Antiretroviral concentrations in the presence and absence of valproic acid.

OBJECTIVES: An unexpected drug-drug interaction has been recently reported between dolutegravir, an HIV integrase inhibitor, and valproic acid. Despite there being several potential underlying mechanisms, plasma protein displacement has been suggested. The aim of this study was to assess plasma concentrations of several antiretrovirals when administered with or without valproic acid. METHODS: We performed a therapeutic drug monitoring registry analysis and identified patients concomitantly taking antiretrovirals and valproic acid and without clinical affecting conditions or interacting drugs. RESULTS: One hundred and thirty-four patients were identified. Median (IQR) age and BMI were 49.7 years (45-56) and 23.4 kg/m2 (20.8-26.3) and 78 were male (58.2%). Despite small groups, we observed no major effect on antiretroviral exposure, even when considering highly protein-bound compounds (such as etravirine), with the exception of dolutegravir trough concentrations [median (IQR) = 132 ng/mL (62-227) in individuals on valproic acid versus 760 ng/mL (333-1407) in those not receiving valproic acid]. CONCLUSIONS: Valproic acid does not have a major effect on antiretrovirals other than dolutegravir. The mechanism of this unexpected drug-drug interaction may be the combination of protein displacement, reduced absorption and CYP3A4 induction.

SLC22A2 variants and dolutegravir levels correlate with psychiatric symptoms in persons with HIV.

BACKGROUND: Neuropsychiatric symptoms (NPs) have been reported with dolutegravir use. We hypothesized that increasing dolutegravir trough concentrations (Ctrough) and/or polymorphism in the SLC22A2 gene, encoding the organic cation transporter-2 (OCT2), which is involved in monoamine clearance in the CNS and is inhibited by dolutegravir, might be associated with NPs. METHODS: A cross-sectional cohort of HIV-positive patients treated with a dolutegravir-containing regimen underwent determination of allelic discrimination for SLC22A2 808 C → A polymorphism and dolutegravir Ctrough. The Symptom Checklist-90-R [investigating 10 psychiatric dimensions and reporting a general severity index (GSI)], a self-reported questionnaire and the Mini-International Neuropsychiatric Interview were offered to investigate current NPs. The effects of dolutegravir Ctrough and the SLC22A2 gene variant on NPs were explored by multivariable logistic regression. RESULTS: A cohort of 203 patients was analysed: 71.4% were male, with median age 51 years and 11 years of ART exposure. Median time on dolutegravir was 18 months. Dolutegravir was associated with different antiretroviral combinations (mainly lamivudine, 38.9%, and abacavir/lamivudine, 35.5%). SLC22A2 CA genotype was independently associated with an abnormal GSI [adjusted OR (aOR) 2.43; P = 0.072], anxiety (aOR 2.61; P = 0.044), hostility (aOR 3.76; P = 0.012) and with moderate to severe headache (aOR 5.55; P = 0.037), and dolutegravir Ctrough was associated with hostility (fourth versus first quartile aOR 6.70; P = 0.007) and psychoticism (fourth versus first quartile aOR 19.01; P = 0.008). Other NPs were not associated with SLC22A2 polymorphism or dolutegravir Ctrough. CONCLUSIONS: A variant of the OCT2-encoding gene, in addition to or in synergy with higher dolutegravir Ctrough, is associated with a set of NPs observed during dolutegravir therapy.

Tenofovir disoproxil fumarate discontinuation for renal outcomes: any room for treatment personalization?

