Lactic acid oligomers (OLAs) as prodrug moieties.

In this paper we propose the use of lactic acid oligomers (OLAs) as prodrug moieties. Two synthetic approaches are presented, on the one hand a non selective oligomerisation of lactic acid and on the other hand a block synthesis to tetramers of lactic acid. Dimers of lactic acid were investigated with respect to their plasma stability and their adsorption to albumine. Ibuprofen was chosen as the first drug for OLAylation. The ester 19 of LA(1)-ibuprofen was evaluated with respect to the degradation to human plasma and the adsorption to albumine. All results indicate that lactic acid oligomers are promising prodrug moieties.

Combined acetaminophen and ibuprofen for pain relief after oral surgery in adults: a randomized controlled trial.

BACKGROUND: Acetaminophen is often used with a non-steriodal anti-inflammatory drug for acute pain. Hitherto, these drugs have had to be given separately, typically at different time intervals. Maxigesic tablets combine acetaminophen and ibuprofen in clinically appropriate doses to simplify administration and dosage regimen. We compared this combination with each of the constituent drugs for the relief of pain after extraction of third molar teeth. METHODS: Adults (more than 16 yr) having one or more wisdom teeth removed under general or local anaesthesia were instructed to take two tablets before operation, then two tablets every 6 h for up to 48 h of: (i) a combination of acetaminophen 500 mg and ibuprofen 150 mg per tablet (Maxigesic); (ii) acetaminophen 500 mg per tablet alone; or (iii) ibuprofen 150 mg per tablet alone. The primary outcome measure was the area under the curve (AUC) of the 100 mm visual analogue scale pain measurements taken for up to 48 h after surgery, divided by time, at rest and on activity. Pharmacokinetic data were collected in a subset of patients. RESULTS: The mean (sem) time-corrected AUC on rest and activity, respectively, were: combination group 22.3 (3.2) and 28.4 (3.4); acetaminophen group 33.0 (3.1) and 40.4 (3.3); and ibuprofen group 34.8 (3.2) and 40.2 (3.4); P<0.01 for each of the four comparisons of combination vs constituent drug. There was no pharmacokinetic interaction between acetaminophen and ibuprofen administered together. CONCLUSIONS: Maxigesic tablets provide superior pain relief after oral surgery to acetaminophen or ibuprofen alone.

A novel liquid-liquid-solid microextraction strategy for bio-sample preparation by in situ self-assembly of zeolitic imidazolate framework 8 on hollow fiber membrane.

A novel liquid-liquid-solid membrane microextraction (LLSMME) method which integrates hollow fiber liquid phase microextraction (HF-LPME) and solid phase microextraction (SPME) was developed for bio-sample preparation. The homogeneous zeolitic imidazolate framework 8 mixed matrix membrane (ZIF-8-MMM) was prepared by in situ self-assembly of ZIF-8 on the inner surface of hollow fiber membrane and employed as a flexible LLSMME device. Incorporating the advantages of both HF-LPME and SPME, the as-fabricated ZIF-8-MMM exhibited excellent performance on the extraction and preconcentration of small molecule drugs of different polarity from complex biological matrices. As a case study, ZIF-8-MMM-based LLSMME coupled with UPLC-MS/MS were developed and validated for determination of ibuprofen, simvastatin and ranitidine at trace levels in rat plasma. The method showed good linearity (r2 > 0.99) and repeatability (RSD < 15%), low limits of detection (2-3 ng mL-1) and high relative recoveries (97.42-103.8%). The enrichment factors were between 87.3 and 112.6. Our study provided a promising strategy for developing more efficient, cost-effective and environmentally friendly technique for bio-sample pretreatment.

A novel hydrophilic adhesive matrix with self-enhancement for drug percutaneous permeation through rat skin.

