Drug Interactions Ppt
Transcript of Drug Interactions Ppt
Drug interactions
ALEKHYA RAVELLAM PHARMACY(PHARMACOLOGY)
MALLAREDDY INSTITUTE OF PHARMACEUTICAL SCIENCES
An interaction is said to occur when the effects of one drug are changed by the presence of another drug, food, drink or by some environmental chemical agent.
Definition
For convenience the mechanisms of interactions can be subdivided into those which involve the pharmacokinetics of a drug and those which are pharmacodynamic.
Mechanisms of drug interaction
Pharmacokinetic interactions are those which can affect the processes by which drugs are absorbed, distributed, metabolized and excreted (the so-called ADME interactions).
Pharmacokinetic interactions
ALTERATIONS IN ABSORPTION
Complexation/Chelation:
Example:
1)antacids + tetracyclineImpact: tetracycline complexes with divalent cations
forming an insoluble complex
Pharmacokinetic interactions
Effects of changes in gastro intestinal ph:
example:
ketoconazole + antacids proton pump inhibitors
Impact: reduced ketoconazole absorption due to reduced dissolution
Change in gastrointestinal motility:Example:anticholinergics + acetaminophenImpact: delay in absorption of acetaminophen
Induction or inhibition of drug transport proteins:Example:Digoxin is a substrate of p glyco protein and drugs
induce this such as rifampicin,may reduce the bioavailability of digoxin.
Malabsorption caused by drugs:
Example: Neomycin causes malabsorption syndrome.the effect
is to impair the absorption of no of drugs including digoxin and methotrexate.
Protein binding interaction: Example: when patients stabilised on warfarin are given chloral
hydrate because its major metabolite, trichloroacetic acid, is a highly bound compound which successfully displaces warfarin, thereby increasing its anticoagulant effects.
Drug distribution interactions
Changes in first pass metabolism:i)changes in blood flow through liver:
Example:Increase in rate of absorption of dofetilide with
verapamil,which has resulted increase of torsade de pointers.
ii)Inhibition or induction of first pass metabolism:
Example :grape fruit juice induce the cyto chrome p450 isoenzyme cyp3A4 ,which increase the metabolism of calcium channel blockers..
Drug metabolism interactions:
Enzyme induction:Example: phenobarbital + warfarinImpact: phenobarbital increases the metabolism of
warfarin, resulting in reduced anticoagulation.
Enzyme inhibition:Example: cimetidine + theophyllineImpact: cimetidine reduces the clearance of
theophylline causing an increase in adverse effects
Changes in urinary ph:
Thus pH changes that increase the amount in the ionised form (alkaline urine for acidic drugs, acid for bases) increase the loss of the drug, whereas moving the pH in the opposite directions will increase their retention.
Example:changes in the excretion of quinidine and salicylate
due to alterations in urinary pH caused by antacids
Drug excretion interactions
Changes in active renal tubular excretion:
Example: probenecid + penicillin Impact: probenecid prolongs the half-life of penicillin,
allowing single dose therapy. Changes in kidney blood flow : The flow of blood through the kidney is partially
controlled by the production of renal vasodilatory prostaglandins. If the synthesis of these prostaglandins is inhibited (e.g. by indometacin), the renal excretion of lithium is reduced and its serum levels rise as a result.
Additive or synergistic interactions and combined toxicity :
Example: alcohol depresses the CNS and, if taken in moderate
amounts with normal therapeutic doses of any of a large number of drugs (e.g. sedatives, tranquillisers, etc.), may cause excessive drowsiness.
Antagonistic or opposing interactions : Example: the oral anticoagulants can prolong the blood
clotting time by competitively inhibiting the effects of dietary vitamin K.
Pharmacodynamic interactions:
A food-drug interaction can occur when the food you eat affects the ingredients in a medication you are taking, preventing the medicine from working the way it should.
Food-drug interactions can happen with both prescription and over-the-counter medications, including antacids, vitamins, and iron pills.
Food-Drug Interactions:
Drug - grapefruit interactions:
Drugs which may exhibit increased serum concentrations based on this interaction
amiodarone astemizole alprazolam atorvastatin benzodiazepines buspirone carbamazepine carvedilol cerivastatin cilostazol
What you should remember about food-drug interactions:
Read the prescription label on the container. If you do not understand something, or think you need more information, ask your physician or pharmacist.
