Aerosolized pentamidine. Approved for HIV-infected individuals at high risk for Pneumocystis carinii pneumonia.

Aerosolized pentamidine isethionate (NebuPent, LyphoMed Inc, Rosemont, Ill) was recently approved by the US Food and Drug Administration for use in prophylaxis against Pneumocystis carinii pneumonia in individuals infected with the human immunodeficiency virus who are at high risk for this infection. The recommended dose is 300 mg of aerosolized pentamidine isethionate administered every 4 weeks via the Respirgard II nebulizer (Marquest Medical Products Inc, Englewood, Colo). The drug is indicated for individuals infected with the human immunodeficiency virus who have a history of P carinii pneumonia or individuals with a CD4 (T4) lymphocyte count less than or equal to 0.2 x 10(9)/L with no history of P carinii pneumonia. We present information about the drug and its use, including safety information and use of the nebulizer.

The effects of rifampin and rifabutin on the pharmacokinetics and pharmacodynamics of a combination oral contraceptive.

BACKGROUND: Rifampin (INN, rifampicin), a CYP34A inducer, results in significant interactions when coadministered with combination oral contraceptives that contain norethindrone (INN, norethisterone) and ethinyl estradiol (INN, ethinylestradiol). Little is known about the effects of rifabutin, a related rifamycin. OBJECTIVES AND METHODS: The relative effects of rifampin and rifabutin on the pharmacokinetics and pharmacodynamics of ethinyl estradiol and norethindrone were evaluated in a prospective, randomized, double-blinded crossover study in 12 premenopausal women who were on a stable oral contraceptive regimen that contained 35 microg ethinyl estradiol/1 mg norethindrone. Subjects were randomized to receive 14 days of rifampin or rifabutin from days 7 through 21 of their menstrual cycle. After a 1-month washout period (only the oral contraceptives were taken), subjects were crossed over to the other rifamycin. RESULTS: Rifampin significantly decreased the mean area under the plasma concentration-time curve from time 0 to 24 hours [AUC(0-24)] of ethinyl estradiol and the mean AUC(0-24) of norethindrone. Rifabutin significantly decreased the mean AUC(0-24) of ethinyl estradiol and the mean AUC(0-24) of norethindrone. The effect of rifampin was significantly greater than rifabutin on each AUC(0-24). Despite these changes, subjects did not ovulate (as determined by progesterone concentrations) during the cycle in which either rifamycin was administered. Levels of mean follicle-stimulating hormone increased 69% after rifampin. CONCLUSION: In this study, rifampin (600 mg daily) was a more significant inducer of ethinyl estradiol and norethindrone clearance than rifabutin (300 mg daily), but neither agent reversed the suppression of ovulation caused by oral contraceptives. The carefully monitored oral contraceptive administration and the limited exposure to rifamycins may restrict the application of this study to clinical situations.

PIP: The relative effects of rifampin and rifabutin (a related rifamycin) on the pharmacokinetics and pharmacodynamics of ethinyl estradiol (EE) and norethindrone were evaluated in a prospective, randomized, double-blinded crossover study in 12 premenopausal women who were on a stable oral contraceptive regimen that contained 35 mcg EE and 1 mg norethindrone. Subjects were randomized to receive 14 days of rifampin or rifabutin from days 7 through 21 of their menstrual cycle. After a 1-month washout period (only the oral contraceptives were taken), subjects were crossed over to the other rifamycin. Findings showed that rifampin significantly decreased the mean area under the plasma concentration-time curve from time 0 to 24 hours [AUC (0-24)] of EE and the mean AUC (0-24) of norethindrone. Rifabutin significantly decreased the mean AUC (0-24) of EE and the mean AUC (0-24) of norethindrone. The effect of rifampin was significantly greater than rifabutin on each AUC (0-24). Despite these changes, subjects did not ovulate (as determined by progesterone concentrations) during the cycle in which either rifamycin was administered. Levels of mean follicle-stimulating hormone increased 69% after rifampin. This study suggests that rifampin (600 mg daily) was a more important inducer of EE and norethindrone clearance than rifabutin, but none of these agents were able to reverse the suppression of ovulation done by oral contraceptives.

Thalidomide does not alter the pharmacokinetics of ethinyl estradiol and norethindrone.

