Echocardiogram by apical-subcostal protocol in prone position during invasive mechanical ventilation in cardiovascular intensive care unit.

AIMS: To evaluate the feasibility of a transthoracic echocardiogram using an apical-subcostal protocol in invasive mechanical ventilation (IMV) and prone position. METHODS: Prospective study of adults who required a prone position during IMV. A pillow was placed only under the left hemithorax in the prone position to elevate and ease the apical and subcostal windows. A critical care cardiologist (prone group) acquired and evaluated the images using the apical-subcostal protocol. Besides, we used ambulatory echocardiograms performed as a comparative group (supine group). RESULTS: 86 patients were included, 43 in the prone and 43 in the supine. In the prone group, the indication to perform an echocardiogram was hemodynamic monitoring. All patients were ventilated with protective parameters, and the mean end-expiratory pressure was 10.6 cmH2O. The protocol was performed entirely in 42 of 43 patients in the prone group because one patient did not have any acoustic window. In the 43 patients in the prone group analyzed and compared to the supine group, global biventricular function was assessed in 97.7% (p = 1.0), severe heart valve disease in 88.4% (p = 0.055), ruled out of the presence of pulmonary hypertension in 76.7% (p = 0.80), pericardial effusion in 93% (p = 0.12), and volume status by inferior vena cava in 93% (p = 0.48). Comparing prone versus supine position, a statistical difference was found when evaluating the left ventricle apical 2-chamber view (65.1 versus 100%, p < 0.01) and its segmental function (53.4 versus 100%, p < 0.01). CONCLUSION: The echocardiogram using an apical-subcostal protocol is feasible in patients in the IMV and prone position.

Interventricular Septal Hematoma Complicating Left Branch Bundle Lead Implantation: Treatment by Covered Stent.

We present a female patient with heart failure with reduced ejection fraction who underwent left bundle branch cardiac resynchronization therapy. Left bundle branch lead implantation was complicated with septal branch perforation causing an iatrogenic coronary fistula complicated by septal hematoma formation and development of shock. Occlusion by covered stents was successfully achieved.

Negative predictive value of IL28B, SLC28A2, and CYP27B1 SNPs and low RBV plasma exposure for therapeutic response to PEG/IFN-RBV treatment.

OBJECTIVES: The response rate to treatment of chronic hepatitis C virus-genotype 1 and 4 infections was recently found to be strongly influenced by many polymorphisms. The aim of our study was to carry out an integrated analysis of the effects of polymorphisms and ribavirin (RBV) plasma exposure on outcome. METHODS: The retrospective analysis included 174 patients. IL28B, CYP27B1, SLC29A1, SLC28A3, and SLC28A2 polymorphisms were genotyped and tested for association with sustained virological response. The impact of RBV plasma exposure during the first 3 months of therapy on outcome was also investigated. RESULTS: Considering patients infected by hepatitis C virus-1/4, 3 polymorphisms (IL28B rs8099917TT, CYP27B1 rs4646536TT, and CNT2 rs11854484TT) were associated with sustained virological response. The number of negative variant allele and low RBV exposure were correlated to percentage increasing to therapy failure, suggesting some degree of cumulative effect of the 4 factors. A cutoff of 2.5 µg/mL of RBV was found to be associated with outcome (area under ROC [AUROC] curve = 0.64, sensitivity = 55.0%, and specificity = 71.2%, P = 0.020). In multivariate logistic regression analyses, each variant allele and RBV plasma exposure cutoff were independently associated with outcome. CONCLUSIONS: In this study, we found that additional polymorphisms and RBV plasma exposure are also able to influence the achievement of response. Regardless of the magnitude of RBV pharmacokinetic exposure, the negative predictive value of the polymorphisms here investigated is much stronger than the positive one.

Inosine triphosphatase polymorphisms and ribavirin pharmacokinetics as determinants of ribavirin-associate anemia in patients receiving standard anti-HCV treatment.

