Detection of Nonadherence to Antihypertensive Treatment by Measurements of Serum Drug Concentrations.

[Figure: see text].

Application of physiologically based biopharmaceutics modeling to understand the impact of dissolution differences on in vivo performance of immediate release products: The case of bisoprolol.

Merck KGaA observed slight differences in the dissolution of Concor® (bisoprolol) batches over the years. The purpose of this work was to assess the impact of in vitro dissolution on the simulated pharmacokinetics of bisoprolol using in vitro-in vivo relationship established with available in vitro dissolution and corresponding plasma concentrations-time data for several bisoprolol batches. A mechanistic absorption model/physiologically based pharmacokinetics model linked with a biopharmaceutics tool such as dissolution testing, namely, physiologically based biopharmaceutics modeling (PBBM), can be valuable in determining a dissolution "safe space." A PBBM for bisoprolol was built using in vitro, in silico, and clinical data. We evaluated potential influences of variability in dissolution of bisoprolol batches on its clinical performance through PBBM and virtual bioequivalence (BE) trials. We demonstrated that in vitro dissolution was not critical for the clinical performance of bisoprolol over a wide range of tested values. Based on virtual BE trials, safe space expansion was explored using hypothetical dissolution data. A formulation with in vitro dissolution reaching 70% dissolved in 15 min and 79.5% in 30 min was shown to be BE to classical fast dissolution of bisoprolol (>85% within 15 min), as point estimates and 90% confidence intervals of the maximum plasma concentration and area under the concentration-time curve were within the BE limits (0.8-1.25).

Direct comparison of inorganic nitrite and nitrate on vascular dysfunction and oxidative damage in experimental arterial hypertension.

Arterial hypertension is one of the major health risk factors leading to coronary artery disease, stroke or peripheral artery disease. Dietary uptake of inorganic nitrite (NO2-) and nitrate (NO3-) via vegetables leads to enhanced vascular NO bioavailability and provides antihypertensive effects. The present study aims to understand the underlying vasoprotective effects of nutritional NO2- and NO3- co-therapy in mice with angiotensin-II (AT-II)-induced arterial hypertension. High-dose AT-II (1 mg/kg/d, 1w, s. c.) was used to induce arterial hypertension in male C57BL/6 mice. Additional inorganic nitrite (7.5 mg/kg/d, p. o.) or nitrate (150 mg/kg/d, p. o.) were administered via the drinking water. Blood pressure (tail-cuff method) and endothelial function (isometric tension) were determined. Oxidative stress and inflammation markers were quantified in aorta, heart, kidney and blood. Co-treatment with inorganic nitrite, but not with nitrate, normalized vascular function, oxidative stress markers and inflammatory pathways in AT-II treated mice. Of note, the highly beneficial effects of nitrite on all parameters and the less pronounced protection by nitrate, as seen by improvement of some parameters, were observed despite no significant increase in plasma nitrite levels by both therapies. Methemoglobin levels tended to be higher upon nitrite/nitrate treatment. Nutritional nitric oxide precursors represent a non-pharmacological treatment option for hypertension that could be applied to the general population (e.g. by eating certain vegetables). The more beneficial effects of inorganic nitrite may rely on superior NO bioactivation and stronger blood pressure lowering effects. Future large-scale clinical studies should investigate whether hypertension and cardiovascular outcome in general can be influenced by dietary inorganic nitrite therapy.

Assessing Adherence to Antihypertensive Medication by Means of Dose-Dependent Reference Plasma Concentration Ranges and Ultra-High Performance Liquid Chromatography-Ion Trap Mass Spectrometry Analysis.

