Polyphamacology

Polyphamacology • Give figures about the extent of polypharmacy in older people. The oldest 15% of the population receive 40% of the drug presecriptions • Explain why detecting drug side effects is not simple in older people. Multiple pathologies can mask side effects from other drugs Elderly people are more likely to have non specific presentations with both illness & SEs • List the main physiological changes in older people affecting pharmacokinetics and pharmacodynamics. Absorption Drug structure Formulation – may have problems swallowing Gastric Emptying – slows with age à longer with acid, delayed absorption First pass metabolism – microzymal enzyme system less efficient (beware paracetamol & chlormethiazone) Absorption from other sites Distribution Heart failure à hepatic congestion à decreased metabolic rate Decreased muscle & fat Total body water reduced Decreased albumin (t ½ 28 days) à decreased binding à increased (non bound) active drug à increased toxicity Elimination Decreased renal flow (atherosclerosis) Decreased GFR (should be 100-130, often 20-30) Urea = produced in liver (decreases with age) Creatinine = produced from muscle (decreases with age) GFR decreases so U&E & creatinine appears normal Should do 24 hr creatinine clearance to calculate GFR MUST recalculate drug doses (eg gentamycin, digoxin, lithium) to maintain therapeutic range & avoid renal toxicity NET RESULT = PLASMA CONC INCREASES BY APPROX 50% CNS Drugs Exaggerated response (increased receptor sensitivity) E.g. opioids (tramadol) avoid if possible à drowsy à poor fluid & nutrition à dehydration à decreased UO & GFR B-Blockers Blunted response Reduced receptors present à barorecptor sensitivity à postural hypotension + bradycardia NB: postural hypotension = drop of 20mmHg systolic + symptoms Check for dehydration (esp if also diuretuc), bleeding (inc occult esp if on aspirin/warfarin) • List special points in the history, examination and investigation of older people that help to establish the presence of iatrogenic disease. Incidence of drug reactions rises with age • Increased no of drugs • Homeostatic changes of ageing • Diuretics over prescribed à overdiuresis à dehydration à pre-renal failure • Digitoxicity • NSAIDs assoc with GI bleed • Anti-parkinsons (L-dopa) & Antipsychotics can cause low BP • NB: Warfarin & Aspirin should never be co-prescribed • • NB: warfarin + fall ?head injury à intracranial bleed Antibiotics overprescribed for UTI, can à C.diff diarrhoea. Wait for +ve culture • Give examples of prescribing habits that are likely to reduce drug side effect problems. At each clinic / admission review the problems and medications • Do the benefits outweigh the risks? (warfarin for AF, but frequent faller) • Is the drug still required? • Nicest drug for the job? Cost v side effects • Could a single drug replace multiple? (ACE for HT and CCF) • Is the formulation appropriate? (syrups & patches may help) • Timings? Once a day will aid adherance • Aid to administration – no childproof tops • Aids to adherance – blister packs, simple regimes • Regular or PRN (analgesic often better regular for chronic elderly pain) • Does patient understand medications, and any SE to report • Cheapest (last consideration) Should a new drug be started • Aim to cure or disease modify • Start low, go slow, but remember to increase to therapeutic range • Give drug for long enough before ruling ineffective (e.g. anti Ds) • Check if renal failure & reference to BNF • Know where to get advice from in the future. BNF or hospital pharmacist