Pharmacokinetics of oral zidovudine (azidothymidine) in patients with AIDS when administered with and without a high-fat meal

Interactions of Antiretroviral Drugs with Food, Beverages, Dietary Supplements, and Alcohol: A Systematic Review and Meta-analyses

Multiple factors may affect combined antiretroviral therapy (cART). We investigated the impact of food, beverages, dietary supplements, and alcohol on the pharmacokinetic and pharmacodynamic parameters of 33 antiretroviral drugs. Systematic review in adherence to PRISMA guidelines was performed, with 109 reports of 120 studies included. For each drug, meta-analyses or qualitative analyses were conducted. We have found clinically significant interactions with food for more than half of antiretroviral agents. The following drugs should be taken with or immediately after the meal: tenofovir disoproxil, etravirine, rilpivirine, dolutegravir, elvitegravir, atazanavir, darunavir, lopinavir, nelfinavir, ritonavir, saquinavir. Didanosine, zalcitabine, zidovudine, efavirenz, amprenavir, fosamprenavir, and indinavir should be taken on an empty stomach for maximum patient benefit. Antiretroviral agents not mentioned above can be administered regardless of food. There is insufficient evidence available to make recommendations about consuming juice or alcohol with antiretroviral drugs. Resolving drug-food interactions may contribute to maximized cART effectiveness and safety.

Didanosine

OBJECTIVE:

To review the chemistry, intracellular metabolism, pharmacokinetics, and clinical experience with didanosine (2',3'-dideoxyinosine [ddI]).

DATA SOURCES:

English-language articles and conference proceedings (indexing terms were didanosine, 2′,3′-dideoxyinosine, and ddI).

STUDY SELECTION:

Available Phase I studies and abstracts determined to have clinical significance were included.

DATA EXTRACTION:

Clinical experience with ddI is limited to uncontrolled Phase I studies and a large “expanded-access” program. The primary outcome parameters used to evaluate ddI were the HIV surrogate markers: CD4+ lymphocytes and p24 antigen. Thus, the clinical data reviewed here must be evaluated critically and be considered preliminary until the results of studies comparing ddI with zidovudine (ZDV) and combination studies are available.

DATA SYNTHESIS:

Didanosine has been approved for the treatment of HIV infection in patients who are unable to tolerate ZDV because of adverse effects (e.g., anemia and neutropenia) or who experience clinical or immunologic deterioration while receiving ZDV. Compared with ZDV, ddI has a long intracellular half-life and negligible bone-marrow toxicity. It also has in vitro activity against ZDV-resistant strains of HIV. Phase I studies indicate that ddI has a beneficial effect on the CD4+ cell counts and HIV p24 antigen concentrations. As a result of the acid-labile nature of ddI, oral formulations are buffered or must be mixed with antacid to neutralize gastric pH. Bioavailability then averages 20–40 percent, depending on the dose and formulation given. The plasma half-life, total body clearance, and volume of distribution of ddI are one to two hours, 0.7–1 L/kg/h, and 0.8–1 L/kg, respectively. Painful peripheral neuropathy and pancreatitis (dose-limiting toxicities of ddI) occurred in 34 and 9 percent of patients in Phase I studies, respectively.

CONCLUSIONS:

Didanosine has demonstrated preliminary efficacy in the treatment of late-stage HIV infection; however, its effect on patient survival, its efficacy relative to ZDV, and its utility in combination with other agents are still under evaluation.

Species Differences in the Metabolism and Disposition of Antiviral Nucleoside Analogues: 2. Zidovudine

Preclinical and clinical studies on the disposition of zidovudine, a thymidine analogue with potent activity against human immunodeficiency virus, identified significant species differences in the metabolism and elimination of the drug. Zidovudine was extensively metabolized to the 5′-O-glucuronide in man and other primates. Rabbits and dogs were intermediate in their extent of biotransformation to the glucuronide conjugate, whereas rats and mice excreted the drug largely unchanged. Decreased metabolism was compensated by increased renal elimination, such that plasma elimination phase half-lives for zidovudine were similar (0.6–1.1 h) in all species. Rapid and extensive absorption and considerable penetration into tissues were also observed for all species studied. Only in the brain and testes were drug levels less than in plasma, although effective antiviral concentrations of zidovudine were achieved in brain and CSF. This review summarizes the variety of studies of the absorption, distribution, metabolism, and elimination of zidovudine in several species, including humans.

HIV nucleoside reverse transcriptase inhibitors efavirenz and tenofovir change the growth and differentiation of primary gingival epithelium

OBJECTIVES

An increasing number of HIV-infected patients are combating HIV infection through the use of antiretroviral drugs, including reverse transcriptase inhibitors. Oral complications associated with these drugs are becoming a mounting cause for concern. In our previous studies, both protease inhibitors and reverse transcriptase inhibitors have been shown to change the proliferation and differentiation state of oral tissues. This study examined the effect of a nonnucleoside and a nucleoside reverse transcriptase inhibitor on the growth and differentiation of gingival epithelium.

METHODS

Organotypic (raft) cultures of gingival keratinocytes were treated with a range of efavirenz and tenofovir concentrations. Raft cultures were immunohistochemically analysed to determine the effect of these drugs on the expression of key differentiation and proliferation markers, including cytokeratins and proliferating cell nuclear antigen (PCNA).

RESULTS

These drugs dramatically changed the proliferation and differentiation state of gingival tissues when they were present throughout the growth period of the raft tissue as well as when drugs were added to established tissue on day 8. Treatment with the drugs increased the expression of cytokeratin 10 and PCNA and, conversely, decreased expression of cytokeratin 5, involucrin and cytokeratin 6. Gingival tissue exhibited increased proliferation in the suprabasal layers, increased fragility, and an inability to heal itself.

CONCLUSIONS

Our results suggest that efavirenz and tenofovir treatments, even when applied in low concentrations for short periods of time, deregulated the cell cycle/proliferation and differentiation pathways, resulting in abnormal epithelial repair and proliferation. Our system could be developed as a potential model for studying the effects of HIV and highly active antiretroviral therapy (HAART) in vitro.

