Do P-glycoprotein Medications Alter the Risk of Ventriculoperitoneal Shunt in Adults with Hydrocephalus?

Hydrocephalus is a disorder caused by excess fluid accumulation in the brain and results in brain damage with consequent cognitive and physical problems. This condition has no cure; the only treatment is brain surgery. Experimental data indicate that P-glycoprotein (P-gp) plays a crucial role in the pathogenesis of hydrocephalus due to its function in clearing macromolecules from the brain. Numerous medications frequently used are classified as P-gp inducers or inhibitors, and comprehending their effects may aid in attaining improved patient outcomes. Therefore, in this single-center retrospective study, we examined the risk of the need for ventriculoperitoneal shunt placement over 10 years among 4588 adult patients with hydrocephalus not exposed to any P-gp inhibitors/inducers or exclusively exposed to either P-gp inhibitors or inducers. Our analysis shows that patients exposed to P-gp inhibitors had a 3.2 times higher risk of requiring ventriculoperitoneal shunt surgery (P < .0001). In contrast, the relative risk was not significantly affected (P = .07) among those exposed to P-gp inducers. Our findings indicate the need for caution when prescribing P-gp inhibitors to patients with hydrocephalus. Additional studies using larger cohorts are required to confirm whether P-gp inducers in patients with hydrocephalus can mitigate the risk of ventriculoperitoneal shunt.

Validation and Clinical Utility of the hERG IC50:Cmax Ratio to Determine the Risk of Drug-Induced Torsades de Pointes: A Meta-Analysis

BACKGROUND

Use of the QT interval corrected for heart rate (QTc) on the electrocardiogram (ECG) to predict torsades de pointes (TdP) risk from culprit drugs is neither sensitive nor specific. The ratio of the half-maximum inhibitory concentration of the hERG channel (hERG IC50) to the peak serum concentration of unbound drug (C_max ) is used during drug development to screen out chemical entities likely to cause TdP.

PURPOSE

To validate the use of the hERG IC50:C_max ratio to predict TdP risk from a culprit drug by its correlation with TdP incidence.

DATA SOURCES

Medline (between 1966 and March 2017) was accessed for hERG IC50 and C_max values from the antihistamine, fluoroquinolone, and antipsychotic classes to identify cases of drug-induced TdP. Exposure to a culprit drug was estimated from annual revenues reported by the manufacturer.

STUDY SELECTION

Inclusion criteria for TdP cases were provision of an ECG tracing that demonstrated QTc prolongation with TdP and normal serum values of potassium, calcium, and magnesium. Cases reported in patients with a prior rhythm disturbance and those involving a drug interaction were excluded.

DATA EXTRACTION AND SYNTHESIS

The Meta-Analysis of Observational Studies in Epidemiology checklist was used for epidemiological data extraction by two authors.

MAIN OUTCOME AND MEASURE

Negligible risk drugs were defined by an hERG IC50:C_max ratio that correlated with less than a 5% chance of one TdP event for every 100 million exposures (relative risk [RR] 1.0).

RESULTS

The hERG IC50:C_max ratio correlated with TdP risk (0.312; 95% confidence interval 0.205-0.476, p<0.0001), a ratio of 80 (RR 1.0). The RR from olanzapine is on par with loratadine; ziprasidone is comparable with ciprofloxacin. Drugs with an RR greater than 50 include astemizole, risperidone, haloperidol, and thioridazine.

CONCLUSIONS

The hERG IC50:C_max ratio was correlated with TdP incidence for culprit drugs. This validation provides support for the potential use of the hERG IC50:C_max ratio for clinical decision making in instances of drug selection where TdP risk is a concern.

