Drug interactions with zidovudine

Zidovudine continuous infusion in an HIV-infected pregnant woman with a phobia of swallowing pills

The authors report the difficulties of preventing mother-to-child transmission in a pregnant HIV-infected woman with a phobia of swallowing pills. After multiple attempts and just as many failures, the authors ended up with cART consisting of small tablets of nevirapine, lamivudine and a continuous intravenous infusion of zidovudine given via an elastomeric pump at home. This case demonstrates the difficulties that HIV physicians can encounter in pregnant women who have difficulties in swallowing tablets. In exceptional circumstances, continuous infusion of zidovudine may be an option, even in an outpatient setting.

Significant Drug Interactions in the HIV Patient

Current treatment guidelines advocate the use of triple combination antiretroviral therapy for the management of human immunodeficiency virus (HIV) infection with one protease inhibitor (PI) or nonnucleoside reverse transcriptase inhibitor (NNRTI) plus two nucleoside reverse transcriptase inhibitors (NRTIs). Additionally, patients often receive medications for prophylaxis and treatment of opportunistic infections and comorbid illnesses. Polypharmacy with potent medications places the patient with HIV at significant risk of drug interactions. The purpose of this review is to assist clinicians regarding awareness and management of clinically significant drug interactions frequently encountered in the HIV population.

Pharmacodynamic and pharmacokinetic interactions are discussed in depth with several tables of significant interactions encountered in the patient with HIV. Certain combinations of NRTIs have antagonistic antiretroviral action (e.g., zidovudine plus stavudine), and thus should be avoided. All of the currently available PIs and delavirdine are cytochrome (CYP) 450 inhibitors and can cause significant inhibition of concomitant drug metabolism. Nevirapine is a CYP 450 inducer and can cause induction of drug metabolism, whereas efavirenz may cause inhibition or induction. Drug-herbal interactions are reviewed, including the decreased concentrations of indinavir following the administration of St. John’s wort. Additionally, the pharmacist’s role as an integral member of the HIV patient care team is discussed.

Effect of Herpesvirus Inhibition on Primary SIV Infection in Cynomolgus Monkeys

Foscarnet and (-)9-[4-hydroxy-2-(hydroxymethyl)butyl] guanine (H2G) have already been shown to inhibit herpesviruses in vitro and also to inhibit viral antigen production in primary SIV infection in monkeys. Attempts have been made to determine if these invivo effects on SIV were due to a direct effect on SIV or were mediated through inhibition of endogenous transactivating herpesviruses. The possible involvement of herpesviruses in primary SIVsm infection in monkeys was studied by the use of various inhibitors of herpesvirus replication. Subcutaneous injections of 3 × 5 mg kg−1 day−1 of aciclovir, 3 × 5 mg kg−1 day−1 of ganciclovir and 3 × 28 mg kg−1 day−1 of phosphonoacetic acid had no effect on primary SIVsm infection in cynomolgus monkeys. These doses of aciclovir, ganciclovir and phosphonoacetic acid are inhibitory to several herpesviruses. The results suggest that the effects of foscarnet and H2G on primary SIVsm infection in monkeys are direct and not mediated through inhibition of a replicating herpesvirus.

Early upper digestive tract side effects of zidovudine with tenofovir plus emtricitabine in West African adults with high CD4 counts

INTRODUCTION

Tenofovir (TDF) with emtricitabine (FTC) and zidovudine (ZDV) is a recognized alternate first-line antiretroviral (ART) regimen for patients who cannot start treatment with non-nucleoside reverse transcriptase inhibitors (NNRTIs). Clinical studies comparing TDF+FTC+ZDV to other regimens are lacking.

METHODS

Participants in a trial of early ART in Côte d'Ivoire (Temprano ANRS 12136) started treatment with TDF/FTC plus either efavirenz (EFV) or ZDV (HIV-1+2 dually infected patients and women refusing contraception or previously treated with nevirapine). We compared rates of upper digestive serious adverse events (sAEs) between TDF/FTC+EFV and TDF/FTC+ZDV patients during the first six months of treatment. sAEs were defined as either grade 3-4 AEs or persistent grade 1-2 AEs leading to drug discontinuation.

