Megatrim DS800 mg+160 mg

Megatrim DS 800 mg+160 mg, also known as Co-trimoxazole or by its generic components Sulfamethoxazole and Trimethoprim (often abbreviated SMX-TMP or TMP-SMX), is a fixed-dose combination antibiotic with broad-spectrum bactericidal activity. It is one of the most widely prescribed antibacterial generics in Bangladesh, available as standard tablets, double-strength (DS) tablets, and oral suspension for both adults and children.

The combination contains Trimethoprim and Sulfamethoxazole in a 1:5 ratio and works by sequentially blocking two separate bacterial enzyme systems involved in folic acid metabolism. This dual blockade produces a synergistic bactericidal effect against a wide range of Gram-positive and Gram-negative organisms, including Streptococcus, Staphylococcus, Pneumococcus, Escherichia coli, Klebsiella, Proteus species, Haemophilus influenzae, Salmonella, Shigella, Vibrio cholerae, Brucella, and Pneumocystis jirovecii (formerly Pneumocystis carinii).

1. Respiratory Tract Infections

Megatrim DS 800 mg+160 mg is indicated for both the treatment and prophylaxis of acute and chronic bronchitis, as well as bronchiectasis, lung abscess, lobar and bronchopneumonia, sinusitis, and otitis media. It is also a first-line agent for the treatment and prevention of Pneumocystis pneumonia (PCP), particularly in immunocompromised patients such as those living with HIV/AIDS.

2. Genito-Urinary Tract Infections

It is commonly used to treat urethritis, acute and chronic cystitis, pyelonephritis, prostatitis, and gonorrhoea. Its high tissue penetration into the urinary tract makes it particularly effective against common uropathogens such as E. coli and Proteus species.

3. Gastrointestinal Tract Infections

Megatrim DS 800 mg+160 mg is effective against infections caused by Salmonella typhi and Salmonella paratyphi, including typhoid fever and the chronic carrier state. It is also used as an adjuvant to fluid and electrolyte replacement in bacillary dysentery and cholera.

4. Other Susceptible Infections

When the therapeutic benefit is judged to outweigh the risk of adverse effects, Megatrim DS 800 mg+160 mg may also be used for:

• Acute and chronic osteomyelitis (bone infections)
• Acute brucellosis
• Skin and soft tissue infections, including pyoderma, abscesses, and wound infections
• Septicaemia (bloodstream infections)
• Nocardiosis and mycetoma

Note: Megatrim DS 800 mg+160 mg should only be taken under the supervision of a registered physician. Self-medication with antibiotics can lead to antimicrobial resistance and should always be avoided.

Anti-diarrhoeal Antimicrobial drugs, Sulphonamides & Trimethoprim

Megatrim DS 800 mg+160 mg combines two synthetic antibacterial agents, Sulfamethoxazole and Trimethoprim, that target sequential steps in bacterial folate (folic acid) synthesis. Because bacteria cannot use pre-formed folate from their environment, this dual blockade is highly effective and produces a synergistic, bactericidal rather than merely bacteriostatic, effect.

Mechanism of Action

Sulfamethoxazole is a structural analogue of para-aminobenzoic acid (PABA). It competitively inhibits the bacterial enzyme dihydropteroate synthase, blocking the conversion of PABA into dihydrofolic acid. Trimethoprim then inhibits the downstream enzyme dihydrofolate reductase, preventing the conversion of dihydrofolic acid into tetrahydrofolic acid (folinic acid), the active form of folate required for bacterial DNA, RNA, and protein synthesis.

By blocking two consecutive steps of the same metabolic pathway, the combination achieves a synergistic bactericidal action that is significantly more potent than either agent used alone, while also reducing the likelihood of resistance developing during treatment.

Pharmacokinetics

Both components of Megatrim DS 800 mg+160 mg are well absorbed after oral administration and distribute widely throughout body tissues and fluids, including the lungs, kidneys, prostate, and cerebrospinal fluid.

Because both drugs are eliminated mainly by the kidneys, their half-lives are prolonged in patients with renal impairment, requiring dose adjustment or avoidance in significant renal disease. Both components also cross the placenta and are excreted in breast milk.

Megatrim DS 800 mg+160 mg can interact with a number of commonly prescribed medicines. Patients should inform their physician or pharmacist about all other medications, supplements, and herbal products they are taking before starting Megatrim DS 800 mg+160 mg.

