Para-aminobenzoic acid PABA

The following molecular model is a representation of para-aminobenzoic acid (PABA), the active ingredient in many sunscreens. Indicate the positions of the multiple bonds, and draw a skeletal structure (gray = C, red = O, blue = N, ivory - H). 

Para-aminobenzoic acid (PABA), HCjH NO is used in some sunscreen agents. A solution is made by dissolving 0.263 mol of PABA in enough water to make 750.0 mL of solution. The solution has [H+] = 2.6 X 10-3 M. What is Ka for PABA ... 

Pharmacology Sulfonamides exert their bacteriostatic action by competitive antagonism of para-aminobenzoic acid (PABA), an essential component in folic acid synthesis. 

Sulfanilamides are antibiotics that serve as structural analogs of para-aminobenzoic acid (PABA), a substrate In the formation of folic acid by many bacteria. Substitution of the sulfanilamide compound In place of PABA In the reaction prevents formation of the critical coenzyme folic acid. 

Both the sulfonamides and trimethoprim interfere with bacterial folate metabolism. For purine synthesis tetrahydrofolate is required. It is also a cofactor for the methylation of various amino acids. The formation of dihydrofolate from para-aminobenzoic acid (PABA) is catalyzed by dihydropteroate synthetase. Dihydrofolate is further reduced to tetrahydrofolate by dihydrofolate reductase. Micro organisms require extracellular PABA to form folic acid. Sulfonamides are analogues of PABA. They can enter into the synthesis of folic acid and take the place of PABA. They then competitively inhibit dihydrofolate synthetase resulting in an accumulation of PABA and deficient tetrahydrofolate formation. On the other hand trimethoprim inhibits dihydrofolate... 

Para-aminobenzoic acid (PABA) and its esters, benzophenones IX Acne preparations... 

Aminosalicylic acid (Paser, PAS) exerts its effects in a manner similar to the sulfonamide drugs that is, aminosalicylic acid is structurally similar to para-aminobenzoic acid (PABA) and inhibits folic acid synthesis by competing with PABA in tuberculosis... 

Animals are unable to synthesize folic acid (6.62) and must consume adequate quantities in their diets. Plants and bacteria, however, are able to make folic acid. The first step of this synthesis is catalyzed by dihydropteroate synthetase and reacts dihydroptero-ate diphosphate (6.69) and para-aminobenzoic acid (PABA, 6.70) (Figure 6.25). Because this pathway is not found in humans, inhibition of the reaction is a method to ultimately stop TMP synthesis in an invading bacterium while not impacting the infected host. The sulfonamides, often called sulfa drugs, are a class of antibiotic that exploits the folic acid pathway and inhibits dihydropteroate synthetase. Sulfa drugs bind in the same fashion as PABA and act as competitive inhibitors. The active form of the first sulfa drug is sulfanilamide (6.71). Sulfamethoxazole (6.72) is a sulfa drug that is widely prescribed today.26... 

Finally, sulfonamides can interfere with intermediary metabolism. Because of their structural similarity to para-aminobenzoic acid (PABA), they can function as competitive inhibitors for dihydropteroate synthase. The result is interruption of microbial synthesis of folic acid by blocking formation of the folic acid precursor dihydropteroic acid. Sensitive microorganisms are those that must synthesize their own folic acid. Conversely, resistant bacteria and normal mammalian cells are unaffected since they do not synthesize folic acid but use the preformed vitamin. 

Alteration of a metabolic pathway, for example some sulphonamide-resistant bacteria switch to using pre-formed fohc acid, rather than synthesise the precursor para-aminobenzoic acid (PABA), which is the reaction inhibited by sulphonamides. 

Tetracaine, an ester of para-aminobenzoic acid (PABA), has been widely used for topical anesthesia of the eye. It is currently available in a 0.5% solution. Its onset, intensity, and duration of anesthesia are comparable with those of proparacaine and benoxinate (Figure 6-2). Onset of anesthesia sufficient to permit tonometry or other minor procedures involving the superficial cornea and conjimc-tiva is 10 to 20 seconds, and duration of anesthesia is 10 to 20 minutes. It has been reported, however, that the 1% solution produces anesthesia lasting nearly an hour. Tetracaine 1% has also been used successfully to provide anesthesia during phacoemulsification cataract surgery and intraocular lens implantation. 