BACKGROUND: Functional variants of inosine triphosphatase (ITPA) were recently found to protect against ribavirin (RBV)-induced hemolytic anemia. However, no definitive data are yet available on the role of plasma RBV concentrations on hemoglobin (Hb) decrement. Moreover, no data have been published on the possible interplay between these 2 factors. METHODS: A retrospective analysis included 167 patients. The ITPA variants rs7270101 and rs1127354 were genotyped and tested using the χ test for association with Hb reduction at week 4. We also investigated, using multivariate logistic regression, the impact of RBV plasma exposure on Hb concentrations. RESULTS: Both single nucleotide polymorphisms were associated with Hb decrease. The carrier of at least 1 variant allele in the functional ITPA single nucleotide polymorphisms was associated with a lower decrement of Hb (-1.1 g/dL), as compared with patients without a variant allele (-2.75 g/dL; P = 4.09 × 10). RBV concentrations were not influenced by ITPA genotypes. A cut-off of 2.3 µg/mL of RBV was found to be associated with anemia (area-under-receiver operating characteristic = 0.630, sensitivity = 50.0%, and specificity = 69.5%, P = 0.008). In multivariate logistic regression analyses, the carrier of a variant allele (P = 0.005) and plasma RBV concentrations <2.3 µg/mL (P = 0.016) were independently associated with protection against clinically significant anemia at week 4. CONCLUSIONS: Although no direct relationship was found between ITPA polymorphisms and plasma RBV concentrations, both factors were shown to be significantly associated with anemia. A multivariate regression model based on ITPA genetic polymorphisms and RBV trough concentration was developed for predicting the risk of anemia. By relying upon these 2 variables, an individualized management of anemia seems to be feasible in recipients of pegylated interferon-RBV therapy.

Pharmacokinetics of switching unboosted atazanavir coadministered with tenofovir disoproxil fumarate from 400 mg once daily to 200 mg twice daily in HIV-positive patients.

BACKGROUND: Use of unboosted atazanavir (ATV) with tenofovir disoproxil fumarate (TDF), although attractive from a clinical view point, has not been tested in trials and is not currently recommended because of the risk of suboptimal ATV pharmacokinetics (PK). In order to improve ATV exposure, plasma and intracellular (IC) PK of ATV in patients administered with ATV 400 mg once daily and TDF/emtricitabine (FTC) and switched to ATV 200 mg twice daily were studied. METHODS: On day 0, 10 subjects on ATV 400 mg plus TDF/FTC once daily underwent intensive plasma and IC PK evaluation and bilirubin measurement. Patients were subsequently switched to ATV 200 mg twice daily for 10 days. On day 11, they once again underwent intensive PK and bilirubin evaluation. RESULTS: Switch to 200 mg twice daily led (in plasma) to a significant increase of the observed concentration at the end of dosing interval (C(trough); ratio twice daily/once daily 2.20; P=0.005), with a decrease from 60% to 20% of suboptimal values, a significant decrease of the maximum concentration (C(max); ratio twice daily/once daily 0.47; P=0.022), whereas no differences of other PK parameters or bilirubin were observed. IC ATV concentrations at 400 once daily showed higher C(trough) (ratio peripheral blood mononuclear cells [PBMCs]/plasma 2.86; P=0.005) and longer half-life (ratio PBMCs/plasma 1.44; P=0.007) as compared with plasma. After the switch, IC ATV accumulation showed changes similar to plasma. CONCLUSIONS: Switch to 200 mg twice daily appeared to optimize plasma and IC ATV PK, by increasing the determinant of efficacy (C(trough)) and decreasing C(max), without significant effect on total ATV plasma exposure and bilirubin. Dosage of 200 mg might provide an option to patients showing suboptimal ATV exposure with standard unboosted dosing.

Comparative evaluation of seven resistance interpretation algorithms and their derived genotypic inhibitory quotients for the prediction of 48 week virological response to darunavir-based salvage regimens.

BACKGROUND: the darunavir genotypic inhibitory quotient (gIQ) has been suggested as one of the predictors of virological response to darunavir-containing salvage regimens. Nevertheless, which resistance algorithm should be used to optimize the calculation of gIQ is still debated. The aim of our study was to compare seven different free-access resistance algorithms and their derived gIQs as predictors of 48 week virological response to darunavir-based salvage therapy in the clinical setting. METHODS: patients placed on two nucleoside reverse transcriptase inhibitors + 600/100 mg of darunavir/ritonavir twice daily  ±â€Š enfuvirtide were prospectively evaluated. Virological response was assessed at 48 weeks. Darunavir resistance interpretation was performed according to seven different algorithms, of which two were weighted algorithms. Analysis of other factors potentially associated with virological response at 48 weeks was performed. RESULTS: fifty-six treatment-experienced patients were included. Overall, 35 patients (62.5%) had a virological response at 48 weeks. Receiver operator characteristic curve analysis showed that De Meyer's weighted score (WS) and its derived gIQ (gIQ WS) were the most accurate parameters defining virological response, and related cut-offs showed the best sensitivity/specificity pattern. In univariate logistic regression analysis, baseline log viral load (P = 0.028), optimized background score ≥ 2 (P = 0.048), WS >5 (P = 0.001) and WS gIQ ≥ 600 (P < 0.0001) were independently associated with virological response. In multivariate analysis, only baseline log viral load (P = 0.008) and WS gIQ ≥ 600 (P < 0.0001) remained in the model. CONCLUSIONS: in our study, although different resistance interpretation algorithms and derived gIQs were associated with virological response, gIQ WS was the most accurate predictive model for achieving a successful virological response.

