Rapid and sensitive high-performance liquid chromatographic method for the determination of ritonavir in human plasma

Prednisolone Pharmacokinetics in the Presence and Absence of Ritonavir After Oral Prednisone Administration to Healthy Volunteers

Corticosteroid therapy has been associated with bone toxicities (eg, osteonecrosis) and Cushing syndrome in HIV-infected patients; this may be partially attributable to a pharmacokinetic drug interaction between HIV protease inhibitors and corticosteroids. The purpose of this study was to characterize the influence of low-dose ritonavir on prednisolone pharmacokinetics in healthy subjects. Ten HIV-seronegative volunteers were given single oral doses of prednisone, 20 mg, before (baseline) and after receiving ritonavir, 200 mg, twice daily for 4 and 14 days. After each prednisone dose, serial blood samples were collected and prednisolone concentrations were determined; pharmacokinetic parameter values were compared between the groups. Geometric mean ratios (GMRs, 90% confidence interval [CI]) of the prednisolone area under the plasma concentration versus time curve (AUC0-infinity) after 4 and 14 days of ritonavir versus baseline were 1.41 (90% CI: 1.08 to 1.74) and 1.30 (90% CI: 1.09 to 1.49), respectively (P = 0.002 and P = 0.004, respectively). GMRs of prednisolone apparent oral clearance (Cl/F) were 0.71 (09% CI: 0.57 to 0.93) and 0.77 (90% CI: 0.67 to 0.92) after 4 and 14 days of ritonavir versus baseline, respectively (P = 0.0004 and P = 0.0003, respectively). Ritonavir significantly increased the systemic exposure of prednisolone in healthy subjects. Results from this investigation suggest that corticosteroid exposure is likely elevated in HIV-infected patients receiving protease inhibitors.

Ritonavir Decreases the Nonrenal Clearance of Digoxin in Healthy Volunteers with Known MDR1 Genotypes

Our objective was to examine the influence of ritonavir on P-glycoprotein (P-gp) activity in humans by characterizing the effect of ritonavir on the pharmacokinetics of the P-gp substrate digoxin in individuals with known MDR1 genotypes. Healthy volunteers received a single dose of digoxin 0.4 mg orally before and after 14 days of ritonavir 200 mg twice daily. After each digoxin dose blood and urine were collected over 72 hours and analyzed for digoxin. Digoxin pharmacokinetic parameter values were determined using noncompartmental methods. MDR1 genotypes at positions 3435 and 2677 in exons 26 and 21, respectively, were determined using PCR-RFLP analysis. Ritonavir increased the digoxin AUC(0-72) from 26.20 +/- 8.67 to 31.96 +/- 11.24 ng x h/mL (P = 0.03) and the AUC(0-8) from 6.25 +/- 1.8 to 8.04 +/- 2.22 ng x h/mL (P = 0.02) in 12 subjects. Digoxin oral clearance decreased from 149 +/- 101 mL/h x kg to 105 +/- 57 mL/h x kg (P = 0.04). Other digoxin pharmacokinetic parameter values, including renal clearance, were unaffected by ritonavir. Overall, 75% (9/12) of subjects had higher concentrations of digoxin after ritonavir administration. The majority of subjects were heterozygous at position 3435 (C/T) (6 subjects) and position 2677 (G/T,A) (7 subjects); although data are limited, the effect of ritonavir on digoxin pharmacokinetics appears to occur across all tested MDR1 genotypes. Concomitant low-dose ritonavir reduced the nonrenal clearance of digoxin, thereby increasing its systemic availability. The most likely mechanism for this interaction is ritonavir-associated inhibition of P-gp. Thus, ritonavir can alter the pharmacokinetics of coadministered medications that are P-gp substrates.

The Distribution of the HIV Protease Inhibitor, Ritonavir, to the Brain, Cerebrospinal Fluid, and Choroid Plexuses of the Guinea Pig

Anti-human immunodeficiency virus (HIV) drug penetration into the brain and cerebrospinal fluid (CSF) is necessary to tackle HIV within the CNS. This study examines movement of [(3)H]ritonavir across the guinea pig blood-brain and blood-CSF barriers and accumulation within the brain, CSF, and choroid plexus. Ritonavir is a protease inhibitor, used in combination therapy (often as a pharmacoenhancer) to treat HIV. Drug interactions at brain barrier efflux systems may influence the CNS penetration of anti-viral drugs, thus the influence of additional protease inhibitors, nucleoside reverse transcriptase inhibitors, and non-nucleoside reverse transcriptase inhibitors on [(3)H]ritonavir CNS distribution was explored. Additionally, the involvement of transporters on [(3)H]ritonavir passage across the brain barriers was assessed. Results from in situ brain perfusions and capillary depletion analysis demonstrated that [(3)H]ritonavir uptake into the guinea pig brain was considerable (6.6 +/- 0.7 ml/100 g at 30 min, vascular space corrected), although a proportion of drug remained trapped in the cerebral capillaries and did not reach the brain parenchyma. CSF uptake was more limited (2.2 +/- 0.4 ml/100 g at 30 min), but choroid plexus uptake was abundant (176.7 +/- 46.3 ml/100 g at 30 min). [(3)H]Ritonavir brain and CSF uptake was unaffected by neither inhibitors of organic anion transport (probenecid and digoxin) or P-glycoprotein (progesterone), nor by any additional anti-HIV drugs, indicating that brain barrier efflux systems do not significantly limit brain or CSF [(3)H]ritonavir accumulation in this model. [(3)H]Ritonavir uptake into the perfused choroid plexus was significantly reduced by nevirapine and abacavir, additional perfusion studies, and isolated incubated choroid plexus experiments were carried out in an attempt to further characterize the transporter involved.

Influence of ritonavir on olanzapine pharmacokinetics in healthy volunteers

HIV infection and psychotic illnesses frequently coexist. The atypical antipsychotic olanzapine is metabolized primarily by CYP1A2 and glucuronosyl transferases, both of which are induced by the HIV protease inhibitor ritonavir. The purpose of this study was to determine the effect of ritonavir on the pharmacokinetics of a single dose of olanzapine. Fourteen healthy volunteers (13 men; age range, 20-28 years) participated in this open-label study. Subjects received olanzapine 10 mg and blood samples were collected over a 120-hour post-dose period. Two weeks later, subjects took ritonavir 300 mg twice daily for 3 days, 400 mg twice daily for 4 days, and 500 mg twice daily for 4 days. The next morning, after 11 days of ritonavir, olanzapine 10 mg was administered and blood sampling was repeated. Plasma samples were analyzed for olanzapine with HPLC. We compared olanzapine noncompartmental pharmacokinetic parameter values before and after ritonavir with a paired Student t test. Ritonavir reduced the area under the plasma concentration-time curve of olanzapine from 501 ng. hr/mL (443-582) to 235 ng. hr/mL (197-294) (p < 0.001), the half-life from 32 hours (28-36) to 16 hours (14-18) (p = 0.00001), and the peak concentration from 15 ng/mL (13-19) to 9 ng/mL (8-12) (p = 0.002). Olanzapine oral clearance increased from 20 L/hr (18-23) to 43 L/hr (38-51) (p < 0.001) after ritonavir. Ritonavir significantly reduced the systemic exposure of olanzapine in volunteers. Patients receiving this combination may ultimately require higher olanzapine doses to achieve desired therapeutic effects.