Asystole Associated with Lidocaine Use in a Hyperkalemic Patient during Advanced Cardiac Life Support

A case report of fatal asystole associated with use of lidocaine in a hyperkalemic patient is presented. The patient was a 61–year-old man with a rapidly increasing serum potassium level related to acute renal failure. Ventricular tachycardia with a pulse developed twice, for which lidocaine was administered according to the American Heart Association's ACLS protocol. Both episodes were immediately followed by asystole, the second of which was terminal. Available information suggests that this phenomenon can be explained by a synergistic effect on membrane responsiveness and conduction velocity. Thus, extreme caution should be exercised in the use of lidocaine when ventricular tachycardia complicates severe hyperkalemia.

The metabolic rationale for a lack of cross-reactivity between sulfonamide antimicrobials and other sulfonamide-containing drugs

Sulfonamide antimicrobials (sulfamethoxazole) contain an arylamine group, oxidized by CYP2C9 to the hydroxylamine with subsequent auto-oxidation to a highly reactive [-nitroso-] intermediate is a necessary (if not sufficient) cause of drug hypersensitivity. Accordingly, xenobiotics that do not contain an arylamine cannot generate this reactive intermediate and do not cross react with sulfonamide antimicrobials. Despite this well-attested observation, product labeling and direct-to-consumer advertising for non-arylamine therapeutic classes of drugs containing the sulfonamido- functional group persist with a warning of the potential for cross-reactivity. It is hoped that by offering an explicit rationale for the lack of cross-reactivity will provide medical practitioners with a level comfort to proceed with prescribing medications such as thiazide diuretics and celecoxib for patients with a history of hypersensitivity to sulfonamide antimicrobials.

The Cardiovascular Toxicity of Selective and Nonselective Cyclooxygenase Inhibitors: Comparisons, Contrasts, and Aspirin Confounding

The premature suspension of the Alzheimer Disease Anti-inflammatory Prevention (ADAPT) and the Adenoma Prevention with Celecoxib (APC) trials prompted intense review of the cardiovascular safety profile of selective and nonselective cyclooxygenase (COX) inhibitors. This article reviews the current state of selective COX-2 inhibitors, discusses the mechanistic evidence underlying the cardiovascular risk associated with selective COX-2 inhibition, outlines the pharmacodynamics of aspirin effects on platelets and the interference of propionic acid derivatives (ibuprofen and naproxen) with these effects, and poses that aspirin confounding may have led to the erroneous conclusion of naproxen-associated adverse cardiovascular outcomes in the ADAPT trial. Finally, recommendations regarding selective COX-2 inhibitors and appropriate timing of aspirin coadministration with traditional NSAIDs are proposed in relevance to patient safety and future trial design.

Hospital Pharmacology: An Alternative Model for Practice and Training in Clinical Pharmacology

External pressures continue to be exerted on hospitals to prioritize programs that minimize costs and improve the safety of medication use. Clinical pharmacologists are in an ideal position to provide leadership for such programs. At academic health centers, an added dimension is the exposure of physicians-in-training to the practical application of clinical pharmacology principles. At SUNY Upstate Medical University, the approach is led by a physician with clinical pharmacists and pharmacy practice residents. To align the clinical pharmacists with the overall goals of the program, a faculty promotions track system designed specifically for them has been enacted within the college of medicine. This report summarizes the "hospital pharmacology" program that provides funding for an academic physician-clinical pharmacologist. With this report, the authors hope to outline an alternative practice and training paradigm to potentially address the decline in physicians being trained in and practicing clinical pharmacology since the late 1970s.

Polymorphisms and the Pocketbook: The Cost-Effectiveness of Cytochrome P450 2C19 Genotyping in the Eradication ofHelicobacter pyloriInfection Associated with Duodenal Ulcer