Prolonged exposure to the sun can allow more UV radiation to reach your skin than melanin can absorb. A commercial sunscreen can offer added protection, however, because it contains conjugated compounds that absorb UV light, thus shielding your skin (for a time) from the harmful effects of UV radiation. Two sunscreens that have been used for this purpose are para-aminobenzoic acid (PABA) and padimate O. 

Folic acid is a conjugated molecule consisting of a pteridine ring structure linked to para-aminobenzoic acid (PABA) that forms pteroic acid. 

The commonest absorbents are para-aminobenzoic acid (PABA) and its derivatives, cinnamates, benzophe-nones, and salicylates, none of which offers significant protection against UVA. Dibenzoylmethane derivatives and anthranilates, which also work by absorbing radiation, are more effective UVA filters. 

In 19 patients with positive photopatch tests to sunscreens among all the patients that were photopatch-tested between 1992 and 1999 (total not stated) there were 21 positive photopatch tests to sunscreen agents (3). Nine patients reacted to oxybenzone, eight to butylmethoxydibenzoylmethane, three to methoxycinnamate, and one to benzophenone. There were no reactions to para-aminobenzoic acid (PABA), reflecting the increased use of PABA-free sunscreens. Six patients also had positive patch tests to components of the... 

Even when the pharmacokinetic parameters of a drug are such to suggest that it will reach the site of the infection, local factors can influence its antimicrobial activity. Aminoglycosides are ineffective in hyperosmolar, anaerobic acidic environments, such as the purulent environment of abscesses. Sulfonamides act by replacing para-aminobenzoic acid (PABA) in the folic acid synthetic pathway of bacteria and are ineffective in purulent material and necrotic tissue, which provide alternative sources of PABA. 

The treatment of choice for coccidiosis is the sulfonamide antimicrobial agents (see Ch. 2). The sulfonamides disrupt folic acid and nicotinamide metabolism and coenzymes I and II by competing with para-aminobenzoic acid (PABA). Coccidia must manufacture their own folic acid and, therefore, this step is mandatory in the pyrimidine pathway of these parasites. Sulfamethazine (sulfadimidine) at 220mg/kg i.v. or orally, or sul-fadimethoxine (55mg/kg) orally or sulfathiazole (66mg/kg) orally, all once daily for 5-7 days, are used commonly for the treatment of equine coccidiosis. The signs of toxicity of the sulfonamides are covered extensively in Chapter 2. Crystalluria,... 

Inhibition of folic acid synthesis in susceptible microorganisms and ultimately the synthesis of nucleic acids. By competing with para-aminobenzoic acid (PABA) for the enzyme dihydropteroate synthetase, sulphonamides prevent the incorporation of PABA into dihydrofolate, while trimethoprin, by selectively inhibiting dihydrofolate reductase, prevents the reduction of dihydrofolate to tetrahydrofolate (folic acid). Animal cells, unlike bacteria, utilize exogenous sources of folic acid. Pyrimethamine inhibits protozoal dihydrofolate reductase, but is less selective for the microbial enzyme and therefore more toxic than trimethoprim to mammalian species. 

The sulfonamides compete with para-aminobenzoic acid (PABA) as shown in Figure V-l -3. The j... 

As shown in Scheme 19.5, however, prontosil is itself an inactive prodrug that, upon oral administration, requires metabolic reduction by the gut microflora to become sulfanilamide, 6. The latter is an active antimicrobial that is very effective against streptococcal infections upon its absorption into the body. Once this was understood, the birth of the sulfonamide antibiotics can be said to have occurred and both Domagk and his daughter lived happily-ever-after. It was later shown that the structure of 6 resembles that of para-aminobenzoic acid (PABA) because... 

Bentiromide, a para-aminobenzoic acid (PABA) derivative (500 mg dose p.o.), is used as a screening test for pancreatic exocrine insufficiency. Following oral administration, bentiromide is cleaved by the pancreatic enzyme chymotrypsin, causing the release of PABA. 

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