Chemotherapy in pharmacology refers to the use of chemical agents to selectively destroy or inhibit disease-causing organisms while causing minimal harm to the host. With the global rise of infectious diseases and antimicrobial resistance, chemotherapy has become a cornerstone of modern medical treatment. Unit 3 focuses on the major classes of chemotherapeutic agents used against bacterial, fungal, viral, protozoal, and helminthic infections. This article presents a comprehensive, news-style overview of these drug classes and their therapeutic significance.
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General Overview of Chemotherapy in Infectious Diseases
Chemotherapeutic agents are designed to target essential biological processes unique to microorganisms, such as cell wall synthesis, nucleic acid replication, or metabolic pathways. Effective chemotherapy depends on selective toxicity, adequate drug concentration at the site of infection, and appropriate duration of therapy. Combination therapy is often employed to enhance efficacy and prevent the development of resistance.
Antitubercular Agents: Fighting a Chronic Bacterial Infection
Importance of Antitubercular Therapy
Tuberculosis is caused by Mycobacterium tuberculosis, a slow-growing organism with a lipid-rich cell wall. Treatment requires prolonged chemotherapy using multiple drugs to prevent resistance and relapse.
Classes and Mechanisms
First-line antitubercular drugs such as isoniazid, rifampicin, ethambutol, and pyrazinamide act by inhibiting mycolic acid synthesis, RNA synthesis, or cell wall formation. Second-line agents are used in resistant cases. These drugs are administered in combination regimens under strict supervision to ensure compliance and treatment success.
Antileprotic Agents: Managing Hansen’s Disease
Chemotherapy of Leprosy
Leprosy is a chronic infection caused by Mycobacterium leprae. Due to the organism’s slow replication, long-term chemotherapy is essential.
Multidrug Therapy (MDT)
Drugs such as dapsone, rifampicin, and clofazimine form the backbone of leprosy treatment. Multidrug therapy prevents resistance, reduces infectivity, and improves patient outcomes. Chemotherapy has played a vital role in reducing the global burden of leprosy and preventing disease-related disabilities.
Antifungal Agents: Targeting Fungal Cell Integrity
Need for Antifungal Chemotherapy
Fungal infections range from superficial skin conditions to life-threatening systemic diseases, particularly in immunocompromised patients. Fungal cells share similarities with human cells, making selective drug targeting challenging.
Mechanisms of Action
Antifungal drugs act by disrupting ergosterol synthesis, damaging fungal cell membranes, or inhibiting mitosis. Polyenes, azoles, echinocandins, and allylamines represent key classes. Proper selection and duration of antifungal chemotherapy are crucial to minimize toxicity and resistance.
Antiviral Drugs: Inhibiting Viral Replication
Challenges in Antiviral Chemotherapy
Viruses depend on host cellular machinery for replication, making selective toxicity difficult. Antiviral drugs target specific viral enzymes or stages of the replication cycle.
Major Antiviral Strategies
Antiviral agents inhibit viral entry, nucleic acid synthesis, protein processing, or viral release. Drugs used in herpes, HIV, hepatitis, and influenza infections have transformed previously fatal diseases into manageable chronic conditions. Combination therapy is especially important in viral chemotherapy to prevent resistance.
Anthelmintic Agents: Eliminating Parasitic Worms
Role of Anthelmintic Drugs
Helminthic infections are common in developing regions and cause significant morbidity. Chemotherapy aims to paralyze, starve, or kill parasitic worms.
Mechanisms and Applications
Anthelmintic drugs act by interfering with neuromuscular transmission, glucose uptake, or membrane permeability of parasites. These agents are widely used in mass deworming programs and play a critical role in public health.
Antimalarial Drugs: Controlling a Life-Threatening Protozoal Disease
Chemotherapy of Malaria
Malaria is caused by Plasmodium species transmitted by mosquitoes. Effective chemotherapy targets different stages of the parasite’s life cycle in humans.
Drug Classes and Use
Antimalarial drugs act by inhibiting heme detoxification, folate metabolism, or mitochondrial function. Combination therapy, especially artemisinin-based combinations, is now standard to combat resistance and reduce mortality.
Antiamoebic Agents: Treating Intestinal and Systemic Protozoal Infections
Amoebiasis and Its Management
Amoebiasis, caused by Entamoeba histolytica, affects the intestine and may spread to the liver and other organs.
Types of Antiamoebic Drugs
Chemotherapy includes tissue amoebicides for invasive disease and luminal amoebicides for eradicating intestinal cysts. Combination therapy ensures complete parasite clearance and prevents recurrence.