Other Drugs
Drugs other than those discussed earlier in this chapter have
implications for anesthetic management. The therapies that have been discussed include
anticoagulants and fibrinolytics (in the hematologic section), endocrinologic preparations
excluding birth control pills but including corticosteroids (in the section on endocrinologic
disease), antihypertensive drugs (earlier in this section and in the section on cardiovascular
diseases), anticonvulsant drugs (in the section on neurologic disorders), and cancer
chemotherapeutic agents (in the section on oncology).
Antiarrhythmic Drugs
Antiarrhythmic drugs include local anesthetics (lidocaine, procaine),
anticonvulsant (phenytoin) or antihypertensive (propranolol) drugs, calcium channel
blocking drugs, or primary antiarrhythmic drugs. These drugs are classified into
five major categories: local anesthetics that alter phase 0 and phase 4 depolarization
(quinidine, procainamide, and flecainide), local anesthetics that affect only phase
4 depolarization (lidocaine, tocainide, phenytoin, encainide), β-adrenergic
receptor antagonists, antiadrenergic drugs (bretylium, disopyramide, amiodarone),
and calcium entry blockers. These drugs are discussed elsewhere in this chapter
and in Chapter 16
. A useful
reference with suggestions about drug therapy for cardiac arrhythmias and monitoring
of side effects was published by the Medical Letter on Drugs
and Therapeutics.[1007]
A lack of adverse
reports does not indicate that all these drugs should be continued through the time
of surgery; pharmacokinetic studies have not yet determined whether anesthesia (or
anesthesia with specific agents) alters the volume of distribution or clearance of
these drugs to an extent sufficient to warrant changing the dosage or dosage schedule
in the perioperative period. The dearth of reports on this subject may be due to
a lack of significant drug interaction or to a lack of awareness that untoward events
could be caused by such an interaction.
The pharmacologic characteristics of the various antiarrhythmic
drugs can affect anesthetic management.
Disopyramide is similar to quinidine and procainamide in its antiarrhythmic effectiveness.
Disopyramide is excreted mainly by the kidneys, but hepatic disease increases its
half-life. This drug often produces anticholinergic effects, including tachycardia,
urinary retention, and psychosis. Hepatitis has also been reported to have occurred
after its use.[1007]
Little is known of the interaction
of bretylium with anesthetics. Because bretylium blocks the release of catecholamines,
chronic therapy with this drug has been associated with hypersensitivity to vasopressors.
[1007]
Quinidine is dependent on the kidneys for
excretion, can produce vagolytic effects that can decrease AV block, and is associated
with blood dyscrasias and GI disturbances.[1007]
Most of the antiarrhythmic drugs enhance nondepolarizing neuromuscular blockade.
Reports have confirmed this enhancement for quinidine, phenytoin, lidocaine, procainamide,
and propranolol.[1008]
[1009]
[1010]
[1011]
[1012]
[1013]
[1014]
[1015]
[1016]
Amiodarone, an antiadrenergic drug used
to treat recurrent supraventricular and ventricular tachycardia, causes thyroid dysfunction
as a result of the large amount of iodine in its structure (see the section on thyroid
disorders earlier in this chapter), as well as peripheral neuropathy, and has been
associated with hypertension, bradyarrhythmias, and reduced cardiac output during
anesthesia.[1017]
The drug has a half-life of
29 days, and pharmacologic effects persist for over 45 days after its discontinuance.
[1018]
No data document such an effect for depolarizing
muscle relaxants.