PURPOSE: In transdermal drug delivery system (TDDS), chemical enhancers and crystallization inhibitors added into the adhesive matrixes to improve drug permeation and formulation stability often result in some negative effect on adhesive properties and dressing performance. The aim of this paper is to develop a hydrophilic pressure sensitive adhesive (PSA) for TDDS without using additional chemical enhancers and crystallization inhibitors. METHODS: A quaternary blend (PDGW) composed of polyvinyl pyrrolidone, D,L-lactic acid oligomers, glycerol and water was prepared. The adhesive strength, drug loading capacity, drug state and stability of PDGW were characterized by using ibuprofen (IBU) and salicylic acid (SA) as model drugs. Moreover, In vitro and in vivo drug permeation through rat skin from PDGW patch in comparison to acrylate adhesive (ACA) and nature rubber adhesive (NRA) was investigated. RESULTS: PDGW performs excellent drug loading and crystallization inhibition capacity. Furthermore, the accumulative amount for 24 h in vitro from PDGW patch is far higher than that from ACA and NRA patch. And the plasma concentration of drugs in vivo from PDGW patch is bigger than that from ACA patch. CONCLUSIONS: PDGW possesses excellent PSA properties and self-enhancement for drug percutaneous permeation, which can be used to develop new formulation of TDDS.

Development of novel ibuprofen-loaded solid dispersion with improved bioavailability using aqueous solution.

To develop a novel ibuprofen-loaded solid dispersion with enhanced bioavailability, various ibuprofen-loaded solid dispersions were prepared with water, HPMC and poloxamer. The effect of HPMC and poloxamer on aqueous solubility of ibuprofen was investigated. The dissolution and bioavailability of solid dispersion in rats were then evaluated compared to ibuprofen powder. When the amount of carrier increased with a decreased in HPMC/poloxamer ratio, the aqueous solubility of ibuprofen was elevated. The solid dispersion composed of ibuprofen/HPMC/poloxamer at the weight ratio of 10:3:2 improved the drug solubility approximately 4 fold. It gave significantly higher initial plasma concentration, AUC and Cmax of drug than did ibuprofen powder in rats. The solid dispersion improved the bioavailability of drug about 4-fold compared to ibuprofen powder. Thus, this ibuprofen-loaded solid dispersion with water, HPMC and poloxamer was a more effective oral dosage form for improving the bioavailability of poor water-soluble ibuprofen.

Rapidly dissolving formulations for quick absorption during pain episodes: ibuprofen.

OBJECTIVE: Pain or its associated trauma impairs oral absorption of drugs due, perhaps, to a diminished disintegration and dissolution rate secondary to suppression of the vagal nervous system. We first examined whether ibuprofen absorption is impaired on suppressing vagus nerve activity in a rat model. Secondly, we examined if ibuprofen absorption in rats during vagal suppression and in humans experiencing dental pain is improved by enhancing disintegration and dissolution rate of the administered formulation. METHODS: Vagal suppression was achieved in rats by administering 20 mg/kg propantheline i.p. 2 h and 1 h before gastric gavage of 20 mg/kg ibuprofen as small crushed pieces of a regular release and a fast-dissolving ibuprofen caplets. In humans, after surgical removal of wisdom teeth and emergence of pain, 2 A 200 mg ibuprofen as regular released (n = 14) and fast-dissolving (n = 12) caplets were administered. Serial blood sample were collected for bioavailability studies. RESULTS: Vagal suppression resulted in significantly decreased absorption rate of ibuprofen enantiomers following administration of the regular release but not after fast-dissolving formulation. Human dental pain was associated with significantly slower absorption of ibuprofen enantiomers from the regular released as compared with the fast-dissolving caplets. Within the first hour post-dose the area under the plasma drug concentration-time curve was raised to 2.7-fold (p < 0.05) after the fast-dissolving as compared with the regular release formulations. There was a 1-h difference in the peak concentration time (tmax) between the two caplets. CONCLUSION: Impaired drug absorption appears to be due to slow disintegration and dissolution encountered during pain episodes.

Dried blood spots and parallel artificial liquid membrane extraction-A simple combination of microsampling and microextraction.