Read directions, warnings, and interaction precautions printed on all medication labels and package inserts. Even over-the-counter medications can cause problems.
Take medication with a full glass of water. Do not stir medication into your food or take capsules apart
(unless directed by your physician). This may change the way the drug works.
Do not take vitamin pills at the same time you take medication - vitamins and minerals can interact with some drugs
Alcohol + Barbiturates
Alcohol and the barbiturates are CNS depressants, which together can have additive and possibly synergistic effects. Activities requiring alertness and good co-ordination, such as driving a car or handling other potentially dangerous machinery, will be made more difficult and more hazardous. Alcohol may also continue to interact the next day if the barbiturate has hangover effects.
Alcoholic drug interactions:
Clinical evidence A study in man of the effects of a single 0.5-g/kg
dose of alcohol, taken in the morning after a dose of amobarbital 100 mg every night for 2 weeks showed that the performance of co-ordination skills was much more impaired than with either drug alone. 1
Mechanisms Both alcohol and the barbiturates are CNS
depressants, and simple additive CNS depression provides part of the effects. 9 Acute alcohol ingestion may inhibit the liver enzymes concerned with the metabolism of the barbiturates. 10
Herbal drug interaction:
Garlic is used for lowering blood cholesterol, triglyceride levels and blood pressure.
Garlic may increase bleeding, especially in patients already taking certain anti-clotting medications.
Ginger is used for reducing nausea, vomiting and vertigo
Ginger may increase bleeding, especially in patients already taking certain anti-clotting medications.
Ginger
St. John's Wort
St. John's Wort is used for mild to moderate depression or anxiety and sleep disorders.
St. John's Wort may prolong the effect of certain anesthetic agents.
Kava-kava Kava-kava is used for
nervousness, anxiety or restlessness; it is also a muscle relaxant.
Kava-kava may increase the effects of certain anti-seizure medications and/or prolong the effects of certain anesthetics. it can enhance the effects of alcohol. It may increase the risk of suicide for people with certain types of depression.
DRUG CATEGORY REASON Astemizole antihistamine serious metabolic drug intxns Bromfenac analgesic hepatotoxicity Dexfenfluramine anorectic cardiovascular tox Felbamate anticonvulsant aplastic anemia Flosequinan vasodilator increased mortality Grepafloxacin antibiotic proarrhythmic Mibefradil Ca channel blocker serious drug intxns Temafloxacin antibiotic severe ADR Terfenadineantihistamine serious drug intxn Travafloxacin antibiotic hepatotoxicity
DRUGS REMOVED FROM THE MARKET DURING THE 1990s
Be on the alert with any drugs which have a narrow therapeutic window or where it is necessary to keep serum levels at or above a suitable level (e.g. anticoagulants, anticonvulsants, antihypertensives, anti-infectives, cytotoxics, digitalis glycosides, hypoglycaemic agents, immunosuppressants, etc.).
Remember those drugs which are enzyme inducing agents (e.g. phenytoin, barbiturates, rifampicin, etc) or enzyme inhibiting agents (e.g. cimetidine).
Think about the basic pharmacology of the drugs under consideration so that obvious problems (additive CNS depression for example) are not overlooked, and try to think what might happen if drugs which affect the same receptors are used together. And don’t forget that many drugs affect more than one type of receptor which results in side-effects.
Keep in mind that the elderly are most at risk because of reduced liver and kidney function on which drug clearance depends.
Conclusion
Fugh-Berman A, Ernst E, Herb-drug interactions: review and assessment of report reliability, British Journal of Clinical Pharmacology 2001, 52(5): 587-595.
Abebe W, Herbal medication: potential for adverse interactions with analgesic drugs, Journal of Clinical Pharmacology and Therapeutics 2002; 27(6): 391-401
.Bailey, D.G., Malcolm, J., Arnold, O. and Spence, J.D. Grapefruit Juice-Drug Interactions, Br. J. Clin. Pharmacol. 1998; 46: p. 101-110.
REFERENCES