Ultrasensitive assessment of residual HIV viraemia in HAART-treated patients with persistently undetectable plasma HIV-RNA: a cross-sectional evaluation.

Improvements in HIV-RNA assays have made accurate detection of as few as 2 copies/ml possible. This study objective was the evaluation of ultrasensitive HIV-RNA quantitation (beneath current threshold: 50 copies/ml) in patients receiving different antiretroviral regimens. A cross-sectional, ultrasensitive measurement of HIV-RNA levels (detection limit: 2.5 HIV-RNA copies/ml) was performed in 154 HIV-1-infected patients receiving ARV therapy, all classed as full responders according to the 50 copies/ml cut-off. Patients were undergoing treatment with two nucleoside/nucleotide reverse transcriptase inhibitors (N/NtRTIs) plus nevirapine (NVP, n = 48), efavirenz (EFV, n = 57) or lopinavir/ritonavir (LPV/r, n = 49). Undetectable HIV-RNA (<2.5 copies/ml) occurred in 29/48 (60.4%), 24/57 (42.1%) and 14/49 (28.6%) NVP, EFV and LPV/r recipients, respectively. Mean virological-suppression (<50 copies/ml) duration was 28.6 months (median = 22, SD = 17.8), and only in LPV/r recipients length of suppression was associated with significantly lower HIV-RNA levels (P = 0.015). Mean nadir CD4+ cell count of 270 cells/mm(3) (median = 240, SD = 194.5) was significantly lower in the LPV/r arm (P < 0.001). Nadir CD4+ level correlated with virological suppression but had opposite trends between NVP (positive) and LPV/r (negative; two tailed P = 0.01). Logistic regression analysis showed NVP was the only independent factor associated with virologic suppression. NVP has demonstrated a distinct virological advantage at sub-clinical viral loads, possibly due to its greater penetration in extra-vascular compartments, warranting further investigation in the context of persistent low-level viraemia in long-term HAART.

Unboosted fosamprenavir is associated with low drug exposure in HIV-infected patients with mild-moderate liver impairment resulting from HCV-related cirrhosis.

OBJECTIVES: The aim of this study was to compare amprenavir pharmacokinetics in HIV/hepatitis C virus (HCV)-co-infected cirrhotic patients receiving non-boosted fosamprenavir 700 mg twice daily with HCV/HIV-co-infected non-cirrhotic subjects and HIV-mono-infected subjects receiving fosamprenavir/ritonavir 700/100 mg twice daily. Liver stiffness at baseline and alanine aminotransferase levels at baseline and during follow-up were measured in order to find a correlation between drug levels and liver fibrosis or hepatotoxicity. METHODS: Amprenavir plasma concentration was determined by HPLC. Liver stiffness was measured by transient elastometry. Liver function tests were determined every 1-3 months during follow-up. RESULTS: Nineteen HIV-infected patients were included. Eight had chronic HCV hepatitis (group NC), five had HCV-related liver cirrhosis (group C) and six were HIV-mono-infected (group M). In group C patients, amprenavir C(trough), AUC(0-12) and half-life were 86%/83%, 64%/55% and 58%/59% lower when compared with controls and co-infected subjects without cirrhosis, respectively; conversely, drug clearance in cirrhotics was 181%/124% higher. In 3/5 cirrhotic patients (60%) and in 2/14 non-cirrhotic patients (14%), C(trough) was below the minimum target concentration of 400 ng/mL; nonetheless, in all these patients, HIV viral load was undetectable. No correlation was found between amprenavir pharmacokinetics and liver stiffness or hepatotoxicity at follow-up. CONCLUSIONS: On the basis of these data, it seems reasonable to boost fosamprenavir with ritonavir even in cirrhotic patients; amprenavir pharmacokinetics could not be predicted by liver stiffness and seem not to predict hepatotoxicity at follow-up.

