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ISONIAZID DRUG PROFILE
PHARMACOLOGICAL CLASS:
Isoniazid is an excellent antitubercular drug and an essential
component of all antitubercular regimens.It is equally active
in acidic or alkaline medium. It is one of the cheapest
antitubercular drugs. The drug is particularly effective against
rapidly growing bacilli(bactericidal)and bacteriostatic against
resting bacteria.
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ISONIAZID DRUG PROFILE
MECHANISM OFACTION:
• INH inhibits synthesis of mycolic acids which are unique
fatty acid components of mycobacterial cell wall.
• Two gene products labelled ‘InhA’ (acyl carrier protein
reductase) and ‘KasA’ β-ketoacyl-ACP synthase ,which
function in mycolic acid synthesis are the targets of INH
action. INH enters sensitive mycobacteria which convert it
by a catalase-peroxidase enzyme into a reactive metabolite.
This then forms adduct with NAD that inhibits InhA and
KasA.
• The reactive INH metabolite forms adduct with NADP as
well which inhibits mycobacterial DHFRase (dihydrofolate
reductase) resulting in interruption of DNA synthesis.
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ISONIAZID DRUG PROFILE
PHARMACOKINETICS:
• Isoniazid is readily absorbed after oral administration.
Absorption is impaired if isoniazid is taken with food,
particularly high-fat meals.
• The drug diffuses into all body fluids, cells, and caseous
material (necrotic tissue resembling cheese that is produced
in tuberculous lesions), placenta and meninges and CSF.
• It is extensively metabolized in liver by N-acetylation
through fast(t½ of INH-1hr) and slow acetylators (t½ of
INH-3hr).
• Excretion is through glomerular filtration and secretion,
predominantly as metabolites(75-90%), also excrete in breast
milk.
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ISONIAZID DRUG PROFILE
PHARMACOKINETICS:
• Peak plasma concentrations:1-2 hours after oral ingestion.
• Half life varies in adults: 1-5 hours.
• Longer serum half life: Renal impairment and liver diseases.
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ISONIAZID DRUG PROFILE
CLINICAL USES:
• Isoniazid is primarily indicated in conditions like
• Acute leukemia
• Mycobacterial infections
• Prophylaxis of TB, Tuberculosis
• Vestibular disorders
• Alternative drug of choice in Pulmonary TB.
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ISONIAZID DRUG PROFILE
ADVERSE EFFECTS:
• Blood and Lymphatic System Disorders:
Agranulocytosis, Eosinophilia, Anemia, Thrombocytopenia,
Vasculitis
• Immune System Disorders:
Allergic reactions, Rheumatoid syndrome, lymphedema,Skin rash
• Nervous System Disorders:
Peripheral neuropathy, Insomnia, Restlessness, muscle twitching.
Convulsions
• Eye and Ear Disorders:
Optic neuritis, Optic atrophy, Tinnitus
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ISONIAZID DRUG PROFILE
ADVERSE EFFECTS:
• Metabolism Disorders:
Hyperglycemia, Metabolic acidosis
• GIT Disorders:
Epigastric distress, Nausea,Vomiting, Constipation
• Hepatobiliary Disorders:
Severe or fatal hepatitis
• Renal and Urinary Disorders:
Prostatic obstruction syndrome
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ISONIAZID DRUG PROFILE
STORAGE CONDITIONS:
• Store at 20°-25°C (68°-77°F).
• Protect from light.
• Protect from freezing.
• Isoniazid Injection USP may crystallize at low temperatures.
• If this occurs, warm the vial to room temperature before use
to redissolve the crystals
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ISONIAZID DRUG PROFILE
PRECAUTIONS
• Impaired renal or hepatic function.
• Alcoholism.
• Diabetes.
• Increased risk of liver damage with increasing age.
• Pregnancy.(Embryocidal)
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ISONIAZID DRUG PROFILE
DRUG INTERACTIONS:
DRUGS EFFECTS
Aluminium
hydroxide
Inhibits/delays INH absorption and serum concentrations.
Phenytoin INH may decrease its excretion or may enhance its effect.
Carbamazepine INH decreases plasma clearance by inhibiting CYP2C19
AND CYP3A4 enzymes
Theophylline INH retards its metabolism by inhibiting CYP2C19 AND
CYP3A4 enzymes.
Warfarin INH retards its metabolism and raise its blood levels.
Para-
aminosalicylic
acid
Inhibits INH metabolism and prolongs its t1/2.
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ISONIAZID DRUG PROFILE
DRUG INTERACTIONS:
• Food
• Isoniazid should not be administered with food.
• Bioavailability of isoniazid is reduced significantly when
administered with food.
• Tyramine- and histamine-containing foods should be avoided in
patients receiving isoniazid. Because isoniazid has some
monoamine oxidase inhibiting activity, an interaction with
tyramine-containing foods (cheese, red wine) may occur.
• Diamine oxidase may also be inhibited, causing exaggerated
response (e.g., headache, sweating, palpitations,hypotension) to
foods containing histamine (e.g., skipjack, tuna, other tropical
fish)
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ISONIAZID DRUG PROFILE
CONTRAINDICATIONS:
• Severe hypersensitivity reactions, including drug-induced
hepatitis;
• Previous isoniazid-associated hepatic injury;
• Severe adverse reactions to isoniazid such as drug fever,
chills, arthritis; and acute liver disease.