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

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

Study on didanosine concentrations in cerebrospinal fluid. Implications for the treatment and prevention of AIDS dementia complex

It has been hypothesized that didanosine has a low efficacy in the prevention and treatment of patients with the dementia complex of acquired immunodeficiency syndrome (AIDS) because "... the drug has not been detected in the cerebrospinal fluid". We investigated didanosine concentrations in cerebrospinal fluid (CSF) and plasma of four patients with AIDS who were using didanosine chronically. Didanosine levels, 4 h after the last drug administration, averaged 0.16 (+/- 0.03) mumol/l in CSF and 0.70 (+/- 0.27) mumol/l in plasma. When compared with historical data from patients using zidovudine, didanosine concentrations in CSF appeared to be approximately half (on a molar base) those of zidovudine concentrations in the CSF. Whether this difference in CSF levels is the explanation for the presumed lower efficacy of didanosine in the prevention and treatment of AIDS dementia complex remains to be proven. However, it is clear from this study, in contrast with earlier suggestions, that didanosine is able to pass the blood-CSF barrier in human immunodeficiency virus-infected individuals.

Treatment of visceral leishmaniasis in a patient with AIDS with antimony and gamma-interferon: remission and prevention of relapse by maintenance therapy with weekly pentamidine

A 41-year-old AIDS patient with fever, nightly perspiration, diarrhoea, anaemia and leukopenia was diagnosed as having visceral leishmaniasis (VL). After 8 weeks of antimony treatment combined with gamma-interferon, given in 2 courses of 3 and 5 weeks, 12 weeks apart, the bone marrow revealed no parasites by microscopy and culture. Parasitic DNA could still be demonstrated by polymerase chain reaction. Weekly intravenous pentamidine maintenance therapy seemed to prevent relapses. Over time the patient was treated for disseminated M. avium infection, CMV retinitis, porphyria cutanea tarda and renal tubular acidosis. Ultimately he succumbed, 2.5 years after the diagnosis of VL and 4.5 years after the diagnosis of AIDS was established.

Reduced toxoplasmastatic activity of monocytes and monocyte-derived macrophages from AIDS patients is mediated via prostaglandin E2

OBJECTIVE

To establish the role of prostaglandin E2 (PGE2) formed and released by monocytes and monocyte-derived macrophages (MDM) in the reduced toxoplasmastatic activity of these cells.

DESIGN

Determination of PGE2 levels in the serum of AIDS patients, the release of PGE2 by monocytes and MDM from AIDS patients, the toxoplasmastatic activity of these cells and the effect of indomethacin, an inhibitor of PGE2 synthesis, on this cell function.

SETTING

Laboratory of Cellular Immunology of the Department of Infectious Diseases, University Hospital, Leiden.

PARTICIPANTS

Twenty-six AIDS patients. Healthy blood donors served as controls.

RESULTS

The concentration of PGE2 in the serum from AIDS patients was significantly higher compared with serum from controls. Non-stimulated monocytes and lipopolysaccharide-stimulated monocytes and MDM from AIDS patients released significantly more PGE2 than corresponding cells from the controls. The proliferation of Toxoplasma gondii in monocytes and MDM from AIDS patients was significantly higher than in the respective cells from controls. Preincubation of these cells with indomethacin resulted in a decreased proliferation of T. gondii in non-activated monocytes and MDM and in interferon-gamma-activated MDM from AIDS patients. Preincubation of monocytes from healthy donors with PGE2 resulted in a dose-dependent increase of Toxoplasma proliferation which confirms that PGE2 can reduce the toxoplasmastatic activity of monocytes.

CONCLUSION

PGE2 is involved in the reduced toxoplasmastatic activity of monocytes and MDM from AIDS patients.

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.

High-performance liquid chromatographic determination of the antifungal drug fluconazole in plasma and saliva of human immunodeficiency virus-infected patients

A high-performance liquid chromatographic (HPLC) assay has been developed for the determination of the antifungal drug fluconazole in saliva and plasma of patients infected with the human immunodeficiency virus (HIV). Samples can be heated at 60 degrees C for 30 min to inactivate the virus without loss of the analyte. The sample pretreatment involves a liquid-liquid extraction with chloroform-1-propanol (4:1, v/v). The chromatographic analysis is performed on a Lichrosorb RP-18 (5 microns) column by isocratic elution with a mobile phase of 0.01 M acetate buffer (pH 5.0)-methanol (70:30, v/v) and ultraviolet (UV) detection at 261 nm. The lower limit of is 100 ng/ml in plasma (using 500-microliters samples) and 1 microgram/ml in saliva (using 250-microliters samples) and the method is linear up to 100 micrograms/ml in plasma and saliva. At a concentration of 5 micrograms/ml the within-day and between-day precision in plasma are 7.1 and 5.7%, respectively. In saliva the within-day and between-day precision is 10.8% (at 5 micrograms/ml). The methodology is now being used in pharmacokinetic studies in HIV-infected patients in our hospital.

