Analysis of the Behavior of Plasma Concentrations of Tacrolimus in Adult Patients with Liver Transplantation: Adverse Reactions and Drug Interactions and Their Relevance to Patient Safety

Abstract

Organ transplantation is a medical treatment often used to restore the function of vital organs. Tacrolimus is one of the most widely used drugs in the immunosuppressive treatment of liver transplants. Aims: To analyze plasma concentrations of tacrolimus in adult liver transplant patients and to characterize adverse effects and drug interactions. Design: retrospective observational studies. The study included 32 patients, of whom 22 were male and 10 female. The average values and range of tacrolimus obtained showed a mean of 8.7 SD 3.2. Low values were found in seventy-five cases, with a percentage of 54.8%. The values within the expected had a frequency of fifty-three times with a percentage of 38.7%. Finally, the frequency of high values was nine times with a percentage of 6.5%. A total of 36 RAM types were found. It was determined that the majority of the ADRs were of moderate damage (13) of 46.4%, while 39.3% of the ADRs were of slight damage (11), 14.3% were of severe damage (4) and no ADR was incidental. Clinically relevant drug interactions in this group of patients were 16.7% contraindicated, 16.7% adjustments based on close follow-up, and 66.6% use with routine follow-up. Similar to the interactions present in the 2013 EMA data sheet. Plasma tacrolimus concentrations are within the range of 38.7% in male patients and 40.8% in female patients. 61.3% of male patients and 59.2% of female patients do not reach the expected tacrolimus plasma levels of 8.0−11.0 ng/ml, similar to those presented in the 2009 FDA data sheet. There were 220 ADRs in this sample of 32 liver transplant patients.

1. Introduction

There are three forms of immunological rejection of liver transplantation, hyperacute, acute, and chronic rejection. Acute rejection of the transplanted liver is the most frequent form in which it is possible to act mainly with drugs [1]. Current immunosuppressive drugs are reducing their incidence from 60−80% in the 1960s−1980s to 30−50% today. From an immunological point of view, the liver is highly resistant to antibody-mediated attack and has a low rate of chronic rejection and high reversibility of acute rejection [2].

Immunosuppressant treatment is used in transplants to prevent acute or chronic graft rejection. The success of immunosuppression is finding the balance between preventing graft rejection and avoiding excessive suppression of individual’s immune system.

Tacrolimus is one of the most widely used drugs in the immunosuppressive treatment of liver transplants, given that it has been shown to be more potent than cyclosporine, another drug used for the same purpose [3]. However, it has a wide intra-individual variability, which ranges between 10 and 40% according to the studies, and inter-individual, which has been estimated between 20 and 60% [4]. It has a bioavailability of 25−40% and, like cyclosporine, is metabolized by cytochrome P450 3A4. Its mechanism of action consists of binding to a cytoplasmic protein (FKBP) that inhibits calcineurin phosphatase [5], blocking the transcription factor for cytokine synthesis (IL-2, IL-4, IL-3, TNF, INF) and also the T-lymphocyte growth factor-beta. The most frequent adverse effects of tacrolimus are nephrotoxicity, neurotoxicity, hypertension, and diabetes, in addition to other, less relevant ones [6].

The advantage of tacrolimus is that it has great immunosuppressive power and, at low doses it is very effective, less toxic, and is generally used as monotherapy. One disadvantage is that it is a drug where the plasma concentration must be constantly monitored. Low levels of tacrolimus present the risk of graft rejection, while high levels produce greater toxic effects and increase the vulnerability of patients to infections and tumors. Another disadvantage of this drug is that it has numerous drug interactions because it is metabolized by the liver in cytochrome P450-3A4. Since many other drugs are metabolized by the same cytochrome, it gives rise to several interactions that may be clinically relevant and potentially serious [6].

2. Aims

To analyze plasma concentrations of tacrolimus in adult liver transplant patients and to characterize adverse effects and drug interactions.

3. Materials and methods

Design: a retrospective observational study on a random sample of adult patients with a history of liver transplantation.

Scope and period of the study: the study was conducted in a high-complexity hospital in Argentina in the period 2017−2018.

Study subjects: adult patients, who after their respective liver transplants, received treatment with tacrolimus as monotherapy or together with other appropriate drugs for their condition, if they needed it, according to the time elapsed from the transplant to the review of the data of this study. Only patients on immediate-release tacrolimus were assessed.

Sample: a sample of 32 patients was analyzed, and the sampling was done using the Excel formulas for W7 (probabilistic sample). The sample was randomly based on the total number of patients with liver transplantation and an indication for tacrolimus. The dose administered orally in adults was initially 0.10−0.15 mg/kg/day 24 hours after transplantation. After discharge, treatment with tacrolimus alone or in combination with other immunosuppressants was continued with doses varied according to clinical evaluation, rejection findings, and drug tolerance.

