Essential Drug Classifications and Mechanisms of Action
Drugs Acting on the Central Nervous System
Anaesthetic Drugs
Anaesthetics are drugs that produce a reversible loss of sensation, with or without loss of consciousness, thereby allowing surgical or diagnostic procedures to be performed without pain.
Mode of Action: General anaesthetics produce CNS depression by enhancing inhibitory neurotransmission, mainly through GABA-A and glycine receptors, and/or reducing excitatory neurotransmission through NMDA and other receptors. Local anaesthetics block voltage-gated sodium channels and prevent the generation and conduction of nerve impulses.
Types and Examples:
- General Anaesthetics: Propofol, Thiopentone, Sevoflurane, Isoflurane, Nitrous oxide, Ketamine.
- Local Anaesthetics: Lidocaine, Bupivacaine, Ropivacaine, Procaine.
Examples: Propofol is commonly used for the induction of general anaesthesia. Lidocaine is commonly used for local and regional anaesthesia.
Sedative-Hypnotic Drugs
Sedatives reduce anxiety and excitement and produce calming effects, while hypnotics produce sleep when given in adequate doses.
Mode of Action: Most sedative-hypnotics enhance inhibitory GABAergic transmission in the CNS. Benzodiazepines increase the frequency of chloride channel opening through GABA-A receptors, while barbiturates increase the duration of channel opening.
Types and Examples:
- Benzodiazepines: Diazepam, Lorazepam, Midazolam, Alprazolam.
- Barbiturates: Phenobarbitone, Pentobarbitone, Thiopentone.
- Non-benzodiazepine Hypnotics: Zolpidem, Zopiclone.
- Melatonin Receptor Agonist: Ramelteon.
Uses: Anxiety, insomnia, seizures, preanaesthetic medication, and alcohol withdrawal.
Antiepileptic Drugs
Antiepileptic drugs are medicines used to prevent or control recurrent seizures by reducing abnormal neuronal excitability.
Mode of Action: They act by decreasing neuronal excitation or increasing neuronal inhibition through mechanisms such as the blockade of voltage-gated sodium or calcium channels, enhancement of GABA activity, or inhibition of excitatory glutamate transmission.
Types and Examples:
- Sodium Channel Blockers: Phenytoin, Carbamazepine, Lamotrigine, Lacosamide.
- GABA Enhancers: Phenobarbitone, Benzodiazepines, Valproate.
- Calcium Channel Blockers: Ethosuximide, Gabapentin, Pregabalin.
- Broad-spectrum Drugs: Valproate, Levetiracetam, Topiramate.
- SV2A Modulator: Levetiracetam.
Examples: Ethosuximide is particularly useful in absence seizures. Phenytoin is used in focal and generalized tonic-clonic seizures.
Antiparkinsonian Drugs
Antiparkinsonian drugs are used to improve the motor symptoms of Parkinsonism, such as tremor, rigidity, and bradykinesia.
Mode of Action: Parkinson’s disease is associated with the degeneration of dopaminergic neurons in the substantia nigra, resulting in reduced dopamine activity in the striatum. Treatment aims to increase dopaminergic activity or reduce excessive cholinergic activity.
Types and Examples:
- Dopamine Precursor: Levodopa + Carbidopa.
- Dopamine Agonists: Pramipexole, Ropinirole, Rotigotine.
- MAO-B Inhibitors: Selegiline, Rasagiline, Safinamide.
- COMT Inhibitors: Entacapone, Tolcapone, Opicapone.
- NMDA Antagonist: Amantadine.
- Anticholinergics: Trihexyphenidyl, Biperiden.
Example: Levodopa crosses the blood-brain barrier and is converted to dopamine in the brain. Carbidopa inhibits the peripheral conversion of levodopa and increases its availability in the CNS.
Antidepressant Drugs
Antidepressants are drugs used primarily for the treatment of depressive disorders and are also useful in several anxiety and other psychiatric disorders.
Mode of Action: They mainly increase the availability of monoamine neurotransmitters such as serotonin, noradrenaline, and dopamine in the synaptic cleft.
Types and Examples:
- SSRIs: Fluoxetine, Sertraline, Escitalopram, Paroxetine.
- SNRIs: Venlafaxine, Duloxetine, Desvenlafaxine.
