Oral absorption of tacrolimus in children with intestinal failure due to short or absent small bowel

Changes of Drug Pharmacokinetics in Patients with Short Bowel Syndrome: A Systematic Review

BACKGROUND AND OBJECTIVES

Short bowel syndrome is a clinical condition defined by malabsorption of nutrients and micronutrients, most commonly following extensive intestinal resection. Due to a loss of absorptive surfaces, the absorption of orally administered drugs is also often affected. The purpose of this study was to systematically review the published literature and examine the effects of short bowel syndrome on drug pharmacokinetics and clinical outcomes.

METHODS

Studies were identified through searches of databases MEDLINE, EMBASE, Web of Science, and SCOPUS, in addition to hand searches of studies' reference lists. Two reviewers independently assessed studies for inclusion, yielding 50 studies involving 37 different drugs in patients with short bowel syndrome.

RESULTS

Evidence of decreased drug absorption was observed in 29 out of 37 drugs, 6 of which lost therapeutic effect, and 14 of which continued to demonstrate clinical benefit through drug monitoring.

CONCLUSIONS

The influence of short bowel syndrome on drug absorption appears to be drug-specific and dependent on the location and extent of resection. The presence of a colon in continuity may also influence drug bioavailability as it can contribute significantly to the absorption of drugs (e.g., metoprolol); likewise, drugs that have a wide absorption window or are known to be absorbed in the colon are least likely to be malabsorbed. Individualized dosing may be necessary to achieve therapeutic efficacy, and therapeutic drug monitoring, where available, should be considered in short bowel syndrome patients, especially for drugs with narrow therapeutic indices.

Systematic review of drug bioavailability following gastrointestinal surgery

PURPOSE

Inter- and intraindividual pharmacokinetics variability in humans affects the way in which drugs act on the body. Gastrointestinal surgery has an impact on this variability and significantly alters the kinetics of drugs in post-surgical patients. The way in which pharmacokinetic profiles are modified depends on the type of operative procedure performed. The extent to which the absorption of different groups of drugs is affected varies according to the site and length of intestinal resections.

METHODS

A literature search was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol. Three databases were searched: MEDLINE, Embase, and the Cochrane Library. For each drug, potential changes in absorption were described, including recommendations extracted from the results of the studies and collected according to authors' criteria as practical conclusions, and grades of recommendation were determined by levels of evidence using the Oxford Centre for Evidence-Based Medicine scale.

RESULTS

Sixty-eight articles were collected during the selection process after the bibliographic search. The main outcomes for 60 drugs from the various studies were classified according to each type of surgery.

CONCLUSIONS

Modifications in the digestive tract secondary to gastrointestinal surgery may compromise the bioavailability of drugs. Decreased absorption surface, gastric emptying speed, and gastric pH alteration are factors to be taken into account in the management of pharmacological treatment after surgery. Evidence supported by data in clinical practice is scarce, but after studying the pharmacokinetic profile of some molecules, it is possible to offer recommendations for its adaptation to the patient's clinical situation.

Tacrolimus trough levels before, during and after jejunostomy in a liver transplant patient: a case report

Although the feasibility of oral tacrolimus administration in the presence of jejunostomy has already been reported, few studies monitoring tacrolimus trough blood levels have been analyzed in detail, either during or after a jejunostomy closure. We report on our experience with a 34-year-old patient who underwent liver transplantations, with a proximal jejunostomy constructed a few days prior to the second transplantation. He was administered tacrolimus by a predominantly oral route, and less frequently received it by jejunostomy. The aim of this paper is to discuss this administration strategy and whether a different method could have been more suitable. This case report highlights that during the jejunostomy period, the tacrolimus doses that were required to maintain trough concentrations within the therapeutic range were four times higher than those administered after the closure of the jejunostomy. We observed an increase in the Dose-Normalized Trough Concentration (DNTC) values when tacrolimus was administered for 4 consecutive days by jejunostomy as compared to oral administration, indicating that the relative bioavailability of tacrolimus increased. Moreover, when returning to oral administration, the subsequent DNTC value was halved, highlighting a reduction in the tacrolimus bioavailability. Thus, in such a case, administration by jejunostomy could be more appropriate.

Clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplantation

The aim of this review is to analyse critically the recent literature on the clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplant recipients. Dosage and target concentration recommendations for tacrolimus vary from centre to centre, and large pharmacokinetic variability makes it difficult to predict what concentration will be achieved with a particular dose or dosage change. Therapeutic ranges have not been based on statistical approaches. The majority of pharmacokinetic studies have involved intense blood sampling in small homogeneous groups in the immediate post-transplant period. Most have used nonspecific immunoassays and provide little information on pharmacokinetic variability. Demographic investigations seeking correlations between pharmacokinetic parameters and patient factors have generally looked at one covariate at a time and have involved small patient numbers. Factors reported to influence the pharmacokinetics of tacrolimus include the patient group studied, hepatic dysfunction, hepatitis C status, time after transplantation, patient age, donor liver characteristics, recipient race, haematocrit and albumin concentrations, diurnal rhythm, food administration, corticosteroid dosage, diarrhoea and cytochrome P450 (CYP) isoenzyme and P-glycoprotein expression. Population analyses are adding to our understanding of the pharmacokinetics of tacrolimus, but such investigations are still in their infancy. A significant proportion of model variability remains unexplained. Population modelling and Bayesian forecasting may be improved if CYP isoenzymes and/or P-glycoprotein expression could be considered as covariates. Reports have been conflicting as to whether low tacrolimus trough concentrations are related to rejection. Several studies have demonstrated a correlation between high trough concentrations and toxicity, particularly nephrotoxicity. The best predictor of pharmacological effect may be drug concentrations in the transplanted organ itself. Researchers have started to question current reliance on trough measurement during therapeutic drug monitoring, with instances of toxicity and rejection occurring when trough concentrations are within 'acceptable' ranges. The correlation between blood concentration and drug exposure can be improved by use of non-trough timepoints. However, controversy exists as to whether this will provide any great benefit, given the added complexity in monitoring. Investigators are now attempting to quantify the pharmacological effects of tacrolimus on immune cells through assays that measure in vivo calcineurin inhibition and markers of immunosuppression such as cytokine concentration. To date, no studies have correlated pharmacodynamic marker assay results with immunosuppressive efficacy, as determined by allograft outcome, or investigated the relationship between calcineurin inhibition and drug adverse effects. Little is known about the magnitude of the pharmacodynamic variability of tacrolimus.

The management of patients with the short bowel syndrome

The surgeon is invariably the primary specialist involved in managing patients with short bowel syndrome. Because of this they will play an important role in co-ordinating the management of these patients. The principal aims at the initial surgery are to preserve life, then to preserve gut length, and maintain its continuity. In the immediate postoperative period, there needs to be a balance between keeping the patient alive through the use of TPN and antisecretory agents and promoting gut adaptation with the use of oral nutrition. If the gut fails to adapt during this period, then the patient may require therapy with more specific agents to promote gut adaptation such as growth factors and glutamine. If following this, the patient still has a short gut syndrome, then the principal options remain either long term TPN, or intestinal transplantation which remains a difficult and challenging procedure with a high mortality and morbidity due to rejection.