Absence of Food Effect on the Pharmacokinetics of Telbivudine Following Oral Administration in Healthy Subjects

The influence of food on the pharmacokinetics of telbivudine, a candidate antiviral agent against hepatitis B virus (HBV), was investigated in healthy adult subjects following a 600-mg oral dose administered with and without a high-fat/high-calorie meal. Telbivudine was well tolerated under fasting and fed conditions. Oral absorption of telbivudine as measured by maximum plasma concentration (Cmax), time to reach Cmax (Tmax), and area under the plasma concentration-time curve (AUC(0-t) and AUC(0-infinity)) was not altered by food intake immediately before oral dosing. Values of Cmax, Tmax, and AUC were comparable when telbivudine was administered under fed and fasting conditions. Results from this study indicated that the absorption of telbivudine was not affected by a high-fat/high-calorie meal; telbivudine can therefore be administered orally with no regard to the timing of meals.

Effect of the HIV nucleoside reverse transcriptase inhibitor zidovudine on the growth and differentiation of primary gingival epithelium

OBJECTIVES

Oral complications associated with HIV infection and with the antiretroviral drugs used to treat it are of increasing concern in HIV-infected patients. Protease inhibitors have been shown to change the proliferation and differentiation state of oral tissues but the effect of nucleoside reverse transcriptase inhibitors is currently unknown. This study examined the effect of zidovudine on the growth and differentiation of the gingival epithelium.

METHODS

Gingival keratinocyte organotypic (raft) cultures were established. The raft cultures were treated with a range of zidovudine concentrations. Haematoxylin and eosin staining was performed to examine the effect of zidovudine on gingival epithelium growth and stratification. Raft cultures were immunohistochemically analysed to determine the effect of this drug on the expression of key differentiation and proliferation markers, including cytokeratins and proliferating cell nuclear antigen (PCNA).

RESULTS

Zidovudine dramatically changed the proliferation and differentiation state of gingival tissues both when it was present throughout the growth period of the tissue and when it was added to established tissue at day 8. Zidovudine treatment increased the expression of cytokeratin 10, PCNA and cyclin A. Conversely, cytokeratin 5, involucrin and cytokeratin 6 expression was decreased. The tissue exhibited characteristics of increased proliferation in the suprabasal layers as well as an increased fragility and an inability to heal itself.

CONCLUSIONS

Zidovudine treatment, even when applied at low concentrations for short periods of time, deregulated the cell cycle/proliferation and differentiation pathways, resulting in abnormal epithelial repair and proliferation. Our system could potentially be developed as a model for studying the effects of HIV and highly active antiretroviral therapy in vitro.

Poly(ethylene oxide/propylene oxide) copolymer thermo-reversible gelling system for the enhancement of intranasal zidovudine delivery to the brain

The purpose of this study was to investigate the olfactory transfer of zidovudine (ZDV) after intranasal (IN) administration and to assess the effect of thermoreversible gelling system on its absorption and brain uptake. The nasal formulation was prepared by dissolving ZDV in pH 5.5 phosphate buffer solution comprising of 20% polyethylene oxide/propylene oxide (Poloxamer 407, PLX) as thermoreversible gelling agent and 0.1% n-tridecyl-β-D-maltoside (TDM) as permeation enhancer. This formulation exhibited a sufficient stability and an optimum gelation profile at 27-30 °C. The in vitro permeation studies across the freshly excised rabbit nasal mucosa showed a 53% increase in the permeability of ZDV from the formulation. For in vivo evaluation, the drug concentrations in the plasma, cerebrospinal fluid (CSF) and six different regions of the brain tissues, i.e. olfactory bulb (OB), olfactory tract (OT), anterior, middle and posterior segments of cerebrum (CB), and cerebellum (CL) were determined by LC/MS method following IV and IN administration in rabbits at a dose of 1mg/kg. The IN administration of Poloxamer 407 and TDM based formulation showed a systemic bioavailability of 29.4% while exhibiting a 4 times slower absorption process (t(max) = 20 min) than control solution (t(max) = 5 min). The CSF and brain ZDV levels achieved after IN administration of the gelling formulation were approximately 4.7-56 times greater than those attained after IV injection. The pharmacokinetic and brain distribution studies revealed that a polar antiviral compound, ZDV could preferentially transfer into the CSF and brain tissue via an alternative pathway, possibly olfactory route after intranasal administration.

Antiretroviral drug interactions

It has recently been estimated that persons with the acquired immunodeficiency syndrome (AIDS) receive on average 5.6 prescription medications throughout their disease course, and this number may be as high as 9 [1,2]. With the development and testing of new antiretroviral agents and drugs for opportunistic infections associated with human immunodeficiency virus (HIV) disease, the issue of polypharmacy and multiple drug interactions will become increasingly complex. Since antiretroviral therapy and treatment or prophylaxis of opportunistic infections is lifelong, the nature of these interactions requires delineation to provide an optimal pharmacologic strategy for the use of these agents in combination. This article will address antiretroviral drug interactions from a pharmacokinetic and pharmacodynamic perspective. A background on the clinical pharmacology of antiretroviral agents is provided as is a discussion of selected interactions.

Food-drug interactions

Interactions between food and drugs may inadvertently reduce or increase the drug effect. The majority of clinically relevant food-drug interactions are caused by food-induced changes in the bioavailability of the drug. Since the bioavailability and clinical effect of most drugs are correlated, the bioavailability is an important pharmacokinetic effect parameter. However, in order to evaluate the clinical relevance of a food-drug interaction, the impact of food intake on the clinical effect of the drug has to be quantified as well. As a result of quality review in healthcare systems, healthcare providers are increasingly required to develop methods for identifying and preventing adverse food-drug interactions. In this review of original literature, we have tried to provide both pharmacokinetic and clinical effect parameters of clinically relevant food-drug interactions. The most important interactions are those associated with a high risk of treatment failure arising from a significantly reduced bioavailability in the fed state. Such interactions are frequently caused by chelation with components in food (as occurs with alendronic acid, clodronic acid, didanosine, etidronic acid, penicillamine and tetracycline) or dairy products (ciprofloxacin and norfloxacin), or by other direct interactions between the drug and certain food components (avitriptan, indinavir, itraconazole solution, levodopa, melphalan, mercaptopurine and perindopril). In addition, the physiological response to food intake, in particular gastric acid secretion, may reduce the bioavailability of certain drugs (ampicillin, azithromycin capsules, didanosine, erythromycin stearate or enteric coated, and isoniazid). For other drugs, concomitant food intake may result in an increase in drug bioavailability either because of a food-induced increase in drug solubility (albendazole, atovaquone, griseofulvin, isotretinoin, lovastatin, mefloquine, saquinavir and tacrolimus) or because of the secretion of gastric acid (itraconazole capsules) or bile (griseofulvin and halofantrine) in response to food intake. For most drugs, such an increase results in a desired increase in drug effect, but in others it may result in serious toxicity (halofantrine).

