Prescription of QT-prolonging drugs in a cohort of about 5 million outpatients

Many drugs prolong the QT interval and increase the risk of torsade de pointes. Concurrent use of two or more of these drugs can further increase the risk, but the prevalence of concurrent prescription of QT-prolonging drugs is not known. Using the administrative claims database of a national pharmaceutical benefit manager, we conducted a retrospective cohort study in 4,825,345 subjects aged 18 years or older. After identifying 50 drugs with QT-prolonging potential, and an additional 26 drugs that inhibit the metabolic clearance of QT-prolonging drugs, we measured the frequency of overlapping prescriptions for two or more of these drugs in the outpatient setting in 1999. Nearly 1.1 million subjects (22.8%) filled 4.4 million prescriptions for QT-prolonging drugs. Of these, 103,119 subjects (9.4%) filled overlapping prescriptions for two or more of the drugs or for a QT-prolonging drug and another drug that inhibits its clearance; 7249 subjects (0.7%) filled overlapping prescriptions for three or more of these drugs. Twenty-two percent of subjects who filled overlapping prescriptions were aged 65 or older; 74% were women. Antidepressants were involved in nearly 50% of the cases. Concurrent prescription of QT-prolonging drugs is common in the outpatient setting, and antidepressants are involved in half of these cases. Large pharmaceutical claims databases are useful for detecting potentially harmful prescribing behaviors, but better clinical evidence on medication safety is needed before such a system can be implemented fully.

Teaching rational prescribing: a new clinical pharmacology curriculum for medical schools

In most U.S. and Canadian medical schools, pharmacology is taught during the preclinical year 2 of the 4-year-long curriculum. This is despite the fact that medical school graduates and residency directors have identified teaching rational therapeutics as a priority. Hence, we have developed a core curriculum in clinical pharmacology for 4th-year medical students that builds on the core principles of rational therapeutics described by Nierenberg 10 years ago (Nierenberg, DW. Clin Pharmacol Ther 1990; 48:606-610). Here we report on our 3-year experience teaching this course, which addresses the following teaching objectives: to teach medical students on how to (1) critically evaluate medications; (2) obtain a complete medication history including herbal and over-the-counter medications; (3) apply pharmacokinetic principles to clinical practice; (4) recognize and report adverse drug events and interactions; (5) optimize pain management; (6) recognize and treat substance abuse and poisoning; and (7) prescribe rationally regardless of prescribing environment. Student assessment was in the form of multiple-choice and formative oral examinations, which were validated against the clinical part of the U.S. medical licensing examination. The course significantly increased the student rating of clinical pharmacology teaching measured by a national survey of U.S. medical school graduates. We conclude that this course may be useful for teaching rational prescribing to medical students. With the guidance and educational material provided by this article, a successful implementation of such a course should be possible in most medical schools.

The roles of CYP2D6 and stereoselectivity in the clinical pharmacokinetics of chlorpheniramine

AIMS

To examine the stereoselective disposition of chlorpheniramine and to evaluate the role of CYP2D6 in chlorpheniramine pharmacokinetics in humans.

METHODS

Eight healthy volunteers (six extensive metabolizers with respect to CYP2D6 and two poor metabolizers) received a single 8 mg oral dose of rac-chlorpheniramine either given alone or following administration of quinidine 50 mg every 6 h for 2 days prior to the study day and every 6 h thereafter until the end of the study. Plasma concentrations of (S)-(+)- and (R)-(-)-enantiomers of chlorpheniramine were determined using liquid chromatography/mass spectrometry.

RESULTS

In extensive metabolizers, mean Cmax was greater (12.55+/-1.51 ng ml-1vs 5.38+/-0.44 ng ml-1) and CLoral was lower (0.49+/-0.08 l h-1 kg-1vs 1.07+/-0.15 l h-1 kg-1) for (S)-(+)- than for (R)-(-)-chlorpheniramine (P<0.005). For (S)-(+)-chlorpheniramine, administration of quinidine, an inhibitor of CYP2D6, resulted in an increase in Cmax to 13.94+/-1.51 (P<0.01), a reduction in CLoral to 0.22+/-0.03 l h-1 kg-1 (P<0.01), and a prolongation of elimination half-life from 18.0+/-2.0 h to 29.3+/-2.0 h (P<0.001). Administration of quinidine decreased CLoral for (R)-(-)-chlorpheniramine to 0.60+/-0.10 l h-1 kg-1 (P<0.005). In CYP2D6 poor metabolizers, systemic exposure was greater after chlorpheniramine alone than in extensive metabolizers, and administration of quinidine resulted in a slight increase in CLoral.

