Common Types of Anti-Infectives

Introduction

Anti-infective drugs are a diverse group of drugs that are used to kill or slow the growth of the many pathogens that can invade the body and cause infection. They can be applied topically (on the surface area of the skin) or systemically (through the bloodstream) to eliminate infections.

 

Anti-Infective Drugs

Anti-infectives include antibiotics, antivirals, antifungals, and antiprotozoals. These four groups of anti-infectives are further subdivided based on several criteria, including the following:

• Chemical structure (for example, penicillins and aminoglycosides)
• What kind of organisms they inhibit or kill (for example, anaerobic bacteria—broad versus narrow spectrum)
• Disease states for which they're used (for example, HIV/AIDS, tuberculosis) 

Ways Anti-Infectives Are Delivered 

Anti-infectives are delivered in a variety of ways, including the following:

• Oral dosage forms (tablets, capsules, suspensions)
• Injectable forms (for IM or IV use)
• Topical forms (creams, lotions, ointments)
• Otic forms (ear drops)
• Ophthalmic forms (drops and ointments)

 

Antibiotics

The antibiotics, or antibacterials, are a class of drugs that inhibit the growth of or kill bacteria. These drugs are effective against bacteria only, not viruses or fungi. It's important that they're used only when they're needed. For example, antibiotics should not be used to treat the common cold, which is caused by a virus. Using antibiotics inappropriately may lead to antibiotic resistance.

Antibiotic resistance occurs when the antibiotic is no longer able to kill or slow down the growth of a target organism. In other words, the organism has now found a way around the effects of the antibiotic, and has, in essence, grown stronger than the drug that once was able to kill it.

1. Antibiotic resistance occurs when antibiotics are misused (prescribed when they're not needed) and when people don't finish the full course of their antibiotic prescription. When patients don't finish a full course of antibiotics, they're killing only the weakest of the bacteria infecting them. The stronger organisms are left to multiply and grow, passing their stronger characteristics on to their progeny. These stronger organisms can now reinfect the person or be passed on to other people.

2. Two examples of antibiotic-resistant bacteria are methicillin-resistant staphylococcus aureus (MRSA) and vancomycin-resistant enterococcus (VRE). MRSA and VRE are sometimes called "superbugs" because there aren't many drugs available to kill them, and people who are infected with them become very sick. Treatment may involve hospitalization with isolation, intravenous antibiotics, sometimes surgery.

3. Antibiotic resistance is a very serious issue. Here are the important points to remember:

• An antibiotic isn't necessary or indicated every time a person gets sick. A prescriber shouldn't be pressured into prescribing antibiotics. The prescriber should be the judge of what treatment is appropriate.
• Antibiotics are useless against colds or the flu, which are caused by viruses and can actually do more harm than good.
• It's very important to take the full course of antibiotics prescribed. A patient may feel better after a few days but should finish the full antibiotic course of therapy to completely kill the bacteria.
• If the prescriber changes an antibiotic therapy, the patient should dispose of the remaining drug properly. It shouldn't be saved "just in case" the patient gets ill in the future. He or she should be examined properly to see if an antibiotic is necessary at that time.
• Antibiotics shouldn't be shared or given to others. Others may have the same symptoms, but it's important that they are examined properly to see if an antibiotic is necessary for them.

4. The major classes of antibiotics covered in this section are:

• Penicillins
• Cephalosporins
• Macrolides
• Tetracyclines
• Aminoglycosides
• Sulfonamides
• Fluoroquinolones 

We'll also present other antibiotics that don't fit in these major classes but are important nonetheless.

 

Types of Antibiotics

In 1928, Sir Alexander Fleming discovered that a mold of the genus Penicillium notatum killed bacteria. From that discovery, the first antibiotic, penicillin, was created. Penicillin was found to be very effective in eradicating pathogenic organisms that cause serious and sometimes life-threatening infections. Since the discovery of the original penicillin, many derivatives have been made from the natural products found in the Penicillium mold. The penicillins are also called beta-lactams because the chemical structure of all penicillins contains a beta-lactam ring.

