5. Adjuvant therapy

Adjuvant analgesics are defined as drugs with a primary indication other than pain that have analgesic properties in some painful conditions. The group includes numerous drugs in diverse classes. Although the widespread use of these drugs as first-line agents, the term "adjuvant" is a misnomer, they usually are combined with a less-than-satisfactory opioid regimen, in particular when administered for cancer pain. Some adjuvant analgesics are useful in several painful conditions and are described as multipurpose adjuvant analgesics (antidepressants, corticosteroids, α2-adrenergic agonists, neuroleptics), whereas others are specific for neuropathic pain (anticonvulsants, local anesthetics, N-methyl-D-aspartate receptor antagonists), bone pain (calcitonin, bisphosphonates, radiopharmaceuticals), musculoskeletal pain (muscle relaxants) or pain from bowel obstruction (octreotide, anticholinergics).

Antidepressants, namely triclyclics (TCAs), which are used as adjuvants for pain management, can sometimes cause lethal cardiotoxicity as an ADR. In order to reduce the likelihood of this, the prescribing physician is advised to order an electrocardiogram in those patients with a history of heart disease, or simply provide a better tolerated alternative, such as desipramine and nortripltyline. Orthostatic hypertension, acute glaucoma and cognitive impairment are also ADRs caused by TCAs which can be avoided by screening patients for pre-existing conditions and previous episodes of these diseases in order to reduce the likelihood of a reaction [51].

Corticosteroids, although well tolerated at moderated doses, can cause ADRs such as increasing the risk of peptic ulcer disease at a higher prolonged dose. One way to ameliorate this side effect is by prescribing a gastro-protective formulation, hence reducing the possible damage to the gastric lining [51].

Medications in the α2-adrenergic drug class (clonidine and tizanidine) are only used as a last resort adjuvant, due to their serious side effects [51] which include somnolence and hypotension.

Olanzapine, along with other neuroleptics, are also used as an adjuvant only in cases where the patient is being treated for dementia or agitation. ADRs caused by olanzapine including tardive dyskinesia and neuroleptic malignant syndrome greatly reduce the quality of life of patients, which is undesirable [51].

Anticonvulsant drugs are now widely used to treat cancer-related neuropathic pain. Gabapentin and lamotrigine have both been proven to improve the condition of patients with neuropathic pain but these also cause side effects such as somnolence, dizziness and unsteadiness [51].

Calcitonin, another adjuvant, may cause a hypersensitivity reaction at the onset of administration when given subcutaneously, this requires skin testing, but has been identified, along with nausea as a minor side effect when used as an adjuvant in palliative care [51].

Radionuclide pharmaceutical agents have been used to treat metastatic bone disease, namely strontium and samarium, but using these medications can lead to myelosuppression, a severe unwanted ADR [51].

Therefore, it can be said that adjuvants also present with their own pertinent adverse drug reactions that could damper the overall effectiveness in improving the condition of a patient with long-term use, which does not improve the patient's quality of life.