In this paper, parallel artificial liquid membrane extraction (PALME) was used for the first time to clean-up dried blood spots (DBS) prior to ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Fundamental studies exploring amongst others desorption from the DBS in alkaline or acidic aqueous conditions, total extraction time and absolute recoveries were executed. Desorption and PALME were performed using a set of two 96-well plates, one of them housing the sample and the other comprising the supported liquid membrane (SLM) and the acceptor solution. In one procedure, amitriptyline and quetiapine (basic model analytes) were desorbed from the DBS using 250 µL of 10 mM sodium hydroxide solution (aqueous), and subsequently extracted through the SLM consisting of 4 µL of 1% trioctylamine in dodecyl acetate, and further into an acceptor solution consisting of 50 µL of 20 mM formic acid. In a second procedure, ketoprofen, fenoprofen, flurbiprofen, and ibuprofen (acidic model analytes) were desorbed from the DBS into 20 mM formic acid, extracted through an SLM with dihexyl ether, and further into an acceptor solution of 25 mM ammonia. Within 60 min of PALME, both basic and acidic model analytes were effectively desorbed from the DBS and extracted into the acceptor solution, which was injected directly into the analytical instrument. Recoveries between 63 and 85% for the six model analytes were obtained. PALME provided excellent clean-up from the DBS samples, and acceptor solutions were free from phospholipids. Linearity was obtained with r2 > 0.99 for five of the six analytes. Accuracy, precision and UHPLC-MS/MS matrix effects were in accordance with the European Medicines Agency (EMA) guideline. Based on these experiments, PALME shows great potential for future processing of DBS in a short and simple way, and with the presented setup, up to 96 DBS can be processed within a total extraction time of 60 min.

Preparation, characterization and in vivo evaluation of ibuprofen binary solid dispersions with poloxamer 188.

Ibuprofen-Poloxamer 188 (P 188) binary solid dispersions (SD) with different drug loadings were prepared, characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), and evaluated for solubility, in vitro release, and oral bioavailability of ibuprofen in rats. Loss of their individual surface properties during melting and solidification as revealed by SEM micrographs indicated the formation of effective SDs. Absence or shifting towards the lower melting temperature of the drug peak in SDs and physical mixtures in DSC study indicated the possibilities of its interactions with P 188. However, no such interactions in the solid state were confirmed by FTIR spectra which showed the presence of drug crystalline in SDs. Immediate and complete release of ibuprofen from SDs might be because of the reduction in the drug crystalline due to eutectic formation, and their dosing to fasted rats resulted in a significant increase in the area under curve (AUC) of the plasma concentration versus time curve and the maximum plasma concentration (Cmax), and a significant decrease in the time to reach Cmax (Tmax) over ibuprofen and physical mixtures.

Controlled release ibuprofen-poloxamer gel for epidural use - A pharmacokinetic study using microdialysis in pigs.

In order to avoid the risks of sideeffects of epidural local anesthetics and opioids, the use of nonsteroidal anti-inflammatory drugs (NSAIDs) epidurally would be an interesting option of analgesic therapy. The fairly short duration of action of spinally administered NSAIDs, e.g., ibuprofen, may be prolonged by using controlled release poloxamer gel formulation. Using a microdialysis technique we studied the epidural and intrathecal pharmacokinetics of ibuprofen after its epidural administration as a poloxamer 407 formulation or a solution formulation. In addition, plasma ibuprofen concentrations were analyzed from central venous blood samples. Ibuprofen concentrations in the epidural space were significantly higher and longer lasting after the epidural gel injection compared with the epidural solution injection. The epidural AUC of ibuprofen was over threefold greater after epidural ibuprofen gel injection compared with the ibuprofen solution injection (p<0.001). The systemic absorption of ibuprofen from 25% poloxamer 407 gel was very low. The in situ forming poloxamer gel acted as a reservoir allowing targeted ibuprofen release at the epidural injection site and restricted ibuprofen molecules to a smaller spinal area. Ibuprofen diffusion from the epidural space to the intrathecal space was steady and prolonged. These results demonstrate that the use of epidurally injectable poloxamer gel can increase and prolong ibuprofen delivery from epidural space to the CSF enhancing thus ibuprofen entry into the central neuroaxis for spinal analgesia. Further toxicological and dose-finding studies are justified.

Determination of ibuprofen enantiomers in human plasma by HPLC-MS/MS: validation and application in neonates.

AIM: An adaptive method to determine ibuprofen enantiomers with limited volume of plasma required is necessary for investigating PK of ibuprofen in neonates. RESULTS: Enantiomer separation was achieved on a Lux cellulose 3 column with mobile phase consisting of methanol water (85:15, v/v) and formic acid (0.0075%) at isocratic rate of 0.2 ml/min. Calibration curve is linear for each enantiomer at the range of 0.1-60 µg/ml. Validation was conducted and results met requirements regarding to intra- and inter-run precision, accuracy and recovery. No matrix effect or interference was observed from neonatal plasma or comedications. Only 20 µl of plasma was requested in this study. CONCLUSION: This assay was specific and reliable to quantify ibuprofen enantiomers in neonate plasma.