Data source: data were obtained from the electronic medical records (EHR) of each patient. Only relevant data regarding the patient’s liver transplant, immunosuppressive treatment with tacrolimus alone or with other immunosuppressants, other concomitant medications, and present adverse effects were disclosed. The medical records began to be read from the date the patient was admitted to the hospital, even before the study period, since they are patients with longer treatment, and with multiple complications and hospitalizations.

4. Instruments

The monitoring of the plasmatic concentrations of tacrolimus obtained by means of dosages through the ELISA [7] technique in valleys after 10 days of therapy with tacrolimus was analyzed, and it was studied whether there was a readjustment of the dose if the patient was infra dosed or supra dosed to avoid graft rejection or increased frequency of adverse reactions. The expected range or optimal range of plasma dosages was considered to be between 8 and 11 ng/ml since this is the range estimated as optimal. In any case, any dosage above 11 or below was considered a deviation, since there are studies that indicate that concentrations between 5 and 8 ng/ml are associated with a lower severe toxicity profile and no graft rejection (Plinio, 2015).

Once the ADRs (adverse drug reactions) related to tacrolimus were classified, they were classified according to the Naranjo algorithm to find causality vs. chance. The algorithm questions were answered for each ADRs and a causality score was assigned to each one. Causality was classified as: definite (9 or more points), probable (5−8 points), possible (1−4 points), and doubtful (0 fewer points). See Annex I.

The 2003 WHO classification of drug safety was used to classify the harms of the ADRs found in this study according to whether they resulted in severe, moderate, slight, or incidental harm.

To determine the type of interactions, the Rothlin® database was used (See Annex II).

The preventability of the ADRs studies was analyzed using the Schumock [8]questionnaire.

5. Data collection

Data were collected in an excel spreadsheet, Windows 7. The software used for statistical analysis was SPSS ® 21 Software, ILLINOIS (USA). Laboratory variables, such as creatinine, TGP, TGO, age, sex, adverse effects, plasma concentrations of tacrolimus and interactions with concomitant medications, were studied.

Training of the data collector: the data were collected by the first author of this work, previously trained in intensive pharmacovigilance by the second author. Subsequently, a double check was made of a sample of 15 patients with tacrolimus, finding a weighted Cohen’s Kappa of 0.73 (95% CI), a good agreement.

6. Results

The study included 32 patients, of whom 22 were male and 10 female. The percentage of men was 68.8% while that of women was 31.20%.

A total of 210 administered doses were studied, ranging from 0.5 mg every 12 hours to 8 mg every 12 hours.

320 trough concentrations in plasma were analyzed.

The average values and range of tacrolimus obtained showed a mean of 8.7 SD 3.2, and the distribution by sex was as follows (Table 1).

Sex	Average	Range
Male	7.6 SD 2.1	2.2–18.8
Female	9.3 SD 5.4	2.6–26.1

Table 1.

Distribution by sex at range of tacrolimus.

Low values were found in 75 cases, with a percentage of 54.8%. The expected values had a frequency of 53 times with a percentage of 38.7%. Finally, the frequency of high values was nine times with a percentage of 6.5%. A total of 36 RAM types were found.

In male patients, 23 different types of ADRs were recorded, 141 ADRs in total. The most frequent ADRs were gastrointestinal problems (34), hypertension (23), hyperglycemia (14), tremor (14), kidney failure (14), and muscle weakness (9). Those with the least frequency were oral ulcers (1), visual disturbances and discomfort (1), arthralgia (1), cytopenia (1), leukopenia (1), nocturia (1), and thrombocytopenia (1).

In female patients, 13 different types of ADRs were recorded, 78 ADRs in total. The most frequent were gastrointestinal problems (17), hypertension (13), renal insufficiency (8), and abnormal hepatogram (8). The least frequent were diarrhea (1), epigastric abdominal pain, and thrombocytopenia (1) (Table 2).

Classification	Type of ADR	Percentage
Sure	6	14.3%
Probable	18	46.4%
Possible	10	28.6%
Improbable	3	10.7%
Total	28	100%

Table 2.

Frequency and percentage of adverse reactions to tacrolimus, according to causality using the Naranjo algorithm.

ADRs of probable causality were the ones with the highest percentage.

The most affected organ systems were blood and lymphatic system disorders (frequency 5−17.9%) and the least affected were cardiovascular disorders (frequency 1−3.6%), respiratory system disorders (frequency 1−3.6%), and disorders of the skin and appendages (frequency 1−3.6%). ADRs were also detected in the central and peripheral nervous systems (frequency 3−10.7%), gastrointestinal system (frequency 4−14.3%), general disorders of the whole organism (frequency 2−7.1%), metabolism and nutrition (frequency 3−10.7%), musculoskeletal system (frequency 3−10.7%), renal system (frequency 3−10.7%) and organs of vision (frequency 2−7.1%) (Table 3).

