Stability of Compounded Digoxin Solution 0.05 mg/mL for Injection.

Background: In 2015, commercial pediatric digoxin injection 0.05 mg/mL was discontinued, leaving only one adult concentration (0.25 mg/mL) for injection on the Canadian market. No published studies have documented the chemical stability over a long period of time of a diluted solution of digoxin for injection. Objective: The aim of this study was to assess the chemical stability of 2 digoxin injection formulations 0.05 mg/mL diluted in 2 vehicles stored at 5°C or a 25°C. Methods: The compounded solution of digoxin 0.05 mg/mL for injection was prepared with digoxin 0.25 mg/mL after dilution in 2 different vehicles, normal saline, and a compounding of the commercial vehicle. Half of the compounding products were stored in 2 mL transparent glass vials at 25°C and the other half at 5°C. Chemical stability was evaluated by HPLC-UV analysis on days 0, 14, 30, 60, 90, 120, 150, 180 for each temperature conditions. In addition, samples were tested for organoleptic change, presence of particular matter as well as sterility. Results: For all tested preparations, the concentration of digoxin remained above 90.0% of the initial concentration throughout the 180-day study. Furthermore, no organoleptic change was observed; particulate matter assessment was in acceptable range; and sterility specifications were met. Conclusions: Digoxin 0.05 mg/mL obtained with a dilution of digoxin 0.25 mg/mL by normal saline or a copy of the commercial vehicle remained stable for at least 180 days at 5°C and 25°C.

Compatibility of Lactated Ringer's Injection With 94 Selected Intravenous Drugs During Simulated Y-site Administration.

Objective: To test the compatibility of intravenous (IV) lactated Ringer's injection (LR) with 94 injectable (IV) drugs during simulated Y-site administration. Methods: Ninety-four IV drugs were investigated for compatibility with LR (Baxter). Each sample was prepared in duplicate and performed at room temperature. Two observers performed visual evaluation independently immediately upon mixing and then 15 minutes, 1 hour, 2 hours, 3 hours, and 4 hours after admixture. Another observer performed a particle counting test on 1 of the 2 duplicates of each admixture that did not immediately show incompatibility and then after 4 hours by a light obscuration particle count test. Results: Of the 94 tested drugs, 86 were found to be compatible with LR. A total of 8 drugs were found to be physically incompatible. Of these incompatible drugs, 7 were directly identified visually and 1 was confirmed by the light obscuration particle count test. Conclusion: Lactated Ringer's injection was physically compatible for 4 hours with 86 tested drugs during simulated Y-site administration. Eight drugs, ciprofloxacin, cyclosporine, diazepam, ketamine, lorazepam, nitroglycerin, phenytoin, and propofol, were found to be incompatible and should not be administered with LR.

A Pilot Randomized Trial Comparing the Effects of 80 versus 160 mg of Aspirin on Midtrimester Uterine Artery Pulsatility Index in Women with a History of Preeclampsia.

OBJECTIVE: To compare the effects of 80 mg and 160 mg of aspirin, initiated in the first trimester of pregnancy, on mid-trimester uterine artery pulsatility index (UtA-PI) in women with a history of preeclampsia. METHODS: We performed a pilot double-blind randomized controlled trial. Pregnant women with a history of preeclampsia were recruited between 100/7 and 136/7 weeks gestation and randomly assigned to take either 80 or 160 mg of aspirin daily at bedtime from randomization to 356/7 weeks gestation. The primary outcome was mean UtA-PI at 22-24 weeks. Secondary outcomes included the rate of fetal growth restriction and preeclampsia, stratified as term (≥37 weeks), preterm (<37 weeks), and early-onset (<34 weeks) preeclampsia. RESULTS: A total of 107 participants were randomized, including 41 (38%) with a history of preterm preeclampsia and 16 (15%) with a history of early-onset preeclampsia. We observed no significant difference in mean UtA-PI at 22-24 weeks between the 2 groups (0.97; 95% CI 0.88-1.05 vs. 0.97; 95% CI 0.88-1.07, P = 0.9). The rates of fetal growth restriction (8% vs. 2%; P = 0.20); preeclampsia (12% vs. 15%; P = 0.78), preterm preeclampsia (4% vs. 2%; P = 0.56), and early-onset preeclampsia (0% vs. 2%; P = 0.52) were similar in both groups. No serious adverse events associated with the study treatment were reported. CONCLUSION: We observed no significant difference in UtA-PI between the two doses of aspirin, but we observed low rates of fetal growth restriction and preterm and early-onset preeclampsia (all less than 5%). The benefits of aspirin for the prevention of preterm preeclampsia is probably not related to the improvement of deep placentation alone.

