Indinavir Concentrations Research Articles

Pharmacokinetics of indinavir/ritonavir (800/100 mg) in combination with efavirenz (600 mg) in HIV-1-infected subjects.

Addition of efavirenz (600 mg) to indinavir/ritonavir (800/100 mg) results in significant decreases in indinavir levels in healthy volunteers. This study evaluated the steady-state pharmacokinetics of indinavir/ritonavir at 800/100 mg twice daily (bid) in combination with efavirenz at 600 mg once daily (qd) in HIV-infected Thai subjects who used this nucleoside-sparing combination in The HIV Netherlands Australia Thailand Research Collaboration 009 study. At week 4 of the study, 12-hour pharmacokinetic profiles for indinavir/ritonavir were obtained for 20 HIV-infected subjects. For efavirenz, the concentrations at 12 hours and 24 hours (Cmin) after dosing were assessed. All subjects (10 males and 10 females) completed the study. The geometric mean area under the concentration versus time curve, Cmin, and maximum plasma concentration of indinavir were 45.7 mg/(L. h) (95% confidence interval [CI], 39.8-52.5), 0.32 mg/L (95% CI, 0.24-0.44), and 11.1 mg/L (95% CI, 9.4-13.0), respectively. A >10-fold variation in indinavir Cmin was observed. All subjects had an indinavir Cmin that was at least comparable with the reported mean population Cmin of indinavir at 800 mg thrice daily without ritonavir (0.15 mg/L). The geometric mean concentration at 12 hours and Cmin of efavirenz were 3.1 mg/L (95% CI, 2.5-3.7) and 2.1 mg/L (95% CI, 1.6-2.6), respectively. Despite the known pharmacokinetic interaction between efavirenz and indinavir/ritonavir, the combination of indinavir/ritonavir at 800/100 mg bid and efavirenz at 600 mg qd results in adequate minimum concentrations of both indinavir and efavirenz for treatment-naive patients.

In vitro hypersusceptibility of human immunodeficiency virus type 1 subtype C protease to lopinavir.

In order to characterize the impact of genetic polymorphisms on the susceptibility of subtype C strains of human immunodeficiency virus type 1 to protease inhibitors (PIs), a subtype B protease that originated from an infectious clone was modified through site-directed mutagenesis to include the amino acid residue signatures of subtype C viruses (I15V, M36I, R41K, H69K, L89 M) with (clone C6) or without (clone C5) an I93L polymorphism present as a molecular signature of the worldwide subtype C protease. Their susceptibilities to commercially available PIs were measured by a recombinant virus phenotyping assay. We could not detect any differences in the 50% inhibitory concentration (IC(50)s) of amprenavir, indinavir, ritonavir, saquinavir, and nelfinavir for the clones analyzed. However, we did observe hypersusceptibility to lopinavir solely in clone C6, which includes the I93L substitution (a 2.6-fold decrease in the IC(50) compared to that for the subtype B reference strain). The same phenotypic behavior was observed for 11 Brazilian and South African clinical isolates tested, in which only subtype C isolates carrying the I93L mutation presented significant hypersusceptibility to lopinavir.

Indinavir reduces Cryptosporidium parvum infection in both in vitro and in vivo models