The clinical outcome of duodenal ulcer treated with proton pump inhibitor (PPI)-based, anti-Helicobacter pylori (H.p.) regimens varies according to cytochrome P450 2C19 (CYP2C19) genotype. CYP2C19 genotypes differ markedly in peoples of Pacific Rim descent compared with another ethnicity. The authors sought to determine the specific impact that these factors have on the cost-effectiveness of duodenal ulcer management. Their model consisted of two patient cohorts with Helicobacter pylori and duodenal ulcer, trichotomized into CYP2C19 homozygous extensive metabolizers (EMs), heterozygous EMs, and poor metabolizers (PMs), altering the anti-H.p. regimen in the genotyped cohort only. The authors took the perspective of a third-party payer, and the denominator was ulcer episode prevented. In the reference case, the use of CYP2C19 genotyping prior to initiating anti-H.p. therapy was dominant (costs were saved with each ulcer episode prevented) in all geographic regions of the United States. The subsequent break-even analysis showed a range of 89.20 dollars to 118.96 dollars--from Hawaii to the Midwest, respectively--required to eliminate the cost-savings from each genotype test performed. Using probabilities most unfavorable to genotyping, the variation of peoples with Pacific Rim origins from 0% to 100% altered the cost-effectiveness from 495 dollars to 2125 dollars per ulcer event prevented, respectively. The results suggest that treatment decisions for H.p. infection that are based on a patient's CYP2C19 genotype decreases expenses for health plans implementing testing. This analysis provides an economic basis to support recent calls to expand this technology into routine clinical care to prevent toxicity of narrow therapeutic index drugs.

Every Error a Treasure: Improving Medication Use with a Nonpunitive Reporting System

BACKGROUND

The fear of reprisal, combined with the additional time required for reporting, are significant disincentives to reporting of medical events. Such considerations provided an incentive for the Upstate Medical University Hospital (Syracuse, New York) to develop monitoring systems to decrease the potential for drug harm. IMPLEMENTING A NONPUNITIVE REPORTING SYSTEM: Previously, a convenient, point-based score card system for punishment and remediation led to underreporting and hindered the identification of safety improvement opportunities in medication use processes. Nursing buy-in was accomplished through careful initial negotiations that emphasized that patients were best served by learning from errors in the medication use process. The revised medication event reporting policy, as established in October 2000 for all staff, severed the link between reporting errors and performance evaluations.

RESULTS

Data collected 18 months before the policy change was compared with data collected after the policy change was enacted in October 2000. The number of reports received each month increased from an average of 19 to 102 (p < .001).

DISCUSSION

Substantive quality improvements in medication have been achieved by using a systematic approach to the analysis of the markedly increased number of reported medication events following the introduction of a nonpunitive reporting system.

Profound metoprolol-induced bradycardia precipitated by acetaminophen-propoxyphene

Pharmacokinetic studies demonstrate that propoxyphene is a potent inhibitor of cytochrome P450 (CYP) 2D6. Clinically significant sequelae have not been previously reported. We report a case of this inhibition manifested by life-threatening bradycardia in a patient receiving a CYP2D6 substrate, metoprolol. A 48-year-old man came to the emergency department complaining of dizziness 3 hours after ingesting metoprolol, at his usual dose, and 2 tablets of propoxyphene, newly begun postoperatively. Four hours after ingestion of both drugs, the patient was noted to have a ventricular rate of about 30 beats/min with underlying atrial fibrillation. The patient's ventricular response returned to normal within 11 hours of ingestion. We have demonstrated the clinical importance of the interaction between propoxyphene and metoprolol likely resulting from inhibition of hepatic clearance of metoprolol by propoxyphene. Underscoring the clinical relevance of CYP2D6 inhibition by an analgesic of questionable efficacy should proscribe its use.

Observation and experiment on the cusp of collaboration: a parallel examination of clinical pharmacology and pharmacoepidemiology

Despite a common interest in the effect of drugs in humans, clinical pharmacologists and pharmacoepidemiologists often operate in isolation since the knowledge base underlying the respective parent disciplines of pharmacology and epidemiology is quite distinct. This lack of communication may lead to a potential for lost opportunities that would otherwise be mutually beneficial. Accordingly, this article juxtaposes the two disciplines to emphasize common areas of interest despite differences in methodology. In addition, weaknesses and strengths are contrasted in an effort to document the mirror image nature of both clinical pharmacology and pharmacoepidemiology in this regard. Specific examples underlying the complementary nature of the two disciplines are also offered that may help to stimulate collaboration. The possibility of greater formal cooperation between societies representing the two disciplines is also suggested to cross-educate both clinical pharmacologists and pharmacoepidemiologists as a means to foster collaboration.