Treatment of poor prognosis epidemic Kaposi's sarcoma with doxorubicin, bleomycin, vindesine and recombinant human granulocyte-monocyte colony stimulating factor (rh GM-CSF)

The efficacy and toxicity of doxorubicin, bleomycin and vindesine in epidemic Kaposi's sarcoma, and the role of rh GM-CSF in chemotherapy-induced neutropenia were evaluated in this Phase II study. Patients with progressive Kaposi's sarcoma were eligible, and were staged according to ACTG criteria. Treatment consisted of 20 mg/m2 doxorubicin, and a fixed dose of 15 mg bleomycin and 4 mg vindesine every 2 weeks. All patients continued antiretroviral medication with severe myelosuppression, patients received subcutaneous 5 micrograms/kg rh GM-CSF (Leucomax) from days 2-12. Response and toxicity were measured according to ACTG and WHO criteria. 27 patients were evaluable, 25 patients classified as having a poor prognosis. The response rate was 70% (3 CR, 16 PR), the duration of response was 18 weeks (range 8-25) and the median survival 30 weeks (range 4-63+). The cause of death was mostly opportunistic infection. 4 patients died of pulmonary Kaposi's sarcoma. The toxicity of this regimen was mainly myelosuppression and 13 patients were treated with rh GM-CSF. Complete recovery of the white blood cells occurred in seven of the 27 courses of rh GM-CSF (26%). No bacterial infections were recorded, but 5 patients (19%) developed an opportunistic infection during treatment. Peripheral neuropathy occurred in 16% of patients. Combination chemotherapy is effective in poor prognosis Kaposi's sarcoma but has a shortlasting effect. The main toxicity of this treatment is severe myelosuppression which can be ameliorated by rh GM-CSF. It remains to be established whether rh GM-CSF is also able to reduce the incidence of opportunistic infections.

Therapeutic drug monitoring of phenytoin in patients with the acquired immunodeficiency syndrome

Serum phenytoin concentrations were investigated in 109 serum samples from 21 patients with the acquired immunodeficiency syndrome (AIDS) and in 1,231 serum samples from 557 control subjects during phenytoin therapy. Total phenytoin concentrations were significantly lower in patients with AIDS than in the reference population (8.8 +/- 0.7 mg/L (mean +/- SE) vs. 10.6 +/- 0.2 mg/L), although phenytoin doses were significantly higher in the AIDS patients. Body weight and the use of folic acid were negatively related to phenytoin concentrations, whereas use of clarithromycin resulted in higher phenytoin levels. Zidovudine did not influence phenytoin levels. Calculation of the Michaelis-Menten parameters showed that Vmax values were similar in seven human immunodeficiency virus (HIV)-infected patients as compared with 12 controls, but a nonsignificant trend of lower Km values in the HIV-positive group was observed. Measurement of free phenytoin concentrations demonstrated that the fraction of unbound drug was increased in patients with AIDS. Hypoalbuminemia was common in this population, which may complicate the interpretation of total phenytoin concentrations.

Effect of IFN-gamma on the proliferation of Toxoplasma gondii in monocytes and monocyte-derived macrophages from AIDS patients

This study was undertaken to determine whether the activity of monocytes and monocyte-derived macrophages (MDM) from acquired immune deficiency syndrome (AIDS) patients against Toxoplasma gondii is altered and whether this activity can be modulated by recombinant interferon-gamma (rIFN-gamma). Untreated and rIFN-gamma-treated monocytes or MDM from AIDS patients and from healthy controls were infected with T. gondii and the proliferation of these protozoa was determined. The H2O2 release by monocytes from AIDS patients and healthy controls was measured upon stimulation with phorbol myristate acetate (PMA) and formyl methionyl leucyl phenylalanine (FMLP). Monocytes from AIDS patients exhibited significantly lower toxoplasmastic activity compared to monocytes from healthy controls. The H2O2 release by monocytes from AIDS patients was also diminished. Incubation of monocytes from AIDS patients with rIFN-gamma for 2 days, but not 1 day, restored their toxoplasmastatic activity. The rate of proliferation of T. gondii was higher in MDM from AIDS patients than in MDM from healthy controls. Treatment of MDM from AIDS patients with rIFN-gamma for 1, 2 or 3 days resulted in partial inhibition of the proliferation of T. gondii. Collectively, these results demonstrate that the reduced toxoplasmastatic activity of monocytes and MDM from AIDS patients can be enhanced by in vitro treatment with rIFN-gamma, which supports the clinical use of rIFN-gamma for the treatment of opportunistic infections in these patients.

