Drug-nutrient interactions in transplant recipients

Food supplement vitamins, minerals, amino-acids, fatty acids, phenolic and alkaloid-based substances: An overview of their interaction with drugs

Food supplements are a widespread group of products ingested as a diet complement, whose consumption has recently skyrocketed due to the consumers' concern with their well-being. Among food supplements, vitamin- and mineral-based ones are the top sellers, and the demand of others, such as those containing polyphenols, is increasing. Owing to their alleged natural characteristics, consumers take the safety of food supplements for granted, and use them even when taking medicines. Thus, their potential interactions with drugs have been sparsely evaluated. This manuscript aims to bring forth an up-to-date overview of the most important knowledge involving the interactions between food supplements and drugs, relevant to be aware by nutritionists and other healthcare professionals. To this end, an extensive bibliographic review was conducted focusing on peer reviewed data from experimental in vivo evidence and clinical studies whenever major clinical interactions have been reported. Elder people and polymedicated or chronic patients are especially vulnerable to the therapeutic ineffectiveness and toxicity caused by these types of interactions. Drugs used to treat cardiovascular, autoimmune, nervous, and oncological diseases are commonly involved in important clinical interactions with food supplements, many with a narrow therapeutic margin.

Lactation stage influences drug milk-to-serum values and neonatal exposure risk

The purpose of our study was to assess the influence of lactation stage-dependent differences in milk-to-serum (M/S) ratio for an actively transported drug (cefepime) on the calculation of 2 exposure indices, EI(Dose) and EI(Conc). Age-dependent differences in cefepime pharmacokinetics at postnatal days 4 and 10 as well as cefepime M/S values at lactation days 4 and 10 in rats were determined. Significantly higher elimination rate constant and systemic clearance and lower half-life were found in day 10 compared to day 4 pups with no differences in oral bioavailability. The EI(Conc) was quantitatively higher than EI(Dose) at both lactation stages. The approximately 7-fold decrease in cefepime M/S values at lactation day 10 resulted in approximately 7-fold reduction in the EI(Dose) and approximately 13-fold reduction in EI(Conc). Our study confirms the need to evaluate M/S at different lactation stages for actively transported drugs to avoid over- or underestimation of neonatal exposure risk.

Clinical pharmacology in the adolescent oncology patient

Numerous studies have documented that adolescents and young adults (AYAs) experience a significant cancer burden as well as significant cancer mortality compared with other age groups. The reasons for the disparate outcomes of AYAs and other age groups are not completely understood and are likely to be multifactorial, including a range of sociodemographic issues unique to these individuals as well as differences between adolescents, younger pediatric patients, and adults in the pharmacology of anticancer agents. Because adolescence is a period of transition from childhood to early adulthood, numerous physical, physiologic, cognitive, and behavioral changes occur during this time. In this review, we provide an overview of the unique developmental physiology of the adolescent and explain how these factors and the behavioral characteristics of adolescents may affect the pharmacology of anticancer agents in this patient population. Finally, we describe examples of studies that have assessed the relation between drug disposition and age, focusing on the AYA age group.

Acute administration of cefepime lowers L-carnitine concentrations in early lactation stage rat milk

Our study investigated the potential for important in vivo drug-nutrient transport interactions at the lactating mammary gland using the L-carnitine transporter substrates, cefepime and L-carnitine, as proof-of-concept. On d 4 (n = 6/treatment) and d 10 (n = 6/treatment) of lactation, rats were administered cefepime (250 mg/h) or saline by continuous i.v. infusion (4 h). Serum and milk L-carnitine and cefepime concentrations were quantified by HPLC-UV. In whole mammary gland, organic cation/carnitine transporter (OCTN)1, OCTN2, OCTN3, amino acid transporter B(0,+) (ATB(0,+)), and L-carnitine transporter 2 expression were determined by quantitative RT-PCR and by western blot and immunohistochemistry when possible. Cefepime caused a 56% decrease in milk L-carnitine concentrations on lactation d 4 (P = 0.0048) but did not affect milk L-carnitine at lactation d 10 or serum L-carnitine concentrations at either time. The mean L-carnitine and cefepime milk:serum ratios (M/S) decreased from 9.1 +/- 0.4 to 4.9 +/- 0.6 (P < 0.0001) and 0.89 +/- 0.3 to 0.12 +/- 0.02 (P = 0.0473), respectively, between d 4 and d 10 of lactation. In both groups, OCTN2 (P < 0.0001), OCTN3 (P = 0.0039), and ATB(0,+) (P = 0.004) mRNA expression and OCTN2 protein (P < 0.0001) were higher in mammary glands at d 4 of lactation compared with d 10. Immunohistochemistry revealed OCTN1 and OCTN2 localization in the mammary alveolar epithelium and OCTN3 expression in the interstitial space and blood vessel endothelium. In conclusion, cefepime significantly decreased milk L-carnitine concentrations only at d 4 of lactation. Relative to d 10, enhanced expression of OCTN2 and ATB(0,+) in mammary glands at d 4 of lactation and higher M/S (L-carnitine and cefepime) suggests cefepime competes with L-carnitine for L-carnitine transporters expressed in the lactating mammary gland to adversely affect L-carnitine milk concentrations and these effects depend upon lactation stage.

