Zidovudine pharmacokinetics in zidovudine-induced bone marrow toxicity

"Severe Anemia: A Case Report of an Uncommon Precipitant of Schizophrenia Relapse"

A 48-year-old patient with stable residual schizophrenia experienced a syndromic psychosis relapse following an episode of severe combined immunohemolytic and pure red cell aplastic anemia, with a hemoglobin level of 4.7 g/dl. The anemia was attributed to her anti-HIV medication zidovudine. Her HIV infection had been well-controlled; no other organic precipitant of the psychosis was found. Following transfusion of 2 units of leukocyte-poor packed red cells, schizophrenia symptoms promptly recovered to her baseline. This was maintained at 3- and 6-month follow-ups without any need for antipsychotic dose adjustment. Following zidovudine discontinuation and a short course of oral prednisolone, her anemia gradually recovered.

COVID-19: Therapeutics and Their Toxicities

SARS-CoV-2 is a novel coronavirus that emerged in 2019 and is causing the COVID-19 pandemic. There is no current standard of care. Clinicians need to be mindful of the toxicity of a wide variety of possibly unfamiliar substances being tested or repurposed to treat COVID-19. The United States Food and Drug Administration (FDA) has provided emergency authorization for the use of chloroquine and hydroxychloroquine. These two medications may precipitate ventricular dysrhythmias, necessitating cardiac and electrolyte monitoring, and in severe cases, treatment with epinephrine and high-doses of diazepam. Recombinant protein therapeutics may cause serum sickness or immune complex deposition. Nucleic acid vaccines may introduce mutations into the human genome. ACE inhibitors and ibuprofen have been suggested to exacerbate the pathogenesis of COVID-19. Here, we review the use, mechanism of action, and toxicity of proposed COVID-19 therapeutics.

Dual therapy with ritonavir-boosted protease inhibitor (PI) plus lamivudine versus triple therapy with ritonavir-boosted PI plus two nucleos(t)ide reverse-transcriptase inhibitor in HIV-infected patients with viral suppression

BACKGROUND

Dual antiretroviral regimens are attractive options to optimize the combination antiretroviral therapy in light of potential toxicities with long-term cumulative exposure to nucleos(t)ide reverse-transcriptase inhibitors (NRTIs).

METHODS

In this retrospective observational study, we included HIV-infected patients on suppressive antiretroviral therapy with plasma viral load (PVL) < 200 copies/mL for at least 6 months who were switched to dual regimens containing lamivudine (3TC) (150 mg twice daily or 300 mg once daily) plus lopinavir/ritonavir (LPV/r) 250/50 mg twice daily or darunavir/ritonavir (DRV/r) 800/100 mg once daily. Patients maintaining on suppressive triple therapy with DRV/r or LPV/r plus two NRTIs were included for comparisons. The primary endpoint was the proportion of patients with PVL <50 copies/mL after 48 weeks of follow-up.

RESULTS

In total, 364 patients were included with 93 (25.5%) switched to dual therapy After 48 weeks of observation, PVL <50 copies/mL was observed in 96.8% and 94.1% of dual-therapy and triple-therapy group, respectively, in per-protocol analysis (difference 2.7%; 95% CI -2.5%-7.9%). Nineteen patients (3 [3.2%] in dual-therapy and 16 [7.6%] in triple-therapy group) developed virologic failure, with none having emergent M184V resistance-associated mutation. A statistically significant increase of cholesterol level (13 mg/dL versus 2 mg/dL, p = 0.003) and high-density lipoprotein (3 mg/dL versus -2 mg/dL, p = 0.019) were observed in dual-therapy than in triple-therapy group. Changes of triglyceride, low-density lipoprotein and glycated hemoglobin levels were similar between the two groups.

CONCLUSION

Dual therapy with DRV/r or LPV/r plus lamivudine demonstrated similar effectiveness in maintaining viral suppression to triple therapy.