Poor adherence to antihypertensive drug therapy is a well-recognized problem and can be assessed by mass spectrometry-based analyses of body fluids. However, contrary statements exist whether drug quantification in blood or qualitative screening in urine is more suitable. The present pilot study aimed to further elucidate the power of blood plasma drug concentrations for adherence monitoring by developing and validating a quantification procedure for nine antihypertensive drugs (amlodipine, bisoprolol, candesartan, canrenone, carvedilol, metoprolol, olmesartan, torasemide, and valsartan) in blood plasma using liquid-liquid extraction and an ultra-high-performance liquid chromatography-ion trap mass spectrometry analysis. The procedure should then be used for an adherence assessment and compared with the results of an established qualitative urine screening. Selectivity, carryover, matrix effect, accuracy, precision, dilution integrity, and stability were successfully validated, except for amlodipine. The applicability was demonstrated by analyzing 19 plasma samples containing 28 antihypertensive drugs and comparing the measured concentrations with calculated dose-dependent reference plasma concentration ranges. The interpretation of plasma concentrations was found to be more sophisticated and time-consuming than that of urine screening results, and adherence could not be assessed in two cases (10%) due to measured plasma concentrations below the lower limit of quantification. However, 14 out of 19 subjects were classified as adherent (75%) and three as nonadherent (15%), in contrast to 19 (100%) that were claimed to be adherent based on the results of the qualitative urine screening. Nevertheless, further data is needed to estimate whether plasma quantification is superior in terms of assessing adherence to antihypertensive medication.

In vitro and in vivo evaluation of a sustained-release once-a-day formulation of the novel antihypertensive drug MT-1207.

Hypertension is one of the most common chronic cardiovascular disorders. Sustained-release formulations are developed to maintain drug therapeutic levels throughout the treatment of hypertension, to promote patient compliance and improve patient outcomes. We have developed and tested in in vivo trials a once-a-day tablet formulation for the novel antihypertensive drug MT-1207. The tablets based upon a hydrophilic polymer matrix underwent post-compression parameter and physicochemical characterisations, along with in vitro drug release testing. The most promising formulation containing 31% w/w HPMC K15M gave a 24-hour release of MT-1207 with an almost constant release rate up to 20 hours. Follow in in vivo studies were carried out in Beagle dogs for the optimised sustained-release tablets in comparison to immediate-release tablets. The results showed that a sustained release of MT-1207 from the new formulation was achieved with a drug t1/2 2-2.5 times longer than the immediate-release tablets. Moreover, the AUC0-24h values of both sustained- and immediate-release tablets were identical at the same dose of 30 mg, indicating that the same amount of drug was absorbed in each case. For treatments based upon MT-1207, this development is significant for future commercial exploitation via scale-up and further trials, and for improved patient outcomes.

Supersaturable self-microemulsifying drug delivery system enhances dissolution and bioavailability of telmisartan.

To enhance the dissolution and oral bioavailability of telmisartan (TMS), a poorly water-soluble anti-hypertensive drug, a supersaturable self-microemulsifying drug delivery system (SuSMEDDS) was developed. Amorphous alkalinized TMS (AAT) was formulated into a SMEDDS, composed of Capmul® MCM (oil), Cremophor® RH40 (surfactant), and tetraglycol (co-surfactant). Although the SMEDDS was rapidly dissolved (>80% within 5 min) in a limited condition (500 mL, pH 6.8), drug precipitation was observed over time, resulting in a decrease in dissolution levels. The precipitation was due to drug recrystallization, as determined by differential scanning calorimetry and powder X-ray diffraction analyses. Several polymers, including Soluplus® (SOL), were screened as precipitation inhibitors; ultimately, SuSMEDDS-SOL was prepared by admixing SOL and the SMEDDS at a 5:100 (w/w) ratio. SuSMEDDS-SOL was superior in terms of dissolution efficiency (>90% over 2 h) and dissolution-retaining time (no precipitation over 2 h). An in vivo pharmacokinetic study in rats revealed that the oral bioavailability of SuSMEDDS-SOL was 4.8-, 1.3-, and 1.2-fold greater than those of the TMS suspension, AAT solution, and SMEDDS, respectively. Therefore, SuSMEDDS-SOL is a promising candidate to enhance the dissolution and oral bioavailability of TMS.

Establishing Serum Reference Ranges for Antihypertensive Drugs.