RESULTS

A total of 197 patients (76% women, median CD4 count 395/mm(3)) started therapy with TDF/FTC, 126 with EFV and 71 with ZDV. During the first six months of ART, 94 patients had digestive AEs (nausea/vomiting) of any grade (EFV 36/126, 29%; ZDV 58/71, 82%, p<0.0001), including 20 sAEs (EFV 3/126, 5%; ZDV 17/71, 24%, p<0.0001). In-patients on TDF/FTC+ZDV with digestive AEs, the median time to the first symptom was two days (IQR: 1-4). Plasma ZDV (Cmax) distributions and pill ZDV dosages were normal. Patients with digestive AEs had higher haemoglobin levels and tended to have higher body mass indices and more frequent past histories of cotrimoxazole (CTX) prophylaxis.

CONCLUSIONS

We observed an unexpectedly high rate of digestive sAEs in West African adults, mostly women, who started a 3-nuc ART with TDF/FTC+ZDV in Côte d'Ivoire. These adults were participating in a trial of early ART and had much higher CD4 counts than those who currently routinely start ART in sub-Saharan Africa. They all received CTX concomitantly with ZDV. We suggest that further early prescriptions of TDF+XTC+ZDV should be carefully monitored and that whenever possible, the rate of early upper digestive adverse events should be compared to that occurring in-patients taking other drug regimens.

CLINICAL TRIAL NUMBER

NCT00495651.

Pharmacokinetic interaction between zidovudine and trimethoprim/sulphamethoxazole in HIV-1 infected children

OBJECTIVE

To evaluate the effect of the antimicrobial agent trimethoprim/sulphamethoxazole (TMP/SMX) on the pharmacokinetic properties of the antiretroviral drug zidovudine (ZDV).

DESIGN

This single dose, open label, crossover study involved the oral administration of ZDV (150 mg/m²) alone and in combination with oral TMP/SMX (2.5 mg/kg) on two separate occasions. Serial blood samples (0 to 8 h) were collected, and concentrations of ZDV and its glucuronide metabolite were quantified using a radioimmunoassay. ZDV pharmacokinetics were determined by noncompartmental analysis.

PATIENTS AND SETTING

Six HIV-1 infected children aged four months to five years were recruited from the HIV clinic at The Hospital for Sick Children, Toronto, Ontario. Only three patients completed both study phases and were included in the pharmacokinetic analysis.

MAIN RESULTS

With TMP/SMX therapy, no statistically significant changes were observed in ZDV pharmacokinetic parameters. However, there was a trend towards increased ZDV half-life and area under the concentration versus time curve, as well as decreased apparent oral clearance. Similarly, a trend towards an increased half-life of the ZDV-glucuronide metabolite was also observed.

CONCLUSION

The changes in ZDV pharmacokinetics in the presence of TMP/SMX did not reach statistical significance, most likely due to the limited number of patients involved. Despite the limited data, a possible interaction between ZDV and TMP/SMX in young HIV-1 infected children should be considered, and patients may require close clinical monitoring.

Zidovudine, diclofenac and ketoprofen pharmacokinetic interactions in rats

Zidovudine (AZT) is widely used for the management of human immunodeficiency virus (HIV) infections. Non-steroidal anti-inflammatory drugs (NSAIDs) are often used for relief of non-specific fever and musculoskeletal pain in patients with HIV including those with AZT-induced myopathy. The effects of single oral doses of diclofenac and ketoprofen on AZT pharmacokinetics were studied in rats. The influence of AZT on the pharmacokinetics of diclofenac or ketoprofen was also investigated. The administration of diclofenac (3 mgkg(-1)) or ketoprofen (1 mgkg(-1)) did not significantly alter AZT (1.5 mgkg(-1)) pharmacokinetic parameters compared with administering AZT alone. There was no significant difference between the pharmacokinetics of ketoprofen given alone or in combination with AZT. However, the co-administration of AZT with diclofenac affected the pharmacokinetics of diclofenac. The Cmax of diclofenac was significantly (P < 0.05) increased by approximately threefold within a shorter time (0.6+/-0.2 h). The mean AUC value for diclofenac was increased from 2.29 to 5.04 microg mL(-1) h in the presence of AZT. AZT decreased the mean apparent clearance of diclofenac by 54%. The increase in diclofenac concentrations could be attributed to a decrease in its clearance or delay in its metabolite formation due to a competitive effect. The results show that diclofenac and AZT should be given with caution because of the possible increase of diclofenac toxicity, in anticipation of follow-up clinical studies to examine this finding in man. AZT and ketoprofen could be a safe combination since no pharmacokinetic interaction was detected.