CONCLUSIONS

Stereoselective elimination of chlorpheniramine occurs in humans, with the most pharmacologically active (S)-(+)-enantiomer cleared more slowly than the (R)-(-)-enantiomer. CYP2D6 plays a role in the metabolism of chlorpheniramine in humans.

The enantioselective determination of chlorpheniramine and its major metabolites in human plasma using chiral chromatography on a beta-cyclodextrin chiral stationary phase and mass spectrometric detection

A sensitive enantioselective high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of plasma concentrations of (-)(R)- and (+)(S)-chlorpheniramine (CP) and their metabolites, desmethyl-chlorpheniramine (DCP), didesmethyl-chorpheniramine (DDCP) and chlorpheniramine N-oxide (CPNO). Enantioselective separations were achieved on a beta-cyclodextrin chiral stationary phase (CYCLOBOND I 2000) with a mobile phase consisting of diethylamine acetate (0.25%, pH 4.4):methanol:acetonitrile [85:7.5:7.5, (v/v/v)]and a flow-rate of 0.5 ml/min. For CP, the enantioselectivity (alpha) of the separation was 1.12 with a resolution factor (R(s)) of 1.17. The method was validated for CP by using mass spectroscopy detection (MSD). Concentrations of each enantiomer could be measured down to 125 pg/ml from a 1-ml plasma sample. Extracted calibration curves were linear from 0.13 to 50.00 ng/ml for each enantiomer. The method was applied to samples from two clinical studies.

Olanzapine-induced rhabdomyolysis

OBJECTIVE

To report a possible case of olanzapine-induced rhabdomyolysis with concomitant lithium-induced pseudo-infarction electrocardiogram changes.

CASE SUMMARY

A 13-year-old white boy was admitted to the hospital with profound weakness and electrocardiogram (EGG) changes suggestive of myocardial damage after starting olanzapine and lithium. An adverse medication effect was not considered at the time of the patient's admission. The time course of onset of weakness was coincident with administration of olanzapine. ECG abnormalities are a known manifestation of lithium therapy

DISCUSSION

This is a case description of olanzapine-induced rhabdomyolysis. Although other antipsychotic agents have been reported to cause rhabdomyolysis, an adverse drug reaction was not initially part of this patient's differential diagnosis. The patient had begun reporting rnyalgias six days after starting olanzapine. Fourteen days later, these symptoms forced him to bed rest; lithium was added for behavior misinterpreted as disobedience and oppositional disorder. Only when medications were considered as cause of the weakness and EGG changes, was the true nature of the patient's illness discovered.

CONCLUSIONS

Olanzapine, like other neuroleptic agents, can cause rhabdomyolysis. Lithium can cause multiple EGG changes that can be misinterpreted as myocardial damage. Medication effects and adverse effects must always be considered in any disease complex.

Visual hallucination and tremor induced by sertraline and oxycodone in a bone marrow transplant patient

The authors report a case of probable serotonin syndrome caused by the coadministration of sertraline and oxycodone. A 34 year-old male patient experienced visual hallucinations and severe tremor after dramatically increasing his dosage of oxycodone while on stable amounts of sertraline and cyclosporin. Discontinuation of cyclosporin did not result in resolution of his symptoms. Consideration of a possible sertraline-oxycodone interaction led to withholding sertraline, which resulted in symptom resolution. Serotonin syndrome has been noted with sertraline in combination with other drugs, but this is the first report in combination with a narcotic analgesic. Possible pharmacological mechanisms are discussed. In complicated patients that are taking multiple medications, physicians should be aware of this possible interaction to avoid delay in the diagnosis of serotonin syndrome.

Determination of clemastine in human plasma by gas chromatography with nitrogen-phosphorus detection

A method for the quantitative determination of clemastine in human plasma has been developed and validated. The assay uses gas chromatography with nitrogen-phosphorus detection and a HP-1 capillary column (25 mx0.22 mm, film thickness 0.33 mm) coated with dimethylpolysiloxane. Clemastine (with orphenadrine as internal standard) was isolated from human plasma using liquid-liquid extraction. A linear relationship was observed between 0.1 and 12.8 ng/ml using the peak area ratio of clemastine to orphenadrine with a correlation coefficient greater than 0.99 (the detection limit for clemastine was 0.06 ng/ml). The intra- and inter-day coefficients of variation were less than 11%. The developed method was used for the analysis of plasma samples from healthy volunteers (n = 19) to examine the pharmacokinetics of the antihistamine clemastine after single and multiple oral doses of clemastine fumarate.

Quantification of human H1 histamine receptor mRNA from peripheral blood

STUDY OBJECTIVE

To develop a reverse transcription (RT)-polymerase chain reaction (PCR) technique to detect and quantify human histamine1 (H1) receptor mRNA in peripheral blood.