Antibiotics
Many antibacterial agents are nephrotoxic or neurotoxic (or both),
and many prolong neuromuscular blockade (also see Chapter
13
).[1010]
[1011]
[1012]
[1013]
[1014]
[1015]
[1016]
The only antibiotics devoid of neuromuscular effects appear to be penicillin G and
the cephalosporins.[1015]
Most enzyme-inducing
drugs do not increase the metabolism of enflurane or isoflurane. However, isoniazid
appears to induce the microsomal enzymes responsible for the metabolism of at least
enflurane, thereby increasing the possibility of fluorine-associated renal damage
after enflurane.[1019]
Appropriate antibiotic
prophylaxis for surgery (see Table
27-37
and Table 27-38
)
requires a knowledge of the probability of infection for that type of surgical procedure
and, if the incidence of infection warrants, the use of a drug regimen directed against
the most likely infecting organisms.[457]
Digitalis
Digitalis preparations have a limited margin of safety, and the
risk of toxicity increases with hypokalemia.[1020]
Although there is good rationale for administering digoxin prophylactically before
surgery,[574]
[1021]
we generally avoid doing so because potassium concentrations can fluctuate widely
during anesthesia as a result of fluid shifts, ventilatory acid-base derangements,
and adjuvant treatments[734]
[770]
[771]
[772]
and
because
intraoperative arrhythmias caused by digitalis toxicity may be difficult to differentiate
from those having other sources. Digitalis intoxication can be manifested by such
diverse cardiac arrhythmias as junctional escape rhythm, PVCs, ventricular bigeminy
or trigeminy, junctional tachycardia, paroxysmal atrial tachycardia with or without
block, sinus arrest, sinus exit block, Mobitz type I or II blocks, or ventricular
tachycardia.[1020]
However, anesthetics appear
to protect against digitalis toxicity, at least in animal studies.[1022]
[1023]
[1024]
[1025]
A titrated cardioversion technique using at first 10- and then 20-, 30-, 40-, 50-,
75-, 100-, 150-, and 200-J doses resulted in safe cardioversion in the presence of
digitalis and propofol or midazolam hypnosis.[1026]
For patients in atrial fibrillation, the ventricular response should guide the choice
of dose of digitalis.
Medications for Glaucoma (also
see Chapter 65
)
Medications for glaucoma include two organophosphates: echothiophate
and isoflurophate. These drugs inhibit serum cholinesterase, which is responsible
for the hydrolysis and inactivation of succinylcholine and estertype local anesthetics
such as procaine, chloroprocaine, and tetracaine.[1027]
[1028]
[1029]
These ester-type local anesthetics should be avoided in patients treated with eye
drops containing organophosphate. Table
27-50
lists other medications related to anesthesia and their side effects
(from the National Registry for Drug-Induced Ocular Side Effects, Oregon Health Sciences
University, 3181 SW Sam Jackson Park Road, Portland, OR 97201; 503-279-8456).
Magnesium, Cimetidine, and Oral Contraceptives
Magnesium is given to treat eclampsia; it can cause neuromuscular
blockade by itself and potentiates neuromuscular blockade by both nondepolarizing
and depolarizing muscle relaxants.[1030]
[1031]
Cimetidine reduces hepatic blood flow and inhibits enzymatic degradation of drugs
by the liver. Thus, higher blood levels and prolonged elimination half-lives may
result when drugs that are metabolized by the liver (e.g., lidocaine, procaine, some
narcotics, and propranolol) are given to patients taking cimetidine chronically or
acutely.[1032]
[1033]
The risk of postoperative venous thrombosis increases when oral contraceptives are
used preoperatively.[1034]
[1035]
Although some authorities recommend changing from oral contraceptives to topical
methods of birth control 2 to 4 weeks before surgery,[1036]
no controlled study has determined whether birth control pills should be discontinued
before surgery or the resulting incidence of pregnancy. Other authorities recommend
preventing venous thromboembolism by using low-dose heparin, guided by a determination
of efficacy and cost-effectiveness.[478]
[479]
[480]
Because estrogens greatly decrease the incidence
of cardiovascular disease and osteoporosis, their use in the elderly is being encouraged.
[346]
Thus, the uncertainty surrounding prophylaxis
for heart disease (created by the dilemma of long-term benefit versus the short-term
risk of thromboembolism) needs better data for resolution.
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