Impact of introducing a new biological matrix into a validated bioanalytical method: Focus on matrix protein content.

International guidance on bioanalytical method validation recommends the practice of partial validation when introducing a new matrix from the same species into a previously fully validated assay. Planning the partial validation protocol should include an evaluation of analyte chemistry, consideration of sample container materials, and a comparison of properties between the relevant biological matrices. Transition of a serum/plasma-validated bioanalytical method to analysis from a low-protein matrix, such as urine, cerebral spinal fluid, or oral fluid can result in inconsistent analyte recovery. The low recovery can potentially be mistaken for signal suppression or lack of drug stability and may be more pronounced in low-concentration or low-volume samples. In addition, adsorption and absorption interactions with containers may be exacerbated in low-protein matrices. Several possibilities exist for mitigating the impact of non-specific binding and low-protein matrices, including surfactants, bovine serum albumin, and ß-cyclodextrin. Finally, higher matrix protein can facilitate analyte stability. Given all this, matrix protein content should not be overlooked when anticipating a partial bioanalytical method validation.

Chemical Stability of Lorazepam Oral Solution Repackaged in Plastic Oral Syringes at Room and Refrigerated Temperature.

Purpose: Generic lorazepam oral solution is supplied in a 30 mL multi-dose bottle requiring protection from light and refrigeration, with a beyond use date of 90 days once the bottle is opened. The repackaging of 1 mL doses of lorazepam oral solution into oral syringes allows for facilitated dispensing, yet no available data supports repackaging and storing lorazepam oral solution in syringes. The validation and application of a stability-indicating high-performance liquid chromatography with ultraviolet detection (HPLC-UV) method for the quantification of lorazepam allowed for the determination of the stability of lorazepam oral solution when stored in oral syringes. Methods: A stability-indicating HPLC-UV method was developed for the quantification of lorazepam in oral solution. The method was validated using guidance from USP < 1225 >. For the stability investigation, 2 mg/mL lorazepam oral solution was aliquoted into clear plastic oral syringes in 1 mLmilliliter doses from 2 multi-dose stock bottles and randomly allocated for storage in room temperature or refrigerated environment. Baseline lorazepam concentrations were measured on the day the study was initiated and designated as 100% initial concentration samples. Subsequent samples were analyzed in triplicate at time points of 24, 48, and 96 hours and 7, 10, 14, 21, 30, and 60 days. Results: The calibration curves on three non-consecutive days met the linearity criteria of R 2 > 0.99. Inter- day and intra-day precision and accuracy (percent relative standard deviation and percent error) were ≤2% over three days. During the stability investigation, percent initial concentration of lorazepam from room and refrigerated syringes remained above 90% for the duration of the study. Conclusion: The stability-indicating HPLC-UV method was successfully applied to the investigation of lorazepam oral solution stability when stored in syringes at room and refrigerated temperatures. The emergent need for use of lorazepam concentrate for inpatients and the restrictions of how the medication is supplied necessitated a need for the evaluation of repackaging into unit dose syringes for immediate availability from automated dispensing cabinets. Lorazepam oral solution stored in clear plastic syringes maintained greater than 90% initial concentration at both room and refrigerated temperatures for 60 days.

Genetically Determined Low-Density Lipoprotein Cholesterol and Risk of Subarachnoid Hemorrhage.

We evaluated whether genetically elevated low-density lipoprotein cholesterol (LDL-C) levels are associated with lower risk of intracranial aneurysms and subarachnoid hemorrhage (IA/SAH). We conducted a 2-sample Mendelian randomization (MR) study. Our primary analysis used the inverse-variance weighted method. In secondary analyses, we implemented the MR-PRESSO method, restricted our analysis to LDL-C-specific instruments, and performed multivariate MR. A 1-mmol/l increase in genetically instrumented LDL-C levels was associated with a 17% lower risk of IA/SAH (odds ratio = 0.83, 95% confidence interval = 0.73-0.94, p = 0.004). Results remained consistent in secondary and multivariate analyses (all p < 0.05). Our results provide evidence for an inverse causal relationship between LDL-C levels and risk of IA/SAH. ANN NEUROL 2022;91:145-149.

Hospital Revisits for Post-Ischemic Stroke Epilepsy after Acute Stroke Interventions.