Tenofovir disoproxil fumarate (TDF) is a very effective antiviral drug that has been associated with tubular dysfunction. The aim of this study was to analyze the demographic, pharmacokinetic, and pharmacogenetic variables associated with TDF discontinuation for renal outcomes in stable HIV-positive patients using multivariable analyses. Three hundred and four patients were included (73% male, with median age and eCrCl of 45.3 years and 90.9 mL/min, respectively). After a median follow-up of 28.3 months, 27 patients discontinued TDF for renal adverse events [persistent urinary abnormalities (n = 21) or eCrCl < 60 mL/min (n = 6)] providing an incidence of 3.77 events per 100 patient-year. The probability of TDF discontinuation was higher with several features (male gender, older age, not Caucasians ancestry, absence of intravenous drug abuse, protease inhibitors, previous indinavir, HCV-positivity, lower CD4 cell count, detectable HIV-RNA, lower eCrCl, spot-urine proteinuria) and higher tenofovir concentrations but not genetic variants. Tenofovir plasma concentrations were prognostic of TDF discontinuation for renal adverse events suggesting that dose-adjustment may be warranted for long-term safety.

Role of CYP24A1, VDR and GC gene polymorphisms on deferasirox pharmacokinetics and clinical outcomes.

ß-Thalassemia patients develop deficiency in vitamin D absorption and liver hydroxylation, resulting in extremely low calcitriol levels. We explored the role of single-nucleotide polymorphisms (SNPs) involved in vitamin D metabolism, transport and activity on deferasirox pharmacokinetics and outcomes (effectiveness trough levels (Ctrough) and the area under the curve (AUC) cutoffs of 20 µg ml-1 and 360 µg ml-1 h-1, respectively; nonresponse AUC limit of 250 µg ml-1 h-1). Ninety-nine ß-thalassemic patients were enrolled. Drug plasma Ctrough and AUC were measured by the high-performance liquid chromatography system coupled with an ultraviolet determination method. Allelic discrimination for VDR, CYP24A1, CYP27B1 and GC gene SNPs was performed by real-time PCR. CYP24A1 22776 TT significantly influenced Cmin and negatively predicted it in regression analysis. CYP24A1 3999 CC was associated with Ctrough and Cmin and was a negative predictor of Tmax, whereas CYP24A1 8620 GG seemed to have a role in Ctrough, AUC, t1/2 and Cmin, and was an AUC negative predictor factor. Considering treatment outcome, Cdx2 and GC 1296 were retained in regression analysis as AUC efficacy cutoff negative predictors.

Cerebrospinal fluid abacavir concentrations in HIV-positive patients following once-daily administration.

Abacavir is a widely used nucleotide reverse transcriptase inhibitor, for which cerebrospinal fluid (CSF) exposure has been previously assessed in twice-daily recipients. We studied abacavir CSF concentrations in 61 and nine HIV-positive patients taking abacavir once daily and twice daily, respectively. Patients on once-daily abacavir had higher plasma and CSF concentrations (96 vs. 22 ng ml-1 , P = 0.038 and 123 vs. 49 ng ml-1 , P = 0.038) but similar CSF-to-plasma ratios (0.8 vs. 0.5, P = 0.500). CSF abacavir concentrations were adequate in patients receiving once-daily treatment.

Therapeutic drug monitoring of boosted PIs in HIV-positive patients: undetectable plasma concentrations and risk of virological failure.

Background: Therapeutic drug monitoring (TDM) of antiretroviral drugs is performed in selected HIV-positive patients. The aim of this study was to estimate the prevalence of undetectable plasma concentrations of ritonavir and boosted PIs and to evaluate the association between those and the 48 week risk of virological failure. Methods: A TDM registry study and a retrospective follow-up study were conducted. Plasma concentrations were measured through validated methods. According to PI and ritonavir concentrations, patients were stratified as adherent, partially non-adherent or non-adherent. Virological outcome was evaluated 48 weeks afterwards. Results: The TDM registry study included 2468 samples collected from 723 patients (68.1% male, median age 43.5 years). Eighty-seven samples (3.5%, 74 patients) and 68 samples (2.8%, 52 patients) were in the partially non-adherent and non-adherent groups, respectively; more patients on atazanavir/ritonavir (7.9%) versus darunavir/ritonavir (2% twice daily and 1.9% once daily) and lopinavir/ritonavir (1.5%; P < 0.001) were observed in the partially non-adherent group. Two hundred and ninety patients were included in the follow-up study (64.1% male, median age 40 years). Patients in the adherent group had a higher chance of viral control [81.9% (167/204)] versus the partially non-adherent group and the non-adherent group [71.7% (33/46) and 53.1% (17/32), respectively; P  =   0.001]. Based on multivariate analysis, baseline HIV RNA >50 copies/mL ( P < 0.001), genotypic susceptibility score ≤2 ( P = 0.001), lower nadir CD4 cell count ( P = 0.003) and not being in the adherent group ( P = 0.029) were independent predictors of HIV RNA >50 copies/mL at 48 weeks. Conclusions: The measurement of PI and ritonavir plasma levels can uncover incomplete compliance with treatment; TDM may represent a useful tool for identifying patients in need of adherence-promoting interventions.

