High incidence of adverse events in healthy volunteers receiving rifampicin and adjusted doses of lopinavir/ritonavir tablets

Objective: Previous research in healthy volunteers has demonstrated that rifampicin and adjusted doses of lopinavir/ritonavir soft-gel capsules resulted in adequate exposure to lopinavir. Our objective was to study the combined use of rifampicin and the newly introduced lopinavir/ritonavir tablets.

Methods: A total of 40 healthy volunteers were planned to start with 600 mg rifampicin once daily from days 1-5. From days 6-15, volunteers were randomized to receive lopinavir/ritonavir tablets dosed as either 600/150 or 800/200 mg twice daily, both in addition to 600 mg rifampicin once daily. A 12 h pharmacokinetic curve was planned on day 15. Safety assessments were conducted regularly throughout the study period.

Results: Eleven volunteers started as the first group in this study. No major complaints occurred during day 1-5 (rifampicin only). After addition of lopinavir/ritonavir, eight volunteers suffered from both nausea and vomiting, one from nausea only, and one from vomiting only. On day 7, increases in aspartate aminotransferase/alanine aminotransferase (AST/ALT) levels were reported in all volunteers and on day 8, the study was prematurely terminated. The AST/ALT levels continued to rise and peaked (grade 2, n = 2; grade 3, n = 1; grade 4, n = 8) on days 9-10. All values returned to normal within 6 weeks.

Conclusions: The study showed a high incidence of adverse events when a higher than standard dose of the new lopinavir/ritonavir tablets was combined with rifampicin. In the future, this drug combination should not be given to healthy volunteers. Liver function should be carefully monitored when rifampicin and lopinavir/ritonavir are combined in patients.

Introduction

Approximately one-third of the 40 million people living with HIV/AIDS worldwide are coinfected with tuberculosis (TB) ^[1]. Rifampicin is not only the most powerful component of current TB treatment but also a strong inducer of cytochrome P450 enzymes, resulting in drug-drug interactions with antiretroviral therapy ^[2,3], in particular, non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors.

The World Health Organization (WHO) recommends to combine rifampicin-based TB treatment with efavirenz-based antiretroviral therapy in TB-HIV coinfected patients ^[3]. The modest decrease in concentrations of the NNRTI efavirenz is not expected to be clinically relevant ^[4,5]. Although rifampicin reduces concentrations of the NNRTI nevirapine by 20-55% ^[6], collected experience is sufficient to make nevirapine an alternative to efavirenz among non-Caucasian patients receiving rifampicin ^[7,8]. A disadvantage of NNRTI drugs is the low genetic barrier for the development of resistance; only one point mutation is required to confer high-level cross-class resistance ^[9].

One alternative for patients with NNRTI-resistant HIV or those unable to take NNRTIs would be triple nucleoside regimens without interaction to rifampicin. However, these regimens are associated with less antiretroviral activity ^[10] and therefore not advisable. An equally active alternative to NNRTI-based therapy among patients being treated with rifampicin may be protease inhibitor-based antiretroviral therapy. However, standard protease inhibitor doses, whether boosted with ritonavir or not, cannot be given with rifampicin because of large decreases in protease inhibitor concentrations ^[11-14].

In HIV-infected adults without active tuberculosis, WHO recommends lopinavir/ritonavir at 400/100 mg twice daily (b.i.d.) in combination with two nucleosides as protease inhibitor-based therapy ^[15]. We have previously evaluated the pharmacokinetics of two adjusted dose regimens of lopinavir/ritonavir (800/200 and 400/400 mg b.i.d.) soft gel capsules when combined with rifampicin in healthy volunteers ^[11]. Because of more variable pharmacokinetics of lopinavir in the better tolerable arm of 800/200 mg lopinavir/ritonavir, therapeutic drug monitoring (TDM) appeared to be indicated. In the absence of TDM, 400/400 mg lopinavir/ritonavir could be combined with rifampicin, while closely monitoring for liver enzyme elevations.

Recently, a new tablet formulation of lopinavir/ritonavir has become available. Compared to the soft gel capsule, the novel tablet formulation shows reduced pharmacokinetic variability and exhibits slightly higher (18%) bioavailability, irrespective of concomitant food intake ^[16].

The aim of this study was to evaluate the pharmacokinetics of two adjusted dose regimens of lopinavir/ritonavir tablets in combination with rifampicin in healthy volunteers. Owing to an unexpectedly high incidence of adverse events, this study was terminated prematurely.

