Clinical Pearls

A fatal mix concocted by intent and inattention: Herb-drug Interactions

It is widely acknowledged that many herbal medicines offer the prospect of novel and effective alternative drug therapy. It is disconcerting, however, that many herbal retailers may be guilty of selling herbal medicines without much more than a desperate hope that the herb will be safe.

Exemestane - the Preferred Adjuvant Hormonal Therapy in Metastatic Breast Cancer after Tamoxifen?

Introduction

Exemestane (EXE) is a steroidal irreversible aromatase inhibitor blocking the conversion of androgens to estrogens in peripheral tissues. It is currently indicated in the treatment of oestrogen-receptor positive advanced breast cancer in women with natural or induced post-menopausal status whose disease has progressed following anti-oestrogen therapy.
In contrast to nonsteroidal aromatase inhibitors (NS-AI), especially the 3rd generation aromatase inhibitors (such as anastrozole and letrozole) which bind reversibly to the cytochrome P450 (heme) moiety of the aromatase enzyme, EXE acts as false substrate that binds irreversibly to the substrate binding site of the enzyme. Both groups are well tolerated and exert similar efficacy with an over 90% reduction in circulating levels of estrogen.[1] However, the difference is EXE causes profound and prolonged reduction in aromatase levels, while NS-AI leads to aromatase up-regulation, thus possibly resulting in an earlier emergence of a resistant cell population [2]. In addition, EXE should theoretically exert a more effective global or some intra-tumoral aromatase inhibition because its metabolite, 17-hydroxyEXE has weak androgenic activity.

Introduction

Traditionally, glutamine has been considered as a non-essential amino acid. It is included in the list of "immunonutrients" that are required only when individuals are at risk of major infection. However, many recent laboratory and clinical data suggest that on top of the immunomodulating property, the multiple anabolic and host protective effects of glutamine may fuel the argument that glutamine may become an "essential" amino acid under certain clinical conditions.

Functions of glutamine

Glutamine is the most abundant free amino acid in the body, some 60% of the free intracellular amino acids in skeletal muscle. The synthesis of glutamine is regulated by glucocorticoids. During stress conditions, the efflux of glutamine from skeletal muscle serves as an important carrier of nitrogen to the splanchnic area and immune system. As a donor of nitrogen, glutamine acts as a precursor for the synthesis of purines, pyrimidines, amino sugars and antioxidant glutathione, it is therefore essential for cell proliferation. Increasing evidence also suggests that glutamine represents an essential substrate, metabolic fuel and energy source for the functions of many organ systems, including maintenance of muscle, preservation of GI tract integrity, acid-base balance, and promotion of the immune system. ^1-5

Introduction

Hormonal contraceptive agents are administered to the body through a variety of routes. The most common delivery methods are oral tablet, depot injection, implants and intrauterine device. EVRA, a contraceptive patch, that delivers an estrogen and a progestin via a transdermal route, has been launched in Hong Kong recently. It offers an additional choice to users and can enhance compliance by once weekly administration.

Description

EVRA is a combination transdermal contraceptive patch containing 6 mg norelgestromin (NGMN) and 600 mcg ethinyl estradiol (EE). The average daily dose absorbed into the systemic circulation is 150 mcg NGMN and 20 mcg EE.

Considerations for Drug-Enteral Tube Feeding Interaction

Continuous enteral feedings has been used extensively in critically ill patients, these patients are often administered medications through their feeding tubes out of necessity. As not all oral medications may be compatible with enteral nutrition, complications associated with administration of medications through feeding tubes may arise. Moreover, improper management of these interactions may lead to therapeutic failure or adversely affect the patients.

In the discussions below, we will highlight some drug - enteral tube feeding interactions which have been found to be clinically important.

Ezetimibe: a new agent for the treatment of hypercholesterolaemia

Hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or statins, are the principal agents for managing hyperlipidaemia. They act by inhibiting cholesterol production in the liver leading to a reduction in low-density lipoprotein (LDL) cholesterol and triglyceride levels, increasing high-density lipoprotein (HDL) cholesterol levels slightly and thus help to decrease the risk of coronary heart disease. Despite their established efficacy, not all patients achieve the recommended LDL cholesterol goals. Inadequate dosing due to adverse effects with high-dose, increased potential for intolerance and drug interactions with combinations of other available agents like bile acid sequestrants, fibric acid derivatives and nicotinic acid are all possible contributing factors. In addition, available statins have only modest effects on HDL. Thus, new lipid-lowering agents are needed for better clinical efficacy.

Erectile dysfunction, the inability to achieve and maintain an erection adequate for satisfactory sexual performance, has been reported to affect as many as 150 million men worldwide (1). Local treatments for erectile dysfunction include vacuum erection devices, penile prostheses and intracavernosal therapy. These treatment options may often limit patient satisfaction because of their invasiveness, unappealing technique or side effects (2). A more user friendly form of therapy for patients with erectile dysfunction is an orally active treatment. Sildenafil (Viagra) was the first oral agent to be launched in recent years. Its success was followed by the introduction of other new drugs into the market, including tadalafil (Cialis) and vardenafil (Levitra).

Drugs and chemicals to be avoided in Glucose-6-phosphate dehydrogenase deficiency

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the commonest enzyme disorder of human beings and a globally important cause of neonatal jaundice, which can lead to kernicterus and death or spastic cerebral palsy. It can also lead to life-threatening haemolytic crises in childhood and at later ages, by interacting with specific drugs and with fava beans in the diet.

The best known morbid effect of G6PD deficiency is hemolysis induced by oxidative drugs. When prescribing drugs for G6PD-deficient subjects, two points should be kept in mind: (1) different genetic variants of G6PD deficiency entail different susceptibility to the hemolytic risk from drugs; thus a drug found to be safe in some G6PD-deficient subjects may not be equally safe in others; (2) the risk and severity of hemolysis is almost always dose-related.

Method to apply Malathion Emulsion 0.5%

1. Take a hot bath and pat the skin dry with a towel.
2. Apply Malathion Emulsion to entire skin surface from the neck down including armpit, finger webs and toe webs.
3. Do not wash or bath for 24 hours.
4. Reapply the lotion to any area of skin which is washed during the 24 hours following application.
5. Clothing and bedding may be washed or dry cleaned in the normal way.
6. Seek medical advice if symptom persists 10 days afterward.

Malathion 0.5% 疥瘡乳劑用法:

1. 先用熱水沐浴。