Plasma AZT Research Articles

Submicron Matrices Embedded in a Polymeric Caplet for Extended Intravaginal Delivery of Zidovudine.

In this study, an intravaginal delivery system able to deliver an anti-HIV-1 agent for the purpose of potentially reducing HIV-1 transmission acting over an extended duration was successfully formulated. This delivery system was a composite polymeric caplet comprising zidovudine-loaded polyethylene glycol enclatherated pectin-mucin submicron matrices embedded within a poly (D,L-lactide), magnesium stearate, Kollidon® SR, and Carbopol® 974P NF-based polymeric caplet matrix. A three-factor and three-level Box-Behnken statistical design was utilized to optimize the polymeric caplet. The optimized directly compressed composite polymeric caplet hardness was 22.1±0.3N and the matrix resilience was 62.4±0.6%. The swelling- and diffusion-controlled fractional zidovudine (AZT) release from the optimized caplet was 0.74±0.01 in simulated vaginal fluid (SVF), which increased to 0.81±0.21 in phosphate-buffered saline (PBS) simulating seminal fluid, over 30days. Caplet matrix swelling was directly related to the percentage Carbopol 974P NF composition. An intravaginal system for AZT delivery was tested in the pig model over 28days. X-ray analysis depicted delivery system swelling with matrix contrast fading over time as vaginal fluid permeated the matrix core. Plasma, vaginal fluid swab eluates, and tissue AZT concentrations were measured by gradient ultra-performance liquid chromatography (UPLC)-tandem photodiode array detection. Vaginal tissue and vaginal fluid swab eluate AZT concentrations remained above effective levels over 28days and were higher than plasma AZT concentrations, availing a system with reduced systemic toxicity and more effective inhibition of viral replication at the site of entry.

High Plasma Concentrations of Zidovudine (AZT) Do Not Parallel Intracellular Concentrations of AZT-Triphosphates in Infants During Prevention of Mother-to-Child HIV-1 Transmission.

Zidovudine (AZT) is mainly used to prevent mother-to-child HIV-1 transmission (PMTCT). Despite serious concerns on AZT-associated toxicity, there is little information on pharmacokinetics of intracellular AZT metabolites in infants. We conducted a prospective study in 31 HIV-uninfected infants who received AZT for PMTCT. Blood samples were obtained from 14 infants on postdelivery days (PDD) 1, 7, 14, and 28 and from 17 infants at 0 and 4 hours after dosing on PDD-1. Plasma AZT concentrations (pAZT) and intracellular concentrations of AZT-monophosphate (icAZT-MP), diphosphate (icAZT-DP), and triphosphate (icAZT-TP) were determined. Plasma AZT and icAZT-MP concentrations were 2713 nmol/L and 79 fmol/10 cells in PDD-1, but decreased to 1437 nmol/L and 31 fmol/10 cells by PDD-28 (P = 0.02 and P = 0.07 for all PDDs, respectively), whereas those of icAZT-DP and icAZT-TP remained low throughout the sampling period (P = 0.29 and P = 0.61 for all PDDs, respectively) There were no differences in icAZT-TP between infants of the 2 mg/kg 4 times a day dose and 4 mg/kg twice daily dose (P = 0.25), whereas pAZT and icAZT-MP levels were higher in the latter (P < 0.01 and <0.01, respectively). The pAZT and icAZT-MP significantly increased from 0 to 4 hours after dosing (P < 0.001 and <0.001, respectively), whereas icAZT-DP, icAZT-TP levels were not changed (P = 0.41 and 0.33, respectively). The level of icAZT-TP did not change with age, time, or a single dose despite the wide range of pAZT concentration. A safer dosage needs to be determined because high pAZT levels do not parallel those of icAZT-TP.

Ultrasensitive method to quantify intracellular zidovudine mono-, di- and triphosphate concentrations in peripheral blood mononuclear cells by liquid chromatography-tandem mass spectrometry.