- Tricyclic Antidepressants: Amitriptyline, Imipramine, Nortriptyline.
- MAO Inhibitors: Phenelzine, Tranylcypromine.
- Atypical Antidepressants: Bupropion, Mirtazapine, Trazodone.
- NDRI: Bupropion.
Examples: SSRIs inhibit serotonin reuptake and are commonly used as first-line drugs for depression and many anxiety disorders. Amitriptyline is also useful in neuropathic pain.
Antianxiety Drugs
Antianxiety drugs, or anxiolytics, reduce excessive anxiety, fear, and tension without producing significant impairment when appropriately used.
Mode of Action: Benzodiazepines enhance GABA-A receptor-mediated inhibition. Buspirone acts mainly as a partial agonist at serotonin 5-HT1A receptors. Some antidepressants reduce anxiety by modifying serotonergic and noradrenergic neurotransmission.
Types and Examples:
- Benzodiazepines: Alprazolam, Diazepam, Lorazepam, Clonazepam.
- 5-HT1A Partial Agonist: Buspirone.
- SSRIs: Sertraline, Escitalopram, Fluoxetine.
- SNRIs: Venlafaxine, Duloxetine.
- β-blocker: Propranolol, mainly useful for physical symptoms of performance anxiety.
Example: Diazepam increases GABA-mediated inhibition and produces anxiolytic, sedative, muscle-relaxant, and anticonvulsant effects.
Opioid Analgesic Drugs
Opioid analgesics are drugs that relieve moderate to severe pain by acting on opioid receptors in the CNS and peripheral tissues.
Mode of Action: Opioids mainly stimulate μ (mu) opioid receptors. Receptor activation decreases adenylate cyclase activity, opens potassium channels, and inhibits voltage-gated calcium channels. This reduces neurotransmitter release and decreases the transmission of pain signals.
Types and Examples:
- Strong Opioid Agonists: Morphine, Fentanyl, Methadone, Oxycodone.
- Moderate/Weak Opioids: Codeine, Tramadol.
- Partial Agonist: Buprenorphine.
- Mixed Agonist-Antagonists: Pentazocine, Nalbuphine.
- Opioid Antagonist: Naloxone, Naltrexone.
Examples: Morphine is a prototype opioid analgesic used for severe pain. Fentanyl is a potent opioid used in anaesthesia and severe acute pain. Naloxone is used to reverse opioid-induced respiratory depression.
Peripheral Somatic Nervous System Drugs
Skeletal Muscle Relaxants
Skeletal muscle relaxants are drugs that reduce skeletal muscle tone and spasm by acting either at the neuromuscular junction or within the CNS.
Mode of Action: They either block neuromuscular transmission at the motor end plate or reduce excitatory activity in the CNS.
Types and Examples:
- Peripherally Acting Neuromuscular Blockers:
- Non-depolarizing: Atracurium, Vecuronium, Rocuronium, Pancuronium.
- Depolarizing: Succinylcholine.
Mode of Action: Non-depolarizing drugs competitively block nicotinic Nm receptors at the neuromuscular junction and prevent acetylcholine-mediated muscle contraction. Succinylcholine produces persistent depolarization of the motor end plate, resulting in initial fasciculations followed by paralysis.
Uses: Skeletal muscle relaxation during surgery, endotracheal intubation, and mechanical ventilation.
- Centrally Acting Muscle Relaxants:
- Baclofen, Tizanidine, Diazepam, Methocarbamol.
Mode of Action: Baclofen stimulates GABA-B receptors and decreases excitatory neurotransmission. Tizanidine stimulates α2 receptors and reduces excitatory motor neuron activity.
Uses: Muscle spasticity, painful muscle spasms, and neurological disorders.
Local Anaesthetics
Local anaesthetics are drugs that produce a reversible loss of sensation in a limited area without loss of consciousness.
Mode of Action: They reversibly block voltage-gated sodium channels in nerve fibres, preventing depolarization and the conduction of action potentials.
Types and Examples:
- Ester Local Anaesthetics: Procaine, Tetracaine, Benzocaine, Chloroprocaine.
- Amide Local Anaesthetics: Lidocaine, Bupivacaine, Ropivacaine, Mepivacaine.
Classification by Duration:
- Short acting: Procaine.
- Intermediate acting: Lidocaine.
- Long acting: Bupivacaine, Ropivacaine.