Management of HIV-infected pregnant patients in malaria-endemic areas: therapeutic and safety considerations in concomitant use of antiretroviral and antimalarial agents

Chemotherapy in pregnancy is an intricate process requiring prudent use of pharmacologic agents. Malarial infection during pregnancy is often fatal, and prophylaxis against the causative parasite necessitates rational therapeutic intervention. Various agents have been used for prophylaxis against malaria during pregnancy, including chloroquine, mefloquine, proguanil, pyrimethamine, and pyrimethamine-sulfadoxine. Use of these agents has been based on a risk-benefit criterion, without appropriate toxicologic or teratologic evaluation. Some of the aforementioned prophylactic agents have been shown to alter glutathione levels and may exacerbate the oxidation-reduction imbalance attendant on HIV infection. HIV-infected patients traveling to or residing in malaria-endemic areas require protection from malarial infection to avoid placing themselves in double jeopardy. Zidovudine (AZT) is recommended for the prevention of vertical transmission of HIV-1 from mother to child. Other agents, such as lamivudine alone or in combination with AZT, nevirapine, or the HIV-1 protease inhibitors, are either being considered or are currently undergoing trials for use in preventing vertical transmission of HIV-1 or managing HIV infection in infants and children. Although the potential for antimalarial agents to cause congenital malformations is low when they are used alone, their ability to cause problems when combined with antiretroviral drugs needs to be evaluated. In developing countries that have high birth rates, a high endemicity of malaria, and alarming rates of new cases of HIV, prophylaxis against both diseases with combination agents during pregnancy is a challenge.

[Anesthesia in the HIV positive or AIDS patient]

OBJECTIVE

To analyze the current anaesthetic management of HIV/AIDS patients.

DATA SOURCES

References were obtained from computerized bibliographic research (Medline), recent review articles, the library of the service, personal files.

STUDY SELECTION

Original articles, reviews, cases reports, letters to the editor in French and English were analyzed and selected.

DATA EXTRACTION

Current data on HIV infection, perioperative clinical and biological symptoms, arguments for choice of the type of anaesthesia, risks of transmitting HIV to health care workers and protective measures were extracted.

DATA SYNTHESIS

Twenty per cent of HIV-positive patients require surgery during their illness. Anaesthesia and surgery decrease cell mediated immunity and modify the activity of immune mediators. These changes are more pronounced under general anaesthesia compared to regional anaesthesia. They are transient and not clinically significant. Poor information is available concerning the perioperative management of HIV-positive patients and the effects of anesthesia on their immune status. Preoperative evaluation focuses on the following three important data: patient's status, surgery, and anaesthesia. In patients in good clinical conditions who comply with treatment, the anesthetist assesses the effects of the antiretroviral treatment and the risk of interactions between anaesthetic and antiretroviral agents. Etomidate, atracurium, cisatracurium, remifentanil and desflurane are not dependent on hepatic metabolism by the cytochrome P450 system. In patients in bad clinical conditions or in patients who do not comply with treatment, attention focuses on cardiovascular, pulmonary, neurologic and nutritional status. The specific antiretroviral treatment is not discontinued in the perioperative period, as far as compatible with the type of surgery and associated dysfunction of the digestive tract. Regional anaesthesia offers the benefits of not interfering with the immune system and antiretroviral agents. However, the viral infection can be enhanced by regional anaesthesia due to the cofactors' effect of local anaesthetic agents in cerebrospinal fluid. Homologous blood transfusion is not recommended as it increases postoperative infection and viral activation. Erythropoietin can be of benefit in selected cases. In the future, supportive immunotherapy will probably be the main tool for perioperative management of HIV and AIDS patients.

