5B - Additional OTC Drugs: Acids and Bases Flashcards
pH
the universal symbol for acidity
pH of (neutral) Water
Then the pH of neutral water is 7
The pH of an acidic solution is less than 7
The pH of a neutral solution equals 7
The pH of a basic solution is greater than 7
pH indicators by colour
Red cabbage extract changes colour when lemon juice is added (pH is lowered)
Anthocyanin (purple pigment) changes its structure slightly (double bonds migrate!) when H+ or OH- added
Alka Seltzer
Effervescent antacid and pain reliever!
Each tablet contains 325 mg ASA (pain relief); 1.9 gr Sodium bicarbonate and 1 gram of citric acid
Why it is an antacid
Hydrolysis of sodium bicarbonate produces a weak acid H2CO3 and a strong base (NaOH), so the resulting solution is basic
Other antacid OTC’s
TUMS (for the tummy!)
Active ingredient is CaCO3: relatively insoluble in water, so it is in a chewable form
Touted as a good source of Calcium!
TUMS also contain
Adipic acid (weak organic acid) Artificial and natural flavours Starch (filler) Coloring Mineral oil (sat’d hydrocarbon: libricant) Sucrose Talc (hydrated magnesium silicate) Sodium hexametaphosphate :raises pH
Effects of added acid and base to a buffer
Added base reacts with the weak acid to neutralize it
Other buffers in the body
Phosphate-also in blood
Amino acids (contain acidic and basic functions) ..so they can act as buffering agents themselves
Also some proteins (made up of amino acids) can act as buffers…COMPLEX TOPIC !!
H2 Blockers
These block the histamine receptor (H2 site) which promotes production of stomach acid
4 OTC drugs available: Pepcid AC, Tagamet, Axid AR and Zantac
Also known as H2 antagonists, since they block the active site without producing a response
Maalox
Effective antacid medication for people on low sodium diets (blood pressure patients)
Advice on using antacids
Do not use any for > 2 weeks
Sodium and calcium bicarbonates OK for occasional use
For more frequent, use Maalox type (no sodium)
Liquids more efficacious than tablets
Do not self medicate for prolonged periods; seek medical advice
Pepto Bismol
Contains the Bismuth Salt of salicylic acid
–ie it is a salicylate
Salt of a weak acid and a strong base (bismuth hydroxide) ..thus in water forms a basic solution and can be used as an antacid
Also a pain reliever, because salicylic acid produced upon hydrolysis
Pleasant wintergreen taste (peppermint)
Drug interactions with antacids
Antacids containing Al, Ca and Mg can bind to tetracycline antibiotics, thus decreasing their absorption from the GI tract
Also can bind to the antipsychotic drug –(major tranquillizer) chlorpromazine (Thorazine), decreasing its efficacy
Milk and tetracycline antibiotics
Calcium in milk binds to tetracyclines
Impairs absorption from the GI tract
So…tetracyclines should NOT be taken at mealtime
