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Hydrolysis of ester- and amide-type drugs by the purified isoenzymes of nonspecific carboxylesterase from rat liver.

Five purified carboxylesterases from rat liver microsomes show a differing capacity for the hydrolysis of ester- and amide-type drugs. The two closely related enzymes that are responsible for the microsomal hydrolysis of palmitoyl-CoA and long chain monoacylglycerides exhibit the highest propanidid-and aspirin-cleaving rates. The predominant nonspecific esterase of microsomes is responsible for the hydrolysis of procaine, clofibrate, isoarecaidine esters, butanilicaine, octanoylamide, and possibly butyryl thiocholine. Finally, the palmitoyl carnitine-cleaving esterase splits phenacetin and acetanilide. The purified nonspecific esterase with the lowest isoelectric point is not involved in the metabolism of the drugs mentioned.

Amides↗

Solution and solid state properties of a set of procaine and procainamide derivatives.

A set of potential Class III antiarrhythmic agents of structure p-HOOC-R-CO-NH-C(6)H(4)-CO-X-C(2)H(5)-N(C(2)H(5))(2) were isolated as crystalline solids of the amide and ester derivatives, I: succinylprocainamide (X=-NH-, R=-C(2)H(4)-); II: succinylprocaine (X=-O-, R=-C(2)H(4)-); III: maleylprocainamide (X=-NH-, R=-C(2)H(2)-) and IV: maleylprocaine (X=-O-, R=-C(2)H(2)-). Although compounds I-IV exhibit similar solution properties (i.e. acid-base speciation, with zwitterionic (+-) to neutral (00) form ratios higher than 10(4)), aqueous solubility of -NH- derivatives is significantly higher than that of -O- derivatives and also, solvent effects on solubility (i.e. the change of water by ethanol) is clearly different in both series. Solution and solid-state properties of I-IV were characterized to account for the observed differences. Results indicate that procainamide derivatives I and III crystallizes as (+-)(s) but procaine derivatives II and IV as (00)(s). Besides, I is anhydrous but II-IV are hydrates. Aqueous solubility and solvent effect on solubility are controlled by the intrinsic solubility of the species (+-) in I and III and (00) in II and IV. The rise of hydrophilicity of species (00) due to the structural change from -O- to -NH- would determine the change in the structure of the precipitating crystals from (00)(s) to (+-)(s). Solid structure (zwitterionic or neutral), as well as composition (anhydrous or hydrated) may be recognized as the main factors in determining the rank of aqueous solubility of the set: (+-)>(+-.H(2)O)>(00.H(2)O).

Anti-Arrhythmia Agents↗

Investigation of the mechanism of action of oxotremorine on the guinea-pig isolated ileum preparation.

1. The effects of oxotremorine on the guinea-pig ileum have been investigated to determine whether any component of its action is due to acetylcholine release.2. Log dose-response curves to oxotremorine and acetylcholine were similar and both drugs were competitively antagonized by atropine.3. Mipafox potentiated acetylcholine but not oxotremorine.4. No evidence of an indirect component of the action of oxotremorine was obtained using various pharmacological procedures (tetrodotoxin, morphine, cooling, procaine and hemicholinium-3).5. Oxotremorine had no effect on acetylcholine release from mipafox treated ileum but decreased the release from physostigmine treated ileum.6. It is concluded that oxotremorine acts directly on muscarinic receptors and not by releasing acetylcholine.

Acetylcholine↗

Comparison of local anesthetics as bronchodilator aerosols.