Effect of food on the pharmacokinetics of (-) and (+) dOTC when administered as an oral racemate

The objective of this study was to evaluate the effect of food on the pharmacokinetics of racemic dOTC, a nucleoside analogue reverse transcriptase inhibitor, in adult male volunteers. Twelve healthy adult male subjects were enrolled in a randomized, open-label, single-dose crossover study. All were nonsmoking, within 15% of ideal body weight, and between 18 and 50 years of age. Subjects received single oral doses of 800mg racemic dOTC, in random order, either fed or fasted. The meal given to fed subjects was the standard Food and Drug Administration high-fat breakfast, and all subjects completed both study periods. Sixteen plasma samples for pharmacokinetic assessments were collected for 72 hours following dosing and assayed for (-) and (+) dOTC concentrations. Area under the plasma concentration-time curve (AUC), maximum observed plasma concentration (Cmax), and time to maximum concentration (tm) were determined for each enantiomer by standard noncompartmental techniques. Statistical hypothesis testing was by Wilcoxon signed rank, and the two one-sided tests procedure was used to determine bioequivalence between thefed and fasted study periods. The only effect of coadministration of racemic dOTC with food was a delay in time to peak concentration (t(max) of between 0.6 and 0.7 hours for both (-) and (+) dOTC stereoisomers (p < or =0.02). Neither AUC (p > or = 0.10) nor Cmax (p > or = 0.35) differed significantly between the fed and fasted study periods for either (-) or (+) dOTC. Both AUC and Cmax were equivalent between the fed and fasted study periods. It was concluded that there is no clinically significant effect of a high-fat meal on the pharmacokinetics of either (-) or (+) dOTC when administered orally as a racemic mixture.

Pharmacokinetic and other drug interactions in patients with AIDS

A variety of medications are used in treating patients infected with the human immunodeficiency virus (HIV). These medications are used to control viremia and to prevent and treat opportunistic infections. An individual is often required to take numerous drugs at the same time and thus clinicians are confronted with potential drug interactions, some of which are significant. Three different groups of anti-HIV drugs are used to treat patients. These groups include nucleoside reverse transcription inhibitors, non-nucleoside reverse transcription inhibitors, and protease inhibitors. This article reviews the most relevant drug interactions that occur during the treatment of HIV-infected patients with traditional and also alternative drugs. The role of therapeutic drug monitoring in the routine management of HIV-infected patients is discussed.

Abacavir/lamivudine/zidovudine as a combined formulation tablet: bioequivalence compared with each component administered concurrently and the effect of food on absorption

A single-center, open-label, three-way crossover study was conducted in 24 healthy subjects to assess (1) the bioequivalence of a combined abacavir 300 mg/lamivudine 150 mg/zidovudine 300 mg (A/L/Z) combination tablet relative to the separate brand-name components administered simultaneously and (2) the effect of food on the bioavailability of the drugs from the combination tablet. The subjects were randomly assigned to receive each of the following three treatments, separated by a 2-day washout period: one A/L/Z combination tablet after an overnight fast, one abacavir 300 mg tablet + one lamivudine 150 mg tablet + one zidovudine 300 mg tablet sequentially after an overnight fast, or one A/L/Z combination tablet 5 minutes after completing a standardized high-fat breakfast (67 g fat, 58 g carbohydrate, and 33 g protein). Serial blood samples were collected up to 24 hours postdose for determination of abacavir, lamivudine, and zidovudine serum concentrations. Standard pharmacokinetic parameters were estimated. Treatments were considered bioequivalent if 90% confidence intervals (CI) for geometric least squares (GLS) mean ratios for abacavir, lamivudine, and zidovudine area under the serum concentration-time curve (AUC(infinity)) and maximum observed serum concentration (Cmax) fell entirely within 0.80 to 1.25 for log-transformed parameters. The combined A/L/Z tablet was bioequivalent in the extent (AUC) and rate of absorption (Cmax and time of Cmax [tmax]) to the individual brand-name drug components administered concurrently under fasted conditions. GLS ratios and 90% CI for AUC(infinity) and Cmax were 0.99 (0.96, 1.03) and 1.00 (0.90, 1.11), respectively, for abacavir; 0.95 (0.91, 0.99) and 0.90 (0.84, 0.99), respectively, for lamivudine; and 0.95 (0.89, 1.02) and 0.96 (0.80, 1.15), respectively, for zidovudine. The extent of absorption of abacavir, lamivudine, and zidovudine from the combination tablet was not altered by administration with meals, indicating that this formulation may be administered with or without food. However, food slowed the rate of absorption, delayed the tmax, and reduced the Cmax of abacavir, lamivudine, and zidovudine. These changes, which were consistent with those observed with the individual reference formulations when administered with food, were not considered clinically important. All formulations were well tolerated underfasted and fed conditions.

Pharmacological basis for concentration-controlled therapy with zidovudine, lamivudine, and indinavir

Conventional antiretroviral therapy involves administration of standard fixed doses to adults and adolescents. This approach ignores interindividual variability in pharmacokinetics and results in substantial differences in systemic concentrations among patients. Thus, variability in systemic concentrations contributes to variability in response to therapy. This study was designed to evaluate the feasibility and safety of a regimen of zidovudine, lamivudine, and indinavir designed to achieve select target concentrations versus standard dose therapy. Twenty-four antiretroviral-naïve subjects completed the 24-week study; 13 received standard therapy, and 11 received concentration-controlled therapy. There were no differences in baseline characteristics. Oral clearance for all three drugs was not different between weeks 2 and 28; average ratios of week 2 oral clearance to week 28 oral clearance were 0.95, 1.09, and 1.06 for zidovudine, lamivudine, and indinavir, respectively, with 95% confidence intervals including 1. The selected target concentrations were average steady-state concentrations of 0.19 mg/liter for zidovudine and 0.44 mg/liter for lamivudine and a trough concentration of 0.15 mg/liter for indinavir; mean concentrations achieved at week 28 in the concentration-controlled arm were 0.20, 0.54, and 0.19 mg/liter, respectively. Concentration-controlled therapy significantly reduced interpatient variability in zidovudine concentrations and significantly increased indinavir concentrations. There was no difference in adverse drug effects or adherence. This investigation has provided a pharmacologic basis for concentration-controlled therapy by demonstrating that it is feasible and has a safety profile no different from that of standard therapy. Additional studies to evaluate the virologic effect of the concentration-controlled approach to antiretroviral therapy are warranted.