Uses: Surface anaesthesia, infiltration anaesthesia, nerve block, spinal anaesthesia, and epidural anaesthesia.
Autacoids and Related Drugs
NSAIDs
Nonsteroidal anti-inflammatory drugs (NSAIDs) are medicines that produce analgesic, antipyretic, and anti-inflammatory effects without producing the steroidal actions of glucocorticoids.
Mode of Action: NSAIDs inhibit cyclooxygenase enzymes, COX-1 and/or COX-2, thereby decreasing prostaglandin and thromboxane synthesis. Reduced prostaglandins decrease inflammation, pain, and fever.
Types and Examples:
- Non-selective COX inhibitors: Aspirin, Ibuprofen, Naproxen, Diclofenac, Indomethacin.
- Preferential COX-2 inhibitors: Meloxicam, Etodolac.
- Selective COX-2 inhibitors: Celecoxib, Etoricoxib.
- Salicylates: Aspirin.
Uses: Pain, inflammation, arthritis, dysmenorrhoea, and fever.
Important Adverse Effects: Gastric irritation, peptic ulceration, renal impairment, and increased bleeding tendency. Selective COX-2 inhibitors have comparatively less gastric toxicity but may increase cardiovascular risk.
Antipyretic Drugs
Antipyretics are drugs that reduce elevated body temperature during fever without significantly lowering normal body temperature.
Mode of Action: They inhibit prostaglandin synthesis in the hypothalamus, particularly by reducing PGE²-mediated elevation of the hypothalamic temperature set point.
Examples: Paracetamol, Aspirin, Ibuprofen, Naproxen.
Paracetamol: It has prominent analgesic and antipyretic activity with relatively weak peripheral anti-inflammatory activity. Uses: Fever, headache, myalgia, and mild to moderate pain.
Analgesic Drugs
Analgesics are drugs that relieve pain without producing loss of consciousness.
Types and Mechanisms:
- Non-opioid Analgesics: Paracetamol, Aspirin, Ibuprofen, Diclofenac, Naproxen.
Mode of Action: Mainly decrease prostaglandin-mediated sensitization of pain receptors through the inhibition of cyclooxygenase.
- Opioid Analgesics: Morphine, Fentanyl, Oxycodone, Codeine, Tramadol, Buprenorphine.
Mode of Action: They activate opioid receptors, mainly μ receptors, in the CNS and inhibit the transmission and perception of pain.
- Adjuvant Analgesics: Amitriptyline, Gabapentin, Pregabalin.
Uses: Neuropathic pain and chronic pain conditions.
Drugs for Respiratory Disorders
Bronchodilators
Bronchodilators are drugs that relax bronchial smooth muscle and increase airway diameter, thereby improving airflow.
Mode of Action: They produce bronchodilation mainly through β²-receptor stimulation, muscarinic receptor blockade, or inhibition of phosphodiesterase.
Types and Examples:
- β²-adrenergic Agonists:
- Short-acting: Salbutamol, Terbutaline.
- Long-acting: Salmeterol, Formoterol.
- Ultra-long acting: Indacaterol, Vilanterol.
Mode of Action: Stimulate β² receptors → activate adenylate cyclase → increase cAMP → relaxation of bronchial smooth muscle.
- Anticholinergics:
- Short-acting: Ipratropium.
- Long-acting: Tiotropium, Glycopyrronium.
Mode of Action: Block muscarinic receptors, particularly M3 receptors, and reduce vagally mediated bronchoconstriction.
- Methylxanthines: Theophylline, Aminophylline.
Mode of Action: Mainly inhibit phosphodiesterase and increase intracellular cAMP, producing bronchodilation.
Uses: Asthma and COPD.
Aerosols and Inhalants
Aerosols or inhalants are preparations in which drugs are administered directly into the respiratory tract in the form of fine particles or droplets.
Advantages: Rapid onset, direct delivery to lungs, lower systemic exposure, and smaller dose requirement.
Types and Examples:
- Metered-dose inhalers: Salbutamol, Beclomethasone, Budesonide.
- Dry powder inhalers: Budesonide, Formoterol, Salmeterol.
- Nebulized preparations: Salbutamol, Ipratropium, Budesonide.
Common Inhaled Drug Groups: β² agonists, anticholinergics, inhaled corticosteroids, and combination preparations.