Lidocaine aerosols have been ineffective at preventing airway constriction provoked by non-reflex stimuli. To determine if there were any advantages to using more potent amide-type local anesthetics or local anesthetics from other chemical classes, the authors compared the protection afforded by pretreatment with aerosols of lidocaine, bupivacaine, hexylcaine, and procaine against a subsequent prolonged challenge (5 min) with 10% citric acid aerosols in barbiturate-anesthetized Basenji-Greyhound dogs. The local anesthetics were administered as aerosols (4% solutions) for 10 min immediately preceding the citric acid challenge. In control experiments, that employed pretreatment with aerosols of isotonic saline rather than local anesthetics, the citric acid challenge aerosol increased pulmonary resistance by an average of 3.3 +/- 0.8 (+/- SE) cmH2O X 1(-1) X s during the first 15-min postchallenge, and reduced dynamic compliance by one-third during this time. None of the local anesthetics prevented citric-acid-induced changes in pulmonary mechanics. The average increases in pulmonary resistance (0-15 min postchallenge) elicited by citric acid aerosols in dogs pretreated with lidocaine, hexylcaine, bupivacaine, and procaine were 2.1 +/- 0.6, 2.1 +/- 0.6, 3.2 +/- 1.3, and 3.3 +/- 1.0 cmH2O X 1(-1) X s, respectively. The authors concluded that local anesthetic aerosols have little or no effect against other than reflex bronchoconstriction, and none of those tested were more effective than lidocaine.

Anesthetics, Local↗

Local anesthetics inhibit uterine activity in vitro. Possible application on preterm labor prevention and treatment.

OBJECTIVE: Analysis of the effects of local anesthetics upon the gravid uterus. METHODS: Isolated strips of pregnant-rat myometrium were placed within tissue baths. Muscular activity was then recorded by a force transducer, at cumulative concentrations of either procaine, lidocaine, or ropivacaine. RESULTS: The effects of myometrial activity were non-monotonic. At lower concentrations, an increase in contraction frequency was noted, concomitant with a depression in amplitude. As the concentrations increased, both amplitude and frequency were depressed until, eventually, activity was abolished. CONCLUSIONS: Local anesthetics administered in situ consistently inhibit or completely arrest overall myometrial activity. These agents may prove clinically useful in preterm labor management, if administered locally to the myometrium via suitable slow release drug delivery systems, warranting further trials in vivo.

Amides↗

Fundamental properties of local anesthetics: half-maximal blocking concentrations for tonic block of Na+ and K+ channels in peripheral nerve.

UNLABELLED: Local anesthetics suppress excitability by interfering with ion channel function. Ensheathment of peripheral nerve fibers, however, impedes diffusion of drugs to the ion channels and may influence the evaluation of local anesthetic potencies. Investigating ion channels in excised membrane patches avoids these diffusion barriers. We investigated the effect of local anesthetics with voltage-dependent Na+ and K+ channels in enzymatically dissociated sciatic nerve fibers of Xenopus laevis using the patch clamp method. The outside-out configuration was chosen to apply drugs to the external face of the membrane. Local anesthetics reversibly blocked the transient Na+ inward current, as well as the steady-state K+ outward current. Half-maximal tonic inhibiting concentrations (IC50), as obtained from concentration-effect curves for Na+ current block were: tetracaine 0.7 microM, etidocaine 18 microM, bupivacaine 27 microM, procaine 60 microM, mepivacaine 149 microM, and lidocaine 204 microM. The values for voltage-dependent K+ current block were: bupivacaine 92 microM, etidocaine 176 microM, tetracaine 946 microM, lidocaine 1118 microM, mepivacaine 2305 microM, and procaine 6302 microM. Correlation of potencies with octanol:buffer partition coefficients (logP0) revealed that ester-bound local anesthetics were more potent in blocking Na+ channels than amide drugs. Within these groups, lipophilicity governed local anesthetic potency. We conclude that local anesthetic action on peripheral nerve ion channels is mediated via lipophilic drug-channel interactions. IMPLICATIONS: Half-maximal blocking concentrations of commonly used local anesthetics for Na+ and K+ channel block were determined on small membrane patches of peripheral nerve fibers. Because drugs can directly diffuse to the ion channel in this model, these data result from direct interactions of the drugs with ion channels.

Anesthetics, Local↗

The discovery and characterization of a proton-gated sodium current in rat retinal ganglion cells.

