Helen E. Reynolds

Pharmacokinetic Interactions of Nevirapine and Methadone and Guidelines for Use of Nevirapine to Treat Injection Drug Users

Administration of nevirapine to HIV-infected injection drug users who also receive methadone results in a significant reduction in methadone exposure after 7-10 days of therapy. Many patients require an increase in methadone dose to counteract this effect.

Clinical use of lopinavir/ritonavir in a salvage therapy setting: pharmacokinetics and pharmacodynamics.

Lopinavir/ritonavir was administered to 35 HIV-infected patients after therapeutic failure with other protease inhibitors. The pharmacokinetics (trough concentrations) and baseline viral genotype were determined, together with the immunovirological outcome. The 22 responders had significantly higher mean lopinavir concentrations and lower baseline numbers of mutations. On multivariate analysis, a lopinavir concentration of 5.7 microg/ml or greater was an independent predictor of viral suppression over a 9-month follow-up period.

The Relationship between Nevirapine Plasma Concentrations and Abnormal Liver Function Tests

Abnormal liver function tests are frequently observed in HIV-infected individuals receiving nevirapine (NVP). Here we investigate the relationship between total and unbound plasma concentrations of NVP and the liver enzymes alanine aminotransferase (ALT) and gamma-glutamyl transferase (gammaGT). HIV-infected individuals [n = 85, 22 female, 34 hepatitis C or B virus (HCV or HBV(+))] receiving NVP (200 mg bd; median duration 66 weeks, range 3-189) and two nucleoside reverse transcriptase inhibitors (NRTIs) were enrolled into this study. Blood samples were taken at C(trough) (12 hr postdose) for measurement of NVP and liver function tests (ALT and gammaGT). Plasma protein bound and unbound drug was separated using ultrafiltration and NVP concentrations quantified using HPLC-MS/MS. A linear relationship was observed between total and unbound NVP C(trough) (r(2) = 0.77, p < 0.0001). Patients with elevated ALT (>37 IU/liter; n = 31) had higher NVP unbound C(trough) than those with ALT within the normal range (median 2268 vs. 1694 ng/ml, p = 0.04) but there was no difference in total C(trough). Logistic regression revealed no association between higher NVP C(trough) and ALT elevations. Significantly higher NVP total and unbound C(trough) were observed in patients with increased gammaGT (>40 IU/liter; n = 63; total 6747 vs. 4530 ng/ml, p = 0.001; unbound 2113 vs. 1557 ng/ml, p = 0.03). Significantly higher unbound NVP C(trough) was observed in HCV/HBV(+) (median 2275 vs. 1726 ng/ml, p = 0.02) and on bivariate analysis, higher NVP C(trough) was associated with HCV/HBV coinfection (chi(2) = 4.228; p = 0.04). Overall we found no strong association between NVP concentrations and hepatotoxicity. Although in this study NVP was well tolerated in HCV/HBV coinfected patients, higher plasma concentrations were observed.

Absence of opioid withdrawal symptoms in patients receiving methadone and the protease inhibitor lopinavir-ritonavir.

A study was designed to determine the interactions, both clinical and pharmacokinetic, between methadone and lopinavir-ritonavir. Results demonstrated a 36% reduction in the methadone area under the plasma concentration-time curve after the introduction of lopinavir-ritonavir, with no coincident symptoms of opioid withdrawal and no requirement for methadone dose adjustment.

Penetration of efavirenz into the male genital tract: drug concentrations and antiviral activity in semen and blood of HIV-1-infected men.

Efavirenz is a potent non-nucleoside reverse transcriptase inhibitor, licensed for the treatment of HIV-1. Data on sanctuary site penetration are limited. Therefore, we measured efavirenz concentrations in the blood and semen of 19 HIV-1-positive men and found concentrations in seminal plasma averaged 10% of those in blood plasma. Furthermore, seminal plasma viral loads were suppressed by 24 weeks of therapy in all patients. These data suggest that efavirenz-containing regimens have antiviral activity within the male genital tract.

