Influence of thyroid dysfunction on drug pharmacokinetics

Thyroid Hormone Plays an Important Role in Cardiac Function: From Bench to Bedside

Thyroid hormones (THs) are synthesized in the thyroid gland, and they circulate in the blood to regulate cells, tissues, and organs in the body. In particular, they exert several effects on the cardiovascular system. It is well known that THs raise the heart rate and cardiac contractility, improve the systolic and diastolic function of the heart, and decrease systemic vascular resistance. In the past 30 years, some researchers have studied the molecular pathways that mediate the role of TH in the cardiovascular system, to better understand its mechanisms of action. Two types of mechanisms, which are genomic and non-genomic pathways, underlie the effects of THs on cardiomyocytes. In this review, we summarize the current knowledge of the action of THs in the cardiac function, the clinical manifestation and parameters of their hemodynamics, and treatment principles for patients with hyperthyroid- or hypothyroid-associated heart disease. We also describe the cardiovascular drugs that induce thyroid dysfunction and explain the mechanism underlying the thyroid toxicity of amiodarone, which is considered the most effective antiarrhythmic agent. Finally, we discuss the recent reports on the involvement of thyroid hormones in the regulation of myocardial regeneration and metabolism in the adult heart.

PDZ domain containing protein 1 (PDZK1), a modulator of membrane proteins, is regulated by the nuclear receptor THRβ

Genome wide association studies revealed single nucleotide polymorphisms (SNP) located within the promoter of PDZ domain containing protein 1 (PDZK1) to be associated with serum uric acid levels. Since modulation of transporters and particularly of membrane proteins involved in uric acid handling by PDZK1 has previously been reported, the aim of this study was to analyze the impact of the polymorphisms rs1967017, rs1471633, and rs12129861 on promoter activity and thereby transcription of PDZK1. Cell-based reporter gene assays showed transactivation of the PDZK1-promoter by triiodothyronine mediated by thyroid hormone receptors (THR) α and β. In silico analysis verified localization of the polymorphism rs1967017 within the most likely THR binding site whose deletion reduced THR-mediated transactivation. Furthermore, our study shows regulation of PDZK1 by thyroid hormones, thereby providing a mechanistic basis for the previously reported associations between thyroid hormone status and uric acid homeostasis.

Atrial fibrillation and hyperthyroidism: A literature review

Atrial fibrillation is the most common arrhythmia worldwide with increasing frequency noted with age. Hyperthyroidism is a well-known cause of atrial fibrillation with a 16%–60% prevalence of atrial fibrillation in patients with known hyperthyroidism Ross et al. (2016). While hyperthyroidism as a causative factor of atrial fibrillation is well established, this literature review aims to answer several questions on this topic including:

1. The relationship of atrial fibrillation to hyperthyroidism

2. Atrial fibrillation as a predictor of hyperthyroidism

3. The pathophysiology of thyrotoxic atrial fibrillation

4. Subclinical hyperthyroidism and the relationship with atrial fibrillation

5. Cardioversion and Catheter ablation of hyperthyroid patients with atrial fibrillation

6. Thrombotic risk of hyperthyroid patients with atrial fibrillation

7. Management of Thyrotoxic Atrial fibrillation

8. Pharmacological rhythm control in patients with hyperthyroidism and atrial fibrillation

9. Treatment of Hyperthyroidism to prevent atrial fibrillation

10. Clinical Implications of Hyperthyroidism and Atrial Fibrillation

Thyroid Crisis in a Patient With Burn Injury

Thyroid crisis is an exacerbation of hyperthyroidism that results in severe systemic disturbances and could be fatal. Similarly, severe burn injury also has a hypermetabolic response as part of its presentation. When these two conditions are present concurrently, one must be cognizant that the patient requires urgent optimization of their hyperthyroid status before surgery, and continuous monitoring in an intensive care unit setting. We offer a systematic approach to managing these patients.

Acute and emergency care for thyrotoxicosis and thyroid storm

Thyroid hormones affect all organ systems and, in excess, can cause increased metabolic rate, heart rate, ventricle contractility, and gastrointestinal motility as well as muscle and central nervous system excitability. Thyroid storm is the extreme manifestation of thyrotoxicosis with an estimated incidence of 0.20 per 100,000 per year among hospitalized patients in Japan. The mortality of thyroid storm without treatment ranges from 80% to 100%; but with treatment, the mortality rate is between 10% and 50%. The diagnostic strategy for thyroid storm may take into consideration Burch-Wartofsky scoring or Akamizu's diagnostic criteria. Multiple treatment aims need to be addressed in managing thyroid storm effectively. This paper puts together all aspects to be considered for the management of hyperthyroidism and thyroid storm during the acute and emergency phase as well as consideration of special populations.