Human Vault Nanoparticle Targeted Delivery of Antiretroviral Drugs to Inhibit Human Immunodeficiency Virus Type 1 Infection

"Vaults" are ubiquitously expressed endogenous ribonucleoprotein nanoparticles with potential utility for targeted drug delivery. Here, we show that recombinant human vault nanoparticles are readily engulfed by certain key human peripheral blood mononuclear cells (PBMC), predominately dendritic cells, monocytes/macrophages, and activated T cells. As these cell types are the primary targets for human immunodeficiency virus type 1 (HIV-1) infection, we examined the utility of recombinant human vaults for targeted delivery of antiretroviral drugs. We chemically modified three different antiretroviral drugs, zidovudine, tenofovir, and elvitegravir, for direct conjugation to vaults. Tested in infection assays, drug-conjugated vaults inhibited HIV-1 infection of PBMC with equivalent activity to free drugs, indicating vault delivery and drug release in the cytoplasm of HIV-1-susceptible cells. The ability to deliver functional drugs via vault nanoparticle conjugates suggests their potential utility for targeted drug delivery against HIV-1.

B, Golla K, Kondapi AK. Improved Safety, Bioavailability and Pharmacokinetics of Zidovudine through Lactoferrin Nanoparticles during Oral Administration in Rats

Zidovudine (AZT) is one of the most referred antiretroviral drug. In spite of its higher bioavailability (50–75%) the most important reason of its cessation are bone marrow suppression, anemia, neutropenia and various organs related toxicities. This study aims at the improvement of oral delivery of AZT through its encapsulation in lactoferrin nanoparticles (AZT-lactonano). The nanoparticles (NPs) are of 50–60 nm in size and exhibit 67% encapsulation of the AZT. They are stable in simulated gastric and intestinal fluids. Anti-HIV-1 activity of AZT remains unaltered in nanoformulation in acute infection. The bioavailability and tissue distribution of AZT is higher in blood followed by liver and kidney. AZT-lactonano causes the improvement of pharmacokinetic profile as compared to soluble AZT; a more than 4 fold increase in AUC and AUMC in male and female rats. The serum C_max for AZT-lactonano was increased by 30%. Similarly there was nearly 2-fold increase in T_max and t_1/2. Our in vitro study confirms that, the endosomal pH is ideal for drug release from NPs and shows constant release from up to 96h. Bone marrow micronucleus assay show that nanoformulation exhibits approximately 2fold lower toxicity than soluble form. Histopathological and biochemical analysis further confirms that less or no significant organ toxicities when nanoparticles were used. AZT-lactonano has shown its higher efficacy, low organs related toxicities, improved pharmacokinetics parameter while keeping the antiviral activity intact. Thus, the nanoformulation are safe for the target specific drug delivery.

A novel anti-HIV dextrin-zidovudine conjugate improving the pharmacokinetics of zidovudine in rats

The aim of this study was to investigate a newly synthesized dextrin-zidovudine (AZT) conjugate designed as a sustained release prodrug of AZT for parenteral administration. AZT was first reacted with succinic anhydride to form a succinoylated AZT which was subsequently coupled with dextrin to yield the dextrin-AZT conjugate. The structure of the conjugate was characterized by FT-IR and (1)H-NMR spectroscopy. The drug content of the conjugate was 18.9 wt.%. The release in vitro of free AZT and succinoylated AZT was investigated in buffer solutions at pH 5.5 and 7.4 and in human plasma. AZT and succinoylated AZT release from the conjugate was 1.4% (pH 5.5), 41.7% (pH 7.4) and 78.4% in human plasma after 24 h. Release was complete in human plasma after 48 h. A pharmacokinetic study in rats following intravenous administration of the conjugate showed prolonged plasma levels of AZT compared to free AZT. The use of the conjugate extended the plasma half-life of AZT from 1.3 to 19.3 h and the mean residence time from 0.4 to 23.6 h. Furthermore, the conjugate provided a significant greater area under the plasma concentration-time curve and reduced the systemic clearance of AZT. This study suggested the potential of this novel dextrin-AZT conjugate as a new intravenous preparation of AZT.