Abacavir: absolute bioavailability, bioequivalence of three oral formulations, and effect of food

STUDY OBJECTIVES

Study A: to determine the absolute bioavailability of a single 300-mg abacavir hemisulfate tablet. Study B: to determine the bioequivalence of two oral abacavir formulations (300-mg hemisulfate tablet, 100-mg succinate caplet), the effect of food on the bioavailability of the 300-mg hemisulfate tablet, and the bioavailability of the hemisulfate tablet relative to the hemisulfate solution.

DESIGN

Phase I, randomized, open-label, balanced two- (study A) and three- or four-period (study B), crossover studies.

SETTING

Two clinical research centers.

SUBJECTS

Six men infected with the human immunodeficiency virus (HIV), aged 27-39 years (study A), and 18 HIV-infected men and women, aged 21-50 years (study B).

INTERVENTIONS

In study A, all subjects received a single, oral 300-mg tablet of abacavir hemisulfate or a single, intravenous infusion of abacavir hemisulfate 150 mg over 60 minutes. In study B, all subjects received each of three single-dose treatments: three 100-mg abacavir succinate caplets in a fasted state, one 300-mg abacavir hemisulfate tablet in a fasted state, and one 300-mg abacavir hemisulfate tablet with a high-fat breakfast. Twelve subjects in study B also received a fourth treatment of abacavir hemisulfate 300 mg as an oral solution in a fasted state. Plasma samples collected for 24 hours (study A) or 12 hours (study B), and urine samples collected for 12 hours (study A) were analyzed by validated high-performance liquid chromatographic methods.

MEASUREMENTS AND MAIN RESULTS

Abacavir pharmacokinetic parameters were calculated using standard, noncompartmental methods. In study A, the geometric least square (GLS) mean absolute bioavailability of oral abacavir was 83% (range 65-107%). In study B, the hemisulfate tablet was bioequivalent to the succinate caplet, but its time to maximum concentration (Tmax) occurred 30 minutes earlier. Administration of the abacavir hemisulfate tablet with food had no effect on area under the curve from time zero to infinity (AUC0-infinity), decreased maximum concentration (Cmax) by 26%, and delayed Tmax by 38 minutes. The relative bioavailability (GLS mean AUC0-infinity ratio) of the 300-mg abacavir hemisulfate tablet to solution was 101%, Cmax was 11% lower, and Tmax was unchanged. The most common drug-related adverse events associated with abacavir were nausea, vomiting, abdominal pain, and headache, all of which were mild.

CONCLUSION

Based on our results, abacavir is safe and well tolerated and can be administered with or without meals.

Single-dose pharmacokinetics and safety of abacavir (1592U89), zidovudine, and lamivudine administered alone and in combination in adults with human immunodeficiency virus infection

Abacavir (1592U89), a nucleoside reverse transcriptase inhibitor with in vitro activity against human immunodeficiency virus type-1 (HIV-1), has been evaluated for efficacy and safety in combination regimens with other nucleoside analogs, including zidovudine (ZDV) and lamivudine (3TC). To evaluate the potential pharmacokinetic interactions between these agents, 15 HIV-1-infected adults with a median CD4(+) cell count of 347 cells/mm3 (range, 238 to 570 cells/mm3) were enrolled in a randomized, seven-period crossover study. The pharmacokinetics and safety of single doses of abacavir (600 mg), ZDV (300 mg), and 3TC (150 mg) were evaluated when each drug was given alone or when any two or three drugs were given concurrently. The concentrations of all drugs in plasma and the concentrations of ZDV and its 5'-glucuronide metabolite, GZDV, in urine were measured for up to 24 h postdosing, and pharmacokinetic parameter values were calculated by noncompartmental methods. The maximum drug concentration (Cmax), the area under the concentration-time curve from time zero to infinity (AUC0-infinity), time to Cmax (Tmax), and apparent elimination half-life (t1/2) of abacavir in plasma were unaffected by coadministration with ZDV and/or 3TC. Coadministration of abacavir with ZDV (with or without 3TC) decreased the mean Cmax of ZDV by approximately 20% (from 1.5 to 1.2 microg/ml), delayed the median Tmax for ZDV by 0.5 h, increased the mean AUC0-infinity for GZDV by up to 40% (from 11.8 to 16.5 microg. h/ml), and delayed the median Tmax for GZDV by approximately 0.5 h. Coadministration of abacavir with 3TC (with or without ZDV) decreased the mean AUC0-infinity for 3TC by approximately 15% (from 5.1 to 4.3 microg. h/ml), decreased the mean Cmax by approximately 35% (from 1.4 to 0.9 microg/ml), and delayed the median Tmax by approximately 1 h. While these changes were statistically significant, they are similar to the effect of food intake (for ZDV) or affect an inactive metabolite (for GZDV) or are relatively minor (for 3TC) and are therefore not considered to be clinically significant. No significant differences were found in the urinary recoveries of ZDV or GZDV when ZDV was coadministered with abacavir. There was no pharmacokinetic interaction between ZDV and 3TC. Mild to moderate headache, nausea, lymphadenopathy, hematuria, musculoskeletal chest pain, neck stiffness, and fever were the most common adverse events reported by those who received abacavir. Coadministration of ZDV or 3TC with abacavir did not alter this adverse event profile. The three-drug regimen was primarily associated with gastrointestinal events. In conclusion, no clinically significant pharmacokinetic interactions occurred between abacavir, ZDV, and 3TC in HIV-1-infected adults. Coadministration of abacavir with ZDV or 3TC produced mild changes in the absorption and possibly the urinary excretion characteristics of ZDV-GZDV and 3TC that were not considered to be clinically significant. Coadministration of abacavir with ZDV and/or 3TC was generally well tolerated and did not produce unexpected adverse events.