Expectorants
Expectorants are drugs that increase bronchial secretion or reduce mucus viscosity, facilitating the removal of sputum from the respiratory tract.
Mode of Action: They increase respiratory tract secretions or alter mucus properties, making sputum easier to expel.
Examples: Guaifenesin, Ammonium chloride, Potassium iodide, Sodium citrate.
Uses: Productive cough associated with excessive or thick bronchial secretions.
Antitussives
Antitussives are drugs that suppress or reduce the cough reflex and are mainly used for troublesome dry cough.
Mode of Action: They suppress the cough centre in the CNS or reduce the sensitivity of peripheral cough receptors.
Types and Examples:
- Centrally acting opioid antitussives: Codeine, Pholcodine.
- Centrally acting non-opioid: Dextromethorphan, Noscapine.
- Peripherally acting: Benzonatate.
Mode of Action: Dextromethorphan suppresses the medullary cough centre. Benzonatate reduces the sensitivity of respiratory stretch receptors. Uses: Dry, irritating, and non-productive cough.
Cardiovascular Drugs
Antihypertensive Drugs
Antihypertensive drugs are medicines used to reduce elevated arterial blood pressure and prevent complications of hypertension.
Mode of Action: They lower blood pressure by reducing cardiac output, decreasing peripheral vascular resistance, reducing blood volume, or inhibiting the renin-angiotensin-aldosterone system.
Types and Examples:
- Diuretics: Hydrochlorothiazide, Chlorthalidone, Furosemide. They increase renal sodium and water excretion, reducing blood volume and blood pressure.
- ACE Inhibitors: Enalapril, Ramipril, Lisinopril. They inhibit the conversion of angiotensin I to angiotensin II, causing vasodilation and reduced aldosterone secretion.
- ARBs: Losartan, Telmisartan, Valsartan. They block AT¹ receptors and inhibit angiotensin II-mediated vasoconstriction and aldosterone secretion.
- Calcium Channel Blockers: Amlodipine, Nifedipine, Verapamil, Diltiazem. They inhibit calcium entry into vascular smooth muscle and/or cardiac muscle, causing vasodilation and reduced cardiac activity.
- β-blockers: Atenolol, Metoprolol, Propranolol. They reduce heart rate, cardiac output, and renin release.
- α¹-blockers: Prazosin, Doxazosin. They produce vasodilation by blocking α¹ receptors.
- Central Sympatholytics: Clonidine, Methyldopa. They reduce sympathetic outflow from the CNS.
Antianginal Drugs
Antianginal drugs are medicines used to prevent or relieve angina by reducing myocardial oxygen demand and/or increasing coronary blood supply.
Mode of Action: They decrease cardiac workload, heart rate, and myocardial oxygen consumption or produce coronary vasodilation.
Types and Examples:
- Organic Nitrates: Nitroglycerin, Isosorbide dinitrate, Isosorbide mononitrate. They release nitric oxide, increase cGMP, and cause predominantly venodilation, reducing preload and myocardial oxygen demand.
- β-blockers: Atenolol, Metoprolol, Propranolol. They decrease heart rate and contractility, reducing myocardial oxygen demand.
- Calcium Channel Blockers: Amlodipine, Diltiazem, Verapamil. They cause coronary and peripheral vasodilation and reduce cardiac workload.
- Potassium Channel Opener: Nicorandil. It produces vasodilation and reduces cardiac preload and afterload.
- If-channel Inhibitor: Ivabradine. It selectively reduces heart rate by inhibiting the funny current in the sinoatrial node.
Drugs Acting on the Kidney
Diuretics
Diuretics are drugs that increase urine formation by promoting the renal excretion of sodium and water.
Mode of Action: They inhibit sodium reabsorption at different sites of the nephron, resulting in increased urinary excretion of sodium and water.
Types and Examples:
- Carbonic Anhydrase Inhibitors: Acetazolamide. They inhibit carbonic anhydrase in the proximal tubule and increase bicarbonate, sodium, and water excretion.
- Loop Diuretics: Furosemide, Bumetanide, Torsemide. They inhibit the Na¹-K¹-2Cl¹ cotransporter in the thick ascending limb and produce powerful diuresis.
