Part 5 Penicillins, Sulfonamides, Tetracyclines

Penicillins and Penicillinase Resistant Antibiotics

Overview of Penicillin

• Penicillin, the first antibiotic used clinically, was discovered by Sir Alexander Fleming in the 1920s from penicillium molds.

• It is important to note that some bacteria produce enzymes (penicillinases) that can render penicillin ineffective.

Types of Penicillins

• Common forms include Penicillin G (benzathine, potassium, propane) and Penicillin V.

• Therapeutically indicated for treating streptococcal infections like pharyngitis, tonsillitis, scarlet fever, endocarditis, and staphylococcal infections.

Administration Guidelines

• Amoxicillin should be taken on an empty stomach for optimal absorption; it is rapidly absorbed in the gastrointestinal tract.

• Caution is advised for patients with allergies to penicillins or cephalosporins and those with renal disease or during pregnancy/lactation.

Adverse Effects and Monitoring

• Major adverse effects include gastrointestinal disturbances (nausea, vomiting), hypersensitivity reactions (rash, anaphylaxis), and superinfections due to disruption of normal flora.

• Monitor patients closely for signs of hypersensitivity reactions which can lead to severe outcomes like anaphylactic shock.

Sulfonamides: Mechanism and Uses

Introduction to Sulfonamides

• Also known as sulfa drugs; they inhibit folic acid synthesis necessary for bacterial growth.

• Common examples include sulfadiazine and a combination drug sulfamethoxazole plus trimethoprim.

Therapeutic Indications

• Effective against both gram-positive and gram-negative bacteria; particularly useful in developing countries due to cost-effectiveness.

• Indicated for conditions such as trachoma, nocardiosis pneumonia, brain abscesses, and urinary tract infections (UTIs).

Pharmacokinetics

• Sulfonamides are teratogenic; caution is required when prescribing to pregnant women. They are metabolized in the liver with a half-life of 7–12 hours.

Contraindications and Adverse Effects

• Known allergies to sulfonamides are contraindicated. Caution is also needed in patients with renal issues or history of kidney stones due to nephrotoxicity risks.

Drug Interactions

Tetracyclines Overview

Introduction to Tetracyclines

• Tetracyclines are semi-synthetic antibiotics characterized by a four-ring structure. They include drugs like tetracycline, minocycline, and doxycycline, commonly used in hospitals ().

Therapeutic Actions and Indications

• These antibiotics exhibit bacteriostatic properties but can be toxic at high concentrations; caution is advised when administering them ().

• Tetracyclines are effective when penicillin is contraindicated, particularly for infections caused by Chlamydia trachomatis and certain protozoal infections ().

Specific Uses of Doxycycline

• Doxycycline treats various infections including sexually transmitted diseases and periodontal disease. It is also indicated for acne vulgaris and minor skin infections ().

Pharmacokinetics and Absorption Considerations

• The absorption of tetracyclines can be affected by food, iron, calcium, and other medications. It is recommended to take these antibiotics on an empty stomach for optimal effectiveness ().

• Concentrated in the liver with a half-life of approximately 24 hours; they can cross the placenta and enter breast milk ().

Contraindications and Cautions

• Known allergies to tetracyclines or tartrazine (a yellow dye) are significant contraindications. Special caution is required for patients under 18 due to potential damage to developing bones and teeth (, ).

• Adverse effects may include gastrointestinal irritation (nausea, vomiting), hepatotoxicity, dermatological reactions (rash, photosensitivity), hematological issues (hemolytic anemia), among others (, ).

Drug Interactions

• Effectiveness of tetracycline decreases when combined with oral contraceptives or certain minerals such as calcium, magnesium, zinc, aluminum, bismuth, iron; these should not be taken together as they hinder absorption ().