Download CLINICALLY IMPORTANT DRUG INTERACTIONS

CLINICALLY IMPORTANT DRUG
INTERACTIONS
Dr.R.JAMUNA RANI
PROFESSOR & HOD
DEPARTMENT OF PHARMACOLOGY
DRUG INTERACTION – A REVIEW
Drug interaction refers to modification
of response to one drug by another when
they are administered simultaneously or
in quick succession.
The modification is mostly quantitative,
i.e the response is either increased or
decreased in intensity, but sometimes it is
qualitative, i.e. an abnormal or a different
type of response is produced.
Many medical conditions are treated with
a combination of drugs and doctors.
DESIRABLE DRUG INTERACTION
ACE inhibitors + diuretics to treat
hypertension
2. Sulfamethoxazole + trimethoprim to treat
bacterial infection
3. Furosemide + amiloride to prevent
hypokalaemia.
1.
4. Probenecid + penicillin used in
gonococcal infections.
5. Allopurinol + 6-Mercaptopurine &
Azathioprine inhibition of metabolism;
Reduce dose of 6-MP/azathioprine to 1/3
and used in cancer chemotherapy.
CLINICALLY IMPORTANT DRUG INTERACTIONS
PRECIPITANT
DRUG
1. Ampicillin
Amoxicillin
OBJECT DRUG
Oral
contraceptives
Tetracyclines
Interruption of enterohepatic circulation of
the estrogen Æ failure of contraception;
Advised alternative contraception
Tetracyclines
2. Ampicillin
Amoxicillin
LIKELY INTERACTION AND COMMENTS
Oral
anticoagulants
Inhibition of gut flora Æ decreased vit K
production in gut Æ risk of bleeding;
Monitor INR and reduce anticoagulant
dose if needed.
3. Carbenicillin
Ticarcillin
Aspirin and other
antiplatelet drugs
Cause additive platelet
inhibition Æ risk of
bleeding;
Avoid concurrent use.
4. Ceftriaxone
Cefoperazone
Oral anticoagulants
Additive
hypoprothrombinaemia
Æ bleeding;
Monitor INR and
reduce dose of
anticoagulant
5. Sulfonamides Phenytoin
Cotrimoxazole
Displacement + inhibition of metabolism
Æ phenytoin toxicity;
Avoid concurrent use.
6. Sulfonamides Warfarin
Cotrimoxazole
Displacement + inhibition of metabolism
+ decreased production of vit K in gut
Ærisk of bleeding;
Monitor INR and reduce dose of warfarin.
7. Sulfonamides
Cotrimoxazole
Sulfonylureas
Displacement + inhibition of
metabolism Æhypoglycaemia;
Avoid concurrent use.
8. Sulfonamides
Cotrimoxazole
Thiazide diuretics
Increased incidence of
thrombocytopenia;
Avoid concurrent use.
9. Metronidazole
Procarbazine
Tinidazole
Griseofulvin
Cefoperazone
Cefotetan
Ceftriaxone
Alcohol
10. Metronidazole
Tinidazole
Lithium salts
Accumulation of acetaldehyde Æ
disulfiram – like or bizarre
reactions;
Warn the patient not to drink
alcohol.
Decreased excretion Æ Li toxicity;
Monitor Li level and reduce
lithium dose
11. Metronidazole
Tinidazole
Warfarin
Inhibition of metabolism Æ risk of
bleeding;
Avoid concurrent use
12. Ciprofloxacin
Norfloxacin
Pefloxacin
Theophylline Inhibition of metabolism Æ toxicity of
object drug;
Warfarin
Monitor and reduce dose of object drug.
13. Erythromycin
Terfenadine
Clarithromycin
Astemizole
Ketoconazole
Cisapride
Itraconazole
Fluconazole
Protease inhibitors
Inhibition of metabolism by CYP3A4 Æ
rise in blood level of object drug Æ
dangerous ventricular arrhythmia;
14. Erythromycin
Clarithromycin
Ketoconazole
Itraconazole
Fluconazole
Protease inhibitors
Inhibition of metabolism by CYP3A4 Æ
toxicity of object drug;
Phenytoin
Carbamazepi
ne
Warfarin
Sulfonylureas
Diazepam
Theophylline
Cyclosporine
HIV protease
inhibitors
Concurrent use contraindicated.
Avoid concurrent use or readjust dose
of object drug.