The use of highly active antiretroviral therapy in persons with acquired immunodeficiency syndrome has reduced the prevalence of infection with Cryptosporidium parvum and the length and severity of its clinical course. This effect has in most cases been attributed to the recovery of the host immunity; however, some works suggest that human immunodeficiency virus protease inhibitors, indinavir in particular, which is one of the human immunodeficiency virus protease inhibitors used in highly active antiretroviral therapy, may be capable of controlling Microsporidia and Cryptosporidium infections, which are refractory to other treatments. The objective of the present study was to investigate the effect of human immunodeficiency virus protease inhibitors on C. parvum infections. Since preliminary experiments using ritonavir, saquinavir, and indinavir showed a drastic reduction of C. parvum infection both in vivo (neonatal Balb/c mice) and in vitro (human ileocecal adenocarcinoma tumour cell line) models, indinavir alone was tested in successive experiments. In vitro, the treatment of the sporulated oocysts with different concentrations of indinavir reduced the percentage of human ileocecal adenocarcinoma tumour cell line infected cells in a dose-dependent manner. For established infection, the treatment with 50 μM of indinavir decreased the percentage of infected cells in a time-dependent manner. In vivo, mice treated with indinavir at the same time they were infected with the oocysts showed a 93% reduction in the number of oocysts present in the entire intestinal contents and a 91% reduction in the number of intracellular parasites in the ileum. For established infection, indinavir treatment reduced the number of oocysts in the entire intestinal content by about 50% and the number of intracellular parasites in the ileum by about 70%. These data show that indinavir directly interferes with the cycle of C. parvum, resulting in a marked reduction in oocyst shedding and in the number of intracellular parasites. Protease inhibitors could be considered as good candidates for the treatment of cyptosporidiosis in immunosuppressed persons.

Persistent leukocyturia and loss of renal function in a prospectively monitored cohort of HIV-infected patients treated with indinavir.

Symptomatic nephrotoxicity is a well-known complication of indinavir treatment. However, little is known about the relevance of other abnormalities, such as leukocyturia during use of indinavir. We determined the prevalence, risk factors, and consequences of persistent leukocyturia in a prospectively monitored cohort of indinavir users in three adult outpatient clinics. Patients were monitored for nephrotoxicity at regular visits (every 3 months) between August 1998 and September 2000. Monitoring involved urine dipstick analysis and microscopy for pH, erythrocytes, leukocytes, and indinavir crystals. The urine albumin concentration/creatinine concentration ratio and serum creatinine and indinavir plasma concentrations were measured, and urinary tract infection was excluded. Urologic symptoms were retrieved from medical records. Of 184 patients with at least one assessment, 35% had leukocyturia (i.e., >75 cells/microL) at least once during the study period, which coincided with mild increase in the serum albumin level, erythrocyturia, and crystalluria. Thirty-two (24%) of 134 patients with two or more assessments had persistent leukocyturia (i.e., on two or more occasions). Risk factors were indinavir plasma concentration of >9 mg/L, urine pH of >5.7, and crystalluria. Persistent leukocyturia was associated with a gradual loss of renal function but not with urologic symptoms. The data show that leukocyturia is a frequent finding and emphasize the need for monitoring renal function during indinavir treatment, even in the absence of urologic symptoms.

Effect of indinavir on the intestinal exsorption of amprenavir, saquinavir and nelfinavir after intravenous administration in rats.

To elucidate drug interaction between human immunodeficiency virus (HIV) protease inhibitors (PIs), the effect of indinavir (IDV) on the intestinal exsorption of other HIV PIs, amprenavir (APV), saquinavir (SQV) and nelfinavir (NFV) was investigated in rats using an in situ single perfusion method. IDV in the intestinal perfusate inhibited the exsorption of rhodamine 123 (Rho123), a known P-glycoprotein (P-gp) substrate, from blood into intestinal lumen in a concentration-dependent manner, and the inhibitory potency of 10 micro M IDV in the perfusate was close to that of 10 micro M cyclosporin A (CsA) in the perfusate. Ten micro M of IDV in the intestinal perfusate also decreased significantly the exsorption clearance of Rho123 after intravenous administration. The IDV concentration in this system was not likely to cause hepatic interaction between HIV PIs, because the plasma IDV concentration was far below its inhibition constants for other HIV PIs in the liver microsomes. Thus, 10 micro M of IDV was chosen to investigate the effect of this inhibition on the exsorption of APV, SQV and NFV. IDV in the intestinal perfusate markedly increased the exsorbed amounts of SQV and NFV but not APV after intravenous administrations. Their exsorption clearances, however, showed only a slight increasing tendency or remained unchanged. These findings suggest that in addition to P-gp inhibition, other factors such as CYP3A inhibition might be important in the drug interaction of IDV with APV, SQV and NFV after intravenous administration in rat small intestine. The results obtained in this study will provide useful information to discuss the interactions among PIs when a double protease therapy is used for in HIV-infected patients.

