Drug interactions: Proteins, pumps, and P-450s

Lack of drug interaction conformity in commonly used drug compendia for selected at-risk dermatologic drugs

BACKGROUND

Systemic treatments that have significant efficacy for dermatologic conditions can often cause severe adverse reactions when improperly combined with interacting drugs. We have noted discrepancies in the reporting of such drug-drug interactions among major drug compendia used in hospitals and physicians' offices.

OBJECTIVE

The aim of this study was to compare the consistency of drug-drug interaction listings among four of the most widely used English language drug compendia in the US.

METHODS

Drug monographs from Mosby's GenRx, USP DI, AHFS Drug Information, and the Physicians' Desk Reference were compared. The respective drug-drug interactions provided by the various compendia for four systemic agents -- dapsone, erythromycin, methotrexate and prednisone -- commonly prescribed for dermatologic purposes were compiled.

RESULTS

We found considerable discrepancies among the compendia with respect to the number of drug interactions listed. Agreement among the compendia was especially poor when more than two sources were compared.

CONCLUSIONS

There is a need for a drug compendium that reconciles drug-drug interaction reporting discrepancies under standardized criteria based on the scientific literature and clinical significance.

Pharmacogenomics and drug response in cardiovascular disorders

There are a total of 17 families of drugs that are used for treating the heterogeneous group of cardiovascular diseases. We propose a comprehensive pharmacogenomic approach in the field of cardiovascular therapy that considers the five following sources of variability: the genetics of pharmacokinetics, the genetics of pharmacodynamics (drug targets), genetics linked to a defined pathology and its corresponding drug therapies, the genetics of physiologic regulation, and environmental–genetic interactions. Examples of the genetics of pharmacokinetics are presented for phase I (cytochromes P450) and phase II (conjugating enzymes) drug-metabolizing enzymes and for phase III drug transporters. The example used to explain the genetics of pharmacodynamics is glycoprotein IIIa and the response to antiplatelet effects of aspirin. Genetics linked to a defined pathology and its corresponding drug therapies is exemplified by ADRB1, ACE, CETP and APOE and drug response in metabolic syndrome. The examples of cytochrome P450s, APOE and ADRB2 in relation to ethnicity, age and gender are presented to describe genetics of physiologic regulation. Finally, environmental–genetic interactions are exemplified by CYP7A1 and the effects of diet on plasma lipid levels, and by APOE and the effects of smoking in cardiovascular disease. We illustrate this five-tiered approach using examples of cardiovascular drugs in relation to genetic polymorphism.

Superficial fungal infections

Superficial fungal infections arise from a pathogen that is restricted to the stratum corneum, with little or no tissue reaction. In this Seminar, three types of infection will be covered: tinea versicolor, piedra, and tinea nigra. Tinea versicolor is common worldwide and is caused by Malassezia spp, which are human saprophytes that sometimes switch from yeast to pathogenic mycelial form. Malassezia furfur, Malassezia globosa, and Malassezia sympodialis are most closely linked to tinea versicolor. White and black piedra are both common in tropical regions of the world; white piedra is also endemic in temperate climates. Black piedra is caused by Piedraia hortae; white piedra is due to pathogenic species of the Trichosporon genus. Tinea nigra is also common in tropical areas and has been confused with melanoma.

Cutaneous fungal infections in the elderly

Because of impaired host defenses and a favorable environment at specific anatomic sites, there is an increased prevalence of seborrheic dermatitis, mucosal and cutaneous candidiasis, tinea pedis, and onychomycosis in the geriatric population compared with other age groups. Both KOH and fungal culture are timely, convenient, and cost-effective methods of diagnosis. Sensitivity of these tests depends on proper technique for specimen collection and experience. KOH 20% with DMSO and DTM are highly recommended. Treatment should be tailored to the diagnosis and the individual patient. This includes the targeted spectrum of coverage (dermatophyte or yeast); topical versus systemic therapy; review of the patient's medication list for potential drug interactions; and likelihood of compliance. Checking baseline laboratories and routine monitoring of complete blood count and liver function tests in healthy patients, without a history of liver disease or active hepatitis, and without potential drug interactions, seems unwarranted for rare adverse events. Successful management requires adequate patient education, correction of underlying predisposing factors, and prophylactic measures against recurrence.

[Drug interactions and the anesthesiologist]

Modern anesthesiology employs the combined administration of several drugs belonging to different pharmacological classes. Additionally, anesthesiologists are facing the challenge of polypharmacy regimens utilized by patients considered for surgical treatment When drugs are combined, the pharmacological effect may considerably differ from the individually expected properties. This may be beneficial or potentially lead to adverse drug reactions harming the patient. The incidence of drug interaction increases exponentially with the number of drugs administered. Depending on the mechanism involved, drug interactions can be classified as pharmaceutical, pharmacodynamic, or pharmacokinetic. Although there are enormous possibilities for adverse drug reactions nd the complexity is hard to identify, prediction of drug interaction is possible. Besides recognizing the general risk factors, fundamental knowledge of basic and clinical pharmacology is important to prevent serious or fatal drug interactions before they occur.