 

The penicillin family is divided into the original penicillins, penicillinase-resistant penicillins, aminopenicillins, and extended-spectrum penicillins.

The penicillinase-resistant penicillins are so called because they resist an enzyme secreted by bacteria called penicillinase. Penicillinase can destroy the penicillin molecule, rendering it ineffective. The extended-spectrum penicillins are so called because they eradicate a broad range of pathogenic bacteria.

 

The spectrum of activity of an antibiotic indicates the range of organisms that are susceptible to its antimicrobial effects. A narrow range usually indicates activity against only specific organisms. A broad range usually indicates effects against many possible organisms and may include both gram-positive and gram-negative bacteria.

Several penicillin-containing products combine penicillin with either potassium clavulanate, sulbactam, or tazobactam. These compounds inhibit penicillinase and protect the penicillin from breakdown by the enzyme. They also extend the antimicrobial spectrum of the penicillin to include bacteria that would normally be resistant to it. The following table shows the different categories of penicillins.

Drug Name                                               Brand Name                                        Classification                             Route

Penicillin G                                                 Bicillin C-R Pfizerpen                            Natural penicillin                        IM, IV

Penicillin V                                                 Pen-Vee K, Veetids, V-Cillin-K              Natural penicillin                        Oral

Dicloxacillin                                               N/A                                                          Penicillinase-resistant               Oral

Nafcillin                                                     N/A                                                          Penicillinase-resistant                IV

Amoxicillin                                                Amoxil, Trimox                                      Aminopenicillin                           Oral

Amoxicillin/clavulanate potassium      Augmentin                                             Aminopenicillin                           Oral

Ampicillin                                                 Principen                                                Aminopenicillin                           Oral, IM, IV

Ampicillin/sulbactam                             Unasyn                                                   Aminopenicillin                           IM, IV

Piperacillin/tazobactam                        Zosyn                                                      Extended-spectrum                    IV

Ticarcillin/clavulanate                           Timentin                                                 Extended-spectrum                    IV

 

 

The cephalosporin group of antibiotics is pharmacologically and chemically related to the penicillins. Like the penicillins, the cephalosporins also contain a beta-lactam ring.

The cephalosporins are classified into four different generations. Each generation differs from the others in its position on the spectrum of antimicrobial activity. First-generation cephalosporins are active against gram-positive organisms and some gram-negative organisms. Second-generation agents have a broader spectrum of activity against gram-negative organisms, and third- and fourth-generation drugs have an even broader spectrum of activity against gram-negative organisms.

 

The following table summarizes the four generations of cephalosporin antibiotics.

Categories of Cephalosporins

                               First-generation cephalosporins

Drug                                                  Route                               Brand Name

Cephalexin                                        Oral                                  Keflex, Keftab

Cefadroxil monohydrate                Oral                                  Duricef

Cefazolin                                           IM, IV                                Ancef, Kefzol

                           Second-generation cephalosporins

Cefaclor                                            Oral                                   Ceclor, Keflor          

Cefpodoxime proxetil                    Oral                                    Vantin

Cefprozil                                           Oral                                   Cefzil

Cefuroxime sodium                       Oral, IM, IV                        Ceftin, Kefurox, Zinacef

Loracarbef                                       Oral                                   Lorabid

                                 Third-generation cephalosporins

Cefixime                                           Oral                                   Suprax

Cefoperazone sodium                   IM, IV                                Cefobid

Ceftriaxone sodium                       IM, IV                                Rocephin

Cefotaxime sodium                       IM, IV                                Claforan 

                                Fourth-generation cephalosporins

Cefepime hydrochloride               IV                                      Maxipime

 

 

The tetracyclines are a series of chemically related compounds used to treat a broad spectrum of infections. Tetracyclines are bacteriostatic, meaning that while they don't kill bacteria outright, they prevent the growth of the bacteria. In addition to treating active infections, tetracycline antibiotics are often used long-term by patients who suffer from severe acne.