Individualizing salvage regimens

Individualizing salvage regimens

The unbound percentage of saquinavir and indinavir remains constant throughout the dosing interval in HIV positive subjects.

To measure the unbound plasma concentrations of saquinavir (SQV) and indinavir (IDV) and to relate them to the total plasma concentrations in order to establish the unbound percentage of protease inhibitors in vivo during a full dosage interval profile. HIV-infected subjects (n = 35; median CD4 cell count = 340 x 10(6) cells l-1, range: 120-825; viral load < 50 copies ml-1 in 22/35) treated with SQV or IDV containing regimens were studied. Plasma drug samples were collected at 0, 2, 4, 8 and 12 h postdose for the twice daily regimens and 0, 1, 2, 4 and 8 h for the three times daily regimens. Ultra-filtration was used to separate unbound IDV and SQV in plasma and their respective concentrations were measured by a fully validated method using high performance liquid chromatography-mass spectometry (h.p.l.c.-MS/MS). Based on the ratio AUCunbound/AUCtotal, the median unbound percentage (95% CI for differences) of SQV and IDV from all the samples studied was 1.19% (0.99, 1.58%) and 36.3% (35.1, 44.2%), respectively. No significant difference was seen in the percentage binding of SQV between patients receiving SQV alone (median = 1.49%) or with ritonavir (median = 1.09%; P = 0.141; 95% CI for difference between medians = -0.145, 0.937) over the pharmacokinetic profile. Similarly, no significant difference was seen in the percentage binding of IDV in patients receiving IDV alone (median 35.2%) or with ritonavir (median = 41.3%; P = 0.069; 95% CI for difference between medians = -0.09, 15.4). The unbound concentrations of SQV (P < 0.0001; 95% CI for r(2) = 0.634, 0.815) and IDV (P < 0.0001; 95% CI for r(2) = 0.830, 0.925) remained constant as a proportion of total concentration over the full dosing profile. These in vivo data confirm previously published in vitro measurements of SQV and IDV protein binding. The unbound percentage of both protease inhibitors remained constant over the dosing interval.

Intestinal metabolism promotes regional differences in apical uptake of indinavir: coupled effect of P-glycoprotein and cytochrome P450 3A on indinavir membrane permeability in rat.

The purpose of this study was to investigate transport and metabolism contributions to low indinavir permeability in rat ileum and enhanced drug permeability in the jejunum. Permeability models utilized included single pass in situ rat intestinal perfusion and rat intestinal tissue mounted in Ussing chambers. Intestinal metabolism was measured by fractional appearance of metabolite (F(met)), determined as the percentage of the predominant metabolite M6 over luminal loss of indinavir in the perfusion model. Among the results, indinavir exhibited bidirectional transport across rat ileum. Verapamil and cyclosporin A inhibited net flux by 37 and 38%, respectively. Intestinal metabolism of indinavir was most significant in upper jejunum (F(met) = 65.78 +/- 19.02%), decreasing in midjejunum (F(met) = 31.58 +/- 5.63%). M6 was not detectable in ileum or colon. Western blot analysis of rat intestinal mucosal tissue samples confirmed that the axial expression of CYP3A was consistent with the regional pattern of formation of M6. Intestinal metabolism was saturable and could be inhibited by the CYP3A inhibitor, ketoconazole. A low luminal concentration of indinavir (1 microM) was associated with high F(met) (87.90 +/- 14.30%), whereas a high luminal concentration of indinavir (50 microM) was associated with low F(met) (35.84 +/- 11.59%). In the presence of ketoconazole, both F(met) and permeability of indinavir were reduced in the jejunum. These results suggest that 1) intracellular metabolism of indinavir enhances apical uptake of indinavir in the rat jejunum as a function of the increased concentration gradient generated across the epithelial cell membrane and 2) the efflux transporter P-glycoprotein limits apical uptake of indinavir in the ileum, resulting in low apparent permeability.