The conduction of acid-evoked currents in central and sensory neurons is now primarily attributed to a family of proteins called acid-sensing ion channels (ASICs). In peripheral neurons, their physiological function has been linked to nociception, mechanoreception, and taste transduction; however, their role in the CNS remains unclear. This study describes the discovery of a proton-gated current in rat retinal ganglion cells termed I(Na(H+)), which also appears to be mediated by ASICs. RT-PCR confirmed the presence of ASIC mRNA (subunits la, 2a, 2b, 3, and 4) in the rat retina. Electrophysiological investigation showed that all retinal ganglion cells respond to rapid extracellular acidification with the activation of a transient Na+ current, the size of which increases with increasing acidification between pH 6.5 and pH 3.0. I(Na(H+)) desensitizes completely in the continued presence of acid, its current-voltage relationship is linear and its reversal potential shifts with E(Na). I(Na(H+)) is reversibly inhibited by amiloride (IC(50), 188 microm) but is resistant to block by TTX (0.5 microm), Cd2+ (100 microm), procaine (10 mm), and is not activated by capsaicin (0.5 microm). I(Na(H+)) is not potentiated by Zn2+ (300 microm) or Phe-Met-Arg-Phe-amide (50microm) but is inhibited by neuropeptide-FF (50microm). Acute application of pH 6.5 to retinal ganglion cells causes sustained depolarization and repetitive firing similar to the trains of action potentials normally associated with current injection into these cells. The presence of a proton-gated current in the neural retina suggests that ASICs may have a more diverse role in the CNS.

Acid Sensing Ion Channels↗

Study on brain uptake of local anesthetics in rats.

Brain uptake of local anesthetics under steady-state plasma condition and/or following intravenous bolus administration was investigated in rats. All ester-type anesthetics examined such as ethyl (Et), propyl (Pr), butyl (Bu) esters of p-aminobenzoic acid (PABA), and procaine disappeared rapidly from plasma in a dose-dependent manner. Plasma profiles of these compounds were well explained by a 2-compartment model with a Michaelis-Menten type elimination process from a central compartment. On the other hand, lidocaine, amide-type anesthetic, showed a linear pharmacokinetic characteristic and its half life in the elimination phase was far longer than those of ester type agents. Extents of brain uptake (brain-to-plasma partition coefficient, Kp value) of these drugs were determined at 3 different steady-state plasma concentrations (1-15 microM). The Kp value of each drug was similar under the three different steady-state plasma concentrations. The Kp value increased in the following order; procaine (1.1) less than PABA-Et (1.9) less than lidocaine (2.2) less than PABA-Pr (2.7) less than PABA-Bu (3.6). A linear relationship was observed between the Kp value and the logarithmic value of the partition coefficient obtained in n-heptane/water or n-octanol/water partition system. The value of PABA-Et and PABA-Bu following intravenous bolus administration were varied with time elapsed but the mean values were almost same with those obtained under steady-state plasma conditions.

4-Aminobenzoic Acid↗

Xylocaine: 50 years of clinical service to dentistry.

In today's dental practice, local anesthesia is safe and effective, and injectable agents only rarely cause allergy. Ester-type agents, like procaine, which served the profession for over 50 years, have now been abandoned and are no longer available in dental cartridges in the U.S. Modern practitioners know of their disadvantages only through historical accounts of local anesthesia, and utilize daily the excellent chemical and pharmacologic characteristics of the amide local anesthetics, a tradition begun with the introduction of Xylocaine in the late 1940s and a tradition which will likely continue into the 21st century. The reader is referred to Table III for a comparison of quantities and dollar-value of sales of amide local anesthetics available in dental cartridges (17). In order to supplant Xylocaine (lidocaine) as a preferred local anesthetic in dentistry, any new agent will have to prove that it is superior in terms of short onset, appropriate duration, stability, excellent safety record, low allergenicity, and topical efficacy. As our understanding of the molecular structure of ion channels and the interactions of local anesthetics with neural sodium channels increase, new agents can be developed rationally. In the meantime, the amide local anesthetics will continue to serve dentists and their patients by providing safe and effective control of pain to facilitate ever-advancing surgical and restorative techniques.