Clinically Significant Interactions

• Warfarin and other oral anticoagulants: Megatrim DS 800 mg+160 mg can enhance the anticoagulant effect by displacing warfarin from plasma proteins and inhibiting its hepatic metabolism, increasing the risk of bleeding. Closer monitoring of INR is recommended.
• Methotrexate: Both drugs interfere with folate metabolism. Co-administration increases the risk of bone marrow suppression and methotrexate toxicity.
• Phenytoin: Megatrim DS 800 mg+160 mg inhibits phenytoin metabolism, which can raise phenytoin blood levels and increase the risk of toxicity.
• Sulphonylurea antidiabetic drugs (e.g., glibenclamide, glimepiride): Megatrim DS 800 mg+160 mg may potentiate their blood-glucose-lowering effect, increasing the risk of hypoglycaemia.
• ACE inhibitors, ARBs, and potassium-sparing diuretics: Trimethoprim can reduce renal potassium excretion, and combined use increases the risk of hyperkalaemia, particularly in elderly patients and those with renal impairment.
• Digoxin: Megatrim DS 800 mg+160 mg may increase serum digoxin levels, especially in elderly patients, requiring monitoring for signs of digoxin toxicity.
• Cyclosporine: Concurrent use may increase the risk of nephrotoxicity and transient deterioration in renal function.
• Rifampicin: May reduce the plasma half-life of trimethoprim through enzyme induction.
• Thiazide diuretics: Increased risk of thrombocytopenia and thrombocytopenic purpura, particularly in elderly patients.
• Azathioprine and 6-mercaptopurine: Increased risk of bone marrow suppression when used with Megatrim DS 800 mg+160 mg.
• Pyrimethamine (high doses, above 25 mg weekly): Increased risk of megaloblastic anaemia due to additive antifolate effects.

This list is not exhaustive. Always consult a physician or pharmacist before combining Megatrim DS 800 mg+160 mg with any other prescription or over-the-counter medication.

Like all medicines, Megatrim DS 800 mg+160 mg can cause side effects, although not everyone experiences them. Most side effects are mild and transient and do not require stopping treatment. Rare but serious reactions can occur and require prompt medical attention.

Common, Mild Side Effects

• Nausea and vomiting
• Loss of appetite
• Headache
• Malaise (general feeling of being unwell)

Gastrointestinal Effects

• Diarrhoea
• Glossitis (inflammation of the tongue)
• Stomatitis (inflammation of the mouth)

Skin Reactions

• Skin rash and itching
• Photosensitivity (increased sensitivity to sunlight)
• Rarely, severe skin reactions such as Stevens-Johnson syndrome or toxic epidermal necrolysis

Blood-Related Effects

• Crystalluria (crystal formation in urine)
• Haemolysis, particularly in patients with G6PD deficiency
• Thrombocytopenia (low platelet count)
• Neutropenia and agranulocytosis (low white blood cell counts)
• Megaloblastic anaemia with prolonged, high-dose therapy

Other Rare Effects

• Elevated serum potassium levels (hyperkalaemia)
• Reversible elevation in serum creatinine
• Interstitial nephritis
• Cholestatic jaundice and, rarely, hepatic necrosis
• Allergic reactions, including fever and serum-sickness-like symptoms

When to seek medical help: Stop the medicine and seek immediate medical attention if you develop a severe skin rash or blistering, difficulty breathing, swelling of the face or throat, unusual bruising or bleeding, persistent sore throat or fever, or yellowing of the skin or eyes.

Pregnancy

Megatrim DS 800 mg+160 mg should generally be avoided during pregnancy, particularly in the first trimester and near term. Both sulfamethoxazole and trimethoprim cross the placenta. Trimethoprim's antifolate action carries a theoretical risk of neural tube defects and other folate-related birth defects if used during early pregnancy. Use close to delivery may increase the risk of neonatal kernicterus, as sulfonamides can displace bilirubin from its plasma protein binding sites.

If antibiotic treatment is essential during pregnancy, alternative agents considered safer in pregnancy are usually preferred. Megatrim DS 800 mg+160 mg should only be used in pregnancy if the physician determines that the benefit clearly outweighs the potential risk, and folic acid supplementation may be advised if treatment cannot be avoided.

Breastfeeding

Both components of Megatrim DS 800 mg+160 mg pass into breast milk. While the amounts are generally small, the drug should be used with caution during breastfeeding, especially when the nursing infant is premature, jaundiced, has G6PD deficiency, or is younger than one month, due to the risk of kernicterus and haemolysis. A doctor should be consulted before using Megatrim DS 800 mg+160 mg while breastfeeding.

