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Selected Drug Interactions
Local Anesthetics
Drug interactions with local anesthetics used in dentistry are rare because the low doses result in low serum levels. However, central nervous system depressants such as alcohol, antidepressants, antihistamines, antipsychotics, barbiturates, benzodiazepines, muscle relaxants, general anesthetics and opiods may result in increased central nervous system depression and respiratory depression.
Lidocaine
Lidocaine is the most frequently employed local anesthetic in all of dentistry. Although two cytochrome P-450 isozymes control its metabolism, dramatic increases in lidocaine blood levels are unlikely to occur by inhibition of one or both single isozymes because the effect of inhibition of these isozymes results in only a small change in the plasma concentration of lidocaine and is not clinically significant. Cimetidine and beta adrenergic blocking agents may prolong the duration of action of lidocaine. Lidocaine can increase the cardiac depressant effects of cardiac antiarrhythmic drugs, but again the amounts used in dentistry do not usually present a clinical problem unless they are inadvertently injected into a blood vessel.
Prilocaine
On rare occasion, it may increase the occurrence of methemoglobinemia associated with Dapsone.
Bupivacaine
High doses may have adverse effects on cardiac rhythm in patients receiving Halothane. Cimetidine may increase bupivacaine’s duration of anesthesia.
Vasoconstrictors
Vasoconstrictors interact with beta-adrenergic blockers, antidepressants, antihypertensive drugs, general anesthetics, and cardiac glycosides. However, in dentistry, when vasoconstrictors are used in local anesthetics in small amounts and with great care to prevent an intravascular injection, their use does not usually result in drug interactions. Possible interactions are listed in Table 1.
Epinephrine-containing local anesthetic solutions may cause hypotension and tachycardia. Initial administration of no more than 40 μg of epinephrine in local anesthetic solutions (approximately one cartridge of local anesthetic with 1:50:000 epinephrine, two cartridges with 1:100,000 epinephrine; four cartridges with 1:200,000 epinephrine) within a short period using careful aspiration technique is reasonable. Additional anesthetic with vasoconstrictor may be administered if vital signs are acceptable.
CNS depressants such as alcohol, opioids and barbiturates have additive sedative effects. Antichloinergic drugs have additive antichloinergic effects.
Tricyclic antidepressants (which may be prescribed for bruxism) have additive anticholinergic effects; combined used of these drugs can lead to alteration of plasma concentration of either drug. Also, they are associated with a possible increased risk of neuroleptic malignant syndrome. With digitalis, increased ventricular contractions are possible. Drug interactions with epinephrine are listed in Table 1. They should be used with caution in hemostatic or gingival retraction agents because of systemic absorption from the gingival crevice. Some epinephrine containing retraction cords contain up to 1 mg of epinephrine per inch of cord. Therefore, practitioners should be aware of the concentration in the cords they use in these patients since systemic absorption may occur, resulting in tachycardia and other cardiovascular effects. Caution should be taken if epinephrine is used as an emergency drug in patients on medications with which vasoconstrictors may interact.
It is noteworthy that many adrenergic drugs that are the same or related to vasoconstrictors, are present in medications used as nasal decongestants, bronchodilators, and over-the-counter cold remedies.
Additional information can be found in the Quality Resource Guide titled Local Anesthetics by Dr. Clarence Trummel published in March 2005.
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