Intracellular Indinavir Pharmacokinetics in HIV-Infected Patients: Comparison with Plasma Pharmacokinetics

To determine intracellular concentrations of indinavir (IDV) and investigate the relationship between plasma and intracellular IDV pharmacokinetics in HIV-infected patients. A pharmacokinetic study of 10 patients receiving IDV plus dual nucleoside analogue therapy. Peripheral blood mononuclear cells were isolated by density gradient centrifugation and cell counts estimated. IDV was extracted from cells in the presence of 60% methanol and evaporated to dryness. Both plasma and intracellular IDV samples were assayed by high performance liquid chromatography linked to mass spectrometry. Data were subjected to non-compartmental pharmacokinetic analysis. The mean intracellular IDV area under the curve over 8 h (AUC0-8) was lower than the plasma AUC0-8 (7574 +/- 1003 vs 25060 +/- 4171 ng/ml/h; P<0.004). However, both the elimination half-life (t1/2) and the mean residence time (MRT) of IDV intracellularly were prolonged compared with plasma (t1/2: 2.0 +/- 0.3 vs 1.2 +/- 0.09 h; MRT: 3.6 +/- 0.6 vs 2.1 +/- 0.1 h; P<0.05). All patients were responsive to therapy at the time of the study, as assessed by HIV plasma RNA levels. Individual plasma versus intracellular time course results suggest that, due to the prolonged intracellular half-life, some patients may achieve acceptable intracellular IDV concentrations despite sub-therapeutic plasma levels. Similarly, potentially inadequate intracellular concentrations may occur despite therapeutic plasma concentrations. There is no significant intracellular accumulation of IDV within the lymphocytes of HIV-1-infected patients relative to plasma. However, intracellular concentrations are compatible with reported IDV-free drug concentrations in plasma. The intracellular elimination half-life and mean residence time of IDV are significantly prolonged compared with plasma. This may in part explain why certain patients maintain adequate viral suppression despite sub-therapeutic plasma IDV levels.

Indinavir induces acute and reversible peripheral insulin resistance in rats.

The use of HIV protease inhibitors (PIs) has been associated with several metabolic changes, including lipodystrophy, hyperlipidemia, and insulin resistance. The etiology of these adverse effects remains unknown. PIs have recently been found to cause acute and reversible inhibition of GLUT4 activity in vitro. To determine the acute in vivo effects of indinavir on whole-body glucose homeostasis, glucose tolerance tests were performed on PI-naïve Wistar rats immediately after a single intravenous dose of indinavir. Glucose and insulin levels were significantly elevated in indinavir-treated versus control rats (P < 0.05) during the initial 30 min of the glucose tolerance test. Under euglycemic- hyperinsulinemic clamp conditions, indinavir treatment acutely reduced the glucose infusion rate required to maintain euglycemia by 18 and 49% at indinavir concentrations of 14 and 27 micromol/l, respectively. Muscle 2-deoxyglucose uptake was similarly reduced under these conditions. Restoration of insulin sensitivity was observed within 4 h after stopping the indinavir infusion. Indinavir did not alter the suppression of hepatic glucose output under hyperinsulinemic conditions. These data demonstrate that indinavir causes acute and reversible changes in whole-body glucose homeostasis in rats and support the contribution of GLUT4 inhibition to the development of insulin resistance in patients treated with PIs.

Drug interactions between HIV protease inhibitors based on physiologically-based pharmacokinetic model