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

A specific and sensitive radioimmunoassay for the determination of levels of zalcitabine in human plasma, urine, and cerebrospinal fluid has been developed. Commercially available radiolabel and antiserum (Sigma Chemicals) were used after dilution in assay buffer. Prior to the immunoassay, standard and patient samples were subjected to solid-phase extraction on silica columns in order to obtain purified samples. The lower limit of quantitation was determined to be 1 ng/ml. Intra- and interassay variations were less than 11% for a number of quality control samples of drug in plasma and urine. Results from parallelism studies with plasma and urine demonstrated that samples outside the standard range (1 to 30 ng/ml) could be diluted by blank plasma or assay buffer, respectively. A large number of related compounds and potentially coadministered drugs were tested for cross-reactivity. Stability tests showed that heat treatment for 30 min at 60 degrees C or storage for 1 month at -30 degrees C did not affect zalcitabine concentrations in plasma or urine. The radioimmunoassay with solid-phase extraction for sample cleanup discussed here has been successfully applied in a pharmacokinetic study of a single patient, demonstrating its applicability for clinical pharmacokinetic research with zalcitabine.

Pharmacokinetic variability of zidovudine in HIV-infected individuals: subgroup analysis and drug interactions

OBJECTIVE

To investigate determinants of inter- and intraindividual variability of zidovudine (ZDV) pharmacokinetics in HIV-infected patients.

DESIGN

A prospective study in a general 525-bed hospital with special funding for treatment and research of HIV-infected patients.

METHODS

Serial blood samples were collected from 68 HIV-infected individuals providing a total of 95 pharmacokinetic curves. ZDV was measured with high-performance liquid chromatography and radioimmunoassay. Pharmacokinetic parameters were calculated by non-compartmental analysis. Patient characteristics were investigated by multivariate analysis for an influence on ZDV pharmacokinetics.

RESULTS

Apparent ZDV clearance was significantly lower in patients with a lower body weight, in women, and in patients with a more advanced stage of HIV disease. Co-administration of methadone with ZDV resulted in higher plasma concentrations of ZDV, while rifampin and ganciclovir increased apparent ZDV clearance. Age, the duration of ZDV use, CD4+ cell count, creatinine clearance, elevated serum liver enzyme levels, and the use of 11 other co-administered medications were not independently related to apparent ZDV clearance.

CONCLUSIONS

The pharmacokinetic profile of ZDV in several subpopulations has been evaluated, as well as the observation of possible drug-drug interactions between ZDV and 14 different drugs or groups of drugs. These data suggest that patient-individualized antiretroviral therapy may be appropriate once pharmacokinetic-pharmacodynamic relationships have been established.

Short-term, combined use of paracetamol and zidovudine does not alter the pharmacokinetics of either drug

OBJECTIVE

To investigate a possible pharmacokinetic interaction between zidovudine and paracetamol.

METHODS

Six patients with AIDS took both zidovudine (AZT; 1000-1200 mg/day) and paracetamol (500 mg every 6 h) for 7 days. Pharmacokinetic monitoring was performed on day 0 (AZT alone) and after 7 days of combined use of paracetamol and AZT.

RESULTS

Combined use of paracetamol and AZT did not result in a significant change in any of the calculated pharmacokinetic parameters of AZT or its primary metabolite AZT-glucuronide. In addition, paracetamol pharmacokinetic parameters at day 7 did not differ from those usually reported in the literature.

CONCLUSION

Short-term, combined use of paracetamol and AZT does not lead to a change in the pharmacokinetics of either AZT or paracetamol. The effect of long-term use of this combination remains unknown. A recent case report of AZT-induced paracetamol hepatotoxicity [Am J Med 1992;93: 94-96] indicates that clinicians should still be aware of potential drug toxicity when prescribing both AZT and paracetamol.

Pharmacokinetics of zidovudine and acetaminophen in a patient on chronic acetaminophen therapy

OBJECTIVE

To report a case of a potential interaction between acetaminophen and zidovudine in a patient who had used high daily doses of acetaminophen over many years.