Treatment with direct-acting antiviral agents of hepatitis C virus infection in injecting drug users: A prospective study.

In this prospective study, we evaluated the effectiveness and tolerability of novel therapies against hepatitis C virus (HCV) in a cohort of PWID enrolled at our centre from April 2015 to July 2016. In this analysis, a total of 174 patients were included: eleven (6.3%) were treated with pegylated interferon (PEG-IFN) and ribavirin (RBV) containing regimens, 163 (93.7%) with IFN-free treatments. RBV has been used in 70 patients (40.2%); 59 (33.9%) patients were in opioid substitution therapy (OST) with methadone or buprenorphine. Overall, sustained virological response (SVR) has been observed in 162 subject (93.1%), breakthrough (BT) in three (1.7%), relapse in one (0.6%) and dropout in eight (4.6%). Treatment was interrupted for clinical conditions in seven patients: six (3.4%) had hepatic decompensation and one died for hepatocellular carcinoma (HCC). In multivariate analysis, predictive factors of treatment failure were as follows: albumin level below 3 g/dL (OR=7.190; 95% IC=1.236-41.837; P<.001), MELD score >10 (OR=5.886; 95% IC=1.411-35.994; P<.001) and years of HCV infection >20 (OR=1.286; 95% IC=0.556-9.455; P=.016). In conclusion, treatment with DAAs was effective and well tolerated in PWID; cirrhotic subjects with MELD > 10 and albumin low level showed a higher risk of developing serious adverse events and treatment failure.

Efficacy of sofosbuvir and ledipasvir in an HCV+ gastro-resected patient.

WHAT IS KNOWN AND OBJECTIVE: The second-generation direct-acting antivirals represented the first major turning point for the eradication of HCV infection in almost all settings of patients. However, no data were available on use in gastro-resected patients. CASE DESCRIPTION: We report on a gastrectomized patient with chronic hepatitis C infection. She was treated with sofosbuvir and ledipasvir (SOF/LDV) for 12 weeks, with measurement of blood levels of the drugs. She obtained sustained virological response at week 12 and 24 without dose adjustment. WHAT IS NEW AND CONCLUSION: This case report can provide information useful for clinical practice in this set of patients and can open new perspectives in evaluating actual SOF/LDV bioavailability.

Clinical pharmacology of tenofovir clearance: a pharmacokinetic/pharmacogenetic study on plasma and urines.

The HIV virus and hepatitis B virus nucleotide reverse transcriptase inhibitor tenofovir has been associated with proximal tubular toxicity; the latter was found to be predicted by plasma concentrations and with single-nucleotide polymorphisms in transporters-encoding genes. A cross-sectional analysis in adult HIV-positive patients with estimated creatinine clearance >60 ml min-1 was performed. Twelve-hour plasma and urinary tenofovir concentrations and single-nucleotide polymorphisms in several transporter-encoding genes were analysed. In 289 patients 12-h tenofovir plasma, urinary and urinary to plasma ratios were 69 ng ml-1 (interquartile range 51.5-95), 24.3 mg ml-1 (14.3-37.7) and 384 (209-560). At multivariate analysis estimated creatinine clearance, protease inhibitors co-administration and SLC28A2 CT/TT genotypes were independently associated with plasma tenofovir exposure; ABCC10 GA/AA genotypes and protease inhibitor co-administration were independently associated with the urinary to plasma tenofovir ratio. Tenofovir clearance was associated with genetic polymorphisms in host genes and with co-administered drugs: if confirmed by ongoing studies these data may inform treatment tailoring and/or dose reductions.