METHODS

Primer pairs were based on the human H1 receptor nucleotide sequence. A competitive reference standard (CRS) was developed that used the same primers as wild-type mRNA but contained a 92-bp deletion. RT-PCR was performed with 5 microg of total RNA obtained from venous blood of six subjects that was added to known concentrations of CRS RNA. Linear regression comparing wild-type with CRS product was used to quantify wild-type mRNA.

MEASUREMENTS AND MAIN RESULTS

Three subjects had detectable H1 mRNA, with a range of 31-435 pg. In three subjects PCR product was not detected, although the presence of RNA was confirmed. Redesigned primer pairs showed mRNA to H1 receptor in two of the remaining subjects, but it was undetectable in the third.

CONCLUSION

RT-PCR can be used to detect and quantify human H1 receptor mRNA from peripheral blood.

Affinities of brompheniramine, chlorpheniramine, and terfenadine at the five human muscarinic cholinergic receptor subtypes

Anticholinergic effects are presumed to be the mechanism for the efficacy of chlorpheniramine in symptomatic relief of the common cold. Terfenadine, a second-generation antihistamine, reportedly lacks anticholinergic side effects. We evaluated affinities of two commonly used over-the-counter antihistamines, brompheniramine and chlorpheniramine, as well as terfenadine in comparison with atropine at the five human muscarinic cholinergic receptor subtypes using CHO cells stably transfected with the individual subtypes. Atropine was more potent than all three drugs at m1-m5 (p<0.01). No significant difference was observed between chlorpheniramine and brompheniramine. Atropine, brompheniramine, and chlorpheniramine could not discriminate between m1-m5. Terfenadine demonstrated subtype selectivity at m3. In vitro comparisons in human muscarinic receptor subtypes could potentially be used to predict clinical anticholinergic effects of antihistamines and to target receptor-specific effects of such agents.

Adenosine A1-receptor occupancy predicts A1-receptor antagonist effects of N-0861

OBJECTIVE

To evaluate the relationship between dose of N-0861 ([+/-]N6-endo-norbornan-2-yl-9-methyladenine), N-0861 plasma concentrations, and antagonism of adenosine-induced slowing of atrioventricular nodal conduction and to evaluate A1-receptor occupancy by antagonist present in plasma of subjects after administration of N-0861 to determine A1-selectivity of these effects.

METHODS

The study was conducted in patients undergoing a clinically indicated electrophysiology study to evaluate atrioventricular nodal conduction. Nineteen subjects were enrolled in the study and received adenosine (60 to 140 microg/kg) before or during a bolus dose and maintenance infusion of specific doses of N-0861. Adenosine-induced slowing of atrioventricular nodal conduction was determined by measuring A-H intervals on the intracardiac electrocardiograms. Plasma concentrations of N-0861 were determined with an HPLC method. A1-Receptor occupancy by antagonist present in plasma from identical time points was determined with use of a radioreceptor assay.

RESULTS

A linear relationship was shown between plasma concentration and dose of N-0861. A-H interval lengthening by 60 microg/kg adenosine was reduced by administration of N-0861. A linear relationship was observed between A1 occupancy and N-0861 concentration and between occupancy and antagonism of adenosine-induced A-H prolongation.

CONCLUSION

The results suggest that the effect of N-0861 on antagonism of adenosine-induced prolongation of A-H interval, at the doses used in this study, were the result of effects at the A1 receptor.

Amiodarone-induced lymphocyte toxicity and mitochondrial function

Amiodarone is one of the most effective antiarrhythmic drugs available. However, its use is often limited by potentially life-threatening toxicities, including hepatotoxicity and pulmonary toxicity. We have used human lymphocytes as a system in which to study amiodarone-induced cytotoxicity. Using a tetrazolium dye reduction assay, we observed amiodarone-induced cytotoxicity with a lethal dose (LD)50 of 10.0 +/- 31.1 microM (mean +/- SD, n = 5) with a cellular concentration of 2.2 +/- 0.2 million/ml and of 55.5 and 39.2 microM with cellular concentrations of 8.9 and 7.2 million/ml, respectively, after only 2.75 h of drug exposure. Damage to mitochondria, but not other organelles, was observed with electron microscopy at an amiodarone concentration of 7.3 microM. Alterations in ATP synthesis and lactate dehydrogenase (LDH) release from cells had concentration-response curves similar to those for cytotoxicity. However, we did not observe extracellular accumulation of adenine nucleotides. These results suggest that amiodarone may have a direct toxic effect on mitochondria, beginning at < 10 microM, with membrane-damaging effects at higher drug concentrations.