OBJECTIVES: Improvements in acute stroke care have led to an increase in ischemic stroke survivors, who are at risk for development of post-ischemic stroke epilepsy (PISE). The impact of therapies such as thrombectomy and thrombolysis on risk of hospital revisits for PISE is unclear. We utilized administrative data to investigate the association between stroke treatment and PISE-related visits. MATERIALS AND METHODS: Using claims data from California, New York, and Florida, we performed a retrospective analysis of adult survivors of acute ischemic strokes. Patients with history of epilepsy, trauma, infections, or tumors were excluded. Included patients were followed for a primary outcome of revisits for seizures or epilepsy. Cox proportional hazards regression was used to identify covariates associated with PISE. RESULTS: In 595,545 included patients (median age 74 [IQR 21], 52% female), the 6-year cumulative rate of PISE-related revisit was 2.20% (95% CI 2.16-2.24). In multivariable models adjusting for demographics, comorbidities, and indicators of stroke severity, IV-tPA (HR 1.42, 95% CI 1.31-1.54, p<0.001) but not MT (HR 1.62, 95% CI 0.90-1.50, p=0.2) was associated with PISE-related revisit. Patients who underwent decompressive craniectomy experienced a 2-fold increase in odds for returning with PISE (HR 2.35, 95% CI 1.69-3.26, p<0.001). In-hospital seizures (HR 4.06, 95% CI 3.76-4.39, p<0.001) also elevated risk for PISE. SIGNIFICANCE: We demonstrate that ischemic stroke survivors who received IV-tPA, underwent decompressive craniectomy, or experienced acute seizures were at increased risk PISE-related revisit. Close attention should be paid to these patients with increased potential for long-term development of and re-hospitalization for PISE.

Stroke Disparities Among Nonracial Minorities in the All of Us Research Program.

[Figure: see text].

Liquid chromatography-mass spectrometry applications for quantification of endogenous sex hormones.

Liquid chromatography, coupled with tandem mass spectrometry, presents a powerful tool for the quantification of the sex steroid hormones 17-ß estradiol, progesterone and testosterone from biological matrices. The importance of accurate quantification with these hormones, even at endogenous levels, has evolved with our understanding of the role these regulators play in human development, fertility and disease risk and manifestation. Routine monitoring of these analytes can be accomplished by immunoassay techniques, which face limitations on specificity and sensitivity, or using gas chromatography-mass spectrometry. LC-MS/MS is growing in capability and acceptance for clinically relevant quantification of sex steroid hormones in biological matrices and is able to overcome many of the limitations of immunoassays. Analyte specificity has improved through the use of novel derivatizing agents, and sensitivity has been refined through the use of high-resolution chromatography and mass spectrometric technology. This review highlights these innovations, among others, in LC-MS/MS steroid hormone analysis captured in the literature over the last decade.

Andexanet Alfa Versus 4-Factor Prothrombin Complex Concentrate for Reversal of Factor Xa Inhibitors in Intracranial Hemorrhage.

BACKGROUND/OBJECTIVE: There are limited data on the risks and benefits of using andexanet alfa (AA) in comparison with four-factor prothrombin complex concentrate (4F-PCC) to reverse factor Xa inhibitors (FXi) associated intracranial hemorrhage (ICH). We sought to describe our experience with AA or 4F-PCC in patients with oral FXi-related traumatic and spontaneous ICH. METHODS: We conducted a retrospective review of consecutive adult patients with FXi-related ICH who received AA or 4F-PCC. FXi-related ICH cases included traumatic and spontaneous intracranial hemorrhages. Our primary analysis evaluated ICH stability on head computed tomography scan (CT), defined as a similar amount of blood from the initial scan at the onset of ICH to subsequent scans, at 6-h and 24-h post-administration of AA or 4F-PCC. For the subset of spontaneous intraparenchymal hemorrhages, volume was measured at 6-h and 24-h post-reversal. In secondary analyses, we evaluated good functional outcome at discharge, defined as a Modified Rankin Score of less than 3, and the incidence of thrombotic events after AA or 4F-PCC adminstration, during hospitalization. RESULTS: A total of 44 patients (16 traumatic and 28 spontaneous ICH) with median age of 79 years [72-86], 36% females, with a FXi-related ICH, were included in this study. The majority of spontaneous ICHs were intraparenchymal 19 (68%). Twenty-eight patients (64%) received AA and 16 patients (36%) received 4F-PCC. There was no difference between AA and 4F-PCC in terms of CT stability at 6 h (21 [78%] vs 10 [71%], p = 0.71) and 24 h (15 [88%] vs 6 [60%], p = 0.15). In a subgroup of patients with spontaneous intraparenchymal hemorrhage, there was no difference in the degree of achieved hemostasis based on hematoma volume between AA and 4F-PCC at 6 h (9.3 mL [6.9-26.4] vs 10 mL [9.4-22.1], adjusted p = 0. 997) and 24-h (9.2 mL [6.1-18.8] vs 9.9 [9.4-21.1], adjusted p = 1). The number of patients with good outcome based on mRS on discharge were 10 (36%) and 6 (38%) in the AA and 4F-PCC groups, respectively (adjusted p = 0.81). The incidence of thromboembolic events was similar in the AA and 4F-PCC groups (2 [7%] vs 0, p = 0.53). CONCLUSION: In this limited sample of patients, we found no difference in neuroimaging stability, functional outcome and thrombotic events when comparing AA and 4F-PCC in patients with FXi-related ICH. Since our analysis is likely underpowered, a multi-center collaborative network devoted to this question is warranted.