Pharmacokinetics and potential interactions amongst antiretroviral agents used to treat patients with HIV infection

There are 3 groups of drugs available for the treatment of patients with HIV disease. These are the nucleoside reverse transcriptase inhibitors ('nucleoside analogues') [zidovudine, didanosine, zalcitabine, lamivudine and abacavir]; the non-nucleoside reverse transcriptase inhibitors (nevirapine, delavirdine and efavirenz); and the protease inhibitors (saquinavir, ritonavir, indinavir, nelfinavir and amprenavir). The preferred initial regimen should reduce and maintain plasma HIV RNA below the level of detection. Presently, the regimen of choice consists of 2 nucleoside analogues plus a protease inhibitor with high in vivo efficacy. An alternative combination consists of 2 nucleoside analogues plus a non-nucleoside reverse transcriptase inhibitor. Drug interactions are one of the major problems associated with these multidrug regimens. Changes in plasma concentrations of the nucleoside analogues are unlikely to be of clinical relevance as drug effect is mainly dependent on the rate and extent of intracellular phosphorylation. Combinations of zidovudine plus stavudine, and probably zalcitabine plus lamivudine, should be avoided as competition for phosphorylating enzymes may occur. The antiviral efficacy of some nucleoside analogues, e.g. stavudine, may be compromised by prior treatment with other nucleosides (e.g. zidovudine). However, these data need to be clarified in further studies. It is unlikely that administration of other antiretrovirals will influence the activity of nucleoside analogues. Protease inhibitors are metabolised by hepatic cytochrome P450 (CYP) 3A4. Combination protease inhibitor therapy can result in drug interactions mediated by enzyme inhibition. Ritonavir is the most potent inhibitor, saquinavir the least. The protease inhibitors also interact with the non-nucleoside reverse transcriptase inhibitors. Nevirapine and efavirenz induce drug metabolising enzymes and may reduce plasma concentrations of protease inhibitors. A study in healthy volunteers showed that nelfinavir concentrations are increased by combination with efavirenz. Delavirdine inhibits drug metabolising enzymes and increases the plasma concentration of coadministered protease inhibitors. The nucleoside analogues would not be expected to interact with the protease inhibitors. Apart from the ability of didanosine to reduce the area under the concentration-time curve of delavirdine, there are no reports of clinically significant interactions of other antiretrovirals with the non-nucleoside reverse transcriptase inhibitors. Triple therapy is the current standard of care for patients with HIV disease. However, studies of quadruple therapy are already under way. Drug interactions are likely to remain one of the major considerations when selecting a therapeutic regimen for patients with HIV.

Analysis of antiretroviral nucleosides by electrospray ionization mass spectrometry and collision induced dissociation

Antiretroviral nucleoside drugs used against the human immunodeficiency virus (HIV) infection have been analyzed using negative ion electrospray ionization (ESI) mass spectrometry and collision-induced dissociation (CID-MS/MS). Mass fragmentation of azidothymidine (AZT), didanosine (ddI), dideoxycytidine (ddC) and dideoxythiacytidine (3TC) were obtained at different cone voltages and collision energies. Fragmentation of purines and pyrimidines occurred by different pathways. For purines (ddI), the fragmentation was similar to those found in endogenous nucleosides; mainly the pseudo molecular ion is present (M-H)- and a cleavage through the glycosidic bond forming (B)- was observed. For pyrimidines (AZT, ddC, 3TC), the fragmentation pathways were different from endogenous nucleosides; for AZT, the fragmentation occurred primarily through the elimination of the azido group in the 3'-position (M-H2-N3)-, whereas ddC and 3TC presented more complex fragmentation patterns. For ddC, fragmentation appeared to be dominated by a retro Diels-Alder mechanism (M-CONH)-. For 3TC, the sulfur atom in the sugar moiety provided greater stability to the charge, producing fragments where the charge resided initially in the dideoxyribose (M-C2O2H6)-.