- Thiazide Diuretics: Hydrochlorothiazide, Chlorthalidone, Indapamide. They inhibit the Na¹-Cl¹ cotransporter in the distal convoluted tubule.
- Potassium-sparing Diuretics: Spironolactone, Eplerenone, Amiloride. Spironolactone and eplerenone block aldosterone receptors, while amiloride blocks epithelial sodium channels.
- Osmotic Diuretics: Mannitol. They increase the osmotic pressure of tubular fluid and reduce water reabsorption.
Uses: Hypertension, edema, heart failure, renal disorders, and raised intracranial pressure.
Drugs Acting on the Blood
Haematinics
Haematinics are substances required for the formation of haemoglobin and red blood cells and are used in deficiency anaemias.
Mode of Action: They provide essential nutrients required for erythropoiesis and haemoglobin synthesis.
Types and Examples:
- Iron preparations: Ferrous sulphate, Ferrous fumarate, Iron sucrose.
- Folic acid: Folic acid.
- Vitamin B12: Cyanocobalamin, Hydroxocobalamin.
- Erythropoietin: Epoetin alfa, Darbepoetin alfa.
Uses: Iron deficiency anaemia, megaloblastic anaemia, and anaemia associated with chronic kidney disease.
Coagulants and Haemostatics
Coagulants or haemostatics are drugs that promote haemostasis and help control bleeding.
Mode of Action: They enhance clot formation, replace deficient coagulation factors, or promote platelet-mediated haemostasis.
Examples: Vitamin K, Tranexamic acid, Fibrin sealants, Factor VIII, Factor IX, Desmopressin.
- Vitamin K: Promotes hepatic synthesis of clotting factors II, VII, IX, and X.
- Tranexamic Acid: Inhibits fibrinolysis by blocking lysine-binding sites on plasminogen.
Anticoagulants
Anticoagulants are drugs that prevent or reduce the formation and extension of blood clots.
Mode of Action: They inhibit clotting factors and interfere with the coagulation cascade.
Types and Examples:
- Heparins: Unfractionated heparin, Enoxaparin. They enhance antithrombin activity and inhibit thrombin and/or factor Xa.
- Vitamin K Antagonist: Warfarin. It inhibits vitamin K epoxide reductase and decreases the synthesis of vitamin K-dependent clotting factors.
- Direct Oral Anticoagulants: Dabigatran (direct thrombin inhibitor); Rivaroxaban, Apixaban, Edoxaban (factor Xa inhibitors).
Uses: Prevention and treatment of deep vein thrombosis, pulmonary embolism, atrial fibrillation, and thromboembolic disorders.
Hypolipidaemic Drugs
Hypolipidaemic drugs reduce abnormal levels of cholesterol, triglycerides, or lipoproteins in the blood.
Mode of Action: They reduce cholesterol synthesis, increase LDL clearance, reduce triglyceride synthesis, or modify lipoprotein metabolism.
Types and Examples:
- Statins: Atorvastatin, Rosuvastatin, Simvastatin. They inhibit HMG-CoA reductase and increase hepatic LDL receptor expression.
- Fibrates: Fenofibrate, Gemfibrozil. They activate PPAR-α and primarily reduce triglycerides.
- Bile Acid Sequestrants: Cholestyramine, Colesevelam. They bind bile acids in the intestine and increase their fecal excretion.
- Cholesterol Absorption Inhibitor: Ezetimibe. It inhibits intestinal cholesterol absorption.
- PCSK9 Inhibitors: Alirocumab, Evolocumab. They increase hepatic LDL receptor availability and markedly reduce LDL cholesterol.
Gastrointestinal Tract Drugs
Antacids
Antacids are weak bases that neutralize gastric hydrochloric acid and increase gastric pH.
Mode of Action: They chemically neutralize gastric acid and reduce acidity and peptic activity.
Types and Examples:
- Systemic: Sodium bicarbonate.
- Non-systemic: Aluminium hydroxide, Magnesium hydroxide, Calcium carbonate.
Uses: Hyperacidity, heartburn, dyspepsia, and symptomatic relief in peptic ulcer disease.
Carminatives
Carminatives are drugs that relieve flatulence and abdominal discomfort by facilitating the expulsion of intestinal gas.
Mode of Action: They reduce intestinal gas formation or facilitate its expulsion and may have mild antispasmodic effects.