BACKGROUND: Therapeutic drug monitoring (TDM) involves the measurement of serum drug concentrations to optimize pharmacotherapy. Traditionally, blood pressure measurements alone, and not TDM, have been used to evaluate the antihypertensive drug response. However, approximately 50% of hypertensive patients treated with lifestyle changes and antihypertensive drugs fail to achieve blood pressure control. Serum drug concentration measurements could be useful to select the optimal drugs in adjusted doses and to identify nonadherence. Implementation of TDM in clinical routine for antihypertensive drugs depends on established serum reference ranges. METHODS: Commonly used antihypertensive drugs were identified based on prescription data. The authors performed a review of authoritative literature on reported serum drug concentrations and calculated expected concentrations from previously reported pharmacokinetic parameters with commonly prescribed daily doses. Finally, serum drug concentrations in samples from patients undergoing antihypertensive treatment were measured. RESULTS: Serum reference ranges for 24 frequently used antihypertensive drugs were established based on results from 3 approaches. CONCLUSIONS: Serum drug concentration measurements, interpreted in light of the established reference ranges, together with blood pressure measurements and other clinical data, may help identify nonadherent patients and tailor individual antihypertensive treatment when deviant drug responses appear in line with the concept of personalized medicine.

Determination of amlodipine, indapamide and perindopril in human plasma by a novel LC-MS/MS method: Application to a bioequivalence study.

A robust and rapid UPLC-MS/MS method has been developed, optimized and validated for determination of amlodipine (AML), indapamide (IND) and perindopril (PRN) in human plasma. A positive electrospray ionization mode was used in a Xevo TQD LC-MS/MS instrument. A single sample preparation step using extraction technique was applied to extract the three analytes from plasma samples. There was no need to extract indapamide from blood samples in a further step. Extraction of the three drugs and internal standards was done using a solvent mixture composed of methyl tertiary butyl ether, dichloromethane and ethyl acetate. The prepared samples were analyzed using an Acquity UPLC HSS C18 (100 × 2.1 mm, 1.7 µm) column. Ammonium acetate and methanol, pumped at a flow rate of 0.3 ml/min, were used as a mobile phase. Method validation was done as per the US Food and Drug Administration guidelines. Linearity was achieved in the range of 0.2-15 ng/ml for AML, 0.5-50 ng/ml for IND and 0.5-120 ng/ml for PRN. Accuracy and precision were estimated and found to be within the acceptable ranges. The rapid chromatography permits analysis of many samples per batch, making the method suitable for clinical and pharmacokinetic investigations. The developed and validated method was applied to estimate AML, IND, and PRN in a fasting bioequivalence study in healthy human volunteers.

Plasma Trough Concentrations of Antihypertensive Drugs for the Assessment of Treatment Adherence: A Meta-Analysis.

Biochemical drug screening by liquid chromatography-tandem mass spectrometry in plasma is an accurate method for the quantification of plasma concentrations of antihypertensive medications in patients with hypertension. Trough concentrations could possibly be used as drug-specific cutoff values in the biochemical assessment of (non-)adherence. We performed a literature review and meta-analysis of pharmacokinetic studies to determine plasma trough concentrations of amlodipine, hydrochlorothiazide, and valsartan. PubMed was searched for pharmacokinetic studies up to September 2020. Eligible studies reported steady-state mean trough concentration and their variance. Pooled trough concentrations were estimated using a three-level random effects meta-analytic model. Moderator analyses were performed to explore sources of heterogeneity. One thousand three hundred eighteen potentially relevant articles were identified of which 45 were eligible for inclusion. The pooled mean trough concentration was 9.2 ng/mL (95% CI, 7.5-10.8) for amlodipine, 41.0 ng/mL (95% CI, 17.4-64.7) for hydrochlorothiazide, and 352.9 ng/mL (95% CI, 243.5-462.3) for valsartan. Substantial heterogeneity was present for all 3 pooled estimates. Moderator analyses identified dosage as a significant moderator for the pooled trough concentration of amlodipine (ß1=0.9; P<0.05), mean age, and mean body weight for the mean trough concentration of hydrochlorothiazide (ß1=2.2, P<0.05, respectively, ß1=-4.0, P<0.05) and no significant moderators for valsartan. Plasma trough concentrations of amlodipine, hydrochlorothiazide, and valsartan, measured with liquid chromatography-tandem mass spectrometry, are highly heterogeneous over the different studies. Use of the pooled trough concentration as a cutoff in the biochemical assessment of adherence can result in inaccurate diagnosis of (non-)adherence, which may seriously harm the patient-physician relationship, and is therefore not recommended.

