The specific set of allergy symptoms caused by a medication depends on the organs affected. In some cases symptoms start soon after therapy begins; in other cases the symptoms begin when the person is well into therapy; in still others the symptoms begin after therapy has been discontinued. Occasionally they disappear spontaneously even though the drug is continued; but most often, the drug must be stopped for the condition to clear.

Skin Eruptions
Most drug allergies involve the skin in some way, and many drugs are capable of eliciting more than one type of skin reaction. Itching, small hives, massive hives, red blotches, measlelike rashes, and eczema conditions are all well-recognized complications of certain topical or systemic drugs. Less common drug-related skin problems include fixed drug eruptions (where a patch or several patches of redness and discoloration appear in the same exact location each time a particular drug is ingested); purpura (black-and-blue marks of varying sizes); blistering eruptions; phototoxic reactions (heightened sensitivity to ultraviolet light leading to severe sunburns); photoallergic reactions (ultraviolet light combines with the drug to provoke a true allergic eczema); erythema multiforme (an exaggerated form of hives), erythema nodosum (deep, painful nodules, typically over the lower extremities), and exfoliative dermatitis (a red, scaly rash that covers more than 90 percent of the skin surface, including the scalp).

With good reason, toxic epidermal necrolysis, a frequently fatal condition in which large sheets of skin and mucous membrane tissue literally slough away, is the most feared skin manifestation of drug allergy. Skin allergies of various kinds have been tied to penicillin and its derivatives (such as ampicillin, amoxicillin, and dicloxacillin), trimethoprim-sulfa antibiotics (Septra and Bactrim), sulfisoxazole (Gantrisin and Gantanol), cephalosporins (Keflex, Velosef, and Duricef), barbiturates (such as phenobarbital), and quinidine (Quinaglute), among numerous others.

Drug Fever
Fever can be the sole manifestation of a drug allergy or may accompany skin eruptions and other organ symptoms. It is believed to be related to the release of pyrogens (temperature-raising chemical mediators) from certain kinds of white blood cells. When fever is the only symptom, it usually begins sometime between the seventh and tenth day following the start of drug treatment. Characteristically, discontinuing the drug leads to a return to normal temperature, but reintroducing the drug quickly leads to the return of the fever. Penicillin is a common fever producer, as are quinidine (Quinaglute), procainamide (Pronestyl), barbiturates (such as Seconal), and phenytoin (Dilantin).

Respiratory Tract Reactions
Like the skin, the respiratory system can react adversely to drugs in a number of ways: fluid buildup in the lungs, infiltration by lymphocytes and other kinds of white cells, inflammation and swelling of the air sacs or of the walls separating them, formation of scar tissue, and the development of acute, potentially life-threatening airway obstruction. Methotrexate (an antiarthritis, anticancer, and antipso-riasis agent), nitrofurantoin (such as Furadantin, an antibiotic for bladder infection), sulfasalazine (such as Azulfidine, an anticolitis drug), and cromolyn sodium (Intal) are all known causes of a drug-induced pneumonialike lung allergy. Hydrochlorothiazide (such as HydroDIURIL, a water pill), heroin, and methadone may all cause pulmonary edema (fluid in the lungs), and aspirin may cause life-threatening bronchospasm in susceptible individuals (as discussed below).

Liver Reactions
Certain drugs have been linked to adverse liver reactions. Most often the symptoms are due either to bile duct congestion and backup within the liver or to direct injury to the liver cells themselves that is, a chemical hepatitis. Certain anticonvulsive (antiepilepsy) medications, erythromycin estolate (Ilosone), gold salts (Myochrisine), halothane (a general anesthetic agent), indomethacin (Indocin), iso-niazid (INH), ketoconazole (Nizoral), methyldopa (Aldomet), phe-nothiazines (such as Thorazine and Mellaril), sulfa drugs (such as Gantrisin), and certain thyroid medications (propylthiouracil, for example) have all been associated with liver abnormalities. Although postulated, allergic mechanisms have not been conclusively demonstrated in any of these instances. In most cases, fortunately, the abnormalities completely subside when the offending drug is withdrawn.

Kidney Problems
Considering that the kidney is the body's main waste filter, it is hardly surprising that it is occasionally adversely affected by the drugs we take. The delicate filtering portions of the kidney and the tissues immediately surrounding them are particularly susceptible to dam-age. Gold injections, methicillin, large doses of penicillin G, cephalosporins, nonsteroidal inflammatory agents (such as Anaprox, Motrin, and Nuprin), and phenytoin (Dilantin) have all been linked to kidney reactions.

Swollen Lymph Nodes
Generalized lymph node enlargement, or as doctors call it, lym-phadenopathy, has been reported in individuals receiving long-term phenytoin (Dilantin), sulfonamide, and penicillin therapy. Believed allergic in nature, lymph gland enlargement can occasionally be so pronounced as to be initially confused with a malignancy. In most instances, discontinuing the culprit medication leads to complete resolution of the problem.

Blood Problems
Drugs can damage the blood system in a variety of ways. As part of cytotoxic reactions, they may induce anemia by destroying red corpuscles. Or they may lead to bruising problems by interfering with platelets, one of the blood's most important clotting components. In a serum sicknesslike fashion, they may inflame and damage the blood vessels themselves in the skin, joints, and kidneys, resulting in a condition technically known as allergic vasculitis. Allopurinol (an antigout medication such as Zyloprim), hydantoin (Dilantin), penicillin, and sulfa have all been associated with this type of kidney reaction.

Anaphylaxis
Fortunately a relatively rare adverse drug reaction, anaphylaxis is the most dreaded of all allergies to medications. Symptoms usually begin within about half an hour of taking the culprit medication. At first the victim usually complains of feeling anxious and tense. This is often succeeded by the onset of a vicious, splitting headache, which in turn is quickly followed by tissue swelling and airway blockage within the respiratory system, fluid accumulation in the lungs, a lowering of blood pressure, heart rhythm abnormalities, and finally heart stoppage. If emergency measures are not instituted immediately, death usually results. Penicillin and anesthetics (local and general) are examples of medications that may provoke anaphylaxis in susceptible individuals.