Pharmacokinetics of loratadine in patients with renal insufficiency

Determination of Loratadine and Its Active Metabolite in Plasma by LC/MS/MS: An Adapted Method for Children

Introduction:

Loratadine (LOR) (Fig. 1), an active H1 receptor antagonist, is often used in the treatment of allergic disorders such as seasonal allergies and skin rash [1]. LOR was clinically approved for symptomatic relief of nasal and non-nasal symptoms of allergic rhinitis in children ≥2years.

Materials and Methods:

An adapted method of liquid chromatography-mass spectrometry (LC/MS/MS) was developed and validated to measure the concentrations of loratadine (LOR) and its active metabolite descarboethoxyloratadine (DCL) from pediatric plasma. After being mixed with the internal standard (IS, propranolol) and precipitated with methanol, samples were centrifuged and 20 μL of the supernatants were injected into the HPLC system. Separation was carried out on a reversed-phase C18 gradient column using a mobile phase consisting of water (containing 0.1 % formic acid) and acetonitrile. The flow rate was 0.5 mL/min and the running time was 5.0 min for each sample.

Results and Conclusion:

Quantitation of LOR, DCL and IS was performed using MRM mode and the transitions were: 383.1 → 337.1 for LOR, 311.1 → 259.0 for DCL and 260.2 → 116.0 for propranolol, respectively. The method was validated according to FDA guidelines, precisions and accuracies met the requirements in all cases. Calibration curves were 0.2–50.0 ng/mL for both LOR and DCL. This method was then applied for a pilot study examining the pharmacokinetics and therapeutic drug monitoring of LOR in children.

Management of Allergic Rhinitisand Sinusitis

Allergic rhinitis and sinusitis are chronic conditions of the airway and cause significant morbidity. Both can require pharmacotherapy with nonprescription products to relieve symptoms or with prescription products to treat the underlying pathophysiology. Because these diseases are prevalent conditions, the pharmacist is in the unique position of being the first health professional contact for many patients. The pharmacist can assist the patient in selection of nonprescription antihistamines, decongestants, and nasal saline sprays as well as provide instruction on the use of steam therapy, aromatic vapors, and warm compresses for the relief of symptoms. Equally important, the pharmacist can encourage patients to seek care from a physician when treatment with intranasal corticosteroids, antibiotics, and nonsedating antihistamines are needed.

Consensus guidelines for oral dosing of primarily renally cleared medications in older adults

OBJECTIVES

To establish consensus oral dosing guidelines for primarily renally cleared medications prescribed for older adults.

DESIGN

Literature search followed by a two-round modified Delphi survey.

SETTING

A nationally representative survey of experts in geriatric clinical pharmacy.

PARTICIPANTS

Eleven geriatric clinical pharmacists.

MEASUREMENTS

After a comprehensive literature search and review by an investigative group of six physicians (2 general internal medicine, 2 nephrology, 2 geriatrics), 43 dosing recommendations for 30 medications at various levels of renal function were created. The expert panel rated its agreement with each of these 43 dosing recommendations using a 5-point Likert scale (1=strongly disagree to 5=strongly agree). Recommendation-specific means and 95% confidence intervals were estimated. Consensus was defined as a lower 95% confidence limit of greater than 4.0 for the recommendation-specific mean score.

RESULTS

The response rate was 81.8% (9/11) for the first round. All respondents who completed the first round also completed the second round. The expert panel reached consensus on 26 recommendations involving 18 (60%) medications. For 10 medications (chlorpropamide, colchicine, cotrimoxazole, glyburide, meperidine, nitrofurantoin, probenecid, propoxyphene, spironolactone, and triamterene), the consensus recommendation was not to use the medication in older adults below a specified level of renal function (e.g., creatinine clearance <30 mL/min). For the remaining eight medications (acyclovir, amantadine, ciprofloxacin, gabapentin, memantine, ranitidine, rimantadine, and valacyclovir), specific recommendations for dose reduction or interval extension were made.

CONCLUSION

An expert panel of geriatric clinical pharmacists was able to reach consensus agreement on a number of oral medications that are primarily renally cleared.