A new assay based on solid-phase extraction procedure with LC-MS to measure plasmatic concentrations of tenofovir and emtricitabine in HIV infected patients.

A new solid-phase extraction (SPE) method has been developed and validated on a liquid chromatography (LC) coupled with a mass spectrometer for the determination of plasma concentrations of tenofovir (TNF) and emtricitabine (FTC) in HIV infected patients. Chromatographic separation was achieved with a gradient (acetonitrile and water with formic acid 0.05%) on an Atlantis 4.6 mm x 150 mm, reversed phase analytical column. Detection of TNF, FTC, and internal standard (IS) was achieved by electrospray ionization mass spectrometry (ESI-MS) in the positive ion mode. Calibration ranged from 15.6 to 4000 ng/mL for TNF and 11.7 to 3000 ng/mL for FTC. Plasma was analyzed, and the limit of quantitation was 15.6 ng/mL for TNF and 11.7 ng/mL for FTC; limit of detection was 2 ng/mL for TNF and 1.5 ng/mL for FTC. Mean recovery of TNF, FTC, and IS were 46.5% [relative standard deviation (RSD): 8.8%] and 88.8% (RSD: 1.0%), and 81.7% (RSD: 3.1%), respectively. The method did not show any significant interference with antiretrovirals or other concomitant drugs administered to patients, and no significant "matrix effects" were observed. The method was applied for the determination of antiretroviral plasma concentration of HIV-positive patients treated with FTC and/or TNF, in combination with various other antiretrovirals.

Pharmacokinetic and pharmacodynamic determinants of early virological response to enfuvirtide-based regimens in HIV-positive patients.

BACKGROUND: Early virological response (VR) to enfuvirtide-based salvage regimens at week 12 has been described as a predictor of long-term therapeutic success. The relationship between enfuvirtide plasma exposure and VR has not yet been investigated in the clinical setting. Our aim was to investigate the role of enfuvirtide plasma exposure as a determinant of early VR in the clinical setting. METHODS: Forty-two multidrug-experienced patients starting a salvage enfuvirtide-based regimen were prospectively evaluated over a 12 week period. HIV-RNA levels and enfuvirtide C(trough) were regularly measured. VR was considered as achievement of viral load (VL) undetectability and/or a decrease of more than 1 log at week 12. RESULTS: Optimized background score (OBS) and enfuvirtide C(trough) concentrations were associated with VL decrease at week 12. An OBS > or =2 and enfuvirtide C(trough) >2100 ng/mL were associated with VR. The pharmacokinetic/pharmacodynamic (PK/PD) analysis confirmed this exposure-response relationship both in the total population and in different groups according to OBS <2 or > or =2. Higher estimates of IC(50) were calculated for the OBS <2 group when compared with the OBS > or =2 group (7551 versus 2330 ng/mL, respectively), without a marked difference in I(0) (0.31 versus 0.21 log) and I(max) (-2.64 versus -3.33 log). CONCLUSIONS: Enfuvirtide plasma exposure and OBS were found to significantly influence the magnitude and rate of early VR. The PK/PD modelling of enfuvirtide concentrations was different in our clinical setting, compared with previous data obtained under trial conditions. Therefore, optimization of enfuvirtide plasma exposure could deserve further evaluation as a determinant of therapeutic response in HIV-positive patients.

Does iatrogenic scleroderma due to injection-site reaction to enfuvirtide impair absorption of the drug?

BACKGROUND: Chronic iatrogenic scleroderma is a possible obstacle to the absorption of subcutaneously administered drugs. This study correlated the clinical and histopathological pattern of injection-site reactions (ISRs) to the pharmacokinetics of enfuvirtide in patients with HIV. METHODS: Fourteen patients treated with an enfuvirtide-based antiretroviral regimen for a median of 45 weeks were enrolled and their ISRs were evaluated. Twelve patients with evidence of ISRs underwent cutaneous biopsies using a 4-mm punch. The maximum plasma enfuvirtide concentration (Cmax) and the area under the enfuvirtide concentration-time curve (AUC) were assessed using blood sampling. RESULTS: Four different macroscopic patterns of ISR were identified: A--no evidence of cutaneous lesions; B--transient infiltrative lesions that auto-resolved within 24 hours; C--transient nodular lesions that auto-resolved within 7-15 days; and D--stable lesions after more than 30 days. Histological examination showed three morphological patterns: (1) acute urticaria/vasculitis-like pattern, (2) subacute pattern and (3) chronic scleroderma-like pattern. No differences among patients with the various patterns of ISRs were observed, except for a higher Cmax and AUC in patients with pattern 1. CONCLUSIONS: These results confirm that although iatrogenic scleroderma is not related to impaired enfuvirtide absorption, higher Cmax and AUC values are observed in patients with urticaria/vasculitis-like patterns.

