| 1. |
- Abulfathi, Ahmed Aliyu, et al.
(författare)
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Clinical Pharmacokinetics and Pharmacodynamics of Rifampicin in Human Tuberculosis
- 2019
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Ingår i: Clinical Pharmacokinetics. - : Springer Science and Business Media LLC. - 0312-5963 .- 1179-1926. ; 58:9, s. 1103-1129
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Forskningsöversikt (refereegranskat)abstract
- The introduction of rifampicin (rifampin) into tuberculosis (TB) treatment five decades ago was critical for shortening the treatment duration for patients with pulmonary TB to 6months when combined with pyrazinamide in the first 2months. Resistance or hypersensitivity to rifampicin effectively condemns a patient to prolonged, less effective, more toxic, and expensive regimens. Because of cost and fears of toxicity, rifampicin was introduced at an oral daily dose of 600mg (8-12mg/kg body weight). At this dose, clinical trials in 1970s found cure rates of >= 95% and relapse rates of < 5%. However, recent papers report lower cure rates that might be the consequence of increased emergence of resistance. Several lines of evidence suggest that higher rifampicin doses, if tolerated and safe, could shorten treatment duration even further. We conducted a narrative review of rifampicin pharmacokinetics and pharmacodynamics in adults across a range of doses and highlight variables that influence its pharmacokinetics/pharmacodynamics. Rifampicin exposure has considerable inter- and intra-individual variability that could be reduced by administration during fasting. Several factors including malnutrition, HIV infection, diabetes mellitus, dose size, pharmacogenetic polymorphisms, hepatic cirrhosis, and substandard medicinal products alter rifampicin exposure and/or efficacy. Renal impairment has no influence on rifampicin pharmacokinetics when dosed at 600mg. Rifampicin maximum (peak) concentration (C-max) > 8.2 mu g/mL is an independent predictor of sterilizing activity and therapeutic drug monitoring at 2, 4, and 6h post-dose may aid in optimizing dosing to achieve the recommended rifampicin concentration of >= 8 mu g/mL. A higher rifampicin C-max is required for severe forms TB such as TB meningitis, with C-max >= 22 mu g/mL and area under the concentration-time curve (AUC) from time zero to 6h (AUC(6)) >= 70 mu g.h/mL associated with reduced mortality. More studies are needed to confirm whether doses achieving exposures higher than the current standard dosage could translate into faster sputum conversion, higher cure rates, lower relapse rates, and less mortality. It is encouraging that daily rifampicin doses up to 35mg/kg were found to be safe and well-tolerated over a period of 12weeks. High-dose rifampicin should thus be considered in future studies when constructing potentially shorter regimens. The studies should be adequately powered to determine treatment outcomes and should include surrogate markers of efficacy such as C-max/MIC (minimum inhibitory concentration) and AUC/MIC.
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| 2. |
- Alvan, G, et al.
(författare)
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The efficiency concept in pharmacodynamics
- 1999
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Ingår i: Clinical pharmacokinetics. - : Springer Science and Business Media LLC. - 0312-5963. ; 36:5, s. 375-389
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Tidskriftsartikel (refereegranskat)
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| 3. |
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| 4. |
- Björkman, S, et al.