Simultaneous determination of rifampicin and efavirenz in plasma

Complex drug interactions involving antiretroviral agents and drugs for the management of opportunistic infections demand the monitoring of plasma drug concentrations to prevent treatment failure. The high occurrence of tuberculosis in HIV-infected subjects makes the management of HIV treatment complex. Rifampicin, a potent inducer of the cytochrome P 450 metabolic pathway, is a very active antituberculosis drug that accelerates the metabolism of protease inhibitors. Regimens containing efavirenz, a non-nucleoside reverse transcription inhibitor, could be an alternative, but efavirenz plasma concentrations may be altered after the coadministration of rifampicin. Efavirenz is also a cytochrome P 450 inducer and may alter rifampicin plasma levels. Due to the increasing need to monitor plasma concentrations in HIV patients with tuberculosis, a high-performance liquid chromatographic (HPLC) method has been developed to measure rifampicin and efavirenz at the same time in a small amount of sample. This HPLC method is highly sensitive and precise, suitable for pharmacokinetic studies or routine clinical monitoring of rifampicin and efavirenz simultaneously in HIV patients with tuberculosis.

Undefined duration of opiate withdrawal induced by efavirenz in drug users with HIV infection and undergoing chronic methadone treatment.

THE CLINICAL EFFICACY of efavirenz and its pharmacokinetic profile allowing once daily administration make this drug an attractive option for the treatment of HIV infection. Efavirenz induces cytochrome P-450 (CYP) enzymes particularly CYP3A4 and CYP2B6 which take part in metabolizing numerous drugs. As a consequence the coadministration of efavirenz with several compounds undergoing CYP3A4 metabolism is contraindicated in order to avoid untoward effects resulting from drug interactions. Where intravenous drug addiction is a major risk factor for HIV infection (e.g. Italy and Spain) a substantial subset of HIV-infected subjects is under chronic treatment with methadone another compound whose metabolism mainly depends on CYP3A4 activity. In spite of the frequent coadministration of efavirenz with methadone only recently has the manufacturer released some indication regarding methadone dose adjustment in dual intakers. This was based on a study by Clarke and co-workers who found that a median 22% increase in methadone dosage was sufficient to restore a subjective state of compensation in new efavirenz recipients. (excerpt)

Effect of intermittent rifampicin on the pharmacokinetics and safety of raltegravir

OBJECTIVES Previous studies of raltegravir and rifampicin have not studied the interaction when rifampicin is dosed intermittently. This study aimed to assess the pharmacokinetics of twice daily raltegravir and intermittently dosed rifampicin. METHODS This was a prospective, open, single-arm, three-part, controlled study in healthy volunteers. Over a period of 38 days subjects received 5 days of standard-dose raltegravir (400 mg twice daily) followed by 28 days of standard-dose raltegravir plus rifampicin three times a week followed by 5 days of high-dose (800 mg twice daily) raltegravir plus rifampicin three times a week. Pharmacokinetic sampling was performed on days 5, 33 and 38. Raltegravir pharmacokinetic parameters were determined by non-compartmental analysis and reported as geometric means and 90% CIs. ClinicalTrials.gov: NCT01424826. RESULTS Sixteen subjects (12 females) completed the study. Raltegravir trough plasma concentration (C12) was significantly lower in the presence of rifampicin when dosed at 400 mg twice daily (40%), which was not observed with 800 mg twice daily dosing. Raltegravir Cmax and AUC0-12 were both significantly higher in the presence of rifampicin when dosed at 800 mg twice daily (76% and 84%, respectively), but this dose was well tolerated. CONCLUSIONS This study suggests that rifampicin induction of raltegravir is comparable between daily and intermittent rifampicin. In the absence of definitive clinical efficacy data to suggest otherwise, doses of 800 mg of raltegravir twice daily with rifampicin thrice weekly are well tolerated and yield higher AUCs and comparable C12 when compared with raltegravir alone.