Tipranavir (TPV) genotypic inhibitory quotient predicts virological response at 48 weeks to TPV-based salvage regimens.

The virological response (VR) to a tipranavir-ritonavir (TPV-RTV)-based regimen had been shown to be associated with a number of mutations in the protease gene, the use of enfuvirtide (T20), and the TPV phenotypic inhibitory quotient (IQ). The role of the TPV genotypic IQ (gIQ) has not yet been fully investigated. The aim of our study was to evaluate the relationship between the TPV gIQ and the VR at 48 weeks to TPV-based salvage regimens. Patients placed on regimens containing two nucleoside reverse transcriptase inhibitors plus TPV-RTV 500/200 mg twice a day with or without T20 were prospectively studied. Regular follow-up was performed over the study period. VR, considered a viral load (VL) decrease of >or=1 log unit and/or the achievement of <50 copies/ml with no VL rebound of >0.5 log unit compared to the maximal VL decrease at week 48, was assessed. Thirty-eight patients who had received multiple drugs were included. At week 48 the VL decrease was -1.48 (interquartile range [IQR], -2.88 to -0.48), 15 patients (39.5%) had VLs of <50 copies/ml, and the CD4+ cell count increase was 37 cells/mm3 (IQR, -30 to +175). Twenty subjects (52.6%) achieved VRs. The TPV gIQ and optimized background score (OBS) were independently associated with higher VL decreases. The TPV gIQ and OBS were also independent predictors of a VR at week 48. TPV gIQ and OBS cutoff values of 14,500 and 2, respectively, were associated with a higher rate of VR. The TPV gIQ was shown to be able to predict the VR at 48 weeks to TPV-containing salvage regimens better than the TPV trough concentration or TPV-associated mutations alone. A possible TPV gIQ cutoff value of 14,500 for reaching a VR at week 48 was suggested. Further studies are needed in order to evaluate the calculation of TPV gIQ as a new tool for the optimization of TPV-based salvage therapy.

Estudio experimental de los efectos producidos por el bromuro de pinaverio y el tegaserod sobre el aparato gastrointestinal en animales de experimentación

Introducción: en un grupo de ratas se produjo diarrea o estreñimiento inducido por el uso de medicamentos favorecedores de la secreción o medicamentos constipadores. En estas ratas se utilizo el bromuro de pinaverio y el tegaserod como medicamentos favorecedores o de la disminución de la frecuencia defecatoria o como promotores de la defecación, respectivamente. Este trabajo tiene como objetivo averiguar hasta que punto estos medicamentos pueden ser utilizados como tratamiento efectivo en el síndrome de intestino irritable. Métodos: se utilizaron 12 ratas femeninas, adultas, de la raza Sprague Dowley, las cuales se distribuyeron de la siguiente manera: 2 ratas control para diarrea, 4 a las que se les indujo diarrea con una mezcla de fenolftaleina y sulfato de magnesio y 2 de ellas se trataron con tegaserod y 2 con bromuro de pinaverio. En el estreñimiento se utilizaron 2 ratas control, a 4 de ellas se les aplicó loperamida para inducir el estreñimiento y se trataron 2 con tegaserod y 2 con bromuro de pinaverio. Resultados: ratas con diarrea: con respecto a estas ratas las variaciones de peso conseguidas entre los controles y la medicadas fueron altamente significativas, indicando que ambos medicamentos mejoraron el estado patológico de las mismas. Ratas con estreñimiento: con respecto a estas ratas lo único importante es que la ganancia de peso fue significativa en las que recibieron bromuro de pinaverio. Conclusión: en nuestro estudio demostramos que tanto el tegaserod como el bromuro de pinaverio pueden ser efectivos en la diarrea, así como en el estreñimiento en un modelo experimental en ratas.