ADR	Types of damage
Oral thrush	Mild
Visual disturbances, burning, and discomfort in the eyes	Mild
Anorexia	Mild
Arthralgia	Mild
Asthenia	Mild
Cramps	Mild
Headache	Mild
Cytopenia	Moderate
Muscular weakness	Moderate
Diarrhea	Mild
Dyslipidemia	Moderate
Epigastric abdominal pain	Mild
Edema in lower limbs	Moderate
COPD	Moderate
Fever	Mild
Altered hepatogram	Moderate
Hyperglycemia	Moderate
Hyperkalemia	Serious
Hypertension	Moderate
Urinary infection	Moderate
Renal insufficiency	Moderate
Leukopenia	Serious
Nocturia	Moderate
Plateletopenia	Serious
Gastrointestinal disorders	Moderate
Pruritus	Mild
Hypertensive retinopathy	Serious
Shaking	Moderate

Table 3.

Classification of ADRs according to the type of damage produced.

It was determined that the majority of the ADRs were of moderate damage (13) of 46.4%, while 39.3% of the ADRs were of slight damage (11), 14.3% were of serious damage (4), and no ADR was incidental.

Of the 30 patients who were administered by another type of medication in parallel to treatment with tacrolimus, it was determined whether there was a drug interaction between tacrolimus and the other drugs. It was found that 17 of the 30 patients, 56.7% received drugs that interacted pharmacokinetically with tacrolimus, while, in the remaining 13 patients, 49.9% had no pharmacodynamic drug interactions (Tables 4–6).

Patient	Interaction drug–drug
1	Tacrolimus vs. omeprazole
2	Tacrolimus vs. omeprazole
3	Tacrolimus vs. omeprazole and isoniazid
4	Tacrolimus vs. omeprazole
5	Tacrolimus vs. omeprazole
6	Tacrolimus vs. metoclopramide
7	Tacrolimus vs. omeprazole, everolimus, acetylsalicylic acid, and amlodipine
8	Tacrolimus vs. omeprazole
9	Tacrolimus vs. omeprazole and amlodipine
10	Tacrolimus vs. omeprazole
11	Tacrolimus vs. omeprazole y acetylsalicylic acid
12	Tacrolimus vs. omeprazole
13	Tacrolimus vs. omeprazole, everolimus and amlodipine
14	Tacrolimus vs. omeprazole and amlodipine
15	Tacrolimus vs. omeprazole
16	Tacrolimus vs. amlodipin
17	Tacrolimus vs. omeprazole

Table 4.

Drugs co-administered with tacrolimus.

Type of relevance according to drug interaction algorithm	Frequency	Percentage
Grade 1: do not use combination	1	16.7%
Grade 2: use, adjust guidelines, and follow the closest	1	16.7%
Grade 3: use with tracking	4	66.6%

Table 5.

Summary table of the frequency and degree of clinical relevance of tacrolimus drug interactions with other prescribed drugs.

Type of ADR	Frequency	Percentage
Preventables	7	25.0%
No preventables	21	75.0%

Table 6.

Summary table of the frequency and percentage of adverse reactions to tacrolimus according to their preventability.

In a logistic regression analysis, it was possible to analyze the association of various variables with the appearance of ADRs (Table 7).

Variable	OR aj	IC95%	p Value
Sex	1.71	1.05−2.25	0.05
Impaired liver function	1.23	0.87−2.13	NS
Impaired kidney function	1.91	1.55−4.32	0.001
Presence of drug interaction	2.3	1.14−3.54	0.001
Age between 20 and 35 years	1.12	0.77−2.13	NS
Age between 36 and 55 years	1.25	0.87−1.69	NS
Between 56 and 65 years	1.09	0.98−2.31	NS
Age over 65 years	1.65	1.02−3.34	0.004
Presence of at least two dosages above the optimal values	3.24	2.45−3.78	0.002

Table 7.

Variables associated with the appearance of ADR.

7. Discussion

The mean plasma levels found coincided in a very similar way to the Varghese study with a very similar number of patients (8.5 vs. 8.3 in our study). The mean values ​​to avoid manifestations of severe toxicity between 5−8 ng/ml were met in males, but not in females, where the standard deviation and the range were higher and wider, respectively.

Plasma tacrolimus levels in male patients averaged 7.6 ng/ml with a range of 2.2−18.8 ng/ml, while female patients averaged higher 9.3 ng/ml with a wider range of 2.6−26.1 ng/ml. In other words, the ranges of this study were wider than those recommended, and patients could be exposed to oscillations in plasma tacrolimus concentrations with their respective clinical consequences, but we see that in the ADR findings, the frequency of severe over the total found was 14.3%, with no relevant findings in terms of neurological consequences such as seizures, leukoencephalopathies, among others, as found in the study by Emiroglu et al. Which found a higher frequency of neurological ADRs, although pediatric patients participated in this study.