Endovascular Treatment of Infective Endocarditis-Related Acute Large Vessel Occlusion Stroke.

OBJECTIVES: Embolic stroke is a frequent complication of infective endocarditis yet lacks acute treatment as intravenous thrombolysis should be avoided due to high risk of intracerebral hemorrhage. Mechanical thrombectomy for large vessel occlusion may be a promising treatment but there is limited data on safety outcomes in infective endocarditis. MATERIALS AND METHODS: In this multi-center retrospective case series, we reviewed data from patients with infective endocarditis-related large vessel occlusion who underwent mechanical thrombectomy in 9 US hospitals. RESULTS: We identified 15 patients at 9 hospitals. A minority presented with signs suggesting infection (2 patients (14%) had fever, 7 (47%) were tachycardic, 2 (13%) were hypotensive, and 8 (53%) had leukocytosis). The median National Institute of Health Stroke Score decreased from 19 (range 9-25) at presentation to 7 post-thrombectomy (range 0-22, median best score post-thrombectomy), and the median modified Rankin Scale on or after discharge for survivors was 3 (range 0-6). Approximately 57% of patients had a modified Rankin Scale between 0 and 3 on or after discharge. Hemorrhagic transformation was observed in 7/15 (47%). The mechanical thrombectomy group had 2/9 petechial hemorrhagic transformation (22%), compared to 4/6 parenchymal hematomas (67%) in the tissue plasminogen activator + mechanical thrombectomy group. CONCLUSIONS: Our findings suggest that patients with large vessel occlusion due to infective endocarditis may not present with overt signs of infection. Mechanical thrombectomy may be an effective treatment in this patient population for whom intravenous thrombolysis should be avoided.

Stability of Ampicillin in Normal Saline Following Refrigerated Storage and 24-Hour Pump Recirculation.

OBJECTIVE: Use of ampicillin in outpatient parenteral antimicrobial therapy (OPAT) has historically been complicated by frequent dosing and limited stability. The purpose of this study was to evaluate stability of ampicillin using high-pressure liquid chromatography (HPLC) in an OPAT dosing model using continuous infusion at room temperature over 24 hours immediately following preparation compared with batches stored under refrigeration for 24 hours, 72 hours, and 7 days. METHODS: An HPLC method was developed and validated as stability indicating using guidance in USP general Chapter <1225>. Four ampicillin batches were prepared for each experimental condition (immediate use and refrigerated storage for 24 hours, 72 hours, and 7 days). A pump was used to recirculate the solutions through medical-grade tubing for 24 hours. Triplicate 1-mL aliquots were removed from each batch at time 0, 4, 8, 12, and 24 hours and analyzed for ampicillin concentration. RESULTS: Each batch was assayed for initial concentration (20.34-21.50 mg/mL), and percent recovery compared with that concentration thereafter. For the duration of infusion, the average recoveries were 96.4%, 95.8%, 94.6%, and 90.3% for immediate use, 24-hour storage, 72-hour storage, and 7-day storage, respectively. The recovery remained above 90% for all batches and time points, except for 7-day storage, which fell below 90% after 4 hours of circulation. CONCLUSION: Ampicillin can be prepared and stored in a refrigerator for up to 72 hours prior to continuously infusing at room temperature over 24 hours with less than a 10% loss of potency over the dosing period. This model supports twice weekly OPAT delivery of ampicillin.