Hallucinations associated with miglitol use in a patient with chronic kidney disease and hypothyroidism

A 71-year-old woman with type 2 diabetes mellitus, chronic kidney disease stage IV, primary hypothyroidism and osteoarthritis, whose prescribed treatment included miglitol 50 mg thrice daily with the first bite of meals, reported that she suffered visual hallucinations while taking miglitol, which resolved within a few days of stopping the drug. When she resumed miglitol, hallucinations recurred within a few days and again resolved within a few days of stopping the drug. To our knowledge, this is the first reported case of hallucinations associated with the use of an α-glucosidase inhibitor and highlights a previously unappreciated risk associated with the use of this generally quite benign drug class.

Hyperthyroidism and cardiovascular complications: a narrative review on the basis of pathophysiology

Cardiovascular complications are important in hyperthyroidism because of their high frequency in clinical presentation and increased mortality and morbidity risk. The cause of hyperthyroidism, factors related to the patient, and the genetic basis for complications are associated with risk and the basic underlying mechanisms are important for treatment and management of the disease. Besides cellular effects, hyperthyroidism also causes hemodynamic changes, such as increased preload and contractility and decreased systemic vascular resistance causes increased cardiac output. Besides tachyarrythmias, impaired systolic ventricular dysfunction and diastolic dysfunction may cause thyrotoxic cardiomyopathy in a small percentage of the patients, as another high mortality complication. Although the medical literature has some conflicting data about benefits of treatment of subclinical hyperthyroidism, even high-normal thyroid function may cause cardiovascular problems and it should be treated. This review summarizes the cardiovascular consequences of hyperthyroidism with underlying mechanisms.

Thyroid disorders

All forms of thyroid diseases are much more frequently observed in women than men, although the reasons are still not completely elucidated.Hyperthyroidism is defined by elevated circulating free thyroid hormones. The prevalence is about 2 % in women and 0.2 % in men. The most frequent causes are various forms of thyroid autonomy in elderly women and Graves' disease, which occurs mostly in younger women.Hypothyroidism is defined by a lack of thyroid hormones. It is a common endocrine disorder caused by autoimmune thyroiditis (Hashimoto thyroiditis), iodine deficiency or following surgery or radioiodine therapy. Thyroxine requirements depend on fat-free mass and are, therefore, somewhat higher in males who are more often undersubstituted. In pregnancy lower TSH-reference ranges have to be considered and thyroid function should be monitored throughout pregnancy to avoid harm to the foetus caused by maternal thyroid dysfunctions. If overtreated women more often feature fractures, whereas males more often develop atrial fibrillation.

Hyperthyroid heart disease

The heart is an organ sensitive to the action of thyroid hormone, and measurable changes in cardiac performance are detected with small variations in thyroid hormone serum concentrations. Most patients with hyperthyroidism experience cardiovascular manifestations, and the most serious complications of hyperthyroidism occur as a result of cardiac involvement. Recent studies provide important insights into the molecular pathways that mediate the action of thyroid hormone on the heart and allow a better understanding of the mechanisms that underlie the hemodynamic and clinical manifestations of hyperthyroidism. Several cardiovascular conditions and drugs can interfere with thyroid hormone levels and may pose a difficulty in interpretation of laboratory data in patients with suspected thyroid heart disease. The focus of this report is a review of the current knowledge of thyroid hormone action on the heart and the clinical and hemodynamic laboratory findings as well as therapeutic management of patients with hyperthyroid heart disease.

A composite screening tool for medication reviews of outpatients: general issues with specific examples

Regular performance of medication reviews is prominent among methods that have been advocated to reduce the extent and seriousness of drug-related problems, such as adverse drug reactions, drug-disease interactions, drug-drug interactions, drug ineffectiveness and cost ineffectiveness. Several screening tools have been developed to guide practising healthcare professionals and researchers in reviewing the medication patterns of elderly patients; however, each of these tools has its own limitations. This review discusses a wide range of general prescription-, treatment- and patient-related issues that should be taken into account when reviewing medication patterns by implicit screening. These include generic and therapeutic substitution; potentially superfluous or inappropriate medications; potentially inappropriate dosages or duration of treatment; drug-disease and drug-drug interactions; under-treatment; making use of laboratory test results; patient adherence, experiences and habits; appropriate dosage forms and packaging. A broad selection of specific examples and references that can be used as a basis for explicit screening of medication patterns in outpatients is also offered.