Determination of l-(+)-bornesitol, the hypotensive constituent of Hancornia speciosa, in rat plasma by LC-MS/MS and its application on a pharmacokinetic study.

Hancornia speciosa is a medicinal plant with proven antihypertensive activity. The cyclitol l-(+)-bornesitol is the main constituent of its leaves and is a potent inhibitor of the angiotensin-converting enzyme. We herein investigated the pharmacokinetic properties of bornesitol administered orally to Wistar rats, as well as bornesitol permeation in Caco-2 cells. Bornesitol was isolated and purified from an ethanol extract of H. speciosa leaves. An ultra-high performance liquid chromatography coupled with electrospray ionization mass spectrometry (UPLC-ESI-MS/MS) method was developed and validated to quantify bornesitol in rat plasma based on Multiple Reaction Monitoring, using pentaerythritol as an internal standard. Pharmacokinetics was evaluated by the administration of single doses via intravenous in bolus (3 mg/kg) and gavage (3, 15 and 25 mg/kg). Bornesitol permeation was assayed in a transwell Caco-2 cells model, tested alone, or combined with rutin, or as a constituent of H. speciosa extract, using a developed and validated UPLC-ESI-MS/MS method. All assayed validation parameters (selectivity, residual effect, matrix effect, linearity, precision, accuracy and stability of analyte in plasma and solution) for the bioanalytical method met the acceptance criteria established by regulatory guidelines. Bornestiol reached peak plasma concentration within approximately 60 min after oral administration with a half-life ranging from 72.15 min to 123.69 min. The peak concentration and area under the concentration-time curve of bornesitol did not rise proportionally with the increasing doses, suggesting a non-linear pharmacokinetics in rats and the oral bioavailability ranged from 28.5%-59.3%. Bornesitol showed low permeability in Caco-2 cells, but the permeability apparently increased when it was administered either combined with rutin or as a constituent of H. speciosa extract. In conclusion, bornesitol was rapidly absorbed after a single oral administration to rats and followed a non-linear pharmacokinetics. The obtained data will be useful to guide further pre-clinical development of bornesitol-containing herbal preparations of H. speciosa as an antihypertensive agent.

Comparative Pharmacokinetics of Nimodipine in Rat Plasma and Tissues Following Intraocular, Intragastric, and Intravenous Administration.

We investigated the pharmacokinetics of nimodipine (NMD) in rats plasma and tissues following intraocular (io), intragastric (ig), and intravenous (iv) administration at doses of 5.0 mg/kg io and iv and 10.0 mg/kg ig. After a single dose of NMD, plasma, heart, liver, spleen, lung, kidney, and brain samples were collected at the scheduled time points. The concentration of NMD in rat plasma and tissues was determined by high-performance liquid chromatography, and the main pharmacokinetic parameters were calculated and compared. NMD was rapidly absorbed and reached the maximum plasma concentration in approximately 5 min after io administration. The absolute bioavailability after io administration was higher than that after ig administration (40.05% vs. 5.67%). There were significant differences in the tissue distribution of NMD with different administration routes. After io administration, NMD was distributed more in the lung, spleen, and brain tissues, and less in the kidney. The maximum drug concentration after io administration in the heart, liver, spleen, lung, kidney, and brain was 1.00, 0.47, 2.02, 1.47, 0.22, and 5.79 times higher than that after via ig administration, and the area under the curve value was 0.59, 0.78, 1.71, 1.84, 0.25, and 4.59 times greater, respectively. Nimodipine appears to achieve systemic effects via io administration. Compared with ig, io administration could significantly increase NMD distribution in the brain tissue, indicating that NMD could be delivered to the brain via io administration.

Benefit of serum drug monitoring complementing urine analysis to assess adherence to antihypertensive drugs in first-line therapy.