Compatibility of Y-Site Injection of Meropenem Trihydrate With 101 Other Injectable Drugs.

Objective: The objective of the study was to establish the compatibility of injectable meropenem with 101 other drugs during Y-site administration. Methods: Meropenem (50 mg/mL, 10 mL) was combined with 101 undiluted injectable drugs (10 mL each) at room temperature. Each preparation was performed twice. The first sample underwent a visual evaluation and a particle count test by light obstruction immediately after mixing. These tests were repeated 4 hours after mixing using the second preparation. Incompatibility was defined as precipitation or other visual change (turbidity, crystal formation, gas formation, color change) or failure to meet United States Pharmacopeia (USP) <788> 1.B specifications at any time point. Results: A total of 83 of the 101 injectable drugs tested with meropenem were found to be compatible both visually and using the USP <788> particle counter. The gross incompatibility of the other 17 drugs was determined by visual observation. One mixture complied with the specifications, but showed an increase of temperature upon mixing and was removed from the study. Conclusion: Of the 101 drugs tested, 83 were found to be compatible while the remaining 17 were incompatible. One drug was removed from the study as its compatibility was unclear.

GM1-Binding Conjugates To Improve Intestinal Permeability.

Drugs and proteins with poor intestinal permeability have a limited oral bioavailability. To remediate this problem, a receptor-mediated endocytosis and transcytosis approach was explored. Indeed, the nontoxic ß subunit of cholera toxin (CTB) can cross the intestinal barrier by binding to receptor GM1. In this study, we explored the use of GM1-binding peptides and CTB as potential covalent carriers of poorly permeable molecules. GM1-binding peptides (G23, P3) and CTB were conjugated to poorly permeable fluorescent probes such as fluorescein isothiocyanate (FITC) and albumin-FITC using triethylene glycol spacers and click chemistry. The affinity of the peptide conjugates with receptor GM1 was confirmed by isothermal titration calorimetry or microscale thermophoresis, and the results suggested the involvement of nonspecific interactions. Conjugating the model drugs to G23 and P3 improved the internalization into Caco-2 and T84 cells, although the process was not dependent on the amount of GM1 receptor. However, conjugation of bovine serum albumin FITC to CTB increased the internalization in the same cells in a GM1-dependent pathway. Peptide conjugates demonstrated a limited permeability through a Caco-2 monolayer, whereas G23 and CTB conjugates slightly enhanced permeability through a T84 cell monolayer compared to model drugs alone. Since CTB can improve the permeability of large macromolecules such as albumin, it is an interesting carrier for the improvement of oral bioavailability of various other macromolecules such as heparins, proteins, and siRNAs.

Length of surface PEG modulates nanocarrier transcytosis across brain vascular endothelial cells.

Diblock PLA-PEG nanoparticles were produced to establish the role of PEG chain length on brain vascular endothelial cell transcytosis. 100-nm nanoparticles tagged with fluorescent pyrene butanol and coated with PEG chains (Mw: 1-10 kDa), at similar PEG surface density, were used to study endocytosis and transcytosis phenomena on mouse vascular endothelial cell monolayers. The transport mechanisms were then investigated through inhibitory processes. Our results show that there is an evident correlation between PEG chain length and nanoparticle translocation. The highest transcytosis rates were obtained with PEG5000 and PEG10000 and macropinocytosis appeared to play a central role in cell uptake. This study constitutes the first systematic exploration of the role of PEG chain length on nanoparticle endocytosis and transcytosis in an in vitro model of the blood-brain barrier.

A comparison of the effects of selective and non-selective mineralocorticoid antagonism on glucose homeostasis of heart failure patients with glucose intolerance or type II diabetes: A randomized controlled double-blind trial.

Mineralocorticoid receptor antagonists (MRAs) decrease morbidity and mortality in patients with heart failure (HF). However, spironolactone, a non-selective MRA, has been shown to exert a harmful effect on glucose homeostasis. The objective of this multicenter, randomized, controlled, double-blind trial was to compare the effects of spironolactone to those of the selective MRA eplerenone on glucose homeostasis among 62 HF patients with glucose intolerance or type II diabetes. Trial registration number:NCT01586442.