 

The erythromycins are known as macrolide antibiotics since they're chemically composed of a large molecule. They're effective in treating infections that are susceptible to penicillins since they have similar spectrums of action. Depending on the infection that needs to be treated, the macrolides may be an option in patients who are allergic to penicillin. Another class of drugs, the ketolides, is structurally similar to the macrolides. Ketek (telithromycin) is a ketolide.

 

The aminoglycosides are a series of compounds that share similar chemical and pharmacological properties. Aminoglycosides have a broad spectrum of activity. They're associated with significant ototoxicity and nephrotoxicity, meaning they can cause damage to hearing (including deafness) and to the kidneys. Patients on aminoglycosides must be monitored to be sure that drug levels are in a safe range.

 

The following table lists specific drugs within these three classes of antibiotics: tetracyclines, macrolides, and aminoglycosides.

Categories of Antibiotics: Tetracyclines, Macrolides, and Aminoglycosides

                                Tetracyclines

Drug                                                                Route                                           Brand Name

Demeclocycline hydrochloride                   Oral                                               Declomycin

Deoxycycline hyclate                                    Oral, IV                                         Doryx, Vibramycin

Minocycline hydrochloride                          Oral, IV                                         Minocin

Tetracycline hydrochloride                          Oral                                              Sumycin

                                Macrolides

Azithromycin                                                 Oral, IV                                         Zithromax, Z-Pak

Clarithromycin                                              Oral                                              Biaxin

Erythromycin base                                       Oral                                              Ery-Tab, ERYC

Erythromycin estolate                                 Oral                                              llosone

Erythromycin ethylsuccinate                     Oral                                               E.E.S., EryPed

Erythromycin stearate                                Oral                                               Erythrocin Stearate

                                Aminoglycosides

Amikacin sulfate                                          IM, IV                                                                           Amikin

Gentamicin sulfate                                      IV, IV, intrathecal                                                       Garamycin

Kanamycin sulfate                                      Oral, IM, IV, Intraperitoneal, inhalation                  Kantrex

Neomycin sulfate                                        Oral                                                                             Mycifradin

Streptomycin sulfate                                  IM                                                                                Streptomycin

Tobramycin sulfate                                     IM, IV                                                                           Nebcin, Tobi

Paromomycin sulfate                                 Oral                                                                             Humatin

 

 

Antibacterials

Our study of anti-infectives continues with the anaerobic, quinolone, and carbapenem antibacterials. In addition, we'll look at the sulfa-type antibacterials, antitubercular agents, antifungals, antivirals, antiretroviral agents, antimalarial drugs, and drugs used to treat trichomoniasis and intestinal parasites.

The carbapenem antibacterials are related to penicillins in that they also contain a beta-lactam ring. These drugs have a broad spectrum and are often used as the antibiotics of last resort with very serious infections where other antibiotics have failed. Patients on carbapenems are usually in a hospital or other skilled-care facility.

Anaerobic antibacterials are useful in the treatment of infections caused by anaerobic bacteria, which won't grow in the presence of oxygen. Clindamycin, whose brand name is Cleocin, is effective in the treatment of infections that resist other antibiotics such as erythromycins and penicillins. Metronidazole (Flagyl) is an agent that has long been used to treat protozoal infections such as trichomoniasis. It's also useful in the treatment of serious anaerobic infections.

 

Fluoroquinolones are used to treat a variety of infections and many of them have a broad spectrum of activity. Examples include ciprofloxacin, levofloxacin, moxifloxacin, gemifloxacin, and ofloxacin.

The FDA recently issued a warning stating that because of potential side effects involving the tendons, muscles, joints, and nerves, these antibiotics should be reserved for patients who can't take other antibiotics for their condition. 

Most of the oral fluoroquinolones can bind to calcium or magnesium, so it's important to tell patients to take these drugs separately from vitamins, antacids, and foods that contain calcium.

