Local reaction to drug
Chemical burns the best known example is that of aspirin tablet held against the mucosa close to an aching tooth ‘it will cause superfacial necrosis and a white patch ,dead epithelium is shed and the mucosa heals.Other irritant chemicals are acid etchants or phenol dropped on the mucosa.Interferance with the oral flora: super infection: prolonged topical use of antibiotic in the mouth kills off sensitive organisms and allow resistant ones, particularly candida albicans, to proliferate, causing thrush in susceptable patients. Use of a topical antibiotic may precipitate candidal infection within 48hrs.
SYSTEMICALLY MEDIATED REACTIONS
1-DEPRESSION OF MARROW FUNCTION : A - few drugs significally depress red cell production alone, though any drug which cause anemia might give rise to oral signs. the main example is prolonged use of phenytoin (for epilepsy) which in susceptible patients, can cause folate deficiency and macrocytic anemia. This inturn can cause severe aphthous stomatitis, response promotly follows administration of foliate, and the blood picture returns to normalB- white cell production depressions: white cell production is depressed by a variety of drugs. Leucopenia may be severe enough to produce the clinical picture of agranulocytosis, with necrotising ulceration of the gingivae and throat which can go on to a severe prostrating illness and septicaemia if untreated, Drugs which may have this effect include:- antibacterial. particularly co-trimoxazole. Chloramphenicol analgesics, particularly amidopyrime ,phenothiazines antithyroid agents.
When the main effect is on granulocytes, low-grad oral pathogens, particularly of the gingival margins, are able to overcome local resistance and produce necrotising ulceration.
C- Other drugs may affect haemostasis and cause oral purpura. Drug-induced purpura is often also an early sign of aplastic anaemia caused by drugs such as chloramphenicol. which depress marrow function. Purpura can produce severe spontaneous gingival bleeding or blood blisters and widespread submucosal ecchymoses.
D- Depression of cell-medical immunity. lmmunosuppression by drugs as such corticosteroids is induced in patients having organ transplants or with immunologically-mediated diseases. Viral and fungal infections of the mouth are common in immunosuppressed patients and can be severe. Recurrences of childhood viral infections such as measles and chickenpox are also possible.
E- Lichenoid reactions. Several drugs:- gold and antimalarials (both used in the treatment of rheumatoid arthritis or other collagen diseases), the antihypertensive agent methyldopa can cause disease indistinguishable from lichen planus, both clinically and histologically. The mechanism of such reactions is unknown.
F- ACUTE ERYTHEMA MULTIFOME: as discussed earlier, Sulphonamides, barbiturates or other drugs are occasionally implicated, but the mechanisms are unknown and more frequently there is no evidence of a drug reaction.
G- TOXIC EPIDERMAL NECROLYSIS: this, which probably represents the extreme end of the spectrum of the erythema multiforme, It is one of the most dangerous and severe types of drug reaction. mucosal involvement is common and cause widespread erosions due to epithelial destructions. Oral ulceration may precede the dermal changes, and cause the patient to seek treatment for the extreme sorness of the mouth. Early diagnosis and treatment is important as the reaction can be lethal.
Example :- Metals such as gold salts are important causes but phenylbutazone ,barbiturates and other drugs have also been implicated. Healing of oral lesions may leave a pattern of lichen planus.
H- FIXED DRUG ERUPTIONS: these consist of sharply circumscribed skin recurring in the same site or sites each time the drug is given. many drugs are capable of causing this reaction :- co-trimixazole , tetracycline but phenolphthaline , awidly use component of purgatives,is one of the more causes . Involvement of the oral mucous memberane has been described but is exceedingly rare.
OTHER DRUG EFFECTS
1- GINGIVAL HYPER PLASIA: phenytoin (Dilantine), Nifidipine (Adalat), Cyclosporine antineoplastic can cause fibrous hyperplasia . Particularly concentrated at the inter dental papillae2- ORAL PIGMENTATION:
heavy metals such as mercury,bismuth,and lead can cause black or brown deposite in the gingival sulcus by interaction with bacterial productes to form sulphides. The blue lead line may be particularly sharply defined and indicate the level of the floor of the pocket. These effects are rarly seen now that mercry and bismuth are no longer used in medicine and lead is no longer a major industrial hazard . How ever , cisplatine, a cytotoxic drug, can cause a blue line. Topical antibiotic & antiseptic may cause dark pigmentaion. Particularly of the dorsum of the tongue, due to over growth of the pigment forming bacteria3- DRY MOUTH: is a relatively common side effect of drugs, particularly those with an atropine like action, such as the tricyclic anti depressants which are widely used.