PharmaNUS

Which fruit to avoid with fexofenadine?

It is advised to avoid taking fexofenadine with fruit juices. But does this apply to all fruit juices or only grapefruit juice? And what about tomato juice – are tomatoes not also fruit? And why the warning only about the juice – what happens if you eat the fruit instead of drinking the juice?

Grapefruit and Drug Metabolism – A Closer Look at CYP Interactions: Many of us might have come across warnings about the potential interaction between grapefruit juice and certain medications. Let’s delve deeper into the science behind this. Grapefruits, along with other specific citrus fruits like pomelos and Seville oranges (often termed as bitter oranges or sour oranges), are rich in polyphenols, notably furanocoumarins. These compounds play a crucial role in inhibiting various cytochrome P450 enzymes, including CYP3A4, CYP1A2, CYP2C9, and CYP2D6.

Why does this matter? The inhibition of the CYP3A4 enzyme, in particular, impedes its ability to effectively metabolize certain drugs. As a result, there can be an unintended increase in the drug levels within the bloodstream, amplifying the risk of side effects or even toxicities. It’s noteworthy that CYP3A4 is pivotal for the metabolism of a wide range of medications. Consequently, grapefruit’s interaction can potentially affect the efficacy and safety of medications such as statins (targeting high cholesterol), calcium channel blockers (for managing hypertension), calcineurin inhibitors (used in immunosuppression), and benzodiazepines (prescribed for anxiety and insomnia).

Fruit and Fexofenadine – Reduced Absorption: Contrary to the increased plasma concentration of drugs seen following inhibition of CYP enzymes, fruit juices decrease intestinal absorption of the second-generation H1 antihistamine, fexofenadine. The mechanism behind this interaction involves intestinal transporters, specifically organic anion-transporting polypeptides (OATPs).

Why are peripheral effects of AChE inhibitors predominantly parasympathomimetic?

August 30, 2023 / phcdgs / 0 Comments

Acetylcholinesterase (AChE) inhibitors will prevent the breakdown of acetylcholine (ACh) and so increase ACh levels. Increased ACh levels at autonomic nervous system ganglia should activate both the sympathetic and parasympathetic nervous systems. However, the adverse effects of AChE inhibitors outside of the CNS are mostly parasympathomimetic. Why do AChE inhibitors not stimulate the sympathetic nervous system as well?

Acetylcholinesterase (AChE) inhibitors increase the concentration of acetylcholine (ACh) at synapses by blocking its breakdown. This will activate both the sympathetic and parasympathetic systems, as the preganglionic neurons in both systems release ACh.

However, the impact of AChE inhibitors is more prominent on the parasympathetic nervous system for several reasons:
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When sympathetic and parasympathetic systems collide: The dominance of excitatory effects

August 30, 2023 / phcdgs / 0 Comments

When the autonomic nervous system ganglia are activated (for example, by low-dose nicotine), both the sympathetic and parasympathetic nervous system innervations of target organs and tissues are simultaneously stimulated. However, the “fright, fight or flight” sympathetic and “rest and digest” parasympathetic nervous systems have opposing effects in most target organs and tissues. So why do the sympathetic and parasympathetic nervous systems not just cancel each other out when activated at the same time?

It is true that in the realm of autonomic nervous system functioning, the sympathetic and parasympathetic systems often represent two sides of the same coin. These systems largely produce opposing effects on the same target organs and tissues. However, what happens when both systems are simultaneously activated? Contrary to intuitive thinking, they don’t simply cancel each other out. Instead, the dominion of activation or excitatory effects takes centre stage.

The Principle of Dominant Excitation: When both the sympathetic and parasympathetic systems are co-activated, it isn’t a zero-sum game. Rather than neutralizing each other, the excitatory effects from each system generally prevail. This principle is observed in a variety of physiological contexts. Continue reading

Why is hydroxychloroquine used for systemic lupus erythematosus (SLE)?

August 27, 2023 / phcdgs / 0 Comments

Why is an antimalarial drug, hydroxychloroquine, used as a rheumatological immunosuppressant in disorders such as systemic lupus erythematosus (SLE)?

Hydroxychloroquine (HCQ), originally developed as an antimalarial, has become a cornerstone in the treatment of autoimmune diseases, including systemic lupus erythematosus (SLE), primary Sjögren’s syndrome, and rheumatoid arthritis. How does this drug help address the challenges posed by these autoimmune diseases?

1. Interference with lysosomal activity and autophagy:
HCQ increases the pH within intracellular lysosomes, interrupting the autophagy of macromolecules and antigen processing in antigen-presenting cells. This leads to diminished T cell stimulation, providing an advantage in autoimmune conditions like SLE by modulating immune responses. Continue reading

Why do corticosteroids increase circulating neutrophils?

August 27, 2023 / phcdgs / 0 Comments

Corticosteroids are anti-inflammatory, reducing the number and activity of various inflammatory cell types, including lowering blood lymphocyte, monocyte, and basophil counts and preventing neutrophils from reaching sites of inflammation. So why do corticosteroids increase the number of neutrophils in circulation?

The effects of corticosteroids reducing the infiltration of neutrophils to sites of inflammation within tissues and increasing the number of neutrophils staying in circulation are two sides of the same mechanism.

Surface expression of proteins, such as L-selectin, is involved in the rolling capture and adherence of neutrophils to blood vessel walls, which is necessary to enable extravasation through blood vessel walls and migration into tissues. Corticosteroids acting via glucocorticoid receptors regulate the expression of many genes involved in inflammatory responses. Continue reading

Thiazide diuretics and hypercalcaemia

February 18, 2022 / phcdgs / 0 Comments

Why is it said that thiazide diuretics may unmask hypercalcemia?