The association of opportunistic infections with the occurrence of trimethoprim/sulfamethoxazole hypersensitivity in patients infected with human immunodeficiency virus

Hypersensitivity from trimethoprim/sulfamethoxazole (TMP/SMX) has been linked to a reactive nitroso intermediate from sulfamethoxazole metabolism, which may be altered in patients with human immunodeficiency virus (HIV) infection. The authors determined the clinical factors that are associated with TMP/SMX hypersensitivity in patients with HIV. In a case control study, 54 controls currently tolerating TMP/SMX prophylaxis were randomly matched by date of hypersensitivity reaction in case patients to 28 patients with a history of a rash consistent with erythema multiforme from TMP/SMX. Demographic data, coadministered medications, laboratory data, and histories of opportunistic infections were extracted on all patients. A highly significant association was observed between the number of opportunistic infections and the occurrence of TMP/SMX hypersensitivity (p < 0.001), despite comparability of CD4 counts between case patients and controls (p > 0.1). A tendency for protection from TMP/SMX hypersensitivity in blacks was also observed (p = 0.066). These observations suggest that the mechanisms by which HIV produces cellular immune dysfunction and alters drug detoxification may be linked.

A pharmacoeconomic model to aid in the allocation of ambulatory clinical pharmacy services

Drugs of choice in secondary prevention strategies reduce complication rates of certain diseases. Unfortunately, these strongly indicated drugs remain underused. A model was developed to predict the cost-effectiveness of clinical pharmacy services assumed to improve use of drugs of choice to unity in hypothetical cohorts of three diseases that commonly accompany hypertension and in which clear drugs of choice exist. Use of angiotensin-converting enzyme (ACE) inhibitors in patients with diabetes who have proteinuria, use of beta blockers after myocardial infarction, and use of ACE inhibitors in patients with asymptomatic left ventricular dysfunction were analyzed. Clinical pharmacy services could be cost-saving in all three diseases in this model if use of the drug of choice in standard practice did not exceed 0.899 in patients with diabetes who have proteinuria, 0.512 in patients after infarct, and 0.804 in patients with asymptomatic left ventricular dysfunction. This model may help decision makers by accessing local patient demographics and prescribing habits before any resource allocation.

The effect of cimetidine on the formation of sulfamethoxazole hydroxylamine in patients with human immunodeficiency virus

Hypersensitivity reactions from trimethoprim/sulfamethoxazole are likely caused by a reactive nitroso intermediate formed from sulfamethoxazole hydroxylamine. This pilot study tested whether cimetidine inhibits the urinary excretion of sulfamethoxazole hydroxylamine. Ten outpatients infected with human immunodeficiency virus (HIV) and currently receiving trimethoprim/sulfamethoxazole prophylaxis were randomly selected from 59 eligible patients. Five received cimetidine 800 mg twice daily for 1 week and five served as controls. Two spot urine samples one week apart were obtained after a trimethoprim/sulfamethoxazole dose for all patients. Patients taking cimetidine had a significant decrease in excretion of sulfamethoxazole hydroxylamine relative to total excreted drug in the two urine samples compared with control patients. Cimetidine likely caused this decrease in sulfamethoxazole hydroxylamine excretion through inhibition of CYP3A4. Because of potential differences between HIV-infected patients and healthy subjects in oxidative metabolism, future studies of inhibitors of sulfamethoxazole hydroxylamine formation should be conducted in the HIV population.

Anticonvulsant usage is associated with an increased risk of procarbazine hypersensitivity reactions in patients with brain tumors

BACKGROUND

Procarbazine usage in brain tumors has a high incidence of hypersensitivity reactions compared with its use in other malignancies. Procarbazine oxidation to a reactive intermediate is enhanced by phenobarbital. Patients with primary brain tumors would have a preferential exposure to anticonvulsants compared to patients with other malignancies.