A Physiologically-based pharmacokinetic (PB-PK) model was developed to describe the aspects of pharmacokinetic interactions between five HIV protease inhibitors (ritonavir, amprenavir, nelfinavir, saquinavir, indinavir) in rats. To increase usefulness of this BP-PK model, liver, intestinal tissue and other organ were assumed as compartments in this model. Each compartment was linked with the blood flow and the blood-to-plasma concentration ratios of those drugs, and the absorption process in the intestinal tract was presumed as a first-order kinetics. In addition, this PB-PK model incorporates two elimination processes due to hepatic and intestinal metabolism constructed by in vitro metabolic clearance rates and inhibition constants between HIV protease inhibitors. Excellent agreements were obtained between the predicted and observed concentrations of HIV protease inhibitors in rat plasma after a 20 mg/kg oral dose or co-administration of two kinds of HIV protease inhibitors (amprenavir/indinavir, nelfinavir/amprenavir, saquinavir/amprenavir, amprenavir/ritonavir, indinavir/ritonavir, nelfinavir/ritonavir, and saquinavir/ritonavir) with each 20 mg/kg oral dose. However, underestimates in the predicted plasma concentrations of saquinavir, indinavir and amprenavir were observed during the terminal phase after co-administration with ritonavir or amprenavir, suggesting that a term of other inhibitory process, such as a mechanism-based inhibition, might be incorporated into this PB-PK model. This BP-PK model enables us to know useful information about pharmacokinetic interaction when HIV infected patients would receive double protease therapy. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:680–689, 2002

Decreased plasma levels of amitriptyline and its metabolites on comedication with an extract from St. John's wort ( Hypericum perforatum ).

Extracts of St. John's wort ( Hypericum perforatum ) became increasingly popular as easily available remedies for mild to moderate depression. Comedication with hypericum extract was recently shown to drastically reduce plasma concentration of ciclosporin, digoxin, and indinavir. We investigated the possible interaction of hypericum extract LI160 with amitriptyline. Both antidepressants have a high probability of concomitant use. Twelve patients requiring amitriptyline treatment received a single dose of hypericum extract (900 mg) at day 1, continued by a 12-to 14-day treatment with retarded amitriptyline (75 mg twice daily). Then hypericum (900 mg/day) was added for another 14 to 16 days. Steady-state pharmacokinetics of amitriptyline were compared before and after multiple-dose treatment with hypericum extract. Furthermore, comparisons were made for single-dose kinetics of hypericum-extract ingredients hypericin, pseudohypericin, and hyperforin between the first day of concomitant treatment and LI160 alone. Multiple-dose comedication with LI160 led to a statistically significant decrease in the area under the plasma concentration-time curve within one dosing interval of amitriptyline by 22% ( p = 0.03) and nortriptyline by 41% ( p = 0.002), as well as of all hydroxylated metabolites, except for 10-E-hydroxynortriptyline. Plasma levels of amitriptyline and hydroxylated metabolites gradually decreased, whereas nortriptyline concentrations were already markedly decreased after 3 days of cotreatment with hypericum. Cumulative urinary amounts of amitriptyline and metabolites decreased to the same extent as plasma concentrations upon hypericum comedication. Induction of cytochrome P-450 enzymes or drug transporters (P-glycoprotein) by St. John's wort extract may explain this pharmacokinetic interaction. Physicians should be aware of this interaction when treating patients with amitriptyline.

A co-culture-based model of human blood–brain barrier: application to active transport of indinavir and in vivo–in vitro correlation

The growing array of in vitro models of the blood–brain barrier (BBB) which have been used makes it difficult to draw firm conclusions concerning the BBB penetration of HIV-1 protease inhibitors. What is needed is a combined in vivo and in vitro study on biological models that mimic as closely as possible the normal human BBB, to establish whether and how indinavir crosses the BBB. We developed a new human BBB model using primary endothelial cells and astrocytes. The biological relevance of this model was checked with respect on the one hand, to the close relationship between the log of drug permeability coefficient normalized to molecular weight and the log of the 1-octanol/water partition coefficient, and on the other hand to the functional P-glycoprotein (P-gp) expression. We employed this model to perform transport studies with indinavir and showed that the rate of in vitro indinavir transport from the basal to apical compartment was higher than the rate of apical to basal transport. Pretreatment of the BBB model with the P-gp inhibitor, quinidine, significantly increased apical to basal transport. Intracellular indinavir accumulation was increased in BBB as a result of inhibition of active transport. These data were correlated with the indinavir-mediated P-gp ATPase modulation showing that indinavir specifically interacted with a binding site on P-gp. Moreover, the activation of P-gp ATPase by indinavir was inhibited by quinidine. In addition, the in vivo brain to plasma concentration ratio of indinavir into mice showed that indinavir concentration was up to five times higher in the brain of mdr1a(−/−) mice than in the brain of mdr1a(+/+) mice. All these results confirm the role of P-gp in preventing the passage of indinavir across BBB and thus its entry into the central nervous system (CNS). Our human BBB model represents a useful tool for the evaluation of drug penetration into the CNS.