CASE SUMMARY

A 43-year-old man presented with HIV-1 infection, recurrent oral candidiasis, and chronic use of acetaminophen, codeine, and diazepam before he started zidovudine therapy. Although literature was available regarding short-term combined use of acetaminophen and zidovudine, information was lacking on zidovudine therapy and kinetics after long-term use of acetaminophen. Acetaminophen and zidovudine pharmacokinetics were determined on several occasions. The results showed extremely rapid absorption of both drugs (tmax the time to reach maximum concentration, 10-15 minutes for acetaminophen and 15-20 minutes for zidovudine) and, consequently, relatively high maximum plasma concentration (Cmax). No influence on other pharmacokinetic parameters of either drug could be detected. Because the effect of high Cmax values of zidovudine is unknown, the patient was treated with a third of the dose of zidovudine used at that time (zidovudine 100 mg q6h). No toxicity or opportunistic infections developed within the next 8 months, after which the patient died of a cause unrelated to HIV infection.

DISCUSSION

The observed pharmacokinetic profiles of both drugs are discussed and compared with two studies dealing with zidovudine therapy in combination with short-term use of acetaminophen and with a case report of acetaminophen-induced hepatotoxicity during concomitant use of zidovudine.

CONCLUSIONS

Long-term use of acetaminophen may accelerate the absorption of zidovudine. Although other causes cannot be ruled out, there was no influence on other pharmacokinetic parameters of zidovudine. No influence of zidovudine on acetaminophen concentrations was found. Combined use of zidovudine 100 mg q6h and acetaminophen 500 mg q4h appeared to be safe and effective for at least eight months.

Penetration of zidovudine into the cerebrospinal fluid of patients infected with HIV

OBJECTIVE

To investigate penetration of zidovudine (ZDV) into the cerebrospinal fluid (CSF) of HIV-infected patients for whom a lumbar puncture was indicated.

DESIGN

A prospective study.

SETTING

General 525-bed hospital with special funding for treatment and research of HIV-infected patients.

PATIENTS, PARTICIPANTS

Thirty-nine patients with a medical indication for lumbar puncture who used ZDV chronically were included in this study (50 samples in total).

MAIN OUTCOME MEASURE

Determination of ZDV and proteins in CSF and plasma samples.

RESULTS

CSF concentrations of ZDV showed little fluctuation 1-8 h after the last ingestion of ZDV. In contrast, plasma levels displayed large variability in this period and decreased exponentially over time. As a result, the CSF/plasma ratio increased linearly over time. No significant relation between the ZDV dose, neither the medical indication for lumbar puncture nor the protein ratio (as a measure for the integrity of the blood-brain barrier), and CSF levels of ZDV was found. The CSF/plasma ratio of ZDV did not give essential information on drug distribution into CSF.

CONCLUSIONS

Penetration of ZDV into the CSF appears to be independent of the dose (range, 200-1250 mg daily), which may be an explanation for the efficacy of low doses of ZDV in the prevention and treatment of HIV-related neurological diseases. ZDV levels were at steady-state during the first 6 h after ingestion. The CSF/plasma ratio of ZDV concentrations is not an appropriate marker for drug penetration into CSF.

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.

2',3'-dideoxyinosine (ddI): its chemical stability and cyclodextrin complexation in aqueous media

The chemical stability of 2',3'-dideoxyinosine has been studied over a wide pH range (0-12). A stability-indicating HPLC method was used to separate the degradation product from the parent drug. The effects of temperature, ionic strength and buffer components on the degradation kinetics were investigated. Furthermore, the influence of some cyclodextrins (alpha-, beta-, HP-beta-, DM-beta- and gamma-cyclodextrin) on the drug stability have been studied.

Ocular complications of the acquired immunodeficiency syndrome. Focus on the treatment of cytomegalovirus retinitis with ganciclovir and foscarnet

The most common ocular complication in patients with the acquired immunodeficiency syndrome (AIDS) is cytomegalovirus retinitis. Incidence figures vary from 20 to 76%. Patients with cytomegalovirus may suffer from mild visual impairment of one or both eyes, but as the disease progresses the retinitis will almost certainly lead to blindness. Although cytomegalovirus retinitis is not a life-threatening infection, it can largely diminish the patient's quality of life. Clinical trials for the treatment of cytomegalovirus retinitis with a number of antiviral drugs have resulted in two drugs of choice, ganciclovir and foscarnet. Both drugs have an initial efficacy with induction therapy of 80-90%, but maintenance therapy is always needed to prevent a relapse. To exclude systemic side-effects of ganciclovir, intravitreal administration has been investigated with good results. Combination therapy of foscarnet and ganciclovir may be worthwhile in resistant cytomegalovirus retinitis.