OBJECTIVE: To evaluate the effect of thalidomide on the plasma pharmacokinetics of ethinyl estradiol (INN, ethinylestradiol) and norethindrone (INN, norethisterone). METHODS: Ten women who had undergone surgical sterilization were enrolled in an open-label crossover study conducted in the Georgetown University Clinical Research Center. The pharmacokinetics of single doses of 0.07 mg ethinyl estradiol and 2 mg norethindrone were measured at baseline and after 3 weeks of 200 mg thalidomide. Compliance with the thalidomide regimen was assessed with use of Medication Event Monitoring System (MEMS) caps. RESULTS: No changes were observed in the pharmacokinetics of ethinyl estradiol or norethindrone with thalidomide therapy. The mean +/- SD area under the plasma concentration-time curve (AUC0-infinity) for ethinyl estradiol was 6580 +/- 1100 ng.h/L at baseline and 5970 +/- 1560 ng.h/L after the thalidomide regimen (paired t test, P > .05). The values for norethindrone were 103 +/- 54 micrograms.h/L and 107 +/- 58 micrograms.h/L (paired t test, P > .05). No changes were observed for other pharmacokinetic parameters assessed for either ethinyl estradiol or norethindrone. No accumulation of thalidomide was seen after 21 days of therapy: day 1 AUC0-infinity 41.1 +/- 13.9 micrograms.h/mL; day 21 AUC0-infinity 59.6 +/- 27.3 micrograms.h/mL (paired t test, P > .05). No changes were observed for other pharmacokinetic parameters assessed for thalidomide between days 1 and 21. Thalidomide was well tolerated but caused variable degrees of sedation. The average thalidomide compliance rate was 97%. CONCLUSIONS: The pharmacokinetics of thalidomide do not change with 3 weeks of daily dosing. Thalidomide does not alter the pharmacokinetics of ethinyl estradiol or norethindrone. Therefore there is no drug interaction between thalidomide and these 2 drugs. The efficacy of oral contraceptives containing ethinyl estradiol and norethindrone should not be affected by concomitant thalidomide therapy.

PIP: An open-label crossover study was conducted to evaluate the effect of thalidomide on the plasma pharmacokinetics of ethinyl estradiol (INN, ethinyl estradiol) and norethindrone (INN, norethisterone) among 10 women who had undergone surgical sterilization at Georgetown University Clinical Research Center. The pharmacokinetics of single doses of 0.07 mg ethinyl estradiol and 2 mg norethindrone were measured at baseline and after 3 weeks of 200 mg thalidomide. Compliance with the thalidomide regimen was assessed with the use of Medication Event Monitoring System caps. The results showed that there were no changes in the pharmacokinetics of ethinyl estradiol or norethindrone with thalidomide therapy. Furthermore, no changes were seen for other pharmacokinetic parameters assessed for thalidomide between days 1 and 21. Thalidomide was well tolerated, but caused variable degrees of sedation. The average compliance rate of thalidomide was 97%. This study concluded that there was no drug interaction between thalidomide and the other two drugs (ethinyl estradiol and norethindrone). The efficacy of oral contraceptives containing ethinyl estradiol and norethindrone should not be affected by concomitant thalidomide therapy.

Pharmacokinetics of F105, a human monoclonal antibody, in persons infected with human immunodeficiency virus type 1.

F105 is a human monoclonal antibody that binds to the CD4 binding site of human immunodeficiency virus type 1 gp120 and neutralizes clinical and laboratory isolates of the human immunodeficiency virus. This phase I study investigated the disposition of the antibody in humans. F105 was administered over a 60-minute period at two dose levels, 100 and 500 mg/m2. Blood samples were obtained for up to 56 days. The clearance of the antibody was 0.33 ml/min with a corresponding half-life of approximately 13 days. Peak concentrations achieved at the higher dose level were 216.19 +/- 9.62 micrograms/ml. The disposition of the drug was linear for the doses studied. Simulations were performed to design future studies aimed at investigating the efficacy of the antibody. This study concluded that F105 can be administered as a bolus dose every 21 days.

Effects of a single intracoronary injection of basic fibroblast growth factor in stable angina pectoris.