Successful pharmacogenetics-based optimization of unboosted atazanavir plasma exposure in HIV-positive patients: a randomized, controlled, pilot study (the REYAGEN study).

BACKGROUND: Atazanavir without ritonavir, despite efficacy and tolerability, shows low plasma concentrations that warrant optimization. METHODS: In a randomized, controlled, pilot trial, stable HIV-positive patients on atazanavir/ritonavir (with tenofovir/emtricitabine) were switched to atazanavir. In the standard-dose arm, atazanavir was administered as 400 mg once daily, while according to patients' genetics (PXR, ABCB1 and SLCO1B1), in the pharmacogenetic arm: patients with unfavourable genotypes received 200 mg of atazanavir twice daily. EudraCT number: 2009-014216-35. RESULTS: Eighty patients were enrolled with balanced baseline characteristics. The average atazanavir exposure was 253 ng/mL (150-542) in the pharmacogenetic arm versus 111 ng/mL (64-190) in the standard-dose arm (P < 0.001); 28 patients in the pharmacogenetic arm (75.7%) had atazanavir exposure >150 ng/mL versus 14 patients (38.9%) in the standard-dose arm (P = 0.001). Immunovirological and laboratory parameters had a favourable outcome throughout the study with non-significant differences between study arms. CONCLUSIONS: Atazanavir plasma exposure is higher when the schedule is chosen according to the patient's genetic profile.

Influence of single-nucleotide polymorphisms on deferasirox C trough levels and effectiveness.

Deferasirox (DFX) is the only once-daily oral chelator for iron overload and its pharmacokinetic has been related with response to therapy. Our aim was to evaluate DFX plasma concentrations according to single-nucleotide polymorphisms in genes involved in its metabolism (UGT1A1, UGT1A3, CYP1A1, CYP1A2 and CYP2D6) and elimination (MRP2 and BCRP1). Further aim was to define a plasma concentration cutoff value predicting an adequate response to therapy. Plasma concentrations were determined at the end of dosing interval (C trough) using an high-performance liquid chromatography-ultraviolet method. Allelic discrimination was performed by real-time PCR. C trough levels were influenced by UGT1A1C>T rs887829, CYP1A1C>A rs2606345, CYP1A2A>C rs762551, CYP1A2C>T rs2470890 and MRP2G>A rs2273697 polymorphisms. A DFX plasma efficacy cutoff value of 20,000 ng ml(-1) was identified; CYP1A1C>A rs2606345 AA and CYP1A2C>T rs2470890 TT genotypes may predict this value, suggesting a negative predictive role in therapy efficacy. Our data suggest the feasibility of a pharmacogenetic-based DFX dose personalization.

Role of CYP27B1+2838 promoter polymorphism in the treatment of chronic hepatitis B HBeAg negative with PEG-interferon.