Methods

Study design

The study was designed as an open-label, sequential, two-period, phase IV multiple dose trial in healthy volunteers. From day 1 until day 5, volunteers received 600 mg rifampicin once daily (q.d.). From day 6 until day 15, volunteers were randomized to receive either three (600/150 mg) or four (800/200 mg) of the new lopinavir/ritonavir (Kaletra; Abbott Laboratories, Abbott Park, Illinois, USA) tablets b.i.d., combined with 600 mg rifampicin q.d.. On days 1, 3, 5, 6, 7, 9, 11, 13 and 15, study medication was planned to be taken under observation and immediately after a standardized breakfast (±350 kcal, ±13 g of fat). The other drug doses were taken at home. All volunteers gave written informed consent and the Ethical Review Board of Radboud University Nijmegen Medical Centre, The Netherlands, approved the study.

Study volunteers

Healthy volunteers, aged 18-55 years were eligible for enrolment after pre-entry and laboratory evaluation. The main exclusion criteria were positive HIV test result; positive hepatitis B or C test result; positive Mantoux test result; abnormal clinical laboratory test results and abnormal ECG.

Pharmacokinetic assessment

Blood samples of 5 ml were planned to be collected at the following time points; on day 5 just before and 2 h postdose (C_2h) for the determination of rifampicin (and desacetylrifampicin) plasma concentrations; on days 7, 9, 11 and 13 predose for the determination of plasma concentrations of lopinavir and ritonavir; and on day 15 predose until 12 h postdose for the analysis of all three drugs. Blood samples were stored in the refrigerator immediately and centrifuged at 2500 g for 10 min. Plasma was separated and stored below -40°C (for the determination of lopinavir and ritonavir) or -80°C (for the determination of rifampicin and desacetylrifampicin) within 4 h after collection. All procedures concerning collection and storage of drug samples have been validated.

Bioanalysis

Plasma lopinavir, ritonavir, rifampicin and desacetylrifampicin concentrations were determined by validated high-performance liquid chromatography (HPLC) methods ^[17,18].

Safety and tolerability

We planned to perform clinical chemistry and haematology tests and to ask volunteers about the occurrence of adverse events at each study visit on day 1, 3, 5, 6, 7, 9, 11, 13 and 15. Adverse events, clinical chemistry and haematology test results were graded according to the grading system of the Division of AIDS ^[19]. After termination of the study, hepatitis B and C tests were repeated. In addition, Epstein-Barr virus and cytomegalovirus antibody tests were performed to exclude acute viral infection.

Results

Study volunteers

Forty healthy volunteers were enrolled in the study. The first group consisted of 11 volunteers of whom eight were Caucasians, two were Caucasian-black and one was black. The median (range) age, body weight and body mass index were 24 (19-51) years, 63 (53-92) kg and 22 (19-30) kg/m², respectively. Five volunteers (three women) received 600/150 mg lopinavir/ritonavir b.i.d. and six (four women) received 800/200 mg lopinavir/ritonavir b.i.d. in addition to rifampicin 600 mg. The remaining 29 volunteers were withdrawn from the study after receiving only one dose of rifampicin (n = 10) or no study medication at all (n = 19).

Pharmacokinetics

The geometric mean (range) of rifampicin and desacetylrifampicin C_2h on day 5 (rifampicin only) was 11.3 (6.8-17.4) and 1.12 (0.74-2.37) mg/l, respectively (n = 11). In five volunteers, plasma concentrations of lopinavir and ritonavir were undetectable in the morning of day 7 due to vomiting after the evening dose on day 6. In the remaining six volunteers, the geometric mean (range) of the lopinavir and ritonavir trough concentrations on day 7 were 7.9 (6.6-10.3) mg/l and 0.71 (0.35-1.61) mg/l in the 600/150 mg group (n = 3) and 10.9 (8.3-13.8) mg/l and 1.20 (0.64-1.85) mg/l in the 800/200 mg group (n = 3). The median (range) of the rifampicin and desacetylrifampicin trough concentrations in the morning of day 7 were 0.41 (0.0-1.13) mg/l and 0.40 (0.0-0.83) mg/l in the 600/150 mg group (n = 5) and 0.47 (0.0-1.17) mg/l and 0.21 (0.0-1.12) mg/l in the 800/200 mg group (n = 6).

