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Medications
Published in Henry J. Woodford, Essential Geriatrics, 2022
The two main mechanisms of drug elimination are hepatic metabolism and renal excretion. Both of these are impaired in older age. The reduced hepatic metabolic capacity may be related to several processes, including reduced blood flow or enzyme activity. An age-related reduction in liver mass (estimated 20% to 50% decrease by age 80) is an important factor. On average, glomerular filtration rate (GFR) progressively declines with advancing age. This is around a 10% reduction per decade after the age of 30, due to a number of physiological changes (see page 9). Digoxin is an example of a drug with reduced renal clearance and increased toxicity risk in older people (see page 364). Some drugs are eliminated by active excretion into the renal tubules, which can also diminish. So, older people are prone to change in drug peak concentrations and half-lives. Adjusting drug doses or administration frequency can compensate for this.
Paediatric clinical pharmacology
Published in Evelyne Jacqz-Aigrain, Imti Choonara, Paediatric Clinical Pharmacology, 2021
Evelyne Jacqz-Aigrain, Imti Choonara
As the time to halve the drug amount in the body is constant, the time to essentially complete drug elimination is constant, usually five half-lives, and independent of the starting amount of drug. In overdose, however, drug elimination may be prolonged if the elimination route is saturated.
Adrenergic Antagonists
Published in Sahab Uddin, Rashid Mamunur, Advances in Neuropharmacology, 2020
It is a selective antagonist of β1 receptor and it does not show intrinsic sympathomimetic action. It shows a slight membrane stabilizing activity (Brunton et al., 2011; Mayama et al., 2013). It is employed in treating hypertension, angina and glaucoma. In ophthalmology, it lowers the production of the aqueous humor therefore reduces the intraocular pressure. It is well absorbed and shows a high bioavail-ability. The drug has a half-life of about 14–22 h. Drug elimination is partly by hepatic and renal route (Brunton et al., 2011; McDevitt, 1987).
Effects of intestinal flora on pharmacokinetics and pharmacodynamics of drugs
Published in Drug Metabolism Reviews, 2023
Amina Džidić-Krivić, Jasna Kusturica, Emina Karahmet Sher, Nejra Selak, Nejra Osmančević, Esma Karahmet Farhat, Farooq Sher
Many studies have been conducted in the last two decades attempting to prove the interplay between gut microbiota and drug pharmacokinetics as shown in Table 1. Four basic processes researched in the area of pharmacokinetics are drug absorption, their distribution in the organism followed by drug metabolism. The final step is drug elimination or excretion. This dialogue between four complex pharmacokinetic processes has an important role in the successful clinical outcome after the treatment with the observed drug in the organism as well as in the occurrence of drug potential side effects. As it is known, the same drug can show positive and toxicological effects. The most important differing factor is the used dosage that is highly influenced by the dynamic of basic pharmacokinetic processes (Chen et al. 2021).
Can COVID-19 have a clinically significant effect on drug metabolism?
Published in Expert Opinion on Drug Safety, 2023
Felicia Ceban, Mehala Subramaniapillai, Joshua D. Rosenblat, Rodrigo B. Mansur, Roger S. McIntyre
Hepatic metabolism is one of three major routes of drug elimination. Drug metabolism generally involves a sequence of two reactions that allow for efficient excretion by the kidneys. Phase I reactions are catabolic and typically involve reduction, oxidation, or hydrolysis to convert lipophilic agents into more polar and reactive products. Phase II reactions are anabolic and consist of conjugation reactions with endogenous hydrophilic substances to further polarize and usually inactivate the parent drug [1]. The Cytochrome P450 (CYP450) enzymes, a set of heme proteins, frequently catalyze reactions involved in phase I metabolism. Although there exist 57 CYP isoforms in humans, not all are involved in drug metabolism, and CYP3A4/5, CYP2D6, CYP2C8/9, and CYP1A2 are responsible for the majority of reactions catalyzed by CYP450 [2]. Herein, we aim to explore the possibility of whether COVID-19 infection and associated inflammation can affect drug metabolism.
A Review of New Medications and Future Directions of Medical Therapies in Glaucoma
Published in Seminars in Ophthalmology, 2020
Netarsudil is metabolized by corneal esterase to its main active metabolite, netarsudil-M1. Most of the medication stays local to the site of application, as little to no quantifiable amount of the medication was found systemically in a study by Levy et al.7 The elimination half-life of netarsudil from the cornea, conjunctiva, and vitreous humor ranged from 12 to 27 hours. While the elimination half-life from the retina-choroid-plexus, lens, and iris/ciliary body was longer, ranging from 68 to 112 hours.6 Clinically, this helps dictate dosing frequency, which is once daily for netarsudil 0.02%. Additionally, the elimination half-life is important in the time to reach steady state concentration as well as time to drug elimination, which are vital in monitoring medication effectiveness. In this case, it can take potentially up to 18 days or 4–5 times the half-life.