Medicines and drugs

Medicines and drugs D2: Antacids D8: Drug Action

D2: Antacids • D.2.1: State and explain how excess acidity in the stomach can be reduced by the use of different bases • Gastric acid is an acid that is found in the stomach and consists highly of HCl and a pH value of 2. • An Antacid is any substance, generally a base or basic salt, which counteracts stomach’s acidity. Antacids are stomach acid neutralizers. They are weak bases such as metal oxides, hydroxides, carbonates, and hydrocarbonates. • Antacids perform a neutralization reaction. They buffer gastric acid, raising the pH to reduce acidity in the stomach

D2: Antacids • Dyspepsia is a condition where it is hard or difficult for the person to digest food. This is due to excess acid, and can be fought by taking antacids. • Examples of antacids and typical neutralization reactions: • NaCHO3(s) + HCl(aq) -----► H2O(l) + NaCl(aq) + CO2(g) • MgO(s) + 2HCl(aq) -----► MgCl2(aq) + H2O(l) • Mg(OH)2 + 2HCl(aq) -----► MgCl2(aq) + 2H2O(l) • Al(OH)3(s) + 3HCl(aq) -----► AlCl3(aq) + 3H2O(l)

Antacids • bad effects from antacids include: • Carbonates: A chemical reaction between the carbonate and hydrochloric acid may produce carbon dioxide gas. This causes gastric distension which may not be well tolerated. Carbon dioxide formation can also lead to headaches and decreased muscle flexibility. • Aluminum hydroxides: aluminium hydroxide may lead to the formation of insoluble aluminium phosphate complexes, with a risk for decrease the level of phosphate in the blood. It can also soften the person's bones. • Sodium hydro carbonates: intake of sodium hydro carbonates may cause heart failure.

Drug action • D.8.1: describe the Importance of geometrical isomerism in drug action • When a drug molecule contains a carbon to carbon double bond, or a ring where there is restricted rotation, then it may have geometric isomerism. The two different geometric isomers may have very biological different effects. For example, diamminedichloroplatinium (II). This compound has a formula of Pt(NH3)2Cl2 has a cis- and a trans- isomer. • The cis- isomer is highly effective in the treatment of testicular and ovarian cancers, as well as other forms of cancer. Trans- platin is not an effective anti-cancer drug.

D.8.2: Discuss the importance of chirality in drug action • Drug molecules that process a chiral carbon atom will exist in two different enantiomeric forms. For example thalidomide. thalidomide alleviates the symptoms of morning sickness in pregnant woman; the other causes severe deformities in the limbs of the baby.

D.8.3: Explain the importance of the beta-lactam ring action of penicillin • All penicillins contain a 4-membered beta-lactam ring. The ring contains 2 carbon atoms that are sp3 hybridized, a nitrogen atom that is sp3 hybridized, and a carbon atom that is sp2 hybridized. This is similar to the combination of two amino acids cysteine and valine. • Penicillin Cysteine Valine • Because of the restrictions of the ring, the normal bond angles of 109.5 and 120 are not able to be obtained, and so the ring becomes strained. This makes the amide highly reactive. The ring opens so that the penicillin can become covalently bonded to the enzyme that synthesizes the cell walls of the bacterium, thus blocking its action.

D.8.4: explain the increased potency of diamorphine (heroin) compared to morphine • Heroin is stronger than morphine. This can be explained due to the difference in polarity of the two substances. • Morphine molecules contain two polar hydroxyl groups; in heroin, these molecules are replaced by ethanoate groups. • These two ester groups make it much less polar than morphine and more soluble in lipids, which are non-polar. • Morphine Heroin Much less Polar groups Polar groups

Medicines and drugs