EFFECT OFCYP2D6*10ALLELE ON THE PHARMACOKINETICS OF LORATADINE IN CHINESE SUBJECTS

Loratadine is known to be a substrate for both CYP3A4 and CYP2D6 based on a previous in vitro study. In view of the large interindividual variability in loratadine pharmacokinetics and the greater genetically determined variability of CYP2D6 activity than of CYP3A4 in vivo, we hypothesized that CYP2D6 polymorphisms may contribute to the pharmacokinetic variability of loratadine. The purpose of this study was to evaluate the effect of CYP2D6 genotype (specifically the CYP2D6*10 allele) on the pharmacokinetics of loratadine in Chinese subjects. Three groups of healthy male Chinese subjects were enrolled: group I, homozygous CYP2D6*1 (*1/*1, n=4); group II, heterozygous CYP2D6*10 (*1/*10 or *2/*10, n=6); and group III, homozygous CYP2D6*10 (*10/*10, n=7) carriers. Each subject received a single oral dose of 20 mg of loratadine under fasting conditions. Multiple blood samples were collected over 48 h, and the plasma concentrations of loratadine and its metabolite desloratadine were determined by high-performance liquid chromatography. In comparing homozygous CYP2D6*10 (group III) to heterozygous CYP2D6*10 (group II) to homozygous CYP2D6*1 (group I) subjects, loratadine oral clearance values were 7.17+/- 2.54 versus 11.06+/-1.70 versus 14.59+/-2.43 l/h/kg, respectively [one-way analysis of variance (ANOVA), p<0.01], and the corresponding metabolic ratios [area under the plasma concentration-time curve (AUC)(desloratadine)/AUC(loratadine)] were 1.55+/-0.73 versus 2.47+/- 0.46 versus 3.32+/- 0.49, respectively (one-way ANOVA, p<0.05), indicating a gene-dose effect. The results demonstrated that CYP2D6 polymorphism prevalent in the Chinese population significantly affected loratadine pharmacokinetics.

Second-Generation Antihistamines

Antihistamines are useful medications for the treatment of a variety of allergic disorders. Second-generation antihistamines avidly and selectively bind to peripheral histamine H1 receptors and, consequently, provide gratifying relief of histamine-mediated symptoms in a majority of atopic patients. This tight receptor specificity additionally leads to few effects on other neuronal or hormonal systems, with the result that adverse effects associated with these medications, with the exception of noticeable sedation in about 10% of cetirizine-treated patients, resemble those of placebo overall. Similarly, serious adverse drug reactions and interactions are uncommon with these medicines. Therapeutic interchange to one of the available second-generation antihistamines is a reasonable approach to limiting an institutional formulary, and adoption of such a policy has proven capable of creating substantial cost savings. Differences in overall efficacy and safety between available second-generation antihistamines, when administered in equivalent dosages, are not large. However, among the antihistamines presently available, fexofenadine may offer the best overall balance of effectiveness and safety, and this agent is an appropriate selection for initial or switch therapy for most patients with mild or moderate allergic symptoms. Cetirizine is the most potent antihistamine available and has been subjected to more clinical study than any other. This agent is appropriate for patients proven unresponsive to other antihistamines and for those with the most severe symptoms who might benefit from antihistamine treatment of the highest potency that can be dose-titrated up to maximal intensity.

Reliable and specific high-performance liquid chromatographic method for simultaneous determination of loratadine and its metabolite in human plasma

A high-performance liquid chromatographic (HPLC) method with fluorescence detection has been developed for the simultaneous determination of loratadine (L) and its metabolite, descarboethoxyloratadine (DCL), in human plasma. Following a two-step liquid-liquid extraction with toluene, the analytes were separated using a gradient mobile phase consisting of methanol-acetonitrile-phosphate buffer. The linearity for L and DCL was within the concentration range of 0.5-16 ng/ml. The coefficient of variation of intra- and inter-day assay was <8.3%, with accuracy ranging from 98.3 to 105.7%. The lower limit of quantification was 0.5 ng/ml for both L and DCL. This method has been demonstrated to be reliable, and is an improvement over existing methods due to its capability for determining L and DCL simultaneously in a single chromatographic run.