P-glycoprotein polymorphism in hypo- and hyper-thyroidism patients

P-glycoprotein (Pgp) is encoded by the multidrug resistance gene (MDR1) in humans and is the product of MDR1. It is expressed in various tissues and is related to drug distribution in intestinal erythrocytes, capillary endotel of brain, proximal tubules cells of kidneys and liver canalicular cells. Expression of Pgp is affected by Pgp polymorphism, and exon 26 C3435T polymorphism is the most common one. It has been thought that expression of Pgp is high in C-allele subjects and this situation is responsible for the resistance against some drugs and substances. Pgp may have a role in the distribution of thyroid hormones, drugs used for hypo- and hyperthyroidism and the resistance occurred. For this purpose possible relationship between T and C alleles and frequency of Pgp polymorphism as well as thyroid hormone distribution in patients with hypo- and hyperthyroidism was investigated. Thirty five hyperthyroidism patients diagnosed as Graves' disease, 78 hypothyroidism patients diagnosed as Hashimoto's thyroiditis and 100 healthy volunteers were included in the study. According to the results obtained no statistically significant difference was found in Pgp C3435T polymorphism between hypo- and hyperthyroidism patients. In addition, the serum free T3 levels of hyperthyroidism patients with C alleles was higher than those of subjects with T alleles. No statistically significant difference was seen in the CC, CT and TT genotype frequencies between the patients and control groups. In conclusion, it seems that Pgp polymorphism is not a predictor factor for the occurrence of hypo- and hyperthyroidism. There is a significant relationship between Pgp and the elevated serum free T3 levels of hyperthyroidism patients, and further research will help understand this situation.

A concomitant review of the effects of diabetes mellitus and hypothyroidism in wound healing

This paper reviews the negative impact of diabetes mellitus or hypothyroidism on wound healing, both in experimental and clinical settings. Since both are metabolic disorders of great clinical importance, special attention is given, not only to their pathophysiology, but also to their biochemical and histological effects on tissue integrity and regeneration. Also, special focus is awarded on wound healing of the gastrointestinal tract, i.e. in intestinal anastomosis, and how these disorders can lead to wound dehiscence. Since diabetes mellitus and hypothyroidism can coexist in clinical settings, more research must be directed on their influence on wound healing, considering them as one clinical entity.

Impact of short-term hypothyroidism on systemic anticoagulation in patients with thyroid cancer and coumarin therapy

Unlike hyperthyroidism, few data exist regarding the impact of hypothyroidism on systemic anticoagulation with coumarin derivates. Therefore, we evaluated a potential impact of short-term hypothyroid conditions on systemic anticoagulation with coumarin derivates in patients after complete thyroidectomy for treatment of thyroid cancer. Fifteen patients with differentiated thyroid cancers and continued international normalized ratio (INR)-adjusted therapy with coumarin derivates were included in this retrospective analysis. A total of 88 laboratory tests was analyzed. INR values were compared between thyroid-stimulating hormone (TSH) values greater than 10 and 10 mU/L or less. An INR value of less than 2.0 was defined as being out of the therapeutic range. Analysis of significant differences between categorized TSH and INR values were performed by using X(2) analysis, correlation of continuous TSH and INR values by using the Pearson's analysis. When TSH was greater than 10 mU/L (n = 50) the INR value was less than 2.0 in 76.0% (n = 38) cases. In contrast, the INR value was less than 2.0 in only 21.1% (n = 8; p < 0.0001) of patients with TSH of 10 mU/L or less (n = 38). Correlation between continuous TSH and INR values was r = -0.589 (p < 0.0001). Based on the results of the present study, it seems to be necessary to monitor the anticoagulation parameters more often in patients with hypothyroidism and either to correct the hypothyroid state, or in cases of desired hypothyroid conditions, to adjust the therapy with coumarin derivates in order to ensure a sufficient anticoagulation.

Modulation of P-glycoprotein expression in hyperthyroid rat tissues

P-glycoprotein (Pgp) is expressed in various normal tissues and plays an important role in drug absorption and disposition. In addition, it is supposed that alterations in the expression levels of Pgp are involved in the inter- and intraindividual variability of pharmacokinetics of many drugs. Since pharmacokinetic properties of various drugs are altered in patients with thyroid disorders, we examined the expression of Pgp and mdr1a/1b mRNA in the kidney, liver, jejunum, and ileum from euthyroid and hyperthyroid rats. Western blot analysis revealed that Pgp expression was markedly increased in the kidney and liver of hyperthyroid rats. In contrast, it was slightly increased in the jejunum and ileum. mdr1a/1b mRNA levels were significantly increased in the kidney of hyperthyroid rats. However, they were not increased in the liver as well as in the jejunum and ileum of hyperthyroid rats. Expression levels of bile salt export pump and mdr2 mRNA were also unchanged in hyperthyroid rat liver. Taken together, these findings suggest that thyroid hormone induces Pgp expression in a tissue-selective manner, and that the modulation of mdr1a/1b mRNA expression in the hyperthyroid state varies among tissues.