Column-switching techniques in the biomedical analysis of stereoisomeric drugs: why, how and when

The application of stereoselective chromatographic techniques to bioanalytical problems has become a routine procedure. However, this approach is not always straightforward; particularly when the separation involves chromatographic chiral stationary phases. Matrix interferences and more importantly, overlapping metabolite peaks often make direct analysis impractical. One strategy to overcome these problems is to combine two or more columns with different selectivities to produce a multi-dimensional chromatographic system. This review addresses the use of coupled column chromatography in HPLC systems including different coupling methods and the application of the resulting arrangements to bioanalytical analyses.

Pharmacokinetic individualisation of zidovudine therapy. Current state of pharmacokinetic-pharmacodynamic relationships

Zidovudine is the cornerstone of current antiretroviral treatment of human immunodeficiency virus (HIV) infection. Its use, however, frequently leads to adverse reactions, including myelosuppression. Zidovudine pharmacokinetics show large interindividual variation with indications of pharmacokinetic-pharmacodynamic relationships, but a clear therapeutic window has not yet been defined. Individualisation of zidovudine therapy with monitoring of drug concentrations might be desirable. This review considers (intracellular) monitoring of zidovudine and anabolites for individualisation of zidovudine therapy and the achievements in describing pharmacokinetic-pharmacodynamic relationships so far.

Metabolism of Zidovudine

1. The anti-HIV drug zidovudine (3'-azido-2',3'-dideoxythymidine; ZDV) has three important pathways of metabolism. ZDV is a prodrug and must be phosphorylated in lymphocytes in order to exert its antiviral action. However, in quantitative terms this is a minor pathway probably accounting for less than 1% of the overall metabolic profile. The predominant pathway of metabolism is glucuronidation to GZDV and the metabolite is renally excreted. A further metabolite, derived by reduction of the azido moiety is 3'-amino-3'-deoxythymidine (AMT). 2. Zidovudine glucuronidation has been characterised in human liver microsomes. A number of drugs (e.g., naproxen, indomethacin and probenecid) have been shown to inhibit the in vitro conjugation of ZDV. Some of these drugs have also been co-administered with ZDV in HIV-positive patients. Significant pharmacokinetic interactions have been demonstrated with probenecid, naproxen and fluconazole. 3. 3'-amino-3'-deoxythymidine formation is probably mediated by both cytochrome P450 isozymes and NADPH-cytochrome P450 reductase. Peak plasma concentrations of AMT are approximately 10-15% of ZDV in patients. This is a potentially important metabolite because of its alleged cytotoxicity. 4. Measurement of intracellular ZDV phosphates in patients provides the key to our understanding of both the efficacy and toxicity of ZDV. Important recent work has demonstrated that as patients deteriorate (i.e., CD4 counts decrease below 100 x 10(6)/L), there is a corresponding increase in intracellular ZDV-monophosphate. This could have toxicological implications.

Pharmacokinetic optimisation of antiretroviral therapy in patients with HIV infection

More than 7 years after the introduction of zidovudine for treatment of HIV infection, little use has been made of the pharmacokinetic properties of this or any of the subsequently approved antiretroviral agents to optimise therapy. This is partly because of the limits of technologies developed to measure clinically relevant forms and concentrations of these drugs, and partly because the clinical community has been slow to recognise the potential benefits of pharmacokinetic optimisation of nucleoside analogue therapy in any disease. Nonetheless, for some of these agents, progress in understanding the relationship between pharmacokinetics and pharmacodynamics has been made. With zidovudine, for example, even though plasma concentrations have little clinical utility, evidence suggests that concentrations of active phosphorylated forms of zidovudine inside target cells are related to disease progression and toxicity. Furthermore, a decreased ability to phosphorylate zidovudine might be a prerequisite for the emergence of zidovudine-resistant HIV strains. Measurements of phosphorylated zidovudine inside cells similarly suggest that 100 mg of oral zidovudine every 8 hours approximates the optimal initial dosage regimen in asymptomatic patients. Increased plasma didanosine concentrations have been associated with several measures of clinical improvement in patients, and may be associated with an increased risk of toxicity as well. For zalcitabine and stavudine, however, the picture is much less clear. Their pharmacokinetic and pharmacodynamic relationships have not been studied in patients. Furthermore, there is insufficient data on the effects of age, gender, race and concurrent underlying conditions on the pharmacokinetics of all of these agents. Mounting evidence suggests that monitoring of these compounds could lead to individually optimised intervention strategies. Given the marginal benefits of therapy with these agents, their proven toxic effects and the lack of proven alternatives, it is critical that the clinical community strive to make the most effective use of these agents in the treatment of their patients.

