Application of a radioimmunoassay for determination of levels of zalcitabine (ddC) in human plasma, urine, and cerebrospinal fluid

Antiretroviral bioanalysis methods of tissues and body biofluids

Research in the many areas of HIV treatment, eradication and prevention has necessitated measurement of antiretroviral (ARV) concentrations in nontraditional specimen types. To determine the knowledgebase of critical details for accurate bioanalysis, a review of the literature was performed and summarized. Bioanalytical assays for 31 ARVs, including metabolites, were identified in 205 publications measuring various tissues and biofluids. 18 and 30% of tissue or biofluid methods, respectively, analyzed more than one specimen type; 35-37% of the tissue or biofluid methods quantitated more than one ARV. 20 and 76% of tissue or biofluid methods, respectively, were used for the analysis of human specimens. HPLC methods with UV detection predominated, but chronologically MS detection began to surpass. 40% of the assays provided complete intra- and inter-assay validation data, but only 9% of publications provided any stability data with even less for the prevalent ARV in treatments.

Zidovudine impairs adipogenic differentiation through inhibition of clonal expansion

Lipoatrophy is a prevalent side effect of treatment with thymidine analogues. We wished to confine the time point of the antiadipogenic effect of zidovudine (AZT) during adipogenesis and to evaluate the antiproliferative effect of AZT on adipocyte homeostasis. We investigated the effects of AZT on adipogenesis in 3T3-F442A cells and studied their proliferation, differentiation, viability, and adiponectin expression. Cells were exposed to AZT (1 microM, 3 microM, 6 microM, and 180 microM), stavudine (d4T; 3 microM), or dideoxycytosine (ddC; 0.1 microM) for up to 15 days. Differentiation was assessed by real-time PCR and quantification of triglyceride accumulation. Proliferation and clonal expansion were determined by a [(3)H]thymidine incorporation assay. When they were induced to differentiate in the presence of AZT at the maximum concentration in plasma (C(max)) and lower concentrations, 3T3-F442A preadipocytes failed to accumulate cytoplasmic triacylglycerol and failed to express normal levels of the later adipogenic transcription factors, CCAAT/enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma. AZT exerted an inhibitory effect on the completion of the mitotic clonal expansion, which resulted in incomplete 3T3-F442A differentiation and, finally, a reduction in the level of adiponectin expression. In addition, AZT impaired the constitutive proliferation in murine and primary human subcutaneous preadipocytes. In contrast, incubation with d4T and ddC at the C(max) did not affect either preadipocyte proliferation or clonal expansion and differentiation. We conclude that the antiproliferative and antiadipogenetic effects of AZT on murine and primary human preadipocytes reveal the impact of the drug on fat tissue regeneration. These effects of the drug are expected to contribute to disturbed adipose tissue homeostasis and to be influenced by differential drug concentration and penetration in individual patients.

Quantitative determination of (-)-2'-deoxy-3'-thiacytidine (lamivudine) in human plasma, saliva and cerebrospinal fluid by high-performance liquid chromatography with ultraviolet detection

A high-performance liquid chromatographic method for the quantitative determination of the HIV reverse transcriptase inhibitor lamivudine ((-)-2'-deoxy-3'-thiacytidine, 3TC, Epivir) in human plasma, saliva and cerebrospinal fluid is described. Lamivudine was extracted from samples using silica extraction columns prior to reversed-phase high-performance liquid chromatography with ultraviolet detection at 270 nm. The method has been validated over the range of 10 (lower limit of quantitation) to 5000 ng/ml using a 0.5-ml sample volume. Between-day and within-day precisions ranged from 3.5 to 9.0%. The assay has been used for the quantitative analysis of lamivudine in plasma and cerebrospinal fluid of HIV-1 infected patients.

Zalcitabine population pharmacokinetics: application of radioimmunoassay

Zalcitabine population pharmacokinetics were evaluated in 44 human immunodeficiency virus-infected patients (39 males and 5 females) in our immunodeficiency clinic. Eighty-one blood samples were collected during routine clinic visits for the measurement of plasma zalcitabine concentrations by radioimmunoassay (1.84+/-1.24 samples/patient; range, 1 to 6 samples/patient). These data, along with dosing information, age (38.6+/-7.13 years), sex, weight (79.1+/-15.0 kg), and estimated creatinine clearance (89.1+/-21.5 ml/min), were entered into NONMEM to obtain population estimates for zalcitabine pharmacokinetic parameters. The standard curve of the radioimmunoassay ranged from 0.5 to 50.0 ng/ml. The observed concentrations of zalcitabine in plasma ranged from 2.01 to 8.57 ng/ml following the administration of doses of either 0.375 or 0.75 mg. A one-compartment model best fit the data. The addition of patient covariates did not improve the basic fit of the model to the data. Oral clearance was determined to be 14.8 liters/h (0.19 liter/h/kg; coefficient of variation [CV] = 23.8%), while the volume of distribution was estimated to be 87.6 liters (1.18 liters/kg; CV = 54.0%). We were also able to obtain individual estimates of oral clearance (range, 8.05 to 19.8 liters/h; 0.11 to 0.30 liter/h/kg) and volume of distribution (range, 49.2 to 161 liters; 0.43 to 1.92 liters/kg) of zalcitabine in these patients with the POSTHOC option in NONMEM. Our value for oral clearance agrees well with other estimates of oral clearance from traditional pharmacokinetic studies of zalcitabine and suggests that population methods may be a reasonable alternative to these traditional approaches for obtaining information on the disposition of zalcitabine.

Zalcitabine. An update of its pharmacodynamic and pharmacokinetic properties and clinical efficacy in the management of HIV infection

Zalcitabine is a dideoxynucleoside antiretroviral agent that is phosphorylated to the active metabolite 2',3'-dideoxycytidine 5'-triphosphate (ddCTP) within both uninfected and HIV-infected cells. At therapeutic concentrations, ddCTP inhibits HIV replication by inhibiting the enzyme reverse transcriptase and terminating elongation of the proviral DNA chain. The results of 3 large pivotal trials comparing zidovudine monotherapy with combination therapy have now clearly established that zalcitabine plus zidovudine combination with an improvement in viral load and CD4+ cell count compared with zidovudine monotherapy. More recently, clinical end-point and surrogate marker data have established the efficacy of zalcitabine in combination with the protease inhibitor saquinavir in zidovudine-experienced patients. Other studies have demonstrated the utility of zalcitabine in combination with ritonavir and the nucleoside analogue lamivudine. Importantly, early use of zalcitabine in the treatment sequence does not appear to limit the therapeutic efficacy of subsequent therapy with other nucleoside analogues such as lamivudine. Peripheral neuropathy is the most frequent dose-limiting adverse effect associated with zalcitabine therapy and is generally reversible on discontinuation of treatment. Stomatitis and mouth ulcers may occur frequently with zalcitabine therapy but tend to resolve with continuing treatment. Haematological toxicity, which is a common adverse effect associated with zidovudine, is reported infrequently with zalcitabine. Overall, combination therapy with zalcitabine plus zidovudine or saquinavir has been shown to have a tolerability profile comparable to that of either agent alone, although treatment with zidovudine plus zalcitabine was associated with a significant increase in the incidence of haematological toxicity compared with zidovudine monotherapy in one study. Therefore, current data suggest that zalcitabine is a useful antiretroviral agent for inclusion as a component of initial double combination therapy with zidovudine or as part of triple combination therapy including zidovudine plus a protease inhibitor in the management of patients with HIV infection.