Effect of Oral Vitamin E and C Therapy on Calcineurin Inhibitor Levels in Heart Transplant Recipients

BACKGROUND

A recent prospective trial demonstrated that oral vitamins C and E retard the early progression of transplant-associated coronary arteriosclerosis; as a result, a number of centers have added these agents to their maintenance regimens. This study reviewed the impact of vitamin E and C supplementation on calcineurin inhibitor trough concentrations.

METHODS

A retrospective chart review of the first 29 heart transplant patients prescribed anti-oxidant agents was performed. Twenty-two patients taking cyclosporin A (CsA) and 7 patients taking tacrolimus were prescribed vitamin C (500 mg twice a day) and vitamin E (400 IU twice a day). Serum chemistries and drug levels were measured before and after vitamin therapy was initiated.

RESULTS

The baseline CsA trough concentration (mean +/- SD) was 137 +/- 39 ng/ml and it declined to 99 +/- 54 ng/ml (p = 0.007) after anti-oxidant therapy was initiated. The average percentage decrease in the CsA trough concentration was 30%. No significant changes were seen in the patients taking tacrolimus.

CONCLUSIONS

These data demonstrate that supplementation with the anti-oxidant agents vitamin C and vitamin E decreases CsA concentrations but does not appear to effect tacrolimus concentrations. Although more detailed pharmacokinetic analysis is necessary to clarify the exact mechanism of this interaction, physicians who take care of transplant recipients should be aware that more frequent CsA concentration monitoring is warranted after initiating these anti-oxidant agents.

The association between vitamin C and vitamin E supplement use before hematopoietic stem cell transplant and outcomes to two years

OBJECTIVE

To examine the prevalence of supplement use in persons before receiving hematopoietic stem cell transplant (HSCT) and the association of select supplements with outcomes.

DESIGN

This observational cohort study included a questionnaire on supplement use before HSCT. Nonrelapse mortality, recurrence/relapse, and mortality or relapse (the inverse of disease-free survival) were followed to two years. Subjects/Setting Persons receiving HSCT at the Fred Hutchinson Cancer Research Center between September 1994 and December 1997 were eligible (N=1,182). Statistical Analyses Performed Descriptive statistics and univariate and Cox regression analyses were conducted.

RESULTS

Sixty-six percent of patients used supplements (31% vitamin C, 19% vitamin E, and 20% herbs or others preparations). Vitamin C at > or =500 mg/day was inversely associated with recurrence among persons with breast cancer (RR=0.11; 95% CI, 0.02-0.89; P=.03). However, among persons with acute leukemia, vitamin C at > or =500 mg/day was positively associated with nonrelapse mortality (RR=2.25; 95% CI, 1.33-3.83; P=.01) and mortality or relapse (RR=1.63; 95% CI, 1.09-2.44; P=.01), respectively. Vitamin E at > or =400 IU/day was positively associated with mortality or relapse (RR=1.77; 95% CI, 1.06 -2.96; P=.02). Applications/Conclusions Though this work was observational, the results suggest supplemental vitamin C before therapy may be beneficial in persons with breast cancer but both vitamin C and vitamin E may increase risk in persons with acute leukemia receiving HSCT. Practitioners should document supplement use in subjects receiving therapy for cancer.