With obesity having doubled in the last decade, hypertension is on the rise. In one-third of hypertensive patients the metabolic syndrome is present. This might be one factor for the increasing number of prescriptions for angiotensin receptor blockers and calcium-channel blockers besides a more favorable risk-to-benefit ratio. The aim of the present study was to evaluate a therapeutic drug monitoring (TDM) method for assessment of adherence based on cut-offs in inpatients and to compare it to an established urine drug screening in outpatients. A method for quantification of calcium-channel blockers and angiotensin receptor blockers using high-performance liquid chromatography-tandem mass spectrometric analysis (LC-MS/MS) was developed and validated. The method was applied to serum samples of 32 patients under supervised medication to establish cut-off values for adherence assessment based on dose-related concentrations (DRC, calculated from pharmacokinetic data). Furthermore, corresponding urine and blood samples of 42 outpatients without supervised medication were analysed and the results compared with regard to adherence assessment. All serum concentrations measured for amlodipine (n = 40), lercanidipine (n = 14), candesartan (n = 10), telmisartan (n = 4) and valsartan (n = 10) in inpatients were above the patient specific lower DRC confirming adherence. Of 42 outpatients the identification of analytes in urine as well as the quantification in serum exhibited differing results. According to urinalysis, adherence was demonstrated in only 87.0% of prescriptions, compared to 91.3% for serum analyses. Differences were observed for amlodipine, lercanidipine and candesartan which can be explained by a higher specificity of the serum analysis approach due to pharmacokinetics. The present study confirms that assessing adherence based on serum drug concentrations with individually calculated lower DRCs is more accurate than using qualitative urine analysis. In particular, drugs with low bioavailability, low renal excretion or high metabolism rate such as lercanidipine and candesartan may lead to underestimation of adherence via urine analysis.

Prediction of lisinopril pediatric dose from the reference adult dose by employing a physiologically based pharmacokinetic model.

BACKGROUND: This study aimed to assess the pediatric lisinopril doses using an adult physiological based pharmacokinetic (PBPK) model. As the empirical rules of dose calculation cannot calculate gender-specific pediatric doses and ignores the age-related physiological differences. METHODS: A PBPK model of lisinopril for the healthy adult population was developed for oral (fed and fasting) and IV administration using PK-Sim MoBI® and was scaled down to a virtual pediatric population for prediction of lisinopril doses in neonates to infants, infants to toddler, children at pre-school age, children at school age and the adolescents. The pharmacokinetic parameters were predicted for the above groups at decremental doses of 20 mg, 10 mg, 5 mg, 2.5 mg, and 1.5 mg in order to accomplish doses producing the pharmacokinetic parameters, similar (or comparable) to that of the adult population. The above simulated pediatric doses were compared to the doses computed using the conventional four methods, such as Young's rule, Clark's rule, and weight-based and body surface area-based equations and the dose reported in different studies. RESULTS: Though the doses predicted for all subpopulations of children were comparable to those calculated by Young's rule, yet the conventional methods overestimated the pediatric doses when compared to the respective PBPK-predicted doses. The findings of previous real time pharmacokinetic studies in pediatric patients supported the present simulated dose. CONCLUSION: Thus, PBPK seems to have predictability potential for pediatric dose since it takes into consideration the physiological changes related to age and gender.

Pharmacokinetic interactions of esaxerenone with amlodipine and digoxin in healthy Japanese subjects.

BACKGROUND: To investigate the effects of coadministration of esaxerenone with amlodipine on the pharmacokinetics (PK) of each drug, and of esaxerenone on the PK of digoxin. METHODS: In three open-label, single-sequence, crossover studies, healthy Japanese males received single oral doses of esaxerenone 2.5 mg (Days 1, 15), with amlodipine 10 mg/day (Days 8-18) (Study 1, N = 24); single doses of amlodipine 2.5 mg (Days 1, 21), with esaxerenone 5 mg/day (Days 8-25) (Study 2; N = 20); or digoxin 0.25 mg/day (Days 1-15) with esaxerenone 5 mg/day (Days 11-15) (Study 3; N = 20). PK parameters and safety were assessed. RESULTS: Study 1: esaxerenone peak plasma concentration (Cmax) and time to Cmax were unaltered by amlodipine coadministration, but mean half-life was slightly prolonged from 18.5 to 20.9 h. Geometric least-squares mean (GLSM) ratios for Cmax, area under the plasma concentration-time curve (AUC) from zero to last measurable concentration and from zero to infinity for esaxerenone + amlodipine versus esaxerenone were 0.958, 1.154, and 1.173, respectively. Study 2: corresponding GLSM ratios for amlodipine + esaxerenone versus amlodipine were 1.099, 1.185, and 1.214. Study 3: esaxerenone did not markedly alter digoxin PK. GLSM ratios for Cmax, trough plasma concentration, and AUC during a dosing interval for digoxin versus esaxerenone + digoxin were 1.130, 1.088, and 1.072, respectively. CONCLUSIONS: No drug-drug interactions are expected during combination therapy with esaxerenone and either amlodipine or digoxin, based on a lack of any clinically relevant PK changes. TRIAL REGISTRATION: Studies 1 and 2: JapicCTI-163379 (registered on 20 September 2016); Study 3: JapicCTI-163443 (registered on 24 November 2016).

