Learn — Chemotherapy, IV fluids, electrolytes & vitamins

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Thiopental sodium (Pentothal)

Thiopental sodium is an ultra-short-acting thiobarbiturate given intravenously to induce general anaesthesia; it enhances GABA-A mediated chloride entry so consciousness is lost in one arm-brain circulation time. It matters at the bedside because it gives no analgesia at all, because it depresses both respiration and myocardial contractility within seconds, and because its strongly alkaline solution destroys tissue if it leaks out of the vein or enters an artery — even though propofol has now displaced it as the routine induction agent in most Indian theatres.

Mechanism: thiopental binds the GABA-A receptor and prolongs chloride channel opening, and at high concentration opens the channel directly, producing rapid unconsciousness together with a fall in cerebral metabolic rate, cerebral blood flow and intracranial pressure.
Dose and route: the adult induction dose is 3 to 5 mg/kg of a freshly prepared 2.5% solution by slow intravenous injection, reduced to about 1 to 2 mg/kg in the elderly, shocked or hypovolaemic patient; it is never given intramuscularly or subcutaneously.
Onset and duration: consciousness is lost within 10 to 30 seconds and returns in 5 to 10 minutes because the drug redistributes from brain to muscle and fat, but elimination is slow, so repeated doses accumulate and give a prolonged hangover.
Thiopental has no analgesic action and is antanalgesic at low dose, so it must always be paired with an opioid; a patient apparently asleep on thiopental alone will still respond to a painful stimulus.
The adverse effects that decide nursing action are apnoea and hypotension immediately after induction, laryngospasm and bronchospasm from histamine release, and the tissue injury of an extravasated or intra-arterial injection with severe pain, blanching and a threatened limb.
There is no antidote; management is supportive — airway and ventilation for the apnoea, fluids and a vasopressor for the hypotension, and for an intra-arterial injection leave the cannula in place, dilute with saline and give the ordered intra-arterial lignocaine or papaverine with heparinisation.
Monitoring: watch blood pressure, oxygen saturation and the ability to ventilate from the moment the drug goes in, aiming to keep the systolic pressure within about 20% of baseline and the saturation above 94%, with suction and a working airway trolley checked before induction begins.
Contraindications: acute intermittent porphyria is absolute because barbiturates induce ALA synthase and can precipitate a fatal attack; status asthmaticus and any airway in which ventilation may prove impossible are also contraindications, and severe hypovolaemia, shock and constrictive cardiac disease demand great caution.
The solution is highly alkaline at about pH 10.5 and precipitates when it meets acidic drugs such as suxamethonium, vecuronium and opioids, so the line is flushed between drugs and the solution is discarded if it becomes cloudy.

Anticancer drugs — classes

Anticancer drugs are grouped by the way they damage a dividing cell: alkylating agents cross-link DNA, antimetabolites masquerade as its building blocks, antitumour antibiotics and topoisomerase inhibitors break the strands, plant alkaloids disable the mitotic spindle, and targeted agents and checkpoint inhibitors act on a defined molecule or on the immune synapse. They matter at the bedside because the same mechanism damages every rapidly dividing normal tissue — marrow, gut lining and hair follicle — and because several of these drugs cause an emergency at the cannula or in the first days of treatment.

Alkylating agents (cyclophosphamide, ifosfamide, chlorambucil, busulfan) and the platinum compounds (cisplatin, carboplatin, oxaliplatin) cross-link DNA at any point in the cell cycle; cyclophosphamide and ifosfamide release acrolein and cause haemorrhagic cystitis, prevented by vigorous hydration and mesna, while cisplatin is nephrotoxic, ototoxic and the most emetogenic drug in common use and needs pre-hydration.
Antimetabolites (methotrexate, 5-fluorouracil, cytarabine, 6-mercaptopurine, gemcitabine) are false substrates that act in the S phase; high-dose methotrexate is rescued with folinic acid (leucovorin) at fixed intervals with urinary alkalinisation, and its toxicity is mucositis, marrow suppression and hepatic and renal injury — folic acid is not a substitute for folinic acid.
Antitumour antibiotics include the anthracyclines (doxorubicin, daunorubicin), whose cumulative dose-dependent cardiomyopathy demands a baseline and serial ejection fraction, and bleomycin, whose pulmonary fibrosis is the reason for baseline and repeated lung function tests.
Plant-derived agents act on the spindle: vinca alkaloids (vincristine, vinblastine) prevent microtubule assembly and cause peripheral neuropathy, constipation and paralytic ileus, while taxanes (paclitaxel, docetaxel) stabilise microtubules and cause neuropathy and hypersensitivity reactions that require premedication.
Vincristine is fatal if given intrathecally, so it is labelled for intravenous use only, is never dispensed at the same time as an intrathecal drug, and is given only into a confirmed free-flowing intravenous line.
Targeted and immune therapy is the modern arm: tyrosine kinase inhibitors such as imatinib, monoclonal antibodies such as trastuzumab (cardiotoxic, and more so after an anthracycline) and rituximab (infusion reactions and hepatitis B reactivation), and checkpoint inhibitors whose adverse effects are autoimmune — colitis, hepatitis, pneumonitis, thyroiditis — and are treated with corticosteroids.
The shared toxicities that decide nursing action are myelosuppression with the nadir usually at 7 to 14 days, nausea and vomiting, mucositis, alopecia and infertility, and the nadir is the reason for temperature charts, scrupulous hand hygiene, mouth care and a written neutropenic sepsis pathway.
Monitoring: a full blood count before every cycle with the absolute neutrophil count as the gate for treatment, renal and liver function, echocardiography for anthracyclines and trastuzumab, lung function for bleomycin, and daily temperature; a cycle is usually held when the absolute neutrophil count falls below about 1000 to 1500 per microlitre or the platelet count below about 100000 per microlitre, according to the protocol in use.
Handling is itself a nursing safety issue: cytotoxics are reconstituted in a biological safety cabinet with gown, double gloves and eye protection, checked by two nurses against the protocol and the body surface area, given through a verified line, and disposed of in dedicated cytotoxic waste with a spill kit kept in the treatment area.

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