Non-Traumatic Subdural Hemorrhage and Risk of Arterial Ischemic Events.

Background and Purpose- The risk of arterial ischemic events after subdural hemorrhage (SDH) is poorly understood. This study aimed to evaluate the risk of acute ischemic stroke and myocardial infarction among patients with and without nontraumatic SDH. Methods- We performed a retrospective cohort study using claims data from 2008 through 2014 from a nationally representative sample of Medicare beneficiaries. The exposure was nontraumatic SDH. Our primary outcome was an arterial ischemic event, a composite of acute ischemic stroke and acute myocardial infarction. Secondary outcomes were ischemic stroke alone and myocardial infarction alone. We used validated International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes to identify our predictor and outcomes. Using Cox regression and corresponding survival probabilities, adjusted for demographics and vascular comorbidities, we computed the hazard ratio in 4-week intervals after SDH discharge. We performed secondary analyses stratified by strong indications for antithrombotic therapy (composite of atrial fibrillation, peripheral vascular disease, valvular heart disease, and venous thromboembolism). Results- Among 1.7 million Medicare beneficiaries, 2939 were diagnosed with SDH. In the 4 weeks after SDH, patients' risk of an arterial ischemic event was substantially increased (hazard ratio, 3.6 [95% CI, 1.9-5.5]). There was no association between SDH diagnosis and arterial ischemic events beyond 4 weeks. In secondary analysis, during the 4 weeks after SDH, patients' risk of ischemic stroke was increased (hazard ratio, 4.2 [95% CI, 2.1-7.3]) but their risk of myocardial infarction was not (hazard ratio, 0.8 [95% CI, 0.2-1.7]). Patients with strong indications for antithrombotic therapy had increased risks for arterial ischemic events similar to patients in the primary analysis, but those without such indications did not demonstrate an increased risk for arterial ischemic events. Conclusions- Among Medicare beneficiaries, we found a heightened risk of arterial ischemic events driven by an increased risk of ischemic stroke, in the 4 weeks after nontraumatic SDH. This increased risk may be due to interruption of antithrombotic therapy after SDH diagnosis.

Monitoring Commercial Ibuprofen Potency Changes Over 1 Year When Stored in a Household Setting.

Background: Most over-the-counter medications are labeled for storage in a dry, room temperature environment. Despite this, many households store medications in the bathroom, where temperature and humidity extremes may be experienced. Objective: In this project, we sought to investigate the effect that long-term storage in a household bathroom had on potency of over-the-counter ibuprofen (IBU) products as well as on the emergence of a known toxic degradation product, 4-isobutylacetophenone (4-IBP). Methods: A liquid chromatography-tandem mass spectrometry method was developed for the quantitative determination of IBU and 4-IBP in aqueous samples. Three brands each of IBU tablets (200 mg) and suspensions (100 mg/5 mL) were assayed for IBU concentration at the initiation of the study and once monthly thereafter. The samples were stored in a household bathroom, with continuous temperature and humidity monitoring. Each sample was assayed in triplicate and percent recovery was calculated against freshly prepared standards of IBU using bulk powder. Results: Tablets maintained >90% average strength through 3 months, with statistically significant deviation from initial concentration (2-way analysis of variance, P = .05) detected after 6 to 7 months. Suspensions maintained >90% average strength through 5 months, with statistically significant changes from initial concentration emerging after 7 months. After 12 months, the average strength was 73% and 83% for tablets and suspensions, respectively. 4-IBP was not detected in any of the samples during the duration of the study. Conclusions: These data indicate that, while 4-IBP was not detected following 12-month bathroom storage of commercial IBU products, significant changes in potency should negatively affect efficacy.

Comparative Stability of Compounded Omeprazole Suspension Versus Commercial Omeprazole Kit When Stored in Oral Syringes Under Refrigerated Conditions.