In HBV-infected patients, the vitamin D deficiency has been related to chronic liver diseases, progression of hepatic fibrosis and poor response to the treatment. The CYP27B1 gene, which encodes the 1-α-hidroxylase and involved in the 1,25-dihydroxyvitamin D synthesis, was recently associated to type-1 diabetes, autoimmune disorders and treatment response in HCV. Then, we aimed to investigate the role of CYP27B1 polymorphisms in HBV treatment with PEG-IFN. We retrospectively enrolled 190 patients with chronic hepatitis B HBeAg negative treated for 48 weeks with PEG-IFN α-2a. We examined the role of rs4646536 CYP27B1 SNP (CYP27B1+2838) according to virological and serological response. Our results showed that the TT genotype of CYP27B1+2838 was significantly prevalent in patients with end-of-therapy virological response (37.6%) vs CT/CC (9.4%) (P < 0.001). Virological relapse was prevalent in patients with CT/CC genotype (12.6%) vs TT genotype (2.1%) (P < 0.001). TT genotype was also related to HBsAg loss (P = 0.004) and anti-HBs appearance (P = 0.002). In the multivariate analysis, the TT genotype resulted to be a good positive predictor of sustained virological response (OR = 5.632, IC = 1.938-16.368, P = 0.001) and serological response (OR = 6.161, IC = 1.856-20.457, P = 0.003). The CYP27B1+2838 polymorphism may be useful as pretreatment factor to selection of patients with higher probability of response to therapy.

Significant early higher ribavirin plasma concentrations in patients receiving a triple therapy with pegylated interferon, ribavirin and telaprevir.

The new standard of care for treatment for infection with genotype 1a/b of HCV now is the combination of telaprevir (TLV) with ribavirin (RBV) and pegylated interferon (Peg-IFN). Although this new therapy gives a higher response rate than the Peg-IFNα plus RBV treatment, a greatly higher rate of anaemia onset has been reported in all clinical trials. Because haemolysis is a typical concentration-dependent side effect of RBV, modulated by ITPA gene polymorphisms, we aimed to compare the early RBV plasma exposure of nine patients after 2 weeks of treatment with triple therapy with RBV concentrations of 187 patients treated with RBV and Peg-IFNα over the same time scale; this comparison was performed also stratifying patients according to ITPA polymorphism genotype and anaemia onset after 1 month of treatment. All TLV-treated patients had unfavourable ITPA genetic profile and developed anaemia. Moreover, both the rate of anaemia onset and the haemoglobin loss at 1 month were significantly higher in patients treated with TLV. This observation has been confirmed also in patients with the same ITPA genetic profile in double therapy. Strikingly, also early RBV plasma concentrations were significantly higher in patients treated with TLV. These unbiased results confirm the observations recently reported and suggest that the high rate of anaemia onset could be mainly due to the increased RBV exposure, probably caused by a 'boosting effect' by TLV. These data highlight the great importance of early therapeutic drug monitoring of RBV in the management of anaemia in the triple therapy.

Pharmacogenetics of tenofovir drug transporters in the context of HBV: Is there an impact?

BACKGROUND: Current treatments for chronic hepatitis B management include orally administered nucleos(t)ide analogues, such as tenofovir (TDF), which is an acyclic adenine nucleotide analogue used both in HBV and human immune deficiency virus (HIV). The course of HBV infection is mainly dependent on viral factors, such as HBV genotypes, immunological features and host genetic variables, but a few data are available in the context of HBV, in particular for polymorphisms of genes encoding proteins involved in drug metabolism and elimination. Consequently, the aim of this study was to evaluate the potential impact of genetic variants on TDF plasma and urine concentrations in patients with HBV, considering the role of HBV genotypes. METHODS: A retrospective cohort study at the Infectious Disease Unit of Amedeo di Savoia Hospital, Torino, Italy, was performed. Pharmacokinetic analyses were performed through liquidi chromatography, whereas pharmacogenetic analyses through real-time PCR. FINDINGS: Sixty - eight patients were analyzed: ABCC4 4976 C>T genetic variant showed an impact on urine TDF drug concentrations (p = 0.014). In addition, SLC22A6 453 AA was retained in the final regression multivariate model considering factors predicting plasma concentrations, while ABCC4 4976 TC/CC was the only predictor of urine concentrations in the univariate model. INTERPRETATION: In conclusion, this is the first study showing a potential impact of genetic variants on TDF plasma and urine concentrations in the HBV context, but further studies in different and larger cohorts of patients are required.