Lamivudine/zidovudine as a combined formulation tablet: bioequivalence compared with lamivudine and zidovudine administered concurrently and the effect of food on absorption

A single-center, open-label, three-way crossover study was conducted in 24 healthy subjects to assess (1) the bioequivalence of a combined lamivudine 150 mg/zidovudine 300 mg tablet relative to the separate brand-name components administered concurrently and (2) the effect of food on the bioavailability of the drugs from the combination tablet. The subjects were randomly assigned to receive each of the following three treatments, separated by a 5- to 7-day washout period: one lamivudine/zidovudine combination tablet after an overnight fast, one lamivudine 150 mg tablet and one zidovudine 300 mg tablet simultaneously after an overnight fast, or one lamivudine/zidovudine combination tablet 5 minutes after completing a standardized high-fat breakfast (67 g fat, 58 g carbohydrate, and 33 g protein). Serial blood samples were collected up to 24 hours postdose for the determination of lamivudine and zidovudine plasma concentrations. Standard pharmacokinetic parameters were estimated. Treatments were considered bioequivalent if 90% confidence intervals for the ratio of least squares (LS) means for the lamivudine and zidovudine area under the plasma concentration-time curve (AUC infinity) and maximum observed plasma concentration (Cmax) fell entirely within 0.80 to 1.25 for log-transformed parameters. The combined lamivudine/zidovudine tablet was bioequivalent in the extent (AUC infinity) and rate of absorption (Cmax and time of Cmax [tmax]) to the individual brand-name drug components administered concurrently under fasted conditions. Geometric LS mean ratios and 90% confidence intervals for AUC infinity and Cmax were 0.97 (0.92, 1.03) and 0.94 (0.84, 1.06), respectively, for lamivudine and 0.99 (0.91, 1.07) and 0.97 (0.82, 1.15), respectively, for zidovudine. The extent of absorption of lamivudine and zidovudine from the combination tablet was not altered by administration with meals, indicating that this formulation may be administered with or without food. However, food slowed the rate of absorption, delayed the tmax, and reduced the Cmax of lamivudine and zidovudine. These changes were not considered clinically important. All formulations were well tolerated under fasted and fed conditions.

Pharmacology of Antiretroviral Drugs

In this paper, an overview of the pharmacokinetics of currently available antiretroviral drugs is provided. Included in this article are the agents zidovudine, stavudine, zalcitabine, lamivudine, didanosine, abacavir, nevirapine, delavirdine, efavirenz, saquinavir, indinavir, ritonavir and nelfinavir. Key pharmacokinetic parameters, drug penetration in body compartments and drug interactions are discussed for each agent.

Effect of food on the bioavailability of stavudine in subjects with human immunodeficiency virus infection

A randomized, three-way crossover study was carried out to determine the effects of food ingestion on the pharmacokinetics of stavudine (d4T). Fifteen subjects with human immunodeficiency virus (HIV) infection and CD4(+) cell counts of >/=200/microliter received 70 mg of d4T in a fasting state or 1 h before or 5 min after a standardized high-fat breakfast. A 7- to 15-day washout period was included between treatments. Blood and urine were collected before and for 10 h after dosing, and plasma and urine d4T concentrations were determined with a validated radioimmunoassay. Plasma drug concentration-time data were analyzed with a noncompartmental model. The mean maximum plasma drug concentration (Cmax) and the time to Cmax (Tmax) for administration of d4T after a meal were significantly lower and longer (P = 0.0001 for both measures) than those observed in the fasting state, although the area under the concentration-time curve from time zero to infinity (AUC0-infinity) was not significantly different. Neither of these parameters was significantly altered when d4T was taken 1 h before a meal. The bioavailability of d4T taken after a meal was 95% of that observed in the fasting state, and it was 97% when d4T was administered before a meal (P > 0.05 for both comparisons with the fasting state). The results of this study indicate that (i) ingestion of food does not affect the bioavailability of d4T and that patients with HIV infection can take it without regard to meals, and (ii) absorption is essentially complete within 1 h when d4T is administered in the fasted state.

An update on drug interactions with zidovudine

Zidovudine remains one of the most commonly prescribed agents for patients with HIV infection. A variety of drug interactions have been reported that may alter blood levels of zidovudine and concomitantly administered drugs or may involve overlapping toxicities. Several concomitant medications have been shown to alter the plasma concentrations of zidovudine, although most of these interactions are not thought to be clinically important. Use of agents that share the bone marrow-suppressive properties of zidovudine require additional monitoring for the development of hematologic toxicity. An understanding of potential mechanisms and important zidovudine-related interactions will aid in the optimal care of the HIV-infected patient.

Chemotherapeutic agents for human immunodeficiency virus infection: mechanism of action, pharmacokinetics, metabolism, and adverse reactions

Since the mid-1980s, four new nucleoside reverse transcriptase (RT) inhibitors (zalcitabine, didanosine, stavudine, and lamivudine), two nonnucleoside RT inhibitors (nevirapine and delavirdine), and four new protease inhibitors (saquinavir, ritonavir, indinavir, and nelfinavir) have been approved by the US Food and Drug Administration for the treatment of patients with acquired immunodeficiency syndrome. The driving force behind the development of these new agents has been the increasing need for more potent agents with reduced or modified toxicity profiles. The purpose of this article is to review the absorption, distribution, metabolism, elimination, toxicities, adverse reactions, and mechanism of action of the currently available drugs.

Pharmacokinetics of saquinavir, zidovudine, and zalcitabine in combination therapy

We investigated the pharmacokinetics of zidovudine, zalcitabine, and saquinavir in AIDS Clinical Trial Group protocol 229. Patients received either saquinavir, zalcitabine, or a combination of both, together with zidovudine three times a day. Approximately 100 patients were enrolled in each treatment arm, and intensive pharmacokinetic studies were performed on about 25 patients per arm at weeks 1 and 12. We estimated the pharmacokinetic parameters of all three drugs by using parametric and nonparametric methods. The mean values of the pharmacokinetic parameters of zidovudine (clearance [CL]/bioavailability [F], 168 liters/h; volume of distribution [V]/F, 185 liters; half-life, 0.76 h) and zalcitabine (CL/F, 25 liters/h; V/F, 92.2 liters; half-life, 2.7 h) were similar to those reported previously. For saquinavir, the mean pharmacokinetic parameter estimates using parametric methods were as follows: maximum concentration of drug in serum [Cmax], 70.8 ng/ml; time to Cmax, 3.11 h; area under the curve, 809 ng x h/ml; CL/F, 989 liters/h; V/F, 1,503 liters; half-life, 1.38 h. For all three drugs, clearance decreased with age. Weight did not influence the clearance of zidovudine, but the clearance of zalcitabine and saquinavir increased with weight. There were no differences in pharmacokinetic parameters between study weeks and arms, suggesting that there is no change in kinetics with chronic administration and that there are no significant pharmacokinetic interactions among these three drugs.