We sought to evaluate safety, tolerability, pharmacokinetics, and pharmacodynamics of basic fibroblast growth factor (bFGF), administered as a single intracoronary injection, to subjects with stable angina pectoris secondary to coronary artery disease. bFGF, an angiogenic growth factor, has been shown to enhance collateral development in animal models of progressive coronary occlusion. To our knowledge, this study represents the initial introduction of parenteral bFGF into humans. This was a phase 1, randomized, dose-escalation trial of bFGF in 25 subjects with coronary artery disease and stable angina. Subjects were randomized 2:1 to a single dose of bFGF or placebo, injected into the left main coronary artery. bFGF doses ranged from 3 to 100 microg/kg, increasing in half-log increments. bFGF was generally well tolerated at doses of 3 to 30 microg/kg. Plasma clearance was 20 +/- 2 ml/kg/min, with an elimination half-life of 85 +/- 11 minutes. bFGF caused acute hypotension ( approximately 10%) that did not appear to be dose-related through the dose range studied. Of the 9 subjects who received 30 to 100 microg/kg bFGF, 2 had sustained hypotension, mild to moderate in severity, lasting 1 to 3 days, and 3 subjects developed bradycardia hours to days after bFGF administration. bFGF dilated epicardial coronary arteries (7.4 +/- 2.5% mean diameter increase, p <0.02). Transient mild thrombocytopenia and proteinuria were observed in some subjects in the 30-microg/kg cohort. No subject had signs suggesting systemic angiogenesis. Thus, intracoronary bFGF, at doses of 3 to 30 microg/kg, was generally well tolerated in subjects with stable angina.

Effect of food on the relative bioavailability of oral ganciclovir.

The steady-state pharmacokinetics of oral ganciclovir in the fasting versus fed state were studied in 20 patients infected with human immunodeficiency virus and with a seropositive test result for cytomegalovirus in a two-way crossover study. Patients received oral ganciclovir at a dose of 1000 mg every 8 hours for 8 days. On days 4 and 8, subjects were randomly assigned to receive the morning dose either after an overnight fast or after a standardized 602-calorie, high-fat (46.5%) breakfast. Serial blood samples were obtained over the 8-hour morning dose interval. The mean time to maximum concentration (tmax) was increased from 1.8 hours in the fasting state to 3.0 hours in the fed state. Mean maximum serum concentration (Cmax) and area under the concentration-time curve from time 0 to 8 hours (AUC0-8) of ganciclovir were significantly higher in the fed state than after an overnight fast. Because food could potentially increase the bioavailability of oral ganciclovir, patients should be instructed to take each dose of oral ganciclovir with food.

Quantitation of vaginally administered nonoxynol-9 in premenopausal women.

A feasibility study was performed in 11 healthy nonpregnant premenopausal women to determine a method for collection and recovery of vaginally administered nonoxynol-9. We also determined if nonoxynol-9 could be quantitated in vaginal lavage fluid obtained 2 h after instillation of a standard precoitol dose of a foam formulation of nonoxynol-9. Samples were analyzed in batch using a validated normal phase high-performance liquid chromatography (HPLC) method. Two hours after instillation of one dose of Delfen Contraceptive Foam (100 mg), the quantity of nonoxynol-9 collected ranged from 10.8 to 67.8 mg (mean: 35.4 mg). This corresponds to a recovery of 11.70%, of the administered dose. Quantitation of vaginally administered nonoxynol-9 is both practical and feasible. These data represent a critical first step in the evaluation of the safety and effectiveness of nonoxynol-9-containing products in the prevention of sexually transmitted diseases.

PIP: In clinical trials, nonoxynol-9 has been shown to protect against the transmission of sexually transmitted pathogens. Conversely, there are concerns that frequent use may lead to vaginal irritation and thus increase the risk of transmission of sexually transmitted diseases (STDs), including human immunodeficiency virus (HIV). Nonoxynol-9 is available as a foam, cream, gel, film, and suppository. These routes of administration differ from each other in their total unit dose, ability to irritate genital tissues, rates of dissolution, and ability to coat the vagina. To determine a method for collection and recovery of vaginally administered nonoxynol-9, and thereby facilitate research on the role of nonoxynol-9 in the prevention of HIV, a feasibility study was performed in 11 healthy, premenopausal US women. Also investigated was whether nonoxynol-9 could be quantitated in vaginal lavage fluid obtained 2 hours after instillation of 100 mg of nonoxynol-9 foam (Delfen). The quantity of nonoxynol-9 collected at this time ranged from 10.8-67.8 mg (mean, 35.4 mg), corresponding to a recovery rate of 11-70% of the original dose. Although further studies are needed to optimize methods for nonoxynol-9 recovery from the vagina, this study suggests it is feasible to quantitate nonoxynol-9 after single-dose vaginal administration.