Tenofovir plasma concentrations according to companion drugs: a cross-sectional study of HIV-positive patients with normal renal function.

As the risk of tenofovir-associated renal toxicity has been found to be proportional to the drug plasma concentration, our aim was to measure the determinants of tenofovir plasma exposure in HIV-positive patients with normal renal function. A cross-sectional analysis was conducted in HIV-positive patients chronically receiving tenofovir-containing highly active antiretroviral therapies (HAARTs). Patients on tenofovir-containing antiretroviral regimens, presenting 22 to 26 h after drug intake, having estimated glomerular filtration rates above 60 ml/min, reporting high adherence to antiretroviral medications (above 95% of the doses), and signing a written informed consent were included. Plasma tenofovir concentrations were measured through a validated high-performance liquid chromatography-mass spectrometry (HPLC/LC-MS) method. The tenofovir trough concentrations in 195 patients (median, 50 ng/ml, and interquartile range, 35 to 77 ng/ml) were significantly associated with the estimated glomerular filtration rate, body mass index, and third-drug class (protease-containing versus protease-sparing regimens) (with the highest exposure in unboosted-atazanavir recipients). The results of multivariate analysis showed that the third-drug class and the weight/creatinine ratio were independent predictors of tenofovir trough concentrations. This cross-sectional study shows that tenofovir trough concentrations are predicted by the weight/creatinine ratio and by the coadministered antiretrovirals, with protease inhibitors (whether boosted or unboosted) being associated with the highest plasma exposure. These data, previously available in healthy subjects or for some drugs only, could be useful for designing strategies to manage tenofovir-associated toxicity, since this toxicity has been reported to be dose dependent.

Sequential therapy with entecavir and PEG-INF in patients affected by chronic hepatitis B and high levels of HBV-DNA with non-D genotypes.

Complete eradication of hepatitis B virus (HBV) is rarely achieved. Treatment options include currently available nucleos(t)ide analogues and pegylated interferon. The aim of our exploratory study was to assess the effectiveness of sequential therapy for chronic hepatitis B (CHB) vs the current standard of care. We evaluated an association with entecavir and pegylated interferon alfa-2a (PEG-IFN) in 20 patients with hepatitis B, high HBV viremia and genotypes A, B, C and E. Patients received entecavir alone for 12 weeks, then entecavir and PEG-IFN for 12 weeks, lastly PEG-IFN alone for 36 weeks. The results were compared with 20 patients (control group) treated in the past with 48 weeks of PEG-IFN monotherapy. Our results show that complete sustained virological response (SVR) and partial SVR were, respectively, 60% and 80% in the study group and 10% and 30% in the control group; anti-HBe seroconversion rate were 76.9% vs 15%, and anti-HBs seroconversion were 20% vs 0%, respectively. We found a correlation among different genotypes and virological and serological outcomes - genotype C has a better virological response, while genotype A had a better serological response, and E genotype had a poor response. These results show that a sequential approach is a promising strategy of treatment in patients with CHB and high viremia in comparison with PEG-IFN monotherapy. The E genotype seems to have the worse rate of response and requires other treatment strategies.

Short-term additional enfuvirtide therapy is associated with a greater immunological recovery in HIV very late presenters: a controlled pilot study.