Introduction: Diarrhea or constipation was induced in a group of rats by the use of drugs that stimulate secretion or drugs inducing constipation. In these rats pinaverium bromide and tegaserod were used as a drug inducing less bowel movement or as a facilitator of defecacion, respectively. This work has as its main objective to find out until what point can these drugs be used as an efective treatment for irritable bowel syndrome. Methods: 12 adult female rats, Sprague Dowley breed, were used. They were distributed in the following way: 2 as control for diarrhea, 4 of them had induced diarrhea with a phenolphthalein mixture and magnesium sulphate; 2 with Tegaserod and 2 with Pinaverium Bromide. In constipation, 2 rats were used as control, 4 of them were administered loperamide to induce constipation, and 2 were treated with Tegaserod and 2 with Pinaverium Bromide. Results: Rats with Diarrhea: With respect to these rats, the variations in weight obtained among controls and the medicated group were highly significant, indicating that both drugs improved their pathological condition. Rats with Constipation: With respect to these rats the one important thing is that gain weight was significant only in the group that received Pinaverium Bromide. Conclusion: In our study we demonstrated that both, Tegaserod and Pinaverium Bromide can be effective treating diarrhea and constipation in an experimental model in rats.

A simple and sensitive assay for determining plasma tipranavir concentration in the clinical setting by new HPLC method.

A simple method for the quantification of tipranavir, the first non-peptidic HIV protease inhibitor, was developed and validated. Quinoxaline, as internal standard, was added to 50 microl of plasma before a liquid-liquid extraction by 600 microl of protein precipitation solution. The extracts were diluted before being injected in the chromatographic system. Chromatographic separation was made on a C18 column using potassium phosphate buffer (pH 3.2) and acetonitrile with gradient. Detection was performed by an UV detector at 260 nm. Relative error at three control quality concentrations ranged from -1.81 to 1.72%. Intra-day (CV%) and inter-day (CV%) precision ranged from 0.94 to 2.55% and from 3.07 to 4.24%, respectively. LOQ and LOD were 0.090 microg/ml and 0.035 microg/ml, respectively. Mean recovery was 87.1%+/-2.4%. Calibration curve was linear up to 180 microg/ml. Concentration range when optimized (0.703-180 microg/ml) proved to be adequate to measure tipranavir concentration in HIV-1-positive patients, therefore this method could be suitable for therapeutic drug monitoring of this drug.

Unexpected drug-drug interaction between tipranavir/ritonavir and enfuvirtide.

Fifty-five patients placed on tipranavir/ritonavir 500/200 mg twice a day (27 with enfuvirtide and 28 without) underwent tipranavir and ritonavir plasma concentration measurements by high-pressure liquid chromatography. Markedly higher tipranavir and ritonavir trough concentrations were observed in enfuvirtide recipients. The modelling of sparse plasma samples using a first order absorption and elimination monocompartmental model without time lag predicted higher tipranavir elimination half-life and volume of distribution in enfuvirtide takers. This unexpected drug-drug interaction warrants further investigation.

Validation of liquid/liquid extraction method coupled with HPLC-UV for measurement of ribavirin plasma levels in HCV-positive patients.

Measurement of ribavirin plasma levels in HCV-positive patients have been shown to be useful in order to optimise individual ribavirin exposure. Efficacy and toxicity of this drug are shown to be concentration-dependant. A simple HPLC-UV method was developed and validated, which has an easy liquid/liquid extraction, sensitive limit of detection, without any interference peaks, reproducible and linear over the range of clinical relevant concentrations. The assay warrants further evaluation as a tool for ribavirin therapeutic drug monitoring in HCV-positive patients.

An improved HPLC fluorimetric method for the determination of enfuvirtide plasma levels in HIV-infected patients.

An improved HPLC fluorimetric method for the quantification of enfuvirtide in plasma of HIV-infected subjects was described and validated. The use of an internal standard improved the reproducibility and precision of the analysis. Our method showed lower limits of detection and quantification (LOD = 32 ng/mL, LOQ = 78 ng/mL), lower intraday (RSD% 1.25-2.95) and interday (RSD% 1.75-4.69) coefficients of variation, greater recovery (>100%), lower duration (16 minutes) and lower cost than previously described fluorimetric methods. Therefore, this method can be used as a reliable tool for pharmacokinetic studies of enfuvirtide.