Type B adverse reactions

Type B adverse reactions are rarer but potentially more serious. Many type B adverse reactions are due to allergy. 

Non-dose-related (idiosyncratic, type B) adverse reactions... 

ADRs are often classified into two major sorts so called Type A and Type B reactions. Type A adverse reactions are those which may be anticipated from the nature of the treatment (perhaps due to knowledge of class effects or mechanisms of action) and are dose-dependent. Type B adverse reactions are those which are unpredictable from background knowledge. They are usually a form of hypersensitivity or immunological reaction peculiar to the individual and may occur even with very small doses. They may be caused by the drug itself or by metabolites. Type B reactions are usually rarer and more serious than type A reactions. 

The spontaneous case report database cannot be used to give an accurate incidence rate of even the Type B adverse reactions, as not all cases are reported, either because someone who should act as the reporter is not sufficiently motivated, or he/ she does not recognize the event as an adverse reaction in that patient (Kessler 1993 Fletcher... 

The adverse, toxic effects of drugs can be divided into one of two t5rpes, A and B. Type A adverse reactions are due to the pharmacological (therapeutic) effect of the drug and are therefore usually predictable and related to the dose. They are usually exaggerated therapeutic effects. Type B are unexpected, idiosyncratic effects. 

Type B adverse drug reactions are much rarer than type A, but they are unpredictable and not dose-related and they are potentially more serious. Many are due to dmg allergy, but there are other causes. 

Table 1 Characteristics of type A and type B adverse drug reactions...

Because of these difficulties in establishing the mechanism for both types of reaction, allergy, and idiosyncrasy (incidentally both are classified as type B adverse drug reactions, according to Rawlins and Thompson s classification, 1977),... 

In order to achieve the desired fiber properties, the two monomers were copolymerized so the final product was a block copolymer of the ABA type, where A was pure polyglycoHde and B, a random copolymer of mostly poly (trimethylene carbonate). The selected composition was about 30—40% poly (trimethylene carbonate). This suture reportedly has exceUent flexibiHty and superior in vivo tensile strength retention compared to polyglycoHde. It has been absorbed without adverse reaction ia about seven months (43). MetaboHsm studies show that the route of excretion for the trimethylene carbonate moiety is somewhat different from the glycolate moiety. Most of the glycolate is excreted by urine whereas most of the carbonate is excreted by expired CO2 and uriae. 

None of these factors alone should be considered to indicate a Type B reaction, and any taken singly can be associated with a Type A reaction. This list should be taken as a starting point in determining if an adverse drug reaction is a type of drug allergy. The following are additional considerations. 

Types of adverse drug reaction There are several classifications of adverse reactions, but the most commonly employed define two principal kinds (A and B) and three subordinate classes (C, D and E). 

A) reactions. Other drugs, e.g. antimicrobials, have a tendency to cause allergy and may lead to bizarre (type B) reactions. Ingredients of a formulation, e.g. colouring, flavouring, sodium content, rather than the active drug may also cause adverse reactions. 

The Hexavalent Study Group has compared the immuno-genicity and safety of a new liquid hexavalent vaccine against diphtheria, tetanus, pertussis, poliomyelitis, hepatitis B, and Haemophilus influenzae type b (DTP + IPV + HB + Hib vaccine, manufactured by Aventis Pasteur MSD, Lyon, France) with two reference vaccines, the pentavalent DTP -I- IPV -i- Hib vaccine and the monovalent hepatitis B vaccine, administrated separately at the same visit (9). Infants were randomized to receive either the hexavalent vaccine (n = 423) or (administered at different local sites) the pentavalent and the HB vaccine (n = 425) at 2, 4, and 6 months of age. The hexavalent vaccine was well tolerated (for details, see the monograph Pertussis vaccines). At least one local reaction was reported in 20% of injections with hexavalent vaccine compared with 16% after the receipt of pentavalent vaccine or 3.8% after the receipt of hepatitis B vaccine. These reactions were generally mild and transient. At least one systemic reaction was reported in 46% of injections with hexavalent vaccine, whereas the respective rate for the recipients of pentavalent and HB vaccine was 42%. No vaccine-related serious adverse event occurred during the study. The hexavalent vaccine provided immune responses adequate for protection against the six diseases. 

The reports of the Institute of Medicine, National Academy of Sciences, Washington (on adverse events after pertussis and mbeUa immnnization (SED-12, 817) (SED-12, 825) and on adverse events after immunization against tetanus, diphtheria, measles, mumps, poliomyelitis, H. influenzae type b, and hepatitis B (SEDA-18,325) have provided useful reviews (13,14). The 1996 Update on vaccine side effects, adverse reactions, contraindications,... 

Safety issues primarily related to drug specific characteristics, e.g. type A (pharmacological) and type B (idiosyncratic) adverse reactions. 

Adverse events are sometimes termed type A (usually pharmacologically predictable, relatively frequent, seldom fatal and usually identified during clinical trials) or type B (unpredictable idiosyncratic reactions which are usually infrequent but can be very serious or fatal) (Rawlins and Thompson, 1977 Venning, 1983). Postmarketing ADR monitoring usually identifies the more serious, type B reactions. The sample size needed in clinical trials to detect differences between an incidence rate of 1/10 000 and 2/10 000 is about 306 000 patients (e.g. for a placebo comparison of chloramphenicol-induced aplastic anemia, which occurs in 1/30 000 Lasagna, 1983). Clinical trials at this scale are simply impractical. 

In Phase I and II studies, Type A reactions are by far the most frequent. Type B are rare, which is fortunate as some can be serious or even fatal. Table 6.3 shows the number of subjects that need to be studied to give a good chance (95%) of detecting an adverse event when there is no background incidence. The problem is many orders of magnitude worse if the adverse reaction closely resembles spontaneous disease that has a background incidence in the population in the trial. 

Adverse reactions to drugs can be divided into type A (augmented) and type B (bizarre). 

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