Safety of antihistamines in children

The histamine H1 receptor antagonists (antihistamines) are an important class of medications used for the relief of common symptoms associated with hyperhistaminic conditions occurring in children and adults. This group of drugs may be subdivided into 3 classes, or generations, based upon their propensity to induce sedation and cardiotoxicity. The first generation (classical) antihistamines are highly effective in treating hyperhistaminic conditions. However, they frequently induce sedation and may adversely affect a child's learning ability. First generation antihistamine-induced sedation has been described to occur in more than 50% of patients receiving therapeutic dosages. Serious adverse events are unusual following overdoses of first generation antihistamines although life-threatening adverse events have been described. When the so-called 'second generation' antihistamines terfenadine and astemizole were introduced they were widely embraced and quickly used by clinicians of all specialities, including paediatricians, as nonsedating alternatives to the first generation compounds. These new agents were found to be equally or more effective than first generation antihistamines in relieving symptoms associated with hyperhistaminic conditions without the soporific effects of the first generation agents. Unfortunately, after approximately 10 years of widespread clinical use, disturbing reports of potentially life-threatening dysrhythmias, specifically torsades de pointes, were described. Both terfenadine and astemizole have been shown in vitro to inhibit several ion channels, and in particular the delayed outward rectifier potassium channel in the myocardium, predisposing the heart to dysrhythmias. The potential life-threatening cardiotoxicities of the second generation antihistamines led to the search for noncardiotoxic and nonsedating agents. Loratadine, fexofenadine, mizolastine, ebastine, azelastine and cetirizine are the first of the new third generation antihistamines. These drugs have been shown to be efficacious with few adverse events including no clinically relevant cytochrome P450 mediated metabolic-based drug-drug interactions or QT interval prolongation/cardiac dysrhythmias. Appropriate treatment of an antihistamine overdose depends upon which class of compound has been ingested. There is no specific antidote for antihistamine overdose and treatment is supportive particularly for ingestions of first generation compounds. Ingestion of excessive doses of terfenadine or astemizole requires immediate medical attention. Children who accidentally ingest excessive doses of a third generation compound may usually be adequately managed at home. However, patients ingesting large amounts (approximately >3 to 4 times the normal therapeutic daily dose) should receive medical attention. These patients should be monitored for 2 to 3 hours after the ingestion and patients ingesting cetirizine should be advised about the potential for sedation. The availability of newer generation antihistamine compounds has clearly added to the clinical effectiveness and patient tolerance of a widely prescribed class of drugs. These advances have also been accompanied by improved safety profiles, particularly in the case of third generation antihistamine overdose.

Therapeutic index of H1-antihistamines: example of cetirizine

BACKGROUND

The second generation H1 antihistamines were considered to have an improved risk/benefit ratio because of their low penetration into the brain and their very low incidence of CNS depressant effects. Nevertheless, the cardiac rhythm disturbances described under terfenadine and astemizole intake drew the attention to the fact that the low penetration into the brain is only one limited item in the evaluation of their respective therapeutic indices. A correct evaluation of the therapeutic index should always comprise a large series of items: all desired and not desired effects and properties should be considered together with the physicobiochemical mechanisms of the drugs at cell and membrane levels.

Loratadine. A reappraisal of its pharmacological properties and therapeutic use in allergic disorders

Loratadine is a long-acting antihistamine agent, exhibiting partial selectivity for peripheral histamine H1-receptors. To date, loratadine has been evaluated in allergic rhinitis, urticaria and, to a limited extent, in asthma. In several large controlled comparative clinical studies, loratadine was superior to placebo, faster acting than astemizole and as effective as azatadine, cetirizine, chlorpheniramine (chlorphenamine), clemastine, hydroxyzine, mequitazine and terfenadine in patients with allergic rhinitis and chronic urticaria. The clinical effectiveness of loratadine in asthma is at present unclear. Loratadine is well tolerated. At dosages of 10 mg daily, commonly reported adverse events were somnolence, fatigue and headache. Sedation occurred less frequently with loratadine than with azatadine, cetirizine, chlorpheniramine, clemastine and mequitazine. Serious ventricular arrhythmias, as reported with some other second generation histamine H1-receptor antagonists, have not been observed with loratadine to date. Thus, loratadine, with its attributes of once daily administration, fast onset of action and essentially nonsedating properties, would appear to be an appropriate first-line agent for the treatment of allergic rhinitis or urticaria.