 

The sulfa drugs (or sulfa-type antibacterials) get their name from the fact that they're all derivatives of sulfanilamide, an antibacterial that was first used in the 1930s. The molecule contains the sulfur atom, hence the name "sulfa" drugs. Sulfamethoxazole and trimethoprim-sulfamethoxazole are examples of sulfa antibiotics and are often used to treat genitourinary tract infections. There are other sulfa drugs that aren't antibiotics. For example, sulfasalazine is used to treat rheumatoid arthritis, ulcerative colitis, and Crohn's disease.

 

Aztreonam (Azactam) is useful in the treatment of serious gram-negative infections. Chloramphenicol is reserved for very limited use, such as typhoid fever. 

Vancomycin is a powerful agent usually reserved as the last line of defense when all other antibacterials or antibiotics have failed. (That's why VRE, vancomycin-resistant enterococci, is such a serious problem).

 

Other Anti-Infectives

Viruses are responsible for many infections ranging from the common cold to acquired immunodeficiency syndrome (AIDS). Some drugs specifically treat viral infections. Amantadine and oseltamivir phosphate are used to treat influenza. Acyclovir, famciclovir, and valacyclovir are used to treat infections caused by the herpes virus, including genital herpes, oral herpes (cold sores), and herpes zoster (shingles). Peramivir injection was approved in 2014 for the treatment of acute uncomplicated influenza in patients over the age of 18.

Antiretroviral agents are used specifically to treat HIV, the human immunodeficiency virus. This is the virus responsible for causing AIDS. Many treatment options are available to treat HIV. HIV therapy is constantly evolving to respond to how the virus changes in the body. There are many combination drugs available that contain multiple medications to cut down on the number of pills patients have to take in a day to improve compliance. Some of these drugs are very toxic, and many of them have black-box warnings.

Antimalarials. Malaria is caused by a parasitic organism that infects the blood and specific organs such as the liver. The following drugs are used to eradicate the malarial parasite: chloroquine (Aralen), pyrimethamine (Daraprim), quinacrine (Atabrine), and quinine. 

Antiparasitic Drugs. Metronidazole is the most effective drug for the treatment of trichomoniasis, primarily a parasitic disease of the vagina.

Helminthiasis, an infestation of parasitic worms in the gastrointestinal (GI) tract, is believed to be the most common form of a parasitic disease that affects humans. Anthelmintic drugs are used for eradicating the worms that cause this condition. Antiparasitic drugs include praziquantel (Biltricide), pyrantel pamoate (Antiminth), thiabendazole (Mintezol), and mebendazole (Ovex, Vermox, Antiox, and Pripsen).

Antiviral Drugs. 

Drugs                                    Brand Name

amantadine                         Symmetrel

acyclovir                               Zovirax

zidovudine                           Retrovir, AZT

didanosine                          Videx

stavudine                            Zerit

oseltamivir                         Tamiflu

famciclovir                          Famvir

valacyclovir                         Valtrex

peramivir injection            Rapivab

 

Fungal infections differ from bacterial infections in that they're more difficult to eradicate. Specific drugs are required to effectively cure fungal infections.

Since many fungal infections occur on the skin, several antifungals are available in topical forms such as creams, ointments, lotions, and shampoo. This allows the drug to be applied directly to the site of infection. 

*Antitubercular drugs are specifically used to treat tuberculosis, a highly contagious disease caused by a specific bacterium that thrives inside the lungs. Some typical antitubercular drugs include isoniazid (also known as INH) and rifampin.

Antitubercular Drugs

Drug                                                            Brand Name

Aminosalicylate sodium                           Sodium P.A.S.