Zidovudine azido-reductase in human liver microsomes: activation by ethacrynic acid, dipyridamole, and indomethacin and inhibition by human immunodeficiency virus protease inhibitors

AZT (zidovudine, 3'-azido-3'-deoxythymidine), although metabolized primarily to AZT-glucuronide, is also metabolized to 3'-amino-3'-deoxythmidine (AMT) by reduction of the azide to an amine. The formation of the myelotoxic metabolite AMT has not been well characterized, but inhibition of AMT formation would be of therapeutic benefit. The aim of this study was to identify compounds that inhibit AMT formation. Using human liver microsomes under anaerobic conditions and [2-14C]AZT, K(m) values of AZT azido-reductase, estimated by radio-thin-layer chromatography, were 2.2 to 3.5 mM (n = 3). Oxygen completely inhibited this NADPH-dependent reduction. Thirteen of the 28 compounds tested inhibited the formation of AMT. In addition to the CYP3A4 inhibitors ketoconazole, fluconazole, indinavir, ritonavir, and saquinavir, metyrapone strongly inhibited AMT formation. An unexpected finding was the more-than-twofold increase in AMT formation in the presence of ethacrynic acid, dipyridamole, or indomethacin. Such activation of toxic metabolite formation would impair drug therapy.

Pharmacokinetic interaction of megestrol acetate with zidovudine in human immunodeficiency virus-infected patients

This nonrandomized, two-period crossover study was performed to assess whether concomitant administration of megestrol acetate influences the steady-state pharmacokinetics of zidovudine and its inactive 5'-O-glucuronide metabolite. Twelve HIV-positive, asymptomatic male volunteers received a 100-mg oral capsule dose of zidovudine at least 30 min before meals five times a day at 0700, 1100, 1500, 1900, and 2300 h on study days 1 to 3 and a single 100-mg dose at 0700 h on day 4. On days 5 to 17, 800 mg of megestrol acetate, as a 40-mg/ml aqueous suspension, was administered orally immediately before the 0700 h dose of zidovudine. On days 5 to 16, zidovudine was also administered at 1100, 1500, 1900, and 2300 h. Serial blood samples were collected for 12 h after the single 100-mg dose of zidovudine on days 4 and 17; trough samples were also obtained just before the 0700 h dose on days 2 to 4 and 15 to 17. Levels of zidovudine and its glucuronide in plasma were assayed by a validated radioimmunoassay. Statistical analysis of trough plasma level data indicated that steady-state levels of zidovudine and its glucuronide in plasma had been attained when pharmacokinetic assessments were made on days 4 and 17. When megestrol acetate and zidovudine were coadministered for 13 days, differences of -14, -6.5, and -4.6% in mean zidovudine peak concentration and areas under the curve at 0 to 4 and 0 to 12 h, respectively, +22.5% in mean trough concentration, +2.6% in mean plasma half-life, and no change in median time to peak were observed compared to conditions when zidovudine was administered alone; for zidovudine 5'-O-glucuronide the respective differences were -9, -7.3, -4.4, +2.3, and +10% and no change. None of the differences were statistically significant (P > 0.05). Concomitant therapy with megestrol acetate, at the dose employed to treat anorexia, cachexia, or an unexplained, significant weight loss in AIDS patients, did not alter the steady-state pharmacokinetics of zidovudine or its 5'-O-glucuronide metabolite.

Management of drug interactions in patients with HIV

OBJECTIVE

To provide a complication of relevant information on drug interactions to assist healthcare practitioners in managing complex HIV-related pharmacotherapy.