Examples: Peppermint oil, Fennel, Dill oil, Ginger, Simethicone.
Digestants
Digestants are preparations that assist digestion by supplying digestive enzymes or promoting digestive processes.
Mode of Action: They supplement deficient digestive enzymes and facilitate the breakdown of carbohydrates, proteins, and fats.
Examples: Pepsin, Pancreatin, Diastase, Lactase.
Antiemetics
Antiemetics are drugs used to prevent or control nausea and vomiting.
Mode of Action: They block neurotransmitter pathways involved in the vomiting centre and chemoreceptor trigger zone.
Types and Examples:
- 5-HT³ antagonists: Ondansetron, Granisetron. Block serotonin 5-HT³ receptors.
- Dopamine D² antagonists: Metoclopramide, Domperidone. Block D² receptors and improve gastric emptying.
- H¹ antihistamines: Promethazine, Dimenhydrinate. Block H¹ receptors and are useful in motion sickness.
- Muscarinic antagonist: Hyoscine. Blocks muscarinic receptors and is useful in motion sickness.
- NK¹ antagonist: Aprepitant. Blocks neurokinin-1 receptors and is useful in chemotherapy-induced vomiting.
Laxatives
Laxatives are drugs that facilitate defecation and relieve constipation.
Types and Examples:
- Bulk-forming: Ispaghula, Bran. Increase stool bulk and retain water.
- Osmotic: Lactulose, Polyethylene glycol, Magnesium hydroxide. Increase osmotic pressure and retain water in the intestine.
- Stimulant: Bisacodyl, Senna, Sodium picosulfate. Stimulate intestinal motility and secretion.
- Stool softeners: Docusate sodium. Facilitate mixing of water with stool.
- Lubricants: Liquid paraffin. Lubricate stool and intestinal mucosa.
Antidiarrhoeal Drugs
Antidiarrhoeal drugs reduce the excessive frequency and fluidity of stools.
Mode of Action: They decrease intestinal motility, reduce intestinal secretion, or adsorb toxins and fluids.
Types and Examples:
- Opioid antimotility: Loperamide, Diphenoxylate.
- Adsorbents: Activated charcoal, Diosmectite.
- Antisecretory: Bismuth compounds.
- ORS: Replaces water and electrolytes and is the mainstay of treatment for dehydration.
Hepatoprotective Drugs
Hepatoprotective drugs are agents that help prevent or reduce hepatic injury and support liver function.
Mode of Action: Depending on the drug, they may reduce oxidative stress, improve bile flow, stabilize hepatocyte membranes, or modify inflammatory processes.
Examples: Ursodeoxycholic acid, Silymarin, N-acetylcysteine, Ademetionine. Uses: Selected hepatic disorders and drug-induced liver injury, depending on the specific agent.
Antibiotics and Antitubercular Drugs
Antibiotics
Antibiotics are antimicrobial drugs that inhibit or kill susceptible bacteria.
Mode of Action: They act selectively on bacterial cell wall synthesis, protein synthesis, nucleic acid synthesis, folate metabolism, or cell membrane integrity.
Types and Examples:
- Cell wall synthesis inhibitors: Penicillin, Amoxicillin, Ceftriaxone, Vancomycin.
- Protein synthesis inhibitors: Aminoglycosides (Gentamicin, Amikacin), Tetracyclines (Doxycycline), Macrolides (Azithromycin, Erythromycin), Oxazolidinones (Linezolid).
- Nucleic acid synthesis inhibitors: Ciprofloxacin, Levofloxacin, Rifampicin.
- Antimetabolites: Cotrimoxazole, Sulfamethoxazole.
- Cell membrane acting drugs: Polymyxin B, Colistin.
Antitubercular Drugs
Antitubercular drugs are medicines used for the treatment and prevention of tuberculosis caused by Mycobacterium tuberculosis.
Mode of Action: They inhibit essential processes of mycobacteria such as cell wall synthesis, RNA synthesis, and protein synthesis.
First-line Drugs:
- Isoniazid: Inhibits synthesis of mycolic acid in the mycobacterial cell wall.
- Rifampicin: Inhibits DNA-dependent RNA polymerase and bacterial RNA synthesis.
- Pyrazinamide: Converted to active pyrazinoic acid and disrupts mycobacterial metabolism.
- Ethambutol: Inhibits arabinosyl transferase and mycobacterial cell wall synthesis.