Determination of stavudine, a new antiretroviral agent, in human plasma by reversed-phase high-performance liquid chromatography with ultraviolet detection

A sensitive high-performance liquid chromatographic assay has been developed to determine the levels of a new antiretroviral agent, stavudine (2',3'-didehydro-3'-deoxythymidine, d4T), in human plasma. Didanosine (2',3'-dideoxyinosine, ddI) was used as the internal standard. The very selective sample pretreatment involved solid-phase extraction using silica gel columns. Chromatography was carried out on a mu Bondapak phenyl column, using a mobile phase of 0.005 M phosphate buffer (pH 6.8)-methanol (90:10, v/v) and ultraviolet detection at 265 nm. The method has been validated, and stability tests under various conditions have been performed. The detection limit is 10 ng/ml (using 500-microliters human plasma samples). The bioanalytical assay has been used in a single pharmacokinetic experiment in a rat to investigate the applicability of the method in vivo.

Didanosine, a new antiretroviral drug. A review

In this article the literature about didanosine, an antiretroviral drug, is reviewed. The mechanism of action, biochemical pharmacology, pharmacokinetics, and clinical results of phase-I trials are discussed. Serious adverse effects such as pancreatitis and peripheral neuropathy have occurred in these trials. An antiretroviral effect was observed in terms of an increase in CD4+ lymphocytes and a decrease in p24 antigen levels in HIV-infected individuals. Didanosine seems to be a promising drug against HIV infection, but knowledge about its clinical efficacy is scanty.

Impaired phagocytosis of Staphylococcus aureus by granulocytes and monocytes of AIDS patients

In the present study the microbicidal activities of granulocytes and monocytes from AIDS patients (CDC group IV) were assessed and compared with those of healthy controls. The phagocytosis and intracellular killing of Staphylococcus aureus by patient and control cells were measured using a method in which the rate of intracellular killing can be assessed independently of the rate of phagocytosis. Both granulocytes and monocytes of AIDS patients showed a decreased phagocytosis of S. aureus in comparison to phagocytes of healthy individuals. The rates of intracellular killing of S. aureus by granulocytes and monocytes did not differ significantly between these patients with late-stage HIV infection and controls.

[Small-cell lung carcinoma with hyponatremia]

Two female patients are described with an unusual clinical presentation of a small-cell bronchogenic carcinoma. Patient A, 61 years old, had a one week history of epigastric pain and nausea accompanied by dizziness and periods of unconsciousness. Patient B, 48 years old, had suffered for four days of general malaise, abdominal pains, nausea and vomiting. The symptoms of both patients could be attributed to severe hyponatraemia, most probably a consequence of the inappropriate ADH syndrome. After correction of the hyponatraemia and treatment of the underlying carcinoma the serum sodium remained normal and symptoms did not recur. The patients died 14 months and 9 months after the diagnosis respectively. In the Netherlands about 2000 small-cell bronchogenic carcinomas are diagnosed each year. About 14% of these are associated with the inappropriate ADH syndrome. The presence of the syndrome implicates a much graver prognosis.

HPLC determination of doxorubicin, doxorubicinol and four aglycone metabolites in plasma of AIDS patients

A high-performance liquid chromatographic (HPLC) assay has been developed for the determination of the anticancer drug doxorubicin and the metabolites doxorubicinol, doxorubicinone, 7-deoxydoxorubicinone, doxorubicinolone and 7-deoxydoxorubicinolone in plasma of AIDS patients. Samples can be heated at 60 degrees C for 30 min to inactivate the human immunodeficiency virus. The sample pre-treatment involves a liquid-liquid extraction of the buffered plasma sample (pH 9) with a chloroform-1-propanol (4:1, v/v) mixture. The chromatographic analysis is performed on a Lichrosorb RP-8 (5 microns) column and by isocratic elution with a mobile phase of acetonitriletetrahydrofuran-phosphate buffer (pH 2.2) (800:5:200, w/w/w) with fluorescence detection (excitation wavelength: 460 nm; emission wavelength: 550 nm). The proposed method has been validated and, subsequently, implemented in a pharmacokinetic study of doxorubicin in AIDS patients with Kaposi's sarcoma who are treated with the combination regimen doxorubicin, vincristine and bleomycin.