(författare)
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Pharmacokinetics of coagulation factors: clinical relevance for patients with haemophilia
- 2001
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Ingår i: Clinical Pharmacokinetics. - 0312-5963. ; 40:11, s. 815-823
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Forskningsöversikt (refereegranskat)abstract
- Haemophilia is a recessively inherited coagulation disorder, in which an X-chromosome mutation causes a deficiency of either coagulation factor VIII (FVIII) in haemophilia A, or factor IX (FIX) in haemophilia B. Intravenous administration of FVIII or FIX can be used to control a bleeding episode, to provide haemostasis during surgery or for long term prophylaxis of bleeding. In special cases, activated factor VII (FVIIa) may be used instead of FVIII or FIX. The aim of this work is to review the pharmacokinetics of FVIII, FIX and FVIIa and to give an outline of the use of pharmacokinetics to optimise the treatment of patients with haemophilia. The pharmacokinetics of FVIII are well characterised. The systemic clearance (CL) of FVIII is largely determined by the plasma level of von Willebrand factor (vWF), which protects FVIII from degradation. Typical average CL in patients with normal vWF levels is 3 ml/h/kg, with an apparent volume of distribution at steady state (Vss) that slightly exceeds the plasma volume of the patient, and the average elimination half-life (t1/2) is around 14 hours. There are still some discrepancies in the literature on the pharmacokinetics of FIX. The average CL of plasma-derived FIX seems to be 4 ml/h/kg, the Vss is 3 to 4 times the plasma volume and the elimination t1/2 often exceeds 30 hours. FVIIa has a much higher CL (average of 33 ml/h/kg), and a short terminal t1/2 (at 2 to 3 hours). The Vss is 2 to 3 times the plasma volume. Since the therapeutic levels of coagulation factors are well defined in most clinical situations, applied pharmacokinetics is an excellent tool to optimise therapy. Individual tailoring of administration in prophylaxis has been shown to considerably increase the cost effectiveness of the treatment. Dosage regimens for the treatment of bleeding episodes or for haemostasis during surgery are also designed using pharmacokinetic data, and the advantages of using a constant infusion instead of repeated bolus doses have been explored. The influence of antibodies (inhibitors) on the pharmacokinetics of FVIII and FIX is in part understood, and the doses of coagulation factor needed to treat a patient can tentatively be calculated from the antibody titre. In conclusion, therapeutic monitoring of coagulation factor levels and the use of clinical pharmacokinetics to aid therapy are well established in the treatment of patients with haemophilia.
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| 5. |
- Björkman, Sven
(författare)
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Prediction of cytochrome p450-mediated hepatic drug clearance in neonates, infants and children : how accurate are available scaling methods?
- 2006
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Ingår i: Clinical Pharmacokinetics. - 0312-5963 .- 1179-1926. ; 45:1, s. 1-11
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Forskningsöversikt (övrigt vetenskapligt/konstnärligt)abstract
- Correct dosing of drugs in neonates, infants and children is hampered by a general lack of knowledge about drug disposition in this population. Suggested methods to improve our knowledge without performing conventional full-scale investigations include population pharmacokinetic studies, allometric scaling of drug disposition according to bodyweight and in silico prediction of pharmacokinetics. The last method entails scaling of pharmacokinetic parameters according to age-dependent changes in drug absorption and elimination capacity, plasma protein binding and physiological characteristics of the subjects. Maturation (or ontogeny) of the drug-metabolising part of the cytochrome P450 (CYP) enzyme system is thus an important factor in the calculations for most drugs. The aim of this commentary is to test and critically examine the proposed methods to estimate hepatic clearance (CL) as a function of age (0-20 years), with CYP3A-mediated metabolism as the case in point. Midazolam and alfentanil were used as model drugs.Allometric scaling failed to predict the CL of midazolam and alfentanil in neonates. Calculations using in vitro findings on CYP maturation gave better estimates for neonates but very divergent ones for older infants and children. This was chiefly due to very different data on CYP3A4/5 ontogeny in three published studies. In the age range where full adult CYP activity per gram of liver could be assumed, allometric scaling and in silico predictions gave similar results. These predictions were also in approximate agreement with clinical data.The findings with the two model drugs can very probably be generalised to most drugs cleared by CYP-dependent hepatic metabolism. Allometric scaling accounts for development of body size and function but not for the fact that the drug-metabolising capacity of the liver is generally low at birth. The crucial question in the prediction of CL is thus when the activity of the applicable CYP isoform(s) attains adult levels. There are still not enough data on this, particularly when different studies even on the same CYP isoform have given very divergent results. It may also be pointed out that CYP ontogeny is an area where we have at least some information. There are several other important developmental changes about which we know practically nothing. Thus, while allometric scaling is generally unreliable for prediction in neonates and infants, the alternative method of in silico prediction can at present be used only to obtain tentative initial estimates of drug CL. Neither of the methods can be used as a substitute for actual clinical studies.
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| 7. |
- Bukkems, V. E., et al.