Although zidovudine (AZT) is not the preferred antiretroviral drug for adult HIV-infected patients, it is still widely used in infants for both prevention of mother-to-infant HIV-1 transmission and treatment of HIV-infected children. However, it is difficult to measure intracellular concentrations of AZT metabolites in small blood samples due to their extremely low concentrations in peripheral blood mononuclear cells and interference by endogenous nucleotide triphosphates, residual plasma phosphates and electrolytes. We developed an ultrasensitive assay using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for measurement of intracellular concentrations of zidovudine (AZT)-monophosphate (AZT-MP), -diphosphate (AZT-DP) and -triphosphate (AZT-TP). The high sensitivity was due to the improvement of peripheral blood mononuclear cells extraction for complete removal of plasma and electrolytes, alkalization of LC buffer and use of alkaline-stable high performance liquid chromatography column and tetrabutylammonium hydroxide as the ion pair. Using this method, the lower limits of quantification of AZT, AZT-MP, -DP and -TP were 6, 6, 10 and 10 fmol per sample, respectively. Accuracy ranged 89-115% and precision was lower than 15% in the quantification range of 6-6000 fmol/sample for plasma AZT and intracellular AZT-MP and 10-10 000 fmol/sample for AZT-DP and -TP. The validation parameters met the international requirements. Among nine AZT-treated HIV-infected adult patients, five had low AZT-TP levels (<10 fmol/10(6) cells). Our assay has high sensitivity and is advantageous for evaluation of AZT phosphates in children and infants based on minimum blood sampling requirement.

An HPLC-UV Method for the Quantification of Zidovudine in Rat Plasma

This work aims to develop and validate a simple methodology to quantify the most used antiretroviral, zi- dovudine (AZT), in rat plasma for preclinical studies. Some assays have been previously reported to quantify AZT in plasma; however, the majority of these methods uses complicated extraction methods. This method uses only 100 �L plasma samples, which were precipitated with 100 �L acidified acetonitrile containing an internal standard (IS). The plasma extracts were injected directly in a chromatographic system consisting of a UV-Vis detector (set at 266 nm) and an RP-C18 column. The mobile phase was an isocratic mixture of acetonitrile, methanol and 0.01% v/v aqueous formic acid (20:20:60 v/v/v) at a flow rate of 0.8 mL/min. Intra- and inter-day assay precision and accuracy variability were lower than 20% for the limit of quantification and 15% for higher concentrations. The applicability of the method was demonstrated by an in vivo study performed in rats. They were treated orally with an AZT-containing syrup and intrave- nously with an AZT solution. The calculated bioavailability of the syrup (56.7%) was in accordance with the literature. Therefore, this method can be used as an alternative to quantify plasma AZT in preclinical studies.

Joint Population Pharmacokinetic Analysis of Zidovudine, Lamivudine, and Their Active Intracellular Metabolites in HIV Patients

The population pharmacokinetic parameters of zidovudine (AZT), lamivudine (3TC), and their active intracellular metabolites in 75 naïve HIV-infected patients receiving an oral combination of AZT and 3TC twice daily as part of their multitherapy treatment in the COPHAR2-ANRS 111 trial are described. Four blood samples per patient were taken after 2 weeks of treatment to measure drug concentrations at steady state. Plasma AZT and 3TC concentrations were measured in 73 patients, and among those, 62 patients had measurable intracellular AZT-TP and 3TC-TP concentrations. For each drug, a joint population pharmacokinetic model was developed and we investigated the influence of different covariates. We then studied correlations between the mean plasma and intracellular concentrations of each drug. A one-compartment model with first-order absorption and elimination best described the plasma AZT concentration, with an additional compartment for intracellular AZT-TP. A similar model but with zero-order absorption was found to adequately described concentrations of 3TC and its metabolite 3TC-TP. The half-lives of AZT and 3TC were 0.81 h (94.8%) and 2.97 h (39.2%), respectively, whereas the intracellular half-lives of AZT-TP and 3TC-TP were 10.73 h (69%) and 21.16 h (44%), respectively. We found particularly a gender effect on the apparent bioavailability of AZT, as well as on the mean plasma and intracellular concentrations of AZT, which were significantly higher in females than in males. Relationships between mean plasma drug and intracellular metabolite concentrations were also highlighted both for AZT and for 3TC. Simulation with the model of plasma and intracellular concentrations for once- versus twice-daily regimens suggested that a daily dosing regimen with double doses could be appropriate.

