Drug Interactions in Clinical Dentistry

By : dr - Ahmad almakhzomi

Numerous studies have documented that drugs are rarely taken in isolation. For example, adults in contemporary society may take an average of four to five drugs daily .

hospitalized patients may receive from 9 to 13 different agents every 24 hours .

Although some of this increase reflects a greater severity of disease and reduced physiologic reserve in patients requiring multidrug therapy .

Drug interactions, in fact, account for 5% to 10% of all adverse reactions to drugs .

Not all drug interactions are clinically significant or

undesired, and some are actively sought in pharmacotherapeutics to increase drug effectiveness, decrease toxicity, or both .

Classification of Drug InteractionsThe simplest clinical classification scheme

recognizes three basic types of drug interactions:

1- antagonism2- potentiation3- unexpected drug effect4- summation5- synergism

1- Antagonism

Antagonism indicates that the biologic or clinical response to a drug is reduced by administering a second agent .

An example of this type of interaction is seen in antibiotic therapy , where the combined use of a drug that acts by inhibiting the synthesis bacterial cell walls .

2 - Potentiation

Potentiation occur when a combination of two drugs that do not share similar pharmacologic activities results in an effect of one of the drugs that is greater than expected.

A typical example of potentiation :

The increased neuromuscular blocking activity of succinylcholine occurring in patients receiving a pseudocholinesterase inhibitor .

3- Unexpected drug effect

the combination of two or more drugs that result in a response typically not observed when any of the drugs is given singly .

Example :

Disulfiram inhibits the intermediary metabolism of alcohol, resulting in the accumulation of acetaldehyde if alcohol is ingested by the patient .

4- Summation

Summation refers to the combined activities of two or more drugs that elicit identical or related pharmacologic effects.

Examples of drugs that summate by acting at identical and at different sites include the opioid analgesics morphine and meperidine .

5-Synergism

the combination of two or more agonists produces an effect that is greater quantitatively than what can be achieved by maximally effective doses of any one drug given alone.

Examples of synergism : The combination of chemotherapeutic agents to treat

certain infections (e.g., tuberculosis) and neoplastic diseases .

Mechanisms of Drug Interactions

The various mechanisms involved in drug interactions can be grouped taxonomically into three broad categories :

1- pharmaceutical interactions .

2- pharmacokinetic interactions .

3- pharmacodynamic interactions .

1- Pharmaceutical interactions

Pharmaceutical interactions can be anticipated between organic acids and bases, resulting in precipitation of one or both drugs.

Most pharmaceutical interactions of importance to dentistry involve drugs that are given parenterally for intravenous sedation.

2- Pharmacokinetic interactions

Pharmacokinetic interactions derive from the influence of one drug on the absorption, distribution, biotransformation, or excretion of another drug.

3- Pharmacodynamic interactions

Pharmacodynamic interactions represent modifications in the pharmacologic effects of a drug independent of any change in the quantitative disposition of that drug. Such interactions may increase, diminish, or qualitatively alter the therapeutic effect.

Factors Influencing Drug Interactions

Several variables can affect the occurrence and intensity of potential drug interactions .

1- interaction may not be clinically discernible each time interacting drugs are administered.

2- The higher the dosage and the longer the administration, the greater the chance that an interaction may occur.

3- Previous exposure affecting drug transport, metabolism, or responsiveness may alter the potential for interaction.

4- Many drugs have a long biologic half-life, and effective concentrations may be present in the blood or tissue for many days after the cessation of therapy; interactions may occur.