DATA SOURCES

Information was retrieved via a MEDLINE search (January 1966-December 1996) using MeSH headings "human immunodeficiency virus," "drug interactions," and names of medications commonly prescribed for the management of HIV infection and related opportunistic infections. Abstracts of international and national conferences, review articles, textbooks, and references of all articles were also searched.

STUDY SELECTION AND DATA EXTRACTION

All literature on pharmacokinetic or pharmacodynamic interactions was considered for inclusion. Pertinent information, as assessed by the authors, was selected and summarized for discussion.

DATA SYNTHESIS

Drug disposition and/or pharmacologic effect may be affected either by HIV-related physiologic changes or by the presence of concomitant drug therapy. Modifications in drug selection, dosage, dosing regimen, or route of administration may be needed to avoid or manage drug-disease, drug-drug, or drug-food interactions. Management options may depend on the mechanism and the clinical significance of the interaction, the availability of therapeutic alternatives, patient convenience, and cost restrictions. In the absence of specific data, consideration of pharmacokinetic and pharmacodynamic characteristics to assist practitioners in predicting the likelihood of possible interactions was included.

RESULTS

A comprehensive table of clinically significant drug interactions is provided. Drug interaction principles and practical management strategies are also discussed.

CONCLUSIONS

The potential for drug interactions is extremely common, given the increasing complexity of managing patients infected with HIV. To avoid compromising therapeutic efficacy or increasing drug toxicity, practitioners need to be aware of potential interactions and are encouraged to use a systematic approach when managing patient drug therapy.

Long-term administration of aerosolized pentamidine as primary prophylaxis against Pneumocystis carinii pneumonia in infants and children with symptomatic human immunodeficiency virus infection. The Italian Pediatric Collaborative Study Group on Pentamidine

SUMMARY

We assessed the long-term feasibility, safety, and tolerability of two regimens of aerosolized pentamidine (AP) as primary prophylaxis of Pneumocystis carinii pneumonia (PCP) in a large sample of infants and children with symptomatic HIV infection in 21 pediatric departments. One hundred forty children were assigned to receive 60 mg every 2 weeks (n = 60) or 120 mg every 4 weeks (n = 80) of AP, delivered by the ultrasonic nebulizer Fisoneb under the supervision of trained personnel. Children underwent monthly clinical and laboratory controls for toxicity and/or development of PCP for an 18-month period. Baseline characteristics were similar in the two treatment groups. The median age was 5 years. The feasibility of administering AP was excellent in 84 (60 percent) and good in 38 (27 percent) children. All children aged <2 years showed excellent or good feasibility. Long-term compliance was good with both regimens. No child had severe adverse reactions requiring discontinuation of the treatment. Cough, sneezing, and bronchospasm were the most frequent side effects occurring, respectively, in 12, 3.7, and 0.7 percent of the 60-mg treatments and in 19.1, 6. 1, and 2.8 percent of 120-mg treatments (p < 0.05). Their incidence was not different in children younger or older than 5 years. Two episodes of PCP were observed in the group receiving 120 mg monthly, whereas none of the 60 children in the biweekly schedule had PCP (p = 0.20). AP can be safely administered to very young children with few adverse side effects.

Absence of effect of trimethoprim-sulfamethoxazole on pharmacokinetics of zidovudine in patients infected with human immunodeficiency virus

Pharmacokinetic parameters of zidovudine (ZDV) were not altered in 16 patients receiving concomitant therapy with ZDV and trimethoprim-sulfamethoxazole by oral administration. ZDV areas under the concentration-time curves were (means +/- standard deviations) 1.80 +/- 0.70 and 1.69 +/- 0.64 micrograms.h/ml in the absence and presence of trimethoprim-sulfamethoxazole, respectively. ZDV clearances were 1.57 +/- 0.61 and 1.74 +/- 0.66 liters/h/kg, respectively.

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.