Spray-dried high-amylose sodium carboxymethyl starch: impact of α-amylase on drug-release profile.

Spray-dried high-amylose sodium carboxymethyl starch (SD HASCA) is a promising pharmaceutical excipient for sustained-release (SR) matrix tablets produced by direct compression. The presence of α-amylase in the gastrointestinal tract and the variations of the gastric residence time of non-disintegrating dosage forms may affect the presystemic metabolism of this excipient and, consequently, the drug-release profile from formulations produced with SD HASCA. In this study, the influence of α-amylase and the residence time in acidic conditions on the drug-release profile was evaluated for a once-daily acetaminophen formulation (Acetaminophen SR) and a once-daily tramadol hydrochloride formulation (Tramadol SR). Both formulations were based on SD HASCA. α-Amylase concentrations ranging from 0 IU/L to 20000 IU/L did not significantly affect the drug-release profiles of acetaminophen and tramadol hydrochloride from SD HASCA tablets (f2 > 50) for all but only one of the studied conditions (f2 = 47). Moreover, the drug-release properties from both SD HASCA formulations were not significantly different when the residence time in acidic medium was 1 h or 3 h. An increase in α-amylase concentration led to an increase in the importance of polymer erosion as the main mechanism of drug-release instead of drug diffusion, for both formulations and both residence times, even if release profiles remained comparable. As such, it is expected that α-amylase concentration and residence time in the stomach will not clinically affect the performance of both SD HASCA SR formulations, even if the mechanism of release itself may be affected.

Compatibility of Cloxacillin Sodium with Selected Intravenous Drugs During Simulated Y-Site Administration.

BACKGROUND: Data regarding Y-site compatibility of intravenous (IV) cloxacillin sodium with other drugs are scarce and incomplete. OBJECTIVE: To establish the compatibility of IV cloxacillin with 89 injectable drugs during simulated Y-site administration. METHODS: Cloxacillin sodium (10 mL, 100 mg/mL) was combined with 89 undiluted IV drugs (10 mL, each). Tests were duplicated and performed at room temperature. Visual evaluation and a light obscuration particle count test were performed on 1 of the 2 solutions immediately after mixing. The second mixture underwent visual evaluation after 15 minutes, 1 hour, and 4 hours, followed by a particle count test at 4 hours. Drugs were considered incompatible if the mixture precipitated or became turbid within the 4-hour period or exceeded the particle count limit allowed by Test 1.B of USP <788> initially or at 4 hours. RESULTS: Of the 89 tested drugs, 64 were compatible for up to 4 hours. The remaining 25 drugs were incompatible. Of these incompatible drugs, 16 were identified visually, and 9 were identified by the light obscuration particle count test. CONCLUSIONS: Sixty-four IV drugs were found to be compatible with cloxacillin via simulated Y-site, whereas 25 drugs were found to be incompatible with the antibiotic. The light obscuration particle count test should be used to complement visual evaluation when samples do not precipitate immediately.

Stability Evaluation of Bracketed Diclofenac Sodium USP in VersaPro™ Cream Base, VersaPro™ Gel Base and PLO Gel Mediflo™ 30 Compound Kit.

Diclofenac Sodium is a nonsteroidal anti-inflammatory drug (NSAID) that has analgesic, anti-inflammatory, and antipyretic properties, and has been found to be effective in treating a variety of acute and chronic pain and inflammatory conditions. A stability study was designed to assess the physical, chemical, and antimicrobial stability of three extemporaneously compounded bracketed Diclofenac Sodium formulations over time using a validated, stability indicating HPLC method. Diclofenac Sodium 1% and 15% were compounded in Medisca VersaPro™ Cream Base, VersaPro™ Gel Base and PLO Gel Mediflo™30 Compound Kit and stored at room temperature, in tightly closed, light resistant, plastic containers for 180 days. The organoleptic properties, pH, viscosity, and Diclofenac Sodium concentration of each formulation were evaluated at predetermined time points. Antimicrobial effectiveness testing of the compounded formulation according to USP <51> was also evaluated at the initial time point and after 180 days. The results demonstrated that all formulations remained within the specified stability criteria for the duration of the study. Therefore, an extended beyond-use-date of 180 days may be assigned to these compounded formulations under the studied conditions.