- Streptomycin: Inhibits bacterial protein synthesis by acting on the 30S ribosomal subunit.
Second-line/Reserve Drugs: Bedaquiline, Linezolid, Clofazimine, Delamanid, Fluoroquinolones such as Levofloxacin and Moxifloxacin.
Antifungal, Antiviral, and Antimalarial Drugs
Antifungal Drugs
Antifungal drugs are medicines used to treat infections caused by pathogenic fungi.
Mode of Action: They interfere with fungal cell membrane synthesis, cell wall synthesis, nucleic acid synthesis, or cell division.
Types and Examples:
- Polyenes: Amphotericin B, Nystatin. Bind ergosterol and form pores in fungal cell membranes.
- Azoles: Fluconazole, Itraconazole, Ketoconazole. Inhibit ergosterol synthesis.
- Echinocandins: Caspofungin, Micafungin. Inhibit β-1,3-glucan synthesis in the fungal cell wall.
- Allylamines: Terbinafine. Inhibits squalene epoxidase and reduces ergosterol synthesis.
- Other: Griseofulvin, which interferes with fungal microtubules.
Antiviral Drugs
Antiviral drugs inhibit the replication or spread of viruses in the host.
Mode of Action: They interfere with viral entry, uncoating, nucleic acid synthesis, protease activity, integration, or release.
Types and Examples:
- Anti-herpes: Acyclovir, Valacyclovir.
- Anti-influenza: Oseltamivir, Zanamivir.
- Anti-HIV: Tenofovir, Lamivudine, Dolutegravir.
- Anti-hepatitis B: Tenofovir, Entecavir.
- Direct-acting anti-HCV: Sofosbuvir, Velpatasvir.
Antimalarial Drugs
Antimalarial drugs are medicines used for the prevention and treatment of malaria caused by Plasmodium species.
Mode of Action: They act on different stages of the parasite’s life cycle, particularly erythrocytic stages.
Types and Examples:
- Artemisinin derivatives: Artesunate, Artemether. Produce toxic free radicals within the parasite.
- 4-aminoquinolines: Chloroquine. Inhibits haem detoxification in susceptible malaria parasites.
- Antifolate drugs: Pyrimethamine, Sulfadoxine. Inhibit folate metabolism.
- Tissue schizonticides: Primaquine, Tafenoquine. Act against hepatic stages and prevent relapse in P. vivax and P. ovale.
- Combination therapy: Artemether + Lumefantrine.
Anthelmintic Drugs
Anthelmintics are drugs used to eliminate parasitic worms from the body.
Mode of Action: They paralyze the parasite, inhibit glucose uptake, interfere with microtubules, or damage the parasite’s neuromuscular system.
Types and Examples:
- Benzimidazoles: Albendazole, Mebendazole.
- Anthelmintic causing paralysis: Pyrantel pamoate.
- Macrocyclic lactone: Ivermectin.
- Trematode/cestode drug: Praziquantel.
- Antinematode: Diethylcarbamazine.
Albendazole: Inhibits microtubule formation and glucose uptake in helminths.
Hormones and Related Drugs
Thyroid Hormones and Inhibitors
Thyroid Hormones: These are synthetic preparations used to replace deficient thyroid hormone or suppress TSH secretion.
Mode of Action: T&sup4; is converted to T³ in tissues. T³ binds nuclear thyroid receptors and regulates gene transcription, increasing metabolic activity, growth, and development. Examples: Levothyroxine (T&sup4;), Liothyronine (T³). Uses: Hypothyroidism, myxoedema, and thyroid hormone replacement.
Thyroid Inhibitors: Drugs that reduce thyroid hormone synthesis, release, or peripheral effects.
Types and Examples:
- Thioamides: Carbimazole, Methimazole, Propylthiouracil. Inhibit thyroid peroxidase and reduce thyroid hormone synthesis.
- Iodides: Potassium iodide, Lugol’s iodine. Inhibit thyroid hormone release and temporarily reduce thyroid gland vascularity.
- Radioactive iodine: Iodine-131. Destroys thyroid tissue by β-radiation.
- β-blockers: Propranolol. Control adrenergic symptoms of hyperthyroidism and at higher doses reduce T&sup4;-to-T³ conversion.