Intracellular activation and cytotoxicity of three different combinations of 3'-azido-3'-deoxythymidine and 2',3'-dideoxyinosine

We measured the intracellular activation and cytotoxicity of 3'-azido-3'-deoxythymidine (zidovudine, ZDV) and 2',3'-dideoxyinosine (ddI) when combined at three different clinically relevant combinations of 1:1, 1:10, and 10:1 (ZDV:ddI). The activation of ddI to ddA-TP was increased in all three combinations with ZDV, compared to ddI alone. A maximum twofold increase in ddA-TP was observed, which could not be further increased by raising the concentration of ZDV in the combination. On the other hand, the concentration of ZDV in the combination could be reduced to one-tenth while retaining increased activation of ddI. We also examined the cytotoxicity of these combinations in CEM cells, phytohemagglutinin (PHA)-stimulated and resting human peripheral blood mononuclear cells (PBMCs). CEM cells were the least sensitive overall to the drugs. ZDV showed greater cytotoxicity in stimulated PBMCs than resting PBMCs, whereas the reverse was true for ddI. This could be explained by the different activation pathways of these two drugs. The 1:1 and 10:1 ZDV:ddI combinations showed reduced toxicity compared to the separate drugs. These results indicate that ZDV and ddI need not necessarily be combined together at a ratio of ZDV:ddI of 1:1, but that some alteration in the dosages of ZDV or ddI in patients could be possible without loss of the benefits of combined ZDV:ddI therapy.

Study of the role of vitamin B12 and folinic acid supplementation in preventing hematologic toxicity of zidovudine

A prospective, randomized study was conducted to evaluate the role of vitamin B12 and folinic acid supplementation in preventing zidovudine (ZDV)-induced bone marrow suppression. Seventy-five human immunodeficiency virus (HIV)-infected patients with CD4+ cell counts < 500/mm3 were randomized to receive either ZDV (500 mg daily) alone (group I, n = 38) or in combination with folinic acid (15 mg daily) and intramascular vitamin B12 (1000 micrograms monthly) (group II, n = 37). Finally, 15 patients were excluded from the study (noncompliance 14, death 1); thus, 60 patients (31 in group I and 29 in group II) were eligible for analysis. No significant differences between groups were found at enrollment. During the study, vitamin B12 and folate levels were significantly higher in group II patients; however, no differences in hemoglobin, hematocrit, mean corpuscular volume, and white-cell, neutrophil and platelet counts were observed between groups at 3, 6, 9 and 12 months. Severe hematologic toxicity (neutrophil count < 1000/mm3 and/or hemoglobin < 8 g/dl) occurred in 4 patients assigned to group I and 7 assigned to group II. There was no correlation between vitamin B12 or folate levels and development of myelosuppression. Vitamin B12 and folinic acid supplementation of ZDV therapy does not seem useful in preventing or reducing ZDV-induced myelotoxicity in the overall treated population, although a beneficial effect in certain subgroups of patients cannot be excluded.

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.

Comparative effects of antifungal agents on zidovudine glucuronidation by human liver microsomes

Zidovudine (ZDV) is extensively metabolised by the liver to an inactive glucuronide (GZDV). Since ZDV is often administered with antimycotic drugs, we studied the effect of six systemic antifungal agents on the in vitro glucuronidation of ZDV by human liver microsomes. 5-fluorocytosine and itraconazole had no inhibitory effect whereas amphotericine B, ketoconazole, miconazole and fluconazole inhibited in vitro GZDV formation (Ki values were 0.13, 0.08, 0.18 and 1.4 mM respectively).

Drug interactions with zidovudine phosphorylation in vitro

We have investigated the effect of a range of drugs (some commonly coadministered with zidovudine [ZDV] to human immunodeficiency virus-positive patients) on intracellular phosphorylation of ZDV by stimulated peripheral blood mononuclear cells, Molt 4 cells, and U937 cells in vitro. Of the drugs tested (azoles, antiviral agents, antibiotics, and anticancer agents), only doxorubicin and ribavirin caused inhibition of anabolite formation as measured by high-performance liquid chromatography. This in vitro approach may provide important leads to potential interactions at the phosphorylation level in patients with human immunodeficiency virus disease. It is reassuring that so many commonly administered drugs do not alter ZDV phosphorylation.

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.

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)