Antipyrine, oxazepam, and indocyanine green clearance in patients with chronic pancreatitis and healthy subjects

BACKGROUND

Hepatic drug metabolism was examined in patients with chronic pancreatitis and healthy controls by using a cocktail design with three different model compounds: antipyrine to express phase-I oxidation, oxazepam to express phase-II conjugation, and indocyanine green (ICG), a high-clearance compound.

METHODS

Eight patients with chronic pancreatitis and seven healthy controls participated. Patients were diagnosed by the presence of typical morphologic changes of the pancreas on imaging and had a moderately but significantly reduced exocrine function and no or only slight impairment of the glucose tolerance. No one had a history or clinical signs of liver disease. Clearance of the three model compounds was estimated after the administration of 1 g antipyrine and 15 mg oxazepam orally and a bolus of indocyanine green, 0.5 mg/kg body weight, intravenously.

RESULTS

The antipyrine clearance and ICG clearance were significantly decreased in the patients compared with the controls (mean, 27.2 ml/min; 95% confidence interval (CI), 19.4-35; versus 46.2 ml/min; 34.7-58.7, and 501 ml/min; 4014601, versus 771 mU/min; 677-865 (P < 0.05), respectively). The oxazepam clearance did not differ significantly between the two groups (181 ml/min (145-217) versus 178 ml/min (152-204)). The model drug clearance ratios between the patient and control clearances showed decreased values for antipyrine and ICG compared with the oxazepam data (0.59 and 0.65 versus 1.02, respectively). Patients and controls were characterized by a body weight of 58.2 kg (53.1-63.3) and 83.4 kg (72.7-94.1), respectively, and a body mass index (BMI) of 19.6 kg/m2 (17.9-21.3) versus 25.9 kg/m2 (23.4-28.4) (P < 0.05 for both).

CONCLUSIONS

Patients with chronic pancreatitis characterized by a moderately reduced exocrine function and absence of diabetes mellitus and overt liver disease had a decreased antipyrine oxidation and ICG clearance, whereas no difference was seen in oxazepam conjugation when compared with healthy volunteers. In chronic pancreatitis the hepatic phase-I oxidation is reduced compared with the phase-II conjugation, as shown by the model drug clearance ratios. The clearance of ICG was also affected, pointing at a reduced hepatic plasma flow, provided that the hepatic extraction fraction is normal for these patients.

Liver volume, portal vein flow, and clearance of indocyanine green and antipyrine in hyperthyroidism before and after antithyroid treatment

BACKGROUND

The aim of the study was to examine liver volume, portal vein flow, and indocyanine green (ICG) and antipyrine clearance in hyperthyroidism before and after antithyroid drug treatment.

METHODS

Liver volume and blood flow in the portal vein were investigated in nine fasting patients with hyperthyroidism by means of computed tomography scan and Doppler ultrasound, respectively. ICG clearance was estimated by bolus injection of ICG (0.5 mg/kg body weight) and antipyrine clearance with a one-sample technique. All patients were investigated before and after 3 months of antithyroid treatment, when euthyroidism had been achieved. The Wilcoxon matched-pairs test was used for statistical analysis.

RESULTS

The median liver volume increased by 238 (155-289) ml (median, 95% confidence interval), corresponding to 19%, and the weight by 5.0 (0.0-8.0) kg (8%), and the antipyrine clearance decreased by 8 (3.1-34.4) ml/min (16%). These changes were all significant (P < 0.05). The relation between liver volume and body weight increased from 19.9 (16.5-23.7) ml/kg to 21.4 (17.1-21.9) ml/kg (P = 0.11). The liver blood flow as estimated by ICG clearance and Doppler ultrasound was not altered significantly after the treatment period (P = 0.07 and 0.77, respectively).

CONCLUSIONS

The liver volume increased by 19% in nine hyperthyroid patients during treatment with antithyroids. Antipyrine clearance was reduced by 16%, whereas liver blood flow, as estimated by ICG clearance and Doppler ultrasound examination of portal vein flow, was not significantly altered. A differential regulation of liver volume and oxidative metabolic capacity in hyperthyroidism was seen.

The heart and thyroid disease

This article discusses the effects of thyroid hormone on the heart, cardiovascular symptoms and signs in elderly patients with hyperthyroidism and hypothyroidism, and the diagnosis and therapy of hyperthyroidism and hypothyroidism in elderly patients. Cardiovascular symptoms of hyperthyroidism include palpitations, angina, pectoris, and dyspnea on exertion, orthopnea, or paroxysmal nocturnal dyspnea. Atrial fibrillation or congestive heart failure may be the only clinical manifestation of hyperthyroidism in elderly patients with apathetic hyperthyroidism. Atrial fibrillation with a rapid ventricular rate due to hyperthyroidism should be treated with propranolol to control the rapid ventricular rate. Elderly patients with coronary artery disease and hypothyroidism should be treated cautiously with thyroid hormone replacement to avoid precipitating or exacerbating angina pectoris, precipitating acute myocardial infarction, and precipitating or aggravating ventricular arrhythmias or congestive heart failure.

