Drug Interactions with Local Anesthetics

1. Cimetidine increases the plasma half life of circulating lidocaine. So this combination is relatively contraindicated in CHF patients.
2. Esters such as procaine and tetracaine may inhibit the bacteriostatic action of sulfonamides.
3. The administration of adrenaline in patients being treated with non-selective beta blockers (such as propranolol, tinolol, atenolol, increases the likelihood of serious elevation of the blood pressure.
4. Tricyclic antidepressants (eg: Imipramine) and monoamine oxidase inhibitors (eg: Isocarbaxazid) potentially increase the cardiovascular actions of exogenously administered vasopressors.

MAOIs potentiate the actions of vasopressors by inhibiting their biodegradation by the enzyme monoamine oxidase.

Cocaine stimulates norepinephrine release and inhibits its reuptake in adrenergic nerve terminals, thus producing a state of catecholamine hypersensitivity.

Tachycardia and hypertension are frequently observed with cocaine administration. The administration of local anesthetics to cocaine abusers can also increase the risk of local anesthetic overdose reaction.

The use of epinephrine impregnated gingival retraction cord is absolutely contraindicated for use in cocaine abusers.

Malignant hyperthermia is one of the most intense and life threatening complications associated with administration of general anesthesia. It is due to defect in distribution of myoplasmic calcium ions.

1. It is characterized by tachycardia, fever, tachypnea, cardiac dysarrhythmias, muscle, rigidity, cyanosis and death.

Two injectable local anesthetics, articaine and prilocaine and the topic anesthetic benzocaine can induce methemoglobinemia. In methemoglobinemia iron is present in Fe+3 form.

1. The treatment includes intravenous administration of methylene blue. Methylene blue acts as an electron acceptor in the transfer of electrons to methemoglobin.
2. The vitamin which is used in treatment of methemoglobinemia is Vit. C (Ascorbic acid). Ascorbic acid accelerates the metabolic pathways that produce ferrous atoms.

Choline-ester substrates such as depolarizing relaxant succinylcholine and the ester local anesthetics are hydrolyzed mainly in the blood by enzyme plasma cholinesterase. Approximately 1 out of every 2820 persons have an atypical form plasma cholinesterase. The patients have increased risk of prolonged apnea if received succinylcholine during general anesthesia.

A typical plasma cholinesterase represents a relative contraindication to the administration of ester local anesthetics. If possible amide type local type anesthetics should be administered. 

Middle superior alveolar nerve is present only in 72% individuals.  In its absence, its usual innervations are provided by either PSA or ASA nerves, mostly by ASA nerves. 

The nerve blocks which are mainly contraindicated in hemophilics because of possibility of a dissecting hematoma. These blocks should be administered only after replacement therapy of factor VIII.

 Hematoma formation is most common with posterior superior alveolar nerve block followed by inferior alveolar block and mental/incisive nerve blocks.

Centbucridine, a quinoline derivative, is 5-8 times more potent that lidocaine and with an equally rapid onset and an equivalent duration of action. It does not affect the CNS and CVS adversely except when administered in very large doses.

 Ropivacaine is long-acting amide anesthetic similar to bupivacaine and etidocaine in duration of activity.

Hyaluronidase is an enzyme that breaks down intracellular cement. It is added to LA to speed both the onset of anesthesia and the area of anesthesia especially in inferior alveolar nerve block. 

Tetrodotoxin and saxitoxin are classified as biotoxins. They are Ultra- Long acting anesthetics.