High Levels of Zidovudine (AZT) and Its Intracellular Phosphate Metabolites in AZT- and AZT-Lamivudine-Treated Newborns of Human Immunodeficiency Virus-Infected Mothers

Newborns from human immunodeficiency virus-infected mothers are given antiretroviral prophylaxis against mother-to-child transmission, including predominantly nucleoside reverse transcriptase inhibitors. Pharmacological monitoring of these drugs in newborns has so far been limited to plasma and cord blood. In this study, samples from newborns (up to 45 days old) treated with zidovudine (AZT) alone (n = 29) or in combination with lamivudine (3TC) (n = 20) were analyzed for both intracellular concentrations of phosphate metabolites in peripheral blood mononuclear cells and levels of parent drugs in plasma. Plasma AZT and intracellular AZT-monophosphate and AZT-triphosphate (TP) concentrations were significantly higher during the first 15 days of life (199 versus 52.7 ng/ml [P < 0.0001], 732 versus 282 fmol/10(6) cells [P < 0.0001], and 170 versus 65.1 fmol/10(6) cells [P < 0.0001], respectively) and then became comparable to those of adults. No difference in intracellular AZT metabolite concentrations was found when AZT- and AZT-3TC-treated groups were compared. Plasma 3TC levels (lower limit of quantification [LLOQ], 1,157 ng/ml; median, 412.5 ng/ml) were not associated with the newborn's age, gender, or weight. Intracellular 3TC-TP concentrations (LLOQ, 40.4 pmol/10(6) cells; median, 18.9 pmol/10(6) cells) determined for newborns receiving the AZT-3TC combination were associated with neither the age nor weight of the newborns. Concentrations in females were significantly higher (1.8-fold [P = 0.0415]) than those in males. Unexpectedly, newborns on AZT monotherapy whose mothers' treatment included 3TC displayed residual plasma 3TC and intracellular 3TC-TP levels up to 1 week after birth.

A computational model of mitochondrial AZT metabolism

The mechanisms of the mitochondrial toxicity of AZT (azidothymidine; zidovudine) are not clear. The two main contenders are the incorporation of phosphorylated AZT into the mtDNA (mitochondrial DNA) and the competitive inhibition of natural deoxynucleotide metabolism. We have built a computational model of AZT metabolism in mitochondria in order to better understand these toxicity mechanisms. The model includes the transport of non-phosphorylated and phosphorylated forms of AZT into mitochondria, phosphorylation, and incorporation into mtDNA. The model also includes the mitochondrial metabolism of the natural deoxynucleotides. We define three simulated cell types, i.e. rapidly dividing, slowly dividing and postmitotic cells. Our standard simulation indicates that incorporation of AZT into mtDNA is highest in rapidly dividing cells because of the higher mitochondrial AZTTP (3'-azidothymidine-5'-triphosphate)/dTTP ratio in this cell type. However, under these standard conditions the rate of incorporation into mtDNA is too low to be a major cause of toxicity. These simulations relied on the assumption that phosphorylated AZT is transported with the same kinetics as phosphorylated thymidine. In simulations with mitochondria set to have a limited ability to transport phosphorylated AZT, AZTTP accumulates to toxic levels in the mitochondria of postmitotic cells, while low levels are maintained in mitochondria from rapidly dividing cells. This result is more consistent with the tissue toxicities observed in patients. Our model also predicts that inhibition by AZT of mitochondrial deoxycytidine phosphorylation by thymidine kinase 2 may contribute to the mitochondrial toxicity, since in simulations using a typical peak plasma AZT level the mtDNA replication rate is decreased by 30% in postmitotic cell simulations.

Pharmacokinetics and safety of oral levofloxacin in human immunodeficiency virus-infected individuals receiving concomitant zidovudine

This phase I, double-blind, randomized, placebo-controlled, parallel-design study was conducted to evaluate the safety and pharmacokinetics of levofloxacin in human immunodeficiency virus (HIV)-infected subjects concomitantly receiving a stable regimen of zidovudine (AZT). Sixteen HIV-infected males with CD4-cell counts ranging from 100 to 550 and not experiencing significant AZT intolerance were enrolled. Subjects received levofloxacin (350 mg of levofloxacin hemihydrate) or a placebo (eight subjects per treatment group) as a single oral dose on day 1, multiple doses every 8 h from days 3 to 9, and a single dose on day 10. On days 1 and 10, an AZT dose (100 mg) was administered concurrently with the study drug. In between these doses, AZT was administered according to the regimen used by the subject prior to entering the study up to a maximum of 500 mg/day. Plasma levofloxacin concentrations were monitored for 36 h after levofloxacin dosing on day 1, immediately prior to the morning doses on days 3 to 9, and for 72 h after dosing on day 10. Plasma AZT concentrations were monitored on day 0 for baseline (for 6 h after the AZT dose) and for 4 h after the AZT doses on days 1 and 10. Levofloxacin was rapidly absorbed (time to maximum plasma concentration, approximately 1.0 h) and extensively distributed in the body with an apparent volume of distribution of approximately 104 liters (approximately 1.34 liters/kg). Steady-state conditions on day 10 were confirmed. Pharmacokinetic profiles of levofloxacin from single doses and multiple (three-times-daily) doses were similar, with a moderate accumulation (observed day 10-to-day 1 ratio of the maximum plasma concentration, approximately 185% versus expected 169%; for the corresponding ratio of the area under the concentration-time curve from 0 to 8 h [AUC(0-8)], the values were observed 217% versus expected 169%) at steady state. Mean average steady-state peak plasma concentration, plasma levofloxacin concentration at the end of the dosing interval, AUC(0-8), terminal half-life, and total body clearance were 7.06 microg/ml, 3.62 microg/ml, 37.4 microg x h/ml, 7.2 h, and 9.4 liters/h (0.12 liters/h/kg), respectively. Pharmacokinetic profiles of levofloxacin in HIV-infected patients did not appear to be affected by the concomitant administration of AZT; nor were AZT pharmacokinetics altered by levofloxacin. Oral administration of 350 mg of levofloxacin hemihydrate every 8 h appeared to be well tolerated by the subjects. There were no apparent differences in adverse events between the two treatment groups. There were no clinically significant changes from baseline in any laboratory parameter or vital sign following treatments observed in this study. The study results suggest that there is no need for levofloxacin dosage adjustment in HIV-seropositive subjects who concomitantly receive AZT.