Therapeutic Drug Monitoring of Indinavir in HIV-Infected Patients Undergoing HAART

Therapeutic drug monitoring (TDM) of protease inhibitors (PI) is gaining increasing importance for the management of HIV-infected patients undergoing highly active antiretroviral therapy (HAART). The PI indinavir (IDV) is widely used in HAART regimens. Combinations of IDV with ritonavir (RTV) have been used to increase the plasma concentration of IDV. However, the desirable IDV concentration range in clinical practice remains to be elucidated. To study the value of TDM for IDV in clinical practice, a retrospective analysis of 501 plasma samples of patients treated with IDV in various dosages was performed. IDV levels were determined during routine outpatient visits. Analysis was performed by high pressure liquid chromatography (HPlC) with UV detection. A widespread range of IDV plasma concentrations was seen both within and between patients. The mean IDV level during therapy with IDV 2.4 g/d was 3,260 ng/ml (95% CI: 2,903 ng/ml; 3,618 ng/ml). IDV levels at a dose of IDV 1.6 g/d in combination with RTV resulted in a mean IDV plasma concentration of 4,191 ng/ml (95% CI: 3,356 ng/ml; 5,026 ng/ml). There was no significant difference between plasma levels at the doses of 2.4 g/d and 1.6 g/d. 35 of all 130 patients treated with IDV reached only suboptimal IDV plasma concentrations below the limit of 150 ng/ml. There was no statistically significant difference between the number of patients below an IDV plasma concentration of 150 ng/ml in the various dosage regimens. During therapy with IDV in a b.i.d. scheme, similar IDV plasma concentrations and a comparable number of patients with subinhibitory plasma concentrations were observed when compared to a therapeutic regimen with t.i.d. dosing. In this study, even at various times of plasma sampling after oral ingestion, TCM facilitated the surveillance of patients compliance.

Indinavir-induced retinoid-like effects: incidence, clinical features and management.

Since 1998, many cases of antiretroviral therapy-related paronychia of the toes or fingers and ingrown toenails have been reported. Most of them were related to indinavir. Other indinavir-induced mucocutaneous disorders resembling the adverse effects of systemic retinoid therapy have also been reported. Although there is some uncertainty in the literature regarding a cause-effect relationship, results of several epidemiological and in vitro studies, together with cumulated clinical experience leave no doubt that indinavir causes a retinoid-like effect and nail alterations. Indeed, indinavir is the only antiretroviral drug that produces these disorders, although ritonavir may enhance indinavir-induced retinoid-like effects through pharmacokinetic interactions leading to increased plasma indinavir concentrations. Approximately 30% of patients receiving indinavir show two or more retinoid-like manifestations and 4-9% develop paronychia. These adverse effects are not related to other epidemiological variables such as the patient's sex, age or other risk factors or immune status. They seem to be exposure dependent and, therefore, largely dose-dependent. Chronic paronychia is considered generally to be caused by contact irritants and candidal infection. Nevertheless, indinavir is currently the most frequent cause of chronic or recurrent paronychia in HIV-infected patients. In addition, retinoid-like manifestations such as cutaneous xerosis and cheilitis are frequent mucocutaneous adverse effects related to indinavir. The exact mechanism of indinavir-induced retinoid-like effects is unclear. Hypotheses for pathogenesis include interference with retinoid metabolism by enhancing the retinoic acid signalling pathway, or by increasing retinoic acid synthesis, or by reducing cytochrome p450-mediated retinoic acid oxidative metabolism. Replacement of therapy by an antiretroviral regimen not containing indinavir, while retaining other protease inhibitors and lamivudine, resolves retinoid-like manifestations without recurrences.