Clarithromycin does not affect phosphorylation of zidovudine in vitro

Zidovudine (ZDV) and clarithromycin (CLR) are often used simultaneously in the management of patients with AIDS. While pharmacokinetic studies show decreased absorption of ZDV when it is administered with CLR, it is unknown if CLR affects the intracellular metabolism of ZDV. We investigated the effects of CLR on the intracellular metabolism of ZDV in vitro. CEM-T4 cells were coincubated with a microM ZDV ([3 H] ZDV, 3 microCi/ml) either alone or with 1 or 10 microM CLR. Cells were also grown in the presence of CLR for 48 h prior to exposure to ZDV. Samples were analyzed for mono-, di-, and triphosphate metabolites of [3 H] ZDV by high-performance liquid chromatography separation and radiochemical detection. There were no significant differences in levels of intracellular metabolites of ZDV following exposure to ZDV, either alone or with 1 or 10 microM CLR and under both coincubated and preincubated conditions. These results show that treatment with CLR does not alter the formation of phosphorylated metabolites of ZDV in this cell line.

Clinical pharmacokinetics of zidovudine. An update

The battle against the acquired immune deficiency syndrome (AIDS) is now into its second decade, and substantial advancements have been made in our understanding of the complex life cycle of, and the immunopathology associated with, human immunodeficiency virus (HIV) infection, as well as of the drugs used to modify the course of disease. Zidovudine was the first agent approved for treatment of HIV disease, and since its widespread availability in 1987 the pharmacokinetic disposition and clinical effects of zidovudine have been extensively evaluated. This article reviews the absorption, distribution, metabolism and elimination characteristics of zidovudine, focusing on more recent information. In addition, factors that may or may not affect zidovudine disposition are discussed. These include selected drug interactions and concomitant disease states such as renal and hepatic insufficiency. Issues such as bodyweight normalisation, maternal-fetal transfer, pregnancy and intracellular phosphorylation are discussed in relation to the pharmacokinetics and clinical efficacy of zidovudine. Finally, information regarding the clinical pharmacodynamics of zidovudine is presented. This includes possible relationships between zidovudine pharmacokinetics and markers of efficacy and toxicity, and the significance of linking pharmacokinetic and pharmacodynamic information.

Pharmacokinetics and bioavailability of zidovudine and its glucuronidated metabolite in patients with human immunodeficiency virus infection and hepatic disease (AIDS Clinical Trials Group protocol 062)

The pharmacokinetics of zidovudine (ZDV) are established in patients with various stages of human immunodeficiency virus (HIV) disease. This study was conducted to determine the pharmacokinetic parameters of ZDV in patients with asymptomatic HIV infection and liver disease. HIV-infected volunteers with normal renal function were stratified according to the severity of liver disease (seven of eight were classified as mild). Each subject received a single intravenous dose of ZDV (120 mg) on the first day, followed by a single oral dose of ZDV (200 mg) on the second day. Blood samples were obtained over a 8-h collection interval, and concentrations of ZDV and its glucuronidated metabolite (GZDV) were determined by high-performance liquid chromatography. The following pharmacokinetic parameters were obtained after oral administration of ZDV to HIV-infected patients with mild hepatic disease; these values were compared with previously reported data in healthy volunteers. The area under the curve (AUC) (1,670 +/- 192 ng.h/ml), maximum concentration of drug in serum (1,751 +/- 180 ng/ml), and half-life (2.04 +/- 0.38 h) of ZDV were increased, while the apparent oral clearance (1.57 +/- 0.31 liter/h/kg of body weight) was decreased; AUC (7,685 +/- 1,222 ng.h/ml) and maximum concentration of drug in serum (5,220 +/- 1,350 ng/ml) of GZDV and the AUC ratio of GZDV to ZDV (2.79 +/- 0.43) after oral administration were decreased. ZDV absolute bioavailability was 0.75 +/- 0.15 in HIV-infected patients with hepatic disease. Although the ZDV apparent oral clearance was not impaired as significantly as in patients with biopsy-proven cirrhosis, our results suggest that ZDV, could accumulate in HIV-infected patients with mild hepatic disease because of impaired formation of GZDV. Patients with mild hepatic disease may require dosage adjustment to avoid accumulation of ZDV after extended therapy.

Pharmacokinetics of orally administered zidovudine in HIV-infected children and adults

The pharmacokinetics of oral zidovudine in HIV-infected children and adults are reported. Fourty-six patients were investigated. For data analysis three groups of similar size were formed: young children 4 months-4 years, n = 15 (group 1), older children up to 13 years, n = 16 (group 2) and young adults, n = 15 (group 3). After a single oral dose repeated blood samples were taken 1/2 hourly during a period of 4 hours and zidovudine concentrations in plasma were determined by high performance liquid chromatography. For better comparison of dose dependent parameters peak concentrations (Cmax) and the area under the time-concentration curves (AUC) were normalized either to the dose/body weight (bw) or the dose/body surface area (bs), respectively. Time to reach peak concentrations and mean terminal elimination half-life times (t1/2 beta = 63.4 +/- 47.6, 74.9 +/- 54.9 and 56.9 +/- 16.4 min in group 1, 2 and 3, respectively, mean +/- SD) were not significantly different between the three groups. With normalization to dose/bw young children in comparison to adults had significantly lower Cmax (2.7 +/- 1.3 vs. 4.6 +/- 2.4 mumol/l, p = 0.016) and AUC (226 +/- 108 vs. 373 +/- 224 mumol.min/l, p = 0.038). Group 2 gave intermediate values. However, with normalization to dose/bs differences in Cmax (6.5 +/- 3.3, 7.3 +/- 4.2 and 6.8 +/- 3.6 mumol/l, in group 1, 2, and 3, respectively) and AUC (563 +/- 313, 691 +/- 351 and 555 +/- 342 mumol.min/l, in group 1, 2 and 3) were not significant between the three groups. It is likely that changes in body water content with age may account for most of these differences observed. In conclusion, a similar pharmacokinetic profile was found in children older than 3 months as compared to older children or adults.