The correlation between blood levels of ibuprofen and clinical analgesic response.

A clinical trial comparing ibuprofen, 400, 600, and 800 mg, with aluminum ibuprofen, 400 mg, and placebo was conducted in patients with moderate or severe pain subsequent to third molar extraction. Pain intensity ratings and ibuprofen serum levels were obtained at baseline, 30 minutes, 1 hour, and hourly thereafter for 3 hours. Pain intensity ratings were also obtained at hours 4, 5, and 6. Serum levels at 1, 2, and 3 hours correlated significantly with the log dose of ibuprofen (r = 0.35, 0.49, and 0.48, respectively) and with global analgesic response as measured by the percentage of the sum of the pain intensity scores (r = 0.28, 0.34, and 0.26, respectively). However, possibly because of differences in drug formulation, the percentage of the sum of the pain intensity scores did not correlate significantly with log dose. The highest correlations were found between contemporaneous serum levels and pain intensity difference values, particularly at hour 1 (r = 0.54). Our results support the proposition that increased ibuprofen serum levels lead to increased analgesia.

Direct injection of large volumes of plasma/serum on a new biocompatible extraction column for the determination of atenolol, propranolol and ibuprofen. Mechanisms for the improvement of chromatographic performance.

Very large volumes of serum/plasma can be directly injected to a new extraction column based on particles with a biocompatible outer surface and C18 groups within the pores. The biocompatibility has been obtained by attaching the human plasma protein alpha 1-acid glycoprotein to the outer surface of the particles. The pores are small enough to exclude the plasma protein molecules. Atenolol and propranolol were extracted on the extraction column as ion-pair with octanesulfonic acid as the counterion. The same counterion was used in the analytical mobile phase. A strong improvement of the recovery can be obtained using octanesulfonic acid as counterion in the extraction mobile phase. The recovery of atenolol increased from about 53.5% to about 93.4% using octanesulfonic acid as counterion. The chromatographic performance was also strongly affected by chromatography of the basic drugs as ion-pair with octanesulfonic acid. The improvement was due to trapping in a smaller section of the extraction column and enrichment of the drug on top of the analytical column. The enrichment was due to the transfer of the analyte to the analytical column in a zone with high concentration of counterion. Furthermore, the sample zone is compressed during the migration on the analytical column. The compression effect was caused by the counterion zone, migrating in front of the sample zone, giving the analyte higher retention on the front side than on the back side of the sample zone. Displacement of protein bound drug (ibuprofen) by addition of octanoic acid, was tested in order to study the influence on the recovery and the effect on the chromatographic performance. The recovery was improved and the chromatographic performance was greatly improved. The improvement obtained on the separation efficiency of ibuprofen was due to enrichment on top of the analytical column and compression during the migration through the analytical column. The enrichment was caused by a reduction of pH in the sample--octanoic acid zone transferred from the extraction column. The octanoic acid zone migrated in front of the sample zone giving a lower pH in front of the ibuprofen zone than behind. Thus, higher retention occurred in front of than behind the sample zone, which gave rise to compression. The methods developed for atenolol, propranolol and ibuprofen could be used for the determination of serum/plasma concentrations after single doses of the drugs with very high accuracy and precision. Linear calibration graphs were obtained and the r values were > or = 0.9999.

Determination of drugs by direct injection of plasma into a biocompatible extraction column based on a protein-entrapped hydrophobic phase.

Drugs were determined by direct injection of plasma samples into a biocompatible extraction column. The column is based on particles with a biocompatible external surface and a hydrophobic internal surface. The pores of the particles are small enough to exclude the protein molecules; the drug molecules can penetrate the porous particle and are retained on the hydrophobic internal surface. Biocompatibility of the particles was obtained by reaction of the external surface with the human plasma protein alpha1-acid glycoprotein. The surface within the pores of the particles contains hydrophobic C8 or C18 groups. The biocompatible extraction column was used in a fully automated system for the determination of ibuprofen, naproxen, propranolol, carbamazepine and phenytoin in plasma. No pressure increase was observed during the analysis of several hundred plasma samples. Plasma concentrations of propranolol in the range 4.5-125 ng/ml were determined with a precision (R.S.D.) of 0.75-1.8%. Linear calibration graphs were observed for the five drugs, and correlation coefficients of 1.0000 were obtained for four of the five model compounds.