Effects of dideoxyinosine and dideoxycytidine on the intracellular phosphorylation of zidovudine in human mononuclear cells

1. Zidovudine (3'-azido-2',3'-dideoxythymidine; AZT; ZDV) is a dideoxynucleoside analogue active against human immunodeficiency virus (HIV). We are currently investigating the intracellular metabolism of ZDV to its putative active triphosphate form (ZDV triphosphate) in peripheral blood mononuclear cells and a lymphoblastoid cell line (h1A2v2). 2. Optimal conditions for intracellular phosphate formation in peripheral blood mononuclear cells occurred following a 72 h preincubation with the mitogen phytohaemagglutinin at a concentration of 10 micrograms ml-1. ZDV was metabolized predominantly to the monophosphate with smaller amounts of the di- and triphosphate anabolites. There was considerable inter- and intraindividual variability in phosphate formation in peripheral blood mononuclear cells. A similar pattern of phosphorylation was seen with the h1A2v2 lymphoblastoid cell line with ZDV monophosphate being the major metabolite. 3. With increasing interest in combination nucleoside analogue therapy in HIV-positive patients it is important to know if an interaction occurs at the level of phosphorylation. Neither dideoxyinosine (ddI) or dideoxycytidine (ddC) significantly reduced the intracellular phosphorylation of ZDV in either peripheral blood mononuclear cells or h1A2v2 cells. In contrast thymidine always gave marked inhibition (e.g. at 2.0 microM, 89% inhibition of total phosphate formation in peripheral blood mononuclear cells and 79% in h1A2v2 cells). It is, therefore, unlikely that in vivo either ddI or ddC will perturb ZDV phosphorylation.

Pharmacokinetics of zidovudine and dideoxyinosine alone and in combination in patients with the acquired immunodeficiency syndrome

1. Zidovudine (ZDV) has proved unsuccessful in controlling disease progression over extended periods of time in patients with AIDS. Combination of ZDV with another reverse transcriptase inhibitor, dideoxyinosine (ddI) may improve the duration of effectiveness of antiretroviral therapy. The aim of this study was to investigate the possibility of a pharmacokinetic drug interaction between ZDV and ddI. 2. The pharmacokinetics of ZDV and ddI were determined in eight patients with AIDS who were randomised to receive ZDV 250 mg orally, ddI 250 mg orally or a combination of ZDV 250 mg plus ddI 250 mg orally on 3 study days separated by 1 week. 3. The administration of ZDV did not significantly alter ddI pharmacokinetics. The mean AUC was 6.8 +/- 2.0 s.d. and 7.6 +/- 2.5 s.d. mumol l-1 h and oral clearance was 2766 +/- 686 and 2660 +/- 1297 ml min-1 in the presence and absence of ZDV, respectively. 4. In the presence of ddI the elimination half-life of ZDV was increased significantly by 18% from 1.1 +/- 0.3 to 1.3 +/- 0.3 h (P < 0.05) and the mean AUC increased significantly by 35% from 4.8 +/- 1.5 to 6.5 +/- 1.5 mumol l-1 h (P < 0.05). The clearance was decreased by 29% from 3518 +/- 1123 to 2505 +/- 575 ml min-1, but this difference was not significant. The renal clearance of ZDV was not altered by ddI. 5. Administration of ddI also resulted in a significant 22% increase in the AUC of GZDV, from 28.5 +/- 15.7 to 34.9 +/- 12.8 mumol l-1 h (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)