This document discusses drug interactions in clinical dentistry. It notes that patients often take multiple drugs daily and hospitalized patients may receive 9-13 drugs every 24 hours. It classifies drug interactions into 5 types: antagonism, potentiation, unexpected drug effect, summation, and synergism. It also discusses the mechanisms of drug interactions, which are categorized into pharmaceutical, pharmacokinetic, and pharmacodynamic interactions. Finally, it outlines several factors that can influence whether and how severely a drug interaction occurs.

1. Drug Interactions in Clinical
Dentistry
By : dr - Ahmad almakhzomi

2. 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 .

3. 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 .

4. Classification of Drug Interactions
The simplest clinical classification scheme
recognizes three basic types of drug
interactions:
1- antagonism
2- potentiation
3- unexpected drug effect
4- summation
5- synergism

5. 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 .

6. 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.

7. A typical example of potentiation :
The increased neuromuscular blocking activity of
succinylcholine occurring in patients receiving a
pseudocholinesterase inhibitor .

8. 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 .

9. 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 .

10. 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 .

11. 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 .

12. 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.

13. 2- Pharmacokinetic interactions
Pharmacokinetic interactions derive from the
influence of one drug on the absorption,
distribution, biotransformation, or excretion of
another drug.

14. 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.

15. 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.

16. 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.