Thyroid disease in older patients. Diagnosis and treatment

Thyroid gland dysfunction is a relatively common clinical problem in elderly people and is associated with significant morbidity if left untreated. The clinical features of thyroid disease may be subtle, easily overlooked or misdiagnosed. Therefore, a high index of suspicion is necessary. If potentially serious sequelae are to be avoided, the selection and interpretation of thyroid function tests must be appropriate. It is particularly important to consider both the effect of concurrent illness and the effect of certain drugs on thyroid function tests. With recent methodological advances, thyroid function tests are now more reliable, though in certain situations they still need to be interpreted with caution. Once the diagnosis is established, the management of both hypothyroidism and hyperthyroidism is relatively simple and effective, though there are special considerations relating to elderly patients.

Acute cyclosporine A nephrotoxicity in a renal allograft recipient with hypothyroidism

Cyclosporine A (CsA) is an important immunosuppressant in kidney transplantation. Acute CsA nephrotoxicity secondary to high drug levels is a well-recognized complication in the immediate posttransplant period. Cyclosporine A is metabolized in the body by the hepatic cytochrome P-450 enzyme system. We present a case of a hypothyroid patient who developed toxic blood CsA levels and acute nephrotoxicity with standard doses of CsA. A reduction of CsA levels led to an improvement of allograft function. Correction of the hypothyroid state resulted in the normalization of CsA requirements, but overcorrection led to an increased requirement of CsA. Thyroid dysfunction should be considered as an interacting factor in the metabolism of CsA.

Thyroid disease

Hyperthyroidism and hypothyroidism are common disorders in the elderly and may remain unrecognised until a patient presents with an apparently unrelated problem. The finding of an elevated level of thyroid stimulating hormone (TSH) with a normal serum thyroxine (T4) level represents "subclinical hypothyroidism", which does not necessarily require treatment. Iodine can precipitate hyperthyroidism in patients with autonomous thyroid tissue and the iodine-rich antiarrhythmic agent, amiodarone, may cause either hyperthyroidism or hypothyroidism. The metabolism and clearance of numerous therapeutic agents is altered when thyroid status is abnormal, so that dose adjustment may be necessary. In cardiac failure secondary to hyperthyroidism, great care must be taken in prescribing beta-blockers and diuretics; dosage of digitalis preparations may need to be increased. Thyroid replacement therapy can aggravate myocardial ischaemia and it may be appropriate to consider coronary artery bypass grafting before hypothyroidism is fully corrected. Antithyroid drugs, surgery and radioactive iodine all have a place in the treatment of hyperthyroidism in the elderly, depending on factors such as disease severity and the characteristics of the goitre. T4 may be given together with an antithyroid drug in a "block-replace" regimen.

Thyrotoxicosis and the heart

Many patients with thyrotoxicosis have clinical features that reflect the effects of excess thyroid hormone on the cardiovascular system. Thyrotoxicosis can aggravate preexisting cardiac disease and can also lead to atrial fibrillation, congestive heart failure, or worsening of angina pectoris. In elderly patients, these cardiac manifestations may dominate the clinical picture and warrant the measurement of the serum thyrotropin concentration. In the absence of preexisting cardiac disease, treatment of thyrotoxicosis usually results in a return of normal cardiac function.

Beta-adrenergic blockade for the treatment of hyperthyroidism

PURPOSE

To review the clinical and biochemical effects of beta-adrenergic blocking drugs on hyperthyroidism.

MATERIALS AND METHODS

Studies published since 1972 were identified through a computerized search of MEDLINE and extensive searching of the bibliographies of the articles identified. Based on an understanding of the differences in beta-blocker metabolism in euthyroid and hyperthyroid patients, we reviewed the differences in pharmacokinetics and metabolic and clinical outcomes during their use in hyperthyroidism, as reported in the articles reviewed.

RESULTS

beta Blockers have been used to modify the severity of the hyperadrenergic symptoms of hyperthyroidism for the past 20 years. The clinical efficacy of these agents is affected by hyperthyroid-induced alterations in their gastrointestinal absorption, hepatic metabolism, and renal excretion. The mechanisms whereby these clinical changes are effected is unknown. The agents differ in their beta 1 cardioselectivity, membrane-stabilizing activity, intrinsic sympathomimetic activity, and lipid solubility. They do not appear to alter synthesis or secretion of thyroid hormone by the thyroid gland. Their effects on thyroxine metabolism are contradictory. Decreased thyroxine to triiodothyronine conversion is caused by some, but not all, beta blockers, and this appears to correlate with membrane-stabilizing activity. There does not appear to be any alteration in catecholamine sensitivity during beta-adrenergic blockade.

