Chemical formula: C₃₁H₃₃F₃N₂O₅S Molecular mass: 602.664 g/mol PubChem compound: 54682461
The human immunodeficiency virus (HIV-1) encodes an aspartyl protease that is essential for the cleavage and maturation of viral protein precursors. Tipranavir is a non-peptidic inhibitor of the HIV-1 protease that inhibits viral replication by preventing the maturation of viral particles.
Tipranavir inhibits the replication of laboratory strains of HIV-1 and clinical isolates in acute models of T-cell infection, with 50% and 90% effective concentrations (EC50 and EC90) ranging from 0.03 to 0.07 µM (18-42 ng/ml) and 0.07 to 0.18 µM (42-108 ng/ml), respectively. Tipranavir demonstrates antiviral activity in vitro against a broad panel of HIV-1 group M non-clade B isolates (A, C, D, F, G, H, CRF01 AE, CRF02 AG, CRF12 BF). Group O and HIV-2 isolates have reduced susceptibility in vitro to tipranavir with EC50 values ranging from 0.164-1 µM and 0.233-0.522 µM, respectively. Protein binding studies have shown that the antiviral activity of tipranavir decreases on average 3.75-fold in conditions where human serum is present.
The development of resistance to tipranavir in vitro is slow and complex. In one particular in vitro resistance experiment, an HIV-1 isolate that was 87-fold resistant to tipranavir was selected after 9 months, and contained 10 mutations in the protease: L10F, I13V, V32I, L33F, M36I, K45I, I54V/T, A71V, V82L, I84V as well as a mutation in the gag polyprotein CA/P2 cleavage site. Reverse genetic experiments showed that the presence of 6 mutations in the protease (I13V, V32I, L33F, K45I, V82L, I84V) was required to confer >10-fold resistance to tipranavir while the full 10-mutation genotype conferred 69-fold resistance to tipranavir. In vitro, there is an inverse correlation between the degree of resistance to tipranavir and the capacity of viruses to replicate. Recombinant viruses showing ≥3-fold resistance to tipranavir grow at less than 1% of the rate detected for wild type HIV-1 in the same conditions. Tipranavir resistant viruses which emerge in vitro from wild-type HIV-1 show decreased susceptibility to the protease inhibitors amprenavir, atazanavir, indinavir, lopinavir, nelfinavir and ritonavir but remain sensitive to saquinavir.
Through a series of multiple stepwise regression analyses of baseline and on-treatment genotypes from all clinical studies, 16 amino acids have been associated with reduced tipranavir susceptibility and/or reduced 48-week viral load response: 10V, 13V, 20M/R/V, 33F, 35G, 36I, 43T, 46L, 47V, 54A/M/V, 58E, 69K, 74P, 82L/T, 83D and 84V. Clinical isolates that exhibited a ≥10-fold decrease in tipranavir susceptibility harboured 8 or more tipranavir-associated mutations. In Phase II and III clinical trials, 276 patients with on-treatment genotypes have demonstrated that the predominant emerging mutations with tipranavir treatment are L33F/I/V, V82T/L and I84V. Combination of all three of these is usually required for reduced susceptibility. Mutations at position 82 occur via two pathways: one from preexisting mutation 82A selecting to 82T, the other from wild type 82V selecting to 82L.
Tipranavir maintains significant antiviral activity (<4-fold resistance) against the majority of HIV-1 clinical isolates showing post-treatment decreased susceptibility to the currently approved protease inhibitors: amprenavir, atazanavir, indinavir, lopinavir, ritonavir, nelfinavir and saquinavir. Greater than 10-fold resistance to tipranavir is uncommon (<2.5% of tested isolates) in viruses obtained from highly treatment experienced patients who have received multiple peptidic protease inhibitors.
The effect of tipranavir with low dose of ritonavir on the QTcF interval was measured in a study in which 81 healthy subjects received the following treatments twice daily for 2.5 days: tipranavir/ritonavir (500/200 mg), tipranavir/ritonavir at a supra-therapeutic dose (750/200 mg), and placebo/ritonavir (-/200 mg). After baseline and placebo adjustment, the maximum mean QTcF change was 3.2 ms (1-sided 95% Upper CI: 5.6 ms) for the 500/200 mg dose and 8.3 ms (1-sided 95% Upper CI: 10.8 ms) for the supra-therapeutic 750/200 mg dose. Hence tipranavir at therapeutic dose with low dose of ritonavir did not prolong the QTc interval but may do so at supratherapeutic dose.
