pharmacokinetic enhancement

OBJECTIVE

To examine the use of low-dose ritonavir as a pharmacokinetic enhancer for HIV protease inhibitors.

DATA SOURCES

Primary articles, review articles, and conference abstracts identified by MEDLINE search (1995-May 2001) and secondary sources.

DATA SYNTHESIS

Low-dose ritonavir (100-200 mg) is increasingly being combined with HIV protease inhibitors to improve their effectiveness and allow less frequent dosing. An evaluation of the clinical evidence supporting this practice was conducted.

CONCLUSIONS

Limited outcome data exist for low-dose ritonavir-based regimens in general. Although preliminary data appear promising, more clinical evidence is needed to determine the optimal dosing, long-term safety, and relative effectiveness of this approach. The role of these regimens in early therapy remains to be defined.

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

BACKGROUND

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

OBJECTIVE

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

OUTCOME

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

Pharmacokinetic modeling and simulations of interaction of amprenavir and ritonavir

Data from three pharmacokinetic drug interaction studies of amprenavir and ritonavir were used to develop a pharmacokinetic interaction model using NONMEM (nonlinear mixed-effect model). A two-compartment linear model with first-order absorption best fit the amprenavir data, while a one-compartment model was used to describe the ritonavir data. The inhibition of elimination of amprenavir by ritonavir was modeled with a maximum effect (Emax) inhibition model and the observed ritonavir concentration. Monte Carlo simulation was then used to predict amprenavir concentrations for various combinations of amprenavir and ritonavir in twice-daily and once-daily dosing regimens. Simulated minimum amprenavir concentrations in plasma (Cmin) in twice-daily and once-daily dosing regimens were compared with protein binding-adjusted 50% inhibitory concentrations (IC50s) for clinical human immunodeficiency virus isolates with different susceptibilities to protease inhibitors (central tendency ratios). The model based on the first two studies predicted the results of the third study. Data from all three studies were then combined to refine the final model. The observed and simulated noncompartmental pharmacokinetic parameters agreed well. From this model, several candidate drug regimens were simulated. These simulations suggest that, in patients who have clinically failed a traditional amprenavir regimen, a regimen of 600 mg of amprenavir with 100 mg of ritonavir twice daily would result in Cmin-to-IC50 ratios similar to that of 1,200 mg of amprenavir twice daily alone for wild-type viruses. In addition, once-daily regimens that result in C(min)s above the protein binding-corrected IC50s for wild-type virus are clearly feasible.