science

Tachyphylaxis

Tachyphylaxis is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Tachyphylaxis rather than just read about it. In short: Tachyphylaxis (from Ancient Greek ταχύς, tachys 'rapid', and φύλαξις, phylaxis 'protection') is a medical term describing an acute, sudden decrease in response to a drug after its administration (i.e., a rapid and short-term onset of drug tolerance). It can occur after an initial dose or after a series of small doses.

Key takeaways

Tachyphylaxis belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tachyphylaxis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tachyphylaxis from memory before moving on to harder problems.

Reference excerpt

Tachyphylaxis (from Ancient Greek ταχύς, tachys 'rapid', and φύλαξις, phylaxis 'protection') is a medical term describing an acute, sudden decrease in response to a drug after its administration (i.e., a rapid and short-term onset of drug tolerance). It can occur after an initial dose or after a series of small doses. Increasing the dose of the drug may be able to restore the original response.

Characteristics Tachyphylaxis is characterized by the rate sensitivity: the response of the system depends on the rate with which a stimulus is presented. To be specific, a high-intensity prolonged stimulus or often-repeated stimulus may bring about a diminished response also known as desensitization.

Molecular interaction In biological sciences, molecular interactions are the physical bases of the operation of the system. The control of the operation, in general, involves interaction of a stimulus molecule with a receptor/enzyme subsystem by, typically, binding to the macromolecule A and causing an activation or an inhibition of the subsystem by forming an activated form of the macromolecule B. The following schematic represents the activity:

A → p B {\displaystyle A{\xrightarrow {\ \ p\ \ }}B}

where p is the activation rate coefficient. It is customary that p is called a rate constant, but, since the p stands for measure of the intensity of the stimulus causing the activation, p may be variable (non-constant). More complete is an open system, namely, in its simplest form,

R → A → p ( S ) B → q , {\displaystyle R{\xrightarrow {}}A{\xrightarrow {\ \ p(S)\ \ }}B{\xrightarrow {\ \ q\ \ }},}

where R stands for the rate of production of A, p(S) is the activation rate coefficient explicitly expressing its dependence on the stimulus intensity S and q represents the rate coefficient of removal from the state B. In this elementally open system the steady state of B always equal to R/q. The above scheme is only the necessary condition for the rate sensitivity phenomenon, and other pathways of deactivation of B may be considered, with the subsequent return to the inactive form of the receptor/enzyme A. Examples offer particular use of such (mathematical) models in endocrinology, physiology and pharmacology.

Examples

Psychedelics

Psychedelics such as LSD and psilocybin (found in psilocybin-containing mushrooms) demonstrate very rapid tachyphylaxis.

Opioids In a patient fully withdrawn from opioids, going back to an intermittent schedule or maintenance dosing protocol, a fraction of the old tolerance level will rapidly develop, usually starting two days after therapy is resumed and, in general, leveling off after day 7. Whether this is caused directly by opioid receptors modified in the past or affecting a change in some metabolic set-point is unclear. Increasing the dose will usually restore efficacy; relatively rapid opioid rotation may also be of use if the increase in tolerance continues.

Beta-2 agonists Inhalation of an agonist for the beta-2 adrenergic receptor, such as salbutamol (albuterol — USAN), is the most common treatment for asthma. Polymorphisms of the beta-2 receptor play a role in tachyphylaxis. Expression of the Gly-16 allele (glycine at position 16) results in greater receptor downregulation by endogenous catecholamines at baseline compared to Arg-16. This results in a greater single-use bronchodilator response in individuals homozygous for Arg-16 compared to Gly-16 homozygotes. However, with regular beta-2 agonist use, asthmatic Arg-16 individuals experience a significant decline in bronchodilator response. This decline does not occur in Gly-16 individuals. It has been proposed that the tachyphylactic effect of regular exposure to exogenous beta-2 agonists is more apparent in Arg-16 individuals because their receptors have not been downregulated prior to agonist administration.

Nicotine Nicotine may also show tachyphylaxis over the course of a day, although the mechanism of this action is unclear.

Methylphenidate Acute tachyphylaxis which does not carry into the next day has been observed in children taking methylphenidate, and inspired the development of OROS methylphenidate.

Other examples Nitroglycerine (or glyceryl trinitrate) and other nitrovasodilators of the nitrate type demonstrates tachyphylaxis, requiring drug-free intervals of 6 to 8 hours. Hydralazine displays tachyphylaxis if given as a monotherapy for antihypertensive treatment. It is administered with a beta-blocker with or without a diuretic. Metoclopramide Dobutamine, a direct-acting beta agonist used in congestive heart failure, also demonstrates tachyphylaxis. Desmopressin used in the treatment of type 1 von Willebrand disease is, in general, given every 12–24 hours in limited numbers due to its tachyphylactic properties. Erythromycin, used for gastroparesis treatment Hormone replacement, when used in menopausal women in the form of estrogen and progesterone implants, is cited as having potential to lead to tachyphylaxis, but that citation is based on a single study done in 1990 and no follow-up research is available to support this interpretation.

Intervention and reversal

Intranasal decongestants Use of nasal decongestants (e.g., oxymetazoline) for more than three days leads to tachyphylaxis of response and rebound congestion, caused by alpha-adrenergic receptor downregulation and desensitization. The mechanism may specifically include receptor internalisation and resistance to endogenous vasoconstrictors causing worsening in symptoms post use of medication. Oxymetazoline-induced tachyphylaxis and rebound congestion are reversed by intranasal fluticasone.

Worked examples

Example 1 — a first encounter with Tachyphylaxis

Start with the simplest possible case. Write down what Tachyphylaxis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tachyphylaxis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tachyphylaxis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tachyphylaxis

In research: Tachyphylaxis appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tachyphylaxis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tachyphylaxis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Pharmacodynamics, so understanding it makes those chapters shorter.
In everyday life: Look for Tachyphylaxis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Tachyphylaxis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tachyphylaxis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tachyphylaxis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tachyphylaxis in simple terms?

Why does Tachyphylaxis matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tachyphylaxis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tachyphylaxis.