CONCLUSIONS

The principal mechanism of action of beta blockers in hyperthyroidism is to antagonize beta-receptor-mediated effects of catecholamines. beta Blockers are effective in treating hypermetabolic symptoms in a variety of hyperthyroid states. Used alone, they offer significant symptomatic relief. They are also useful adjuvants to antithyroid medications, surgery, and radioactive iodide treatment in patients with Graves' disease and toxic nodular goiters.

Pharmacokinetics and pharmacodynamics of oxazepam and metabolism of paracetamol in severe hypothyroidism

1. The effect of severe hypothyroidism on the pharmacokinetics and pharmacodynamics of oxazepam 15 mg given orally (n = 10) and the metabolism of paracetamol 750 mg given intravenously (n = 8) was investigated before and after treatment with levothyroxine. 2. The median total and unbound clearance of oxazepam increased significantly during the study period from 0.78 ml min-1 kg-1 (0.40-1.25) to 1.22 ml min-1 kg-1 (0.66-1.94) and from 9.3 ml min-1 kg-1 (5.2-14.2) to 15.9 ml min-1 kg-1 (7.8-21.8), respectively (P less than 0.01). 3. The elimination half-life of oxazepam was prolonged by hypothyroidism to a median (range) value of 9.3 h (5.4-21.9) compared with 7.5 h (4.8-10.5) in the euthyroid state (P less than 0.05). 4. Hypothyroidism did not affect the protein binding of oxazepam; median values of the free percentage being 8.2% as compared with 7.7% when euthyroid. 5. The median (range) clearance of paracetamol under hypothyroid conditions was 3.12 ml min-1 kg-1 (1.64-4.40) and 4.70 ml min-1 kg-1 (3.18-5.70) following replacement therapy (P less than 0.01). This increase was associated with a comparable increase in the partial clearance to the glucuronide metabolite: 1.86 ml min-1 kg-1 to 2.70 ml min-1 kg-1. 6. Hypothyroidism was associated with decreased performance in a finger tapping test that was exacerbated by oxazepam. When the patients were euthyroid oxazepam did not produce any effect.

Mefenamic acid-induced neutropenia and renal failure in elderly females with hypothyroidism

We report mefenamic acid-induced non-oliguric renal failure and severe neutropenia occurring simultaneously in two elderly females. The neutropenia was due to maturation arrest of the myeloid series in one patient. Both patients were also hypothyroid, but it is not clear whether this was a predisposing factor to the development of these adverse reactions. However, it would seem prudent not to use mefenamic acid in hypothyroid patients until the hypothyroidism has been corrected.

Haemostasis in hypothyroidism

Abnormalities that have been reported for platelet indices and function, coagulation factors and tests, and the fibrinolytic system in hypothyroidism are reviewed. These abnormalities, although usually of limited importance clinically, may occasionally lead to major bleeding episodes and to diagnostic confusion.

Evolution of atenolol kinetics when hypothyroidism is corrected

A single oral dose of atenolol 100 mg was given to 7 hypothyroid patients (4 F, 3 M), before and after correction of hypothyroidism, mean delay 3.5 months (2 to 6.5 months). There was no change in the elimination parameters of atenolol, but the maximal plasma atenolol concentration was increased (1.66 to 7.37 mg.l-1) as was the AUC (14.9 to 52.1 mg.l-1.h) when the hypothyroidism had been treated. Only one patient differed: he had had a supra-selective vagotomy, and had similar curves before and after treatment of the hypothyroidism, both being similar to the plasma concentration curves found in the other patients after correction of the hypothyroidism. The results suggest an increase in the bioavailability of atenolol when hypothyroidism is corrected. The findings in the patient with vagotomy suggest that the decreased bioavailability during hypothyroidism might be related to changes in intestinal pH. Further studies are needed of the impact of hypothyroidism on gastric and pancreatic or biliary function and its consequences for drug absorption, and drug pharmacokinetics.

Pharmacokinetics and dromotropic activity of ajmaline in rats with hyperthyroidism

1. The pharmacokinetics and the dromotropic action (increased PQ interval) of intravenously administered ajmaline (2 mg kg-1) were studied in hyperthyroid rats with sinus tachycardia. The hyperthyroidism was induced by intraperitoneal injection of 3,5,3'-triiodo-L-thyronine (0.5 mg kg-1) for 4 days. 2. The change in the ajmaline concentration in whole blood could be described by a biexponential equation. The steady state distribution volume of ajmaline decreased from 4.81 l kg-1 in control rats to 3.80 l kg-1 in hyperthyroid rats and the total body blood clearance was slightly higher in hyperthyroid rats than in control rats. 3. Ajmaline exhibited a saturable binding to rat plasma proteins, and one kind of binding site was found in the observed range of concentrations. The binding capacity was 2 fold higher in hyperthyroid rats than in control rats. 4. On the basis of the plasma unbound concentration, ajmaline exhibited an increased negative dromotropic activity in hyperthyroid rats compared with control rats. 5. A positive correlation was found between the pacing rate and the dromotropic action of ajmaline on atrioventricular conduction in isolated perfused hearts. There was no significant difference in the rate-dependence of the effect of ajmaline on the heart between control and hyperthyroid rats. 6. Our findings suggest that the increased dromotropic activity of ajmaline is mainly due to the increased heart rate in hyperthyroid rats.