Duration of vaginal retention and potential duration of antiviral activity for five nonoxynol-9 containing intravaginal contraceptives.

OBJECTIVE: The purpose of this study was to determine the vaginal retention of five nonoxynol-9 intravaginal contraceptives. METHOD: An open-label crossover study in 10 premenopausal volunteers was performed at an outpatient clinical research center. The outcomes are described utilizing the median and range. RESULT: At 8 h post-instillation, the median amounts of nonoxynol-9 present in the vagina were: Delfon 7.68 mg, Conceptrol 5.18 mg, Advantage 24 1.95 mg, VCF 1.74 mg, and Semicid 1.51 mg respectively. Our calculated theoretical minimal amount needed to protect against HIV infection is 2.00 mg. CONCLUSION: The best vehicle for retaining nonoxynol-9 in the vagina appears to be foam. Further research in the effectiveness of nonoxynol-9 in prevention of the spread of HIV infection should be directed toward the use of foam vehicles to deliver nonoxynol-9 to the vagina.

Saquinavir as Fortovase: why does it matter?

AIDS: Roche has developed and received Food and Drug Administration (FDA) approval for a new, soft gel dosage form, Fortovase, to overcome problems of bioavailability of the protease inhibitor saquinavir. Fortovase has much higher availability that hopefully correlates to increased clinical efficacy. Study results show an 8-fold increase in concentration in the system. Fortovase should be taken with food to keep it in the system longer and thereby increase its absorption. A table compares the two formulations.^ieng

Clinical pharmacology of thalidomide.

AIDS: Thalidomide is being investigated for its potential use in treating HIV wasting syndrome and other HIV-related conditions. Thalidomide is primarily broken down by hydrolysis; however, the metabolite responsible for its clinical effect is unknown. The optimum concentration of thalidomide or its metabolites to maximize benefits while minimizing toxicities is also unknown. Once daily administration is feasible because of thalidomide's 14- to 18-hour half-life. Because of thalidomide's known potential for causing birth defects, pregnant women are cautioned not to take the drug. One of the two thalidomide stereoisomers was presumed to be responsible for teratogenicity; trials using each isomer individually do not support this notion.^ieng

Metabolism of rifabutin and its 25-desacetyl metabolite, LM565, by human liver microsomes and recombinant human cytochrome P-450 3A4: relevance to clinical interaction with fluconazole.

Rifabutin and fluconazole are often given concomitantly as therapy to prevent opportunistic infections in individuals infected with the human immunodeficiency virus. Recent reports have shown increased levels of rifabutin and its 25-desacetyl metabolite, LM565, in plasma when rifabutin is administered with fluconazole. Since fluconazole is known to inhibit microsomal enzymes, this study was undertaken to determine if this rifabutin-fluconazole interaction was due to an inhibition of human hepatic enzymes. The metabolism of both rifabutin and LM565 was evaluated in human liver microsomes and recombinant human cytochrome P-450 (CYP) 3A4 in the presence of fluconazole and other probe drugs known to inhibit CYP groups 1A2, 2C9, 2D6, 2E1, and 3A. The concentrations of rifabutin (1 microg/ml), LM565 (1 microg/ml), and fluconazole (10 and 100 microg/ml) used were equal to those observed in plasma after the administration of rifabutin and fluconazole at clinically relevant doses. High-performance liquid chromatography was used to assess the metabolism of rifabutin and LM565. Rifabutin was readily metabolized to LM565 by human microsomes, but the reaction was independent of NADPH and was not affected by the P-450 inhibitors. No rifabutin metabolism by recombinant CYP 3A4 was found to occur. LM565 was also metabolized by human microsomes to two products, but metabolism was dependent on NADPH and was affected by certain P-450 inhibitors. In addition, LM565 was readily metabolized by the recombinant CYP 3A4 to the same two products found with its metabolism by human microsomes. Therefore, rifabutin is metabolized by human microsomes but not via cytochrome P-450 enzymes, whereas LM565 is metabolized by CYP 3A4.

Increased plasma rifabutin levels with concomitant fluconazole therapy in HIV-infected patients.