Insulins
Insulin is a peptide hormone that lowers blood glucose by promoting glucose uptake and storage and inhibiting hepatic glucose production.
Mode of Action: Insulin binds to insulin receptors with intrinsic tyrosine kinase activity, increasing GLUT4-mediated glucose uptake in skeletal muscle and adipose tissue and promoting glycogen, fat, and protein synthesis.
Types and Examples:
- Rapid acting: Insulin lispro, Aspart, Glulisine.
- Short acting: Regular insulin.
- Intermediate acting: NPH insulin.
- Long acting: Glargine, Detemir.
- Ultra-long acting: Degludec.
Uses: Type 1 diabetes mellitus, type 2 diabetes mellitus when insulin is required, diabetic ketoacidosis, and gestational diabetes in selected patients.
Oral Antidiabetic Drugs
Oral antidiabetic drugs are medicines used to control blood glucose mainly in patients with type 2 diabetes mellitus.
Types and Examples:
- Biguanide: Metformin. Decreases hepatic gluconeogenesis and improves insulin sensitivity.
- Sulfonylureas: Glimepiride, Glibenclamide. Stimulate pancreatic β-cells to release insulin by closing ATP-sensitive potassium channels.
- Meglitinides: Repaglinide, Nateglinide. Stimulate rapid insulin secretion.
- Thiazolidinediones: Pioglitazone. Activate PPAR-γ and increase insulin sensitivity.
- α-glucosidase inhibitors: Acarbose, Voglibose. Delay intestinal carbohydrate digestion and glucose absorption.
- DPP-4 inhibitors: Sitagliptin, Linagliptin. Increase endogenous incretin activity and glucose-dependent insulin secretion.
- SGLT2 inhibitors: Empagliflozin, Dapagliflozin. Reduce renal glucose reabsorption and increase urinary glucose excretion.
- Oral GLP-1 receptor agonist: Oral Semaglutide. Enhances glucose-dependent insulin secretion, suppresses glucagon, and delays gastric emptying.
Hormonal Contraceptives
Hormonal contraceptives are preparations containing estrogen, progestin, or both that prevent pregnancy by suppressing ovulation and producing changes in cervical mucus and endometrium.
Mode of Action: They suppress hypothalamic-pituitary-ovarian activity, inhibit ovulation, thicken cervical mucus, and make the endometrium less suitable for implantation.
Types and Examples:
- Combined oral contraceptives: Ethinyl estradiol + Levonorgestrel.
- Progestin-only pills: Desogestrel.
- Injectable contraceptives: Depot medroxyprogesterone acetate.
- Implants: Etonogestrel implant.
- Emergency contraception: Levonorgestrel, Ulipristal acetate.
- Hormonal intrauterine system: Levonorgestrel-releasing IUS.
Uterine Stimulants and Relaxants
Uterine Stimulants: Drugs that increase uterine contraction and are used mainly to induce or augment labour and control postpartum haemorrhage.
Mode of Action: They increase uterine smooth muscle contraction through oxytocin receptors or prostaglandin receptors.
Types and Examples:
- Oxytocics: Oxytocin, Carbetocin. Stimulate oxytocin receptors and produce rhythmic uterine contractions.
- Prostaglandins: Misoprostol, Dinoprostone, Carboprost. Stimulate uterine contractions and promote cervical ripening.
- Ergot alkaloid: Methylergometrine. Produces powerful uterine contraction.
Uses: Induction/augmentation of labour and management of postpartum haemorrhage.
Uterine Relaxants: Uterine relaxants or tocolytics are drugs that reduce uterine contractions and may delay preterm labour.
Mode of Action: They reduce intracellular calcium or inhibit pathways responsible for uterine smooth muscle contraction.
Types and Examples:
- β² agonists: Terbutaline, Salbutamol. Increase cAMP and relax uterine smooth muscle.
- Calcium channel blocker: Nifedipine. Blocks calcium entry into uterine smooth muscle.
- Oxytocin receptor antagonist: Atosiban. Blocks oxytocin receptors and reduces uterine contractions.
- Prostaglandin synthesis inhibitor: Indomethacin. Reduces prostaglandin synthesis and uterine contractions.
- Magnesium sulfate: Reduces neuromuscular excitability and may have a role in specific obstetric settings, particularly for fetal neuroprotection rather than routine tocolysis.