Capreomycin sulfate                                Capastat Sulfate

Cycloserine                                                Seromycin 

Ethambutol                                               Myambutol

Isoniazid                                                    Nydrazid

Rifabutin                                                   Mycobutin

Antifungal Drugs

Drug                            Brand Name

Nystatin                       Mycostatin

Miconazole                 Monistat

Ketoconazole             Nizoral

Fluconazole                Diflucan

Itraconazole               Sporanox

Griseofulvin               Fulvicin

 

Corticosteroid Preparations

Corticosteroids are anti-inflammatory agents used to treat a variety of diseases associated with inflammation. They replace or enhance the steroids that are normally produced by the body. A wide variety of corticosteroids on the market are used as inhalers, intranasal applications, tablets to be taken orally, and topical creams and ointments to be applied locally (in one spot).

Corticosteroids promptly relieve symptoms associated with many allergic conditions, including asthma, allergic rhinitis, hay fever, adverse drug reactions, and allergic dermatitis. The inhaled and intranasal products are useful in treating and controlling asthma or allergic rhinitis.

 

Anti-inflammatory medications used in asthma inhalers help prevent asthma attacks y reducing swelling and mucus production in the airways. Examples of inhaled corticosteroids include Qvar (beclomethasone), Flovent (fluticasone), and Pulmicort (budesonide). The inhaled corticosteroid may be combined with another agent called a long-acting beta2-agonist (LABA). Examples of combination corticosteroid/LABA inhalers include Advair (fluticasone/salmeterol) and Symbicort (budesonide/formoterol).

 

Corticosteroids are available in dosage forms other than inhalers, including topical, oral, and intravenous forms. The topical corticosteroids are divided into four degrees of potency: low, medium, high, and very high. Oral and intravenous corticosteroids have several different indications. Some examples are asthma, COPD exacerbations, and rheumatoid arthritis.

Inhaled Corticosteroids

Drug                                  Brand Name

Beclomethasone              Qvar

Budesonide                      Pulmicort

Ciclesonide                       Alvesco

Fluticasone                       Flovent

Flunisolide                        Aerobid

Intranasal Corticosteroids

Drug                                     Brand Name

Fluticasone                          Flonase

Budesonide                         Rhinocort

Beclomethasone                Beconase, Vancenase

Oral and Intravenous Corticosteroids

Drug                                              Brand Name

Methylprednisolone                   Medrol

Prednisone                                  Deltasone

Prednisolone                               Prelone

Dexamethasone                         Decadron

Betamethasone                          Celestone

Topical Corticosteroids (Creams and Ointments)

Low potency

Drug                                        Brand Name

Alclometasone                       Aclovate

Dexamethasone                    Decadron

Medium potency

Drug                                      Brand Name

Betamethasone                   Diprosone, Diprolene, Valisone

Fluocinolone                        Synalar

Fluticasone                           Cutivate

High potency

Drug                             Brand Name

Fluocinonide               Lidex

Triamcinolone            Aristocort

Halcinonide                Halog

Very high potency

Drug                        Brand Name

Clobetasol              Temovate

Halobetasol            Ultravate 

 

Key Points

• Anti-infective drugs are a diverse group of drugs used to kill or slow the growth of pathogens that cause infection. Anti-infectives include antibiotics, antivirals, antifungals, and antiprotozoals.
• Antibiotics, or antibacterials, inhibit the growth of or kill bacteria; they aren't effective against viruses or fungi. Classes of antibiotics include penicillin, cephalosporins, macrolides, tetracyclines, and aminoglycosides.
• Antitubercular drugs are specifically used to treat tuberculosis.
• Antifungals are used to treat fungal infections, which can be difficult to eradicate; many fungal infections occur on the skin.
• Antivirals treat viruses that cause infections ranging from the common cold to AIDS.
• Antiretrovirals are used specifically to treat HIV.
• Antimalarials are used to treat malaria, which is caused by a parasite that infects the blood and organs.
• Antiparasitic drugs treat various parasitic diseases.
• Corticosteroids are powerful anti-inflammatory agents used to treat a variety of diseases associated with inflammation. Corticosteroids replace or enhance the steroids that are normally produced by the body.