Indinavir Pharmacokinetics during Different Phases of the Menstrual Cycle in HIV-Infected Women

To characterise the pharmacokinetics of indinavir during different phases of the menstrual cycle in HIV-infected women. Open-label study. The immunodeficiency clinic at Erie County Medical Center, Buffalo, New York. Ten HIV-infected women were enrolled in the study. Eligibility criteria included an acceptable medical history, chemistry profile, complete blood count with differential, lymphocyte profile, urinalysis and history of a regular menstrual cycle. PATIENTS had to be on a stable antiretroviral regimen that included indinavir 800mg taken every 8 hours. Blood sampling over an 8-hour period following an 800mg dose of indinavir during the menstrual, follicular and luteal phases of the menstrual cycle. Pharmacokinetic parameters in ten HIV-infected women adherent with indinavir 800mg every 8 hours during the menstrual, follicular and luteal phases of the menstrual cycle. Serum estradiol and progesterone levels were also obtained during each menstrual cycle phase. The peak plasma concentration, plasma concentration 8 hours after administration of a given dose of indinavir, elimination half-life and oral clearance of indinavir were not significantly different across the menstrual cycle phases. Indinavir exposure varied among the female patients with some individuals having similar areas under the concentration-time curve (AUCs) during the three phases while others had notable differences in AUC. Maximum plasma indinavir concentrations were highest during the follicular phase in four subjects, highest during the luteal phase in two individuals, and highest during the menstrual phase in three patients. No differences were found in indinavir pharmacokinetics during the menstrual cycle phases. Significant intra- and interpatient variability in indinavir pharmacokinetics were observed; however, indinavir exposure in women did not appear to be excessive compared with pharmacokinetic data obtained from prior studies conducted in men.

Therapeutic drug monitoring of HIV protease inhibitors using high-performance liquid chromatography with ultraviolet or photodiode array detection.

Published data suggest that therapeutic drug monitoring of human immunodeficiency virus protease inhibitors would improve the management of antiretroviral therapy. The authors have developed a high-pressure liquid chromatographic assay allowing simultaneous determination of six protease inhibitors (ritonavir, saquinavir, indinavir, nelfinavir, amprenavir, and lopinavir), using carbamazepine as internal standard. Detection was based on a dual wavelength ultraviolet spectrophotometer and can be improved by the use of a photodiode array detector. Monitoring was performed 1 month after initiation of therapy or in instances of therapeutic failure, side effects, suspicion of noncompliance, drug interactions, or malabsorption. Trough concentrations were 0.15 to 13.6 mg/L for ritonavir, 0.06 to 9.7 mg/L for indinavir, 0.03 to 5.5 mg/L for saquinavir, and 0.15 to 4.15 mg/L for nelfinavir. Concentrations below the limit of quantification were observed in 63/438 (14%) of the patients. Target concentrations are not well established, and reported in vitro inhibitory concentrations may be of limited value. The authors therefore chose to compare observed concentrations with mean plasma concentrations reported in clinical trials. Observed saquinavir and indinavir concentrations were often below or close to these target concentrations, particularly when used as a single protease inhibitor. Concentration-controlled studies should now be used to select proper target concentrations for each protease inhibitor, either prescribed alone or in combination.

Targeted delivery of indinavir to HIV-1 primary reservoirs with immunoliposomes

The tissue distribution of indinavir, free or incorporated into sterically stabilized anti-HLA-DR immunoliposomes, has been evaluated after a single subcutaneous injection to C3H mice. Administration of free indinavir resulted in low drug levels in lymphoid organs. In contrast, sterically stabilized anti-HLA-DR immunoliposomes were very efficient in delivering high concentrations of indinavir to lymphoid tissues for at least 15 days post-injection increasing by up to 126 times the drug accumulation in lymph nodes. The efficacy of free and immunoliposomal indinavir has been evaluated in vitro. Results showed that immunoliposomal indinavir was as efficient as the free agent to inhibit HIV-1 replication in cultured cells. The toxicity and immunogenicity of repeated administrations of liposomal formulations have also been investigated in rodents. No significant differences in the levels of hepatic enzymes of mice treated with free or liposomal indinavir were observed when compared to baseline and control untreated mice. Furthermore, histopathological studies revealed no significant damage to liver and spleen when compared to the control group. Liposomes bearing Fab′ fragments were 2.3-fold less immunogenic than liposomes bearing the entire IgG. Incorporation of antiviral agents into sterically stabilized immunoliposomes could represent a novel therapeutic strategy to target specifically HIV reservoirs and treat more efficiently this retroviral infection.