The haematology of hyperthyroidism: abnormalities of erythrocytes, leucocytes, thrombocytes and haemostasis

The abnormalities of erythrocytes, leucocytes, thrombocytes and coagulation that have been reported, particularly in more recent years, to be associated with hyperthyroidism are surveyed. Several areas are highlighted where further investigations could lead to clinically useful insights, improved information about the haematological processes involved or to a better understanding of thyroid hormone action.

The effect of thyrotoxicosis on isoniazid acetylation

Isoniazid acetylation was assessed in 10 thyrotoxic patients before and after standard antithyroid therapy. The group contained five fast and five slow acetylators and all remained within the same phenotypic classification when rendered euthyroid. There was no significant change in the elimination half-life of isoniazid between thyrotoxicosis and euthyroidism for the group as a whole or for fast and slow acetylators considered separately. Thyrotoxicosis does not appear to be an important determinant of isoniazid acetylation in man.

Pharmacokinetics of theophylline in hyperthyroid and hypothyroid patients with chronic obstructive pulmonary disease

The pharmacokinetics of theophylline was investigated in five hyperthyroid, five hypothyroid, and five euthyroid patients, all with chronic obstructive pulmonary disease. Wide individual variability was found in theophylline kinetics, but the rate of elimination of theophylline was significantly higher in hyperthyroid, and lower in hypothyroid patients than in the euthyroid patients (kel = 0.155, 0.060 and 0.107 h-1, respectively). The values for clearance and volume of distribution were not consistently changed compared with those in the euthyroid group, although all the parameters except AUC were significantly different in hyperthyroid and hypothyroid patients. There was a positive correlation between both thyroxine and triiodothyronine serum concentrations and total body clearance of theophylline (r = 0.795 and r = 0.791, respectively). It is concluded that in spite of the wide interindividual variability and the relatively small differences in the pharmacokinetics of theophylline in thyroid dysfunction compared with the euthyroid status, these differences have to be considered in certain clinical situations, as they may require changes in the therapeutic regimen for administration of theophylline in hyperthyroid or hypothyroid patients.

Amiodarone pharmacokinetics. II. Disposition kinetics following subchronic administration in rats

A 30 mg kg-1 intravenous bolus of 14C-amiodarone (19 microCi kg-1) was given to male Sprague-Dawley rats pretreated with 0 (vehicle), 25 or 100 mg kg-1 day-1 of amiodarone HCl orally for 37-42 days to determine the effects of dose and duration of administration on the disposition kinetics of amiodarone. Serial blood samples and total urine were collected over 48 hours and assayed for 14C-amiodarone by liquid scintillation counting following separation by HPLC. In all three groups, the blood 14C-amiodarone concentration-time curves declined bioexponentially with terminal half-lives (t1/2 beta) ranging from 14-22 hours. No differences in beta, t1/2 beta, or central compartment volume (Vc) were observed between the three groups of rats. In the rats pretreated with 100 mg kg-1 day-1 of amiodarone HCl for 5-6 weeks, amiodarone clearance (CL) and steady state volume of distribution (Vss) were reduced 52 per cent (12.2 to 5.9 ml min-1 kg-1) and 41 per cent (11.73 to 6.97 l kg-1), respectively. At the lower amiodarone daily dose, no changes in CL or Vss were observed. Negligible levels of radioactivity were detected in the urine. Amiodarone accounted for approximately 30-40 per cent of the total radioactivity in each blood specimen. This study demonstrated that CL and Vss were dose-dependent, and that beta, t1/2 beta and Vc were dose-independent. The results further suggested that the disposition kinetics of amiodarone were independent of the duration of drug administration.

Metabolic efficiency of the liver in patients with breast cancer as determined by pharmacokinetics of phenazone

Phenazone pharmacokinetics was determined in 24 healthy women and in 39 women with breast cancer; in the latter before and after antineoplastic treatment. The mean phenazone half-life time (t0.5) was significantly shorter in patients with breast cancer (8.880 +/- 2.5585 h) than in healthy persons (12.024 +/- 3.8486 h, P less than 0.001). Mean elimination rate constant (K, 0.063 +/- 0.0197 h-1) and mean metabolic clearance rate (MCR, 54.968 +/- 20.3476 ml/min) differed statistically (P less than 0.01) from the same parameters in control group, where K was 0.063 +/- 0.0197 h-1, MCR was 41.832 +/- 14.7153 ml/min. In patients receiving antineoplastic drugs, pharmacokinetic parameters of phenazone did not differ significantly in comparison with the initial values. Our results obtained with phenazone as a model substance suggest that in breast cancer elimination of other drugs metabolized by the pathway similar to phenazone also may be changed. This should be considered in selection of their dosage.