OBJECTIVES: To evaluate whether the addition of enfuvirtide to standard highly active antiretroviral therapy (HAART) could confer immunovirological benefits in human immunodeficiency virus (HIV)-infected very late presenters. The current study is an open comparative therapeutic trial of standard protease inhibitor (PI)-based HAART ± additional enfuvirtide in treatment-naïve deeply immunologically impaired HIV-positive patients. METHODS: Very late presenters (CD4 <50/mm(3)), without tuberculosis and neoplasms, were alternatively allocated to two nucleoside reverse transcriptase inhibitors (NRTIs) and lopinavir/ritonavir without (control arm, CO) or with (ENF arm) enfuvirtide 90 mg bid. Enfuvirtide was administered until the achievement of viral load <50 copies/ml and for at least 24 weeks. The primary objective was the magnitude of CD4+ cell recovery at 6 months. HIV RNA was intensively monitored in the first month, and, thereafter, monthly, as for CD4+ cell count and percentage, clinical data, and plasma drug concentrations. RESULTS: Of 22 enrolled patients (11 per arm), 19 completed the study (10 in the ENF arm). Baseline CD4+ cell counts and % were comparable, with 20 CD4+/mm(3) (12-37) and a percentage of 3.3 (1.7-7.1) in the ENF arm, and 16 CD4+/mm(3) (9-29) and a percentage of 3.1 (2.3-3.8) in the CO arm, respectively. The baseline viral load was also comparable between the two arms, with 5.77 log10 (5.42-6) and 5.39 log10 (5.06-6) in the ENF and CO arms, respectively. Enfuvirtide recipients had higher CD4+ percentage at week 8 (7.6 vs. 3.6%, p = 0.02) and at week 24 (10.7 vs. 5.9%, p = 0.02), and a greater CD4+ increase at week 24 (207 vs. 134 cells/mm(3), p = 0.04), with 70% of enfuvirtide intakers versus 12.5% of controls who achieved a CD4+ cell count >200/mm(3) (p = 0.01). At 48 weeks, patients in the ENF arm had CD4+ cell counts higher than controls (251 vs. 153cells/mm(3), p = 0.04) and were also found to be faster in reaching a CD4 cell count over 200/mm(3): 18 (8-24) versus 48 (36-108) weeks (p = 0.01). Viral load decay at week 4 was greater in the ENF arm (-3 vs. -2.2 log, p = 0.04), while the proportion of patients with viral load <50 copies/ml at week 24 was comparable. CONCLUSIONS: In this pilot study, the addition of enfuvirtide to a lopinavir-based HAART was shown to be associated with a significantly faster and greater immunological recovery in newly discovered HIV-positive patients with very low CD4+ cell counts. Induction strategies using an enfuvirtide-based approach in such subjects warrant further investigation.

Pharmacokinetic and safety profile of raltegravir and ribavirin, when dosed separately and together, in healthy volunteers.

BACKGROUND: Treatment of chronic hepatitis C virus (HCV) infection in HIV-1-co-infected individuals remains challenging due to numerous factors, including drug-drug interactions. The aim of this study was to assess the safety and pharmacokinetic (PK) profile of raltegravir and ribavirin when dosed separately and together. METHODS: Fourteen healthy volunteers [mean (standard deviation) age 35 (10) years, 71% male] entered this phase 1 PK study and received single-dose ribavirin (800 mg) on day 1 (phase 1). Following a washout period, subjects received raltegravir (400 mg twice daily) on days 15-19 (phase 2) and single-dose ribavirin (800 mg) with raltegravir (400 mg) on day 20 (phase 3). Intensive PK sampling was undertaken on days 1, 19 and 20 and differences in geometric mean ratios (GMRs) for PK parameters between study periods were assessed. RESULTS: No statistically significant differences in PK parameters were observed for raltegravir between phases 2 and 3. A statistically significant decrease in maximum plasma concentration (C(max)) and an increase in time to maximum plasma concentration (T(max)) were observed for ribavirin in phase 3 compared with phase 1 [GMR (95% confidence interval) 0.79 (0.62-1.00) and 1.39 (1.08-1.78), respectively], whereas no significant differences in other ribavirin PK parameters were observed between study phases. No clinically significant safety concerns were reported. CONCLUSIONS: The PK profile of ribavirin is altered when administered with raltegravir (reduced C(max) and increased T(max)), with no safety concerns identified. This is unlikely to be of clinical significance or have an impact on the antiviral effects of ribavirin in HIV-1- and HCV-co-infected subjects.