A Genome-Wide Association Study of Oxypurinol Concentrations in Patients Treated with Allopurinol.

Cohort studies have identified several genetic determinants that could predict the clinical response to allopurinol. However, they have not been commonly used for genome-wide investigations to identify genetic determinants on allopurinol metabolism and concentrations. We conducted a genome-wide association study of a prior cross-sectional investigation of patients from the Montreal Heart Institute Biobank undergoing allopurinol therapy. Four endpoints were investigated, namely plasma concentrations of oxypurinol, the active metabolite of allopurinol, allopurinol, and allopurinol-riboside, as well as allopurinol daily dosing. A total of 439 participants (mean age 69.4 years; 86.4% male) taking allopurinol (mean daily dose 194.5 mg) and who had quantifiable oxypurinol concentrations were included in the genome-wide analyses. Participants presented with multiple comorbidities and received concomitant cardiovascular medications. No association achieved the predefined genome-wide threshold values for any of the endpoints (all p > 5 × 10-8). Our results are consistent with prior findings regarding the difficulty in identifying genetic determinants of drug concentrations or pharmacokinetics of allopurinol and its metabolites, as well as allopurinol daily dosing. Given the size of this genome-wide study, collaborative investigations involving larger and diverse cohorts may be required to further identify pharmacogenomic determinants of allopurinol and measure their clinical relevance to personalize allopurinol therapy.

Nystatin nanosizing enhances in vitro and in vivo antifungal activity against Candida albicans.

OBJECTIVES: In this study, we developed a nanoparticulate nystatin formulation and performed a comparative evaluation against a commercial nystatin preparation of its in vitro and in vivo antifungal activities. METHODS: A nystatin nanosuspension was prepared from a commercially available suspension by wet-media milling. The nanosuspension was characterized for particle size by laser diffraction and assayed for content by HPLC. Its in vitro activity was evaluated against Candida albicans strains SC5314 and LAM-1 (12.5-5000 µg/mL) using an agar plate assay and its in vivo efficacy was evaluated using a murine model of oral candidiasis. Briefly, DBA/2 mice were immunosuppressed with cortisone acetate, orally infected with C. albicans strain LAM-1, and treated for 14 days with conventional nystatin suspension, nystatin nanosuspension or saline control. Efficacy endpoints were oral fungal burden, mouse survival and organ histopathology. A single-dose pharmacokinetic study was also performed. RESULTS: The median particle size of the nystatin suspension was reduced from 6577 to 137 nm. The HPLC assay demonstrated a nystatin content of 98.7% ±â€Š0.8% of the label claim. In vitro activity was superior to that of the conventional nystatin suspension at 100-5000 µg/mL concentrations. Beginning on day 3 of treatment, lower oral burdens of C. albicans were found in the nanosuspension group compared with the suspension and control groups. Mouse survival was also superior in the nanosuspension group. No systemic absorption was observed. CONCLUSIONS: Taken together, these data reveal that nanonization of nystatin provides a novel approach to enhancing its efficacy in the treatment of oral candidiasis.

PEGylated bile acids for use in drug delivery systems: enhanced solubility and bioavailability of itraconazole.

Itraconazole is a drug of choice for the treatment of severe fungal infections and parasitic diseases, but its use is limited by its low water solubility and varying bioavailability. New self-emulsifying drug delivery systems (SEDDS) based on PEGylated bile acids (BA-PEGs) were designed and prepared, where the number and length of PEG arms were varied to optimize the loading of itraconazole in the final drug formulation. The use of both BA-PEGs and oleic acid improved the solubilization and absorption of the drug, which was in a glassy state in the SEDDS prepared with the melting method. High loading efficiencies of itraconazole (up to 20%) and stable liquid formulations were obtained at neutral pH, and full dispersion of itraconazole was reached in 2 h in simulated intestinal fluid (pH 6.8). Aqueous emulsions consisting of spherical micelles with mean hydrodynamic diameters (Dh) of ca. 75-220 nm, as verified by transmission electron microscopy and dynamic light scattering, are expected to improve the intestinal absorption of the drug. The new SEDDS showed good cytocompatibility by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays of BA-PEGs with Caco-2 and RAW 264.2 cells, and a low degree of hemolysis of human erythrocytes. The SEDDS based on PEGylated bile acids provide a controlled release system with significant improvement of the bioavailability of itraconazole in rats, as demonstrated by the pharmacokinetic studies.

