Drugs for Cough - Overview

Cough helps remove secretions and foreign particles from the airways.

Cough can be useful (productive) or useless (non-productive). Productive cough helps clear secretions, while non-productive coughing needs suppressing.

Drugs that increase the volume of mucus, helping to clear airways.

Substances that break down mucus, making it easier to clear.

Drugs that suppress the cough reflex.

Mucolytics are specifically useful for patients with thick, sticky mucus or mucus plugs in their airways. They thin out the mucus, making it easier to cough up.

Antitussives are drugs that suppress the cough reflex. They work by acting on the central nervous system to raise the threshold of the cough center or by acting peripherally in the respiratory tract to reduce tussal impulses.

Non-opioid antitussives are preferred as they are less likely to cause dependence or addiction compared to opioid-based antitussives. They are also generally safer for long-term use.

Non-opioid antitussives control rather than eliminate cough. They either raise the threshold of the cough center in the brain or reduce the signals from the respiratory tract that trigger coughing.

Pholcodine has practically no analgesic or addictive properties, unlike many opioids. It is a long-acting antitussive, effective for about 12 hours.

Noscapine is a non-narcotic, non-addictive antitussive that is particularly useful for spasmodic coughs.

While both are antitussives, ethylmorphine, closely related to codeine, is believed to be less constipating. They both work by depressing the cough center in the brain.

Carbocisteine is a mucolytic. It breaks down the mucus in the airways, making it easier to expel.

Methylxanthines have a variable and unpredictable effect on blood pressure. They can cause both an increase (due to vasomotor center stimulation and direct cardiac action) and decrease (due to vagal stimulation and direct vasodilation) in blood pressure.

Methylxanthines cause bronchodilation by increasing the levels of cyclic nucleotides (cAMP and cGMP) in smooth muscles. This occurs through two mechanisms: inhibiting phosphodiesterase, the enzyme that breaks down these nucleotides, and increasing intracellular calcium release.

Theophylline is a more potent bronchodilator than caffeine. It produces a slower, more sustained, and dose-dependent effect on bronchodilation.

Methylxanthines have a mild diuretic effect, increasing urine production. This effect is mostly attributed to their actions on the kidneys.

Methylxanthines relax all smooth muscles, but they have a particularly strong effect on the bronchi, especially in asthmatics.

Methylxanthines inhibit the enzyme phosphodiesterase (PDE) preventing the breakdown of cyclic nucleotides, cAMP and cGMP. This leads to increased levels of these nucleotides, which promote smooth muscle relaxation, especially in the bronchi.

Methylxanthines increase the release of calcium ions from the sarcoplasmic reticulum, mainly in skeletal and cardiac muscle. This action contributes to the relaxation of smooth muscle, including bronchodilation.

Theobromine, a methylxanthine, has no significant therapeutic value and is rarely used in medicine.

Theophylline, even at low doses, can help reduce airway inflammation by enhancing histone deacetylation, which suppresses pro-inflammatory gene transcription.

Theophylline is well absorbed orally, distributes throughout the body including the placenta and breast milk, and is primarily metabolized in the liver. Only a small amount is excreted unchanged in urine.

Theophylline can cause adverse effects like nausea, vomiting, restlessness, tremor, insomnia, and even cardiac arrhythmias at higher doses.

Theophylline is used to treat asthma by its bronchodilator effect and its ability to suppress airway inflammation even at sub-bronchodilator doses.

Histone deacetylation is a process that reduces the activity of genes by making them less accessible to the cellular machinery that reads them.

Pro-inflammatory genes are genes that produce proteins that promote inflammation. When these genes are suppressed, inflammation decreases.

Theophylline and caffeine share similar pharmacokinetic properties and adverse effects. Both are well absorbed orally, metabolized by the liver, and can cause similar side effects like restlessness and insomnia.

Theophylline can be administered orally, rectally (via suppositories), and intravenously. However, rectal absorption is erratic and rapid intravenous injection can be dangerous.

Theophylline is eliminated from the body through metabolism. The rate of elimination varies based on age, with children eliminating it faster, elderly slower, and premature infants very slowly.

Theophylline dosage needs to be adjusted based on age, liver and heart function, and certain medical conditions.

Drugs like erythromycin, ciprofloxacin, cimetidine, oral contraceptives, and allopurinol inhibit theophylline metabolism, increasing its levels in the blood.

Smoking, phenytoin, rifampicin, phenobarbital, charcoal broiled meat, and certain medications increase theophylline metabolism, leading to lower blood levels.

Theophylline enhances the effects of sympathomimetics, digoxin, oral anticoagulants, and hypoglycemics. It also decreases the effects of phenytoin and lithium.

Theophylline has a narrow margin between effective doses and toxic doses. Adverse effects can occur at the upper end of the therapeutic range.

Theophylline's adverse effects primarily affect the gastrointestinal tract, central nervous system, and cardiovascular system.

Theophylline's toxicity increases with higher doses. This is because its elimination follows zero-order kinetics at high doses.

Theophylline, a bronchodilator, is mainly used for long-term maintenance of asthma, especially for nocturnal asthma and COPD. It's often used in combination with other medications.

Theophylline comes in different forms, including immediate-release tablets, sustained-release tablets, and capsules. Sustained-release forms are preferred to maintain consistent blood levels.

Aminophylline, a water-soluble theophylline compound, is used intravenously (IV) for severe cases of asthma like status asthmaticus. However, it is not used intramuscularly or subcutaneously due to irritation.

Hydroxyethyl theophylline, also called Etophylline, is a water-soluble theophylline compound that can be given intravenously, intramuscularly, or orally.

Theophylline helps reduce the frequency and duration of apnoea (breathing pauses) in premature infants during their first few weeks of life.

Atropinic drugs, a type of anticholinergic, cause bronchodilation by blocking the action of acetylcholine on M3 receptors, mainly affecting larger airways.

M3 receptors are found on the larger airways, but recent research suggests they might also be present on peripheral bronchiolar muscles, even though these are not directly controlled by nerves.

Anticholinergics are effective because they block the action of acetylcholine, a neurotransmitter responsible for bronchoconstriction, particularly in larger airways.