The effect of food on pharmacokinetics of zalcitabine in HIV-positive patients

PURPOSE

The purpose of this study was to determine the effect of food on the pharmacokinetics of zalcitabine in HIV-positive patients.

METHODS

Twenty patients received single oral 1.5 mg doses of zalcitabine with and without a standard breakfast in an open-label, randomized crossover study with at least a one week washout period between treatments. Serial blood and urine samples were collected over 24 hours and assayed for zalcitabine by a modified GC/MS method.

RESULTS

Administration with food delayed and prolonged absorption resulting in a decrease of approximately 39% in maximal plasma concentrations compared to dosing under fasting conditions. Comparison of plasma AUC values indicated a small (14%) reduction in bioavailability when given with food. Approximately 59% and 45% of the dose were excreted unchanged in the urine under fasting and fed conditions, respectively.

CONCLUSIONS

The results of this study show that the administration of zalcitabine with food results in a mild reduction in bioavailability. Although these changes are not expected to be of clinical importance, further studies must be conducted for confirmation.

Concise overview of the clinical pharmacokinetics of dideoxynucleoside antiretroviral agents

In this paper aspects of the clinical pharmacokinetics of the antiretroviral agents zidovudine, didanosine and zalcitabine are reviewed. Special attention is paid to possibly altered pharmacokinetics in special circumstances, such as hepatic and renal dysfunction, pregnancy, stage of disease, etc. The dideoxynucleoside antiretroviral agents have some clinical pharmacokinetic properties in common (rapid absorption and elimination), but substantial differences exist in their degree of absorption, metabolism and penetration into the cerebrospinal fluid. All agents display wide interpatient variability in pharmacokinetic parameters. The relevance of therapeutic drug monitoring of antiretroviral agents is also discussed.

Management of antiretroviral drug therapy in human immunodeficiency virus infection

Nucleoside analog reverse transcriptase inhibitors, including zidovudine, didanosine, and zalcitabine, remain the cornerstone of therapy against human immunodeficiency virus (HIV) infection, the cause of AIDS. Although therapeutic regimens have been designed that are effective in slowing the progression of disease, therapy with these agents has not been optimized. Ultimately, therapy is destined to fail in most patients. Decisions regarding when to begin therapy and the course of action to take when failure of therapy occurs are largely in the hands of the patient's physician, and currently must be made without the support of conclusive clinical data. In addition to an understanding of the recommended dosing guidelines, proper management of AIDS therapy requires a fundamental knowledge of the disease process, the pharmacology and limitations of the agents employed against the virus, and close cooperation with the clinical laboratory. Therefore, this article reviews the pharmacology of the three drugs currently approved for treatment of HIV infection, and the current guidelines for their use. The article also reviews the clinical and laboratory management of these agents, including the use of surrogate markers and the potential for pharmacokinetic optimization of therapy.

Effects of standard breakfast on pharmacokinetics of oral zidovudine in patients with AIDS

The influence of a standard breakfast on the single-dose pharmacokinetics of zidovudine (AZT) after oral administration of 100 and 250 mg of AZT was studied in 27 subjects with advanced human immunodeficiency virus infection (Centers for Disease Control stage IV). Concentrations of AZT and the 5'-glucuronide metabolite (GAZT) in serum and urine were measured by a high-pressure liquid chromatographic method. Pharmacokinetic analysis was done by an open one-compartment model as well as noncompartmentally. The results were summarized as medians with 50% confidence ranges because of the high degree of interindividual variability. Peak levels in plasma were moderately reduced after administration of 100 mg AZT in the nonfasting group (1.79 mumol/liter in the fasting group [F], 1.12 mumol/liter in the group that received breakfast [B]) and were markedly reduced after administration of 250 mg AZT (6.51 mumol/liter [F], 1.79 mumol/liter [B]). The terminal half-life in plasma was prolonged almost twofold after breakfast with 100 and 250 mg of AZT (100 mg, 36.4 min [F] and 51.6 min [B]; 250 mg, 35.3 min [F] and 63.6 min [B]). Recoveries (AZT and GAZT) in urine varied with both dosages, reflecting more a problem of accounting for the metabolite GAZT in urine than a relevant difference (100 mg, 115% [F] and 76.5% [B]; 250 mg, 71% [F] and 99.4% [B]). Our data suggest that absorption of AZT in human immunodeficiency virus-infected subjects is extremely variable, with a high degree of interindividual differences. Furthermore, breakfast had a marked influence on the absorption of AZT, suggesting that the drug should be taken in a fasting state.

Zidovudine. An update of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Zidovudine remains the mainstay in the treatment of patients infected with human immunodeficiency virus (HIV). The drug delays disease progression to acquired immunodeficiency syndrome (AIDS) and to AIDS-related complex (ARC), reduces opportunistic infections, and increases survival in patients with advanced HIV infection. There is evidence to suggest that zidovudine also delays disease progression in patients with mild symptomatic disease. Although one study has shown zidovudine to have no significant beneficial effects on survival or disease progression in patients with asymptomatic HIV infection, several other studies have shown zidovudine to delay disease progression in this patient group. Results from related ongoing studies are awaited with interest. Zidovudine reduces the incidence of AIDS dementia complex (ADC) and appears to prolong survival in these patients, and improves other neurological complications of HIV infection. The drug also appears to enhance the efficacy of interferon-alpha in patients with Kaposi's sarcoma. Although zidovudine is widely used as postexposure prophylaxis following accidental exposure to HIV, its efficacy in preventing seroconversion is unclear. Whether zidovudine prevents vertical transmission also remains to be determined. The overall efficacy of zidovudine in the treatment of children with HIV infection appears similar to that in adults despite more rapid disease progression in younger patients. Zidovudine-resistant isolates can emerge as early as after 2 months' therapy, and primary infection with zidovudine-resistant strains has been documented. Both zidovudine resistance and the syncytium-inducing HIV phenotype appear to be associated with poor clinical outcome. However, zidovudine resistance may revert on drug withdrawal or switching to an alternative therapy. Zidovudine-associated haematotoxicity may be dose-limiting. Nonhaematological adverse events associated with zidovudine therapy are generally mild and usually resolve spontaneously. Dosages of approximately 500 to 600 mg/day appear to be at least as effective as dosages of 1200 to 1500 mg/day and are better tolerated in patients with less advanced disease. However, optimal dosage are unclear. Despite beneficial effects, zidovudine monotherapy is not curative. There is evidence to suggest that the concomitant administration of zidovudine with didanosine or zalcitabine is effective in patients with HIV disease progression despite receiving zidovudine monotherapy, and there is some evidence that concomitant zidovudine plus didanosine therapy is more effective than alternating monotherapy. However, results from studies of combination therapy in asymptomatic patients, and from comparative combination therapy studies are awaited. Cotherapy with agents that augment haematopoiesis allows the continuation of therapeutic zidovudine dosages.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetic interaction between rifampin and zidovudine

