An Outline on Drug Interactions for Dentists

1. Essential Outlines on Drug Interaction
for Dental Practice
- It is the modifications of response to one drug
by another when they are administered
simultaneously or on quick succession.
- This response is either increased or decreased
in intensity of response .Some times it is a
qualitative change in type.
-The chance for drug interaction increases
whenever the number of drugs increase.
AMNA B. MEDANI, 2015,UMST

2. -Dental conditions often need combinations of
drugs , so they should be selected to
complement with each other e.g. antibiotics
and analgesics for the remedy of painful
infections and adrenaline and lignocaine for
anesthesia.
Combinations of drugs are used to treat
patients with more than one disease at a time.
Some drug interactions are desirable like
synergism cases e.g. angiosensin converting
enzyme inhibitors (ACEI) and diuretics in the
treatment of hypertension
AMNA B. MEDANI, 2015,UMST

3. Similar synergistic conditions are exemplified
by sulphonamides and trimethoprim in the
treatment of bacterial infections or frusamide
and amiloride to prevent hypokalemia
because they do not induce undue risk to the
patient.
AMNA B. MEDANI, 2015,UMST

4. Dentists should know about drugs already in use
by the patients before prescribing otherones
especially in the elderly with chronic medications
. Detailed medical history of the patient should
be elicited in a special record that is regularly
updated.
Regular medications include:
Antibiotics Antihypertensives
Antianginal Antiarthritis
Antiepleptics Anticontraceptives
Anticoagulants Antiasthmatics
Antipeptic ulcer Corticosteroids
Psychopharmacological agents
AMNA B. MEDANI, 2015,UMST

5. Drugs identified most likely to induce
interactions:
1/ those with narrow margin of saftey e.g. digoxin
,aminoglycosides ,lithium.
2/ drugs affecting closely regualted body functions
e.g. antihypertensives , antidiabetics
,anticoagulants.
3/ drugs metabolized by saturation kinetics e.g
phenytoin and theophylline.
4/ highly plasma protein-bound drugse.g.
nonsteroidal anti-infalmmatory drugs, oral
anticoagulants ,sulfonureas.
AMNA B. MEDANI, 2015,UMST

6. Mechanisms of Drug Interactions
Pharmacokinetics:
a/ Alteration of absorption or first pass effect of
oral drugs by other concurrent drugs yielding
insoluble poorly absorbed complexes in the
gut lumen e.g tetracycline ,Ca and Fe ions
,antacids, sucralfade, antibiotics and oral
contraceptives.
b/Displacement of plasma protein bound drugs
at the phase of metabolism.
AMNA B. MEDANI, 2015,UMST

7. c/ Alteration of drug binding to tissues thus
affecting volume of distribution and clearance
which may sometimes increase the blood level of
free drug leading to toxicity e.g. oral
anticoagulants ,sulfonylurea ,non-steroidal anti-
inflammatory drugs , anti-epileptics ,quanidine
antagonism with digoxin.
d/ Inhibition / induction of metabolism due to
competition on the same subtype of CYP 50 e.g.
macrolide antibiotics ,azole antifungal
,chloramphenicol , omeprazole ,cimetidine
,ciprofloxacin , metronidazole lignocaine
,propranolol.s
AMNA B. MEDANI, 2015,UMST

8. e/ Alteration of excretion in actively excreted
drugs by tubular transport e.g. probencid and
penicillin , aspirin blocks probencid and
decrease excretion of methotrexate , change
of urinary Ph used in the treatment of
poisoning, angiotensin converting enzyme
inhibitors and non-steroidal inti-infalmmatory
drugs increase the blood level of lithium and
decrease its excretion.
AMNA B. MEDANI, 2015,UMST

9. Pharmacodynamic Interactions
These are derived from the modifications of the
action of one drug at the target site by
another drug independent of its
concentrations.This can result in synergism
(enhanced response ) , antagonism (
attenuated response)or abnormal response.
antagonism concurrent advertent–Synergism
administration of more than one drug:
AMNA B. MEDANI, 2015,UMST

10. 1/ Excessive sedation ,respiratory depression ,
motor in coordination in case of concurrent
use of benzodiazepine , a sedating
antihistamine , a neuroleptic , an opioid , or
taking alcoholics while using any of the above
drugs .
2/ Excessive fall in blood pressure and fainting
due to concurrent use of α adrenergic blockers
, vasodilators , ACE inhibitors ,high ceiling
diuretics and cardiac depressants.They are all
Ca2+ channel blockers and anti-ᾳ adrenergic
receptor.
AMNA B. MEDANI, 2015,UMST

11. 3/ Additive prolongation of prothrombin time and
bleeding by administration of ceftriaxone or
cefoperazone to patients on anti coagulant
therapy or alcoholics .
4/ Excessive platelet inhibition leading to bleeding
due to the concurrent use of aspirin , ticlopidine
,clopidogrel and cabencillin i.e. adenosine
diphosphate recptor blockers.
5/ Additive ototoxicity due to concurrent use of
aminoglycoside antibiotics in patients receiving
frusamide variably with dose concentration and
interval. Aminoglycosides accumulate in proximal
tubule epithelium leading to cellular injury and
nephrotoxicity .
AMNA B. MEDANI, 2015,UMST

12. 6/Antagonism of bacterial action of β lactam
antibiotics by combining with a bacteriostatic
drug like tetracycline , erythromycin or
clindamycin.
7/ Mutual antagonism of antibacterial action of
macrolides , clindamycin and chloamphenicol
due to interference with each otherˈs binding
to bacterial 505 ribosomes.
AMNA B. MEDANI, 2015,UMST

13. 8/ Blockade of anti-parkinsonian action of
levodopa by neuroleptics and metclopramide
antidopaminergic actions.
9/ Attinuation of antihypertensive effect of ACE
inhibitors ,β blockers and diuretics by non-
steroidal anti-inflammatory drugs due to renal
inhibition of prostaglandin synthesis.
AMNA B. MEDANI, 2015,UMST

14. 10/ Abnormal responses sometimes result from
the pharmacodynamic interactions between
metronidazole with alcohol leading to fast
heart beats , warmth and redness of under
skin , tingly feeling ,nausia and vomiting or
cefoperazone with alcohol.
11/Interaction with unknown basis like
ampicillin with allopurinol resulting in skin
rash.
AMNA B. MEDANI, 2015,UMST

15. Drug Interactions before
Adminstration
In oral , parentral or combination therapy do not
mix:
1/Peniciilin G or ampicillin with gentamycin or
any of the aminoglycosides.
2/ Thiopentone Na with succinylcholine or
morphine .
3/ Heparin with gentamycin , penicillin or
hydrocortisone .
4/Noeadrenaline with Na bicabonates
solutions.
AMNA B. MEDANI, 2015,UMST