Applying Different Techniques to Improve the Bioavailability of Candesartan Cilexetil Antihypertensive Drug.

PURPOSE: The objective of this study was to compare different techniques to enhance the solubility and dissolution rate, and hence the bioavailability of candesartan cilexetil. METHODS: To achieve this target, various techniques were employed such as solid dispersions, inclusion complexes, and preparation of candesartan nanoparticles. Following the preparations, all samples were characterized for their physicochemical properties, and the samples of the best results were subjected to further bioavailability studies. RESULTS: Results of dissolution studies revealed an increase in the dissolution rate of all samples. The highest dissolution rate was achieved using solid dispersion of the drug with PVP K-90 (1:4). Physicochemical investigations (XR, DSC, and FT-IR) suggested formation of hydrogen bonding and changing in the crystalline structure of the drug. Regarding the inclusion complexes, more stable complex was formed between HP-ß-CD and CC compared to ß-CD, as indicated by phase solubility diagrams. Antisolvent method resulted in the preparation of stable nanoparticles, as indicated by ζ potential, with average particle size of 238.9 ± 19.25 nm using PVP K-90 as a hydrophilic polymer. The best sample that gave the highest dissolution rate (CC/PVP K-90 1:4) was allowed for further pharmacokinetic studies using UPLC MS/MS assay of rabbit plasma. Results showed a significant increase in the bioavailability of CC from ~15% to ~48%. CONCLUSION: The bioavailability of CC was significantly improved from ~15% to ~48% when formulated as SDs with PVP K-90 with 1:4 drug:polymer ratio.

Optimization of solid self-dispersing micelle for enhancing dissolution and oral bioavailability of valsartan using Box-Behnken design.

A novel solid self-dispersing micelle (S-SDM) was developed to enhance the oral bioavailability of valsartan (VST) and to reduce the total mass of solidified supersaturable self-microemulsifying drug delivery system (S-SuSMEDDS), composed of Capmul MCM, Tween 80 (T80), Gelucire 44/14 (G44), Poloxamer 407, Florite PS-10 (FLO), and low-substituted hydroxypropyl cellulose B1 (HPC). Excluding oil component from S-SuSMEDDS, S-SDM was optimized using a Box-Behnken design with three independent variables: X1 (T80/G44, 0.63), X2 (FLO/HPC, 0.41), and X3 (solid carrier, 177.6 mg); and three response factors: Y1 (droplet size, 191.9 nm), Y2 (dissolution efficiency at 15 min, 55.0%), and Y3 (angle of repose, 32.4°). The desirability function was 0.636, showing an excellent agreement between the predicted and experimental values. With approximately 75% weight of S-SuSMEDDS, no distinct crystallinity of VST was observed in S-SDM, resulting in critical micelle concentration value of 32 µg/mL. Optimized S-SDM showed an approximate 4-fold improved dissolution (pH 1.2, 500 mL) compared with raw VST. Following oral administration in rats, optimized S-SDM improved relative bioavailability by approximately 235%, 216%, and 127% versus raw VST, Diovan® (commercial reference), and S-SuSMEDDS, respectively. Thus, optimized S-SDM could be a selectable candidate for developing water-insoluble drugs in reduced quantity.

Simultaneous LC-MS analysis of plasma concentrations of sildenafil, tadalafil, bosentan, ambrisentan, and macitentan in patients with pulmonary arterial hypertension.