Anesthesia, Dental↗

[New anesthetics].

Since the introduction of cocaine local analgesia in 1886, and the subsequent development of procaine (1904) and other closely related ester-type compounds, dentistry has prided itself on being as close to 'painless' as possible. In the late 1940s the newest group of the local anesthetic compounds, the amides, was introduced. The initial amide local analgesic, lignocaine (Xylocaine), revolutionised pain control in dentistry worldwide. In succeeding years other amide-type local anesthetics, mepivacaine, prilocaine, bupivacaine and etidocaine, were introduced. They gave the dental practitioner a local anesthetic armamentarium which provided pulpal analgesia for periods of from 20 minutes (mepivacaine) to as long as three hours (bupivacaine and etidocaine with adrenaline). In addition these popular drugs proved to be more rapid-acting than the older ester-type drug and, at least from the perspective of allergenicity, more safe. In 1976, in Germany, the newest amide local analgesic, carticaine HCl was introduced into dentistry. Articaine (the generic name was changed) possesses properties similar to lignocaine but has additional properties which made the drug quite attractive to the general dental practitioner. In 1986 articaine was introduced in North America (Canada) where it has become the most used local anesthetic, supplanting lignocaine. Articaine has been approved for use in the United Kingdom. In this introductory discussion we review the development of articaine and discuss its place in the dental local analgesic armamentarium.

Anesthesia, Dental↗

[Local anesthetics from ester to isomer].

The use of chemical substances to prevent or treat local pain had its origin in South America. It was known that central nervous system stimulation occurred among the natives of Peru who chewed the leaves of an indigenous plant (Erythroxylon coca). Circumoral numbness was believed to have occurred as a by-product of this custom. Attempts to isolate the active principle from these leaves finally resulted in the isolation of the alkaloid, cocaine, by Niemann in 1860. The clinical usefulness of cocaine was not appreciated until 1884, when Koller reported upon topical anesthesia of the eye. The chemical identification of cocaine as a benzoic acid ester led to the synthesis of numerous compounds which were basically benzoic ester derivates. In 1905, Einhorn reported the synthesis of procaine. Tetracaine, the most potent ester of the benzoic acid series appeared in 1930. A major breakthrough in the chemistry of local anesthetic agents occurred in 1943 when Loefgren synthesized lidocaine, since it was not an ester but an amide derivate of diethylamino acetic acid. Concerning structure-activity relationships, local anesthetic agents, in general, possess the chemical arrangement of: aromatic portion--intermediate chain--amine portion. Changes in the aromatic or amine portion of a local anesthetic substance will alter its lipid/water distribution coefficient and its protein-binding characteristics which, in turn, will markedly alter the anesthetic profile. The toxic effects of long-acting local anesthetics on brain and heart, firstly reported by Albright, provided the initial stimulus to develop new amide-type local anesthetics. The first of these drugs, which has come into clinical practice was ropivacaine, the S-enantiomer of two possible optical isomers. It is structurally related to bupivacaine and mepivacaine, exerting a different pharmacodynamic profile, specifically on cardiac electrophysiology (less arrhythmogenic than bupivacaine). Studies on the anesthetic activities and toxicity of the individual enantiomers of bupivacaine and mepivacaine generally indicate, that the S-enantiomers are longer-acting and less toxic than the R-enantiomers.

Anesthetics, Local↗

Assessment of allergy to local anesthetics.

Regional analgesia is much too important to be denied to patients on the basis of questionable allergic histories. Often, adverse reactions can be traced directly to the pharmacologic properties of the agents involved. The dentist must adequately distinguish these reactions from those directly related to allergic phenomena. For the comprehensive management of patients with allergic histories, the significance as well as the limitations of intracutaneous skin testing must be appreciated. The practitioner should recognize the need, make proper referrals, and interpret the results of skin tests appropriately. Hopefully, this report has served to disperse the confusion surrounding local anesthetic hypersensitivity and will enable more dentists to proceed with confidence in the assessment and management of their allergic patients.

Adolescent↗