In order to achieve effective tipranavir plasma concentrations and a twice daily dosing regimen, coadministration of tipranavir with low dose ritonavir twice daily is essential. Ritonavir acts by inhibiting hepatic cytochrome P450 CYP3A, the intestinal P-glycoprotein (P-gp) efflux pump and possibly intestinal cytochrome P450 CYP3A as well. As demonstrated in a doseranging evaluation in 113 HIV-negative healthy male and female volunteers, ritonavir increases AUC0-12h, Cmax and Cmin and decreases the clearance of tipranavir. 500 mg Tipranavir co-administered with low dose ritonavir (200 mg; twice daily) was associated with a 29-fold increase in the geometric mean morning steady-state trough plasma concentrations compared to tipranavir 500 mg twice daily without ritonavir.
Absorption of tipranavir in humans is limited, though no absolute quantification of absorption is available. Tipranavir is a P-gp substrate, a weak P-gp inhibitor and appears to be a potent P-gp inducer as well. Data suggest that, although ritonavir is a P-gp inhibitor, the net effect of tipranavir, coadministered with low dose ritonavir, at the proposed dose regimen at steady-state, is P-gp induction. Peak plasma concentrations are reached within 1 to 5 hours after dose administration depending upon the dosage used. With repeated dosing, tipranavir plasma concentrations are lower than predicted from single dose data, presumably due to hepatic enzyme induction. Steady-state is attained in most subjects after 7 days of dosing. Tipranavir, co-administered with low dose ritonavir, exhibits linear pharmacokinetics at steady state.
Dosing with tipranavir capsules 500 mg twice daily concomitant with 200 mg ritonavir twice daily for 2 to 4 weeks and without meal restriction produced a mean tipranavir peak plasma concentration (Cmax) of 94.8 ± 22.8 µM for female patients (n=14) and 77.6 ± 16.6 µM for male patients (n=106), occurring approximately 3 hours after administration. The mean steady-state trough concentration prior to the morning dose was 41.6 ± 24.3 µM for female patients and 35.6 ± 16.7 µM for male patients. Tipranavir AUC over a 12 hour dosing interval averaged 851 ± 309 µM•h (CL=1.15 l/h) for female patients and 710 ± 207 µM•h (CL=1.27 l/h) for male patients. The mean half-life was 5.5 (females) or 6.0 hours (males).
Food improves the tolerability of tipranavir with ritonavir. Therefore tipranavir, co-administered with low dose ritonavir, should be given with food.
Absorption of tipranavir, co-administered with low dose ritonavir, is reduced in the presence of antacids.
Tipranavir is extensively bound to plasma proteins (>99.9%). From clinical samples of healthy volunteers and HIV-1 positive subjects who received tipranavir without ritonavir the mean fraction of tipranavir unbound in plasma was similar in both populations (healthy volunteers 0.015% 0.006%; HIV-positive subjects 0.019% 0.076%). Total plasma tipranavir concentrations for these samples ranged from 9 to 82 M. The unbound fraction of tipranavir appeared to be independent of total concentration over this concentration range.
No studies have been conducted to determine the distribution of tipranavir into human cerebrospinal fluid or semen.
In vitro metabolism studies with human liver microsomes indicated that CYP3A4 is the predominant CYP isoform involved in tipranavir metabolism.
The oral clearance of tipranavir decreased after the addition of ritonavir which may represent diminished first-pass clearance of the substance at the gastrointestinal tract as well as the liver.
The metabolism of tipranavir in the presence of low dose ritonavir is minimal. In a 14C-tipranavir human study (500 mg 14C-tipranavir with 200 mg ritonavir, twice daily), unchanged tipranavir was predominant and accounted for 98.4% or greater of the total plasma radioactivity circulating at 3, 8, or 12 hours after dosing. Only a few metabolites were found in plasma, and all were at trace levels (0.2% or less of the plasma radioactivity). In faeces, unchanged tipranavir represented the majority of faecal radioactivity (79.9% of faecal radioactivity). The most abundant faecal metabolite, at 4.9% of faecal radioactivity (3.2% of dose), was a hydroxyl metabolite of tipranavir. In urine, unchanged tipranavir was found in trace amounts (0.5% of urine radioactivity). The most abundant urinary metabolite, at 11.0% of urine radioactivity (0.5% of dose) was a glucuronide conjugate of tipranavir.