OBJECTIVE

To determine whether anticonvulsant exposure is associated with procarbazine hypersensitivity reactions in patients with primary brain tumors.

METHODS

This retrospective cohort study included 83 patients with primary brain tumors who were treated with procarbazine between 1981 and 1996 at a university hospital-based regional oncology center. Data were extracted by chart review. The data collected included age, sex, race, tumor type, smoking, alcohol usage, and all concomitant medications, as well as creatinine, aspartate aminotransferase, total bilirubin, and anticonvulsant serum levels. Anticonvulsant exposure was determined by the presence of detectable serum levels. Cases of procarbazine hypersensitivity reactions were identified through a review of progress notes.

RESULTS

There were 20 patients with procarbazine hypersensitivity reactions. A significant association between the exposure to anticonvulsants and the development of procarbazine hypersensitivity reactions was found (p = 0.05). In addition, there was a significant dose-response association between the development of procarbazine hypersensitivity and the presence of therapeutic anticonvulsant serum levels (p = 0.03).

CONCLUSIONS

Concomitant exposure to anticonvulsants is associated with procarbazine hypersensitivity reactions, possibly though a reactive intermediate generated by CYP3A isoform induction. All patients in this cohort received enzyme-inducing anticonvulsants. New anticonvulsants devoid of this property are available. These data support trials that use these newer agents for the prophylaxis of seizures in patients with brain tumors who are to receive procarbazine.

Comparisons of oxidative metabolism and reductive capacity in sulfonamide-tolerant and -intolerant patients with human immunodeficiency virus

Hypersensitivity reactions to trimethoprim/sulfamethoxazole occur with a high frequency in human immunodeficiency virus (HIV)-infected patients. This study tested whether differences in oxidative metabolism and plasma reductive capacity correlate with sulfonamide intolerance in patients with HIV. Eighteen stable outpatients with HIV were prospectively studied. Nine patients had documented histories of hypersensitivity reactions to trimethoprim/sulfamethoxazole and nine did not. Urinary caffeine metabolite ratios assessed the activity of two oxidative enzymatic pathways: cytochrome P-450 1A2 (demethylation) and 8-hydroxylation. Plasma cyst(e)ine was used as a measure of reductive capacity. The trimethoprim/sulfamethoxazole-intolerant group showed greater rates of 8-hydroxylation, lower rates of demethylation, and lower cyst(e)ine levels. The results of this pilot study extend previous observations of differences in oxidative metabolism and reductive capacity that exist within the population of HIV-infected individuals. In addition, these findings lay the groundwork for future interventional studies that could use agents to inhibit sulfonamide oxidation and increase reductive capacity in sulfonamide-intolerant patients with HIV when rechallenged with trimethoprim/sulfamethoxazole.

Primidone crystalluria following overdose. A report of a case and an analysis of the literature

Seven cases of crystalluria following primidone overdose have been reported since the 1950s. An eighth case of primidone crystalluria following overdose is presented. Because of low aqueous solubility (600 mg/L at 37 degrees C) which is directly proportional to temperature, any factor increasing renal excretion of unchanged primidone predisposes to crystal formation. Renal clearance is dependent on dosage because of negligible protein binding, zero-order conversion to phenobarbitone (phenobarbital) and first-order conversion to phenylethylmalonamide. Therapy with other anticonvulsants known to induce the metabolism to phenobarbitone does not appear to be protective against crystalluria in overdose situations. The critical serum primidone concentration for crystalluria presence seems to be 80 mg/L. There is evidence for nephrotoxicity of the crystals themselves if formed in vivo (actual crystal presence during voiding). The chemical phenomenon of supersaturation of a solution is protective against in vivo crystal formation with subsequent nephrotoxicity. Vigorous hydration to augment elimination and to lessen the propensity for renal toxicity is recommended.