1. Ampicillin is known to undergo pH-dependent polymerization reactions (especially in concentrated solutions) that involve nucleophilic attack of the side chain amino group of one molecule on theβ-lactam carbonyl carbon atom of a second molecule, and so on.

2. Classification Different approaches where used used to classify penicillins, based on Based on sources- Natural Semisynethetic. Totally synthesic 2-according to the chemistry. Acidresistance. Non acid resistance.

3. 3-resistance to enzymatic spectrum of activity Resistance to penicillinase (beta lactamase) Not resistance 4-spectum of activity Intermediate Broad or extended spectrum. 5-clinical use Multi purpose limited clinical 6-parmacokinetic –orally- parentraly

4. Products ---For years, the most popular penicillin has been penicillin G,or benzylpenicillin. In fact, with the exception of patients allergic to it, penicillin G remains the agent of choice for the treatment of more different kinds of bacterial infection than any other antibiotic. It was first made available as the watersoluble salts of potassium, sodium, and calcium.

5. These salts of penicillin are inactivated by the gastric juice and are not effective when administered orally unless antacids, such as calcium carbonate, aluminum hydroxide, and magnesium trisilicate; or a strong buffer, such as sodium citrate, is added. Also, because penicillin is absorbed poorly from the intestinal tract, oral doses must be very large, about five times the amount necessary with parenteral administration.

6. Only after the production of penicillin had increased enough to make low-priced penicillin available did the oral dosage forms become popular. --The water- soluble potassium and sodium salts are used orally and parenterally to achieve high plasma concentrations of penicillin G rapidly. The more water-soluble potassium salt usually is preferred when large doses are required. --Situations in which hyperkalemia is a danger, however, as in renal failure, require use of the sodium salt; the potassium salt is preferred for patients on salt-free diets or with congestive heart conditions

8. The rapid elimination of penicillin from the bloodstream through the kidneys by active tubular secretion and the need to maintain an effective concentration in blood have led to the development of “repository” forms of this drug. Suspensions of penicillin in peanut oil or sesame oil with white beeswax added were first used to prolong the duration of injected forms of penicillin. --This dosage form was replaced by a suspension in vegetable oil, to which aluminum monostearate or aluminum distearate was added. Today, most repository forms are suspensions of high–molecular weight amine salts of penicillin in a similar base.

9. 2-Penicillin G Procaine The first widely used amine salt of penicillin G was made with procaine. Penicillin G procaine (Crysticillin,Duracillin, Wycillin) can be made readily from penicillin G sodium by treatment with procaine hydrochloride. This salt is considerably less soluble in water than the alkali metal salts, requiring about 250 mL to dissolve 1 g. Free penicillin is released only as the compound dissolves and dissociates. Some commercial products are mixtures of penicillin G potassium or sodium with penicillin G procaine; the water- soluble salt provides rapid development of a high plasma concentration of penicillin, and the insoluble salt prolongs the duration of effect.

11. Penicillin G Benzathine The salt of a diamine, 2 moles of penicillin are available from each molecule. It is very insoluble in water, requiring about 3,000 mL to dissolve 1 g. This property gives the compound great stability and prolonged duration of effect. At the pH of gastric juice, it is quite stable, and food intake does not interfere with its absorption. It is available in tablet form and in several parenteral preparations. The activity of penicillin G benzathine is equivalent to 1,211 units/mg.

13. Penicillin V Because of its resistance to hydrolysis by gastric juice and its ability to produce uniform concentrations in blood (when administered orally). For parenteral solutions, the potassium salt is usually used. This salt is very soluble in water. Solutions of it are made from the dry salt at the time of administration. Oral dosage forms of the potassium salt are also available, providing rapid, effective plasma concentrations of this penicillin.

15. Methicillin Sodium During 1960, methicillin sodium, 2,6-dimethoxyphenylpenicillin sodium (Staphcillin), the second penicillin produced as a result of the research that developed synthetic analogs, was introduced for medicinal use. The sodium salt is a white, crystalline solid that is extremely soluble in water, forming clear, neutral solutions. As with other penicillins, it is very sensitive to moisture, losing about half of its activity in 5 days at room temperature. Refrigeration at 5°C reduces the loss in activity to about 20% in the same period. Methicillin sodium is particularly resistant to inactivation by the penicillinase found in staphylococci and somewhat more resistant than penicillin G to penicillinase from Bacillus cereus. Methicillin sodium has been introduced for use in the treatment of staphylococcal infections caused by strains resistant to other penicillins. It is recommended that it not be used in general therapy, to avoid the possible widespread development of organisms resistant to it.