Phosphodiesterase-5 (PDE-5) inhibitors and endothelin receptor antagonists (ERAs) are standard therapies for pulmonary arterial hypertension (PAH). The inter-individual variability of these pharmacokinetics is reported remarkably large, and therapeutic drug monitoring (TDM) can be useful to improve the likelihood of the desired therapeutic and safety outcomes. This study aimed to develop a LC-MS method to determine the concentrations of five PAH drugs (PDE-5 inhibitors: sildenafil and tadalafil, ERAs: bosentan, macitentan, and ambrisentan) from plasma samples using a simple process followed by a single mass spectrometric run, and to validate this approach through pharmacokinetic analyses in patients. A solid extraction method was used for sample preparation of the drugs from human plasma. The total run time for a single injection was within 10 min. The calibration curves for all drugs were linear, and the lower limits of quantitation were 1 (sildenafil), 2 (tadalafil), 5 (ambrisentan), and 10 ng/mL (bosentan, macitentan). The accuracy and precision values suggested that the assay had high accuracy and reliability. To prove the utility of this method, the plasma concentrations of the five PAH drugs were determined after their oral administration to nine PAH patients.

Clinical Applicability of Monitoring Antihypertensive Drug Levels in Blood.

Dried blood spot (DBS) analysis is a novel analytical method for therapeutic drug monitoring to identify nonadherence to antihypertensive drugs. This study was conducted to evaluate the clinical applicability of measuring drug concentrations of 8 antihypertensive drugs, using DBS and venipuncture. Furthermore, this study aimed to provide more insight into the between-patient variability in drug concentrations. False-negative values from DBS compared with a venipuncture were determined to assess drug adherence. A generalized estimating equation was used to estimate the model parameters, including sex, dose, age, weight, and the time interval, between drug intake and sampling, on the Cplasma (drug concentration in plasma). No false-negative values were found when measuring nonadherence using DBS compared with venipuncture. A high variability in Cplasma between patients was observed, especially at peak concentrations with a fold change reaching from 2.3 to 35.2. The time of intake was significantly related to the height of the Cplasma in 7 of the 8 measured drugs with a P<0.05, but the influence of dose, weight, age, and sex on drug levels differed largely between the measured drugs. DBS is a reliable and convenient method to assess nonadherence to antihypertensive drugs in clinical practice. The Cplasma of the 8 antihypertensive drugs in this study show a large interindividual difference, and therefore, low plasma concentrations do not necessarily mean nonadherence. Nonadherence can only be confirmed if drug levels are undetectable, that is, values below the lower limit of detection.

Assessment of adherence to diuretics and ß-blockers by serum drug monitoring in comparison to urine analysis.

Purpose: Toxicological screenings for identifying antihypertensive drugs proved to be a useful tool for assessing adherence. However, misinterpretation may occur in case of highly metabolised drugs with low renal excretion, as well as for drugs with a prolonged detectability. The aim of the present study was to compare a recently developed therapeutic drug monitoring (TDM) method based on serum concentrations to an urine drug detection method for assessing adherence in outpatients.Materials and methods: Corresponding urine and blood samples were obtained at the same time from 26 outpatients without supervised medication. Urine and serum analyses were performed using established high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) methodologies. Adherence was assumed if drugs were detectable in urine or if serum concentrations were above individually calculated lower dose-related concentrations (DRC) or literature-based therapeutic reference ranges (TRR) used as cut-off, respectively.Results: The identification of analytes in urine as well as the quantitative serum assay were performed for atenolol (n = 6 patients), bisoprolol (n = 8), nebivolol (n = 6), canrenone (n = 6, metabolite of spironolactone), hydrochlorothiazide (n = 12) and furosemide (n = 2). On the basis of drug detectability in urine, adherence was assumed in 88% of prescriptions. In 81% (DRC) and 50% (TRR) of the serum analyses the cut-off value was exceeded, which confirms patients' adherence in a lower number. Differences in adherence rates were found in five patients, mainly for ß-blockers.Conclusion: This study suggests that assessment of adherence can be performed more precisely on the basis of serum drug concentrations with individually calculated lower DRC than by using the TRR or qualitative urinalysis.