Background: Omeprazole is a proton pump inhibitor used to manage gastrointestinal disorders. Special populations may require omeprazole to be given as an oral suspension. Objective: The purpose of this project was to compare the stability of omeprazole in the FIRST kit product to a traditionally compounded omeprazole suspension, when stored in refrigerated unit-dosed syringes. NG tube delivery of the 2 products was also investigated. Methods: Five batches of compounded omeprazole oral suspension and 5 kits of FIRST-Omeprazole were prepared to an initial concentration of 2 mg/mL. Suspensions were aliquoted into 5-mL doses in clear plastic oral syringes, and stored at 2-8 °C. Syringes from each batch were analyzed at baseline and after 7, 14, 21, and 30 days for omeprazole potency using HPLC. To assess suitability for NG tube administration, 20 mL of each suspension were administered through NG tubes (8Fr, 10Fr, and 18Fr), and percent omeprazole recovery assessed. Results: The chemical potency remained within 90-110% for 14 days and 30 days for compounded samples and FIRST-Omeprazole samples, respectively. There was a statistically significant difference in initial concentration; 1.89 mg/mL versus 1.98 mg/mL for compounded and FIRST-Omeprazole, respectively. After 30 days, FIRST-Omeprazole demonstrated 97.20% API recovery. Neither suspension experienced statistically significant loss of potency following NG tube passage. Conclusion: FIRST-Omeprazole suspension may be stored in refrigerated clear luer-lock oral syringes for 30 days. Traditionally compounded omeprazole suspension should be used within 14 days. Both suspensions are suitable for NG tube administration.

Comparative Stability of Oral Vitamin K Liquids Stored in Refrigerated Amber Plastic Syringes.

Background: Compounded vitamin K oral liquids may be useful in some patient populations, or when an appropriate solid dosage form is not available. While vitamin K oral liquid is typically prepared with sterile water for injection (SWFI), other compounding agents may be more palatable. Objective: To evaluate stability of compounded vitamin K liquids in SWFI, Ora-Sweet, simple syrup, cherry syrup, and SyrPalta stored in amber plastic oral syringes. Methods: Five types of compounded vitamin K liquids were prepared in triplicate-Ora-Sweet, simple syrup, cherry syrup, SyrPalta, and SWFI without flavoring; aliquoted into amber plastic oral syringes; and stored in a laboratory refrigerator (4.9°C to 5.4°C). On study days, 3 syringes from each batch were removed, diluted to assay concentration, and compared with a freshly prepared US Pharmacopeia reference solution. The samples and reference were analyzed using a previously validated high-performance liquid chromatography-ultraviolet method. Product stability was defined as 90% to 110% labeled amount. Results were further compared using a 2-way ANOVA (analysis of variance; P = .05) with post hoc Tukey's correction for multiple comparisons. Results: Vitamin K in SWFI, SyrPalta, and cherry syrup was stable for 21 days, 7 days, and 24 hours, respectively, under refrigeration in amber plastic oral syringes. Vitamin K in Ora-Sweet and simple syrup demonstrated high within-day variability and low potency. Statistically significant differences were detected between the SWFI formulation and all other vehicles. Conclusion: Vitamin K in SWFI is appropriate for longer-term storage of unit-dosed vitamin K; however, SyrPalta and cherry syrup may be used for short-term storage or immediate administration of vitamin K.

Chromatographic methods in HIV medicine: Application to therapeutic drug monitoring.

HIV antiretroviral therapy spans several different drug classes, meant to combat various aspects of viral infection and replication. Many authors have argued the benefits of therapeutic drug monitoring (TDM) for the HIV patient including compliance assurance and assessment of appropriate drug concentrations; however, the array of drug chemistries and combinations makes TDM an arduous task. HPLC-UV and LC-MS/MS are both frequent instruments for the quantification of HIV drugs in biological matrices with investigators striving to balance sensitivity and affordability. Plasma, the dominant matrix for these analyses, is prepared using protein precipitation, liquid-liquid extraction or solid-phase extraction depending on the specific complement of analytes. Despite the range of polarities found in drug classes relevant to HIV therapeutics, most chromatographic separations utilize a hydrophobic column (C18 ). Additionally, as the clinically relevant samples for these assays are infected with HIV, along with possible co-infections, another important aspect of sample preparation concerns viral inactivation. Although not routine in clinical practice, many published analytical methods from the previous two decades have demonstrated the ability to conduct TDM in HIV patients receiving various medicinal combinations. This review summarizes the analytical methods relevant to TDM of HIV drugs, while highlighting respective challenges.