Visual compatibility and particle counter evaluations of syringes of intramuscular psychotropic coadministered solutions.

BACKGROUND: Patients in the acute phase of agitation can require the administration of multiple drugs by intramuscular injection in order to temporarily stabilise their condition. Administration of multiple psychotropic medications in a single syringe can be beneficial to both the patient and healthcare professionals. However, there are very little data in the literature regarding psychotropic drug compatibility in syringes for acute agitation. OBJECTIVE: The aim of this study was to assess the visual compatibility of various combinations of 12 intramuscular psychotropic medications in syringes, and to validate compatibility with the use of a particle counter. The medications evaluated were benztropine mesylate, diazepam, dimenhydrinate, diphenhydramine hydrochloride, haloperidol lactate, hydroxyzine, lorazepam, loxapine, methotrimeprazine, midazolam, olanzapine and zuclopenthixol acetate. METHODS: Compounded solutions of medication combinations underwent visual inspection initially and after 0.25, 0.5, 1, 2 and 4 hours using a white background and a black background. In order to validate the compatibility results, the presence of particulate matter was determined by light obscuration. RESULTS: This study identified 35 combinations that were visually compatible and 35 that were visually incompatible. We chose eight highly clinically relevant combinations to test using the requirements of the United States Pharmacopoeia (USP) chapter 788 (Particulate Matter in Injections). Of those eight, six were physically compatible, including the triple combinations of lorazepam and haloperidol with either benztropine or diphenhydramine. CONCLUSION: These physical compatibility results will give healthcare professionals an idea of the possible compatible combinations of psychotropic drugs in syringes, and thus complete some of the missing data in the literature.

Transfer of Mexiletine into Breast Milk: A Case Report.

Background: Mexiletine is a class 1B antiarrhythmic agent, used to treat ventricular arrhythmias, and noncardiac-related problems such as myotonia. Limited safety data are available on the transfer of this drug into breast milk. Case Report: We report the case of a woman diagnosed with myotonia congenita who breastfed two children after two consecutive pregnancies. During the breastfeeding of the first and the second infant, she collected, respectively, five and seven samples at 0, 2, 4, 6, and 8 hours and 0, 1, 2, 3, 4, 6, and 8 hours after taking 200 mg of mexiletine thrice daily for seven doses. One week after the collection, samples were analyzed with a validated liquid chromatography tandem mass spectrometry method. No side effect was observed in either child according to the mother. Results: Using the mean milk concentrations, it is estimated that an exclusively breastfed infant would receive a maximum of 5.14% of the initial pediatric mexiletine dosage. We calculated a maximum of 2.67% for the first infant in our case, considering a nonexclusive breastfeeding. Maximal concentrations were observed 1-2 hours after the dose of mexiletine. Results seem to be in accordance with the two cases previously published. Conclusions: Mexiletine transfers into breast milk in low levels. However, results are obtained from only one woman. Therefore, caution should be used when mexiletine is prescribed to breastfeeding women. More cases are needed to evaluate the interindividual variability and to guide women regarding breastfeeding with mexiletine.

Y-site simulation compatibility study of 10% calcium salts with various injectable solutions during toxicological resuscitation.

PURPOSE: To determine the physical compatibility of 10% calcium chloride and 10% calcium gluconate in combination with injectable solutions, administered in the paediatric and adult intensive care unit setting during toxicological resuscitation involving calcium channel blockers and beta-blockers. METHODS: Forty-eight combinations were prepared at room temperature, including the following products: calcium chloride, calcium gluconate, insulin, epinephrine, norepinephrine, highly concentrated dextrose solution, sodium chloride, Plasma-Lyte A and Ringer's lactate. A visual evaluation at times 0, 1, 4, 24, 48 and 72 hours and a particle count test with the LS-20 particle counter at times 0, 4, 24 and 72 hours were performed. The admixtures were considered incompatible if there was a precipitate, a colour change, turbidity, viscosity or a gas formation. The stability of calcium salts was also tested in empty IV bags and syringes by the particle count test. RESULTS: All drug mixtures were found to be compatible by visual evaluation and using the particle counter based on United States Pharmacopoeia chapter 788 (USP<788>) specifications. Calcium salts were compatible with insulin and vasopressors in the tested combinations. The stability of 10% calcium salts in empty IV bags and polypropylene syringes was demonstrated for up to 48 hours at room temperature. CONCLUSION: All the combinations tested were physically compatible for up to 72 hours at room temperature. Clinical use of calcium salt infusions, at an undiluted concentration, in combination with these injectable solutions in a toxicological resuscitation context is considered clinically acceptable.