Tolerability

No major complaints or abnormal aspartate aminotransferase/alanine aminotransferase (AST/ALT) levels occurred during day 1-5, when rifampicin was given only (Table 1). After addition of lopinavir/ritonavir, eight volunteers suffered from both nausea and vomiting, one had nausea only, and one vomited only. Eight volunteers were given the antiemetic drug metoclopramide. All six volunteers in the 800/200 mg lopinavir/ritonavir group vomited, compared to three out of five in the 600/150 mg group. On day 7, increases in AST and ALT levels were reported in all volunteers and increases in gamma glutamyl transferase (GGT) in all but one volunteer. Study medication was stopped on day 7 for eight volunteers and on day 8 for the remaining three volunteers. The AST/ALT levels continued to rise and peaked (range 125-1400 and 201-1657 U/l, respectively) on days 9-10 (Table 1). The GGT levels increased more gradually and peaked (range 21-177 U/l) on days 10-12 (Table 1). Four out of six volunteers in the 800/200 mg lopinavir/ritonavir group experienced grade 4 AST or ALT toxicity versus four out of five in the 600/150 mg group. All clinical parameters returned to normal within six weeks after study termination (Fig. 1). Test results for hepatitis B and C, Epstein-Barr virus and cytomegalovirus were all negative after study termination.

Table 1

Fig. 1

Discussion

The present study showed an unexpected high incidence of nausea, vomiting and liver enzyme elevations when a higher than standard dose of the recently introduced lopinavir/ritonavir tablets was combined with rifampicin in healthy volunteers. Therefore, the study was terminated prematurely.

In our previous study in which rifampicin and adjusted doses of lopinavir/ritonavir capsules were combined ^[11], toxicity of this magnitude was not observed. However, the current study differed from our previous study ^[11] in several aspects, and this may explain the higher incidence of adverse events. First, rifampicin was introduced prior to lopinavir/ritonavir; second, the adjusted dose of lopinavir/ritonavir tablets was not escalated; and third, the new lopinavir/ritonavir tablet formulation was used instead of the capsule formulation.

First, the sequence of introduction of rifampicin and lopinavir/ritonavir may have played a role. Termination of a study because of unexpected hepatotoxicity in healthy volunteers using the combination of rifampicin and saquinavir/ritonavir, was reported before ^[20]. The majority of the adverse events was observed in the study arm in which rifampicin usage was followed by the combination of rifampicin and the protease inhibitors ^[20], analogous to the current study. However, this sequence is a reflection of the clinical situation of TB-HIV coinfected patients as TB is preferably treated first. Besides, TB-HIV coinfected patients seem to tolerate the combination of rifampicin and saquinavir/ritonavir well in both sequences ^[14,21], suggesting a yet unidentified difference between patients and healthy volunteers. It has not been investigated so far, whether TB-HIV coinfected patients tolerate the combination of rifampicin and lopinavir/ritonavir better than healthy volunteers.

With respect to the second difference, the absence of a dose escalation scheme for the adjusted dose of lopinavir/ritonavir may have contributed to the high incidence of adverse events in the current study. We decided to omit dose escalation because the liver enzymes had been induced by rifampicin already. The efflux transporter P-glycoprotein (P-gp) can mediate the transport of lopinavir and ritonavir ^[22,23] as well as rifampicin ^[24]. A time-dependent effect by lopinavir/ritonavir on P-gp was previously suggested; inhibition after single-dose and induction after repeated administration ^[25]. The immediate administration of the high dose of lopinavir/ritonavir in the current study may have resulted in inhibition of the efflux transporter P-gp and therefore to the relatively high trough concentrations of the study medication observed. This may explain part of the adverse events.

Finally, unidentified toxic excipients of the new tablet formulation and its slightly higher bioavailability may have played a role. Studies show that this slight increase in bioavailability of lopinavir/ritonavir tablets may compensate for the inductive effect of efavirenz ^[26]. This same compensation may occur when combined with rifampicin, as in the current study in which we found relatively high nonsteady-state lopinavir trough levels compared to the steady-state levels in the previous study ^[11]. In short, data from interaction studies with one formulation cannot be extrapolated to another formulation.

In conclusion, this study demonstrates the challenging character of the compatibility of rifampicin and protease inhibitors in TB-HIV therapy. We advise that further studies investigating the interaction between rifampicin and lopinavir/ritonavir tablets be performed in the actual target population of TB-HIV coinfected patients rather than in healthy volunteers. Awaiting these results, simultaneous treatment with rifampicin and lopinavir/ritonavir should not be applied. In case no alternatives are available, extreme caution and close monitoring of liver enzymes and plasma drug concentrations is warranted.

Acknowledgements

We would like to thank the healthy volunteers for their participation in this study. The staff at the Clinical Research Centre Nijmegen (CRCN) is acknowledged for their cooperation and effort. The technicians of the Department of Clinical Pharmacy, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands are acknowledged for the analysis of the plasma samples.

Sponsorship: This study was funded by Radboud University Nijmegen Medical Centre.