Conservative management of pelvic abscess following sacrocolpopexy: a report of three cases and review of the literature.

INTRODUCTION AND HYPOTHESIS: After sacrocolpopexy, intra-abdominal pelvic abscesses are often managed with intravenous antibiotics, excision of the mesh involved, and debridement of compromised tissue. METHODS AND RESULTS: Three cases of successful management of pelvic abscesses after sacrocolpopexy using long-term antibiotics and percutaneous drainage of intra-abdominal abscesses without removing the mesh are presented. CONCLUSIONS: In selected patients who have undergone sacrocolpopexy, with careful counseling, conservative management of pelvic abscesses with percutaneous drainage and long-term antibiotic treatment without the surgical excision of the mesh may play a role.

The impact of phospholipids and phospholipid removal on bioanalytical method performance.

Phospholipids (PLs) are a component of cellmembranes, biological fluids and tissues. These compounds are problematic for the bioanalytical chemist, especially when PLs are not the analytes of interest. PL interference with bioanalysis highly impacts reverse-phase chromatographic methods coupled with mass spectrometric detection. Phospholipids are strongly retained on hydrophobic columns, and can cause significant ionization suppression in the mass spectrometer, as they outcompete analyte molecules for ionization. Strategies for improving analyte detection in the presence of PLs are reviewed, including in-analysis modifications and sample preparation strategies. Removal of interfering PLs prior to analysis seems to be most effective atmoderating thematrix effects fromthese endogenous cellular components, and has the potential to simplify chromatography and improve column lifetime. Products targeted at PL removal for sample pre-treatment, as well as products that combine multiplemodes of sample preparation (i.e. Hybrid SPE), show significant promise inmediating the effect on PL interference in bioanalysis.

UHPLC-MS/MS quantification of buprenorphine, norbuprenorphine, methadone, and glucuronide conjugates in umbilical cord plasma.

Opioid use during pregnancy can result in the newborn being physically dependent on the substance, thus experiencing drug withdrawal, termed neonatal abstinence syndrome (NAS). Buprenorphine and methadone are two drugs used to treat opioid withdrawal and are approved for use in pregnancy. Quantification of these compounds in umbilical cord plasma would help assess in utero exposure of neonates in cases of buprenorphine or methadone use during pregnancy. An LC-MS/MS method using solid-phase extraction sample preparation was developed and validated for the simultaneous quantification of methadone, buprenorphine, norbuprenorphine, and glucuronide metabolites in umbilical cord plasma. The average accuracy (percentage error) and precision (relative standard deviation) were <15% for each validated concentration. Our data establishes a 2 week maximum freezer storage window in order to achieve the most accurate cord plasma concentrations of these analytes. Additionally, we found that the umbilical cord tissue analysis was less sensitive compared with analysis with umbilical cord blood plasma, indicating that this may be a more appropriate matrix for determination of buprenorphine and metabolite concentrations. This method was successfully applied to the analysis of cord blood from women with known buprenorphine or methadone use during pregnancy.

Assays for determination of ertapenem for applications in therapeutic drug monitoring, pharmacokinetics and sample stability.

Carbapanems are a class of ß-lactam antibiotics with broad-spectrum potency and high ß-lactamase resistance. Ertapenem, a member of this class, sold under the trade name Invanz™, has been of interest in the world of antibiotic therapeutic drug monitoring owing to its highly standardized 1 g dose and its high degree of plasma protein binding. Owing to the relative newness of this drug, fewer than 30 methods for ertapenem quantification have been published. Among these about half utilize biological matrices at the sample type. Liquid-liquid extraction and protein precipitation prevail as the most frequently used sample preparation techniques, despite their low recoveries compared with solid-phase extraction. Additionally, high-performance liquid chromatography with ultraviolet detection (HPLC-UV) is the instrumentation choice for most ertapenem assays. While these approaches may not achieve the highest possible sensitivity for ertapenem quantification, they provide clinically relevant tools for monitoring ertapenem in real patients. Sample stability is an ongoing concern for laboratories that handle ertapenem analysis, with buffering being of paramount importance, as well as low temperature (<-70°C) storage, to ensure minimal drug degradation in situ.