Females present higher dose-adjusted drug concentrations of metoprolol and allopurinol/oxypurinol than males.

Females present a higher risk of adverse drug reactions. Sex-related differences in drug concentrations may contribute to these observations but they remain understudied given the underrepresentation of females in clinical trials. The aim of this study was to investigate whether anthropometric and socioeconomic factors and comorbidities could explain sex-related differences in concentrations and dosing for metoprolol and oxypurinol, the active metabolite of allopurinol. We conducted an analysis of two cross-sectional studies. Participants were self-described "White" adults taking metoprolol or allopurinol selected from the Montreal Heart Institute Hospital Cohort. A total of 1007 participants were included in the metoprolol subpopulation and 459 participants in the allopurinol subpopulation; 73% and 86% of the participants from the metoprolol and allopurinol subpopulations were males, respectively. Females presented higher age- and dose-adjusted concentrations of both metoprolol and oxypurinol (both p < 0.03). Accordingly, females presented higher unadjusted and age-adjusted concentration:dose ratio of both metoprolol and allopurinol/oxypurinol compared to males (all p < 3.0 × 10-4 ). Sex remained an independent predictor of metoprolol concentrations (p < 0.01), but not of oxypurinol concentrations, after adjusting for other predictors. In addition to sex, age, daily dose, use of moderate to strong CYP2D6 inhibitors, weight, and CYP2D6 genotype-inferred phenotype were associated with concentrations of metoprolol (all p < 0.01). Daily dose, weight, estimated glomerular filtration rate (eGFR), and employment status were associated with oxypurinol concentrations (all p < 0.01). Females present higher dose-adjusted concentrations of metoprolol and oxypurinol than males. This suggests the need for sex-specific dosing requirements for these drugs, although this hypothesis should be validated in prospective studies.

Pharmacogenomic markers of metoprolol and α-OH-metoprolol concentrations: a genome-wide association study.

Aim: Few genome-wide association studies (GWASs) have been conducted to identify predictors of drug concentrations. The authors therefore sought to discover the pharmacogenomic markers involved in metoprolol pharmacokinetics. Patients & methods: The authors performed a GWAS of a cross-sectional study of 993 patients from the Montreal Heart Institute Biobank taking metoprolol. Results: A total of 391 and 444 SNPs reached the significance threshold of 5 × 10-8 for metoprolol and α-OH-metoprolol concentrations, respectively. All were located on chromosome 22 at or near the CYP2D6 gene, encoding CYP450 2D6, metoprolol's main metabolizing enzyme. Conclusion: The results reinforce previous findings of the importance of the CYP2D6 locus for metoprolol concentrations and confirm that large biobanks can be used to identify genetic determinants of drug pharmacokinetics at a GWAS significance level.

Impact of amiodarone use on metoprolol concentrations, α-OH-metoprolol concentrations, metoprolol dosing and heart rate: A cross-sectional study.

Small studies suggest that amiodarone is a weak inhibitor of cytochrome P450 (CYP) 2D6. Inhibition of CYP2D6 leads to increases in concentrations of drugs metabolized by the enzyme, such as metoprolol. Considering that both metoprolol and amiodarone have ß-adrenergic blocking properties and that the modest interaction between the two drugs would result in increased metoprolol concentrations, this could lead to a higher risk of bradycardia and atrioventricular block. The primary objective of this study was to evaluate whether metoprolol plasma concentrations collected at random timepoints from patients enrolled in the Montreal Heart Institute Hospital Cohort could be useful in identifying the modest pharmacokinetic interaction between amiodarone and metoprolol. We performed an analysis of a cross-sectional study, conducted as part of the Montreal Heart Institute Hospital Cohort. All participants were self-described "White" adults with metoprolol being a part of their daily pharmacotherapy regimen. Of the 999 patients being treated with metoprolol, 36 were also taking amiodarone. Amiodarone use was associated with higher metoprolol concentrations following adjustment for different covariates (p = .0132). Consistently, the association between amiodarone use and lower heart rate was apparent and significant after adjustment for all covariates under study (p = .0001). Our results highlight that single randomly collected blood samples can be leveraged to detect modest pharmacokinetic interactions.