Valproic Acid Increases Cerebrospinal Fluid Zidovudine Levels in a Patient With AIDS

AbstractValproic acid is an anticonvulsant drug known to inhibit the glucuronidation of zidovudine (AZT) in human liver microsomes. Zidovudine is metabolized by glucuronidation to the inactive 5*-glucuronide with a short plasma half-life (1.0 ± 0.2 hour). This case presentation confirms that valproic acid inhibits glucuronidation in vivo, and this is the first documented observation of increased cerebrospinal fluid levels of zidovudine because of an interaction with valproic acid in a patient with acquired immune deficiency syndrome (AIDS). The peak plasma AZT level for the control period was 119 ng/mL, which increased almost 3fold to 344 ng/mL with valproic acid (1.5 g/day). The plasma AZT trough was 47 ng/mL, which also increased almost 3-fold to 124 ng/mL with valproic acid. The molar ratio of plasma 5’- glucuronide/AZT at the peak was reduced from 1.77 (control) to 1.07 with valproic acid. The 5’- glucuronide/AZT ratio at the trough was reduced markedly from 5.0 (control) to 0.93 with valproic acid, suggesting in vivo inhibition of glucuronidation. Cerebrospinal AZT levels, drawn 30 minutes after peak plasma levels, increased from 27 ng/mL for the control to 47 ng/mL with valproic acid, which paralleled the change in peak plasma concentrations. This interaction with valproic acid may contribute to higher AZT levels in the brains of patients with human immunodeficiency virus-related (HIV) encephalopathy. KEY INDEXING TERMS:[Am J Med Sci 1997;313(4):244-246.]

Comparative pharmacokinetics of two prodrugs of zidovudine in rabbits: enhanced levels of zidovudine in brain tissue

The pharmacokinetics of two prodrugs of zidovudine (AZT), 1,4-dihydro-1-methyl-3-[(pyridylcarbonyl)oxy] ester and isoleucinyl ester (DPAZT and IAZT, respectively), were investigated in a rabbit model to determine their potential utility as drugs against human immunodeficiency virus. Drugs were administered by intravenous infusion over 5 min at doses equal to 10 mg of AZT per kg of body weight. The levels of the prodrugs and of released AZT in plasma, cerebrospinal fluid (CSF), and brain were determined by high-performance liquid chromatography analysis. DPAZT disappeared rapidly from plasma, whereas IAZT maintained a sustained level in plasma for up to 4 h. The levels in plasma of AZT released from DPAZT were consistently lower than the levels of AZT released from IAZT or AZT itself. At 75 min after infusion of AZT, DPAZT, and IAZT, the CSF plasma AZT ratios were 0.23, 0.30, and 0.25, while the brain/CSF AZT ratios were 0.32, 0.63, and 0.64, respectively. These results indicate that the administration of each of the prodrugs produced a higher concentration of AZT in the brain than did the direct administration of AZT. Both prodrugs therefore may be superior to AZT itself with respect to achieving anti-human immunodeficiency virus concentrations within the central nervous system.