Determination of ibuprofen in capillary and venous plasma by high-performance liquid chromatography with ultraviolet detection.

A high-performance liquid chromatographic (HPLC) method is described which determines ibuprofen in human capillary or venous plasma. Ibuprofen plus the internal standard, flurbiprofen, were extracted from acidified plasma with pentane-ether, back-extracted into base, and then extracted into the pentane-ether solution after acidification of the aqueous phase. A reverse-phase octadecylsilane column with acetonitrile-water-phosphoric acid as mobile phase and UV detection provided a quantifiable peak for 1 microgram/mL of ibuprofen in 0.1 mL of plasma. Capillary and venous plasma level curves were virtually superimposable after administration of 400 mg of ibuprofen to four normal volunteers. No ibuprofen was detected in the saliva of the subjects.

Bioavailability and in vitro oesophageal sticking tendency of hydroxypropyl methylcellulose capsule formulations and corresponding gelatine capsule formulations.

The overall aim of the present study was to widen our knowledge about the biopharmaceutical behaviour of novel hydroxypropyl methylcellulose (HPMC)-based two-piece capsules by comparing them with the classic hard gelatine capsules. Firstly, the tendency of the HPMC capsules to stick to isolated porcine oesophageal preparation was evaluated. The force needed to detach the HPMC capsules from the oesophagus was significantly lower than that for the gelatine capsules (P<0.001), which is evidently an advantage of this new dosage form. The second aim was to investigate the possibility of preparing sustained-release capsules using different powdered HPMCs as diluents (K100, K4M and K15M) and the effect of the molecular weight of HPMC powder on the in vitro and in vivo behaviour of the capsules. In addition to peroral drug administration also rectal dosing was applied. Two groups of eight healthy volunteers participated in randomised, cross-over, single-dose studies. One group was administered capsules orally and the other rectally. There were no marked differences in the bioavailability properties of either the oral or rectal HPMC capsules containing ibuprofen as model drug as compared with corresponding gelatine capsule formulations. Using different viscosity grades of HPMC powders as diluents it was possible to control the absorption rate of the model drug both from gelatine and HPMC capsules as far as the oral route was concerned. After rectal administration there were no statistically significant differences between the formulations containing different grades of HPMC powder. Only partial correlation was observed between the results of the bioavailability studies and the in vitro dissolution studies. From a biopharmaceutical point of view these two shell materials can be regarded as interchangeable.

HPLC on Chiralcel OJ-R for enantiomer separation and analysis of ketoprofen, from horse plasma, as the 9-aminophenanthrene derivative.

Racemic ketoprofen is a non-steroidal anti-inflammatory drug used to treat musculoskeletal and colic conditions in horses. The enantioselective chiral inversion of ketoprofen administered to horses has been studied by use of cellulose tris(4-methylbenzoate), also known as Chiralcel OJ-R, as chiral stationary phase; acetonitrile - 0.02 M perchlorate buffer (pH 2.0)-methanol, 60:15:25 (v/v/v) was used as mobile phase. Before chromatography, to effect adequate chiral interaction with the chiral stationary phase ketoprofen was derivatized with 9-aminophenanthrene, under acid conditions, after solid-phase (C18) extraction and then liquid-liquid extraction, to ensure effective removal of endogenous plasma materials. The 9-aminophenanthrene derivative of S-ibuprofen was used as internal standard. The enantiomers of ketoprofen were separated to baseline (Rs = 6.44, alpha = 1.76) within a short analysis time. The results indicate that the bio-inversion of R-ketoprofen to the S isomer is significant in equine species. However, considerable differences in pharmacokinetic parameters were observed, indicating large inter-animal variation.

The effect of colestipol and cholestyramine on the systemic clearance of intravenous ibuprofen in rabbits.