OBJECTIVE: To determine the effect of fluconazole on rifabutin pharmacokinetics. DESIGN: An open-label, crossover, phase 1 trial. SETTING: Outpatient clinical research center at a university medical center in Washington, D.C. PATIENTS: 12 persons with human immunodeficiency virus (HIV) infection whose CD4 lymphocyte counts were between 200 and 500 cells/mm3 and who were receiving maintenance therapy with zidovudine. INTERVENTION: Fluconazole, 200 mg/d for 2 weeks; then a combination of fluconazole, 200 mg/d, and rifabutin, 300 mg/d, for 2 weeks; and then rifabutin, 300 mg/d, for the final 2 weeks of the study. MEASUREMENTS: Blood and urine samples were obtained at regular intervals for 24 hours at the end of each 2-week dosing period to ascertain concentrations of fluconazole and rifabutin and the 25-desacetyl metabolite of rifabutin, LM565. RESULTS: Fluconazole significantly increased the plasma concentrations of both rifabutin and LM565. Mean increases in the area under the plasma concentration curve compared with the time curve over a 24-hour dosing interval were 82% (5442 +/- 2404 ng.h/mL compared with 3025 +/- 1117 ng.h/mL; P less than or equal to 0.05) for rifabutin and 216% (959 +/- 529 ng.h/mL compared with 244 +/- 141 ng.h/mL; P less than or equal to 0.05) for LM565. CONCLUSIONS: Fluconazole significantly increases the systemic exposure of both rifabutin and LM565. This pharmacokinetic interaction offers a mechanism that may explain the changes reported in both the efficacy and toxicity of rifabutin with concomitant fluconazole therapy.

Glucuronidation of 3'-azido-3'-deoxythymidine (zidovudine) by human liver microsomes: relevance to clinical pharmacokinetic interactions with atovaquone, fluconazole, methadone, and valproic acid.

Zidovudine (3'-azido-3'-deoxythymidine [AZT]), an antiviral nucleoside analog effective in the treatment of human immunodeficiency virus infection, is primarily metabolized to an inactive glucuronide form, GAZT, via uridine-5'-diphospho-glucuronosyltransferase (UGT) enzymes. UGT enzymes exist as different isoforms, each exhibiting substrate specificity. Published clinical studies have shown that atovaquone, fluconazole, methadone, and valproic acid decreased GAZT formation, presumably due to UGT inhibition. The effect of these drugs on AZT glucuronidation was assessed in vitro by using human hepatic microsomes to begin understanding in vitro-in vivo correlations for UGT metabolism. The concentrations of each drug studied were equal to those reported with the usual clinical doses and at concentrations at least 10 times higher than would be expected with these doses. High-performance liquid chromatography was used to assess the respective metabolism and formation of AZT and GAZT. All four drugs exhibited concentration-dependent inhibition of AZT glucuronidation. The respective concentrations of atovaquone and methadone which caused 50% inhibition of GAZT were > 100 and 8 micrograms/ml, well above their usual clinical concentrations. Fluconazole and valproic acid exhibited 50% inhibition of GAZT at 50 and 100 micrograms/ml, which are within the clinical ranges of 10 to 100 and 50 to 100 micrograms/ml, respectively. These data suggest that inhibition of AZT glucuronidation may be more clinically significant with concomitant fluconazole and valproic acid. Factors such as inter- and intraindividual pharmacokinetic variability and changes in AZT intracellular concentrations should be considered as other mechanisms responsible for changes in AZT pharmacokinetics with concomitant therapies.

Thalidomide for the treatment of esophageal aphthous ulcers in patients with human immunodeficiency virus infection. National Institute of Allergy and Infectious Disease AIDS Clinical Trials Group.

A multicenter, double-blind, randomized, placebo-controlled clinical trial was conducted to determine the safety and efficacy of thalidomide for treating esophageal aphthous ulceration in persons infected with human immunodeficiency virus (HIV). Twenty-four HIV-infected patients with biopsy-confirmed aphthous ulceration of the esophagus were randomly assigned to receive either oral thalidomide, 200 mg/day, or oral placebo daily for 4 weeks. Eight (73%) of 11 patients randomized to receive thalidomide had complete healing of aphthous ulcers at the 4-week endoscopic evaluation, compared with 3 (23%) of 13 placebo-randomized patients (odds ratio, 13.82; 95% confidence interval, 1.16-823.75; P=.033). Odynophagia and impaired eating ability caused by esophageal aphthae were improved markedly by thalidomide treatment. Adverse events among patients receiving thalidomide included somnolence (4 patients), rash (2 patients), and peripheral sensory neuropathy (3 patients). Thalidomide is effective in healing aphthous ulceration of the esophagus in patients infected with HIV.