Supersensitivity of salivary glands following treatment with bretylium or guanethidine

ADVERSE DRUG INTERACTIONS IN DENTAL PRACTICE: INTERACTIONS ASSOCIATED WITH VASOCONSTRICTORS

BACKGROUND

Adrenergic vasoconstrictors are commonly used by dentists to enhance the pain-relieving action of local anesthetics and to control local bleeding. Although normally considered safe for these applications, vasoconstrictors can participate in drug interactions that potentially are harmful to patients.

METHODS

The faculty of a March 1998 symposium entitled "Adverse Drug Interactions in Dentistry: Separating the Myths From the Facts" extensively reviewed the literature on drug interactions. They then established a significance rating of alleged adverse drug interactions pertaining to dentistry, based on the quality of documentation and severity of effect. The author of this article focused on the adrenergic vasoconstrictors epinephrine and levonordefrin.

RESULTS

Vasoconstrictor drug interactions involving tricyclic antidepressants, nonselective beta-adrenergic blocking drugs, certain general anesthetics and cocaine are well-documented in both humans and animals as having the potential for causing serious morbidity or death. Evidence for adverse interactions involving adrenergic neuronal blocking drugs, drugs with alpha-adrenergic blocking activity, local anesthetics and thyroid hormones is much less compelling, suggesting for the most part that clinically significant reactions may occur only when both the vasoconstrictor and the interacting drug are used in excessive doses. In the case of monoamine oxidase inhibitors, there is no credible evidence of a significant interaction with epinephrine or levonordefrin.

CONCLUSIONS

Potentially serious adverse drug interactions involving adrenergic vasoconstrictors can occur in dental practice. In most circumstances, careful administration of small doses of vasoconstrictors and avoidance of gingival retraction cord containing epinephrine, coupled with monitoring of vita signs, will permit these drugs to be used with no risk or only minimally increased risk. Only in the case of cocaine intoxication must adrenergic vasoconstrictors be avoided completely.

CLINICAL IMPLICATIONS

For optimal patient safety, dentists must recognize potential drug interactions involving adrenergic vasoconstrictors and modify their use of these agents accordingly.

LEAKAGE OF TRANSMITTERS IN SALIVARY GLANDS

Salivary secretion evoked by sympathetic stimulation or by injection of guanethidine, adrenaline or synephrine is slightly reduced by parasympathetic antagonists in doses which abolish the secretory responses to stimulation of the parasympathetic nerve. Similarly, an adrenaline antagonist caused a small diminution of the salivary flow elicited by parasympathetic stimulation or by injection of methacholine chloride. Secretion caused by pilocarpine could be accelerated by physostigmine. We conclude that transmitter leaks in subliminal concentrations, as far as secretion is concerned, from the sympathetic and parasympathetic postganglionic nerve endings.

Expression of NGF in sympathetic neurons leads to excessive axon outgrowth from ganglia but decreased terminal innervation within tissues

The effects of nerve growth factor (NGF) on sympathetic axon growth were investigated by generating transgenic mice in which the beta subunit of NGF was expressed in sympathetic neurons using the human dopamine beta-hydroxylase (DBH) promoter. In DBH-NGF mice, the sympathetic trunk and nerves growing to peripheral tissues were enlarged and contained an increased number of sympathetic fibers. Although sympathetic axons reached peripheral tissues, terminal sympathetic innervation within tissues was decreased in DBH-NGF mice. This effect could be reversed in the pancreas by overexpression of NGF in pancreatic islets. The observations are consistent with a model in which NGF gradients are not required to guide sympathetic axons to their targets, but are required for the establishment of the normal density and pattern of sympathetic innervation within target tissues.

Mechanism of lithium action on the adrenergic function

The intravenous injection of Lithium chloride (LiCl) in two dose levels (25 & 50 mg/kg) has led to a significant potentiation of the pressor response of rabbits to the i.v administration of both epinephrine and norepinephrine. The i.v injection of LiCl (50 mg/kg) resulted in a marked depression of the carotid occlusion reflex in rabbits. In vitro experiments revealed that LiCl (1.6 mcg/ml) and guanethidine (0.8 mcg/ml) exert the same action on the rabbit mesenteric nerve-intestine preparation and abolish the intestinal relaxation induced by electrical stimulation of the mesenteric nerve. Results confirm the assumption that Li might display a pre-synaptic, guanethidine-like, adrenergic neuronal blocking activity.

Possible involvement of parotid beta-adrenergic receptors in the etiology of sialadenosis

The concentration of beta-adrenergic receptors was determined in rat and human parotid glands, in normal tissue as well as after sympathetic denervation of the rat, and in human sialadenosis. Receptor levels were clearly elevated after denervation of the rat and in sialadenosis. The possible implications of these findings for the etiology of human sialadenosis are discussed.

A comparison and an investigation of a potential synergistic effect of labetalol and bethanidine in patients with mild hypertension

1 The effects of labetalol, bethanidine and combined treatment with both drugs were compared in a within-patient randomized cross-over study in mild essential hypertension. Attention was directed to whether or not labetalol and bethanidine differed in their pattern of effect on arterial BP and whether evidence of synergism was apparent. 2 At the doses used labetalol significantly lowered systolic and diastolic BPs and heart rate lying, sitting, standing and after exercise. The dose of bethanidine used did not affect heart rate significantly while lowering systolic and diastolic BPs only after exercise and less clearly on standing. Combined treatment lowered BPs on standing and after exercise and heart rate after exercise. 3 The type and frequency of side-effects were similar with bethanidine and labetalol but were much less with combined treatment. 4 No evidence of synergism was observed.