In this study, 54.8% of the men showed plasma concentrations lower than those recommended (8.0−11.0 ng/dL). Only 6.5% had concentrations higher than those recommended and 38.7% were found within the mentioned range.

40.8% of women showed optimal plasma concentrations (8.0−11.0 ng/dL). 19.7% had higher concentrations than recommended, and 39.5% had lower concentrations than recommended.

The range mentioned as optimal to avoid serious toxicity: 5−8 ng/ml, was present in 98 valleys measured in 14 patients; it is already seen that the inter- and intra-individual variability is high, as mentioned above. All RAM registered in this study are listed in the technical data sheet [9].

The causality of the ADRs recorded in this study was determined using the Naranjo algorithm. It was found that there were 14.3% of ADRs surely related to tacrolimus, 46.4% ADRs probably related, 28.6% possibly related, and 10.7% probably unrelated. These results were compared with the article, “Tacrolimus Toxicity with Minimal Clinical Manifestations: A Case Report and Literature Review” which discusses the toxicity of tacrolimus and compiles data from various sources of available literature about himself. Our study found similar results to those of this article [10].

There were 93.8%, 30 out of 32, patients with the administration of other medications along with tacrolimus treatment. The patients who presented drug interactions were 17 out of 30, 56.7%, who administered drugs together with tacrolimus. Drug interactions were found according to inter drug of rothlin drugs with omeprazole, isoniazid, metoclopramide, everolimus, acetylsalicylic acid, and amlodipine. Their degree of clinical relevance was then assessed using the clinically relevant drug interactions algorithm. One grade 1, 16.7% (everolimus), one grade 2, 16.7% (isoniazid), and four grade 3, 66.6% (omeprazole, metoclopramide, amlodipine, and acetylsalicylic acid) were found. In comparison, few drug interactions were found in the technical data sheet compared to the large number of interactions listed, there was only one contraindicated interaction, and the others were for use with caution and regular or careful monitoring. (Drug Inter, Rothlin Medicines, 2013).

Of the 28 ADRs, 7 of them, 25%, could have been prevented, while the remaining 21 ADRs could not.

The prevention of 25% of ADRs could have been achieved prior to subjecting the patient to treatment with tacrolimus. One way to prevent these ADRs would have been to treat the patient with medication prior to or together with the administration of tacrolimus, carrying out early monitoring of tacrolimus concentrations in plasma, and above all, educating the patient in a more systematic way and with a method that the patient can understand without giving rise to doubts, or erroneous interpretations that could lead to problems related to the medication.

The variables sex, impaired renal function, elderly patients, patients with some levels out of range, and the presence of drug interaction are the variables found to be related to the appearance of adverse events in this sample of patients.

The 2013 EMA data sheet states that drug interactions and patients older than 65 years increase the probability that tacrolimus values are outside the range of 8.0−11.0 ng/dL.

Similar results were found in the article “Adverse Drug Events in Hospitalized Patients with Chronic Kidney Disease” by Yahaya Hassan, which mentions that renal impairment increases the incidence of ADRs compared to patients without RF .

The study by Bates DW, Miller EB, Cullen DJ, et al., “Patient Risk Factors for Adverse Drug Events in Hospitalized Patients”, as in this study, establishes that patients who present drug interactions are more likely to manifest reactions adverse than patients without drug interactions [5].

The study “Adverse drug reactions in older people” by Tangiisuran C coincides with the results found in this study that elderly patients are more likely to manifest ADRs than younger patients.

We have found, in this study, a wide range of plasmatic concentrations of tacrolimus in 32 patients; this variability has been evaluated by multiple published studies, and added to this, its narrow therapeutic index and the potentiality of its multiple pharmacological interactions, the control of concentrations blood pressure of tacrolimus is useful in optimizing therapy and dosing regimen design.

8. Conclusions

Plasma tacrolimus concentrations are within range by 38.7% in male patients and 40.8% in female patients. 61.3% of male patients and 59.2% of female patients do not reach the expected tacrolimus plasma levels of 8.0–11.0 ng/ml. Similar to those presented in the 2009 FDA data sheet.

There were 220 ADRs in this sample of 32 liver transplant patients, and the most common ADRs were gastrointestinal problems, hypertension, renal failure, tremor, and hyperglycemia.

There are several variables associated with the appearance of adverse effects.

Patients treated with tacrolimus as immunosuppressive therapy for liver transplantation should be closely monitored. Plasma concentrations of the same should be maintained within the normal or optimal range, 8.0–11.0 ng/ml in plasma to avoid rejection of the transplanted liver, infections due to excess immunosuppression, and preventable adverse reactions.