Administration of 14C-tipranavir to subjects (n=8) that received 500 mg tipranavir with 200 mg ritonavir; twice daily dosed to steady-state demonstrated that most radioactivity (median 82.3%) was excreted in faeces, while only a median of 4.4% of the radioactive dose administered was recovered in urine. In addition, most radioactivity (56%) was excreted between 24 and 96 hours after dosing. The effective mean elimination half-life of tipranavir with ritonavir in healthy volunteers (n=67) and HIV-infected adult patients (n=120) was approximately 4.8 and 6.0 hours, respectively, at steady state following a dose of 500 mg/200 mg twice daily with a light meal.
Although data available at this stage are currently limited to allow a definitive analysis, they suggest that the pharmacokinetic profile is unchanged in older people and comparable between races. By contrast, evaluation of the steady-state plasma tipranavir trough concentrations at 10-14 h after dosing from the RESIST-1 and RESIST-2 studies demonstrate that females generally had higher tipranavir concentrations than males. After four weeks of tipranavir 500 mg with 200 mg ritonavir (twice daily) the median plasma trough concentration of tipranavir was 43.9 µM for females and 31.1 µM for males. This difference in concentrations does not warrant a dose adjustment.
Tipranavir pharmacokinetics have not been studied in patients with renal impairment. However, since the renal clearance of tipranavir is negligible, a decrease in total body clearance is not expected in patients with renal impairment.
In a study comparing 9 patients with mild (Child-Pugh A) hepatic impairment to 9 controls, the single and multiple dose exposure of tipranavir and ritonavir were increased in patients with hepatic impairment but still within the range observed in clinical studies. No dosing adjustment is required in patients with mild hepatic impairment but patients should be closely monitored.
The influence of moderate (Child-Pugh B) or severe (Child-Pugh C) hepatic impairment on the multiple dose pharmacokinetics of either tipranavir or ritonavir has so far not been investigated. tipranavir is contraindicated in moderate or severe hepatic impairment.
The oral solution has been shown to have greater bioavailability than the soft capsule formulation.
Animal toxicology studies have been conducted with tipranavir alone, in mice, rats and dogs, and coadministered with ritonavir (3.75:1 w/w ratio) in rats and dogs. Studies with co-administration of tipranavir and ritonavir did not reveal any additional toxicological effects when compared to those seen in the tipranavir single agent toxicological studies.
The predominant effects of repeated administration of tipranavir across all species toxicologically tested were on the gastrointestinal tract (emesis, soft stool, diarrhoea) and the liver (hypertrophy). The effects were reversible with termination of treatment. Additional changes included bleeding in rats at high doses (rodents specific). Bleeding observed in rats was associated with prolonged prothrombin time (PT), activated partial thromboplastin time (APTT) and a decrease in some vitamin K dependent factors. The co-administration of tipranavir with vitamin E in the form of TPGS (d-alphatocopherol polyethylene glycol 1000 succinate) from 2,322 IU/m² upwards in rats resulted in a significant increase in effects on coagulation parameters, bleeding events and death. In preclinical studies of tipranavir in dogs, an effect on coagulation parameters was not seen. Co-administration of tipranavir and vitamin E has not been studied in dogs.
The majority of the effects in repeat-dose toxicity studies appeared at systemic exposure levels which are equivalent to or even below the human exposure levels at the recommended clinical dose.
In in vitro studies, tipranavir was found to inhibit platelet aggregation when using human platelets and thromboxane A2 binding in an in vitro cell model at levels consistent with exposure observed in patients receiving Aptivus with ritonavir. The clinical implications of these findings are not known.
In a study conducted in rats with tipranavir at systemic exposure levels (AUC) equivalent to human exposure at the recommended clinical dose, no adverse effects on mating or fertility were observed. At maternal doses producing systemic exposure levels similar to or below those at the recommended clinical dose, tipranavir did not produce teratogenic effects. At tipranavir exposures in rats at 0.8-fold human exposure at the clinical dose, foetal toxicity (decreased sternebrae ossification and body weights) was observed. In pre- and post-natal development studies with tipranavir in rats, growth inhibition of pups was observed at maternally toxic doses approximating 0.8-fold human exposure.
Carcinogenicity studies of tipranavir in mice and rats revealed tumourigenic potential specific for these species, which are regarded as of no clinical relevance. Tipranavir showed no evidence of genetic toxicity in a battery of in vitro and in vivo tests.
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