The effect of oral administration of the non-absorbable anion-exchange resins cholestyramine and colestipol on the systemic clearance and other pharmacokinetic parameters of intravenously administered ibuprofen (25 mg kg-1) was studied in rabbits. Single doses of colestipol hydrochloride (0.4 g kg-1) or cholestyramine (0.17 g kg-1) were given 30 min before ibuprofen administration. In cholestyramine-treated rabbits a significant reduction in ibuprofen plasma concentration was observed compared with both control (water only) and colestipol-treated rabbits. Cholestyramine treatment resulted in a significant decrease in the terminal elimination half-life and the mean residence time. Furthermore, a 31% increase in the systemic clearance and 23% decrease in the area under the plasma concentration-time curve were also observed in cholestyramine-treated rabbits. Colestipol treatment did not change these parameters. The volume of distribution parameters (Vdss and Vd(area)) did not change following either treatment. The changes in the pharmacokinetic parameters are compatible with an acceleration of ibuprofen elimination induced by oral administration of cholestyramine and not by colestipol. This effect is thought to be due to augmentation of net biliary excretion through enteric binding.

Are the pharmacokinetics of ibuprofen important determinants for the drug's efficacy in postoperative pain after third molar surgery?

The aim of the present placebo-controlled, crossover study was to evaluate the efficacy and pharmacokinetics of ibuprofen after a single oral dose of soluble ibuprofen 400 mg in 18 patients with postoperative pain after bilateral third molar surgery. Throughout a 5-hour investigation period, patients reported significantly less pain (P < 0.001) after treatment with soluble ibuprofen than after placebo. Peak plasma concentrations of ibuprofen occurred approximately 30 minutes after dosage. No significant correlations (P > 0.05) were observed between efficacy measures and the various pharmacokinetic parameters (AUC0-300, Cmax and Tmax) for ibuprofen after the soluble dose. It is concluded that a single dose of soluble ibuprofen 400 mg is an effective analgesic for the control of postoperative pain in the early period after third molar surgery. Efficacy of this preparation does not appear to be directly related to the drug's pharmacokinetic variables in plasma.

Modeling the onset and offset of dental pain relief by ibuprofen.

Onset and offset of dental pain relief by ibuprofen following third molar extraction were modeled in a randomized, double-blind, placebo-controlled, parallel-group, 8-hour study of patients receiving either a novel effervescent ibuprofen tablet (400 mg; N = 30), standard ibuprofen tablets (Nurofen(®) 2 × 200 mg; N = 22), or placebo (N = 37). An Emax model was fit to pain relief scores. Linear hazard models were used to analyze the time to first perceptible relief (TFPR), the time to meaningful pain relief (TMPR), and time to remedication (REMD). Nomograms were created to correlate TFPR, TMPR, and REMD with different ibuprofen pharmacokinetic profiles. Effervescent ibuprofen was absorbed rapidly with 95% completion within 15 minutes. Maximum pain relief score by ibuprofen was 1.8 units greater than placebo, with an EC50 (effect-site) for ibuprofen concentration of 10.2 µg·mL(-1). The likelihood to achieve TFPR and TMPR was doubled for every 10 µg·mL(-1) increase in ibuprofen plasma concentration. REMD risk decreased 40-fold as the categorical pain relief score increased from 0 to 3. Rapid absorption of ibuprofen effervescent resulted in an earlier TFPR and TMPR, and a lower REMD rate than standard ibuprofen. The nomograms may be useful in predicting the onset and offset of new faster acting ibuprofen formulations, based on pharmacokinetic profiles.

Effect of microgravity on the pharmacokinetics of Ibuprofen in humans.

The pharmacokinetics of ibuprofen were studied under microgravity (µG) conditions and compared with those at normal gravity (1G) in humans. Six healthy human volunteers were given 600 mg oral dose ibuprofen during 1-day simulated µG antiorthostatic bed rest position, then at normal position (1G) in a sequential design with 7 days washout time. Saliva and plasma samples were obtained up to 8 hours after dosing. Ibuprofen was not detected in all saliva samples. Pharmacokinetic parameters in plasma were calculated by either noncompartmental analysis or a 1- compartment model using the Kinetica program. Absorption kinetic parameters were then predicted by ADAM and PE modules using the Simcyp program. Results have showed an increased rate of ibuprofen dissolution and absorption and hence faster onset of action under µG conditions. However, rate of drug elimination and bioavailability was not affected by µG, suggesting no need for dose adjustment.