Indinavir crystallization around the loop of Henle: experimental evidence.

To determine the probable site of the nephron and the plasma indinavir (IDV) concentration at which intrarenal IDV crystallization occurs. We performed in vitro crystallization experiments in IDV solutions simulating conditions found in the nephron. To determine intrarenal IDV concentrations at which conditions in the nephron allow crystallization, several concentrations of IDV basic solutions (0-800 mM) were titrated from pH 4.0 to higher pH values until crystals formed within 1 minute. Based on the combination of pH and ionic strength at which crystals formed, we determined the site of the nephron at which this combination was first attained. Based on the capacity for concentration at that site, we were able to measure the corresponding plasma IDV concentration. Under conditions normally found at the proximal tubule (i.e., pH 6.7 and ionic strength of 200 mM), IDV crystallized at 200 mg/L. Under conditions applying to the loop of Henle, pH 7.4 and ionic strength of 200 mM, IDV crystallized at 125 mg/L, which would correspond to a plasma IDV concentration of 8 mg/L. IDV crystallization is most likely in the loop of Henle and may already start at plasma IDV concentrations as low as 8 mg/L. Increasing hydration does not reduce the risk of IDV crystallization in the loop of Henle but instead prevents IDV crystallization and aggregation in the lower urinary tract. It remains to be confirmed whether prevention of high IDV plasma concentrations will reduce the risk of IDV crystallization in the loop of Henle.

A pilot trial of indinavir, ritonavir, didanosine, and lamivudine in a once-daily four-drug regimen for HIV infection.

To evaluate the tolerance, pharmacokinetics, and virologic and immunologic outcomes of once-daily indinavir, ritonavir, didanosine, and lamivudine in HIV-seropositive individuals. Open-label 24-week pilot study. Ten HIV-seropositive subjects who were either antiretroviral-naive or minimally experienced with short-term single-or dual-nucleoside therapy provided informed consent and were enrolled. All subjects received didanosine (400 mg) 30 to 60 minutes before a meal followed by indinavir (1200 mg), ritonavir (400 mg), and lamivudine (300 mg) concurrent with the aforementioned meal. Safety laboratory tests, including a complete blood cell count and amylase, lipase, liver transaminase, and nonfasting lipid monitoring as well as plasma HIV viral load and CD4+ lymphocyte count, were carried out at monthly intervals. Genotyping was performed at baseline. Pharmacokinetic studies for indinavir and ritonavir were performed at week 8. Nine of 10 subjects completed 24 weeks of therapy. No subject demonstrated primary protease inhibitor mutations at baseline. Toxicities experienced by subjects were typically mild and consistent with those commonly reported for each of the medications, including two cases of hematuria. By week 24, median nonfasting cholesterol and triglyceride levels increased by 49% and 108%, respectively. Median baseline plasma HIV viral load and CD4+ lymphocyte count were 29,292 (4.47 log10) copies/ml and 224 cells/mm3, respectively. Eight of 10 subjects had a plasma HIV viral load of <50 copies/ml by week 12. The 2 subjects with a detectable HIV viral load reached <50 copies/ml by week 28. Median CD4+ lymphocyte counts increased by 193 cells/mm3 at week 24. Indinavir and ritonavir plasma concentrations remained above respective inhibitory and effective concentrations (IC95 and EC50) (uncorrected for protein binding) throughout the 24-hour dosing interval for 6 of 10 and 8 of 10 subjects, respectively. Our pilot study demonstrates excellent virologic suppression despite low minimum protease inhibitor concentrations during a dosing interval in some patients and is supportive of further study.