(författare)
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Prediction of Maternal and Fetal Doravirine Exposure by Integrating Physiologically Based Pharmacokinetic Modeling and Human Placenta Perfusion Experiments
- 2022
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Ingår i: Clinical Pharmacokinetics. - : Springer Nature. - 0312-5963 .- 1179-1926. ; 61:8, s. 1129-1141
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Tidskriftsartikel (refereegranskat)abstract
- Background and Objective Doravirine is currently not recommended for pregnant women living with human immunodeficiency virus because efficacy and safety data are lacking. This study aimed to predict maternal and fetal doravirine exposure by integrating human placenta perfusion experiments with pregnancy physiologically based pharmacokinetic (PBPK) modeling.Methods Ex vivo placenta perfusions were performed in a closed-closed configuration, in both maternal-to-fetal and fetal-to-maternal directions (n = 8). To derive intrinsic placental transfer parameters from perfusion data, we developed a mechanistic placenta model. Next, we developed a maternal and fetal full-body pregnancy PBPK model for doravirine in Simcyp, which was parameterized with the derived intrinsic placental transfer parameters to predict in vivo maternal and fetal doravirine exposure at 26, 32, and 40 weeks of pregnancy. The predicted total geometric mean (GM) trough plasma concentration (C-trough) values were compared with the target (0.23 mg/L) derived from in vivo exposure-response analysis.Results A decrease of 55% in maternal doravirine area under the plasma concentration-time curve (AUC)(0-24h) was predicted in pregnant women at 40 weeks of pregnancy compared with nonpregnant women. At 26, 32, and 40 weeks of pregnancy, predicted maternal total doravirine GM C-trough values were below the predefined efficacy target of 0.23 mg/L. Perfusion experiments showed that doravirine extensively crossed the placenta, and PBPK modeling predicted considerable fetal doravirine exposure.Conclusion Substantially reduced maternal doravirine exposure was predicted during pregnancy, possibly resulting in impaired efficacy. Therapeutic drug and viral load monitoring are advised for pregnant women treated with doravirine. Considerable fetal doravirine exposure was predicted, highlighting the need for clinical fetal safety data.
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| 8. |
- Bååthe, Sofie, et al.
(författare)
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Population pharmacokinetics of melagatran, the active form of the oral direct thrombin inhibitor ximelagatran, in atrial fibrillation patients receiving long-term anticoagulation therapy
- 2006
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Ingår i: Clinical Pharmacokinetics. - : Springer Science and Business Media LLC. - 0312-5963 .- 1179-1926. ; 45:8, s. 803-819
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Tidskriftsartikel (refereegranskat)abstract
- Background: Ximelagatran is an oral direct thrombin inhibitor for the prevention of thromboembolic disease. After oral administration, ximelagatran is rapidly absorbed and bioconverted to its active form, melagatran. Objective: To characterise the pharmacokinetics of melagatran in patients with nonvalvular atrial fibrillation (NVAF) receiving long-term treatment for prevention of stroke and systemic embolic events. Methods: A population pharmacokinetic model was developed based on data from three phase 11 studies (1177 plasma concentration observations in 167 patients, treated for up to 18 months) and confirmed by including data from two phase III studies (8702 plasma concentration observations in 3188 patients, treated for up to 24 months). The impact of individualised dosing on pharmacokinetic variability was evaluated by simulations of melagatran concentrations based on the pharmacokinetic model. Results: Melagatran pharmacokinetics were consistent across the studied doses and duration of treatment, and were described by a one-compartment model with first-order absorption and elimination. Clearance of melagatran was correlated to creatinine clearance, which was the most important predictor of melagatran exposure (explained 54% of interpatient variance in clearance). Total variability (coefficient of variation) in exposure was 45%; intraindividual variability in exposure was 23%. Concomitant medication with the most common long-term used drugs in the study population had no relevant influence on melagatran pharmacokinetics. Simulations suggested that dose adjustment based on renal function or trough plasma concentration had a minor effect on overall pharmacokinetic variability and the number of patients with high melagatran exposure. Conclusion: The pharmacokinetics of melagatran in NVAF patients were predictable, and consistent with results from previously studied patient populations. Dose individualisation was predicted to have a low impact on pharmacokinetic variability, supporting the use of a fixed-dose regimen of ximelagatran for long-term anticoagulant therapy in the majority of NVAF patients.
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