Local anesthetics disadvantages

HRT implants are another means of achieving constant hormone levels while removing the responsibility of the patient to take or apply a daily dose of HRT. Implants are inserted in the fat under the skin (usually in the lower abdomen) by a simple surgical procedure involving a local anesthetic and a few stitches. However, this type of HRT has the major disadvantage that if the therapy does not suit then it is almost impossible to remove the implants. 

This involves considerable art, which must be learned in the clinic. It falls into two divisions (1) surface application to the mucous membranes, especially of the eye, nose, throat, and urethra and (2) injections about nerves, in different parts of their course and distribution, from their spinal roots to their ultimate fibrils. The advantages and disadvantages in comparison with general anesthesia and the selection of the local anesthetic agent also depend on clinical discrimination. Nervous, fearful, and excitable patients often suffer severely from apprehension, which also disposes toward accidents. They may be at least somewhat quieted by sedatives, morphine (0.015 g hypodermically) half an hour before the operation, or by barbiturates. The latter also tend to prevent convulsions. 

Clinically used local anesthetics are either esters or amides. Even drugs containing a methylene bridge, such as chlorpromazine (p.233) or imipramine (p.229) would exert a local anesthetic effect with appropriate application. Ester-type local anesthetics are subject to inactivation by tissue esterases. This is advantageous because of the diminished danger of systemic intoxication. On the other hand, the high rate of bioinactivation and, therefore, shortened duration of action is a disadvantage. 

Disadvantage Local anesthetic injection itself is associated with pain and burning sensation... 

Local anesthetic activity Local anesthetic activity ( membrane stabilizing activity ) is a disadvantage when beta-blockers are used topically in the eye because it decreases protective reflexes and increases the risk of corneal ulceration. Local anesthetic effects are absent from timolol and several other beta-blockers. 

Another disadvantage of epidural fentanyl is that it reduces the shivering threshold when combined with epidural local anesthetic. Epidural local anesthetics and IV opioids both decrease the core temperature, which triggers shivering. Fentanyl is often added to local anesthetic to improve the quality of epidural blockade and to reduce side effects. However, it has been shown that patients are at increased risk of hypothermia when fentanyl is added to local anesthetics. 

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