Chlorpheniramine plasma concentration and histamine H1-receptor occupancy

The plasma concentration-response relationship of the antihistamine chlorpheniramine is poorly characterized. This study examined concurrently the concentrations of chlorpheniramine and presence of H1-receptor antagonist in plasma after administration of 8 mg chlorpheniramine in normal volunteers. Six extensive metabolizers and five poor metabolizers, as judged by CYP2D6 phenotype (dextromethorphan metabolic ratio), were enrolled in the study. More than 80% occupancy of H1-receptors by antagonist in plasma was observed for 12 hours after the dose in extensive metabolizers and greater than 60% from 12 to 30 hours in poor metabolizers, when plasma concentrations had fallen below those that should result in 50% occupancy of receptors. The results suggest that (+/-)-chlorpheniramine plasma concentrations do not predict H1-receptor antagonist in plasma. In addition, a role is suggested for CYP2D6 in formation of a potent active metabolite of chlorpheniramine.

Changing Patterns of Resistance to Ampicillin/Sulbactam

Objective:

To report on methods to halt the increasing resistance of gram-negative organisms to ampicillin/sulbactam.

Design:

A before-after observational design was used to evaluate susceptibility of organisms to ampicillin/sulbactam.

Setting:

A university teaching hospital.

Interventions:

An educational program regarding appropriate prescribing of ampicillin/sulbactam and restriction of the use of ampicillin/sulbactam.

Main Outcome Measures:

Antimicrobial susceptibility to ampicillin/sulbactam.

Results:

The trend in increasing resistance was halted for Escherichia coli and Enterobacter. Emerging resistance of other organisms was not observed.

Conclusions:

The trend in increasing resistance was halted by restrictions on prescribing and by providing education regarding rational prescribing of ampicillin/sulbactam. We recommend that this combination not be used empirically to treat nosocomial infections or for bacteria against which ampicillin alone is effective.

Reducing inappropriate prescribing of sublingual nifedipine

OBJECTIVE

To report a program to reduce the practice of prescribing sublingual nifedipine.

MONITORING AND EDUCATIONAL PROGRAM

Pharmacy records were used to identify orders for sublingual nifedipine at Georgetown University Medical Center. Initial review showed 30-40 orders/month, or approximately 11% of all nifedipine orders. A newsletter was published outlining Pharmacy and Therapeutics Committee guidelines for the use of nifedipine when rapid onset of action is desired. Further educational efforts involved correspondence with each attending physician responsible for the sublingual nifedipine orders. A reduction in orders for sublingual nifedipine to approximately 10 orders/month (3.9% of total nifedipine orders) was observed after using this educational approach. The reduction in orders has been maintained by frequent contact with the attending physicians.

CONCLUSIONS

Repeated educational measures have resulted in a reduction in the inappropriate prescribing of sublingual nifedipine.

d-sotalol reduces heart rate in vivo through a beta-adrenergic receptor-independent mechanism

d-Sotalol was developed as an antiarrhythmic agent with a relative lack of antagonist activity at beta-adrenergic receptors. Exercise heart rate reduction has been observed after administration to humans. The purpose of this study was to determine directly whether this effect of d-sotalol was attributable to beta-blockade. Plasma samples from normal volunteers who randomly received either atenolol, d-sotalol, or placebo were used in an in vitro radioreceptor assay to determine occupancy of beta 1-adrenergic receptors by antagonist present in the plasma. Occupancy was compared with the observed pharmacologic effects. A reduction in exercise heart rate of 7.7% +/- 3.8% for d-sotalol and 15.9% +/- 3.0% for atenolol occurred with beta 1-adrenergic receptor occupancy of 0% and 33.9% +/- 21.4%, respectively. Absence of antagonist effect in the radioreceptor assay eliminates the potential role of beta 1-blockade in d-sotalol-induced heart rate reduction. This effect is most likely a result of prolongation of the sinus node action potential duration.

Nimodipine in the treatment of subarachnoid hemorrhage

Nimodipine, a calcium-channel antagonist with a relatively selective vasodilatory effect on cerebral blood vessels, has recently been approved for improvement of neurologic deficits due to spasm following subarachnoid hemorrhage. Nimodipine has low oral bioavailability (2.7-27.9 percent), a short half-life (2 h), is highly protein bound (98-99 percent), and is hepatically metabolized. Clinical studies have evaluated topical, intravenous, and oral administration of nimodipine for the treatment of cerebral artery spasm associated with subarachnoid hemorrhage. These studies document some benefit of the drug in reducing the occurrence of severe neurologic deficit, although this effect is not universal. Few adverse effects have been noted. Further studies are necessary to evaluate the pharmacologic and pharmacokinetic characteristics, the appropriate dose and route of administration, adverse effects, drug interactions, and the therapeutic efficacy of nimodipine before routine use can be recommended.