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-25 and 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In a patient fully withdrawn from opioids, going back to an intermittent schedule or maintenance dosing protocol, a fraction of the old tolerance level will rapidly develop, usually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 in the US), 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.
Ropivacaine (rINN)  is a local anaesthetic drug belonging to the amino amide group. The name ropivacaine refers to both the racemate and the marketed S-enantiomer. Ropivacaine hydrochloride is commonly marketed by AstraZeneca under the brand name Naropin. History
Ropivacaine was developed after bupivacaine was noted to be associated with cardiac arrest, particularly in pregnant women. Ropivacaine was found to have less cardiotoxicity than bupivacaine in animal models. Clinical use
Contraindications
Ropivacaine is contraindicated for intravenous regional anaesthesia (IVRA). However, new data suggested both ropivacaine (1.2-1.8 mg/kg in 40ml) and levobupivacaine (40 ml of 0.125% solution) can be used, because they have less cardiovascular and central nervous system toxicity than racemic bupivacaine. Adverse effects
Adverse drug reactions (ADRs) are rare when it is administered correctly. Most ADRs relate to administration technique (resulting in systemic exposure) or pharmacological effects of anesthesia, however allergic reactions can rarely occur. Systemic exposure to excessive quantities of ropivacaine mainly result in central nervous system (CNS) and cardiovascular effects – CNS effects usually occur at lower blood plasma concentrations and additional cardiovascular effects present at higher concentrations, though cardiovascular collapse may also occur with low concentrations. CNS effects may include CNS excitation (nervousness, tingling around the mouth, tinnitus, tremor, dizziness, blurred vision, seizures followed by depression (drowsiness, loss of consciousness), respiratory depression and apnea). Cardiovascular effects include hypotension, bradycardia, arrhythmias, and/or cardiac arrest – some of which may be due to hypoxemia secondary to respiratory depression. Postarthroscopic glenohumeral chondrolysis
Ropivacaine is toxic to cartilage and their intra-articular infusions can lead to Postarthroscopic glenohumeral chondrolysis.