15. Erythromycin
Clarithromycin
Ketoconazole
Itraconazole
Fluconazole
Protease inhibitors
Statins
16. Gemfibrozil
Nicotinic acid
Statins
Inhibition of metabolism, higher
risk of myopathy;
Avoid concurrent use.
Increased risk of myopathy;
Caution in concurrent use.
17. Tetracyclines
Lithium salts
Rise in plasma Li level due to decreased
excretion;
Avoid use of tetracycline or monitor and
reduce dose of lithium.
18. Iron salts
Calcium salts
Antacids
Sucralfate
Tetracyclines
Decreased absorption due to formation of
Fluoroquinolones complexes in g.i.t Æ failure of antibiotic
therapy;
Stager drug administration by 2-3hours
19. Furosemide
Minocycline
Aminoglycoside
antibiotics
Enhanced vestibular toxicity;
Avoid concurrent use.
Additive ototoxicity and nephrotoxicity;
Avoid concurrent use.
20. Diuretics
Tetracycline
Antianabolic effect of tetracycline increases
urea production which is retained by the
diuretic;
Avoid concurrent use.
21. Diuretics
Lithium
Decreased excretion – rise in Li level – toxicity;
Reduce dose of lithium and monitor level.
22. Diuretics
Digoxin
Hypokalaemia caused by diuretic increases digoxin
toxicity;
Give K+ sparing diuretic /K+ supplements.
23. Tetracyclines
Chloramphenicol
Macrolide antibiotics
Clindamycin
Penicillins
Cephalosporins
Bactericidal action of penicillins
and cephalosporins may be
antagonized by the bacteriostatic
antibiotics;
Avoid concurrent use.
24. Clindamycin
Erythromycin
Mutual antagonism of antibacterial
action due to proximal binding
Clarithromycin
sites on bacterial ribosomes;
Azithromycin
Chloramphenicol
Avoid concurrent use.
25. Phenobarbitone
Phenytoin
Carbamazepine
Rifampin
Metronidazole
Doxycycline
Chloramphenicol
Protease inhibitors
Warfarin
Corticosteroids
Oral contraceptives
Sulfonyl ureas
Antidepressants
Induction of metabolism Æ loss of
efficacy of object drug;
26. NSAIDs
Ciprofloxacin and
Other
fluoroquinolones
Enhanced CNS toxicity, seizures;
Avoid concurrent use or increase
dose of object drug with monitoring.
Avoid concurrent use.
27. Aspirin and
other NSAIDs
Displacement and /or reduced elimination Æ
Sulfonyl
toxicity of object drug;
ureas
Phenytoin
Valproate
Avoid concurrent use/ substitute NSAID
Methotrexate with paracetamol
28. Aspirin and
other NSAIDs
Warfarin
Heparin
Enhanced risk opf bleeding due to
antiplatelet action and gastric mucosal
damage;
Avoid concurrent use
29. Aspirin and
other NSAIDs
ACE inhibitors
Reduced antihypertensive effect due to
inhibition of renal PG synthesis;
β blockers
Thiazide diuretics
Avoid concurrent use
30. Aspirin and
other NSAIDs
Furosemide
Reduced diuretic action due to PG
synthesis inhibition in kidney;
Avoid concurrent use
31. Allopurinol
Ampicillin
Increased incidence of rashes;
Avoid concurrent use
32. Chronic
alcoholism
Paracetamol Hepatotoxic dose of paracetamol is reduced;
Doses < 3 g/day are safe.
33.Chlorpromazine Levo dopa - carbidopa
Haloperidol
Metoclopramide
34. Sildenafil
Tadalafil
Nitrates
Antagonism of antiparkinsonian
effect;
Concurrent use contraindicated
Marked potentiation Æ
precipitous fall in BP;
Concurrent use contraindicated
DRUG INTERACTIONS BEFORE
ADMINISTRATION
Certain drugs react with each other and get inactivate
if their solutions are mixed before administration.
1. Penicillin G or ampicillin mixed with gentamicin or another
aminoglycoside antibiotic.
2. Thiopentone sodium when mixed with succinylcholine or
morphine.
3. Heparin when mixed with penicillin/ gentamicin/ hydrocortisone.
4. Noradrenaline when added to sodium bicarbonate solution.
Not all patients taking inter acting drugs
experience adverse consequences,
However, it is prudent to consider the
possibility of drug interaction whenever two
or more drugs are prescribed to a patient,
or any drug is added to what the patient is
already taking.