Thiazide diuretics increase the risk of hypercalcaemia. There are several mechanisms by which they have been reported to contribute to increased serum calcium levels, but most important is that they increase renal tubular reabsorption of calcium resulting in reduced calcium excretion in urine. Normally, this is not a problem for otherwise healthy individuals. However, thiazide diuretics are contraindicated in patients at risk of hypercalcaemia, for example, because of primary hyperparathyroidism or sarcoidosis.

Primary hyperparathyroidism is the most common cause of hypercalcaemia. Excessive secretion of parathyroid hormone (PTH), a key factor in calcium metabolism, results in the leaching of calcium from bone and increased production of calcitriol, the active form of Vitamin D, which increases intestinal absorption of calcium and reabsorption in the kidneys. Sarcoidosis is clinically observed to be associated with increased risk of hypercalcaemia, which is most frequently explained by overproduction of calcitriol by activated macrophages.

PPIs and C. difficile infection

February 1, 2022 / phcdgs / 0 Comments

Does the use of proton-pump inhibitors (PPIs) increase the risk of Clostridioides difficile infection?

Medical literature has debated whether PPIs increase the risk of C. difficile enteric infections for many years. Analysis of the issue has been complicated because proton-pump inhibitors are often taken together with antibiotics in triple therapy to eradicate Helicobacter pylori. Antibiotics can alter the normal gut microbiota allowing the proliferation of C. difficile.

While the pathophysiological mechanisms remain unknown, the evidence increasingly supports the conclusion that PPIs increase the risk of C. difficile infection even without antibiotic use (Wolfe et al., 2021). There is a greater risk of C. difficile infection with PPIs than H2 receptor blockers (Kwok et al., 2012; Leonard et al., 2007). Although there is considerable variation among studies, overall PPIs also increase the risk of recurrent C. difficile infection (Kwok et al., 2012; Tariq et al., 2017).
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Hashimoto’s thyroiditis versus Hashimoto’s encephalopathy

September 10, 2021 / phcdgs / 0 Comments

Is Hashimoto’s encephalopathy related to Hashimoto’s thyroiditis?

• Hashimoto’s thyroiditis is an autoimmune disease in which the thyroid gland is gradually destroyed, resulting in chronic hypothyroidism.
• Hashimoto’s encephalopathy is a rare neurological condition characterized by encephalopathy and thyroid autoimmunity. It shows a good clinical response to corticosteroids.

Hashimoto’s thyroiditis, so named because it was first described in a medical publication by Hakaru Hashimoto (1881-1934) in 1912, is an autoimmune disease. Typically the autoantibodies include antibodies against thyroid peroxidase (TPO). TPO is an enzyme expressed in the thyroid gland that is essential for the production of thyroid hormones. In Hashimoto’s thyroiditis, the thyroid gland is gradually destroyed, resulting in chronic hypothyroidism unless treated with thyroid hormone replacement. It is the most common form of hypothyroidism, affecting about 5% of people.

Hashimoto’s encephalopathy, also known as steroid-responsive encephalopathy associated with autoimmune thyroiditis (SREAT), is an extremely rare (2.1 in 100,000) neurological condition characterized by encephalopathy and thyroid autoimmunity, which shows a good clinical response to corticosteroids. First described by Brain, Jellinek and Ball in 1966, the condition was named for its association with Hashimoto’s thyroiditis, but the pathogenic autoantibodies are thought to be against alpha-enolase, a ubiquitous enzyme invovled in glycolysis. Glycolysis is the metabolic pathway that converts glucose to pyruvic acid releasing energy in the form of adenosine triphosphate (ATP).

Levothyroxine and cancer?

September 10, 2021 / phcdgs / 0 Comments

Is there an association between levothryoxine and breast cancer?

The short answer is that there is not sufficient evidence to draw any conclusion at this time. Patients who require levothyroxine should continue to take their medication as prescribed by their doctor. The risk of ultimately fatal myxedema due to severe untreated hypothyroidism is proven and real. The risk of cancer is speculative and not definitively proven.

When this question came up at the end of the lecture, my initial thought was that an association between levothryoxine and cancer is highly improbable. Oral levothyroxine essentially replaces your own endogenous thyroxine (T4). Treatment normalises T4 levels but should not cause supraphysiological levels of T4. Even the route of absorption is largely physiological as endogenous T4 is recycled through enterohepatic circulation and is absorbed in the small intestine after being excreted in the bile. The only potentially “unnatural” exposure is as the levothryoxine tablet passes from the mouth to the stomach. In theory, there is no reason why taking levothyroxine should expose anyone to greater risk than having physiologically normal thyroid function would.
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Folate, folic acid or folinic acid to reduce adverse effects of methotrexate?

May 9, 2021 / phcdgs / 0 Comments

What is the difference between folate, folic acid, and folinic acid? And how do each of them contribute or are involved in the methotrexate pathway?

Folate is the naturally occurring salt form of vitamin B9. Folic acid is a synthetic water-soluble acid form of vitamin B9. Folate and folic acid are metabolised by dihydrofolate reductase, the enzyme inhibited by methotrexate, to FH2 and then FH4, which in turn is converted to N5, N10-methylene-FH4.

Folinic acid (also known as leucovorin) is N5-formyl-FH4 and can be converted rapidly to N5, N10-methylene-FH4 without the need for dihydrofolate reductase and so bypasses the inhibition of the pathway by methotrexate.

In the treatment of rheumatoid arthritis with methotrexate, adverse effects include nausea and vomiting, mouth and gastrointestinal ulcers, and hair loss are caused by the reduction in N5, N10-methylene-FH4, which is required for the synthesis of amino acids and nucleic acids necessary for cell proliferation. Folic acid at high enough doses to overcome the methotrexate inhibition of dihydrofolate reductase or folinic acid is therefore used to reduce the adverse effects of methotrexate.