Zidovudine removal during plasma exchange

Pharmacokinetics of zidovudine (azidothymidine, AZT) were investigated after oral administration (300 mg every 8 hours) in a human immunodeficiency virus seropositive patient who was also treated with plasma exchange (60 ml/kg). Plasma AZT concentrations were measured using high performance liquid chromatography assay. Plasma exchange clearances reached 1-3.8% of the total clearance. The fraction of AZT removed from separated plasma accounted for only 1% of the administered dose. The contribution of plasma exchange to the elimination of AZT appears to be negligible. Solely on the basis of AZT pharmacokinetic data, no particular dose adjustment appears to be necessary in patients treated with multiple plasma exchanges.

Probenecid inhibits the metabolic and renal clearances of zidovudine (AZT) in human volunteers.

The effect of probenecid on the disposition of AZT was investigated in a pilot study in two healthy volunteers. The pharmacokinetics of AZT were examined after a single oral dose of 200 mg with and without probenecid coadministration in a balanced crossover study. Administration of 500 mg probenecid every 6 hr prior to and during AZT dosing resulted in an increase in the average AUCAZT from 89 micrograms.min/ml (control) to 191 micrograms.min/ml during probenecid treatment. This was manifested by a corresponding decrease in CLTOT/F, which is attributed to the inhibitory effect of probenecid on the glucuronidation and renal excretion of AZT. Average CLR and CLTOT/F of AZT decreased from 4.76 and 28.7 to 2.98 and 14.1 ml/min/kg during control and probenecid treatment, respectively. AZT glucuronidation was affected to a greater extent than its renal excretion, as reflected by the decreased ratio of GAZT/AZT urinary recoveries. The terminal half-life of AZT was slightly longer during probenecid administration. That only a small change in the half-life occurred indicates that probenecid also reduced the volume of distribution of AZT. The CLR of GAZT decreased from an average of 11.3 ml/min/kg (control) to 2.63 ml/min/kg during probenecid treatment, resulting in a greater than 3.5-fold increase in AUCGAZT. Probenecid did not affect the blood/plasma distribution or the plasma protein binding of AZT. These preliminary findings suggest that it may be possible to maintain effective plasma AZT concentrations in AIDS patients receiving a reduced daily dose, in combination with probenecid.

Pharmacokinetics and saturable renal tubular secretion of zidovudine in rats

The purpose of this study was to assess the effects of dose on the pharmacokinetics of zidovudine (3′-azido-3′-deoxythymidine; AZT) in rats. Zidovudine (AZT) was administered intravenously at doses of 10, 50, 100, and 250 mg/kg. Plasma and urine AZT concentrations were determined by HPLC. Plasma AZT concentrations declined rapidly with a terminal half-life ranging from 0.76h at a dose of 10 mg/kg to 1.58h at 250 mg/kg. Total clearance (CLT) was similar at the doses of 10 and 50 mg/kg, with values of 2.80 and 2.73 L/h/kg, respectively. However, there was a trend toward nonlinearity at the dose of 100 mg/kg (CLT = 2.13 L/h/kg) and a significant decrease in CLT (1.22 L/h/kg) at the dose of 250 mg/kg. Nonrenal clearance remained unaffected by dose with a mean value of 0.98 L/h/kg. Renal clearance (CLR) was similar at the doses of 10 and 50 mg/kg, with values of 1.89 and 1.37 L/h/kg, respectively. However, significant decreases in CLR were observed at the doses of 100 (CLR = 1.30 L/h/kg) and 250 mg/kg (CLR = 0.57 L/h/kg). The maximum transport capacity (Tmax) and the Michaelis-Menten constant (Km) for renal tubular secretion obtained after simultaneously fitting plasma concentration—time profiles at the four doses to a renal clearance model were 215.5 ± 82.1 mg/h and 119.3 ± 80.5 mg/L, respectively, thereby yielding an unbound secretory intrinsic clearance (CLus,int) of 1.81 L/h. The high Tmax and Km values account for the high CLR of AZT and explain the linearity of CLR over a wide range of AZT plasma concentrations. Active tubular secretion of AZT, however, is saturable at very high AZT concentrations, resulting in decreased CLR and, thus, CLT at higher doses. The steady-state volume of distribution (Vdss) was similar at the doses of 10 and 50 mg/kg (1.57 and 1.66 L/kg, respectively). There was a pattern towards decrease in Vdss at the dose of 100 mg/kg (Vdss = 1.17 L./kg) and a significant decrease at the dose of 250 mg/kg (Vdss = 0.81 L/kg) suggesting saturable tissue uptake or binding. Thus, the pharmacokinetics of AZT behaves linearly at low doses, but becomes dose dependent as the dose is further increased.