• Folate deficiency risk: Prolonged, full-dose treatment is associated with a risk of macrocytic (megaloblastic) anaemia, caused by interference with the conversion of folic acid into folinic acid. If this occurs, it can usually be reversed by administering folinic acid (leucovorin) without discontinuing the antibiotic, under medical supervision.
• Diabetic patients on sulphonylureas: Care should be taken when prescribing Megatrim DS 800 mg+160 mg to diabetic patients receiving sulphonylurea medication, as it may potentiate the blood-glucose-lowering effect and increase the risk of hypoglycaemia.
• Renal impairment: Use with caution and adjust the dose in patients with reduced kidney function, since both components are mainly excreted by the kidneys.
• Hepatic impairment: Use with caution in patients with liver disease, and avoid in those with marked liver damage.
• G6PD deficiency: Use with caution, as it may precipitate haemolysis in susceptible individuals.
• Elderly patients: Older adults, particularly those also taking diuretics, ACE inhibitors, or ARBs, are at greater risk of severe adverse reactions including thrombocytopenia and hyperkalaemia.
• Adequate hydration: Patients should maintain good fluid intake during treatment to reduce the risk of crystalluria.
• Sun exposure: Megatrim DS 800 mg+160 mg may increase sensitivity to sunlight; excessive sun and UV exposure should be avoided, and sun protection is recommended during treatment.
• HIV/AIDS patients: Patients with HIV infection have a notably higher incidence of adverse reactions, particularly skin rash, fever, and blood count abnormalities, and should be monitored closely.
• Laboratory interference: Megatrim DS 800 mg+160 mg may cause a false elevation in some laboratory tests for serum creatinine.
• Antibiotic resistance: As with all antibiotics, Megatrim DS 800 mg+160 mg should be used only when clinically indicated, at the correct dose, and for the full prescribed duration, to reduce the development of bacterial resistance.

Symptoms of Overdose

Acute overdose with Megatrim DS 800 mg+160 mg may present with the following symptoms:

• Nausea, vomiting, and loss of appetite
• Dizziness, confusion, and headache
• Drowsiness or, in severe cases, unconsciousness
• Crystalluria and haematuria
• Bone marrow depression, with associated blood count abnormalities
• Jaundice, in cases of significant hepatic involvement

Management of Overdose

There is no specific antidote for Megatrim DS 800 mg+160 mg overdose. Treatment is largely supportive and may include:

• Gastric lavage or induced emesis if the overdose is recent and the patient is conscious
• General supportive measures and close monitoring of vital signs
• Maintaining adequate hydration with increased fluid intake to promote urinary excretion
• Acidification of urine, which can increase the renal excretion of sulfamethoxazole
• Folinic acid (leucovorin) administration to counteract bone marrow suppression caused by folate antagonism
• Haemodialysis, which is effective in removing both sulfamethoxazole and trimethoprim from the circulation in severe cases
• Regular monitoring of blood counts and renal function in the days following the overdose

In case of suspected overdose, seek emergency medical attention immediately rather than attempting to manage it at home.

• Store below 30°C, away from direct light and moisture.
• Keep tablets in their original strip or container until ready to use.
• Shake the oral suspension well before each use and keep the bottle tightly closed.
• Do not store in damp areas such as bathrooms; keep in a cool, dry place.
• Keep out of the reach and sight of children.
• Do not use the medicine after the expiry date printed on the pack.
• Dispose of any unused or expired medicine safely, and do not pour liquid suspension down the drain unless advised to do so.

Renal Impairment

Since both sulfamethoxazole and trimethoprim are eliminated primarily by the kidneys, dose adjustment is required in patients with impaired renal function. In patients with moderate renal impairment, the dose may need to be reduced by approximately half. Megatrim DS 800 mg+160 mg should generally be avoided in patients with severe renal insufficiency unless renal function can be closely monitored, as it may be used only if no suitable alternative exists.

Hepatic Impairment

Megatrim DS 800 mg+160 mg should be used with caution in patients with mild to moderate liver impairment and should be avoided altogether in those with marked liver parenchymal damage, due to the risk of accumulation and hepatotoxicity.

Elderly Patients

Elderly patients are more susceptible to severe adverse reactions, including thrombocytopenia, bone marrow suppression, and hyperkalaemia, particularly when Megatrim DS 800 mg+160 mg is combined with diuretics, ACE inhibitors, or ARBs. Renal function should be assessed before starting treatment, and elderly patients should be monitored closely throughout the course.

Paediatric Use

Megatrim DS 800 mg+160 mg oral suspension is suitable for infants from 6 weeks of age onward, following the weight- and age-based dosing schedule. It should not be used in infants younger than 6 weeks of age because of the risk of kernicterus and the immaturity of their enzyme systems.

G6PD Deficiency

Patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency are at increased risk of haemolytic anaemia with sulfonamide-containing medicines such as Megatrim DS 800 mg+160 mg. This combination should generally be avoided in known G6PD-deficient individuals.