Ethchlorvynol pharmacokinetics during long-term administration in a patient with hyperlipidemia and hypothyroidism

A 33-year-old obese, hypothyroid, white male with several medical problems was admitted to University Hospital in September 1984 for treatment of drug intoxication. Admitting medications included ethchlorvynol in addition to other central nervous system depressants. Initial serum concentrations were reported at 70 micrograms/ml in this somnolent yet totally conscious adult. Established therapeutic concentrations are 2-8 micrograms/ml, with toxic exceeding 20 micrograms/ml. A tolerance phenomenon seemed evident. Serum ethchlorvynol concentrations were monitored daily during early hospitalization and continued to be substantially greater than reported toxic concentrations. Kinetic values were as follows: total body clearance 9.92 ml/min, volume of distribution 68.0 liters, and half-life 78 hours. These values are unique in that they were calculated from a patient who had not suffered an acute overdose, thereby differing markedly from previously published values. The influence of hypothyroidism and hyperlipidemia on these markedly different values appears to be significant. Ethchlorvynol should probably be added to the list of drugs influenced by thyroid disease.

Complications of surgery in hypothyroid patients

Hypothyroidism has generally been considered a contraindication to surgery. To determine the actual risks of perioperative complications in hypothyroid patients, the clinical courses of 40 hypothyroid surgical patients (serum thyroxine concentration 1.9 +/- 1.0 micrograms/dl) were retrospectively compared with those of 80 control patients matched for age, sex, and operative procedure. The two study groups were comparable in preoperative anesthetic physical class, prevalence of other medical conditions, and year of operation. During noncardiac surgery, intraoperative hypotension was encountered more frequently in the hypothyroid patients than in the control patients (61 versus 30 percent, p less than 0.05). Cardiac surgery was complicated by heart failure more often in the hypothyroid patients (29 versus 6 percent, p less than 0.05). Postoperatively, the hypothyroid patients more commonly had gastrointestinal (19 versus 1 percent, p less than 0.02) and neuropsychiatric (38 versus 18 percent, p less than 0.02) complications than control patients. Despite comparable rates of perioperative infection (38 versus 33 percent, p = NS), the hypothyroid patients less frequently manifested fever (35 versus 79 percent, p less than 0.001). There were no differences in perioperative blood loss, duration of hospitalization, or the prevalences of perioperative arrhythmia, hypothermia, hyponatremia, delayed anesthetic recovery, abnormal tissue integrity, impaired wound healing, pulmonary complications, or death. Preoperative clinical and chemical features of hypothyroidism were not useful in defining a subgroup of patients at special risk. Thus, surgery in hypothyroid patients is associated with an increased risk of several minor perioperative complications, which should be anticipated and preemptively managed in the course of their anesthetic and surgical care.

Impaired nitrazepam metabolism in hypothyroidism

Delayed metabolism of a number of drugs has been described in hypothyroid patients. We report an elderly hypothyroid female who had prolonged delay in the metabolism of a commonly-used sedative, nitrazepam, and discuss the importance of delayed drug metabolism in hypothyroidism.

Oxazepam pharmacokinetics in thyroid disease

The pharmacokinetics of oxazepam, a drug mainly eliminated by a single step glucuronidation reaction, were studied in seven hyperthyroid and six hypothyroid patients before and after treatment. Oxazepam elimination half-life was shorter and apparent oral clearance higher in untreated hyperthyroid patients than after treatment. There was no significant change in oxazepam elimination in hypothyroid subjects. Time to peak concentration (tmax) was reduced in the hyperthyroid state. Hypothyroidism had no significant effect on tmax. Serum bilirubin concentration was lower in the patients while hyperthyroid before treatment than when euthyroid and also lower than in the hypothyroid patients. There was no significant correlation between serum bilirubin concentrations and oxazepam elimination. These results suggest that glucuronyl transferase activity is increased in hyperthyroidism but is not altered in most patients with hypothyroidism. The extent of increase in glucuronyl transferase activity is similar to that produced by enzyme inducing drugs.

Drug toxicity and hormonal dysfunction

Abnormal levels of hormones can exert profound changes in drug disposition and the number and affinity of receptors. In endocrine diseases a variety of organ functions change. These disease related changes in the function of organs involved with the distribution, metabolism and excretion of drugs can profoundly alter drug disposition. If not taken into account when devising dosage regimens drug toxicity can result.