A potential pharmacokinetic interaction between rifampin (Rimactan, Rifadin) and zidovudine (AZT, Retrovir) was investigated in the population of human immunodeficiency virus-infected patients at our hospital. The results from four patients who were on long-term (> or = 6 months) combination therapy with zidovudine and rifampin are presented. In all cases of combined use of zidovudine and rifampin, a lower area under the plasma concentration-time curve (AUC) and, consequently, a higher apparent clearance of zidovudine were found, compared with a reference population of zidovudine users. Patients had a low to normal maximum concentration of zidovudine in plasma. Elimination half-lives were normal in all but one patient. Zidovudine glucuronide concentrations were determined in three patients and three control subjects. The patients all had relatively higher peak plasma concentrations and higher AUCs of zidovudine glucuronide than the control subjects. In one patient, zidovudine and zidovudine glucuronide were also measured 2.5 months after discontinuation of rifampin. The AUC of zidovudine increased by a factor of 2. These data are in agreement with an enzyme-inducing effect of rifampin on the glucuronidation of zidovudine. They indicate that long-term combination therapy of rifampin and zidovudine leads to increased clearance of zidovudine, which may have therapeutic consequences.

Absorption of zidovudine in patients with diarrhoea

Many patients with AIDS have gastrointestinal complaints, including the major clinical disorder of chronic diarrhoea. The pharmacokinetics of zidovudine was studied in 9 male patients with HIV infection and diarrhoea to establish whether drug absorption was impaired in them. The peak plasma concentration and AUC after a single oral dose of 200 mg, were the same as those reported in 6 healthy male volunteers (3.1 vs 4.0 mumol.l-1 and 7.2 vs 5.2 mumol.h.l-1, respectively). Since the bioavailability of zidovudine is not particularly impaired, oral zidovudine therapy can be maintained in patients with diarrhoea.

Zalcitabine

OBJECTIVE

To review the chemistry, intracellular metabolism, pharmacokinetics, and clinical trials of zalcitabine (2'3'-dideoxycytidine, ddC).

DATA SOURCES

English-language articles and conference procedings. The indexing terms used were zalcitabine, 2'3'-dideoxycytidine, and ddC.

STUDY SELECTION

In addition to the manufacturer's package insert, available Phase I and Phase I/II studies were reviewed.

DATA EXTRACTION

Clinical experience with ddC has been limited to uncontrolled studies and an expanded-access program. Efficacy was evaluated solely on surrogate markers of HIV disease: CD4+ lymphocyte counts and p24 antigen determinations. Clinical endpoints, such as disease progression and survival rates, must be provided to the Food and Drug Administration (FDA) for continued approval.

DATA SYNTHESIS

The FDA has approved use of ddC in combination with zidovudine (ZDV) as therapy of HIV infection for patients with CD4+ lymphocyte counts < or = 300 cells/mm3 who have experienced significant clinical or immunologic deterioration. Although ddC has the same mechanism of action as other nucleoside analogs, it is more potent on a molar basis. The drug is stable in gastric pH and has good bioavailability (approximately 70-90 percent), but is rapidly cleared from plasma (half life approximately 1-3 h). Intracellular concentrations of ddC triphosphate, the active form, are probably related to plasma concentrations, yet may persist in cells longer than the parent drug persists in plasma. When used as primary therapy in patients with CD4+ < or = 300 cells/mm3, ddC/ZDV increased CD4+ lymphocyte counts and reduced plasma p24 antigen concentrations. In comparison to ZDV monotherapy data taken from other studies, ddC/ZDV appeared to demonstrate a more pronounced and sustained increase in CD4+ cell counts; however, this observation cannot be confirmed until the results of ZDV-controlled comparisons are available. Overall, 17-31 percent of the patients receiving the currently recommended initial dosage of ddC experience peripheral neuropathy.

CONCLUSIONS

In combination with ZDV, ddC appears to augment the CD4+ cell response of ZDV monotherapy in the treatment of HIV infection for ZDV-naive patients, although controlled studies and rigorous statistical analyses are lacking at present. The efficacy of ddC/ZDV in patients who received prior treatment with ZDV monotherapy is unclear at the present.

Pharmacokinetics of concomitantly administered foscarnet and zidovudine for treatment of human immunodeficiency virus infection (AIDS Clinical Trials Group protocol 053)

Foscarnet and zidovudine (ZDV) pharmacokinetic parameters were not altered in five patients receiving 14 days of concomitant therapy. Foscarnet clearance in plasma averaged (+/- standard deviation) 0.16 +/- 0.03 and 0.13 +/- 0.05 liter/h/kg of body weight in the absence and presence of ZDV. ZDV parameters were also not significantly altered, with a mean (+/- standard deviation) oral clearance of 2.7 +/- 1.0 and 2.6 +/- 0.8 liter/h/kg for the 2 study days, respectively.

The effect of a protein meal on zidovudine pharmacokinetics in HIV-infected patients

Eleven HIV-infected men participated in a randomized, two-treatment, two-period crossover study to determine the effect of a 25 g protein meal on zidovudine pharmacokinetics. On two separate occasions, 1 week apart, each patient received 200 mg zidovudine in a fasting state or immediately following the protein meal. A protein meal significantly decreased Cmax [532 (228 s.d.) vs 802 (452 s.d.) ng ml-1, P = 0.004] and increased mean residence time (138 (26 s.d.) vs 114 (26 s.d.) min, corrected for lag times, P = 0.001). However, AUC, tmax, terminal half-life and renal clearance were not significantly altered (P greater than 0.05). The power to detect a 20% change in AUC was 98% at the 5% significance level. In contrast to fat-containing foods, protein-based meals may not alter the extent of zidovudine absorption.